,transcriber's ,note3 ,in this1 the text file1 italics delimited by underscores1 and bold text delimited by equal signs4 ,illustration3 ,,radiolaria4 ,,the ,,microscope ,,its ,,history1 ,,construction1 ,,and ,,application ,,being ,a ,,familiar ,,introduction ,,to ,,the ,,use ,,of ,,the ,,instrument1 ,,and ,,the ,,study ,,of ,,microscopical ,,science ,,by ,,jabez ,,hogg1 ,m4,r4,c4,s41 ,f4,r4,m4,s41 ,,formerly ,,and ,,for ,,twenty-,,five ,,years ,,surgeon ,,to ,,the ,,royal ,,westminster ,,ophthalmic ,,hospital2 ,,past ,,president ,,of ,,the ,,medical ,,microscopical ,,society2 ,,honorary ,,fellow ,,of ,,the ,,academy ,,of ,,sciences1 ,,philadelphia2 ,,of ,,the ,,medico-,,legal ,,society1 ,,new ,,york2 ,,of ,,the ,,belgian ,,microscopical ,,society1 ,,etc42 ,,author ,,of 8,,elements ,,of ,,natural ,,philosophy10 8,a ,,manual ,,of ,,ophthalmoscopic ,,surgery10 ,,etc4 ,,with ,,upwards ,,of ,,nine ,,hundred ,,engraved ,,and ,,coloured ,,illustrations ,,by ,,tuffen ,,west ,,and ,,other ,,artists ,illustration3 ,an #ahth ,century ,microscope4 ,,fifteenth ,,edition ,,re-,,constructed1 ,,re-,,written1 ,,revised1 ,,and ,,enlarged ,,throughout ,,london ,,and ,,new ,,york ,,george ,,routledge ,,sons1 ,,limited #ahih ,,bradbury1 ,,agnew1 ,,co4 ,i4,d41 ,,printers1 ,,london ,,and ,,tonbridge4 ,,preface ,,to ,,the ,,fifteenth ,,edition4 ,the ,first ,edition of this work appeared in #ahed1 a time in the history of the ,microscope when the instrument1 as an aid to original scientific research1 may be said to have been in its infancy4 ,then certainly it was seldom employed in the laboratory or the medical schools4 ,now1 however1 as ,i anticipated1 it has asserted its proper position1 and has at length become one of the most important auxiliaries to science1 and a direct incentive to original work1 while it has doubtless exercised considerable influence over the student's power of observation1 and materially assisted in his studies1 let his ultimate object and pursuits be what they may4 ,the greater use made of the ,microscope has likewise conferred benefits of untold value upon the arts and industries of the country1 thereby adding to the national prosperity in ways as manifold as unique4 ,the ,microscope has also proved of immense value in the promotion of the health of the community1 and the art and science of healing1 since the theory of medicine has become a science1 resting on the minute microscopical examination of animal tissues4 ,the work of research in the sister sciences and by other methods has1 during the last decade1 received a corresponding impetus1 while it has undoubtedly tended towards elaboration and specialisation in all departments4 ,in consequence1 the progress of microscopical science has become more dependent upon the specialist for gaining accurate knowledge and for certain important details seen to be branching out in many directions4 ,there never was a time when the instrument was so constantly and generally resorted to and with so much confidence and advantage1 as the present4 ,it has shown itself equal to the task imposed--that of teaching the eye to see things that are new1 and also1 what is perhaps of more importance1 to perceive things which had been entirely overlooked4 ,the older defects1 perhaps1 arose from two causes2 the want of more careful training of the organ of vision1 and the want of sufficient power and precision in the optical part of the ,microscope itself4 ,both of these obstacles have been to a considerable extent removed1 and all educational systems are looked upon as incomplete without a knowledge of the ,microscope4 ,a step has already been taken in another direction1 that of furnishing special forms of instruments1 better adapted to the uses to which they will hereafter be put1 and purposely designed for chemical and analytical processes1 for petrological pursuits1 the geometrical measurement of crystals1 for special work in connection with manufacturing industries1 for the dairyman1 and the farmer4 ,for the detection of adulterations--that of butter1 for example--a newer form of instrument has been devised1 namely1 a 8,butro-refractometer10 by the help of which any adulteration of this universal article of diet will at once be revealed4 ,the form of instrument upon which the optician has expended a greater amount of skill than perhaps on any other is the ,bacteriological ,microscope1 as may be inferred from the larger space ,i have devoted to this important adjunct1 since by original research1 there can be no doubt a still greater future is in store for science in this special department of microscopy4 ,but perfect success in this direction remains very much with the practical optician1 and the further improvements made in the optical part of the instrument1 since it is admitted that the highest theoretical perfection has not yet been reached4 ,it is a commonplace remark that every question solved is a step towards new problems waiting solution4 ,it is equally obvious that many difficulties must be encountered by every author who uses his best endeavours to supply a standard volume or even a fairly comprehensive text-book on the ,microscope1 one that will remain a sure guide for any lengthened period4 ,such a success ,i regard as scarcely possible4 ,i may1 however1 notice that my earlier work has met with a great amount of appreciation1 and its utility acknowledged in the past by a demand almost unprecedented1 edition after edition being called for4 ,it is hardly necessary to add that my task has been accomplished with an earnest desire to assist in diffusing a love for an instrument which has been my constant companion for upwards of sixty years4#a ,moreover1 ,i have a firm conviction of the real utility of the ,microscope in the work of education1 its practical value in many branches of science1 art1 and manufacturing industries4 ,these are my chief reasons for applying myself once more to the task of revision1 rewriting1 and rearranging and bringing this book as far as possible into line with the knowledge gained in chemical pathology and bacteriology4 ,it will be noticed that in the first part1 my subjects have as far as possible been treated from a historical point of view4 ,this method has enabled me to affix dates of introduction of special inventions and improvements made in the instrument and its appliances4 ,the enlargement of my pages has enabled me to devote more space to bacteriological processes1 and by the further addition of plates and several hundred illustrations to more fully elucidate the subject matter of my text4 ,in an ,appendix ,i have introduced a selection of 8,formul and ,methods0 of staining1 mounting1 etc41 also tables of the 8,metrical ,system10 now in general use in the laboratory2 together with comparative thermometric values1 all of which ,i trust may prove of service to the student4 ,before bringing these few prefatory remarks to a close1 a pleasing duty devolves upon me--that of tendering my thanks for cordial aid received from ,professor ,dr4 ,,edgar ,,crookshank in dealing with his special subject1 ,bacteriology4 ,from his valuable 8,text-,book on ,bacteriology0 ,i have extracted much useful matter4 ,i am equally indebted to ,professor ,,marshall ,,ward1 ,f4,r4,s41 ,cambridge1 for much information on 8,economic ,botany10 and the great advances made in the knowledge of the uses of plants1 and the industrial value of bacteria in particular4 ,my acknowledgments are also due to the ,messrs4 ,,warne for many illustrations placed at my disposal1 and for useful facts derived from their 8,royal ,natural ,history40 ,it will1 however1 be seen that the results of a large amount of independent observation have been consigned to my pages4 ,as the references show1 recourse has been had to original sources for trustworthy1 reliable information on many subjects4 ,these are constantly1 almost daily1 being added to1 as is made manifest by the numerous periodical publications of the day devoted to this and kindred sciences2 the foremost and most important among which is that almost exclusively given to microscopical science1 8,the ,journal of the ,royal ,microscopical ,society of ,london10 the perusal of which ,i commend to my readers4 ,,london1 ,,july1 #ahih4 ,,preface ,,to ,,the ,,first ,,edition4 ,the ,author of this ,publication entered upon his task with some hesitation and diffidence2 but the reasons which influenced him to undertake it may be briefly told1 and they at once explain his motives1 and plead his justification1 for the work which he now ventures to submit to the indulgent consideration of his readers4 ,it had been to him for some time a subject of regret that one of the most useful and fascinating studies--that which belongs to the domain of microscopic observation--should be1 if not wholly neglected1 at best but coldly and indifferently appreciated by the great mass of the general public2 and he formed a strong opinion that this apathy and inattention were mainly attributable to the want of some concise1 yet sufficiently comprehensive1 popular account of the ,microscope1 both as regards the management and manipulation of the instrument1 and the varied wonders and hidden realms of beauty that are disclosed and developed by its aid4 ,he saw around him valuable1 erudite1 and splendid volumes1 which1 however1 being chiefly designed for circulation amongst a special class of readers1 were necessarily published at a price that renders them practically unattainable by the great bulk of the public4 ,they are careful and beautiful contributions to the objects of science1 but they do not adequately bring the value and charm of microscopic studies home1 so to speak1 to the firesides of the people4 ,day after day1 new and interesting discoveries1 and amplifications of truth already discerned1 have been made1 but they have been either sacrificed in serials1 or1 more usually1 devoted to the pages of class publications2 and thus this most important and attractive study has been1 in a great measure1 the province of the few only1 who have derived from it a rich store of enlightenment and gratification3 the many not having1 however1 participated1 to any great extent1 in the instruction and entertainment which always follow in the train of microscopical science4#b ,the manifold uses and advantages of the ,microscope crowd upon us in such profusion1 that we can only attempt to enumerate them in the briefest and most rapid manner in these prefatory pages4 ,it is not many years since this invaluable instrument was regarded in the light of a costly toy2 it is now the inseparable companion of the man of science4 ,in the medical world1 its utility and necessity are fully appreciated1 even by those who formerly were slow to perceive its benefits2 now1 knowledge which could not be obtained even by the minutest dissection is acquired readily by its assistance1 which has become as essential to the anatomist and pathologist as are the scalpel and bedside observation4 ,the smallest portion of a diseased structure1 placed under a ,microscope1 will tell more in one minute to the experienced eye than could be ascertained by long examination of the mass of disease in the ordinary method4 ,microscopic agency1 in thus assisting the medical man1 contributes much to the alleviation of those multiplied 8ills which flesh is heir to40 ,so fully impressed were the ,council of the ,royal ,college of ,surgeons with the importance of the facts brought to light in a short space of time1 that1 in #ahda1 they determined to establish a ,professorship of ,histology1 and to form a collection of preparations of the elementary tissues of both animals and vegetables1 healthy and morbid1 which should illustrate the value of microscopical investigations in physiology and medical science4 ,from that time1 histological anatomy deservedly became an important branch of the education of the medical student4 ,in the study of ,vegetable ,physiology1 the ,microscope is an indispensable instrument2 it enables the student to trace the earliest forms of vegetable life1 and the functions of the different tissues in the growth of plants4 ,valuable assistance is derived from its agency in the detection of adulterations4 ,in the examination of flour1 an article of so much importance to all1 the ,microscope enables us to judge of the size and shape of the starch-grains1 their markings1 their isolation and agglomeration1 and thus to distinguish the starch-grains of one meal from those of another4 ,it detects these and other ingredients1 invisible to the naked eye1 whether combined in atoms or aggregated in crystals1 which adulterate our food1 our drink1 and our medicines4 ,it discloses the lurking poison in the minute crystallisations which its solutions precipitate4 8,it tells the murderer that the blood which stains him is that of his brother1 and not of the other life which he pretends to have taken2 and as a witness against the criminal1 it on one occasion appealed to the very sand on which he trod at midnight40 ,the zoologist finds in the ,microscope a necessary coadjutor4 ,to the geologist it reveals1 among a multiplicity of other facts1 8that our large coal-beds are the ruins of a gigantic vegetation2 and the vast limestone rocks1 which are so abundant on the earth's surface1 are the catacombs of myriads of animal tribes1 too minute to be perceived by the unaided vision40 ,by 8conducting the eye to the confines of the visible form10 the ,microscope proves an effective auxiliary in defining the geometric properties of bodies4 ,its influence as an instrument of research upon the structure of bodies has been compared to that of the galvanic battery1 in the hands of ,davy1 upon ,chemistry4 ,it detects the smallest structural difference1 heretofore inappreciable1 and1 as an ally of ,chemistry1 enables us to discover the very small changes of form and colour effected by test-fluids upon solids2 and dissects for us1 so to speak1 the most multiplex compounds4 ,it opens out to the mind an extended and vast tract1 opulent in wonders1 rich in beauties1 and boundless in extent4 ,the ,microscope not only assists studies1 and develops objects of profound interest1 but also opens up innumerable sources of entertainment and amusement1 in the ordinary conventional acceptation of these terms2 disclosing to us peculiarities and attractions in abundance2 impressing us with the wonderful and beautifully skilful adaptation of all parts of creation1 and filling our minds with additional reverence and admiration for the beneficent and ,almighty ,creator4 ,the ,author will conclude these prefatory observations with a few words in explanation of his arrangements1 by way of dealing with the instrument and development of his subject4 ,he has sought1 in the volume that he now lays before the public1 to point out and elucidate at once in a practical manner and in a popular style1 the vast fund of utility and amusement which the ,microscope affords1 and has endeavoured to touch upon most of the interesting subjects for microscopic observation as fully as the restrictions of a limited space1 and the nature of the succinct summary1 would permit4 ,to have dwelt upon each in complete detail would have necessitated the issue of many expensive volumes--and this would have entirely frustrated the aim which the writer had in view2 he has1 therefore1 contented himself with the humble1 but1 he trusts1 not useless1 task of setting up a finger-post1 so to say1 to direct the inquirer into the wider road4 ,in the section of the work devoted to the minuter portion of creation1 he has ventured to dwell somewhat longer1 in the belief that that department is more especially the province of the microscopist4 ,he has arranged his topics under special headings1 and in separate chapters1 for the sake of perspicuity and precision2 and has brought the ever-welcome aid of illustration to convey his explanatory remarks more vividly to the minds of his readers4 ,finally1 it is the ,author's hope that1 by the instrumentality of this volume1 he may possibly assist in bringing the ,microscope1 and its valuable and delightful studies1 before the general public in a more familiar1 compendious1 and economical form than he found it at the period of its publication1 so that1 in these days of a diffused taste for reading and the spread of cheap publications1 he may thus supply further exercise for the intellectual faculties2 contribute to the additional amusement and instruction of the family circle1 and aid the student of nature in investigating the wonderful and exquisite works of the ,almighty4 ,if it shall be the good fortune for this work1 which is now confided with great diffidence to the consideration of the public1 to succeed1 in however slight a degree1 in furthering this design1 the ,author will feel fully repaid for the amount of time and labour expended4 ,,london1 ,may1 #ahed4 ,,contents4 ,,part ,i4 ,,page ,,early ,,history ,,of ,,the ,,microscope #a ,,chapter ,i4 ,,light--,,its ,,propagation--,,refraction--,,spherical ,,and ,,chromatic ,,aberration--,,human ,,eye--,,formation ,,of ,,images--,,visual ,,angle--,,abb',s ,,theory ,,of ,,microscopic ,,vision--,,definition ,,of ,,aperture--,,numerical ,,aperture--,,abb',s ,,apertometer--,,stereoscopic ,,binocular ,,vision #ab ,,chapter ,,ii4 ,,simple ,,and ,,compound ,,microscopes--,,evolution ,,of ,,the ,,modern ,,achromatic ,,microscope--,,improvements ,,in ,,the ,,modern ,,microscope3 ,,the ,,ross-,,jackson1 ,,powell ,,and ,,lealand1 ,,beck',s1 ,,baker',s1 ,,pillischer1 ,,zeiss1 ,,leitz1 ,,watson',s1 ,,van ,,heurck',s ,,edinburgh ,,students'1 ,,swift',s1 ,,and ,,bacteriological #gb ,,chapter ,,iii4 ,,applied ,,optics--,,eye-,,pieces--,,achromatic ,,objectives ,,and ,,condensers--,,magnifying ,,power ,,of ,,eye-,,pieces ,,and ,,objectives--,,method ,,of ,,employing ,,the ,,condenser--,,its ,,illumination ,,mirror--,,accessories ,,of ,,the ,,microscope--,,finders--,,micrometers-- ,,camera-,,lucida--,,microscope ,,in ,,position ,,for ,,drawing--,,abb',s ,,test-,,plate--,,micro-,,photography--, ,polarisation ,,of ,,light--,,the ,,micro-,,spectroscope #aci ,,chapter ,,iv4 ,,practical ,,microscopy--,,manipulation--,,mode ,,of ,,employing ,,the ,,microscope--,,working ,,accessories--,,methods ,,of ,,preparing1 ,,hardening1 ,,staining1 ,,and ,,section ,,cutting--,,cutting ,,hard ,,structures--,,injecting ,,apparatus1 ,,material1 ,,etc41 ,,employed ,,in ,,bacteriological ,,investigations--,,warm ,,chambers ,,and ,,incubators--,,preparing1 ,,mounting1 ,,cementing1 ,,and ,,collecting ,,objects #beh ,,part ,,ii4 ,,chapter ,i4 ,,microscopic ,,forms ,,of ,,life--,,thallophytes1 ,,pteridophyta1 ,,phanerogam--,,structure ,,and ,,properties ,,of ,,the ,,cell--,,pathogenic ,,fungi ,,and ,,moulds--,,parasitic ,,diseases ,,of ,,plants1 ,,man1 ,,and ,,animals--,,industrial ,,uses ,,of ,,fungi ,,and ,,saccharomycetes--,,desmidiace ,,and ,,diatomace--,,lichens1 ,,mosses1 ,,ferns1 ,,flowering ,,plants #cec ,,chapter ,,ii4 ,,sub-,,kingdom ,,protozoa--,,rhizopoda--,,gromia ,,and ,,foraminifera--,,infusoria--,,ciliata-- ,,rotifera--,,porifera--,,sponges #dgh ,,chapter ,,iii4 ,,zoophytes--,c,,lenterata--,,medus--,,c orals--,,hydrozoa--,,mollusca-- ,,annulosa--,,worms--,,entozoa--,,anneli da--,,crustacea #eae ,,chapter ,,iv4 ,,arthropoda--,,insecta--,,arachnida--,, acarina--,,ixodid--,,mites ,,and ,,ticks #ehc ,,chapter ,v4 ,,vertebrata--,,internal ,,and ,,external ,,structures #fcc ,,chapter ,,vi4 ,,the ,,mineral ,,and ,,geological ,,kingdoms #fgj ,,appendix4 ,,dr4 ,,mercer ,,on ,,illumination1 ,,and ,,abb',s ,,theory--,,micro-,,spectroscope--,,form ul1 ,,methods1 ,,cementing1 ,,clearing1 ,,hardening1 ,,and ,,mounting--,,tables1 ,,metric ,,and ,,thermometric #fgb ,,index #fia ,,description ,,of ,,plates1 ,,coloured ,,and ,,plain4 ,,frontispiece4 ,,radiolaria4 ,in this ,plate ,fig4 #a shows the elegant lattice-sphere of ,rhizosphra2 ,fig4 #b represents ,sphrozoum1 whose skeleton consists of loose spicules1 arranged tangentially2 ,actinomma1 ,fig4 #c1 possesses three concentric lattice-spheres1 joined by radiating spines2 ,figs4 #d1 #e1 and #f1 represent ,lithomespilus1 ,ommatocampe1 and ,carpocanium2 ,fig4 #g represents a deep-sea form 7,challengeria71 whose oval case is formed of a regular1 very fine-meshed1 network2 ,fig4 #h depicts the elegant lattice-sphere of ,heliosphra2 ,figs4 #i and #aj1 ,clathrocyclas and ,dictyophimus4 ,,plate ,i4--,page #djj4 ,,protophyta4 ,,thallophytes4 ,fig4 #a4 ,peziza bicolor--#b4 ,truffle3 a4 ascus of spores2 b4 mycelium--#c4 ,sphria herbarum3 a4 piece of dead plant1 with ,s4 herbarum natural size2 b4 section of same1 slightly magnified2 d4 ,ascus with spores1 and paraphyses more magnified--#d4 ,peziza pygma--#e4 ,apical form of same--#f4 ,p4 corpulasis3 ,ascus with spores and paraphyses1 merely given as a further illustration of structure in ,peziza--#g4 ,yeast healthy--#h4 ,yeast exhausted--#i4 ,phyllactinia guttata--#aj4 ,yeast with favus spores and mycelium of fungus--#aa4 ,favus ferment1 with odium and bacteria--#ab4 ,puccinia spores1 growing in a saccharine solution--#ac4 ,aerobic bacteria--#ad4 ,spores and mycelia from eczema produced by yeast--#ae4 ,volvox globator--#af4 ,amboid condition of portion of volvox--#ag4 ,puccinia buxi--#ah4 ,ditto1 more enlarged--7#ag to #bj illustrate ,ascomycetes47--#ai4 cidium grossulari from transverse section of leaf of currant3 a4 spermogones on upper surface2 b4 perithecia with spores--#bj4 ,phragmidium bulbosum1 development of--#ba4 ,palmella parietina1 trans4 section through a spermogone1 showing green gonidia and spermatia escaping--#bb4 cidium berberida1 from leaf of berberry--#bc4 ,vaucheria sessilis--#bd4 ,stephanosphra pluvialis3 a4 ,full-grown example1 germ cells spindle-shaped with flagella2 b4 ,resting-cell2 c4 division into four2 d4 ,free-swimming ciliated young specimen2 e4 ,amboid condition--#be4 a1 b1 c1 d1 e1 f and g1 ,development of lichen gonidia--#bf4 ,palmella stellaris 7lichen71 vertical section through apothecium1 showing asci1 spores1 and paraphyses1 with gonidia and filamentous medulla3 a4 ,spermatophore with spermatia--#bg4 ,moss gonidia assuming amboid form4 ,typical forms of ,protophyta2 #g to #ad1 modes of development or rudimentary conditions2 ,confervoide1 #bc2 ,vaucheria1 ,stephanosphra1 #bd2 ,volvox1 #ae1 c4 ,,plate ,,ii4--,page #dab4 ,,protophyta4 ,,alg4 ,fig4 #bg4 ,ceramium acanthonotum--#bh4 ,closterium1 ,triploceras gracilis--#bi4 ,cosmarium radiatum--#cj4 ,micrasterias denticulata--#ca4 ,docidium pristid--#cb4 ,callithamnion plumula--#cc4 ,diatoma1 living3 a4 ,licmophora splendida2 b4 ,achnanthes longipes2 c4 ,grammatophora marina4 ,these figures are intended to show the general character of the endochrome and growth of frustule--#cd4 ,callithamnion refractum--#ce4 ,jungermannia albicans2 b4 representing elater and spores--#cf4 ,leaf with antheridia1 or male elements1 represented more magnified at a to the left of the figure--#cg4 ,ceramium echinotum--#ch4 ,pleurosigma angulatum1 side view--#ci4 ,delesseria hypoglossum--#dj4 ,pleurosigma angulatum1 front view1 endochrome not represented--#da4 ,ceramium flabelligerum4 ,,plate ,,iii4--,page #dgi4 ,,protozoa4 ,figs4 #dc1 #dd1 #de1 #df1 #dg1 #dh1 #di1 #ej1 #ea1 #eb4 ,these figures are from drawings made by ,major ,owen1 to illustrate forms of living ,polycystina1 sketched from life2 these convey a faint idea of the richly coloured appearance of the natural structure2 ,figs4 #dh to #eb--ec4 ,gregarina lumbricorum1 round form--#ed4 ,gregarina lumbricorum1 the usual elongated form--#ee4 ,gregarina serpul--#ef4 ,gregarina ,sieboldii2 illustration of septate form1 with reflexed hook-like processes--#eg4 ,gregarina lumbricorum1 encysted--#eh4 ,gregarina lumbricorum1 more advanced and pseudo-navicell forming--#ei4 ,gregarina lumbricorum1 free pseudo-navicella of--#fj1 #fa4 ,gregarina lumbricorum1 amboid forms of--#fb4 ,cruciate sponge-spicule--#fc4 ,astromma ,humboldtii--#fd4 ,ezoon ,canadense1 represents appearance of a portion of the natural size--#fe4 ,ezoon ,canadense1 magnified1 showing portions of cell-walls left uncoloured1 the animal sarcode inhabiting it coloured dark green as in nature1 and converted by fossilisation into a silicious mineral2 the narrow bands passing between these are processes 7stolons7 of the same substance--#ff4 ,actinophrys sol1 budding--#fg4 ,euglena viridis3 a4 contracted2 b4 elongated form--#fh4 ,acineta tuberosa--#fi4 cistes longicornis 7,davis7--#gj4 ,oxytricha gibba 7side view7--#ga4 ,oxytricha pellionella--#gb4 ,thuricola valvata1 expanded--#gc4 ,cyclidium 7glaucoma7--#gd4 ,oxytricha scintillans--#ge to #gi1 #hj to #he1 illustrate types of ,foraminifera discovered by ,major ,owen1 living--#ge4 ,globigerina acerosa1 n4 sp41 broken open to show interior--#gf4 ,globigerina1 n4 sp41 broken open to show interior--#gg4 ,globigerina hirsuta--#gh4 ,globigerina universa--#gi and #ha4 ,g4 ,bulloides--#hj4 ,conochilus vorticella--#hb4 ,globigerina inflata1 sinistral shell--#hc4 ,pulvinulina ,micheliniana--#hd4 ,p4 ,canariensis--#he4 ,p4 ,menardii4 ,,plate ,,iv4--,page #ead4 ,,metazoa4 ,,bryozoa4 ,fig4 #hf4 ,hartea elegans--#hg4 ,side view of ,synapta spicula--#hh4 ,ophioglypha rosula 7very immature specimen73 a4 ,claw hooks2 b4 palmate spicula4 ,the development of this species is described by ,g4 ,hodge1 in 8,transactions of ,tyneside ,naturalists' ,field-,club0--#hi4 ,spine of a star-fish1 particularly interesting as showing the reticular calcareous network obtaining in this as in all other hard parts of the ,echinodermata--#ij4 ,very minute ,spatangus1 obtained from stomach of a bream3 many of the spines are gone1 but the structure of the shell is intact and forms a beautiful object1 interesting in connection with the source whence obtained--#ia4 ,ophioglypha neglecta3 wriggling or brittle starfish4 ,the plate does not admit of a figure on a scale sufficient to show the full beauty of this object--#ib4 ,tubularia ,dumortierii--#ic4 ,pedicellaria mandibulata from ,uraster glacialis--#id4 ,pedicellaria forcepiforma1 from the same--#ie4 ,cristatella mucedo2 #if4 ,edge-view of statoblast2 #ig4 early stage in development of same--#ih4 ,lophopus crystallinus--#ii4 ,plumatella repens with ova1 on submerged stem--#ajj4 ,tnia echinococcus--#aja4 ,hydatids from human liver--#ajb4 ,bilharzia hmatobia--#ajc4 ,amphistoma conicum--#ajd4 ,trichina spiralis from fleshy part of ,hambrc' pork--#aje4 ,trichina spiralis male1 separated from muscle4--#ajf1 #ajg4 ,fasciola gigantea4 ,,plate ,v4--,page #eef4 ,,mollusca4 ,fig4 #ajh4 ,velutina lvigata1 portion of lingual membrane--#aji4 ,velutina lvigata1 part of mandible--#aaj4 ,hybocystis blennius1 portion of palate--#aaa4 ,sepia officinalis1 portion of palate--#aab4 ,aplysia hybrida1 part of mandible--#aac4 ,loligo vulgaris1 part of palate--#aad4 ,haliotis tuberculatus1 part of palate--#aae4 ,cistula catenata1 part of palate--#aaf4 ,patella radiata1 part of palate--#aag4 ,acma virginea1 part of palate--#aah4 ,cymba olla1 part of palate--#aai4 ,scapander ligniarius--#abj4 ,oneidoris bilamellata1 part of palate--#aba4 ,testacella ,maugei1 part of palate--#abb4 ,pleurobranchus plumula1 part of mandible--#abc4 ,turbo marmoratus1 part of palate4 ,lingual membranes of ,mollusca2 drawings made from specimens in the collection formed by ,f4 ,e4 ,edwards1 ,esq41 now in the ,british ,museum4 ,typical examples of the numerous forms of ,odontophors met with in ,gasteropod and ,cephalopod ,mollusca4 ,,plate ,,vi4--,page #ehb4 ,,insecta4 ,fig4 #abd4 ,egg of ,caradrina morpheus1 mottled rustic moth--#abe4 ,egg of tortoise-shell butterfly1 ,vanessa urtic--#abf4 ,egg of common footman1 ,lithosia complanula--#abg4 ,egg of shark moth1 ,cucullia umbratica--#abh4 ,maple-aphis--#abi4 ,egg shell of acarus1 empty--#acj4 ,egg of house-fly--#aca4 ,mouth of ,tsetse-fly1 ,glossina morsitans--#acb4 ,vapourer moth1 ,orgyia antiqua3 antenna of male--#acc4 ,vapourer moth3 antenna of female2 a4 branch more magnified to show rudimentary condition of the parts--#acd4 ,tortoise-shell butterfly2 head in profile1 showing large compound eye1 one of the palpi1 and spiral tongue--#ace4 ,tortoise-beetle1 ,cassida viridis2 under surface of left fore-foot1 to show the bifurcate tenent appendages1 one of which is given at a more magnified4 ,this form of appendage is characteristic of the family4 8,west on ,feet of ,insects10 ,linn4 ,trans4 vol4 xxiii4 tab4 #dc-acf4 ,egg of blue argus butterfly1 ,polyommatus argus--#acg4 ,egg of mottled umber1 ,erannis defoliaria--#ach4 ,egg of ,ennomos erosaria1 thorn-moth--#aci4 ,egg of ,aspilates gilvaria1 straw-belle--#adj4 ,blow-fly1 ,musca vomitoria3 left fore-loot1 under-surface1 to show tenent hairs2 a b more magnified2 a from below1 b from the side--#ada4 ,house-fly larva--#adb4 ,amara communis3 left fore-foot1 under-surface1 to show form of tenent appendages1 of which one is given more magnified at a4 ,these1 in ground beetles1 are met with only in the males1 believed to be used for sexual purposes4 ,these appendages are carefully protected when not in use1 as explained by ,west--#adc4 ,ephydra riparia3 left fore-foot1 under-surface4 ,this fly is met with sometimes in immense numbers on the water in salt-marshes2 it has no power of climbing on glass1 as seen by the structure of the tenent hairs2 the central tactile organ also is peculiar1 the whole acting as a float1 one attached to each foot1 enabling the fly to rest on the surface of the water2 a4 an enlarged external hair--#add4 ,egg of bot-fly1 the larva just escaping--#ade4 ,egg of parasite of pheasant--#adf4 ,egg of ,scatophaga--#adg4 ,egg of parasite of magpie--#adh4 ,egg of ,jodis vernaria1 small emerald moth4 ,,plate ,,vii4--,page #fcc4 ,,vertebrata4 ,fig4 #adi4 ,toe of mouse1 integuments1 bone of foot1 and vessels--#aej4 ,tongue of mouse1 showing erectile papill and muscular layer--#aea4 ,brain of rat1 showing vascular supply--#aeb4 ,vertical section of tongue of cat1 fungi-form papill and capillary loops passing into them1 vessels--#aec4 ,kidney of cat1 showing ,malpighian turfts and arteries--#aed4 ,small intestine of rat1 with villi and layer of mucous membrane exposed--#aee4 ,nose of mouse1 showing vascular supply to roots of whiskers--#aef4 ,vascular supply to internal gill of tadpole1 during one phase of development--#aeg4 ,section through sclerotic coat and retina of cat's eye1 showing vascular supply of choroid vessels cut cross-ways--#aeh4 ,interior of fully-developed tadpole1 exhibiting heart1 vascular arrangement and vascular system throughout body and tail4 ,this plate is designed to show the value1 in certain cases1 of injected preparations in the delineation of animal structures4 ,by thus artificially restoring the blood and distending the tissues1 a better idea is obtained of the relative condition of parts during life4 ,,plate ,,viii4--,page #bbj4 ,,polariscope ,,objects4 ,fig4 #aeh4 ,new ,red ,sandstone--#aei4 ,quartz--#afc4 ,granite--#afa4 ,sulph4 ,copper--#afb4 ,saliginine--#afc4 ,sulph4 ,iron and ,cobalt1 crystallized in the way described by ,thomas--#afd4 ,borax--#afe4 ,sulph4 ,nickel and ,potash--#aff4 ,kreatine--#afg4 ,starch granules--#afh4 ,aspartic ,acid--#afi4 ,fibro-cells1 orchid4--#agj4 ,equisetum cuticle--#aga4 ,holothuria spicula1 ,australia--#agb4 ,holothuria spicula1 ,port ,essington--#agc4 ,deutzia scabra2 upper and under surface--#agd4 ,cat's tongue1 process--#age4 ,prawn shell1 exuvia with crystals of lime--#agf4 ,grayling scale--#agg4 ,scyllium caniculum scale--#agh4 ,rhinoceros horn1 transverse section--#agi4 ,horse hoof--#ahj4 ,dytiscus1 elytra with crystals of lime4 ,,plate ,,ix4--,page #cfb4 ,,typical ,,plate ,,of ,,bacteria ,,and ,,schizomycetes4 ,fig4 #a4 ,cocci1 singly1 and varying in size--#b4 ,cocci in chains or rosaries 7streptococcus7--#c4 ,cocci in a mass 7staphylococcus7--#d and #e4 ,cocci in pairs 7diplococcus7--#f4 ,cocci in groups of four 7merismopedia7--#g4 ,cocci in packets 7sarcina7--#h4 ,bacterium termo--#i4 ,bacterium termo #djjj 7,dallinger and ,drysdale7--#aj4 ,bacterium septicmi hmorrhagic--#aa4 ,bacterium pneumoni croupos--#ab4 ,bacillus subtilis--#ac4 ,bacillus murisepticus--#ad4 ,bacillus diphtheri--#ae4 ,bacillus typhosus 7,eberth7--#af4 ,spirillum undula 7,cohn7--#ag4 ,spirillum volutans 7,cohn7--#ah4 ,spirillum choler ,asiatic--#ai4 ,spirillum ,obermeieri 7,koch7--#bj4 ,spirochta plicatilis 7,flgge7--#ba4 ,vibrio rugula 7,prazmowski7--#bb4 ,cladothrix ,frsteri 7,cohn7--#bc4 ,cladothrix dichotoma 7,cohn7--#bd4 ,monas ,okenii 7,cohn7--#be4 ,monas ,warmingii 7,cohn7--#bf4 ,rhabdomonas rosea 7,cohn7--#bg4 ,spore-formation of ,bacillus alvei--#bh4 ,spore-formation 7,bacillus anthracis7--#bi4 ,spore-formation in bacilli cultivated from rotten melon 7,frnkel and ,pfeiffer7--#cj4 ,spore-formation in bacilli cultivated from earth 7,frnkel and ,pfeiffer7--#ca4 ,involution-form of ,crenothrix 7,zopf7--#cb4 ,involution-forms of ,vibrio serpens 7,warming7--#cc4 ,involution-forms of ,vibrio rugula 7,warming7--#cd4 ,involution-forms of ,clostridium polymyxa 7,prazmowski7--#ce4 ,involution-forms of ,spirillum choler ,asiatic--#cf4 ,involution-forms of ,bacterium aceti 7,zopf and ,hansen7--#cg4 ,spirulina-form of ,beggiatoa alba 7,zopf7--#ch4 ,various thread-forms of ,bacterium merismopedioides 7,zopf7--#ci4 ,false-branching of ,cladothrix 7,zopf74 ,,plate ,x4--,page #dbj4 ,,desmidiace4 ,fig4 #a4 ,euastrum oblongum--#b4 ,micrasterias rotata--#c4 ,desmidium quadrangulatum--#d4 ,didymoprium ,grevillii--#e4 ,micrasterias1 sporangium of--#f4 ,didymoprium ,borreri--#g4 ,cosmarium ,ralfsii--#h1 #i4 ,xanthidi--#aj4 ,x4 armatum--#aa4 ,cosmarium crenatum--#ab4 ,c4 ,sphrozosma vertebratum--#ac1 #ag4 ,sporangia of ,cosmarium--#ad4 ,x4 fasiculatum--#ah4 ,staurastrum hirsutum--#ai4 ,arthrodesmus convergens--#ae4 ,staurastrum tumidum--#af4 ,staurastrum dilitatum--#ba4 ,penium--#bb4 ,euastrum ,didelta--#bc4 ,docidium clavatum--#bd4 ,pediastrum biradiatum--#be4 ,closterium1 showing conjugation or self-division--#bf4 ,volvox1 parent cell about to break up--#bg4 ,penium ,jennerii--#bh4 ,aptogonum desmidium--#bi4 ,pediastrum pertusum--#cj4 ,ankistrodesmus falcatus--#ca4 ,parent cell of ,closterium--#cb4 ,staurastrum gracilis4--#cc4 ,conjugation of ,penium margaritaceum--#cd4 ,spirotnia--#ce4 ,closterium ,,plate ,,xi4--,page #dbh4 ,,diatomace4 ,fig4 #a4 ,arachnoidiscus--#b4 ,actinocyclus 7,bermuda7--#c4 ,cocconeis 7,algoa ,bay7--#d4 ,coccinodiscus 7,bermuda7--#e4 ,isthmia enervis--#f4 ,zygoceros rhombus--#g4 ,campilodiscus clypeus--#h4 ,biddulphia--#i4 ,gallionella sulcata--#aj4 ,triceratium1 found in ,thames mud--#aa4 ,gomphonema geminatum1 with their stalk-like attachments--#ab4 ,dictyocha fibula--#ac4 ,eunotia--#ad4 ,cocconema--#ae4 ,fragilaria pectinalis--#af4 ,meridion circulare--#ag4 ,diatoma flocculosum4 ,,plate ,,xii4--,page #dch4 ,,micro-,,photograph ,,of ,,test ,,diatoms4 ,taken with ,zeiss's #c mm4 ,n4,a4 #adj by ,mr4 ,a4 ,a4 ,carvell for the ,author4 ,fig4 #a4 ,portion of ,surirella gemma1 magnified #a1jjj--b4 ,broken ,frustule of ,pleurosigma angulatum1 #gej--c and #e4 ,triceratium favus --#a1jjj--d4 ,navicula rhomboides #a1cjj--f4 ,pleurosigma formosum1 showing black dots--#g4 ,p4 formosum1 showing white dots1 #gej4 ,,plate ,,xiii4--,page #ded4 ,,phanerogami--,,elementary ,,tissue ,,of ,,plants4 ,fig4 #a4 ,elementary ovid cells--#b4 ,branching tissue--#b;,a and #c4 ,spiral vessels from ,opuntia vulgaris--#d4 ,stellate tissue1 section of rush--#e4 ,mushroom spawn--#f4 ,starch from ,tous-les-mois--#g4 ,starch from sago--#h4 ,starch from rice--#i4 ,wheat-starch--#aj4 ,rhubarb starch in isolated cells--#aa4 ,maize-starch--#ab4 ,oat-starch--#ac4 ,barley-starch--#ad4 ,section of ,potato cells1 filled with healthy starch--#ae4 ,potato starch more highly magnified--#af4 ,section of ,potato with nearly all starch absent--#ag4 ,potato with starch destroyed by fungoid disease--#ah4 ,ciliated spermagones--#ai4 ,hairs of stinging-nettle--#bj4 ,section of cellular parenchyma of ripe strawberry4 ,,plate ,,xiv4--,page #dgb4 ,,stellate ,,and ,,crystalline ,,tissue4 ,fig4 #a4 ,epidermis of husk of wheat1 spiral vessels and silicious crystals--#b4 ,section of cane1 silicious cell walls1 internal portion filled with granular bodies--#c4 ,cuticular layer of the onion1 showing crystals of calcium carbonate and oxalate--#d4 ,cells of garden rhubarb1 with crystalline bodies and raphides--#d;a4 ,another layer filled with starch grains--#e4 ,section of pear1 testa1 sclerogenous and granular tissue--#f4 ,stellate hairs1 sinuous cells and silicious parenchyma of leaf of ,deutzia scabra1 under surface--#g4 ,silicious cuticle layer of grass1 ,pharus cristatus4 ,,plate ,,xv4--,page #dhb4 ,,rhizopoda4--,,gromia4--,,foraminifera4 ,fig4 #a4 ,astrorhiza limicola--#b4 ,lieberkhnia paludosa--#c4 ,micro-gromia socialis undergoing fission--#d4 ,a colony of ,hertwig's ,micro-gromia socialis--#e4 ,g4 ,lieberkhnia--#f4 ,egg-shaped ,gromia1 ,g4 oviformis1 with pseudopodia extended1 magnified #ejj diameters4 8,hertwig ,ueber ,micro-gromia1 archiv4 fr ,mickr4 ,anat4 bdx40 ,,plate ,,xvi4--,page #eaj4 ,,sponge ,,spicules4 ,fig4 #a4 ,a portion of sponge1 ,halichondria simulans1 showing silicious spicula imbedded in the sarcode matrix--#b4 ,spicula divested of its matrix by acid--#c4 ,gemmule ,spongilla fluviatallis enclosed in spicula--#d4 ,birotulate spicula from same--#e4 ,gemmule after being steeped in acid showing reticulated coating of birotulate spicula--#f4 ,gemmules of ,geodia--#g4 ,gemmule in more advanced stage of growth--#h4 ,skeleton of the acerate form covered by rows of spines--#i4 ,showing rings of growth and horny covering1 and bundles of spicula of the genus ,verongia--#aj4 ,sphero-stellate spicula of ,tethya--#aa4 ,tricuspidanchorate and sphero-stellate spicula--#ab4 ,acuate-bi-clavate and other forms of spicula from ,geodia--#ac4 ,clavate spicula covered with short spines4 ,,plate ,,xvii4--,page #eah4 ,,zoophytes1 ,,asteroids1 ,,nudibranchs1 ,,and ,,echinoids4 ,fig4 #a4 a4 ,astrophyton scutatum--b4 ,doris pinnatifida1 back and side view--c4 quorea ,forbesina--d4 ,medus bud--e4 ,thaumantias corynetes--f4 ,echinus in an early free stage--g4 ,echinus sphra--h4 ,cydippe pyleus--i4 ,ascidi--k4 ,botryllus violaceus1 on a ,fucus--l4 ,corystes cassivelaunus--m4 ,eurynome aspera--n4 ,ophiocoma rosula--o4 ,pagurus ,prideauxii--p4 ,ebalia ,permantii4 ,,plate ,,xviii4--,page #eeh4 ,,shells ,,of ,,mollusca4 ,fig4 #a4 ,transverse section of spine of ,echinus--#b4 ,another section of ,echinus1 showing reticulated structure1 the calcareous portion dissolved out by acid--#c4 ,horizontal section of shell of ,haliotis splendens1 showing stellate pigment--#d4 ,shell of crab with granules in articular layer--#e4 ,another section of same shell1 showing hexagonal structure--#f4 ,horizontal section of coach-spring shell1 ,terebratulata rubicunda1 showing radiating perforations--#g4 ,transverse section of shell of the ,pinna ingens--#h4 ,crystals of carbonate of lime1 from oyster shell4 ,,plate ,,xix4--,page #fcf4 ,,vertebrata4 ,fig4 #a4 a4 ,spheroidal epithelium cells1 filled with central nuclei and granular matter2 b4 mucous membrane of stomach1 showing cells1 with open mouths of tubes at the bottom of each1 magnified #ej diameters--#b4 a4 ,diagram of a portion of the involuted mucous membrane1 showing continuation of its elements in the follicles and villi1 with a nerve entering the submucous tissue4 ,the upper surface of one villus is covered with cylindrical epithelium2 the other denuded1 and with dark line of basement membrane running around it2 b4 epithelium cells1 separated and magnified #bjj diameters1 a central nucleus1 with a nucleolus1 seen in centre2 c4 pavement epithelium cells1 from the mucous membrane of bronchial or air tubes with nuclei1 and nucleoli in some2 d4 vibratile or ciliated epithelium1 nuclei visible1 and cilia at the upper free surface1 magnified #bjj diameters--#c4 a4 is one of the tubular follicles from a pig's stomach1 cut obliquely to display upper part of cavity1 and the cylindrical epithelium forming its walls1 a few cells detached2 b4 shows a section of a lymphatic1 with capillary blood-vessels1 distributed beneath the mucous surfaces--#d4 ,cells of adipose tissue1 or fat1 magnified #ajj diameters--#e4 a single fat-cell separated1 and magnified #bej diameters--#f4 ,a capillary of blood-vessels distributed through tissue--#g4 ,section of the ,tendo-,achillis as it joins the cartilage1 showing stellate cells of tendon1 seen to be gradually coalescing to form round or oval cells of cartilage--#h4 ,a vertical section of cartilage1 with clusters of cells arranged in columns previous to their conversion into bone--#i4 ,a small transverse section of the same1 showing the gradual change of the cartilage cells at a4 into the true bone cells1 lacun1 at b4 with characteristic canaliculi--#aj4 ,a stellate nerve corpuscle1 with tubular processes issuing forth1 at a4 filled with corpuscles containing black pigment1 above which is a corpuscle the nucleus of which is seen to have nucleoli2 at b4 a corpuscle enclosed within sheath1 and filled with granular matter taken from the root of a spinal nerve--#aa4 ,the continuity of muscle1 the upper portion1 with connective tissue of the lower portion1 from the tongue of a lamb--#ab4 ,branched muscle1 ending in stellate connective cells1 from the upper lip of the rat--#ac4 ,choroidal black pigment-cells from the human eye4 ,,plate ,,xx4--,page #feh4 ,,bone ,,structure4 ,figs4 #a4 and #b4 ,transverse section of the human clavicle 7collar bone71 showing ,haversian canals1 concentric lamin1 and concentric arrangement of bone cells--#c4 ,transverse section of the femur of an ostrich--#d4 ,transverse section of humerus 7fore-arm7 bone of a turtle1 ,chelonia mydas--#e4 ,horizontal section of the lower jaw-bone of a conger eel1 in which no ,haversian canals are present--#f4 ,a portion of the cranium of a siren1 ,siren lacertina--#g4 ,portion of bone taken from the shaft of humerus of a ,pterodactyle1 showing elongated bone-cells characteristic of the order ,reptilia--#h4 ,horizontal section of a scale1 or flattened spine1 from the skin of a ,trygon 7sting-ray71 showing large ,haversian canals1 numerous wavy parallel tubes1 also bone-cells with canaliculi communicating as in dentine4 ,,errata4 ,prefaces1 page vi41 line #bb ,insert 8a0 into 8admitted40 x41 line #ac ,insert 8the0 before 8assistance40 xii4 ,insert 8for0 at commencement of line #bd4 ,page #cc1 line #ac ,for 8,rabbit0 read 8,kitten40 #dhf1 #dth line from bottom ,strike out 8,the late40 #eaa1 two lines from bottom ,for 8,plate ,,xiii40 read 8,plate ,,xvi40 #ehd1 #eth line from bottom ,insert 8,stalk-,eyed0 before 8crustaceans40 #fbd1 line #ab ,for 8or0 read 8and40 #fcc1 ,plate ,,vii4 ,numbering of figures-- ,for 8#aeb0 read 8#aeh40 ,for 8#aeb;a0 read 8#aeb40 7,professor ,abbe1 erroneously referred to more than once as 8the late0 is1 the author is happy to say1 in excellent health74 ,,the ,,microscope4 ,,part ,i4 ,early ,history of the ,microscope4 ,the instrument known as the ,microscope derives its designation from two ,greek words1 7mikros71 small1 and 7skopeo71 to see or observe2 and is an optical instrument by means of which objects are so magnified that details invisible or indistinct to the naked eye are clearly seen4 ,its origin1 so far as yet can be traced back1 seems to be of a doubtful nature4 ,it is tolerably certain the ancients had little or no conception of the magnifying power of lenses2 this may be surmised from their writings4 ,the elder ,pliny incidentally states that the physicians of his day cauterised by means of 8a globe of crystal40 ,the learned ,greek physician1 ,galen1 however1 demonstrates conclusively that in the first and second centuries of our era the use of magnifying lenses was quite unknown either to ,greek or ,roman4 ,moreover1 the writings of ,archimedes1 ,ptolemy1 and other learned men1 show that1 although they had some idea of the action of refraction at plane surfaces1 as of water1 yet of the refraction at curved surfaces they had formed no conception4 ,indeed1 they refer quite indiscriminately to the spherical form1 or the disc1 or the plane surface of the water1 but not one of them speaks of the lenticular form1 or the curvature of their surfaces4 ,as to the more powerful optical instruments1 the telescope and microscope1 although it would appear that ,alhazen in the #ajth or #aath century1 ,roger ,bacon in the #acth1 and ,fracastoro and ,baptist ,porta in the #afth1 had formed some idea that lenses might be made and combined so that distant objects might be seen clearer1 or near ones magnified beyond the power of normal vision2 yet we hold with ,kepler1 that no instrument analogous to our telescope was known before the early part of the #agth century4 ,the combination of lenses associated with the name of ,galileo1 was1 he tells us1 of ,dutch origin1 and of a date anterior to that of his telescope1 constructed by him in #afji2 and this would appear to be the probable origin of the microscope consisting of a combination of a convex object lens with a concave eye lens4#c ,it now appears almost impossible to assign the exact date of the first production of the microscope 7as distinguished from the simple magnifying lens71 but those who have made a special investigation1 agree that it must have been invented between #aeij and #afji1 and that either of the three spectacle-makers of ,middelburg1 ,holland1 ,hans ,janssen1 his son ,zacharias ,janssen1 and ,hans ,lippershey1 may have been the inventor1 the probabilities being in favour of the ,janssens1 and there the question must remain4 ,the history of the modern microscope1 like that of nations and arts1 has had its brilliant periods1 in which it shone with uncommon splendour1 and was cultivated with extraordinary ardour2 these periods have been succeeded by intervals marked with no discovery1 and in which the science seemed to fade away1 or at least to lie dormant1 till some favourable circumstance--the discovery of a new object1 or some new improvement in the instruments of observation--awakened the attention of the curious1 and reanimated the spirit of research4 ,thus1 soon after the invention of the microscope1 the field it presented to observation was cultivated by men of the first rank in science1 and who enriched almost every branch of natural history by the discoveries made by means of this instrument4 ,the ,modern ,microscope4 ,to the celebrated ,dr4 ,hooke belongs the honour of publishing an account of the compound instrument in #affe in his 8,micrographia40 ,his first claim1 however1 is founded on the application of a lamp adjustable on a pillar1 together with a glass globe of water and a deep plano-convex condensing lens4 ,by means of this arrangement1 he says1 8,the light can be directed more directly on the object under examination40 ,in the further description given of his microscope1 he explains3 8,it has four draw-tubes for lengthening the body1 and a third lens to the optical combination40 ,this1 it would appear1 was only brought into use when he wished to see the whole object at once3 8,the middle-glass lens1 conveying a very great company of radiating pencils 7of light7 which would stray away2 but when ,i had occasion to examine the small parts of a body1 ,i took out the middle glass and made use of one eye-glass with the object-glass40 ,from ,hooke's description ,i gather that he also introduced the ball-and-socket movement into the construction of the body of his instrument4 ,this has found many imitators since his day2 some of them have gone so far as to claim the invention as one quite new4 ,for small accessories1 where the leverage need not be considered1 the ball-and-socket has proved convenient enough2 but not1 however1 if applied to the stand of the microscope4 ,hooke1 in his early work1 expressed dissatisfaction with the ,english-made lenses he had in use4 ,he complains of the 8apertures of the object-glasses1 which are so small that very few rays are admitted2 none will admit a sufficient number of rays to magnifie the object beyond a determinate bigness40 ,so we may take it that he thus early discovered the great importance of an increase in the aperture of his microscope4 ,other improvements of importance were made1 and he was the first to describe a useful method of estimating the magnifying power of his lenses1 and the difficulty of distinguishing between a prominence and a depression in the object under investigation1 which he was made more fully aware of when preparing drawings for the illustration of his 8,micrographia ,illustrata02 this would be in #affd1 if not earlier4 ,his book created no little sensation on its first appearance1 and it soon became scarce4 ,hooke 7says ,mr4 ,mayall7 8must undoubtedly be credited with the first suggestion of immersion lenses40 ,nevertheless1 in his 8,lectures and ,collections10 published in #afgf1 he appears to be no longer enthusiastic over his double microscope1 and once more he reverts to the simpler instrument of his earlier days4 ,whether this change of opinion was due to the publication of ,leeuwenhoek's observations with his simple microscopes it is impossible to say4 ,as early as #afgc ,leeuwenhoek communicated some important discoveries made by a simple microscope of his own construction to the ,royal ,society2 he1 however1 gave no particulars of the construction of the instrument4 ,dr4 ,adams1 writing to his friend 7,sir7 ,hans ,sloane1 says3 8,they appear to be spherules lodged between two plates of gold or brass1 in a hole whose diameter appears to be no bigger than that of a small pin's head40 ,at his death he bequeathed to the ,royal ,society a cabinet containing twenty-six of these microscopes2 the cabinet and the microscopes long ago disappeared1 but not before they were carefully examined and described by ,mr4 ,henry ,baker1 ,f4,r4,s4 ,in his report to the ,royal ,society1 he says3 8,they consisted of a series of convex-lenses1 ranging in power from #abj to #ae1 and magnifying from #afj to #dj diameters40 ,this must now be regarded as an eventful period in the history of the microscope1 since ,leeuwenhoek's discoveries created a great sensation throughout ,europe4 ,and all further improvements in compound instruments appear to have been laid aside for some considerable period in consequence3 and the pocket instrument of ,wilson1 together with that of his scroll standard 7seen on the cover of this book71 and which was one of the first simple microscopes with a mirror mounted on the base in a line with the optic axis4 ,the discoveries once more made1 and at a much later period 7#agch71 by ,dr4 ,nathaniel ,lieberkuhn with his simple microscopes1 and by means of which he discovered the minute structure of the mucous membrane of the alimentary canal1 and which alone would have immortalised his name had we not preserved in use to this day an important adjunct of every modern instrument1 the ,lieberkuhn reflector4 ,in the ,museum of the ,royal ,college of ,surgeons of ,england1 there is a small cabinet of two drawers1 containing a set of twelve of his simple microscopes1 each being provided with an original injection4 ,the form of the instrument is shown in ,figs4 #a and #b4 a b represents a piece of brass tubing about an inch long and an inch in diameter and provided with a cap at each extremity4 ,the one at a carries a small double-convex lens of half an inch focal length2 while at b there is fixed a condensing lens three-quarters of an inch in diameter4 ,in ,fig4 #b the instrument is seen in section1 and explains itself4 ,it is held by the handle in such a position that the rays of light1 from a lamp or a white cloud1 may fall on the condenser b1 and concentrate on the speculum l4 ,this again further condenses the rays on the disc c1 where the object is held1 and its adjustment made by the milled-head screw d1 so as to bring it within the focus of the lens a4 ,illustration3 ,fig4 #a4 ,from this digression ,i pass on to the evolution of the compound microscope4 ,the earliest workable form known was that designed by ,eustachio ,divini1 who brought it to the notice of the ,royal ,society in #affh4 ,it consisted of two plano-convex lenses1 combined with their convex surfaces retained in apposition4 ,his idea was subsequently improved upon by a ,london optician4 ,not long afterwards1 ,philip ,bonnani published an account of his improved compound microscope2 and we are certainly indebted to him for two or more forms of the movable horizontal microscopes1 and for the compound condenser fitted with focussing gear for illuminating transparent objects by transmitted light4 ,i must1 however1 pass by the many changes made in the structure and form of the instrument by the celebrated ,dr4 ,culpeper1 ,scarlet1 ,cuff1 and many other inventors4 ,illustration3 ,fig4 #b4--,lieberkuhn's ,microscope4 ,benjamin ,martin's ,microscope4--,benjamin ,martin1 about #agdb1 was busily engaged in making improvements in the microscope1 and ,i may say he was certainly the first to provide accurate results for determining the exact magnifying power of any object-lens1 so that the observer might state the exact amplification in a certain number of diameters4 ,he devised numerous improvements in the mechanism and optical arrangements of the instrument2 the rack and pinion focussing adjustments2 the inclining movements to the pillar carrying the stage2 and the rectangular mechanical motions to the stage itself4 ,he was familiar with the principles of achromatism1 since it appears he produced an achromatic objective about #agei1 and he is said to have sent an achromatic objective to the ,royal ,society about that date4 ,but an ingeniously constructed microscope by ,martin found its way to ,george the ,third1 the grandfather of our ,queen1 and afterwards came into the possession of the late ,professor ,john ,quekett1 of the ,royal ,college of ,surgeons1 who presented it to the ,royal ,microscopical ,society of ,london4 ,this microscope will ever associate ,martin's name with the earliest and best form of the instrument1 even should he not receive full recognition as the inventor of the achromatic microscope4 ,on this account ,i introduce a carefully made drawing of so singularly perfect a form of the early ,english microscope to the notice of my readers4 7,fig4 #c47 ,the description given of it by the late ,professor ,quekett is as follows3--8,it stands about two feet in height1 and is supported on a tripod base1 ,a2 the central part of the stem1 ,b1 is of triangular figure1 having a rack at the back1 upon which the stage1 ,o1 and frame1 ,d1 supporting the mirror1 ,e1 are capable of being moved up or down4 ,the compound body1 ,f1 is three inches in diameter2 it is composed of two tubes1 the inner of which contains the eye-piece1 and can be raised or depressed by rack and pinion1 so as to increase or diminish the magnifying power4 ,at the base of the triangular bar is a cradle joint1 ,g1 by which the instrument can be inclined by turning the screw-head1 ,h 7connected with an endless screw acting upon a worm-wheel74 ,the arm1 ,i1 supporting the compound body1 is supplied with a rack and pinion1 ,k1 by which it can be moved backwards and forwards1 and a joint is placed below it1 upon which the body can be turned into the horizontal position2 another bar1 carrying a stage and mirror1 can be attached by a screw1 ,l ,n1 so as to convert it into a horizontal microscope4 ,the stage1 ,o1 is provided with all the usual apparatus for clamping objects1 and a condenser can be applied to its under surface2 the stage itself may be removed1 the arm1 ,p1 supporting it1 turned round on the pivot1 ,c1 and another stage of exquisite workmanship placed in its stead1 the under surface of which is shown at ,q40 ,illustration3 ,fig4 #c4--,martin's ,universal ,microscope4 #aghb4 ,this stage is strictly a micrometer one1 having rectangular movements and a fine adjustment1 the movements being accomplished by the fine-threaded screws1 the milled heads of which are graduated4 ,the mirror1 ,e1 is a double one1 and can be raised or depressed by rack and pinion2 it is also capable of removal1 and an apparatus for holding large opaque objects1 such as minerals1 can be substituted for it4 ,the accessory instruments are very numerous1 and amongst the more remarkable may be mentioned a tube1 ,m1 containing a speculum1 which can take the place of the tube1 ,r1 and so form a reflecting microscope4 ,the apparatus for holding animalcules or other live objects1 which is represented at ,s1 as well as a plate of glass six inches in diameter1 with four concave wells ground in it1 can be applied to the stage1 so that each well may be brought in succession under the magnifying power4 ,the lenses belonging to this microscope are twenty-four in number2 they vary in focal length from four inches to one-tenth of an inch2 ten of them are supplied with ,lieberkuhns4 ,a small arm1 capable of carrying single lenses1 can be supplied at ,t1 and when turned over1 the stage of the instrument becomes a single microscope2 there are four lenses suitable for this purpose1 their focal length varying from one-tenth to one-fortieth of an inch4 ,the performance of all the lenses is excellent1 and no pains appear to have been spared in their construction4 ,there are numerous other pieces of accessory apparatus1 all remarkable for the beauty of their workmanship4#d ,in addition to the movements described by ,quekett1 the body-tube with its support can be moved in an arc concentrically with the axis of the triangular pillar1 on the top of which it is fitted with a worm-wheel and endless-screw mechanism1 actuated by the screw-head1 ,t1 below4 ,it must therefore be admitted that ,martin led the way far beyond his contemporaries1 both in the design and the evolution of the microscope4 ,furthermore1 in his 8,new ,elements of ,optics10 #agei1 he dealt with the principle of achromatism1 by the construction of an achromatic telescope4 ,at a somewhat later period there lived in ,london a philosophical instrument maker of some repute1 ,george ,adams1 who published in #agdf a quarto book1 entitled 8,micrographia ,illustrata1 or the ,knowledge of the ,microscope ,explained40 ,this work fairly well describes 8the nature1 uses1 and magnifying powers of microscopes in general1 together with full directions how to prepare1 apply1 examine1 and preserve minute objects40 ,adams' book was the first of the kind published in this country1 and it contributed in no small degree to the advancement of microscopical science4 ,adams writes3 8,we owe the construction of the variable microscope to the ingenuity and generosity of a noble person4 ,the apparatus belonging to it is more convenient1 more certain1 and more extensive than that of any other at present extant2 consequently1 the advantage and pleasure attending the observations in viewing objects through it must be as extensive in proportion40 ,this is believed to apply to ,martin's several microscopes1 and that especially constructed for the king1 afterwards improved upon by ,adams4 ,another early form of microscope1 ,wilson ,simple ,scroll 7#agdf71 stamped on the cover of this book1 and has thus become familiar to microscopists1 was also made by ,adams4 ,we now closely approach a period fertile in the improvement of the microscope1 and in the discoveries made by its agency4 ,the chief of those among the honoured names of the time we find ,trembley1 ,ellis1 ,baker1 ,adams1 ,hill1 ,swammerdam1 ,lyonet1 ,needham1 and a few others4 ,adams somewhat sarcastically observes 8that every optician exercises his talents in improving 7as he calls it7 the microscope1 in other words1 in varying its construction and rendering it different in form from that sold by his neighbour2 or at the best rendering it more complex and troublesome to manage40 ,there were no doubt good reasons for these and other strictures upon inventors as well as makers of microscopes1 even in the ,adams' day4 ,in the year #aghg the 8,microscopical ,essays0 of his son were published1 in which he described all the instruments in use up to that period4 ,looking back1 and taking a general survey of the work of nearly two centuries in the history of the microscope1 it cannot be said that either in its optical or mechanical construction any great amount of progress was made4 ,this in part may have arisen from the fact that no pressing need was felt for either delicate focussing or higher magnification4 ,at all events1 it was not until the application of achromatism to the instrument that new life was infused into its use1 and a great impetus was given to its development1 both optically and mechanically4 ,in the year #ahbc a strong desire became manifest for improved forms of the instrument1 in ,france by ,m4 ,selligue1 by ,frauenhofer in ,munich1 by ,amici in ,modena1 by ,m4 ,chevalier in ,paris1 and by ,dr4 ,goring1 ,mr4 ,pritchard1 and ,mr4 ,tully in ,london4 ,the result was that in #ahbd a new form of achromatic object-glass was constructed of nine-tenths of an inch focal length1 composed of three lenses1 and transmitting a pencil of eighteen degrees2 and which1 as regards accurate correction throughout the field1 was for some years regarded as perfect4 ,sir ,david ,brewster was the first to suggest the great importance of introducing materials of a more highly refracting nature into the construction of lenses4 ,he wrote3 8,there can be no essential improvement expected in the microscope unless from the discovery of some transparent substance which1 like the diamond1 combines a high refractive with a low dispersive power40 ,having experienced the greatest difficulty in getting a small diamond cut into a prism in ,london1 he did not conceive it practicable to grind1 polish1 and form it into a lens4 ,mr4 ,pritchard1 however1 was led to make the experiment1 and on the #ast of ,december1 #ahbd1 8he had the pleasure of first looking through a diamond microscope40 ,dr4 ,goring also tried its performance on various objects1 both as a single microscope and as an objective of a compound instrument1 and satisfied himself of its superiority over other kinds of lenses4 ,but here ,mr4 ,pritchard's labours did not end4 ,he subsequently found that the diamond used had many flaws in it1 which led him to abandon the idea of finishing it4 ,having been prevented from resuming his operations on this refractory material for a time he made a third attempt1 and met with another unexpected defect2 he found that some lenses1 unlike the first1 gave a double or triple image instead of a single one1 in consequence of some of their parts being either harder or softer than others4 ,these defects were found to be due to polarisation4 ,mr4 ,pritchard having learned how to decide whether a diamond is fit for a magnifier or not1 subsequently succeeded in making two planoconvex lenses of adamant2 these proved to be perfect for microscopic purposes4 8,one of these1 of one-twentieth of an inch in focal length1 is now in the possession of his ,grace the ,duke of ,buckingham2 the other1 of one-thirtieth of an inch focus1 is in his own hands40 8,in consequence of the high refracting power of a diamond lens over a glass lens1 the former material may be at least one-third as thin as that of the latter1 and if the focal length of both be equal1 say1 one-eightieth of an inch1 the magnifying power of the diamond lens will be #b1acc diameters1 whereas that of glass will be only #hjj40 ,at a date 7#ahab7 before ,brewster proposed diamond lenses he demonstrated a simple method of rendering both single and compound microscopes achromatic4 8,starting10 he says1 8with the principle that all objects1 however delicate1 are best seen when immersed in fluid1 he placed an object on a slip of glass1 and put above a drop of oil1 having a greater dispersive power than the single concave lens1 which formed the object-glass of the microscope4 ,the lens was then made to touch the fluid1 so that the surface of the fluid was formed into a concave lens1 and if the radius of the outward surface was such as to correct the dispersion1 we should have a perfect achromatic microscope40 ,here we have the immersion system foreshadowed4 ,shortly after these experiments of ,brewster's were in progress1 ,dr4 ,goring is said to have discovered that the structure of certain bodies could be readily seen in some microscopes and not in others4 ,these bodies he named test objects4 ,he then examined these tests with the achromatic combinations of the ,tullys1 and was led to the discovery that 8the penetrating power of the microscope depends upon its angle of aperture40 8,while these practical investigations were in progress10 writes ,andrew ,ross1 8the subject of achromatism engaged the attention of some of the most profound mathematicians in ,england1 ,sir ,john ,herschel1 and ,professors ,airy and ,barlow4 ,mr4 ,coddington and others contributed largely to the theoretical examination of the subject2 and although the results of their labours were not applicable to the microscope1 they essentially promoted its improvement40 ,about this period 7#ahab7 ,professor ,amici1 of ,modena1 was experimentally engaged in the improvement of the achromatic object-glass1 and he invented a reflecting microscope superior to those of ,newton1 ,baker1 or ,smith1 made as early as #agch1 and long ago abandoned4 ,in #ahae ,amici made further experiments1 and introduced the immersion system2 while ,frauenhofer1 of ,munich1 about the same time constructed object-glasses for the microscope of a single achromatic lens1 in which the two glasses1 although placed in juxtaposition1 were not cemented together4 ,dolland1 it has been said1 introduced achromatic lenses2 but although he constructed many achromatic telescopes1 he did not apply the same principle to microscopes1 and those which he sold were only modifications of the compound microscope of ,cuff4 ,dr4 ,wollaston employed a new form of combination in a microscope constructed for his own use1 and by which 8he was able to see distinctly the finest markings upon the scales of the ,lepisma and ,podura1 and upon those of the gnat's wing40 ,his doublet is still employed1 and to which ,i shall refer under 8,simple ,microscopes40 ,illustration3 ,fig4 #c;a4--,sir ,david ,brewster's ,microscope1 of the early part of the century1 recently presented to the ,british ,museum4 ,,chapter ,i4 ,elementary ,optics4 ,value of ,inductive ,science--,light3 ,its ,propagation1 ,refraction1 ,reflection--,spherical and ,chromatic ,aberrations--,human ,eye1 formation of ,images of ,external ,objects in--,visual ,angle increased--,abbe's ,theory of ,microscopic ,vision4 ,the advances made in physics and mechanics during the #agth and #ahth centuries fairly opened the way to the attainment of greater perfection in all optical instruments4 ,this has been particularly exemplified with reference to the invention of the microscope1 as briefly sketched out in the previous chapter4 ,indeed1 in the first half of the present century the microscope can scarcely be said to have held a position of importance among the scientific instruments in frequent use4 ,since then1 however1 the zoologist and botanist by its aid have laid bare the intimate structure of plants and animals1 and thereby have opened up a vast kingdom of minute forms of life previously undreamt of2 and in connection with chemistry a new science has been founded1 that of bacteriology4 ,for these reasons it will be of importance to the student of microscopy to begin at the beginning1 and it will be my endeavour to introduce to his notice such facts in physical optics as are closely associated with the formation of images1 and1 so to speak1 systematise such stepping stones for work hereafter to be accomplished4 ,elementary principles only will be adduced1 and without attempting to involve my readers in intricate mathematical problems1 and which for the most part are unnecessary for the attainment of the object in view4 ,i therefore pass at once to the consideration of the propagation of light through certain bodies4 ,the microscope1 whether simple or compound1 depends for its magnifying power on the influence exerted by lenses in altering the course of the rays of light passing through them being ,,refracted4 ,refraction takes place in accordance with two well-known laws of optics4 ,when a ray of light passes from one transparent medium to another it undergoes a change of direction at the surface of separation1 so that its course in the second medium makes an angle with its course in the first4 ,this change of direction is a resultant of refraction4 ,the broken appearance presented by a stick partly immersed in water1 and viewed in an oblique position1 is an illustration of the law of refraction4 ,liquids have a greater refractive power than air or gases4 ,as a rule1 with some few exceptions1 the denser of the two substances has the greater refractive power2 hence it is customary in enumerating some of the laws of optics to speak of the denser medium and the rarer medium4 ,the more correct designation would be the more refractive and the less refractive4#e ,illustration3 ,fig4 #d4--,law of ,refraction4 ,let ,r ,i 7,fig4 #d7 be a ray incident at ,i on the surface of separation of two media1 and let ,i ,s be the course of the ray after refraction4 ,then the angles which ,r ,i and ,i ,s make with the normal are the angle of incidence and the angle of refraction respectively1 and the first law of refraction is that these angles lie in the same plane1 or the plane of refraction is the same as the plane of incidence4 ,the law which connects the magnitudes of these angles1 and which was discovered by ,snell1 a ,dutch philosopher1 can only be stated either by reference to a geometrical construction1 or by using the language of trigonometry4 ,describe a circle about the point of incidence1 ,i as a centre1 and drop perpendiculars from the points where it cuts the rays on the normal4 ,the law is that these perpendiculars1 ,r ,p1 ,s ,p1 will have a constant ratio1 or the sines of the angles of incidence and refraction are in a constant ratio2 that is1 so long as the media through which the ray first passes1 and by which it is afterwards refracted1 remain the same1 and the light also of the same kind1 then it is referred to as the law of sines4 ,indices of ,refraction4 ,the ratio of the sine of the angle of incidence to the sine of the angle of refraction1 when a ray passes from one medium to another is termed the relative index of refraction4 ,when a ray passes from vacuum into any medium1 this ratio is always greater than unity1 and is called the absolute index of refraction1 or simply the index of refraction for the medium in question4 ,the absolute index of air is so small that it may be neglected in comparison with those of solids and liquids2 but strictly speaking1 the relative index for a ray passing from air into a given substance must be multiplied by the absolute index of the air1 in order to obtain the true index of refraction4 ,illustration3 ,fig4 #e4--,vision through a ,glass ,plate4 ,critical ,angle4--,it will be seen from the law of sines that1 when the incident ray is in the less refractive of the two media1 to every possible angle of incidence there is a corresponding angle of refraction4 ,the angle referred to is termed the critical angle1 and is readily computed if the relative index of refraction be given4 ,when the media are air and water1 this angle is about #dh #cj4 ,for air and ordinary kinds of glass its value varies from #ch to #da4 ,the phenomenon of total reflection may be observed in several familiar instances4 ,for example1 if a glass of water1 with a spoon in it1 is held above the level of the eye1 the under side of the surface is seen to shine like a mirror1 and the lower part of the spoon is seen reflected in it4 ,effects of the same kind are observed when a ray of sunlight passes into an aquarium--on the other hand rays falling normally on a uniform transparent plate of glass with parallel faces keep their course2 but objects viewed obliquely through the same are displaced from their true position4 ,let ,s 7,fig4 #e7 be a luminous point which sends light to an eye not directly opposite to it1 on the other side of a parallel plate4 ,the emergent rays which enter the eye are parallel to the incident rays2 but as they have undergone lateral displacement1 their point of concourse is changed from ,s to ,s1 and this is accordingly the image of ,s4 ,the rays in such a case which compose the pencil that enters the eye will not exactly meet in any one point2 there will be two focal lines1 just as in the case of spherical mirrors4 ,the displacement produced1 as seen in the figure referred to above1 increases with the thickness of the plate1 its index of refraction1 and the obliquity of incidence4 ,this furnishes one of the simplest means of measuring the index of refraction of a glass substance1 and is thus employed in ,pichot's refractometer 78,deschanel074 ,illustration3 ,fig4 #f4--,refraction through a ,prism4 ,refraction through a ,prism4--,a prism is a portion of a refracting medium bounded by two plane surfaces1 inclined at a definite angle to one another4 ,the two plane surfaces are termed the faces of the prism1 and their inclination to one another is the refracting angle of the prism4 ,a prism preserves the property of bending rays of light from their original course by refraction4 ,a cylinder may be regarded as the limit of a prism whose sides increase in number and diminish in size indefinitely3 it may also be regarded as a pyramid whose apex is removed to an indefinite distance4 ,let ,s ,i 7,fig4 #f7 be an incident ray in the plane of the principal section of the prism4 ,if the external medium be air1 or other substance of less refractive power than the prism1 the ray on entering the same will be bent nearer to the normal1 taking such a course as ,i ,e1 and on leaving the prism will be bent away from the normal1 taking the course ,e ,b4 ,the effect of these two refractions is1 therefore1 to turn the ray away from the edge 7or refracting angle7 of the prism4 ,in practice1 the prism is usually so placed that ,i ,e1 the path of the ray through the prism1 makes equal angles with the two faces at which refraction occurs4 ,if the prism is turned very far from this position1 the course of the ray may be altogether different from that represented in the figure2 it may enter at one face1 be internally reflected at another1 and come out at the third4 ,it is evident1 therefore1 that the minimum number of sides1 i4e41 the bounding faces1 exclusive of the ends1 which a prism can have is three4 ,in this form1 it constitutes a most valuable instrument of research in physical optics4 ,a convex lens is practically merely a curved form of two prisms combined1 their bases being brought into contact2 on the other hand the concave lens is simply a reversal of the position of the apices brought into contact1 as shown in ,fig4 #aa4 ,both convex and concave lenses are therefore closely related to the prism4 ,reflection4--,the laws that govern the change of direction which a ray of light experiences when it strikes upon the surfaces of separation of two media and is thrown back into the same medium from which it approached is as follows3--,when the reflecting surface is plain the direction of the reflected ray makes with the normal to the surface the same angle which the incident ray makes with the same normal2 or1 as it is usually expressed1 the angles of reflection and incidence are equal4 ,when the surfaces are curved the same law holds good4 ,in all cases of reflection the energy of the ray is diminished1 so that reflection must always be accompanied by absorption4 ,the latter probably precedes the former4 ,most bodies are visible by light reflected from their surfaces1 but before this takes place the light has undergone a modification1 namely1 that which imparts colour peculiar to the bodies viewed4 ,when light impinges upon the surface of a denser medium part is reflected1 part absorbed1 and part refracted4 ,but for a certain angle depending upon the refractive index of the refracting medium no refraction takes place4 ,this angle is termed the angle of total reflection1 since all the light which is not absorbed is wholly reflected4 ,multiple images are produced by a transparent parallel plate of glass4 ,if the glass be silvered at the back1 as it usually is in the microscope-mirror1 the second image is brighter than the first1 but as the angle of incidence increases the first image gains upon the second2 and if the luminous object be a lamp or candle1 a number of images1 one behind the other1 will be visible to an eye properly placed in front4 ,this is due to the fact that the reflecting power of a surface of glass increases with the angle of incidence4 ,illustration3 ,fig4 #g4--;,conjugate ,foci of ,curved ,surfaces4 ,concave ,surfaces4--,rays of light proceeding from any given point in front of a concave spherical mirror1 are reflected so as to meet in another point1 and the line joining the two points passes through the centre of the sphere4 ,the relation between them is or should be mutual1 hence they are termed conjugate foci4 ,by a focus in general is meant a point in which a number of rays of light meet1 and the rays which thus meet1 taken collectively1 are termed a pencil4 ,fig4 #g represents two pencils of rays whose foci1 ,s s1 are conjugate1 so that1 if either of them be regarded as an incident pencil1 the other will be the corresponding reflected pencil4 ,each point1 in fact1 sends a pencil of rays which converge1 after reflection1 to the conjugate focus4 ,the principal focal distance is half the radius of curvature4 ,but it will not escape attention that concave mirrors have two reflecting surfaces1 a front and a back4 ,this1 however1 does not practically disturb its virtual focus1 since the achromatic condenser when brought into use collects and concentrates the light received from the mirror upon an object for the purpose of rendering it more distinctly visible to the eye when viewing an object placed on the stage of the microscope4 ,the images seen in a plane mirror are always virtual1 and any spherical mirror1 whether concave or convex1 is nearly equivalent to a plane mirror when the distance of the object from its surface is small in comparison with the radius of curvature4 ,lenses4 ,forms of ,lenses4--,a lens is a portion of a refracting medium bounded by two surfaces which are portions of spheres1 having a common axis1 termed the axis of the lens4 ,lenses are distinguished by different names1 according to the nature of their surfaces4 ,illustration3 ,fig4 #h4--;,converging and ,diverging ,lenses4 ,lenses with sharp edges 7thicker at the centre7 are convergent or positive lenses4 ,lenses with blunt edges 7thinner at the centre7 are divergent or negative lenses4 ,the first group comprises3--7#a7 ,the bi-convex lens2 7#b7 the plano-convex lens2 7#c7 the convergent meniscus4 ,the second group3--7#d7 ,the concave lens2 7#e7 the plano-concave lens2 7#f7 the divergent meniscus 7,fig4 #h74 ,principal ,focus4--,a lens is usually a solid of revolution1 and the axis of revolution is termed the principal axis of the lens4 ,when the surfaces are spherical it is the line joining the centre of curvature4 ,from the great importance of lenses1 especially convex lenses1 in practical optics1 it will be necessary to explain their properties somewhat at length4 ,illustration3 ,fig4 #i4--,principal ,focus of a ,convex ,lens4 ,principal ,focus of ,convex ,lens4--,when rays which were originally parallel to the principal axis pass through a convex lens 7,fig4 #i71 the effect of the two refractions which they undergo1 one on entering and the other on leaving the lens1 is to make them all converge approximately to one point ,f1 which is called the principal focus4 ,the distance ,a ,f of the principal focus from the lens is called the principal focal distance1 or more briefly and usually1 the focal length of the lens4 ,the radiant point and its image after refraction are known as the conjugate foci4 ,in every lens the right line perpendicular to the two surfaces is the axis of the lens4 ,this is indicated by the line drawn through the several lenses1 as seen in the diagram 7,fig4 #h74 ,the point where the axis cuts the surface of the lens is termed the verte4 ,parallel rays falling on a double-convex lens are brought to a focus in the centre of its diameter2 conversely1 rays diverging from that point are rendered parallel4 ,hence the focus of a double-convex lens will be at just half the distance1 or half the length1 of the focus of a plano-convex lens having the same curvature on one side4 ,the distance of the focus from the lens will depend as much on the degree of curvature as upon the refracting power 7termed the index of refraction7 of the glass of which it may be formed4 ,a lens of crown-glass will have a longer focus than a similar one of flint-glass2 since the latter has a greater refracting power than the former4 ,for all ordinary practical purposes we may consider the principal focus--as the focus for parallel rays is termed--of a double-convex lens to be at the distance of its radius1 that is1 in its centre of curvature2 and that of a plano-convex lens to be at the distance of twice its radius1 that is1 at the other end of the diameter of its sphere of curvature4 ,the converse of all this occurs when divergent rays are made to fall on a convex lens4 ,rays already converging are brought together at a point nearer than the principal focus2 whereas rays diverging from a point within the principal focus are rendered still more diverging1 though in a diminished degree4 ,rays diverging from points more distant than the principal focus on either side1 are brought to a focus beyond it3 if the point of divergence be within the circle of curvature1 the focus of convergence will be beyond it2 and vice-vers4 ,the same principles apply equally to a plano-convex lens2 allowance being made for the double distance of its principal focus2 and also to a lens whose surfaces have different curvatures2 the principal focus of such a lens is found by multiplying the radius of one surface by the radius of the other1 and dividing this product by half the sum of the radii4 ,illustration3 ,fig4 #aj4--,principal ,focus of ,concave ,lens4 ,in the case of a concave lens 7,fig4 #aj71 rays incident parallel to the principal axis diverge after passing through2 and their directions1 if produced backwards1 would approximately meet in a point ,f2 this is its principal focus4 ,it is1 however1 only a virtual focus1 inasmuch as the emergent rays do not actually pass through it1 whereas the principal focus of a converging lens is real4 ,illustration3 ,fig4 #aa4--,principal ,centre of ,lens4 ,optical ,centre of a ,lens4--,secondary ,axes4--,let ,o and ,o 7,fig4 #aa7 be the centres of the two spherical surfaces of a lens4 ,draw any two parallel radii1 ,o ,i1 ,o ,e1 to meet these surfaces1 and let the joining line ,i ,e represent a ray passing through the lens4 ,this ray makes equal angles with the normals at ,i and ,e1 since these latter are parallel by construction2 hence the incident and emergent rays ,s ,i1 ,e ,r also make equal angles with the normals1 and are therefore parallel4 ,in fact1 if tangent planes 7indicated by the dotted lines in the figure7 are drawn at ,i and ,e1 the whole course of the ray ,s ,i ,e ,r will be the same as if it had passed through a plate bounded by these planes4 ,let ,c be the point in which the line ,i ,e cuts the principal axis1 and let ,r1 ,r denote the radii of the two spherical surfaces4 ,then from the similarity of the triangles ,o ,c ,i1 ,o ,c ,e1 we have 7,o ,c7_/7,c ,o7 ,r_/,r2 which shows that the point ,c divides the line of centres ,o ,o in a definite ratio depending only on the radii4 ,every ray whose direction on emergence is parallel to its direction before entering the lens1 must pass through the point ,c in traversing the lens2 and conversely1 every ray which in its course through the lens traverses the point ,c1 has parallel directions at incidence and emergence4 ,the point ,c which possesses this remarkable property is called the centre1 or optical centre1 of the lens4 ,this diagram may also be taken to prove my former proposition1 that the convex lens is practically a form of two prisms combined4 ,illustration3 ,fig4 #ab4--;,conjugate ,foci1 one ,real1 the other ,virtual4 ,conjugate ,foci1 one ,real1 one ,virtual4--,when two foci are on the same side of the lens1 one 7the most distant of the two7 must be virtual4 ,for example1 in ,fig4 #ab1 if ,s1 ,s are a pair of conjugate foci1 one of them ,s being between the principal focus ,f and the lens1 rays sent to the lens at a luminous point at ,s1 will1 after emergence1 diverge as if from ,s2 and rays coming from the other side of the lens1 if they converge to ,s before incidence1 will in reality be made to meet in ,s4 ,as ,s moves towards the lens1 ,s moves in the same direction more rapidly2 and they become coincident at the surface of the lens4 ,formation of ,real ,images4--,let ,a ,b 7,fig4 #ac7 be an object in front of a lens1 at a distance less than the principal focal length4 ,it will have a real image on the other side of the lens4 ,to determine the position of the image by construction1 draw through any point ,a of the object a line parallel to the principal axis1 meeting the lens in ,a4 ,the ray represented by this line will1 after refraction1 pass through the principal focus1 ,f1 and its intersection with the secondary axis1 ,a ,o1 determines the position of a1 the focus conjugate to ,a4 ,we can in like manner determine the position of b1 the focus conjugate to ,b1 another point of the object2 and the joining line a b will then be the magnified image of the line ,a ,b4 ,it is evident that if a b were the object1 ,a ,b would be the image4 ,illustration3 ,fig4 #ac4--,real and ,magnified ,image4 ,the figures #ab and #ac represent the cases in which the distance of the object is respectively greater and less than twice the focal length of the lens4 ,the focal length of a lens is determined by the convexity of its surfaces and the refractive power of the material of which it is composed1 being shortened either by an increase of refractive power1 or diminution of the radii of curvature of the faces of the lens4 ,the increase or decrease of spherical aberration is determined by the shape or curvature of the lens2 it is less in the bi-convex than in other forms4 ,when a lamp or other source of light is placed at the focus of the rays constituting that portion of its light which falls upon the lens1 the light is so refracted as to become parallel4 ,should the source of light be brought nearer to the lens than the focus the refracted rays are still divergent1 though not to the same extent2 on the other hand1 if the source be beyond the focus1 the refracted rays are rendered convergent so as to meet at a point which is mathematically related to the distance of the luminous source from the focus4 ,the former arrangement is that with which we are most familiar1 since it is the ordinary magnifying glass4 ,concave ,lenses4 ,the refracting influence of a concave lens 7,fig4 #ad7 will be precisely the opposite of that of a convex4 ,rays which fall upon it in a parallel direction will be made to diverge as if from the principal focus1 which is here called the negative focus4 ,this will be1 for a plano-concave lens1 at the distance of the diameter of the sphere of curvature2 and for a double-concave1 in the centre of that sphere4 ,illustration3 ,fig4 #ad4--;,a ,virtual ,image formed by ,concave ,lens4 ,in ,fig4 #ad ,a ,b is the object and a b the image4 ,rays incident from ,a and ,b parallel to the principal axis will emerge as if they came from the principal focus ,f2 hence1 the points a b are determined by the intersections of the dotted lines in the figure with the secondary axis1 ,o ,a1 ,o ,b4 ,an eye on the other side of the lens sees the image a b1 which is always virtual1 erect and diminished4 ,in the construction of the microscope1 either simple or compound1 the curvature of the lenses employed is usually spherical4 ,convergent lenses1 with spherical curvatures1 have the defect of not bringing all the rays of light which pass through them to one and the same focus4 ,each circle of rays from the axis of the lens to its circumference has a different focus1 as shown in ,fig4 #ae4 ,the rays a a1 which pass through the lens near its circumference1 are seen to be more refracted1 or come to a focus at a shorter distance behind it than the rays b b1 which pass through near its centre or axis1 and are less refracted4 ,the consequence of this defect of lenses with spherical curvatures1 which is called spherical aberration1 is that a well-defined image or picture is not formed by them1 for when the object is focussed1 for the circumferential rays1 the picture projected to the eye is rendered indistinct by a halo or confusion produced by the central rays falling in a circle of dissipation1 before they have come to a focus4 ,on the other hand1 when placed in the focus of the central rays1 the picture formed by them is rendered indistinct by the halo produced by the circumferential rays1 which have already come to a focus and crossed1 and now fall in a state of divergence1 forming a circle of dissipation4 ,the grosser defects of spherical aberration are corrected by cutting off the passage of the rays a a1 through the circumferences of the lens1 by means of a stop diaphragm1 so that the central rays1 b b1 only are concerned in the formation of the image4 ,this defect is reduced to a minimum1 by using the meniscus form of lens1 which is the segment of an ellipsoid instead of a sphere4 ,illustration3 ,fig4 #ae4--,spherical ,aberration of ,lens4 ,the ellipse and the hyperbola are forms of lenses in which the curvature diminishes from the central ray1 or axis1 to the circumference b2 and mathematicians have shown that spherical aberration may be practically got rid of by employing lenses whose sections are ellipses or hyperbolas4 ,the remarkable discovery of these forms of lenses is attributed to ,descartes1 who mathematically demonstrated the fact4 ,if a l1 a l1 for example 7,fig4 #af7 be part of an ellipse whose greater axis is to the distance between its foci f f as the index of refraction is to unity1 then parallel rays r l1 r l incident upon the elliptical surface l a l1 will be refracted by the single action of that surface into lines which would meet exactly in the farther focus f1 if there were no second surface intervening between l a l and f4 ,but as every useful lens must have two surfaces1 we have only to describe a circle l a l round f as a centre1 for the second surface of the lens l l4 ,illustration3 ,fig4 #af4--;,converging ,meniscus4 ,as all the rays refracted at the surface l a l converge accurately to f1 and as the circular surface l a l is perpendicular to every one of the refracted rays1 all these rays will go on to f without suffering any refraction at the circular surface4 ,hence it should follow1 that a meniscus whose convex surface is part of an ellipsoid1 and whose concave surface is part of any spherical surface whose centre is in the farther focus1 will have no appreciable spherical aberration1 and will refract parallel rays incident on its convex surface to the farther focus4 ,illustration3 ,fig4 #ag4--;,aplanatic ,doublet4 ,the spherical form of lens is that most generally used in the construction of the microscope4 ,if a true elliptical or hyperbolic curve could be ground1 lenses would very nearly approach perfection1 and spherical aberration would be considerably reduced4 ,even this defect can be further reduced in practice by observing a certain ratio between the radii of the anterior and posterior surfaces of lenses2 thus the spherical aberration of a lens1 the radius of one surface of which is six or seven times greater than that of the other1 will be much reduced when its more convex surface is turned forward to receive parallel rays1 than when its less convex surface is turned forwards4 ,it should be borne in mind that in lenses having curvatures of the kind the object would only be correctly seen in focus at one point--the mathematical or geometrical axis of the lens4 ,chromatic ,aberration4--,we have yet to deal with one of the most important of the phenomena of light1 ,,chromatic ,,aberration1 upon the correction of which1 in convex lenses in particular1 the perfection of the objective of the microscope so much depends4 ,chromatism arises from the unequal refrangibility and length of the different coloured rays of light that together go to make up white light2 but which1 when treated of in optics1 is always associated with achromatism1 so that a combination of prisms1 or lenses1 is said to be achromatic when the coloured rays arising from the dispersion of the pencil of light refracted through them are combined in due proportions as they are in perfectly white light4 ,a lens1 however1 of uniform material will not form a single white image1 but a series of images of all colours of the spectrum1 arranged at different distances1 the violet being nearest1 and the red the most remote1 every other colour giving a blurred image2 the superposition of these and the blending of the different elementary rays furnishing a complete explanation of the beautiful phenomenon of the rainbow4 ,sharpness of outline is rendered quite impossible in such a case1 and this source of confusion is known as chromatic aberration4 ,in order to ascertain whether it is possible to remedy this evil by combining lenses of two different materials1 ,newton made some trials with a compound prism composed of glass and water 7the latter containing a little sugar of lead71 and he found it impossible by any arrangement of these two1 or by other substances1 to produce deviation of the transmitted light without separation into its component colours4 ,if this ratio were the same for all substances1 as ,newton supposed1 achromatism would be impossible2 but1 in fact1 its value varies greatly1 and is far greater for flint than for crown glass4 ,if two prisms of these substances1 of small refracting angles1 be combined into one1 with their edges turned in opposite directions1 they will achromatise each other4 ,the chromatism of lenses may1 however1 be somewhat further reduced by stopping out the marginal rays1 but as the most perfect correction possible is required when lenses are combined for microscopic uses1 other means of correction are resorted to1 as will be seen hereafter4 ,i shall first proceed to show the deviations which rays of white light undergo in traversing a lens4 ,if parallel rays of light pass through a double-convex lens the violet rays1 the most refrangible of them1 will come to a focus at a point much nearer to the lens than the focus of the red rays1 which are the least refrangible2 and the intermediate rays of the spectrum will be focussed at points between the red and the violet4 ,a screen held at either of these foci will show an image with prismatic fringes4 ,the white light1 ,a ,a 7,fig4 #ah71 falling on the marginal portion of the lens is so far decomposed that the violet rays are brought to a focus at ,c1 and crossing there1 diverge again and pass on to ,f ,f1 while the red rays1 ,b ,b1 do not come to a focus until they reach the point ,d1 and cross the divergent violet rays1 ,e ,e4 ,the foci of the intermediary rays of the spectrum 7red1 green1 and blue7 are intermediate between these extremes4 ,the distance1 ,c ,d1 limiting the blue or violet1 and the red is termed the longitudinal chromatic aberration of the lens4 ,if the image be received upon a screen placed at ,c1 violet will predominate and appear surrounded by a prismatic fringe1 in which violet will predominate4 ,if the screen be now shifted to ,d1 the image will have a predominant red tint1 surrounded by a series of coloured fringes in an inverted order to those seen in the former experiment4 ,the line ,e ,e joins the points of intersection between the violet and red rays1 and this marks the mean focus1 the point where the coloured rays will be least apparent4 ,illustration3 ,fig4 #ah4--;,chromatic ,aberration of ,lens4 ,in the early part of this century the optical correction of chromatic aberration was partially brought about by combining a convex lens of crown-glass with a concave lens of flint-glass1 in the proportion of which these two kinds of glass respectively refract and disperse rays of light2 so that the one medium may by equal and contrary dispersion neutralise the dispersion caused by the other1 without at the same time wholly neutralising its refraction4 ,it is a curious fact that the media found most available for the purpose should be a combination of crown and flint-glass1 of crown-glass whose index of refraction is #aeai1 and dispersive power #jjcf1 and of flint-glass whose index of refraction is #aehi1 and dispersive power #jjcic4 ,the focal length of the convex crown-glass lens must be #d-a_/c inches1 and that of the concave flint-glass lens #g-b_/c inches1 and the combined focal length #aj inches4 ,the diagram 7,fig4 #ai7 shows how rays of light are brought to a focus1 nearly free from colour4 ,the small amount of residual colour in such a combination is termed the secondary spectrum2 the violet ray ,f ,y1 crossing the axis of the lens at ,v1 and going to the upper end ,p of the spectrum1 the red ray ,f ,b going to the lower end ,t4 ,but as the flint-glass lens l l1 on the prism ,a a ,c1 which receives the rays ,f ,v1 ,f ,r1 at the same points1 is interposed1 these rays will unite at f1 and form a small circle of white light1 the ray ,s ,f being now refracted without colour from its primitive direction ,s ,f ,y into the direction ,f f4 ,in like manner1 the corresponding ray ,s ,f will be refracted to f1 and a white colourless image be the result4 ,illustration3 ,fig4 #ai4--;,correction of ,chromatic ,aberration4 ,the achromatic aplanatic objective constructed on the optical formula enunciated1 did not meet all the difficulties experienced by the skilled microscopist1 in obtaining resolution of the finest test objects1 and whereby the intrinsic value of the objective 7in his estimation7 must stand or fall4 ,there were other disturbing residuary elements besides those of the secondary spectrum1 and which at a later period were met by the practical skill of the optician1 who applied the screw-collar1 and by means of which the back lens of the objective is made to approach the front lens1 thus more accurately shortening the distance between the eye-piece1 where the image is eventually formed1 and the back lens of the objective4 ,in this diagram ,l ,l is a convex lens of crown-glass1 and l l a concave one of flint-glass4 ,a convex lens will refract a ray of light 7,s7 falling at ,f on it exactly in the same manner as the prism ,a ,b ,c1 whose faces touch the two surfaces of the lens at the points where the ray enters1 and quits4 ,the ray ,s ,f1 thus refracted by the lens ,l ,l1 or prism ,a ,b ,c1 would have formed a spectrum 7,p ,t7 on a screen or wall1 had there been no other lens4 ,illustration3 ,fig4 #bj4--,virtual ,image formed by ,convex ,lens4 ,formation of ,virtual ,images4--,the normal eye possesses a considerable power of adjusting itself to form a distinct image of objects placed at varying distances2 the nearer1 within a certain limit1 the larger it appears1 and the more distinctly the details are brought out4 ,when brought within a distance of two or three inches1 the images become blurred or quite indistinct1 and when brought closer to the eye1 cannot be seen at all1 and it simply obstructs the light4 ,now the utility of a convex lens1 when interposed between the object and the eye1 consists in reducing the divergence of the rays forming the several pencils which issue from it1 and send images to the retina in a state of moderate divergence1 that is1 as if they had issued from an object beyond the nearest point of distinct vision1 and so that a more clearly defined image may reach the sensitive membrane of the eye4 ,but1 not only is the course of the several rays in each pencil altered as regards the rest1 but the course of the pencils themselves is changed1 so that they enter the eye under an angle corresponding with that under which they would have arrived from a larger object situated at a greater distance1 and thus the picture formed by any object corresponds in all respects with one which would have been made by the same object increased in its dimensions and viewed at the smallest ordinary distance of distinct vision4 ,for instance1 let an object ,a ,b 7,fig4 #bj7 be placed between a convex lens and its principal focus4 ,then the foci conjugate to the points ,a ,b are virtual1 and their positions can be found by construction from the consideration that rays through ,a1 ,b1 parallel to the principal axis1 will be refracted to ,f1 the principal focus on the other side4 ,the refracted rays1 if produced backwards1 must meet the secondary axis ,o ,a1 ,o ,b in the required points4 ,an eye placed on the other side of the lens will accordingly see a virtual image erect1 magnified1 and at a greater distance from the lens than the object4 ,this is the principle of the simple microscope4 ,the ,human ,eye4 ,to gain a clear insight into the mode in which a single lens serves to magnify objects1 it will be necessary to revert to the phenomena of ordinary vision4 ,an eye free from any defect has a considerable power of adjusting itself to very considerable distances4 ,one of the special functions of the eye is bringing the rays of light1 by a series of dioptric mechanisms1 to a perfect focus on its nervous sensitive layer1 the retina4 ,the eye in this respect has been compared to a photographic camera4 ,but this is not quite correct4 ,the retina is destined simply to receive the images furnished by the dioptric apparatus1 and has no influence upon the formation of these images4 ,the luminous rays are refracted by the dioptric apparatus2 the images would be formed quite as well--indeed1 even better in certain cases--if the retina were not there4 ,the dioptric apparatus and its action are absolutely independent of the retina4 ,the same laws with regard to the passage of the rays of light into the human eye hold good1 as those already enunciated in the previous pages4 ,as to change of direction when rays are passing obliquely from a medium of low density to that of a higher density1 i4e41 it changes its course1 and is bent towards the perpendicular4 ,on leaving the denser for the rarer medium it is bent once more from the perpendicular4 ,again1 by means of a convex lens1 the rays of light from one source will be refracted so as to meet at a point termed the principal focus of vision4 ,in the eye there are several surfaces separating the different media where refraction takes place4 ,the refractive index of the aqueous humour and the tears poured out by the lachrymal gland is almost equal to that of the cornea4 ,we may1 therefore1 speak of the refracting surfaces as three1 viz43 ,anterior surface of cornea1 anterior surface of lens1 and posterior surface of lens2 and also of the refracting media as three--the aqueous humour1 the lens1 and vitreous humour4 ,these several bodies are so adapted in the normal eye that parallel rays falling on the cornea are converged to a focus at the most sensitive spot 7the yellow spot1 or fovea centralis7 in the retina1 a point representing to the principal focus of the eye4 ,a line drawn from this point through the centre of the cornea is called the optic axis of the eye-ball4 ,illustration3 ,fig4 #ba4--,nerve and ,stellate ,cell ,layer of ,cornea1#f stained by chloride of gold2 magnified #cjj diameters4 a1 ,nerve cells4 b1 ,stellate cells4 ,illustration3 ,fig4 #bb4--;,anterior section of ,eye1 showing changed form of lens during the act of accommodation1 a voluntary action in the eye4 ,m1 ,ciliary muscle2 ,i1 ,iris2 ,l1 ,lens2 ,v1 ,vitreous ,humour2 ,a1 ,aqueous ,humour2 ,c1 ,cornea and optic axis4 ,but as we are able to form a distinct image of near objects1 and as we notice when we turn our gaze from far to near objects there is a distinct feeling of muscular effort in the eyes1 there must be some means whereby the eye can readily adapt itself for focussing near and distant objects4 ,in a photographic camera the focus can be readily altered1 either by changing the lenses1 employing a lens of greater or less curvature1 or by altering the distance of the screen from the lens4 ,the last method is obviously impossible in the rigid eye-ball1 and therefore the act of focussing for near and distant objects is associated with a change in the curvature of the lens1 a faculty of the eye termed accommodation 7,fig4 #bb71 a change chiefly accomplished by the ciliary 7muscle7 processes1 which pull the lens forwards and inwards by virtual contracting power of the ciliary muscle1 and by which its suspensory ligament is relaxed1 and the front of the lens allowed to bulge forward4 ,in every case1 however1 accommodation is associated with contraction of the iris1 the special function of which is that of a limiting diaphragm 7an iris-diaphragm71 ,fig4 #bc4 ,in an ordinary spherical bi-convex lens1 as already pointed out1 the rays of light passing through the periphery of the lens come to a focus at a nearer point than the rays passing through the central portion4 ,in this way a certain amount of blurring of the image takes place1 and which1 in optical language1 is termed spherical aberration4 ,this defect of the eye is capable of correction in three possible ways1 and which it may be well to repeat3 #a4 ,by making the refractive index of the lens higher at its centre than at its circumference2 7#b7 ,by making the curvature of the lens less near the circumference than at the centre2 7#c7 ,by stopping out the peripheral rays of light by a diaphragm4 ,the two latter methods are those resorted to in most optical instruments4 ,illustration3 ,fig4 #bc4--a4 ,equatorial section of ,eyeball1 showing ,iris and ,ciliary ,processes1 after washing away the pigment1 three diameters4 #b4 ,nerves of the ,cornea of ,kitten's ,eye1 stained with iodine4 #c4 ,fibres or ,tubules of ,lens1 #bej1 seen to be made up of superimposed crenated layers1 and is therefore not homogeneous in structure1 but made up of a number of extremely fine tubules1 whose curvatures are nearly spherical4 ,in the human eye an attempt is made to apply all these methods1 but the most important is the third1 that of applying the diaphragm formed by the iris1 a circular semi-muscular curtain lying just in front of the anterior surface of the lens4 ,the iris is also furnished with a layer of pigmental cells which effectually stop out all peripheral rays of light that otherwise would pass into the eye1 creating circles of diffusion of a disturbing nature to perfect vision4 ,this delicate membrane1 then1 is kept in constant action by a two-fold nerve supply1 derived from five or six sources1 which it is unnecessary to describe at length4 ,but the eye1 with all its marvellous adaptations1 has an obvious defect1 that of secondary or uncorrected chromatic aberration4 ,chromatic ,aberration of the ,eye4--,white light1 as previously explained1 is composed of different wave lengths2 and accordingly as these undulations are either longer or shorter1 so do they produce on the eye the impression of different colours4 ,we have seen how a pencil of white light may1 by means of a prism1 be decomposed into a multi-coloured band4 ,in an ordinary magnifying reading-glass these coloured fringes are always seen around the margins4 ,in practical optics chromatic aberration is partially corrected by employing two different kinds of glass in the construction of certain combined lenses4 ,in the human eye chromatism cannot be corrected in this way2 hence a blue light and a red light placed at the same distance from the eye appears to be unequally distant3 the red light requiring greater accommodation in the eye than the blue1 and this accordingly appears to be the nearer of the two4 ,this visual error may be experimentally shown and explained4 ,there is a kind of glass which at first sight appears dark blue or violet1 but which really contains a great deal of red4 ,take an ordinary microscope lamp1 having a metal or opaque chimney1 and drill a circular hole in it1 about #c mm4 in diameter4 ,this opening should be just at the height of the flame2 cover it over with a piece of ground glass and a piece of the red-blue glass4 ,thus will be formed a luminous point whose light is composed of red and blue1 i4e41 of colours far apart from each other in the spectrum4 ,illustration3 ,fig4 #bd4--;,chromatic ,aberration of ,eye1 showing the wave differences of the blue and red rays of light 7,landolt74 ,if rays coming from this point enter the eye1 the blue rays 7,fig4 #bd71 being more strongly reflected than the red1 will come to a focus sooner than the latter4 ,the red rays1 on the contrary1 will be brought to a focus later than the blue1 while the latter1 past their focus1 are diverging4 ,let ,a ,b ,c ,d 7,fig4 #bd7 be the section of a pencil of rays given off from a red-blue point sufficiently distant so that these rays may be regarded as parallel4 ,the focus of the blue is at b1 that of the red at r4 ,an eye is adapted to the distance of the luminous point when the circle of diffusion1 received upon the retina1 is at its minimum4 ,this is the case when the sentient layer of the retina lies between the two foci ,e4 ,in this case the point will appear as a small circle1 composed of the two colours1 that is to say--violet4 ,if the retina be in front of this point1 at the focus of the blue rays for instance1 the eye will perceive a blue point surrounded by a red circle1 the latter being formed by the periphery of the luminous cone of red rays1 which are focussed only after having passed the retina4 ,the blue point will become a circle of diffusion larger in proportion as the retina is nearer the dioptric system1 or as the focus for blue is farther behind it4 ,but the blue circle will always be surrounded by a red ring4 ,if1 on the contrary1 the retina is behind the focus for red1 the blue cone will be greater in diameter than the red1 and we shall have a red circle of diffusion1 larger in proportion as the retina is farther from the focus1 but always surrounded by a blue ring ,m4 ,if the blue-red point is five metres1 or more1 distant1 the emmetropic#g eye will evidently see it more distinctly1 i4e41 as a small violet point2 the hyperopic eye1 whose retina is situated in front of the focus of its dioptric system1 will see a blue circle1 surrounded by red2 the myopic eye1 whose retina is behind its focus1 will see a red circle1 surrounded by blue4 ,the size of these circles will be either larger or smaller when the principal focus of the eye is either in front of or behind the retina4#h ,the refractive surfaces of a perfectly formed eye are very like an ellipsoid of revolution with two axes1 one of which1 the major axis of the ellipse1 is at the same time the optic axis and that of rotation2 the other is perpendicular to it1 and is equal in all meridians4 ,eyes1 however1 perfectly constructed are rarely met with4 ,the curvature of the cornea is nearly always greater in one meridian than in another4 ,its surfaces then cannot be regarded as entirely belonging to an ellipsoid of revolution1 since the solid figure1 of which the former would constitute a part1 has not only two axes1 but three1 and these unequal4 ,this irregularity is not1 however1 always great enough to produce discomfort and it is therefore disregarded4 ,but in other cases the difference of curvature in the different meridians of the eye attain to a higher degree1 and vision falls far below the average4 ,illustration3 ,fig4 #be4--,lines as seen by the ,astigmatic4 ,the refractive anomaly alluded to is termed astigmatism 7from the ,greek1 privative1 1 a point--inability to see a point74 ,the way in which objects appear to such a person will mainly result from the way in which he sees a point4 ,take1 for example1 the vertical to be the most1 and the horizontal to be the least1 refractive meridian3 place a vertical line 7,fig4 #be1 ,i7 at a stated distance before the eye1 and the line will appear elongated1 owing to the diffusion image of each of the points composing it4 ,it will also seem to be somewhat broadened1 as at ,,ii4 ,if the vertical meridian is adapted to the distance of the vertical1 the line will appear very diffuse and broadened1 as at ,,iii4 ,all these little diffusion lines overlap each other1 and give the line an elongated appearance4 ,hence a straight line is seen distinctly by an astigmatic eye only when the meridian to which it is perpendicular is perfectly adapted to its distance4 ,a vertical line is seen distinctly when the horizontal meridian is adapted to its distance4 ,it appears indistinct when its image is formed by the vertical meridian4 ,the way in which an astigmatic person sees points and lines led to the discovery of this remarkable irregularity in the refraction of the eye4 ,the late ,astronomer ,royal1 ,sir ,george ,airy1 suffered for some years until1 indeed1 he discovered how it could be corrected4 ,this anomaly of curvature of the refractive surfaces of the eye is now known to prevail largely among the more civilised races of mankind4 ,it is1 then1 of very great importance when using high powers of the microscope4 ,in most persons the visual power of both eyes is rarely quite equal2 on the other hand1 the mind exerts an important influence1 dominates1 as it were1 the eye in the interpretation of visual sensations and images4 ,an example of this is presented in ,wheatstone's pseudoscope1 known to produce precisely the opposite effect of his stereoscope--conveys1 in fact1 the converse of relief produced by the latter and better known instrument4 ,visual ,judgment4--,the apparent size of an object is determined by the magnitude of the image formed on the retina1 and this is inversely proportional to the distance4 ,thus the size of an image on the retina of an object two inches long at a distance of a foot1 is equal to the image of an object four inches long at a distance of two feet4 ,an object can be seen if the visual angle subtended by it is not less than sixty seconds4 ,this is equivalent to an image on the fovea centralis of the retina of about #d #i across1 and which corresponds to the diameter of a cone3 so that while we have had under consideration the optical and physical conditions of human vision1 we have likewise taken a lesson on the action of lenses used in the construction of the microscope4 ,the ,theory of ,microscopical ,vision4 ,it has been said that no comparison can be instituted between microscopic vision and macroscopic2 that the images formed by minute objects are not delineated microscopically under ordinary laws of diffraction1 and that the results are dioptrical4 ,this assertion1 however1 cannot be accepted unconditionally1 as will be seen on more careful examination of the late ,professor ,abbe's masterly exposition of 8,the ,microscopical ,theory of ,vision10 and also his subsequent investigations on the estimation of aperture and the value of wide-angled immersion objectives1 published in the 8,journal of the ,royal ,microscopical ,society40 ,the essential point in ,abbe's theory of microscopical vision is that the images of minute objects in the microscope are not formed exclusively on the ordinary dioptric method 7that is1 in the same way in which they are formed in the camera or telescope71 but that they are largely affected by the peculiar manner in which the minute construction of the object breaks up the incident rays1 giving rise to diffraction4 ,the phenomena of diffraction in general may be observed experimentally by plates of glass ruled with fine lines4 ,fig4 #bf shows the appearance presented by a single candle-flame seen through such a plate1 an uncoloured image of the flame occupying the centre1 flanked on either side by a row of coloured spectra of the flame1 which become dimmer as they recede from the centre4 ,a similar phenomenon may be produced by dust scattered over a glass plate1 and by other objects whose structure contains very minute particles1 or the meshes of very fine gauze wire1 the rays suffering a characteristic change in passing through such objects2 that change consisting in the breaking up of a parallel beam of light into a group of rays1 diverging with wide angle and forming a regular series of maxima and minima of intensity of light1 due to difference of phase of vibration4#aj ,illustration3 ,fig4 #bf4 ,in the same way1 in the microscope1 the diffraction pencil originating from a beam incident upon1 for instance1 a diatom1 appears as a fan of isolated rays1 decreasing in intensity as they are further removed from the direction of the incident beam transmitted through the structure1 the interference of the primary waves giving a number of successive maxima of light with dark interspaces4 ,when a diaphragm opening is interposed between the mirror1 and a plate of ruled lines placed upon the stage such as ,fig4 #bg1 the appearance shown in ,fig4 #bg;a1 will be observed at the back of the objective on removing the eye-piece and looking down the tube of the microscope4 ,the centre circles are the images of the diaphragm opening produced by the direct rays1 while those on the other side 7always at right angles to the direction of the lines7 are the diffraction images produced by the rays which are bent off from the incident pencil4 ,in homogeneous light the central and lateral images agree in size and form1 but in white light the diffraction images are radially drawn out1 with the outer edges red and the inner blue 7the reverse of the ordinary spectrum71 forming1 in fact1 regular spectra the distance separating each of which varies inversely as the closeness of the lines1 being for instance with the same objective twice as far apart when the lines are twice as close4 ,illustration3 ,fig4 #bg4 ,illustration3 ,fig4 #bg;a4 ,the influence of these diffraction spectra may be demonstrated by some very striking experiments1 which show that they are not by any means accidental phenomena1 but are directly connected with the image which is seen by the eye4 ,the first experiment shows that with the central beam1 or any one of the spectral beams alone1 only the contour of the object is seen1 the addition of at least one diffraction spectrum being essential to the visibility of the structure4 ,illustration3 ,fig4 #bh4 ,illustration3 ,fig4 #bh;a4 ,when by a diaphragm placed at the back of the objective1 as in ,fig4 #bh1 we cover up all the diffraction spectra of ,fig4 #bg;a1 and allow only the central rays to reach the image1 the object will appear to be wholly deprived of fine details1 the outline alone will remain1 and every delineation of minute structure will disappear1 just as if the microscope had suddenly lost its optical power1 as in ,fig4 #bh;a4 ,this experiment illustrates a case of the obliteration of structure by obstructing the passage of the diffraction spectra to the eye-piece4 ,the next experiment shows how the appearance of fine structure may be created by manipulating the spectra4 ,illustration3 ,fig4 #bi4 ,illustration3 ,fig4 #bi;a4 ,when a diaphragm such as that shown in ,fig4 #bi is placed at the back of the objective1 so as to cut off each alternate one of the upper row of spectra in ,fig4 #bg;a1 that row will obviously become identical with the lower one1 and if the theory holds good1 we should find the image of the upper lines identical with that of the lower4 ,on replacing the eye-piece1 we see that it is so1 the upper set of lines are doubled in number1 a new line appearing in the centre of the space between each of the old 7upper7 ones1 and upper and lower set having become to all appearance identical1 as seen in ,fig4 #bi;a4 ,illustration3 ,fig4 #cj4 ,illustration3 ,fig4 #cj;a4 ,in the same way1 if we stop off all but the outer spectra1 as in ,fig4 #cj1 the lines are apparently again doubled1 as seen in ,fig4 #cj;a4 ,a case of apparent creation of structure1 similar in principle to the foregoing1 though more striking1 is afforded by a network of squares1 as in ,fig4 #ca1 having sides parallel to this page1 which gives the spectra shown in ,fig4 #ca;a1 consisting of vertical rows for the horizontal lines and horizontal rows for the vertical ones4 ,but it is readily seen that two diagonal rows of spectra exist at right angles to the diagonals of the squares1 just as would arise from sets of lines in the direction of the diagonals1 so that if the theory holds good we ought to find1 on obstructing all the other spectra and allowing only the diagonal ones to pass to the eye-piece1 that the vertical and horizontal lines have disappeared and are replaced by two new sets of lines at right angles to the diagonals4 ,illustration3 ,fig4 #ca4 ,illustration3 ,fig4 #ca;a4 ,illustration3 ,fig4 #cb4 ,illustration3 ,fig4 #cb;a4 ,on inserting the diaphragm1 ,fig4 #cb1 and replacing the eye-piece1 we find in the place of the old network the one shown in ,fig4 #cb;a1 the squares being1 however1 smaller in the proportion of #a 3 #b1 as they should be in accordance with the theory propounded4 ,an object such as ,pleurosigma angulatum1 which gives six diffraction spectra arranged as in ,fig4 #cc1 should1 according to this theory1 show markings in a hexagonal arrangement4 ,for there will be one set of lines at right angles to b1 a1 e1 another set at right angles to c1 a1 f1 and a third at right angles to g1 a1 d4 ,these three sets of lines will obviously produce the appearance shown in ,fig4 #cc;a4 ,illustration3 ,fig4 #cc4 ,illustration3 ,fig4 #cc;a4 ,illustration3 ,fig4 #cd4 ,a great variety of appearances may be produced with the same arrangement of spectra4 ,any two adjacent spectra with the central beam 7as b1 c1 a7 will form equilateral triangles and give hexagonal markings4 ,or by stopping off all but g1 c1 e 7or b1 d1 f71 we again have the spectra in the form of equilateral triangles2 but as they are now further apart1 the sides of the triangles in the two cases being as #c 3 #a1 the hexagons will be smaller and three times as numerous4 ,their sides will also be arranged at a different angle to those of the first set4 ,the hexagons may be entirely obliterated by admitting only the spectra g1 c1 or g1 f1 or b1 f1 etc41 when new lines will appear at right angles1 or obliquely inclined1 to the median line4 ,by varying the combinations of the spectra1 therefore1 different figures of varying size and positions are produced1 all of which cannot1 of course1 represent the true structure4 ,not only1 however1 may the appearance of particular structure be obliterated or created1 but it may even be predicted before being seen under the microscope4 ,if the position and relative intensity of the spectra in any particular case are given1 the character of the resultant image1 in some instances1 may be worked out by mathematical calculations4 ,a remarkable instance of such a prediction is to be found in the case recorded by ,mr4 ,stephenson1 where a mathematical student who had never seen a diatom1 worked out the purely mathematical result of the interference of the six spectra b-g of ,fig4 #cc 7identical with ,p4 angulatum71 giving the drawing copied in ,fig4 #cd4 ,the special feature was the small markings between the hexagons1 which had not1 before this time1 been noticed on ,p4 angulatum4 ,on more closely scrutinizing a valve1 stopping out the central beam and allowing the six spectra only to pass1 the small markings were found actually to exist1 though they were so faint they had previously escaped observation until the result of the mathematical deduction had shown that they ought to be seen4 ,these experiments seem to show that diffraction plays a very essential part in the formation of microscopical images1 since dissimilar structures give identical images when the differences of their diffractive effect is removed1 and conversely similar structures may give dissimilar images when their diffractive images are made dissimilar4 ,whilst a purely dioptric image answers point for point to the object on the stage1 and enables a safe inference to be drawn as to the actual nature of that object1 the visible indications of minute structure in a microscopical image are not always or necessarily conformable to the real nature of the object examined1 so that nothing more can safely be inferred from the image as presented to the eye1 than the presence in the object of such structural peculiarities as will produce the particular diffraction phenomena on which these images depend4 ,further investigations and experiments led ,abbe to discard so much of his theoretical conclusions relating to superimposed images having a distinct character as well as a different origin1 and as to their capability of being separated and examined apart from each other4 ,in a later paper he writes3 8,i no longer maintain in principle the distinction between the absorption image or direct dioptrical image and the diffraction image1 nor do ,i hold that the microscopical image of an object consists of two superimposed images of different origin or a different mode of production4 ,thus it appears that both the absorption image and the diffraction image he held to be equally of diffraction origin2 but while a lens of small aperture would give the former with facility1 it would be powerless to reveal the latter1 because of its limited capacity to gather in the strongly-deflected rays due to the excessively minute bodies the microscopical objective has to deal with40#aa ,abbe's theory of vision has been questioned by mathematicians1 and since his death ,lord ,rayleigh went more deeply into the question of 8the theory of the formation of optical images10 with special reference to the microscope and telescope4 ,he has shown that two lines cannot be fairly resolved unless their components subtend an angle exceeding that subtended by the wave-length of light at a distance equal to the aperture2 also1 that the measure of resolution is only possible with a square aperture1 or one bounded by straight lines1 parallel to the lines resolved4 ,lord ,rayleigh's ,theory of the ,formation of ,optical ,images1 with ,special ,reference to the ,microscope4#ab ,of the two methods adopted1 that of ,helmholtz's consists in tracing the image representative of a mathematical point in the object1 the point being regarded as self-luminous2 that of ,abbe's the typical object was not1 as we have seen1 a luminous point1 but a grating illuminated by plane waves of light4 ,in the latter method1 ,lord ,rayleigh argues that the complete representation of the object requires the co-operation of all the spectra which are focussed in the principal focal plane of the objective2 when only a few are present the representation is imperfect1 and wholly fails when there is only one4 ,he then proceeds to show1 by the aid of diagrams and mathematical formula1 how the resolving power can be adduced4 ,on further criticism of the ,abbe spectrum theory1 he observes 8that although the image ultimately formed may be considered to be due to the spectra focussed to a given point1 the degree of conformity of the image to the object is another question4 ,the consideration of the case of a very fine grating1 which might afford no lateral spectra at all1 shows the incorrectness of the usually accepted idea that if all the spectra are utilised the image will still be incomplete1 so that the theory 7originally promulgated by ,abbe7 requires a good deal of supplementing2 while it is inapplicable when the incident light is not parallel1 and when the object is1 for example1 a double point and not a grating4 ,even in the case of a grating1 the spectrum theory is inapplicable1 if the grating is self-luminous2 for in this case no spectra can be formed since the radiations from the different elements of the grating have no permanent phase-relations40 ,for these reasons ,lord ,rayleigh advises that the question should be reconsidered from the older point of view1 according to which the typical object is a point and not a grating4 ,such treatment will show that the theory of resolving power is essentially the same for all instruments4 ,the peculiarities of the microscope1 arising from the divergence-angles not being limited to be small1 and from the different character of the illumination1 are theoretically only differences of detail4 ,these investigations can be extended to gratings1 and the results so obtained confirm for the most part the conclusions of the spectrum theory4 ,furthermore1 that the function of the condenser in microscopic practice in throwing upon the object the image of the lamp-flame is to cause the object to behave1 at any rate in some degree1 as if it were self-luminous1 and thus to obviate the sharply-marked interference bands which arise when permanent and definite phase-relations are permitted to exist between the radiations which issue from various points of the object4 ,this is capable of mathematical proof2 and in the case where the illumination is such that each point of the row or of the grating radiates independently1 the limit to resolution is seen to depend only on the width of the aperture1 and thus to be the same for all forms of aperture as for those of the rectangular4 ,that ,abbe's theory of microscopic vision is fairly open to the criticisms passed on it by ,lord ,rayleigh must be taken for granted4 ,definition of ,aperture2 ,principles of ,microscopic ,vision4 ,it must be well within the last half-century that the achromatic objective-glass for the microscope was brought to perfection and its value became generally recognised4 ,prior to the discovery of the achromatic principle in the construction of lenses it was assumed that the formation of the microscopic image took place 7as we have already seen7 on ordinary dioptric principles4 ,as the image is formed in the camera or telescope1 so it was said to be in the microscope4 ,this belief existed1 it will be remembered1 at a time when dry objectives only were in favour and the use of the term angle of aperture was misunderstood1 when it was supposed that the different media with diffraction-indices were used2 and the angle of the radiant pencil was believed not only to admit of a comparison of two apertures in the same medium1 but likewise to admit of a standard of comparison when the media were entirely different in their refractive qualities4 ,it was during my tenure of office as secretary of the ,royal ,microscopical ,society 7#ahfg to #ahgc71 that the aperture question1 and also that of numerical aperture1 came under discussion1 both being met by the majority of the ,fellows of the ,society and practical opticians by a non-possumus4 ,opticians alleged1 that is1 before the value of aperture became fully recognised 7#ahfj71 that the achromatic objective had reached a stage of perfection1 beyond which it was not possible to go2 indeed1 not only opticians1 but physicists of high standing1 as ,professor ,helmholtz1 who made many important contributions to the theory of the microscope1 and who1 after duly weighing all the known physical laws on which the formation of images can be explained1 emphatically stated that in his opinion 8the limit of possible improvement of the microscope as an instrument of discovery had been very nearly reached40 ,a quarter of a century ago ,i ventured to throw a doubt upon so questionable a statement4 ,i determined1 if possible1 to submit the aperture question to an exhaustive examination4 ,my views were accordingly submitted to two of the highest authorities in this country--,sir ,george ,airy1 the then ,astronomer ,royal1 and ,sir ,george ,stokes1 ,professor of ,physics at ,cambridge ,university--both of whom agreed with me that the possible increase of aperture would be attended with great advantage to the objective1 and open the way to an extension of power resolution in the microscope4#ac ,the discussion afterwards took a warm turn1 as will be seen on reference to 8,the ,monthly ,microscopical ,journals0 of #ahgd1 #ahge and #ahgf4 ,the confusion into which the aperture question at this period had lapsed was no doubt due to the fact that its opponents had not yet grasped the true meaning of the term aperture4 ,it was believed to be synonymous with 8angular aperture10 much in use at the time4 ,it will1 however1 appear quite unaccountable that even the older opticians should have confounded the latter with the former2 and so entirely disregarded the fact that the angles of the pencil of light admitted by the objective cannot serve as a measure of its aperture1 and that high refractive media can greatly reduce the value length of waves of light4 ,when the medium in which the objective works is the same as air1 it is not that a comparison can be made by the angles of the radiant pencils only1 but by their sines4 ,for example1 if two dry objectives admit pencils of #fj and #ahj1 their real apertures are not as #a 3 #c1 but as #a 3 #b only4 ,aperture in fact is computed by mathematicians by tracing the rays from the back focus through the system of lenses to the front focus1 the front focus being the point at which the whole cone of rays converge as free as may be from aberration4 ,if the front focus be in air1 no pencil greater than #hb1 8double the angle of total reflection10 can emerge from the plane front of the lens2 and1 obviously1 if no greater cone can emerge to a focus one way1 neither can any greater cone enter the body of the lens from the radiant4 ,this angle1 then1 of #hb1 must be regarded as the limit for dry lenses or objectives4 ,this limit1 it will be seen on more careful examination1 is very nearly the maximum angle that can be computed for a lens to have a front focus in air4 ,this can be proved by the consideration of the angle of the image of rays1 as they are radiated from the object itself in balsam3 for although this angle of image rays viewed as nascent from a self-luminous object capable of scattering rays in all directions1 may be #ahj in the substance of the balsam and cover-glass1 of the #ahj only #hb of the central portion will emerge into air--all rays beyond this limit are internally reflected at the cover-glass4 ,this cone1 then1 of #hb becomes #ahj in air1 and a large part must necessarily be lost by reflection at the first incidence on the plane front of the lens4 ,but with a formula permitting the use of a water medium between the front lens and the cover-glass1 the aperture of the image rays may reach #abf--;double the critical angle from glass to water2 and with an oil medium1 the aperture will be found to be limited only by the form of the front lens that can be constructed by the optician4 ,to sum up1 then1 the effect of the immersion system1 greatly assists in the correction of aberration1 gives increased magnification and angular aperture1 increase of working distance between the objective and object1 and renders admissible the use of the thicker glass-cover4 ,the aperture question would in all probability have remained unsolved many years longer 7ten or twelve years elapsed after ,i brought the question under discussion before opticians gave way71 but for the fortunate circumstance that the eminent mathematical and practical optician1 ,professor ,abbe1 of ,jena1 was about to visit ,london4 ,this came off in the early part of the seventies1 when the late ,mr4 ,john ,mayall and myself had the good fortune to interview him4 ,the subject discussed was naturally the increase of aperture and the theory of microscopical vision4 ,he readily at our request undertook to re-investigate the question in all its bearings on the microscope4 ,it is almost unnecessary to add that the conclusions he came to1 and the results obtained1 have proved of inestimable value to the microscopist and practical optician1 and it may well seem necessary to explain somewhat at greater length the conclusions the learned ,professor came to1 and by the adoption of which the microscope has been placed on a more scientific basis than it had before attained to4 ,several papers were published in extenso in the 8,journal of the ,royal ,microscopical ,society10 and ,i am greatly indebted to ,mr4 ,frank ,crisp1 ,,ll4,d41 for an excellent resum of ,abbe's ,monograph4#ad ,the essential step in the consideration of aperture is1 as ,i have said1 to understand clearly what is meant by the term4 ,it will at once be recognised that its definition must necessarily refer to its primary meaning of opening1 and must1 in the case of an optical instrument1 define its capacity for receiving rays from the object1 and transmitting them to the image received at the eye-piece4 ,in the case of the telescope-objective1 its capacity for receiving and transmitting rays is necessarily measured by the expression of its absolute diameter or 8opening40 ,no such absolute measure can be applied in the case of the microscope objective1 the largest constructed lenses of which having by no means the largest apertures1 being1 in fact1 the lower powers of the instrument1 whose apertures are for the most part but small4 ,the capacity of a microscope objective for receiving and transmitting rays is1 however1 as will be seen1 estimated by its relative opening1 that is1 its opening in relation to its focal length4 ,when this relative opening has been ascertained1 it may be regarded as synonymous with that denoted in the telescope by absolute opening4 ,that this is so will be better appreciated by the following consideration3-- ,in a single lens1 the rays admitted within one meridional plane evidently increase as the diameter of the lens 7all other circumstances remaining the same71 and in the microscope we have1 at the back of the lens1 the same conditions to deal with as are in front in the case of the telescope2 the larger or smaller number of emergent rays will therefore be measured by the clear diameter1 and as no rays can emerge that have not first been admitted1 this will give the measure of the admitted rays under similar circumstances4 ,if the lenses compared have different focal lengths but the same clear 8openings10 they will transmit the same number of rays to equal areas of an image at a definite distance1 because they would admit the same number if an object were substituted for the image2 that is1 if the lens were used as a telescope-objective4 ,but as the focal lengths are different1 the amplification of the images is different also1 and equal areas of these images correspond to different areas of the object from which the rays are collected4 ,therefore1 the higher power lens with the same opening as the lower power1 will admit a greater number of rays in all from the same object1 because it admits the same number as the latter from a smaller portion of the object4 ,thus1 if the focal lengths of two lenses are as #b 3 #a1 and the first amplifies ,n diameters1 the second will amplify #b ,n with the same distance of the image1 so that the rays which are collected to a given field of #a mm4 diameter of the image are admitted from a field of #a_/,n mm4 in the first case1 and of #a_/7b,n7 mm4 in the second4 ,as the 8opening0 of the objective is estimated by the diameter 7and not by the area7 the higher power lens admits twice as many rays as the lower power1 because it admits the same number from a field of half the diameter1 and1 in general1 the admission of rays by the same opening1 but different powers1 must be in the inverse ratio of the focal lengths4 ,in the case of the single lens1 therefore1 its aperture is determined by the ratio between the clear opening and the focal length4 ,the same considerations apply to the case of a compound objective1 substituting1 however1 for the clear opening of the single lens the diameter of the pencil at its emergence from the objective1 that is1 the clear utilised diameter of the back lens4 ,all equally holds good whether the medium in which the objective is placed is the same in the case of the two objectives or different1 as an alteration of the medium makes no difference in the power4 ,illustration3 #ahj ,oil ,angle4 7,numerical ,aperture #aeb47 ,illustration3 #ahj ,water ,angle4 7,numerical ,aperture #acc47 ,illustration3 #ahj ,air ,angle4 #if ,water ,angle4 #hb ,oil ,angle4 7,numerical ,aperture #ajj47 ,illustration3 #ig ,air ,angle4 7,numerical ,aperture #ge47 ,illustration3 #fj ,air ,angle4 7,numerical ,aperture #ej47 ,fig4 #ce4--,relative diameters of the 7utilized7 back lenses of various dry and immersion objectives of the same power 7#a_/d-;in47 from an air angle of #fj to an oil angle of #ahj4 ,thus we arrive at a general proposition for all kinds of objectives3 #ast1 when the power is the same1 the admission of rays 7or aperture7 varies with the diameter of the pencil at its emergence2 #bnd1 when the powers are different1 the same aperture requires different openings in the ratio of the focal lengths1 or conversely with the same opening the aperture is in inverse ratio to the focal lengths4 ,we see1 therefore1 that just as in the telescope the absolute diameter of the object-glass defines its aperture1 so in the microscope the ratio between the utilised diameter of the back lens and the focal length of the objective defines its aperture also1 and this is clearly a definition of aperture in its primary and only legitimate meaning as 8opening20 that is1 the capacity of the objective for admitting rays from the object and transmitting them to the image4 ,if1 by way of illustration1 we compare a series of dry and oil-immersion objectives1 and commencing with small air angles1 progress up to #ahj air angle1 and then take an oil-immersion of #hb and progress again to #ahj oil angle1 the ratio of opening to power progresses also1 and attains its maximum1 not in the case of the air angle of #ahj 7when it is exactly equivalent to the oil angle of only #hb71 but is greatest at the oil angle of #ahj4 ,if we assume the objectives to have the same power throughout we get rid of one of the factors of the ratio1 and we have only to compare the diameters of the emergent beams1 and can represent their relations by diagrams4 ,fig4 #ce illustrates five cases of different apertures of #a_/d-;in4 objectives1 viz43 those of dry objectives of #fj1 #ig1 and #ahj air angle1 a water-immersion of #ahj water angle1 and an oil-immersion of #ahj oil angle4 ,the inner dotted circles in the two latter cases are of the same size as that corresponding to the #ahj air angle4 ,a dry objective of the maximum air angle of #ahj is only able to utilise a diameter of back lens equal to twice the focal length1 while an immersion lens of even only #ajj utilises a larger diameter1 i4e41 it is able to transmit more rays from the object to the image than any dry objective is capable of transmitting4 ,whenever the angle of an immersion lens exceeds twice the critical angle for the immersion fluid1 i4e41 #if for water or #hb for oil1 its aperture is in excess of that of a dry objective of #ahj4 ,illustration3 ,fig4 #cf4 ,this excess will be seen if we take an oil-immersion objective of1 say #abb balsam angle1 illuminating it so that the whole field is filled with the incident rays1 and use it first on an object not mounted in balsam1 but dry4 ,we then have a dry objective of nearly #ahj angular aperture1 for1 as will be seen by reference to ,fig4 #cf1 the cover-glass is virtually the first surface of the objective1 as the front lens1 the immersion fluid1 and the cover-glass are all approximately of the same index1 and form1 therefore1 a front lens of extra thickness4 ,when the object is close to the cover-glass the pencil radiating from it will be very nearly #ahj1 and the emergent pencil 7observed by removing the eye-piece7 will be seen to utilise as much of the back lens of the objective as is equal to twice the focal length1 that is1 the inner of the two circles at the head of ,fig4 #ce4 ,if now balsam be run in beneath the cover-glass so that the angle of the pencil taken up by the objective is no longer #ahj1 but #abb only 7that is1 smaller71 the diameter of the emergent pencil is larger than it was before1 when the angle of the pencil was #ahj in air1 and will be approximately represented by the outer circle of ,fig4 #ce4 ,as the power remains the same in both cases1 the larger diameter denotes the greater aperture of the immersion objective over a dry objective of even #ahj angle1 and the excess of aperture is made plainly visible4 ,having settled the principle1 it is still necessary1 however1 to find a proper notation for comparing apertures4 ,the astronomer can compare the apertures of his various objectives by simply expressing them in inches1 but this is obviously not available to the microscopist1 who has to deal with the ratio of two varying quantities4 ,in consequence of a discovery made by ,professor ,abbe in #ahgc1 that a general relation existed between the pencil admitted into the front of the objective and that emerging from the back of the objective1 he was able to show that the ratio of the semi-diameter of the emergent pencil to the focal length of the objective could be expressed by the formula n ,sin u1 i4e41 by the sine of half the angle of aperture 7u7 multiplied by the refractive index of the medium 7n7 in front of the objective 7n being #aj for air1 #acc for water1 and #aeb for oil or balsam74 ,when1 then1 the values in any given cases of the expression n ,sin u 7which is known as the 8numerical aperture07 has been ascertained1 the objectives are instantly compared as regards their aperture1 and1 moreover1 as #ahj in air is equal to #aj 7since n #aj and the sine of half #ahj #aj7 we see1 with equal readiness1 whether the aperture is smaller or larger than that corresponding to #ahj in air4 ,thus1 suppose we desire to compare the apertures of three objectives1 one a dry objective1 the second a water immersion1 and the third an oil immersion2 these would be compared on the angular aperture view as1 say #gd air angle1 #he water angle1 and #aah oil angle1 so that a calculation must be worked out to arrive at the actual relation between them4 ,applying1 however1 the numerical#ae notation1 which gives #fj for the dry objective1 #ij for the water immersion1 and #acj for the oil immersion1 their relative apertures are immediately recognised1 and it is seen1 for instance1 that the aperture of the water immersion is somewhat less than that of a dry objective of #ahj1 and that the aperture of the oil immersion exceeds that of the latter by #cj4 ,the advantage of immersion1 in comparison with dry objectives1 becomes at once apparent4 ,instead of consisting merely in a diminution of the loss of light by reflection or increased working distance1 it is seen that a wide-angled immersion objective has a larger aperture than a dry objective of maximum angle1 so that for any of the purposes for which aperture is essential an immersion must necessarily be preferred to a dry objective4 ,that pencils of identical angular extension but in different media are different physically1 will cease to appear in any way paradoxical if we recall the simple optical fact that rays1 which in air are spread out over the whole hemisphere1 are in a medium of higher refractive index such as oil compressed into a cone of #hb round the perpendicular1 i4e41 twice the critical angle4 ,a cone exceeding twice the critical angle of the medium will therefore embrace a surplus of rays which do not exist even in the hemisphere when the object is in air4 ,the whole aperture question1 notwithstanding the innumerable perplexities which heretofore surrounded it1 is in reality completely solved by these two simple considerations3 ,first1 that 8aperture0 is to be applied in its ordinary meaning as representing the greater or less capacity of the objective for receiving and transmitting rays2 and second1 that when so applied the aperture of an objective is determined by the ratio between its opening and its focal length2 the objective that utilises the larger back lens 7or opening7 relatively to its focal length having necessarily the larger aperture4 ,it would hardly1 therefore1 serve any useful purpose if we were here to discuss the various erroneous ideas that gave rise to the contention that #ahj in air must be the maximum aperture4 ,amongst these was the suggestion that the larger emergent beams of immersion objectives were due to the fact that the immersion fluid abolished the refractive action of the first plane surface which1 in the case of air1 prevented there being any pencil exceeding #hb within the glass4 ,also the very curious mistake which arose from the assumption that a hemisphere did not magnify an object at its centre because the rays passed through without refraction4 ,a further erroneous view has1 however1 been so widespread that it seems to be desirable to devote a few lines to it1 especially as it always appears at first sight to be both simple and conclusive4 ,illustration3 ,fig4 #cg4 ,illustration3 ,fig4 #cg;a4 ,if a dry objective is used upon an object in air1 as in ,fig4 #cg1 the angle may approach #ahj1 but when the object is mounted in balsam1 as in ,fig4 #cg;a1 the angle at the object cannot exceed #hb1 all rays outside that limit 7shown by dotted lines7 being reflected back at the cover-glass and not emerging into air4 ,on using an immersion objective1 however1 the immersion fluid which replaces the air above the cover-glass allows the rays formerly reflected back to pass through to the objective1 so that the angle at the object may again be nearly #ahj as with the dry lens4 ,the action of the immersion objective was1 therefore1 supposed to be simply that it repaired the loss in angle which was occasioned when the object was transferred from air to balsam1 and merely restored the conditions existing in ,fig4 #cg;a with the dry objective on a dry object4 ,as the result of this erroneous supposition1 it followed that an immersion objective could have no advantage over a dry objective1 except in the case of the latter being used upon a balsam-mounted object1 its aperture then being 7as was supposed7 8cut down40 ,the error lies simply in overlooking the fact that the rays which are reflected back when the object is mounted in balsam 7,fig4 #cg;a7 are not rays which are found when the object is in air 7,fig4 #cg71 but are additional and different rays which do not exist in air1 as they cannot be emitted in a substance of so low a refractive index4 ,lastly1 it should also be noted that it is numerical and not angular aperture which measures the quantity of light admitted to the objective by different pencils4 ,illustration3 ,fig4 #ch4 ,illustration3 ,fig4 #ch;a4 ,first take the case of the medium being the same4 ,the popular notion of a pencil of light may be illustrated by ,fig4 #ch1 which assumes that there is equal intensity of emission in all directions1 so that the quantity of light contained in any given pencils may be compared by simply comparing the contents of the solid cones4 ,the ,bouguer-,lambert law1 however1 shows that the quantity of light emitted by any bright point varies with the obliquity of the direction of emission1 being greater in a perpendicular than in an oblique direction4 ,the rays are less intense in proportion as they are more inclined to the surface which emits them1 so that a pencil is not correctly represented by ,fig4 #ch1 but by ,fig4 #ch;a1 the density of the rays decreasing continuously from the vertical to the horizontal1 and the squares of the sines of the semi-angles 7i4e41 of the numerical aperture7 constituting the true measure of the quantity of light contained in any solid pencil4 ,if1 again1 the media are of different refractive indices1 as air 7#aj71 water 7#acc71 and oil 7#aeb71 the total amount of light emitted over the whole #ahj from radiant points in these media under a given illumination is not the same1 but is greater in the case of the media of greater refractive indices in the ratio of the squares of those indices 7i4e41 as #aj1 #agg and #bbe74 ,the quantity of light in pencils of different angle and in different media must therefore be compared by squaring the product of the sines and the refractive indices1 i4e4 7n ,sin u#b71 for the square of the numerical aperture4 ,the fact is therefore made clear that the aperture of a dry objective of #ahj does not represent1 as was supposed1 a maximum1 but that aperture increases with the increase in the refractive index of the immersion fluid2 and it should be borne in mind that this result has been arrived at in strict accordance with the ordinary propositions of geometrical optics1 and without any reference to or deductions from the diffraction theory of ,professor ,abbe4 ,there still remains one other point for determination1 namely1 the proper function of aperture in respect to immersion objectives of large aperture4 ,the explanation of the increased power of vision obtained by increase of aperture was1 that by the greater obliquity of the rays to the object 8shadow effects0 were produced1 a view which overlooked the fact1 first1 that the utilisation of increased aperture depends not only on the obliquity of the rays sent to the object1 but also to the axis of the microscope2 and exactly as there is no acoustic shadow produced by an obstacle1 which is only a few multiples of the length of the sound waves1 so there can be no shadow produced by minute objects1 only a few multiples from the light waves1 the latter then passing completely round the object4 ,the ,abbe diffraction theory1 however1 supplies the true explanation of this1 and shows that the increased performance of immersion objectives of large aperture is directly connected 7as might have been anticipated7 with the larger 8openings0 in the proper sense of the term1 which1 as we have already explained1 such objectives really possess4 ,furthermore1 in order that the image exactly corresponds with the object1 all diffracted rays must be gathered up by the objective4 ,should any be lost we shall have not an actual image of the object1 but a spurious one4 ,now1 if we have a coarse object1 the diffracted rays are all comprised within a narrow cone round the direct beam1 and an objective of small aperture will transmit them all4 ,with a minute object1 however1 the diffracted rays are widely spread out1 so that a small aperture can admit only a fractional part--to admit the whole or a very large part1 and consequently to see the minute structure of the object1 or to see it truly1 a large aperture is necessary1 and in this lies the value of aperture and of a wide-angled immersion objective for the observation of minute structures4 ,numerical ,aperture4 ,measure of ,apertures of ,objectives4 ,n4,a4--,numerical aperture1 as it is termed1 is measured by the scale of measurement calculated by the late ,professor ,abbe1 and which has since been generally recognised and adopted4 ,he showed that even in lenses made for the same medium 7as air7 their comparative aperture as compared with their focus was not correctly measured by the angle of the rays grasped1 but by the actual diameters of the pencil of rays transmitted1 which depend1 as already seen1 more upon the back of the lens than the front4 ,to get a geometric measure for comparison1 he took the radii1 or half diameters 7whose relative proportions would be the same71 and which geometrically are the sines of the semi-angle of the outermost rays grasped4 ,abbe further showed that if this sine of half the outside angle were multiplied by the refractive index of the medium used we should have a number which would give the comparative aperture of any lens1 whatever the medium4 ,this number1 then1 determines both the numerical aperture and the resolving power of the objective4 ,the following table of numerical apertures shows the respective angular pencils which they express in air1 water and cedar oil1 or glass4#af ,the first column gives the numerical apertures from #jbj to #acc2 the second1 third1 and fourth1 the air1 water and oil 7or balsam7 angles of aperture from #bc #d air angle to #ahj balsam angle4 ,the theoretical resolving power in lines to the inch is shown in the sixth column2 the line ,e of the spectrum being taken from about the middle of the green1 the column giving 8illuminating power0 being of less importance2 while in using that of penetrating power1 it must be remembered that several data beside that of #a_/;a go to make up the total depth of vision with the microscope4 ,,abridged ,,numerical ,,aperture ,,table4 ,corresponding ,angle ,limit of ,resolving ,power1 7#b u7 for in ,lines to an ,inch4 ---------------------------------------- ------- 7#a7 7#b7 7#c7 7#d7 7#e7 7#f7 7#g7 7#h7 7#i7 ---------------------------------------- ------------------------ #acc 444 #ahj #jabb #f #abh1bbe #ach1ihiafh1ijg #agfi #geb #acb 444 #afe #efabj #cc #abg1bfa #acg1iddafg1fcg #agdb #geh #acj 444 #aee #chaag #ce #abe1ccc #ace1hedafe1jig #afij #gfi #abh 444 #adh #dbaad #dd #abc1dje #acc1gfdafb1eeg #afch #gha #abf 444 #adb #ciaaa #ei #aba1dgg #aca1fgdafj1jag #aehh #gid #abd 444 #acg #cfaji #bj #aai1edh #abi1ehdaeg1dgg #aech #hjf #abb 444 #acc #dajf #de #aag1fbj #abg1didaed1icg #adhh #hbj #abj 444 #abh #eeajd #ae #aae1fib #abe1djdaeb1cig #addj #hcc #aah 444 #abe #caja #ej #aac1gfd #abc1cadadi1heg #acib #hdg #aaf 444 #aba #bf #ii #bi #aaa1hce #aba1bbdadg1cag #acdf #hfb #aad 444 #aah #j #ig #aa #aji1ijg #aai1acdadd1ggg #acjj #hgg #aab 444 #aad #dd #id #ee #ajg1igi #aag1jddadb1bcg #abed #hic #aaj 444 #aaa #cf #ib #dc #ajf1jea #aad1iedaci1fih #abaj #iji #ajh 444 #ajh #cf #ij #cd #ajd1abc #aab1hfdacg1aeh #aaff #ibf #ajf 444 #aje #db #hh #bg #ajb1aie #aaj1ggdacd1fah #aabd #idc #ajd 444 #ajb #ec #hf #ba #ajj1bff #ajh1fhdacb1jgh #ajhb #ifb #ajb 444 #ajj #aj #hd #ah #ih1cch #ajf1eicabi1ech #ajdj #ihj #ajj #ahj #j #ig #ca #hb #ag #if1daj #ajd1ejcabf1iih #ajjj #ajjj #jih #aeg #b #id #ef #hj #ag #id1dhb #ajb1dacabd1deh #ifj #ajbj #jif #adg #bi #ib #bd #gh #bj #ib1eed #ajj1cbcaba1iah #ibb #ajdb #jid #adj #f #hi #ef #gf #bd #ij1fbe #ih1bbcaai1cgh #hhd #ajfd #jib #acc #ea #hg #cb #gd #cj #hh1fig #if1adcaaf1hch #hdf #ajhg #jij #abh #ai #he #aj #gb #cf #hf1gfi #id1jecaad1bih #haj #aaaa #jhh #abc #ag #hb #ea #gj #dd #hd1hda #ia1ifcaaa1geh #ggd #aacf #jhf #aah #ch #hj #cd #fh #ed #hb1iac #hi1hgcaji1bah #gdj #aafc #jhd #aad #ag #gh #bj #fg #f #hj1ihd #hg1ghcajf1fgh #gjf #aaij #jhb #aaj #aj #gf #h #fe #ah #gi1jef #he1ficajd1ach #fgb #abbj #jhj #ajf #af #gc #eh #fc #ca #gg1abh #hc1fjcaja1eih #fdj #abej #jgh #ajb #ca #ga #di #fa #de #ge1bjj #ha1eac #ii1jeh #fjh #abhb #jgf #ih #ef #fi #db #fj #j #gc1bgb #gi1dbc #if1eah #egh #acaf #jgd #ie #bh #fg #cg #eh #af #ga1cdc #gg1ccc #ic1igi #edh #acea #jgb #ib #f #fe #cb #ef #cb #fi1dae #ge1bdb #ia1dci #eah #achi #jgj #hh #ea #fc #ca #ed #ej #fg1dhg #gc1aeb #hh1hii #dij #adbi #jfh #he #da #fa #cj #ec #i #fe1eei #ga1jfb #hf1cei #dfb #adga #jff #hb #cf #ei #cj #ea #bh #fc1fca #fh1igb #hc1hai #dcf #aeae #jfd #gi #cf #eg #ca #di #dh #fa1gjb #ff1hhb #ha1bgi #daj #aefb #jfb #gf #ch #ee #cd #dh #i #ei1ggd #fd1gib #gh1gci #chd #afac #jfj #gc #dd #ec #ch #df #cj #eg1hdf #fb1gjb #gf1aii #cfj #affg #jeh #gj #ed #ea #db #dd #ea #ee1iah #fj1fab #gc1fei #ccf #agbd #jef #fh #f #di #dh #dc #ad #ec1iij #eh1ebb #ga1aai #cad #aghf #jed #fe #bb #dg #ed #da #cg #eb1jfa #ef1dcb #fh1egi #bib #aheb #jeb #fb #dj #df #b #dj #j #ej1acc #ed1cdb #ff1jci #bgj #aibc #jej #fj #j #dd #aj #ch #bd #dh1bje #eb1beb #fc1dii #bej #bjjj #jde #ec #cj #ci #cc #cd #bg #dc1che #dg1jbf #eg1adi #bjc #bbbb #jdj #dg #i #ce #j #cj #ca #ch1efd #da1hja #ej1gii #afj #bejj #jce #dj #eh #cj #cj #bf #ch #cc1gdd #cf1egf #dd1ddi #abc #bheg #jcj #cd #ef #bf #d #bb #df #bh1ibc #ca1cea #ch1jii #jij #cccc #jbe #bh #eh #ba #dj #ah #ef #bd1ajc #bf1abf #ca1gdi #jfc #djjj #jbj #bc #d #ag #ah #ae #g #ai1bhb #bj1ija #be1djj #jdj #ejjj 7#a7 ,numerical ,aperture4 7n sin u a47 7#b7 ,air 7n #ajj74 7#c7 ,water 7n #acc74 7#d7 ,homogeneous ,immersion 7n #aeb74 7#e7 ,white ,light4 7 #jebfi 1 ,line ,e47 7#f7 ,monochromatic 7,blue7 ,light47 #jdhfa 1 ,line ,f47 7#g7 ,photography4 7 #jdjjj 1 ,near ,line hk47 7#h7 ,illuminating ,power 7a#b47 7#i7 ,penetrating ,power 7#a_/;a47 ,abbe's ,apertometer4 ,illustration3 ,fig4 #ci4--;,abbe's ,apertometer4 ,the apertometer is an auxiliary piece of apparatus invented by ,abbe1 for testing the fundamental properties of objectives and determining their numerical and angular apertures4 ,this accessory of the microscope involves the same principles as that of ,tolles1 which the late ,mr4 ,j4 ,mayall and myself brought to the notice of the ,royal ,microscopical ,society of ,london in #ahgf4 ,abbe's apertometer 7,fig4 #ci7 consists of a flat cylinder of glass1 about three inches in diameter1 and half an inch thick1 with a large chord cut off1 so that the portion left is somewhat more than a semicircle2 the part where the segment is cut is bevelled from above downwards1 to an angle of #de1 and it will be seen that there is a small disc with an aperture in it denoting the centre of the semicircle4 ,to use this instrument the microscope is placed in a vertical position1 and the apertometer is placed upon the stage with its circular part to the front and the chord to the back4 ,diffused light1 either from the sun or lamp1 is assumed to be in front and on both sides4 ,suppose the lens to be measured is a dry one-quarter inch2 then with a one-inch eye-piece having a large field1 the centre disc1 with its aperture on the apertometer1 is brought into focus4 ,the eye-piece and the draw-tube are now removed1 leaving the focal arrangement undisturbed1 and a lens supplied with the apertometer is screwed into the end of the draw-tube4 ,this lens1 with the eye-piece in the draw-tube1 forms a low-power compound microscope4 ,this is now inserted into the body-tube1 and the back lens of the objective whose aperture we desire to measure is brought into focus4 ,in the image of the back lens will be seen stretched across1 as it were1 the image of the circular part of the apertometer4 ,it will appear as a bright band1 because the light which enters normally at the surface is reflected by the bevelled part of the chord in a vertical direction1 so that in reality a fan of #ahj in air is formed4 ,there are two sliding screens seen on either side of the figure of the apertometer2 they slide on the vertical circular portion of the instrument4 ,the images of these screens can be seen in the image of the bright bands4 ,these screens should now be moved so that their edges just touch the periphery of the back lens4 ,they act1 as it were1 as a diaphragm to cut the fan and reduce it1 so that its angle just equals the aperture of the objective and no more4 ,this angle is now determined by the arc of glass between the screens2 thus we get an angle in glass the exact equivalent of the aperture of the objective4 ,as the numerical apertures of these arcs are engraved on the apertometer1 they can be read off by inspection4 ,a difficulty is not infrequently experienced from the fact that it is not easy to determine the exact point at which the edge of the screen touches the periphery of the back lens1 or rather the limit of the aperture4 ,zeiss1 to meet this difficulty1 made a change in the form of the apparatus--furnished a glass disc mounted on a metal plate1 with a slot for the purpose of its more accurate adjustment4#ag ,stereoscopic ,binocular ,vision4 ,professor ,wheatstone's remarkable discovery of stereoscopic vision led1 at no distant period1 to the application of the principle to the microscope4 ,it may therefore prove of interest to inquire how stereoscopic binocular vision is brought about4 ,indeed1 the curious results obtained in the stereoscope cannot be well understood without a previous knowledge of the fundamental optical principles involved in this contrivance1 whereby two slightly dissimilar pictures of any object become fused into one image1 having the actual appearance of relief4 ,the invention of the stereoscope by ,sir ,charles ,wheatstone1 ,f4,r4,s41 #ahch1 and improved by ,brewster1 was characterised by ,sir ,john ,herschel as 8one of the most curious discoveries1 and beautiful for its simplicity1 in the entire range of experimental optics10 led to a more general appreciation of the value of the conjoint use of both eyes in conveying to the mind impressions of the relative form and position of an object1 such as the use of either eye singly does not convey with anything like the same precision4 ,when a near object having three dimensions is looked at1 a different perspective representation is seen with each eye4 ,certain parts are seen by the right eye1 the left being closed1 that are invisible to the left eye1 the right being closed1 and the relative positions of the portions visible to each eye in succession differ4 ,these two visual impressions are simultaneously perceived by both eyes1 and combined in the brain into one image1 producing the effect of perspective and relief4 ,if truthful right-and-left monocular pictures of an object be so presented to the two eyes that the optic axes when directed to them shall converge at the same angle as when directed to the object itself1 a solid image will be at once perceived4 ,the perception of relief referred to is closely connected with the doubleness of vision which takes place when the images on corresponding portions of the two retina are not similar4 ,but1 if in place of looking at the solid object itself we look with the right and left eyes respectively at pictures of the object corresponding to those which would be formed by it on the retina of the two eyes if it were placed at a moderate distance in front of them1 and these visual pictures brought into coincidence1 the same conception of a solid form is generated in the mind just as if the object itself were there4 ,professor ,abbe1 however1 contended that the method by which dissimilar images are formed in the binocular microscope differs materially from that of ordinary stereoscopic vision1 and that the pictures are united solely by the activity of the brain1 not by the prisms which ordinarily give rise to sensations of solidity4 ,this can be only partially true1 as binocularity in the microscope is due to difference of projection exhibited by the different parallax displacement of the images1 and also to the perception of depth imparted by the instrument4 ,wheatstone was firmly convinced that his stereoscopic principle could be applied to the microscope1 and he therefore applied first to ,ross and then to ,powell to assist him in its adaptation4 ,but whether either of these opticians made any attempt to give effect to his wishes and suggestions is not known4 ,in the year #ahea ,professor ,riddell1 of ,america1 succeeded in constructing a binocular microscope by employing two rectangular prisms behind the objective4 ,m4 ,nachet also constructed a binocular with two body-tubes and a series of prisms4 ,but neither ,riddell's nor ,nachet's instrument was ever brought into use2 they were either too complicated or too costly4 ,it will be understood1 however1 that the binocular stereoscope combines two dissimilar pictures1 while the binocular microscope simply enables the observer to look with both eyes at images which are essentially identical4 ,stereoscopic vision1 to be effective1 requires that the delineating pencil shall be equally separated1 so that one portion of the admitted cone of light is conducted to one eye1 and the other portion to the other eye4 ,select any object lying in an inclined position1 and place it in the centre of the field of view of the microscope2 then1 with a card held close to the object-glass1 stop off alternately the right or left hand portion of the front lens3 it will then appear that during each alternate change certain parts of the object will change their relative positions4 ,illustration3 ,fig4 #dj4--,portions of ,eggs of ,cimex4 ,to illustrate this1 ,fig4 #dj a1 b are enlarged drawings of a portion of the egg of the common bed-bug 7,cimex lecticularis71 the operculum which should cover the opening having been forced off at the time the young was hatched4 ,the figures exactly represent the two positions that the inclined orifice will occupy when the right- and left-hand portions of the object-glass are stopped off4 ,this object is viewed as an opaque object1 and drawn under a two-thirds object-glass of about #bh aperture4 ,if this experiment is repeated1 by holding the card over the eye-piece1 and stopping off alternately the right and left half of the ultimate emergent pencil1 exactly the same changes and appearances will be observed in the object under view4 ,the two different images just produced are such as are required for obtaining stereoscopic vision4 ,it is therefore evident that if instead of bringing them confusedly together into one eye we can separate them so as to bring together a1 b into the left and right eye1 in the combined effect of the two projections we obtain at once all that is necessary to enable us to form a correct judgment of the solidity and distance of the several parts of the object4 ,nearly all objectives from the one inch upwards of any considerable aperture give images of the object seen from a different point of view with the two opposite extremes of the margin of the cone of rays2 the resulting effect is that there are a number of dissimilar perspectives of the object blended together at one and the same time on the retina4 ,for this reason1 if the object under view possesses bulk1 a more accurate image will be obtained by reducing the aperture of the objective4 ,illustration3 ,fig4 #da4 ,diagram #c1 ,fig4 #da1 represents the method employed by ,mr4 ,wenham for bringing the two eyes sufficiently close to each other to enable them both to see through the double eye-piece at the same moment4 a a a are rays converging from the field lens of the eye-piece2 after passing the eye-lens b1 if not intercepted1 they would come to a focus at c2 but they are arrested by the inclined surfaces1 d d1 of two solid glass prisms4 ,from the refraction of the under incident surface of the prisms1 the focus of the eye-piece becomes elongated1 and falls within the substance of the glass at e4 ,the rays then diverge1 and after being reflected by the second inclined surface f1 emerge from the upper side of the prism1 when their course is rendered still more divergent1 as shown by the figure4 ,the reflecting angle given to the prisms is #dg-a_/b1 to accommodate which it is necessary to grind away the contact edges of the prisms1 as represented1 otherwise they prevent the extreme margins of the reflecting surfaces from coming into operation1 which are seldom made quite perfect4 ,illustration3 ,fig4 #db4--,professor ,abbe's ,stereoscopic ,eye-pieces4 ,fig4 #db represents a sectional view of ,abbe's stereoscopic eye-pieces1 which consist of three prisms of crown glass1 a1 b and b1 placed below the field-glass of the two eye-pieces2 the tube c is slipped into the tube or body like an ordinary eye-piece4 ,the two prisms a and b are united so as to form a thick plate with parallel sides1 inclined to the axis at an angle of #che4 ,the cone of rays from the objective is thus divided into two parts1 one being transmitted and the other reflected2 that transmitted passing through a b and forming an image of the object in the axial eye-piece ,b4 ,adjustment for different distances between the eyes is effected by the screw placed to the right-hand side of the figure1 which moves the eye-piece ,b1 together with the prism b1 in a parallel direction4 ,the tubes can also be drawn out1 if greater separation is required4 ,the special feature of this instrument is that on halving the cone of rays by turning the caps1 an orthoscopic or pseudoscopic effect is produced4 ,this double-eyed piece arrangement of ,abbe's has not been at all brought into use in this country2 this is partly owing to its original adaptation for use with the shorter ,continental body-tube of #afj mm41 and not for our #aj-;inch body4 ,the most perfect method of securing pleasing satisfactory stereoscopic vision of objects is that devised by ,mr4 ,wenham4 ,in his binocular microscope an equal division of the cone of rays1 after passing through the objective is secured and again united in the eye-pieces1 which act as one1 so that each eye is furnished with an appropriate and simultaneous view of the object4 ,the methods contrived by the earlier experimenters not only materially interfered with the definition of the objective and object1 but also required expensive alterations and adaptations of the microscope1 and sometimes separate stands for their employment4 ,mr4 ,wenham's invention1 on the contrary1 offers no such obstacle to its use1 and the utility of the microscope as a monocular is in no way impaired either when using the higher powers4 ,illustration3 ,fig4 #dc4 ,the most important improvement1 then1 effected by ,wenham consists in the splitting up or dividing the pencil of rays proceeding from the objective by the interposition of a prism of the form shown in ,fig4 #dc4 ,this is placed in the body or tube of the microscope so as to interrupt only one-half 7a c7 of the pencil1 the other half 7a b7 proceeding continuously to the field-glass1 eye-piece1 of the principal body4 ,the interrupted half of the pencil on its entrance into the prism is subjected to very slight refraction1 since its axial ray is perpendicular to the surface it meets4 ,within1 the prism is subjected to two reflections at b and c1 which send it forth again obliquely on the line b towards the eye-piece of the secondary body1 to the left-hand side of the figure2 and since at its emergence its axial ray is again perpendicular to the surface of the glass1 it suffers no further refraction on passing out of the prism than on entering4 ,by this arrangement1 the image sent to the right eye is formed by rays which have passed through the left half of the objective2 whilst the image sent to the left eye is formed by rays which have passed through the right half1 and which have been subjective to two reflections within the prism1 and passing through two surfaces of glass4 ,the prism is held by the ends only on the sides of a small brass drawer1 so that all the four polished surfaces are accessible1 and should slide in so far that its edge may just reach the central line of the objective1 and be drawn back against a stop1 so as to clear the aperture of the same4 ,illustration3 ,fig4 #dd4--,sectional view of the ,wenham ,binocular4 ,the binocular1 then 7,fig4 #dd71 consists of a small prism mounted in a brass box ,a1 which slides into an opening immediately above the object-glass1 and reflects one-half of the rays which form an image of the object1 into an additional tube ,b1 attached at an inclination to the ordinary body ,c4 ,one half of the rays take the usual course with their performance unaltered2 and the remainder1 though reflected twice1 show no loss of light or definition worthy of notice1 if the prism be well made4 ,as the eyes of different persons are not the same distance apart1 the first and most important point to observe in using the binocular is that each eye has a full and clear view of the object4 ,this is easily tried by closing each eye alternately without moving the head1 when it may be found that some adjustment is necessary by racking out the draw-tubes ,d1 ,e1 of the bodies by means of the small milled head near the eye-pieces2 this will increase the distance of the centres2 and1 on the contrary1 the tubes1 when racked down1 will suit those eyes that are nearer together4 ,if the prism be drawn back till stopped by the small milled head1 the field of view in the inclined body is darkened1 and the rays from the whole aperture of the object-glass pass into the main body as usual1 neither the prism nor the additional body interfering in any way with the use of the instrument as a monocular microscope4 ,the prism can be withdrawn altogether for the purpose of being wiped3 this should be done frequently1 and very carefully1 on all four surfaces1 with a perfectly clean cambric or silk handkerchief or a piece of wash-leather2 but no hard substance must be used4 ,during this process the small piece of blackened cork fitted between the prism and the thick end of the brass box may be removed2 but it must be carefully replaced in the same position1 as it serves an important purpose in stopping out extraneous light4 ,as the binocular microscope gives a real and natural appearance to objects1 this effect is considerably increased by employing those kinds of illumination to which the naked eye is accustomed4 ,the most suitable are all the opaque methods where the light is thrown down upon the surface2 but for those objects that are semi-transparent1 as sections of bone or teeth1 diatomace1 living aquatic animalcules1 c41 the dark-field illumination by means of the parabolic reflector will give an equally good result4 ,for perfectly transparent illumination1 it is much better to diffuse the light by placing under the object various substances1 such as tissue-paper1 ground glass1 very thin porcelain1 or a film of yellow bees' wax1 run between two pieces of thin glass4 ,to ensure the full advantage and relief to both eyes in prolonged observations with high as well as low powers1 and with objectives of large aperture1 ,mr4 ,wenham devised a compound prism for use with his binocular microscope1 the body tubes of which are also made expressly to suit the prism1 as extreme accuracy is necessary to bring them into proper position4 ,the main prism somewhat resembles in form the ordinary ,wenham prism4 ,over the first reflecting surface is placed a second smaller prism1 the top plane of which is parallel with the base of the first1 so that direct rays pass through without deviation1 but at the two inclined surfaces of the prisms 7nearly in contact7 there is a partial reflection from each1 which1 combined1 give as much light as in the direct tube4 ,the reflected image from these two surfaces is directed up into the inclined tube as usual4 ,a somewhat later improvement is that of ,dr4 ,schroeder1 the high power prism1 by means of which the whole of the rays emanating from the objective pass through it1 and the full aperture of any power is thereby effectively utilised4 ,furthermore1 ,messrs4 ,ross have also constructed a right- and left-hand pair of eye-pieces1 which ensure greater perfection of the image4 ,it was1 in fact1 noticed that the size of the image in the left-hand field glass slightly differed from that of the right when examined by the ordinary ,huyghenian eye-pieces4 ,to compensate for this difference1 the left-hand eye-piece has been carefully calculated1 and its focus is now so accurately adjusted that the position of each eye in observing is brought into one plane of the binocular4 ,the pairs of the several series of eye-pieces ,a1 ,b and ,c have also been altered1 and the effect is to greatly improve the image and give increased comfort to the observer4 ,dr4 ,carpenter1 who warmly espoused the binocular1 and constantly employed it in his work1 very truly said of it3 8,the important advantages ,i find it to possess are in penetrating power1 or focal depth1 which is in every way superior to that of the monocular microscope1 so that an object whose surface presents considerable inequalities is very much more distinctly seen with the former than with the latter40 ,this difference may in part be attributed to the practical modification in the angle of aperture of the objective1 produced by the division of the cone of rays transmitted through the two halves1 so that the picture or image received through each half of the objective of #fj is formed by rays diverging at an angle of only about #cj4 ,he confesses1 however1 that this does not satisfactorily explain the fact that the binocular brings to the mind's eye the solid image of the object1 and thus gives to the observer a good idea of its form and which could hardly be obtained by the monocular microscope4 ,carpenter cites in support of his views the wing of a little-known moth1 ,zenzera sculi1 which has an undulating surface1 whereon the scales are set at various angles instead of having the usual imbricated arrangement1 a good object for demonstrating2 the general inequality of surface and the obliquity of its scales1 which are at once seen by the binocular with a completeness not obtained by the monocular instrument4 ,to one unaccustomed to work with the binocular the views expressed by ,dr4 ,carpenter as to the extreme value of the instrument for ordinary work may appear somewhat exaggerated1 but from my own experience1 having long had in constant use a ,ross-,zentmayer binocular1 furnished with a special prism1 constructed for working with a #a_/h dry objective or a #a_/aj immersion1 the perfection of picture obtained was in every case quite equal to that of the monocular microscope4 ,the relief to the eyes can hardly be over-estimated2 the slight inequality of the pencil rays may be regarded rather as a part of the welcome rest afforded when a prolonged examination is made2 it certainly appears to me to equalise the slight physiological difference known to exist between the eyes of most people4 ,if one image is seen a little clearer by the stronger eye1 the weaker eye assists rather more the stereoscopic effect of the object under observation4 ,the advantage gained by the binocular is perhaps more appreciated when opaque objects are under examination1 as the eggs of insects1 and the tongue of the blow-fly1 specimens of mosses1 lichens1 parasites 7vegetable and animal71 whose planes and inequalities of surface require penetration1 and which usually demand more time for their observation4 ,illustration3 ,fig4 #de4--,swift-,stephenson's ,erecting ,binocular4 ,no variation or change of any kind proposed either in the form of the instrument or the prism has proved of sufficient value or importance to bring it into use1 and therefore ,wenham's instrument is scarcely likely to be superseded4 ,it must be admitted that the improvement effected in the eye-piece form by ,mr4 ,tolles1 of ,boston1 ,u4,s41 is an exception to the rule laid down4 ,it consists in mounting the prisms in a light material1 vulcanite1 made to fit into the monocular microscope body1 thus taking the place of the ordinary eye-piece4 ,the image transmitted by the objective is brought to a focus on the face of the first equilateral triangular prism by the intervention of an erector-eye-piece inserted beneath it4 ,the second set of prisms have a rack and pinion movement to adjust them to any visual angle4 ,the illumination of both fields in this eye-piece is nearly equal in brightness4 ,mr4 ,stephenson's erecting binocular 7,fig4 #de7 has proved to be of some practical value4 ,it has the advantage of being of equal use with high and low powers1 and with little loss of definition4 ,when used for dissecting purposes it gives an erect image of the object4 ,it is equally useful as a working microscope1 for arranging diatoms and botanical specimens of every kind4 ,the sub-stage tube will receive a diaphragm or illuminating apparatus2 the eye-pieces have a sliding adjustment for regulating the widths between eyes4 ,illustration3 ,fig4 #df4--;,an early form of the ,ross-,wenham ,binocular2 nose-piece and prism-holder detached4 ,,chapter ,,ii4 ,simple and ,compound ,microscope4 ,microscopes are known as simple and compound4 ,the simple microscope may1 for convenience1 be divided into two classes2 those used in the hand 7hand magnifiers71 and those provided with a stand 7mounted1 as it is termed7 for supporting the object to be viewed1 together with an adjustment for the magnifying power1 and a mirror for reflecting the light through the object4 ,illustration3 ,fig4 #dg4--,visual ,angle4 ,a simple microscope1 mounted1 is preferable to a single lens1 being usually composed of two or more lenses separated by a small distance on a common axis2 the increase of the size of an object being the angle it subtends to the eye of the observer1 or the angle formed by the combination drawn from the axis of vision to the extremity of the object1 as in ,fig4 #dg4 ,the lines drawn from the eye to a and r form an angle1 which1 when the distance is small1 is nearly twice as large as the angle from the eye to o w1 formed by lines drawn at twice the distance4 ,this is called the angle of vision1 or the visual angle4 ,now1 the utility of a convex lens interposed between a near object and the eye consists in its reducing the divergence of the rays forming the several pencils issuing from it1 so that they enter the eye in a state of moderate divergence1 as if they were issuing from an object beyond the near point of distinct vision1 and a well-defined image is thereby formed upon the retina4 ,in the next ,fig4 7#dh71 a double-convex lens illustrates the action of the simple microscope1 the small arrow being the object brought under view1 and the large arrow the magnified image4 ,the rays having first passed through the lens are bent into nearly parallel lines1 or pencils diverging from some point within the limits of distinct vision4 ,thus altered1 the eye receives rays precisely as if they had emanated directly from a larger arrow placed about ten inches away from it4 ,the difference between the real and the imaginary object represents the magnifying power of the lens4 ,the object in this case is magnified nearly in the proportion the focal distance of the lens bears to the distance of the object when viewed by the unassisted eye2 and this is due to the object being more distinctly viewed so much nearer to the eye than it otherwise could be without the lens4#ah ,illustration3 ,fig4 #dh4--,virtual ,image formed by ,convex ,lens4 ,it should be remembered that the shorter the focus and the nearer the eye the magnifying lens is placed the smaller will be the diameter of the sphere of which it forms a part1 and unless its aperture be proportionally reduced1 the distinctness of the image will be destroyed by the spherical and chromatic aberrations of its high curvature4 ,nevertheless1 it was by the use of lenses so constructed that the older microscopists--of whom ,leeuwenhoek was the more eminent--were enabled to do so much excellent work4 ,the various kinds of simple pocket lenses for the most part consist of a double-convex1 or a plano-convex1 or a combination of both1 varying in focal length from a quarter of an inch to two inches4 ,sometimes they are set in pairs with a hole1 a small diaphragm1 cut in the piece of horn placed between them4 ,these are extremely useful for carrying in the waistcoat pocket2 to the anatomist and field botanist for examining various objects and preparations4 ,illustration3 ,fig4 #di4--,wollaston's ,doublet4 ,perhaps the most important improvement effected in this form of the simple microscope was that ascribed to the celebrated ,dr4 ,wollaston1 who devised a doublet of two plano-convex lenses having their focal lengths1 in the proportion of one to three1 mounted with their convex side directed towards the eye of the observer1 and the lens of shorter focal length next the object4 ,the explanation given of the correction thus effected in ,dr4 ,wollaston's doublet will be best understood on reference to the annexed diagram1 l l1 in ,fig4 #di1 being the object for a segment of the cornea of the eye1 and d d the stop or diaphragm4 ,now1 it will be seen that each pencil of light proceeding from l l1 the object1 is rendered excentrical by the limiting aperture or the diaphragm d d2 consequently1 they pass through the lenses on opposite sides of their common axis o p2 thus each becomes affected by opposite errors1 which to some extent balance and correct each other4 ,to take the pencil l1 for instance1 as it enters the eye at r b2 r b is bent to the right at the first lens1 and to the left at the second2 and as each bending alters the direction of the blue ray more than the red1 and as the blue ray falls nearer the margin of the second lens1 where the refraction is greater than that nearer the centre1 and compensates to some extent for the greater focal length of the second lens1 the blue rays will emerge very nearly parallel1 and colourless to the eye4 ,at the same time1 its spherical aberration has been diminished1 since the side of the pencil as it proceeds through one lens passes nearer the axis1 and in the other nearer the margin4 ,this must be taken to apply to pencils farthest from the centre of the object4 ,central rays1 it is obvious1 would pass both lenses symmetrically1 the same portions of rays occupying nearly the same relative places in both lenses4 ,the blue ray would enter the second lens nearer its axis than the red2 and being thus less refracted than the red by the second lens1 some amount of compensation would take place1 differing in principle1 and inferior in degree1 to that which is found in the excentrical pencils4 ,in the intermediate spaces the corrections are still more imperfect and uncertain2 and this explains the cause of aberrations which must of necessity exist even in the best-made doublet4 ,it is1 however1 infinitely superior to a single lens1 and will transmit a pencil of an angle of from #ce to #ej4 ,the next step towards improving the simple microscope was in relation to the eye-piece1 and was effected by ,holland4 ,it consisted in substituting two lenses for the first in the doublet1 and placing a stop between them and the third4 ,the first bending of the pencils of light being effected by two lenses instead of one1 produces less spherical and chromatic aberration1 which are more nearly balanced or corrected at the second bending1 and in the opposite direction1 by the third lens4 ,another form of simple lens was devised by ,dr4 ,wollaston1 the 8,periscopic40 ,this combination consists of two hemispherical lenses cemented together by their plane faces1 with a stop between them to limit the aperture4 ,a similar proposal1 made by ,sir ,david ,brewster in #ahbj1 is known as the ,coddington lens1#ai shown at ,fig4 #ej3 this has a somewhat larger field1 and is equally balanced in all directions1 as is made evident1 the pencils a b and b a passing through under precisely the same circumstances4 ,its spherical form has the further advantage of rendering the position in which it is held of comparatively little consequence4 ,it is still used as a hand magnifier1 although its definition is certainly not so good as that of a well-made doublet4 ,it is usually set in a folding case1 as represented in the figure1 and so contrived as to be admirably adapted for the waistcoat-pocket4 ,it is usually sold with the small holder1 ,fig4 #ej;a1 for holding and securing small objects during examination4 ,browning's ,platyscopic ,pocket ,lens is a useful form of pocket lens for the botanist and mineralogist4 ,its focus is nearly three times longer than that of the ,coddington1 and allows of opaque objects being more easily examined2 it has also a magnifying power of #ae1 #bj1 and #cj diameters4 ,illustration3 ,fig4 #ej4--,the ,coddington ,lens4 ,illustration3 ,fig4 #ej;a4 ,one of the best combinations of the hand or pocket form of lens is that known as ,steinheil's aplanatic lens 7,fig4 #ea72 it consists of a bi-convex lens cemented between two concavo-convex lenses1 giving a relatively long focal distance and a large flat field4 ,the higher powers of this lens are much used for dissecting purposes4 ,this handy magnifier appears to have suggested a later combination1 the apochromatic of ,zeiss4 ,no hand lens can compare with ,steinheil's 8loups40 ,illustration3 ,fig4 #ea4--,steinheil's ,aplanatic ,lens4 ,illustration3 ,fig4 #eb4--,simple ,microscope4 ,when the magnifying power of a lens is considerable1 or when its focal length is short1 or it is wished to use it with greater precision and steadiness1 it should be mounted on a short stand with a tubular stem1 with rack-work focussing movement and mirror illumination4 ,fig4 #eb represents a simple dissecting microscope1 with a glass circular stage1 #d-a_/b inches in diameter1 supported on three legs--a handy and useful form of instrument for many purposes4 ,the ,compound ,microscope4 ,the compound microscope differs from the simple1 inasmuch as the image is formed by an object-glass1 and further magnified by one or more lenses forming an eye-glass4 ,for a microscope to be a compound one1 its essential qualification is that it should have an object-glass or objective1 and an eye-glass or eye-piece1 so called because they are respectively near the object and the eye of the observer when the instrument is in use4 ,the microscope consists of a tube or body1 and a stand1 an arrangement for carrying the body1 combined with which is a stage for holding the object1 and a mirror for its illumination4 ,to the more modern instrument has been added a substage1 to carry a condenser and other accessories4 ,the body of a microscope1 which carries the system of magnifying lenses1 must be placed at one particular distance from the object1 termed the focus1 in order that a clear image may be obtained4 ,for the purpose of focussing two motions are supplied1 the one for coarse adjustment1 with lower powers2 the other for higher powers1 termed the fine adjustment4 ,it is in this wise that the magnifying power of the compound microscope is turned to good account4 ,there are1 however1 limits to the use to which lenses can be put with advantage in the direction of magnifying the object1 just as there are in varying the magnifying power of the eye-glass4 ,defects in either1 although not first seen1 that is1 when the image is but moderately enlarged1 are brought into prominence by greater amplification4 ,in practice1 therefore1 it is found to be of advantage to vary the power by employing object-glasses of different values 7foci74 ,in whatever way increase of amplification is brought about1 two things will always result from the change3 the proportion of surface of the object of which an image can be formed must be diminished1 and the amount of light spread over the image proportionally lessened4 ,in addition to the two lenses mentioned1 it was found to be of considerable advantage to introduce a third lens between the object-glass and the image formed by it at eye-piece1 the purport of which is to change the course of the rays 7bend in the pencil7 so that the image may not be found of too great a dimension for the whole to be brought within the circumference of the eye-glass4 ,this1 it will be readily seen1 allows more of the object to be viewed at the same time by the field-glass1 as the eye-piece of the microscope is termed4 ,illustration3 ,fig4 #ec4 ,fig4 #ec represents the body of an ordinary compound microscope with its triplet object-glasses2 o is an object1 above it is the triple achromatic object-glass1 in connection with the eye-piece e e1 f f the plano-convex lenses2 e e being the eye-glass1 and f f the field-glass1 between which1 at b b1 the arrow represents the diaphragm4 ,the course of the light is shown by three rays drawn from the centre1 and three from each end of the object o2 these rays1 if not prevented by the lens f f1 and the diaphragm b b1 would form an image at a a2 but here1 as they meet with the lens f f in their passage1 are converged by it at b b1 the diaphragm at b b intercepting a portion of peripheral rays1 permitting only those to pass that are necessary for the formation of the image1 the further magnification of which is1 however1 here brought about by the eye-glass e e1 precisely as if it were that of the original object under examination4 ,it will be apparent1 then1 that the field-lens f f belongs in principle to the object-glass1 or objective1 taking a share in the image-forming rays1 although this is taken to be a part of the eye-piece4 ,evolution of the ,modern ,achromatic ,microscope4 ,the great advances made in the optical arrangements of the modern microscope necessitated important changes and improvements in its several mechanical parts4 ,indeed1 as the apertures of objectives became increased1 and focal planes became correspondingly shallower1 it was absolutely necessary to apply a more sensitive system of focussing than that for many years past commonly in use4 ,the leading manufacturers at once grasped the situation1 and in a short space of time the older model microscopes were discarded1 and replaced by instruments better in workmanship and finish1 and in every way more suitable for the student and the promotion of original scientific research4 ,from an early period ,english amateurs appear to have bestowed greater attention on the improvement of the microscope than those of any other country4 ,between #ahbj and #ahce ,tully1 ,pritchard1 ,dolland1 ,james ,smith1 ,andrew ,ross1 and ,hugh ,powell1 encouraged by ,wollaston1 ,brewster1 ,goring1 ,herschel1 and ,lister1 worked out innumerable combinations of single and compound lenses to be employed as simple microscopes1 explained in a previous chapter4 ,the theories propounded about this time for the improvement of lenses and the various combinations for amateurs were not of lasting value4 ,nevertheless1 they were not wholly made in vain1 as during the last twenty years they have indirectly borne good fruit1 inasmuch as by working in another direction ,professor ,abbe was led to the discovery of new and better kinds of glass1 by which the secondary spectrum has been so nearly eliminated1 and the optical parts of the microscope so materially improved4 ,in pursuing this subject ,i would not have it supposed that ,continental opticians were either idle or supine4 ,on the contrary1 ,oberhuser1 ,fraunhofer1 ,chevalier1 ,nachet1 ,hartnach1 and others took an active part in the work4 ,the compound microscope made for anatomists by the first-named optician about #ahbe has not been entirely superseded4 ,he was the first to make a rotating stage1 to apply mechanism to focussing1 and to introduce the system of direct push or pull of the condenser tube within the sub-stage socket4 ,nachet made other improvements on the ,oberhuser microscope by applying under the stage a tail-piece having a dove-tailed groove in which a slide carrying the sub-stage was moved by a stud-pin4 ,more recently the lever movement was superseded by ,american opticians1 who made other changes4 ,hartnach ultimately very much improved ,oberhuser's model1 and this remains with us4 ,the ,english modern compound microscope1 together with the achromatic objective1 we owe to a mind teeming with scientific inventions1 ,joseph ,jackson ,lister1 ,f4,r4,s41 who in #ahbf supplied ,mr4 ,tully1 a well-known ,london optician of that period1 with original drawings for the important improvements in its mechanical details and accessory apparatus which followed so soon afterwards4 ,among the many ingenious novelties enumerated in his published papers we find the graduated lengthening of the body-tube of the microscope2 a stage-fitting for clamping and rotating the object2 a subsidiary stage2 a dark-well1 and a large disc to incline and rotate opaque objects2 a ground-glass light moderator2 a live-box with bevelled flat-glass plate2 an erector-eye-piece2 an adapter for using ,wollaston's camera lucida for microscopical drawing2 and1 above all1 a combination of lenses to act as a condenser under the object 7evidently the first approach to the present achromatic sub-stage condenser74 ,the value of the erector-eye-piece for facilitating dissections under the microscope is not even yet sufficiently appreciated4 ,tully published a descriptive account of ,lister's microscope1 the first one of which he made1 and acknowledged his indebtedness to 8,mr4 ,lister's ingenuity and skill40 ,shortly afterwards ,lister made known his discovery of the two aplanatic foci in a double achromatic object glass1 and gave verbal directions to the three principal makers of microscopes in ,london1 ,james ,smith1 ,andrew ,ross1 and ,hugh ,powell1 for the future construction of the achromatic objective1 all of whom were intent on the improvement of their several models4 ,to the latter the ,society of ,arts awarded1 in #ahcb1 a medal for his improved mechanical stage movements1 on the 8,turrell system10 which ,powell first constructed for ,edmund ,turrell4 ,this stage was made to rotate completely on its optic axis by means of an obliquely-placed pinion acting on a bevelled rack on the inner face of the stage-ring supporting the mechanism4 ,in #ahcd ,powell once more received a ,society of ,arts medal1 8the ,iris10 for improvements in the application of a new form of fine adjustment4 ,about the same date 7#ahce7 ,andrew ,ross introduced the socket-carrier of the body-tube of the microscope on a strong stem1 with rack bent in the middle1 thus affording space for a larger stage4 ,he likewise devised the hollow cross-bar1 placed at right angles to the rack-stem1 whereby he was enabled to use a new system of fine adjustment1 consisting of a delicate screw with large milled head1 acting by a point on the long arm of a lever1 the short arm of which ends in a fork in contact with a stud placed on either side of a cylindrical sliding tube forming the nose-piece of the body-tube1 and into which the objective is screwed4 ,a spiral spring presses down the nose-piece1 and against this the screw and lever act4 ,this appears to have been the first really sensitive focussing method applied to the nose-piece2 it was1 and probably is1 one of the most delicate systems ever applied to the microscope4 ,it has enjoyed a long period of popularity1 and ,i believe it still survives in ,powell and ,lealand's instruments1 which are very generally admitted to be of superior excellence for all purposes where extreme delicacy of focussing is an essential element4 ,the rival system of fine adjustment--the short lever and screw applied externally to the body-tube--known as the ,lister-,jackson system1 which appears to have been contrived to allow the body-tube to be supported more firmly on the limb or stem1 has had its merits ably realised in the microscopes of ,smith and ,beck and their successors1 but1 except as modified by the successors of ,andrew ,ross 7,schrder's form71 it is1 ,i believe1 admitted that it has been superseded by other modifications lately introduced into the ,ross-,jackson instrument4 ,the year #ahcj was1 however1 a propitious period in the history of the modern microscope1 as in ,january of that year ,mr4 ,lister published his epoch-making paper1 8,on the ,improvement of the ,achromatic ,microscope40 ,this appeared together with certain personal practical directions 7for no man was ever more anxious to communicate his knowledge than ,mr4 ,lister7 to the before-mentioned opticians1 which led up to changes lasting until #ahdj1 when1 by the efforts of this gentleman and his personal friends1 8,the ,microscopical ,society of ,london0 came into existence4 ,among the more prominent members of the ,society was ,mr4 ,george ,jackson1 a name still well known to microscopists1 and who1 jointly with ,mr4 ,lister1 gave us the ,jackson-,lister form of microscope4 ,this was forthwith accepted as a perfect model4 ,soon after ,andrew ,ross effected a further change in the instrument1 shown in ,fig4 #ed in its complete form as left by this optician4 ,it is here represented as having a bar movement1 with a claw foot bolted to two uprights to carry the trunnions with the body and stage4 ,this base1 is insufficiently wide and extended to carry so large an instrument with its centre of gravity so high4 ,the coarse adjustment bar also was rectangular1 and the fine adjustment a lever1 with the milled head in the middle of the bar1 which involved a certain amount of tremor2 withal it was an instrument of excellent workmanship1 and its defects were not regarded as irremediable4 ,messrs4 ,ross1 however1 preferred to construct an entirely new model designed by ,zentmayer1 the 8,ross-,jackson-,zentmayer10 to which ,i shall refer presently4 ,a later model1 however1 has to some extent taken its place1 8the ,histological and ,bacteriological ,microscope10 ,fig4 #ee4 ,illustration3 ,fig4 #ed4--;,an early ,ross-,jackson ,microscope4 ,my reference to the older form of instrument is chiefly with the view of directing attention to the sensitive focussing system1 applied in the first instance to the nose-piece2 now placed below the coarse adjustment4 ,it certainly is a delicate form of fine adjustment4 ,this model possesses other points of interest well worth preserving1 which fully entitle it to occupy the prominent place given in the list of the house of ,ross4 ,in the ,ross-,jackson 8,histological and ,bacteriological ,microscope0 much attention seems to have been given to eliminate certain weak points in the earlier ,ross-,jackson model--defects still extant in stands of certain ,english and foreign makers--while retaining the more practical improvements of both constructions4 ,steadiness is secured by an extension of the tripod or claw-foot and the shorter and more solid uprights that sustain the whole weight of the instrument4 ,illustration3 ,fig4 #ee4--,the ,ross-,jackson ,histological ,microscope4 ,illustration3 ,fig4 #ef4--,powell and ,lealand's ,students' ,microscope1 with ,amici prism arranged for oblique illumination1 the ,sub-stage and ,condenser being detached4 ,the ,ross-,jackson1 then1 survives1 together with the original tripod stand of ,hugh ,powell's1 upon which he expended all the resources of the practical optician1 and applied the early principles involved in the ,lister-,jackson instrument1 but from different points of view4 ,however1 there is hardly a choice between one and the other in workmanship1 both opticians having furnished microscopes of a typical class and very high order4 ,the firm of ,powell and ,lealand have but one form of stand1 from which they have never been tempted to deviate4 ,it is supported on a true tripod base1 forming a solid and substantial support to the body1 which is of such a length as to give as nearly as possible the standard optical interval of #aj inches between the posterior principal focus of the objective and the anterior focus of the eye-piece2 the variation in the optical tube length does not exceed a quarter of an inch with objectives of #a_/b inch and upwards4 ,the arm on which the body is fixed is #e-c_/d inches long1 which not only gives a clearance of #c-a_/b inches from the optic axis1 but also permits of the introduction of a long fine-adjustment lever4 ,illustration3 ,fig4 #eg4--,powell's larger ,no4 #b ,instrument4 ,illustration3 ,fig4 #eh4--,powell and ,lealand's ,students' ,microscope arranged for direct illumination4 ,a4 ,secondary or ,sub-stage racked up to bring the ,achromatic ,condenser close to the object4 ,the cross arm encloses the lever mechanism for the fine adjustment1 as originally devised by ,andrew ,ross4 ,this cross arm is longer than that used by ,ross1 and carries the body more forward1 so as to provide radial space for the complete rotation of the stage and the optic axis1 and at the same time the lever of the adjustment is lengthened1 and delicacy of motion secured4 ,the stage retains the mechanical movements invented by ,e4 ,turrell1 and first applied by ,hugh ,powell4 ,it also rotates completely by means of an obliquely placed pinion acting on a bevelled rack on the inner face of the stage-ring supporting the mechanism4 ,finders are engraved on the plates1 and the main support of the stage-ring is graduated for angle measuring1 a pointer on the ring marking the unit of motion in arc4 ,the sub-stage is carried by rack-work1 and has rectangular centring movements1 supporting an inner socket that can be rotated by rack and pinion1 and which carries the several sub-stage accessories4 ,a fine adjustment1 by screw-cone and stud1 is applied by means of an extra slide4 ,the stage is attached to the sheath of the stem by a special arrangement of screws1 by which the rotation in the optic axis can be centred2 sliding spring clips and a movable and a removable and adjustable angle-piece to hold the slides are applied on the upper surface4 ,the body-tube is pivoted to move laterally on the top of the stem1 and an adjustable steel stud beneath serves to stop the movement in the axis4 ,such is ,powell's present instrument1 and it represents the results of sixty years' steady devotion to secure perfection1 and at the same time embody the best ideas of mechanical design by ,andrew ,ross4 ,a cheaper form of students' microscope is furnished by ,powell and ,lealand1 with #c_/d-;inch stage movement1 coarse and fine adjustments to body1 plane and concave mirrors1 revolving diaphragm1 two eye-pieces1 and ,lister's dark wells4 ,these makers also adopt a gauge of tubing1 the size being such that it will take in a binocular body1 a ,huyghenian #b inch eye-piece having the largest field-glass possible4 ,the tube of the sub-stage is the same size1 so as to secure one gauge of tubing throughout4 ,this allows of a ,kellner or other eye-piece to be used as a condenser4 ,ross's ,microscopes4 ,messrs4 ,ross have more recently introduced several changes and modifications in the ,zentmayer stand1 all tending to improve it1 so that the ,ross-,zentmayer model takes its place as a first-class microscope4 ,messrs4 ,ross have lately manufactured other forms of microscopes2 one especially designed for those commencing the study of bacteriology 7,fig4 #ei74 ,this instrument is one of the steadiest among those lately constructed for high-class work4 ,the circular foot and short stout pillar support the whole instrument1 and a substantial knee-joint sustains the full weight in the upright or inclined positions1 while the centre of gravity is by no means disturbed1 and absolute steadiness secured4 ,the stage is of the horse-shoe form1 which affords convenient space for the fingers to lift the slide up while the oil is placed in contact with the objective4 ,the fine adjustment is extremely sensitive1 working smoothly and direct2 this is entirely covered1 to prevent injury by dust4 ,the micrometer screw works directly in the centre of its fittings1 the milled head being divided to read to #a_/ejj of an inch4 ,the sub-stage is fitted with a new centring coarse and fine adjustment1 so that when using high powers with the ,abbe condenser accurate focus can be secured with the least amount of trouble4 ,illustration3 ,fig4 #ei4--,ross's 8,bacteriological and ,histological0 ,microscope4 ,the amount of activity shown during the last few years by opticians in the manufacture of new forms of microscopes renders it somewhat difficult to keep pace with improvements1 some of which are novel4 ,a further source of congratulation is that economy has all along been studied2 so much so1 that the instruments in question are within the reach of persons of moderate means4 ,messrs4 ,ross and ,co4 have taken a new departure in this respect1 and their 8,eclipse0 ,microscope is an entirely new form of stand with a ring foot4 ,this microscope has been produced for the especial use of students1 and can be purchased for a moderate sum4 ,it will be seen at a glance 7,fig4 #fj7 how steady this form of stand must necessarily be1 since the centre of gravity is secured in every direction and inclination4 ,the body-tube carries eye-pieces1 numbered1 of the ,continental size and optical tube-length 7#afj mm471 for which the object glasses are adjusted1 and a draw-tube extending to eight inches4 ,illustration3 ,fig4 #fj4--,ross's ,rigid ,pattern 8,eclipse0 ,microscope4 ,the fine adjustment is independent of set screws1 and not subject to derangement4 ,it is extremely sensitive and direct in action1 and from its construction is equal in perfection of working to the best that can be made4 ,its fitting1 by a new contrivance1 is completely covered at all points1 being thus preserved from disturbance or injury by dust4 ,the ,eclipse is furnished with two eye-pieces1 #a and #a_/d object glasses of highest excellence and large angular aperture1 both adjusted to a double nose-piece1 so that they focus in the same plane2 and a swinging mirror and stage iris diaphragm4 ,in 8,wenham's ,radial0 ,microscope the chief aim has been directed towards providing a very considerable range of effects1 both in altitude and azimuth4 ,the leading principle followed throughout in the construction of this form of stand is that of facilitating the work of the microscopist and of obtaining the maximum range of oblique illumination in all directions4 ,this is fairly well attained by causing all the movements of inclination and rotation to radiate from the object as a common centre4 ,thus it has been found possible to combine seven radial motions1 so that when the instrument is inclined backwards1 as in ,fig4 #fa1 or placed in the horizontal1 as in ,fig4 #fb or rotated from in the brass plate1 a pencil of light from a fixed source shall always reach the object and pass to the objective4 ,the stage is made to rotate completely1 and its rectangular motions are effected by milled heads acting entirely within the circumference4 ,the sub-stage is mounted on the ,zentmayer system1 with two centring screws1 by means of which the optic axis is secured4 ,it is also provided with rectangular and rotating motions4 ,the coarse adjustment is that of the ,ross-,jackson form--a spiral pinion and diagonal rackwork1 while the fine is on an entirely new principle designed by ,dr4 ,h4 ,schrder4 ,illustration3 ,fig4 #fa4--,ross's ,wenham ,radial ,microscope4 ,the 8,ross-,zentmayer ,microscope0 is a thoroughly substantial and practical instrument1 combining elegance of appearance with strength and firmness4 ,illustration3 ,fig4 #fb4--,the ,ross-,wenham ,radial ,microscope4 ,it is a true tripod model1 consisting of a triangular base with two pillars rising from a cross-piece1 which carries the trunnions4 ,the slow movement is obtained by a second slide close behind the first2 but to avoid the friction of rubbing surfaces1 hardened steel rollers are inserted between them1 which give a frictionless fine motion1 amenable to the slightest touch of the milled-head screw situated conveniently at the back of the limb1 through which a steel lever passes which actuates the slow motion slide4 ,the body of the instrument is therefore not touched during the fine focussing1 so that all lateral movement is avoided4 ,the mechanical stage rotates axially1 and the outer edge of the lower plate is divided into degrees1 in order to register the angles2 a simple mode of adjustment is provided for setting the centre of rotation exactly coincident with the focal point of the objective4 ,as the plates of the stage have no screw or rackwork between them 7these are placed externally71 they are brought close together1 thus affording the advantage of a thin substantial stage1 and ensuring rigidity where most required2 phosphor-bronze being used in its construction4 ,the stage is attached to the limb by a conical stem1 with a screw and clamp nut at the back1 so that it can be easily removed for the substitution of a simple plate or other stage2 by turning the stem in the socket the stage may be tilted sideways at any angle required4 ,a feature in the ,ross-,zentmayer stand is the swinging sub-stage and bar carrying the mirror1 having its axis of rotation situated from an axial point in the plane of the object1 which consequently receives the light without requiring alteration of focus in any position of the bar2 by this means facilities are afforded for the resolution of objects requiring oblique light and for the development of their structure4 ,rays are thus obtained from any angle and indicated by the graduated circle round the top of the swing-bar1 and many troublesome and expensive pieces of sub-stage apparatus dispensed with4 ,the value of this arrangement was long ago recognised in ,grubb's 8,sector ,stand10 the movement of which was obtained in a far less efficient manner4 ,illustration3 ,fig4 #fc4--,the ,improved ,ross-,zentmayer ,model4 ,the base or foot of the ,ross-,zentmayer instrument is made in one piece4 ,preference must be given to the double pillar support1 as this is firmer1 and allows the sub-stage to swing free while the microscope is in a vertical position1 as in working with fluid preparations4 ,the sub-stage is provided with screws for centring1 and1 when determined1 secured by a clamping screw4 ,the sub-stage1 with its apparatus in place1 can be instantly removed1 by being drawn out sideways1 so as to use the mirror alone1 which is a great convenience4 ,the mechanical movements of this instrument are perfect1 and well adapted to their purpose4 ,messrs4 ,ross have other typical forms of microscopes4 ,their 8,new ,industrial0 ,microscope1 for the use of farmers1 horticulturists1 textile and other trades1 for the examination of produce and raw materials1 is a surprisingly cheap one1 and deserving of commendation4 ,the great utility of microscopical research to purposes of advanced agriculture is fully recognised1 and a less costly instrument than that usually supplied for more complex investigations was much needed4 ,it is provided with a broad square stage for the purpose of receiving a glass dish to contain liquids or manifold objects1 and which may be moved on the stage to bring the various particles under observation4 ,a fitting beneath the stage carries a plate with diaphragm apertures for modifying the light1 and as seeds1 textile fibres1 and other opaque objects form a large portion of those to be examined1 this sub-stage plate has a space between the perforations which1 when brought into position1 provides a dark ground by preventing the passage of light from underneath4 ,a condensing lens is1 however1 provided for the better lighting of opaque objects4 ,here we have a microscope which combines efficiency with stability1 while its very simplification allows of a really good and effective instrument for the small sum of #c #cs4 ,illustration3 ,fig4 #fd4--,ross's 8,new ,industrial0 ,microscope4 ,messrs4 ,beck's ,microscopes4 ,messrs4 ,beck have adopted what may be termed a rival system of fine adjustment in their modern microscopes4 ,the short lever and screw applied externally to the body tube is peculiar1 ,i may say1 to the ,ross-,jackson system1 and was originally devised to allow of the body tube being supported somewhat more firmly on the limb4 ,this change had its merits fully realised in the early microscopes of ,smith and ,beck4 ,to their successors1 ,r4 ,j4 ,beck1 the microscope owes much1 and very many important improvements1 while all their instruments and accessories are excellent examples of good workmanship and finish4 ,in their ,pathological ,microscope we have a movement originally found in ,tolles' microscopes3 a vertical disc1 by which the centre can be raised or depressed to correspond with the thickness of the slide4 ,the stage can also be brought into an inverted position by rack and pinion4 ,their fine adjustment has been greatly improved1 as we shall presently see1 whereby it has been made more sensitive and delicate of adjustment4 ,the general construction of their microscopes as a rule possess the following advantages3 the stands are strong1 firm1 and yet not too light or too heavy1 the instruments cannot alter from the position in which they are placed1 as1 unfortunately1 will occasionally happen when joints work loose2 in every position the heavier part of the stand maintains the centre of gravity4 ,beck's ,pathological ,microscope 7,fig4 #fe7 is a nearly perfect instrument1 furnished with a firm triangular foot1 which ensures great steadiness in any position4 ,it has a well adapted joint for placing the instrument at any angle of inclination2 coarse adjustment by spiral rack and pinion2 fine adjustment by delicate lever and micrometer screw motion2 rack and pinion focussing and screw centring sub-stage1 made to carry all condensers and other sub-stage apparatus2 mechanical stage with horizontal and vertical traversing motions4 ,the stage is attached to the instrument by two screws and can therefore be removed at pleasure1 leaving a large square flat glass stage for the culture-plate4 ,it is likewise provided with finder divisions1 and as it always fits on to the same place1 any particular portion of the object can be recorded and found at any moment4 ,the triple nose-piece is a convenient addition1 and a very acceptable one to the student while diligently engaged in histological research4 ,illustration3 ,fig4 #fe4--;,beck's ,pathological ,microscope1 with square and removable stage4 ,illustration3 ,fig4 #ff4--;,beck's ,large 8,continental ,model0 ,microscope4 ,beck's ,large 8,continental ,model0 ,microscope is of superior finish4 ,it is provided with a substantial horse-shoe foot1 which gives support to the strong1 well-balanced body1 jointed for giving the microscope any angle of inclination4 ,the body is provided with a draw-tube which can be racked down to the ,continental measurement4 ,it has a spiral rack and pinion coarse adjustment1 and a fine adjustment of the most perfect workmanship1 which will be described in detail presently4 ,it has a large square stage with vulcanite top plate to receive culture preparations4 ,the sub-stage is of the most approved form for centring1 and carries an achromatic or ,abbe condenser1 iris diaphragm1 c4 ,the double mirror can be swung out of place for direct illumination and micro-photography4 ,altogether1 this instrument is in every way fitted for critical or class-room work4 ,illustration3 ,fig4 #fg4--;,beck's 8,new ,fine ,adjustment40 ,to return to the fine adjustment of this1 as of other forms of ,messrs4 ,beck's microscopes1 the applied mechanism of which is believed to be one of the most sensitive and delicate character yet contrived4 ,it is constructed as shown in the accompanying figure4 ,the body of the instrument is supported upon the barrel ,d ,d2 this barrel is accurately and smoothly fitted to the triangular core ,e ,e4 ,at the top of barrel ,d ,d is screwed the cap ,g1 to which is attached the rod ,c2 this rod passes through the centre of the core ,e ,e and connects with the lever arm ,a at ,b4 ,the action of the spring ,j1 which is wrapped spirally around the rod ,c1 raises the body of the microscope and holds the lever arm ,a tightly against the screw arm ,f4 ,the slightest motion1 therefore1 of the screw ,f is communicated through the lever ,a and the rod ,c to the body of the microscope4 ,the great delicacy of this arrangement will be appreciated when it is noticed that the distance from ,i ,h is double the distance of ,i ,b1 therefore any motion at ,b is only half that at ,h4 ,this adjustment is one of the most delicate made for use with high powers4 ,illustration3 ,fig4 #fh4--;,beck's ,national ,binocular ,microscope4 ,in the construction of ,beck's ,binocular ,national ,microscope1 the body is held in a sliding fitting in the limb1 and is moved up or down by means of a rack and pinion motion4 ,this constitutes the coarse focussing adjustment4 ,the fine adjustment is effected by the milled head1 which acts upon the body by means of a lever inside the limb4 ,the upper circular surface of the stage is made of glass1 and carries the object holder1 which is provided with a ledge and spring to hold the object by means of the pressure of an ivory-tipped screw1 so that it can be moved about readily and smoothly4 ,the pressure of the screw is adjusted by the milled head1 which permits of more or less pressure being made upon the edge of the object4 ,illustration3 ,fig4 #fi4--;,beck's ,star ,microscope4 ,when the stage is required for other purposes the object holder can be unscrewed and removed4 ,beneath the stage there is a cylindrical fitting for the reception of a diaphragm1 a polariser1 or other apparatus4 ,the mirror1 besides swinging in a rotatory semi-circle1 is made to slide up or down the stem4 ,the microscope is supported by a firm pillar on a tripod base1 and the body can be inclined at any angle convenient for working4 ,a sub-stage can be added at any time for the reception of an achromatic condenser fitted with concentric screws--a necessity for more delicate microscopical research work4 ,beck's ,star ,microscope is in every sense a students' or class-room instrument4 ,it is firm and well made1 with joint for inclination1 large square stage1 sliding coarse adjustment and fine adjustment by micrometer screw1 draw-tube1 iris diaphragm1 double mirror on swinging crank arm1 ,a or ,b eye-piece1 a one-inch and quarter-inch objective1 the magnifying power of which ranges from #che to #ahc4 ,illustration3 ,fig4 #gj4--;,beck's ,binocular ,dissecting ,microscope4 ,an early binocular microscope for dissecting purposes was devised by the late ,mr4 ,r4 ,beck4 7,fig4 #gj47 ,this took the form of a simple instrument built up on a square mahogany base ,a raised about four inches upon four brass supports ,b ,b1 having a large circular stage plate made to revolve on a second plate1 on which the object is placed and brought under the eye for dissection4 ,on the left hand side is a milled head rack and pinion ,k1 which acts upon a horizontal bar ,i for focussing the magnifying lens4 ,another bar1 ,r1 carries the prism ,p and a pair of eye-pieces arranged on the principle of ,m4 ,nachet's binocular microscope4 ,mr4 ,beck preferred to adopt ,wenham's method of arranging these prisms2 that is1 by allowing half the cone of rays to proceed to one eye without interruption1 while the other half is intercepted by the prisms and transmitted to the other eye4 ,beneath the stage is the ordinary mirror ,l4 ,the condensing lens ,m is supported on a separate brass holder let into one of the supports of the stand4 ,in practice1 however1 this arrangement was found inconvenient1 and the microscope has therefore not been brought into general use4 ,messrs4 ,watson's ,microscopes4 ,among ,london opticians1 the various microscopes manufactured by ,messrs4 ,watson1 of ,holborn1 are of high finish and good workmanship4 ,those specially designed for the use of students possess merits of their own in their mechanical construction1 and also embody a provision1 as indeed do all their instruments1 whether for students or more pretentious work1 whereby wear and tear in their frictional parts can be compensated for by the user himself4 ,this is effected in a simple but efficient manner4 ,the fittings are sprung1 and screws set just outside the dove-tails4 ,the very slightest turn of the screws compresses the dove-tails1 and a very large amount of wear can in this way be prevented4 ,i am glad to notice that ,messrs4 ,watson have adopted certain standard sizes recommended some time ago by the ,royal ,microscopical ,society for the diameters of eye-pieces4 ,it would be a great advantage if the same standard became generally recognised and brought into use1 since it is a matter of much importance to microscopists4 ,watson's ,edinburgh ,students' ,microscope 7,fig4 #ga7 is a thoroughly efficient one for all practical purposes1 great care having been bestowed upon its smallest details1 and it is not difficult to perceive the reason of its popularity among students4 ,the tripod form of foot ensures great steadiness and firmness2 the body carries the smaller #jib eye-piece1 and with draw-tube closed is of the ,continental length4 ,the draw-tube is graduated to millimetres1 and when fully extended the body measures #aj inches4 ,the stage is provided with mechanical and rotary movements2 the compound sub-stage with centring screws1 rack and pinion to focus1 and a means of lifting the condenser out of the optical axis when not required for use4 ,notwithstanding1 none of the movements are at all cramped2 a clear distance is maintained beneath the stage1 affording plenty of room for manipulating the mirror4 ,both coarse and fine adjustments work with smoothness1 the latter being on ,watson's latest improved principle--one revolution of the milled head moves the body #a_/cjj of an inch4 ,the stage is of extra large size1 to allow of the use of large culture-plates4 ,no ,continental stand of higher price compares with the ,edinburgh microscope4 ,its height when placed in the vertical position is #aa-a_/b inches4 ,illustration3 ,fig4 #ga4--,watson's ,edinburgh ,students' ,microscope4 ,illustration3 ,fig4 #gb4--,sub-stage of ,edinburgh ,students' ,microscope4 ,this view of underside of stage of students' instrument shows the mirror set at an angle for oblique illumination1 and sub-stage turned aside4 ,the various sizes of oculars adopted by opticians and at present in vogue cause considerable confusion4 ,a standard size is specially needed for students' and small microscopes4 ,the standard long used by ,continental manufacturers is #jib of an inch4 ,the adoption of this size would place the eye-piece in the same position as that of the universal screw for the objective1 formulated by the ,royal ,microscopical ,society many years ago4 ,the desirability of using standard sizes has been fully recognised by ,messrs4 ,watson and they are now adapted to most of their microscopes4 ,the ,english diameter1 #ace of an inch1 known as the 8,ross0 size1 is retained in all their microscopes of large size4 ,watson's ,mechanical ,draw-tube4 ,illustration3 ,fig4 #gc4--,watson's ,mechanical ,draw-tube 7full-size74 ,an important feature in connection with the body-tube of ,watson's ,edinburgh ,students' ,microscope 7as1 indeed1 in all their fully furnished instruments7 is that they are provided with two draw-tubes2 one moved by rack-work1 the other sliding inside the body-tube4 ,the advantage is1 that the body can be made very short or extremely long1 while sufficient latitude can be given to objectives corrected for either ,continental or ,english tube-lengths1 and to adjusting the same for thickness of cover-glass by variation of tube length4 ,should the cover-glass be thicker than that for which the objective is corrected1 a shorter tube-length is necessary2 if thinner1 the body must be lengthened4 ,this is effected by means of the rackwork draw-tube4 ,the length of the body when closed is #adb millimetres 7#e-e_/h inches71 and when the two draw-tubes are extended1 #cje millimetres 7#ab inches71 being1 therefore1 shorter than the ,continental and longer than the ,english tube lengths4 ,both draw-tubes are divided into millimetres1 and on the rackwork draw-tube a double scale is engraved1 reading continuously from the sliding draw-tube when fully drawn out1 or giving the body length when the rackwork draw-tube alone is in use4 ,the utility of this mechanical draw-tube is that it permits of quick manipulation with perfect results4 ,illustration3 ,fig4 #gd4--,watson's ,histological ,microscope4 ,stand 8,a40--,height1 when placed vertically and tube pushed home1 #i-a_/b inches4 ,the inside top of the draw-tube is smaller than the remainder1 the former making a fitting for the eye-piece about #a inch long1 permitting of the tube being blackened inside up to this fitting1 thus minimising reflection4 ,the end of the draw-tube has the universal screw for using the apertometer1 c4 ,watson's ,histological ,microscope 7,fig4 #gd7 is a somewhat cheaper form of instrument1 designed for the student2 although of plainer construction it is quite as well made as the costlier model4 ,it is provided with spiral rack and pinion coarse adjustment1 and with this motion the greatest smoothness is preserved4 ,there is no backlash1 the teeth of the pinion never leaving the rack2 so effective is it that a high power can be perfectly focussed by its means4 ,it is also furnished with their universal pattern of fine adjustment4 ,this can be had for #c #cs4 ,illustration3 ,fig4 #ge4--,watson's ,semi-,mechanical ,stage4 ,messrs4 ,watson have among other accessories of value introduced in connection with their several microscopes a semi-mechanical stage1 whereby they are enabled to reduce the cost of manufacture4 ,fig4 #ge is an outline sketch of the same4 ,this stage is of the horse-shoe shape1 with cut-out centre1 constructed of #a_/d-;inch brass plate1 and measures over all #e-a_/d inches wide by #d inches deep4 ,fitting on the edges of the main stage is a frame which is actuated vertically by means of a double rack and pinion from beneath1 giving #c_/d-;inch of movement1 having controlling heads on either side of the stage2 on the edges of this mechanical frame a sliding bar is fitted1 consequently movement may be imparted either by rackwork or by hand4 ,the mechanical movement1 however is in one direction only2 but as the bar carries the object1 the worker can easily move the object out horizontally with the finger4 ,the advantage of this stage is that the whole surface is perfectly flush1 and the pinion heads are below its level1 so that culture plates or continuous sections may be conveniently examined4 ,illustration3 ,fig4 #gf4--,new ,centring ,underfitting for ,microscope4 ,another addition of considerable value is the centring underfitting for students' microscopes4 ,this fitting places in the hands of student workers a means of accurately centring the sub-stage condenser1 at a low cost4 ,it consists of the usual underfitting tube1 having a flange at the top which is fitted in a box between two plates4 ,the centring is effected by means of two screws1 which press the flange against a spring1 as in the ordinary sub-stage centring movement4 ,the fitting can be adapted to any form of ,messrs4 ,watson's and most other makers of students' microscopes4 ,watson's ,bacteriological ,improved ,van ,heurck's ,microscope 7,fig4 #gg7 is in every way a superior instrument1 and it at once conveys a favourable impression to the practical worker4 ,when set up for use its many convenient points--its excellence of workmanship and the precision of its movements--seem to imply its special adaptation for the bacteriological laboratory and for other high-class work where absolute reliance has to be placed in the results obtained4 ,every detail of the instrument is carried out in the best possible manner4 ,the coarse adjustment is effected by means of a diagonal rack and spiral pinion1 which ensures the smoothest possible motion2 while the fine1 the most important movement in the instrument1 is made with an extra long lever1 a specialty of ,messrs4 ,watson's1 and which imparts an extremely slow action3 this is now one of the most delicate and reliable forms of fine adjustment4 ,by its means the entire body is raised or lowered by means of a milled head fixed to a screw having a hardened steel point acting on a lever against a point attached to the body slide1 in a dove-tailed fitting about #b-a_/b inches long4 ,owing to the position of the controlling milled head on the limb1 it can be worked with either hand4 ,another feature of importance is that1 in using the fine adjustment the distance between the eye-piece and objective remains unaltered4 ,all the frictional parts of the microscope have spring slots to the dove-tailed fittings1 in which compensating screws are fitted4 ,these are some few of the more important points1 to which much thought and attention have been given4 ,the body permits also of the use of objectives of any other optician1 since its total length when the draw tubes are closed up is only #adc mm42 when extended1 a total length of #cbj mm4 is available4 ,by this means an ample margin is left for the correction for cover-glass thickness1 whether the objective used be intended for the #afj mm4 or #bej mm4 tube length4 ,the height of the microscope when placed in the vertical position is #ac-a_/h inches4 ,illustration3 ,fig4 #gg4--,watson's ,improved 8,van ,heurck ,bacteriological0 ,microscope4 ,the ,stage4--,a somewhat new design has been used in building this up so as to reduce vibration to a minimum4 ,the bracket carrying the stage1 instead of being screwed on to the front of the limb1 as is usually done1 is made in a solid casting1 taking the sub-stage beneath1 and passing into the joint at the top of the foot4 ,the joint bolt goes through the whole 7limb and stage bracket71 rendering the limb stage and sub-stage as firm as if it were one piece2 a point of considerable importance4 ,the mirrors1 which are plain and concave1 are mounted on a swing arm1 so that they may be turned aside when direct illumination of the object is required4 ,on the right hand side also there is a steel clamping bar for fixing the microscope at any angle of inclination4 ,the tripod foot1 which has superseded most other forms1 is adopted4 ,at the points of contact with the table the feet are provided with cork pads1 which give increased firmness and prevent vibration to some extent4 ,the sub-stage is provided with a fine adjustment of similar design to that employed for the focussing of the objective4 ,it has become needful to embody such a refinement1 in order that sub-stage condensers of large aperture1 such as are in constant use for critical high-power work1 may be adjusted with the same facility and precision as the objective--they1 in fact1 require it if the best work is to be got out of them4 ,no pains have been spared by ,messrs4 ,watson to render it absolutely perfect4 ,watson's ,portable ,microscope4--,this instrument is similar in general detail to the ,histological ,microscope1 but the foot1 mirror stem1 c41 are made to fold up in exceedingly compact form1 and when set up for use the stand is perfectly rigid4 ,portable microscopes are1 as a rule1 but makeshifts4 ,this1 however1 is a thoroughly sound1 practical instrument and capable of best work with the highest power objectives1 having good adjustments and universal size fittings throughout1 so that the objectives and apparatus made for the larger instruments can be employed with it4 ,illustration3 ,fig4 #gh4--,watson's ,portable ,microscope4 ,height of instrument when placed vertically and racked down is #i-c_/h inches4 ,watson's ,petrological ,microscope 7,fig4 #gi7 is a modification of their ,edinburgh ,students' pattern1 and designed specially for petrological and mineralogical work4 ,illustration3 ,fig4 #gi4--,students' ,petrological ,microscope4 ,a polariscope having prisms of large size is supplied with it1 the analyser being fitted in the body1 and the polariser in the under-stage fitting4 ,the latter has a divided circle and a spring catch at every quarter circle4 ,by removing the polariser and withdrawing the analyser1 for which provision is made1 the microscope can be used for purposes of ordinary research4 ,a ,klein's quartz plate is fitted beneath the analyser1 also in the body of the microscope4 ,the stage1 which has a glass surface1 rotates concentrically1 and has a divided circumferential edge reading by the verniers4 ,the eye-piece has cross webs to the diaphragm1 and when it is desired1 an analyser1 having a divided circle fitted with a calc-spar plate1 can be used above the eye-piece1 and condenser lenses attached to the polariser for stereoscopic purposes4 ,all the fittings have the universal thread1 and are interchangeable4 ,illustration3 ,fig4 #hj4--,swift's ,histological and ,physiological ,microscope4 ,messrs4 ,swift's ,microscopes4 ,messrs4 ,swift's ,microscopes have a well-established reputation for quality and good workmanship1 and therefore can in no way suffer by comparison when placed beside those of other opticians4 ,one of the characteristics of ,messrs4 ,swift's microscopes--and this runs through the whole series--is that they are all made to a standard gauge1 so that the several parts of the instruments1 as well as their accessories1 are interchangeable2 the cheaper forms1 with those of the first quality and finish4 ,should the student1 then1 start with a ,no4 #a model1 he can at any time build it up1 as it were1 with the accessories designed for a ,no4 #c or #d1 that is1 for an instrument of double the price he started with4 ,the optical centre is preserved throughout the whole series of microscopes4 ,illustration3 ,fig4 #ha4--,swinging ,leg ,attachment of ,swift ,son's ,four-,legged ,microscope ,stand4 ,the tripod foot has1 it appears1 taken the place of some of their other forms of instruments1 while their four-legged tripod1 if it can be so designated1 is a novelty of quite an unusual character4 ,the swing leg is attached to the framework of the tripod by the screw 7,fig4 ,a71 which is provided with a powerful steel spiral spring1 compressed between two steel collets when the screw is driven home1 as shown in ,fig4 ,b4 ,the expansion of this spring will obviously take up and compensate automatically any wear and tear that is likely to occur between the bearing surfaces1 and it is therefore impossible for the fitting to get loose4 ,swift's ,four-legged ,microscope 7,fig4 #hj7 is one possessing great stability in whatever position it may be placed2 the body being supported on a horse-shoe platform1 from which its four legs spring1 the two front legs being fixed1 while the hind legs are pivoted to the platform4 ,this arrangement of pivoting the hind legs enables the microscope to adapt itself to any uneven surface1 thus keeping it always in a steady position1 while it also reduces the danger of being upset by any lateral movement of an accidental nature4 ,the feet are studded with corks1 an additional aid to steadiness and fixity for microphotography4 ,the length of the body from the ocular to the nose-piece is #f-a_/b inches1 and can be extended to #i or #aj inches by means of the draw-tube1 which has a millimetre graduation4 ,the stage1 which is of horse-shoe shape1 is provided with spring clips1 to which a movable mechanical stage can at any time be attached4 ,the sub-stage partakes of two forms1 one being an ordinary fitting1 taking an ordinary condenser2 the other1 the regular rack and pinion achromatic condenser with centring adjustments4 ,it has a diagonal rack and pinion coarse adjustment1 the fine adjustment being made by micrometer screw of the finest character4 ,illustration3 ,fig4 #hb4--,swift's ,spiral ,rack and ,pinion ,coarse ,adjustment4 ,fig4 #hb is intended to illustrate the advantage of the spiral rack and pinion which ,messrs4 ,swift fit to their microscopes1 in place of the ordinary conventional horizontal rack and pinion movement4 ,the advantage will at once be seen1 since there is more gearing contact between rack and pinion1 thus ensuring durability and reducing loss of time or back lash to a minimum1 with less wear and tear4 ,the leaves of the pinion also roll into the teeth of the rack by degrees1 ensuring a very much smoother action1 which1 if properly made and fitted1 prevents the gearing of the two being felt by the hand whilst focussing4 ,illustration3 ,fig4 #hc4--;,graduated ,supplementary ,draw-,tube4 ,fig4 #hc is a supplementary draw-tube with rack and pinion movement1 which can be adapted to any of ,swift's microscopes in place of the ordinary draw-tube1 the size of the thread being of the same diameter1 so as to render all draw-tubes1 as well as other parts of these instruments1 interchangeable4 ,the draw-tube being divided into millimetres can be extended from #afj to #bej millimetres4 ,one advantage of this arrangement is that the correct adjustment of any objective with each eye-piece is easily found and recorded for future observations with the same combination4 ,messrs4 ,swift's ,three-legged ,tripod ,microscope 7,fig4 #hf74 ,in most respects the description already given of the four-legged instrument is applicable to this stand4 ,although of an apparently different form1 it can be built up1 as already explained1 into one of a higher class4 ,it is suitable in every way for histological investigations4 ,the horse-shoe platform in this1 as in the preceding stand1 is extremely serviceable1 as it allows the pillar of the instrument to rest firmly upon it1 thus rendering the stand very rigid4 ,swift's ,bacteriological ,microscope 7,fig4 #hd71 designed by ,professor ,wright1 of the ,army ,medical ,school1 ,netley1 a sufficient warranty of its excellency and perfect adaptation for bacteriological high-class work4 ,one of the advantages connected with this microscope is the facility with which it can be adapted for either high or low power investigation1 without the necessity of adding or detaching any part4 ,the objectives1 arranged on a triple nose-piece1 are approximately in focus when revolved into position for immediate use1 thus effecting a saving of time in changing the objective4 ,moreover1 the nose-piece carrying the objectives is of new construction1 and fitted in such a way that the entry of dust is rendered impossible4 ,illustration3 ,fig4 #hd4--,swift's ,army ,bacteriological ,microscope4 ,illustration3 ,fig4 #he4 ,under-,stage of same4 ,the ,abbe condenser1 fitted with an iris diaphragm1 is mounted on an eccentric arm1 so that it can readily be thrown out of the axis of the microscope when not required1 without having to re-arrange the focus when again brought into position4 ,the condenser must be turned aside when plate cultivations and preparations of unstained bacteria are being looked over for selection of colonies for mounting1 in which case an arm carrying a quadrant with three apertures is brought into position in place of the condenser1 the apertures being severally centred by a spring catch and used with oblique light4 ,this arrangement1 shown in ,fig4 #he1 is seen from the under surface of the stage4 ,the stage is sufficiently large1 so that when ,petrie plates are being examined at the extreme edges there is little fear of their overbalancing4 ,illustration3 ,fig4 #hf4--,swift's ,histological ,students' ,microscope4 ,the fine adjustment is the ,swift's ,patent ,campbell ,differential ,screw1 which offers great facilities for delicate focussing with the highest power objectives4 ,the stand is of the most substantial and rigid form1 and thus ensures the microscope from vibration4 ,the under-stage of microscope 7,fig4 #he7 is seen to be of the most approved form4 ,illustration3 ,fig4 #hg4--,swift's ,advanced ,students' ,microscope4 ,swift's ,advanced ,students' ,microscope4--,in this microscope 7,fig4 #hg7 we have a superior instrument for the use of the advanced student1 which may be described as of high mechanical excellence1 well suited for every requirement of work4 ,the stand is the well-known tripod form of their ,challenger ,microscope1 and admits of the instrument being placed at any angle of inclination2 the body is short enough to work with objectives of ,continental makers1 and is provided with a draw-tube1 to elongate it to the standard of #aj inches1 with a diameter of #a-c_/af inch to take the same eye-pieces as the larger stands4 ,the coarse adjustment is by spiral rack and pinion2 the fine1 by a carefully made differential screw motion for delicate focussing4 ,the stage is of the horse-shoe pattern1 to which a mechanical stage can at any time be adapted1 as well as an achromatic condenser to the sub-stage seen beneath4 ,here the student will find the foundation for a superior instrument4 ,messrs4 ,baker's ,microscopes4 ,of ,messrs4 ,baker's larger stands1 the ,improved 8,nelson ,model10 ,no4 #b 7,fig4 #hh7 stand is selected in preference to their more elaborate ,no4 #a1 and their simpler form1 ,no4 #c1 as a high-class instrument1 and one well suited for fine critical work2 the former being somewhat better1 only from having extra adjustments2 the latter possessing no superior advantage over the 8,advanced ,students'0 ,microscope4 ,this microscope is mounted on a solid tripod foot1 which insures stability1 whether placed in a vertical1 horizontal1 or inclined position2 the front toes are slotted1 so that they may be clamped to the base plate of a photo-micrographic apparatus1 first introduced for photo-micrographic work1 and will also be found convenient in ordinary work2 as the fine adjustment milled head is placed at the bottom of the pillar1 instead of at the top1 the more usual place4 ,for photo-micrographic work the advantage is that the strain of the pulley in such apparatus actuates the fine adjustment1 and is less liable to cause vibration of the instrument4 ,the advantage when the instrument is used for ordinary work lies in the fact that the weight of the hand is rested on the top of the tripod1 thus admitting of steadier movement of the milled head4 ,the fine adjustment is obtained by a 8,campbell0 differential screw1 each revolution of which is equal to #a_/bjj m4m4 ,the draw-tubes being graduated in m4m41 allow of either short or long tube objectives being used1 closing up to #aej m4m4 and extending to #bhj m4m41 the rack and pinion adjustment to the lower tube affording a ready means of correction for cover-glass thicknesses4 ,the eye-piece gauge1 as will be seen from its dimensions1 is of large size1 being the same as that adopted by ,zeiss for his long tube compensating oculars2 smaller eye-pieces can1 however1 be adapted at any time4 ,illustration3 ,fig4 #hh4--;,baker's ,improved 8,nelson ,model0 ,microscope4 ,dimensions4--,height when in vertical position and body racked down1 #aa2 ,height of stage1 #d-a_/h2 ,height of optic axis when in horizontal position1 #h-a_/b2 ,spread of tripod foot1 #h #h-a_/b2 ,diameter of mirrors1 #b-c_/h2 ,internal diameter of draw-tube1 #a-c_/aj4 ,the mechanical rotating stage is divided on brass to #a_/ajj inch1 with clamping bars and stop1 by which a specimen can always be brought back to a certain position for registration4 ,the sub-stage has rack-work focussing adjustment1 and centring screws2 a fine adjustment is added1 if desired4 ,on the whole1 the instrument is suitable for special critical work1 and is equally well suited for photo-micrography4 ,illustration3 ,fig4 #hi4--;,baker's ,advanced ,students' ,microscope4 ,dimensions4--,height when in vertical position and body racked down1 #aa-a_/d2 ,height of stage1 #d-c_/d2 ,width of stage1 #d2 ,height of optic axis when in horizontal position1 #f-a_/b2 ,spread of foot1 #f #f2 ,diameter of mirrors1 #a-c_/d2 ,internal diameter of draw-tube1 #aa_/ab4 ,explanatory lettering of instrument3 ,a1 ,huyghenian eye-piece2 ,b1 draw-tube graduated in millimetres2 ,c1 nose-piece2 ,d1 coarse adjustment2 ,e1 fine adjustment with millimetre screw2 ,f1 horse-shoe sliding stage1 graduated with sliding bar in vertical and horizontal directions for use as finder2 ,g1 sub-stage rack and pinion screw2 ,h and ,i1 centring screws to sub-stage2 ,j1 carrier for condenser2 ,k1 mirror with movable arm supported on solid tripod foot4 ,the points of difference between this stand and the ,no4 #a model are that in the latter the fine adjustment carries the body only1 and not the rack adjustment2 the limb carrying both the body and the sub-stage is in one piece1 giving1 if possible1 still greater rigidity2 the rotation of the mechanical stage1 which is divided on silver1 is complete1 and can be actuated by hand or rack work2 it has a clamping screw and fine adjustment to sub-stage4 ,baker's ,advanced ,students' ,microscope 7,fig4 #hi7 may be described as a typical instrument1 equally suitable for histological work and that of the advanced student4 ,the intention of the maker in simplifying the adjustments and reducing the instrument in size1 was to furnish a well-finished portable instrument at a moderate cost4 ,this object has not been attained by supplying adjustments of second-rate quality1 but by reducing their number to a minimum4 ,illustration3 ,fig4 #ij4--,the ,mayall ,removable ,mechanical ,stage4 ,the tripod foot of the 8,nelson ,model0 is replaced by a claw foot1 which is in effect a tripod1 as it rests on three points2 it has not the same wide spread1 but this1 far from being a disadvantage1 renders the instrument more portable4 ,it has rack and pinion coarse and ,campbell differential screw fine adjustments1 draw-tube graduated in m4m41 extending to #ahj m4m41 eye-piece gauge the same as the ,continental size1 large square open stage to afford the greater freedom of manipulation2 sliding bar with graduations on bar and stage1 which suffice for registering any given field under a low power2 holes are also drilled in the stage ready to receive an attachable mechanical stage should it be thought advisable to add one at a later date4 ,the sub-stage is of the universal size with rack-work focussing1 adjustment1 and centring screws4 ,illustration3 ,fig4 #ia4--;,baker's ,model ,histological ,microscope4 ,dimensions4--,height when in vertical position and body racked down1 #aj-a_/b2 ,height of stage1 #d2 ,width of stage1 #c-a_/b2 ,height of optic axis when in horizontal position1 #e-a_/d2 ,spread of foot1 #e-a_/d2 ,diameter of mirrors1 #a-e_/h2 ,internal diameter of draw-tube1 #aa_/ab4 ,messrs4 ,baker have recently introduced a similar instrument with swing-out sub-stage and adjustments for compensating for wear and tear of rack4 ,the stage is also somewhat larger from back to front4 ,these stands are very suitable for bacteriological research1 and for amateurs wishing to obtain a stand which will carry all the apparatus they are likely to need1 without going to the expense of the larger models1 no better instrument could be desired4 ,their 8,removable ,mechanical ,stage0 7,fig4 #ij7 is a modification of the pattern designed by the late ,mr4 ,j4 ,mayall4 ,the vertical movement is by rack and pinion1 giving a range of #a-a_/h inch4 ,the horizontal motion of #a-a_/b inch is accomplished by means of a quick-acting screw4 ,the object is pressed tightly to the stage of the microscope by means of three points1 and the whole of the mechanical part is firmly clamped by two thumb screws which can be readily removed4 ,the stage is made to carry slides of any size less than #a-c_/d inch wide4 ,baker's ,histological ,microscope 7,fig4 #ia7 is of a different type to the preceding1 and is intended to represent one of medium power1 affording magnification of about #djj as a maximum4 ,it is supplied with a diaphragm beneath the stage1 without other illuminating apparatus than that of the mirror4 ,but if the adjustments of such a stand are good1 there is no reason why some form of sub-stage condenser should not be added1 to make the instrument somewhat more serviceable4 ,there is1 however1 a rather too limited space beneath the stage of an instrument of this kind to admit of a sub-stage condenser1 consequently it cannot be said to be suitable for critical work4 ,for all ordinary students' work this microscope is certainly available4 ,illustration3 ,fig4 #ib4--,rousselet's ,tank ,microscope4 ,the stand of the ,model ,histological ,microscope has the same form of foot as the more advanced student's stand4 ,it is somewhat lighter1 and more portable1 a matter of consideration in a student's microscope1 which often has to be carried to and from a class-room4 ,it is provided with rack and pinion coarse adjustment1 and a ,campbell differential screw fine adjustment1 draw-tube1 and diaphragm2 the diaphragm carrier being of the universal size1 so that it can be replaced by an ,abbe condenser at any time4 ,with the additions suggested1 this instrument can be made equal to those of a higher standard4 ,rousselet's ,tank ,microscope 7,fig4 #ib71 for rapidly looking over pond water and weeds1 consists of a jointed arm moving parallel to the side of the tank to carry an aplanatic lens2 the arm is focussed by means of rack and pinion fixed to the upright of a mahogany stand1 upon which the tank can be placed1 or it can be clamped directly to the tank by means of a screw4 ,this handy form of pond microscope is made by ,messrs4 ,baker4 ,pillischer's ,microscopes4 ,mr4 ,pillischer 7,new ,bond ,street7 is favourably known for the excellency of his instruments4 ,he has lately brought out several microscopes of an improved form4 ,his larger model1 the 8,new ,international10 consists of a solid1 well-built1 firm tripod stand of the ,ross-,jackson pattern1 which appears to be quite in the ascendant among ,london opticians2 rack and pinion coarse adjustment1 and a superior micrometer fine adjustment2 sub-stage with centring screws and rack and pinion focussing adjustment2 a new form of sliding pin-hole diaphragm and iris diaphragm2 ,b and ,c eye-pieces2 #e_/h and #a_/g objectives2 ,abbe condenser1 ,n4,a4 #abj2 in every respect a perfect model1 neatly packed in a mahogany case1 for a very moderate sum4 ,mr4 ,pillischer's ,no4 #b 7,fig4 #ic7 8,international0 ,microscope1 being the ,army pattern as well as the student's1 is well adapted for clinical work4 ,a firm tripod stand supports two dark bronze uprights1 with rack and pinion coarse adjustment1 e1 and fine adjustment1 d1 the stage1 i1 is wide and suitable for clinical work1 and large enough for dissecting upon4 ,the whole instrument is well made2 the coarse adjustment is so good that the one-eighth inch can be focussed with ease1 and without using the fine adjustment4 ,for a few shillings extra1 a mechanical stage can be added1 consisting of levers1 having an action similar to the movements of a parallel ruler1 which is so easy of adjustment that it can be worked under the eighth-inch objective with the hands--an advantage in a clinical microscope4 ,illustration3 ,fig4 #ic4--,pillischer's 8,international0 ,microscope4 ,the following reference letters serve to explain the general construction of the microscope 7,fig4 #ic73--;a1 the eye-piece2 b1 the draw-tube2 c1 the sliding-tube2 d1 micrometer or fine adjustment2 e e1 the coarse adjustment2 g1 the mirror arm and mirror2 h1 sub-stage carrying ,abbe condenser2 i1 the stage with spring-clips2 j1 objectives screwed into place and double nose-piece4 ,the 8,kosmos0 is ,pillischer's cheaper model4 ,the stand of this somewhat novel and original microscope is framed entirely of brass and gun-metal4 ,the fine adjustment is very sensitive and perfectly steady1 admitting of the highest immersion objectives being used4 ,the optical parts are constructed upon principles consistent with the latest improvements4 ,it has a claw-foot stand with a semi-circular arm1 which carries the body1 with sliding-tube coarse adjustment1 and micrometer screw fine adjustment1 with a large square stage diaphragm and mirror4 ,the instrument is neatly packed in a mahogany box1 together with the ,a or ,b eye-piece1 #a-;inch and #a_/e-;inch objectives of good defining and penetrating power1 magnifying from #cj to #chj diameters1 in mahogany cabinet1 for the moderate sum of #e4 ,pillischer's ,binocular ,microscope 7,fig4 #id7 is constructed on a plan somewhat intermediate between that of ,beck's and ,ross's well-known patterns1 and in point of finish is equal to any student's microscope in use4 ,the semi-circular form given to the arm carrying the body increases the strength and solidity of the instrument1 although it is doubtful whether it adds to its steadiness when placed in the horizontal position4 ,the straight body rests for a great part of its length upon a parallel bar of solid brass ploughed into which is a groove for the reception of the rack attached to the body1 the groove being of such a form that the rack is held firmly while the pinion glides smoothly through it4 ,a steady1 uniform motion is thus obtained1 which almost renders the fine adjustment unnecessary4 ,the binocular bodies are inclined at a smaller angle to one another than in most instruments2 nevertheless1 the range of motion given to the eye-pieces by the rack and pinion enables those whose eyes are widely separated to use the instrument with comfort4 ,the prism is so well set that it illuminates both fields with equal intensity4 ,the stage is provided with rectangular traversing movements to the extent of an inch and a quarter in each direction4 ,the milled heads which effect these are placed on the same axis1 instead of side by side1 one of them--the vertical one--being repeated on the left of the stage1 so that the movements may be communicated either by the right hand alone or by both hands acting in concert4 ,the stage-plate has the ordinary vertical and rotatory motions1 but to a much greater extent than usual2 and the platform which carries the object is provided with a spring clip to secure the object when the stage is placed in the vertical position4 ,a new form of sub-stage with centring screws is made to carry the ,abbe achromatic condenser1 diaphragm1 polarising and other apparatus4 ,illustration3 ,fig4 #id4--,pillischer's ,binocular ,microscope4 ,continental ,microscopes4 ,continental ,microscopes4--,the better known among continental opticians are ,zeiss1 ,leitz1 ,seibert1 ,reichert and ,hartnack4 ,all seem to have vied with each other in the attainment of perfection in the manufacture of the most useful forms of microscopes4 ,the late ,carl ,zeiss did more for the modern microscope than either of the opticians referred to above4 ,i therefore take a medium typical model of his from a long series of highly-finished instruments for my illustration4 ,zeiss's successors have of late endeavoured to perfect the mechanical details of their instruments in three or four directions1 i4e41 fundamental features of the stand1 stage arrangements1 means of focussing1 and illumination4 ,the ,stand4--,the general form of the stand still partakes too much of the original sameness of type introduced by ,oberhuser1 and modified and improved by ,hartnack2 the 8,babuchin0 stand being still in favour with some few makers4 ,the greater firmness and steadiness of ,zeiss's stand 7,fig4 #ie7 is secured by the horse-shoe form of foot1 which1 for the most part1 is massive and well adapted to carry the stout uprights1 which support a well-balanced1 substantial body-tube and a graduated draw-tube1 circular stage with a vulcanite disc1 #d inches in diameter2 a sub-stage with centring arrangement for ,abbe's illuminating apparatus1 and iris diaphragm and other diaphragms for use when the condenser is thrown aside4 ,the mirror is full-sized1 plane and concave4 ,the coarse adjustment is regulated by a rack and pillion movement so perfect that objectives of medium power can be focussed by it alone4 ,the fine adjustment is made by micrometer screw1 the force exercised by which is transferred to the movable body by a single contact between two hardened steel surfaces4 ,this ensures extremely delicate and uniform motion of the body which carries the tube4 ,the divisions in the milled head of the screw furnish a means for the registration of the vertical movements of the tube4 ,in the latest stands1 each division corresponds to an elevation or depression of the tube in the direction of the optic axis of #jja mm4 ,by this means measurements of thicknesses may be made with a considerable degree of accuracy1 the upper and lower surfaces of the object being successively focussed1 and the amount read off on the milled-head1 by the fixed index4 ,in doing this1 care must be taken to make both adjustments by a rotation of the screw in the same direction4 ,the thickness of an object in air is then equal to the difference between the two readings4 ,by this means the thickness of any other substance may be measured--that1 for instance1 of the cover-glass of the object4 ,illustration3 ,fig4 #ie4--,zeiss's ,medium ,stand ,microscope4 ,the medium tube-length of the microscope is #afj mm4 from the attachment of the objective to the eye-piece end4 ,the draw-tube admits of the length being increased or diminished1 and this may be read off by means of the millimetre scale engraved on the tube4 ,my description of this model also applies to the higher class microscopes1 which will be found in every way well finished and adapted to biological and scientific research4 ,illustration3 ,fig4 #if4--;,e4 ,leitz's ,medium-sized ,microscope4 ,e4 ,leitz's of ,wetzlar ,microscopes4--,this optician publishes a series of twelve high-class forms of instruments4 ,by preference1 the horse-shoe form of stand 7,fig4 #if7 is adopted in the whole of this maker's models1 the body being supported on a hinge joint and clamped over1 and fitted with a circular revolving centred mechanical stage1 attached to the ordinary stage by means of a set pin1 which fixes the stage in position4 ,by removing the screw1 the stage can be detached2 in this way1 the stage serves for searching over large surfaces and registering the results4 ,illustration3 ,fig4 #ig4--,leitz's ,dissecting ,microscope4 ,the coarse adjustment is made by rack and pinion1 and the fine adjustment by micrometer screw1 the head of which is provided with a scale reading #a_/ajj mm4 ,the draw-tube is also cut and ruled to millimetre scale4 ,the sub-stage has rack and pinion movement1 and is arranged for the ,abbe condenser and iris diaphragm4 ,this is attached to the upper stage by means of a set pin1 which fixes and retains it in position after perfect centring4 ,by removing the pin1 the sub-stage can be either detached or swung aside by pressing a button4 ,in short1 this microscope is in all respects well furnished and fitted with the requisite complex mechanism necessitated by modern high-class technicological work4 ,leitz's students' microscope1 with sliding body1 micrometer screw fine adjustment1 concave mirror1 two eye-pieces and two objectives1 #c_/d inch and #a_/h inch1 in mahogany case1 costs #c #ajs4 ,leitz's dissecting microscope1 with a heavy foot and rests1 is fitted with two aplanatic lenses1 magnifying #aj1 #bj diameters4 ,reichert and ,seibert adhere to the same model as that of ,zeiss1 and therefore require only a brief notice4 ,their microscopes are characterised by substantial workmanship1 suitable construction1 and exact centring4 ,the coarse adjustment is obtained in the usual way by rack and pinion1 the fine by micrometer screws1 which work easily1 and are protected against wear and tear by having their working surfaces hardened4 ,the stands of the better class instruments have micrometer screws graduated1 and draw-tubes cut to millimetre scale4 ,their mechanical stages and sub-stages and accessories are in every way well finished2 stage forceps1 tests1 and an assortment of cover glasses and slides being added4 ,their first-class microscopes are sent out in mahogany boxes4 ,on going through the continental makers' catalogues1 it will be noticed that their well-equipped microscopes are rather more costly than that of their ,english confreres4 ,it is understood ,messrs4 ,baker and ,watson are the constituted agents for these opticians4 ,nachet's ,microscope1 a new form of which was first seen at the ,antwerp ,exhibition #ahib1 is very solidly built1 and has all the qualities necessary for histological work4 ,the stage rotates about the optic axis1 and carries a movable slide holder4 ,the coarse adjustment is by rack and pinion movement1 the fine by the new system of micrometer screw 7described in the journal of the ,royal ,microscopical ,society of #ahhf71 with divided head indicating the #a_/djj part of a mm4 ,the plane and convex mirror is mounted on a jointed arm4 ,the draw-tube is divided into millimetres4 ,the illuminating system1 consisting of a wide-angled ,abbe condenser 7,n4,a4 #adj7 with iris diaphragm1 is raised or lowered by rack and pinion screws4 ,the iris diaphragm1 being mounted on a wheel1 is worked by a tangent screw1 which by a very slight movement causes the aperture of the diaphragm to pass from the centre to the periphery of the condenser4 ,altogether the arrangement of the sub-stage is novel1 and the instrument is extremely well arranged and adapted to modern requirements4 ,nachet and ,hartnack1 of ,paris1 hold an almost equal rank as makers of first-class microscopes1 and in point of excellence of workmanship fairy rival those of our ,english makers4 ,illustration3 ,fig4 #ih4--,nachet's ,class ,demonstrating ,microscope4 ,there are very many other ,london and ,continental makers of microscopes besides those especially mentioned1 who have well-sustained reputations as opticians1 and who1 from want of space1 ,i have been obliged to pass over4 ,messrs4 ,newton's ,students' ,microscope must be mentioned with respect4 ,it is a good and useful instrument1 has a firm stand with a reversible 7rotatory7 body movement1 which seems to ensure steadiness when brought into the horizontal position for micro-photographic purposes4 ,there are other opticians whose microscopes have stood the test of time--,messrs4 ,collins1 ,crouch1 c4 ,it may1 however1 be taken as a well-established fact that those opticians known to manufacture the more highly-finished models also produce the more serviceable forms of students' class-room1 and other microscopes4 ,the ,bacteriological ,microscope4 ,the microscope required for bacteriological studies should be perfect in all its parts4 ,with regard to the choice of an instrument1 it is very much a matter of price1 since the most perfect is usually the most costly2 ,i shall therefore proceed to give a typical example of the instrument in use in a bacteriological laboratory4 ,the microscope should possess the following qualifications1 all of which are absolutely necessary for the study of such minute objects as bacteria and other micro-organisms4 8,the typical bacteriological microscope should be well equipped with objectives of sufficiently high magnifying power1 and with a special form of illuminating apparatus2 while the mechanical arrangements for focussing should act with the greatest smoothness and precision2 the stage1 also1 should be wide enough to admit of the examination of plate cultivations40 ,we will consider these several points and recommendations seriatim1 commencing with the stand4 ,messrs4 ,watson ,sons' ,van ,heurck model stand so well answers the several conditions laid down by an experienced teacher of bacteriology1 that ,i have no hesitation in presenting it to my readers as a typical instrument1 one in every way worthy of the high praise it has already received from those who have worked with it1 and whose judgment may be relied upon in every way4 ,the microscope is fully described among ,messrs4 ,watson's instruments1 page #ajh4 ,the ,stand4--,a good firm stand is undoubtedly of the first importance for all high-class work4 ,the steadiness of the instrument and its entire freedom from vibration depends largely upon the form of the stand4 ,i am glad to find ,dr4 ,crookshank in accord with me as to the ,ross-,jackson model1 one which1 in my opinion1 has not been entirely superseded by models of a more recent date4 ,indeed1 the latest improvement effected in the ,ross-,jackson form1 in which attention has been given to the spreading-out of the feet1 has converted it into as solid and firm a stand as ,powell's2 it is equally free from vibration when placed in the horizontal position4 ,there are1 however1 four different forms of stands--the tripod2 the plate with double columns2 the single column ending in a plate or a bent claw2 and the horse shoe4 ,the tripod stand1 with cork feet1 is by far the steadiest form of model4 ,the single upright pillar support should unquestionably be condemned1 as it admits of considerable vibration1 and is most inconvenient for laboratory work4 ,the heavy horse-shoe form is compact and firm1 and the weight of it can hardly be considered an objection4 ,the ,tubular ,body is from eight to ten inches in length1 to which is added a draw-tube with an engraved millimetre scale4 ,by extending the draw-tube greater magnification is obtained1 but since this is at the cost of definition it should hardly ever be employed in the examination of bacteria4 ,a ,triple ,nose-piece is doubtless a convenience1 saving time which is otherwise spent in replacing objectives of different magnifying powers2 there is also less risk of injuring them4 ,focus should be obtained by means of a rack and pinion coarse adjustment1 together with the most approved kind of fine adjustment4 ,the sliding tube cannot be recommended1 as the motion may be stiff1 encouraging the use of force1 which in turn may result in the objective being brought violently into contact with the specimen1 thus doing injury to the lens or damage to the preparation2 or it may get too loose and readily slip out of focus4 ,the ,stage should be flat and rigid1 either rectangular or circular1 so long as it is sufficiently large to accommodate plate cultivation4 ,a removable mechanical stage is of great advantage for working with high powers1 as a motile bacterium can be constantly kept in view1 while one hand is engaged in working the fine adjustment2 it may also be employed as a finder1 if engraved with a longitudinal and vertical scale1 and provided with a stop4 ,the mechanical stage must be removable1 so that the stage proper may be free from any attachments when required for the examination of cultures4 ,diaphragms4--,the plan of using a series of separate discs of different sizes should be avoided1 as they are easily lost1 and bacteriological investigations may have to be made under conditions in which it is difficult to replace them4 ,a better plan is a revolving plate with apertures of different sizes1 but the most convenient form is the iris diaphragm4 ,the ,sub-stage ,condenser is as necessary in biological work as in the objective--in fact1 the condenser and the objective should be considered as forming one piece of optical apparatus2 the microscope must be regarded as incomplete without it4 ,it is by the sub-stage condenser that the rays of light are concentrated at one point1 or on one particular bacterium2 for the best definition it is essential that there should be mechanical arrangements for accurately centring and focussing the condenser4 ,all this will be explained and enlarged upon under 8,practical ,optics40 ,in the historical review presented to my readers on the evolution of the modern microscope1 ,i have for the most part relied upon my long and close association1 extending over a period of upwards of half a century1 with microscopy4 ,i need hardly say ,i could have very much extended my remarks with pleasure and profit had space permitted1 and thereby much increased the number of names of manufacturers1 who have well-established reputations for the quality of their work1 and whose instruments1 more or less complete in design1 realise the wants of students and of that large class of present-day workers engaged in microscopical pursuits to whom economy of outlay is almost a first consideration4 ,no valid reason1 however1 can be assigned for splitting up1 as some writers do1 the several forms of microscopes into some six different classes1 which implies inferiority in mechanical details or finish1 whereas the difference wholly consists in luxurious appliances to save time1 and in accessories for special work or original research4 ,before bringing these remarks to a close1 it is my wish to direct the student's attention to one or two points of importance in connection with the use of the instrument1 viz43 variations in body-lengths of microscopes1 especially between those of ,english and of ,continental manufacture4 ,the optical-standard measurement adopted in this country for the body-tube-length is #aj inches2 and for its mechanical1 #h-c_/d inches4 ,that of ,continental opticians is1 optical-tube-length #gjh inches1 or #ahj mm42 the mechanical1 #fc inches to #afh mm4 ,professor ,abbe constructed an apochromatic immersion objective especially for the ,english optical tube-length of #ajf inches 7 to #bgj m4m471 and mechanical tube-length somewhat less in measurement4 ,this may be taken to mean a slight increase in the standard value of the tube1 and therefore the addition of the rack-and-pinion to the draw-tube1 now generally made a part of the microscope1 is certainly of some practical value4 ,this difference1 however1 when working with the ,english body-tube of #aj inches1 may be discarded2 it is1 in fact1 only where the shorter ,continental body is in use1 that so small a difference of tube-length exercises a disturbing effect over adjustment4 ,moreover1 an object placed on the stage of the shorter body microscope will not be seen with the same distinctness by the draughtsman should he wish to make use of the camera lucida4 ,the optical tube-length of the body is measured from the back lens of the objective to the front lens or principal focus of the eye-piece2 the mechanical tube-length from the end of nose-piece of objective to the top lens of the eye-piece4 ,illustration3 ,the ,hartnach ,students' ,model ,microscope4 ,,chapter ,,iii4 ,applied ,optics3--,eye-pieces2 ,achromatic ,objectives2 ,condensers4 ,it is almost unnecessary to say that the eye-piece forms a most important part of applied optics in the microscope4 ,it is an optical combination designed to bring the pencil of rays from the objective to assist in the formation of a real or virtual image before it arrives at the eye of the observer4 ,greater attention has been given of late years to the improvement of the eye-piece1 since flatness of field much depends upon it4 ,opticians have therefore sought to make it both achromatic and compensatory4 ,there are several forms of eye-pieces in use1 some of which partake of a special character1 and these will receive attention in their proper places4 ,it is1 however1 customary among ,english opticians to denote the value of their several eye-pieces by ,roman capitals1 ,a1 ,b1 ,c1 ,d1 and ,e4 ,continental opticians1 on the other hand1 have a preference for numerals1 #a1 #b1 #c1 #d1 #e and #f1 or more1 and by which they are recognised4 ,the eye-piece in more general use is that known as the ,huyghenian 7,fig4 #ii72 this came into use upwards of two centuries ago4 ,it was constructed by ,christian ,huyghens1 a ,dutch philosopher and eminent man of science1 secretary to ,william ,,iii4 ,it was made for the eye-piece of a telescope he constructed with his own hands1 and it has been in constant use as the eye-piece of the microscope for nearly two centuries4 ,it consists of two plano-convex lenses1 with their plane surfaces turned towards the eye1 and divided at a distance equal to half the sum of their focal lengths--in other words1 at half the sum of the focal length of the eye-glass and of the distance from the field-glass at which an image from the object glass would be formed1 a stop1 or diaphragm1 being placed between the two lenses for the reason about to be explained4 ,huyghens himself appears to have been quite unaware of the value of an eye-piece so cleverly constructed4 ,illustration3 ,fig4 #ii4--;,huyghenian ,eye-piece ,a1 the dotted lines show position of lenses4 ,it was reserved for ,boscovich to point out that1 by this important arrangement1 he had corrected a portion of the chromatic aberration incidental to the earlier form of eye-pieces4 ,let ,fig4 #ajj represent the ,huyghenian eye-piece of a microscope1 f f being the field-glass1 and e e the eye-glass1 and l m n the two extreme rays of each of the three pencils emanating from the centre and ends of the object1 of which1 but for the field-glass1 a series of coloured images would be formed from r r to b b2 those near r r being red1 those near b b blue1 and the intermediate ones green1 yellow1 and so on1 corresponding with the colours of the prismatic ,spectrum4 ,the effect described1 that of projecting the blue image beyond the red1 over-correcting the object-glass as to colour1 is purposely produced2 it is also seen that the images b b and r r are curved in the wrong direction to be seen distinctly by the convex eye-lens2 this then is a further defect of the compound microscope made up of two lenses4 ,but the field-glass1 at the same time that it bends the rays and converges them to foci at b b and r r1 also reverses the curvature of the images as here shown1 giving them the form best adapted for distinct vision by the eye-glass e e4 ,the field-glass has at the same time brought the blue and red images closer together1 so that they produce an almost colourless image to the eye4 ,the chromatic aberration of lenses has been clearly explained in a previous chapter4 ,but let it be supposed that the object-glass had not been over-corrected1 that it had been perfectly achromatic2 the rays would then have appeared coloured as soon as they had passed the field-glass2 the blue rays of the central pencil1 for example1 would converge at b1 and the red rays at r1 which is just the reverse of what is required of the eye-lens2 for as its blue focus is also shorter than its red1 it would require that the blue image should be at r1 and the red at b4 ,this effect is due to over-correction of the object-glass1 which removes the blue foci b b as much beyond the red foci r r as the sum of the distances between the red and the blue foci of the field-lens and eye-lens2 so that the separation b r is exactly taken up in passing through those two lenses1 and the several colours coincide1 so far as focal distance is concerned1 as the rays pass the eye-lens4 ,so that while they coincide as to distance1 they differ in another respect--the blue image is rendered smaller than the red by the greater refractive power of the field-glass upon the former4 ,in tracing the pencil l1 for instance1 it will be noticed that1 after passing the field-glass1 two sets of lines are drawn1 one whole and one dotted1 the former representing the red1 and the latter the blue rays4 ,this accidental effect in the ,huyghenian eye-piece was pointed out by ,boscovich4 ,the separation into colours of the field-glass is like the over-correction of the object-glass--and opens the way to its complete correction4 ,if the differently-coloured rays were kept together till they reached the eye-glass1 they would still be coloured1 and present coloured images to the eye4 ,the separating effected by the field-glass causes the blue rays to fall so much nearer the centre of the eye-glass1 where1 owing to its spherical figure1 the refractive power is less than at the margin1 so that spherical error of the eye-lens may be said to constitute a nearly equal balance to the chromatic dispersion of the field-lens1 and the blue and red rays l and l emerge nearly parallel1 presenting a fairly good definition of a single point to the eye4 ,the same may be said of the intermediate colours of the other pencils4 ,the eye-glass thus constructed not only brings together the images b b1 r r1 but it likewise has the most important effect of rendering them flatter1 and assisting in the correction of chromatic and spherical aberration4 ,illustration3 ,fig4 #ajj4--;,huyghenian ,eye-piece4 ,illustration3 ,fig4 #aja4--,ramsden's ,eye-piece4 ,the later form of the ,huyghenian eye-piece is that of the late ,sir ,george ,airy1 the field-glass of which is a meniscus with the convex side turned towards the objective1 and the eye-lens a crossed convex with its flatter side towards the eye4 ,another negative eye-piece is that known as the ,kellner1 or orthoscopic eye-piece4 ,it consists of a bi-convex field-glass and an achromatic doublet eye-lens4 ,this magnifies ten times1 but it in no way compares with the ,huyghenian in value4 ,neither does it afford the same flatness of field4 ,the ,ramsden1 or positive eye-piece1 is chiefly employed as a micrometer eye-piece for the measurement of the values of magnified images4 ,the construction of this eye-piece is shown in ,fig4 #aja1 a divided scale being cut on a strip of glass in #a_/ajjths of an inch1 every fifth of which is cut longer than the rest to facilitate the reading of the markings1 and at the same time that of the image of the object1 both being distinctly seen together1 as in the accompanying reduced micro-photograph of blood corpuscles1 ,fig4 #ajb4 ,the value of such measurements in reference to the real object1 when once obtained2 is constant for the same objective4 ,it becomes apparent1 then1 that the value of the divisions seen in the eye-piece micrometer must be found with all the objectives used1 and carefully tabulated4 ,it was ,mr4 ,lister who first proposed to place on the stage of the microscope a divided scale of a certain value4 ,viewing the scale as a microscopic object1 he observed how many of the divisions on the scale attached to the eye-piece corresponded with one or more of a magnified image4 ,if1 for instance1 ten of those in the eye-piece correspond with one of those in the image1 and if the divisions are known to be equal1 then the image is ten times larger than the object1 and the dimensions of the object ten times less than that indicated by the micrometer4 ,if the divisions on the micrometer and on the magnified scale are not equal1 it becomes a mere rule-of-three sum2 but in general this trouble is taken by the maker of the instrument1 who furnishes a table showing the value of each division of the micrometer for every object-glass with which it will be employed4 ,illustration3 ,fig4 #ajb4--;,blood ,corpuscles and ,micrometer1 magnified #acejj4 ,mr4 ,jackson's simple and cheap micrometer is represented in ,fig4 #ajc4 ,it consists of a slip of glass placed in the focus of the eye-glass1 with the divisions sufficiently fine to have the value of the ten-thousandth part of an inch with the quarter-inch object-glass1 and the twenty-thousandth with the eighth2 at the same time the half1 or even the quarter of a division may be estimated1 thus affording the means of attaining considerable accuracy1 and may be used to supersede the more complicated and expensive screw-micrometer1 being handier to use1 and not liable to derangement in inexperienced hands4 ,the positive eye-piece affords the best view of the micrometer1 the negative of the object4 ,the former is quite free from distortion1 even to the edges of the field2 but the object is slightly coloured4 ,the latter is free from colour1 and is slightly distorted at the edges4 ,in the centre of the field1 however1 to the extent of half its diameter1 there is no perceptible distortion1 and the clearness of the definition gives a precision to the measurement which is very satisfactory4 ,illustration3 ,fig4 #ajc4--;,jackson's ,eye-piece ,micrometer4 ,short bold lines are ruled on a piece of glass1 a1 ,fig4 #ajc1 to facilitate counting1 the fifth is drawn longer1 and the tenth still longer1 as in the common rule4 ,very fine levigated plumbago is rubbed into the lines to render them visible2 they are then covered with a piece of thin glass1 cemented by ,canada balsam1 to prevent the plumbago from being wiped out4 ,the slip of glass thus prepared is secured in a thin brass frame1 so that it may slide freely into its place4 ,slips are cut in the negative eye-piece on each side1 so that the brass frame may be pressed across the field in the focus of the eye-glass1 as at m2 the cell of which should have a longer screw than usual1 to admit of adjustment for different eyes4 ,the brass frame is retained in its place by a spring within the tube of the eye-piece2 and in using it the object is brought to the centre of the field by the stage movements2 the coincidence between one side of it and one of the long lines is made with great accuracy by means of the small screw acting upon the slip of glass4 ,the divisions are then read off as easily as the inches and tenths on a common rule4 ,the operation1 indeed1 is nothing more than the laying of a rule across the body to be measured2 and it matters not whether the object be transparent or opaque1 mounted or unmounted1 if its edges can be distinctly seen1 its diameter can be taken4 ,previously1 however1 to using the micrometer1 the value of its divisions should be ascertained with each object-glass2 the method of doing this is as follows3-- ,place a slip of ruled glass on the stage2 and having turned the eye-piece so that the lines on the two glasses are parallel1 read off the number of divisions in the eye-piece which cover one on the stage4 ,repeat this process with different portions of the stage-micrometer1 and if there be a difference1 take the mean4 ,suppose the hundredth of an inch on the stage requires eighteen divisions in the eye-piece to cover it2 it is plain that an inch would require eighteen hundred1 and an object which occupied nine of these divisions would measure the two-hundredth of an inch4 ,take the instance supposed1 and let the microscope be furnished with a draw-tube1 marked on the side with inches and tenths4 ,by drawing this out a short distance1 the image of the stage micrometer will be expanded until one division is covered by twenty in the eye-piece4 ,these will then have the value of two-thousandths of an inch1 and the object which before measured nine will then measure ten2 which1 divided by #b1jjj1 gives the decimal fraction #jje4 ,enter in a table the length to which the tube is drawn out1 and the number of divisions on the eye-piece micrometer equivalent to an inch on the stage2 and any measurements afterwards taken with the same micrometer and object-glass may1 by a short process of mental arithmetic1 be reduced to the decimal parts of an inch1 if not actually observed in them4 ,in ascertaining the value of the micrometer with a deep objective1 if the hundredth of an inch on the stage occupies too much of the field1 then the two-hundredth or five-hundredth should be used and the number of the divisions corresponding to that quantity be multiplied by two hundred or five hundred1 as the case may be4 ,the micrometer should not be fitted into too deep an eye-piece1 as it is essential to preserve good definition4 ,a middle-power ,kellner or ,huyghenian is frequently employed2 at all events1 use the eye-piece of lower power rather than impair the image4 ,the eye-lens above the micrometer should not be of shorter focus than three-quarters of an inch1 even with high-power objectives4 ,the ,ramsden ,eye-piece4--,the cobweb micrometer is the most efficient piece of apparatus yet brought into use for measuring the magnified image4 ,it is made by stretching across the field of the eye-piece two extremely fine parallel wires or cobwebs1 one or both of which can be separated by the action of a micrometer screw1 the trap head of which is divided into a hundred or more equal parts1 which successively pass by an index as the milled head is turned1 shown in ,fig4 #ajd4 ,a portion of the field of view is cut off at right angles to the filaments by a scale formed of a thin plate of brass having notches at its edges1 the distances between which correspond to the threads of the screw1 every fifth notch 7as in the previous case7 being made deeper than the rest1 to make the work of enumeration easier4 ,the number of entire divisions on the scale shows then how many complete turns of the screw have been made in the separation of the wires1 while the number of index points on the milled head shows the value to the fraction of a turn1 that may have been made in addition4 ,a screw with one hundred threads to the inch is that usually employed2 this gives to each division in the scale in the eye-piece the value of #a_/ajjth of an inch4 ,the edge of the milled head is also divided into the same number of parts4 ,illustration3 ,fig4 #ajd4--,ramsden ,screw ,micrometer ,eye-piece4 ,in ,watson's ,ramsden screw micrometer1 ,fig4 #ajd1 the micrometer scale 7seen detached7 is ruled on a circular piece of glass1 and this1 by unscrewing the top1 is dropped into its place1 and one of the wires1 both being fixed1 is set a little to the side of the field1 the teeth of the screw being cut to #a_/ajjths1 and the drum giving the fractional space between the teeth to #a_/ajjths1 so that the #a_/ajjjjth of an inch can be read off4 ,this micrometer eye-piece is constructed entirely of aluminium1 a decided advantage1 being so much lighter than brass to handle4 ,in the screw micrometer of other makers1 other modifications are found4 ,an iris diaphragm being placed below the web to suit the power of the eye-piece employed1 a guiding line at right angles to the web is sometimes added4 ,care should be taken to see that when the movable web coincides exactly with the fixed web1 the indicator on the graduated head stands at zero4 ,the ,compensating ,eye-piece4--,the very important improvements effected in the construction of the objective naturally led up to an equally useful change for the better in the eye-piece4 ,all objectives of wide aperture1 from the curvature of their hemispherical front lenses1 show a certain amount of colour defect in the extra-axial portion of the field1 even if perfectly achromatic in the centre4 ,whether an image be directly projected by the objective1 or whether it be examined with an aplanatic eye-piece1 colour fringes may be detected1 possibly in an increasing degree towards the periphery4 ,this residual chromatic aberration has at length been very nearly eliminated by the aid of the compensating eye-piece4 ,the construction of compensating eye-pieces is somewhat remarkable1 since they have an equivalent error in an opposite direction--that is1 the image formed by the red rays is greater than that corresponding to the blue rays2 consequently1 eye-pieces so constructed serve to compensate for the unequal magnification produced by different coloured rays1 and images appear free from colour up to the margin of the field4 ,zeiss's compensating eye-pieces are so arranged that the lower focal points of each series lie in the same plane when inserted in the body-tube of the microscope2 no alteration of focus is therefore required on changing one eye-piece for another4 ,this of itself is not only an advantage but also a saving of time1 while the distance between the upper focal point of the objective and the lower one of the eye-piece1 which is the determining element of magnification1 remains constant4 ,illustration3 ,fig4 #aje4--;,a sectional view of ,zeiss's ,compensating series of ,eye-pieces1 #a_/b the full size4 ,a4--,plane of the upper edge of the tube4 ,b4--,lower focal plane of eye-pieces1 with their lenses in situ4 ,the ordinary working eye-pieces1 ,huyghenian and others1 commencing with a magnification of four diameters1 are so constructed that they can be conveniently used1 as we are accustomed to use them in ,england1 with high powers1 ,zeiss's ,nos4 #ab and #ah compensating eye-pieces being adapted for use with his lower power apochromatic lenses of #af and #h mm4 ,the numbering of the eye-pieces is carried out on the plan originally proposed by ,professor ,abbe--that is1 the number denotes how many times an eye-piece1 when employed with a given tube-length1 increases the initial magnifying power of the objective1 and at the same time furnishes figures for their rational enumeration4 ,it is on this basis that the ,german compensating eye-pieces have been arranged in series1 and in agreement with their magnifying power and distinctive numberings of #b1 #d1 #f1 #h1 #ab1 #ah4 ,of these several eye-pieces1 #ab is found to be the most useful4 ,the magnification obtained by combining a compensating eye-piece with any apochromatic objective is found by multiplying its number by the initial magnification of the objective1 as given in the following proof3--,an objective of #cj mm4 focus1 for example1 gives in itself a magnification of #hcc 7calculated1 for the conventional distance of vision1 #bej mm472 eye-piece #ab therefore gives with this objective a magnification of #ab #hcc #ajjj diameters4 ,the classification1 however1 of these eye-pieces1 as furnished by ,abbe1 is dependent upon increase in the total magnifying power of the microscope obtained by means of the eye-piece as compared with that given by the objective alone4 ,the numbering1 then1 denotes how many times an eye-piece increases the magnifying power of the objective when used with a given body-tube2 the proper measure of the eye-piece magnification2 and1 at the same time1 the figures for rational enumeration4 ,illustration3 ,fig4 #ajf4--;,b and ,c ,achromatic ,eye-pieces4 ,compensating eye-pieces have been introduced for the correction of certain errors in high-power objectives--those made with hemispherical fronts4 ,all such lenses1 whether apochromatic or not1 are greatly improved by the compensating eye-piece1 but the dry objective and the lower powers are certainly deteriorated4 ,the lower power compensating eye-pieces are ,huyghenian1 the higher are combinations1 with no field-lens1 and therefore in working act as a single or positive eye-piece4 ,this is of importance to those who work with low powers--the older forms of objectives4 ,messrs4 ,watson and ,swift have adopted a new formula for their series of achromatic eye-pieces1 whereby their magnification and flatness of field are improved4 ,these also bear a constant ratio to the initial power of their objectives4 ,the compensating eye-pieces of these makers are constructed on the same principle as those of ,zeiss's for the correction of errors of colour in the marginal portion of the field1 and consequently are in every way as effective as those of ,continental manufacture4 ,figs4 #ajf1 #ajg1 and #ajh show in dotted outline the form and position of the several lenses combined in these eye-pieces4 ,projection ,eye-pieces are chiefly used in micro-photography1 and for screen demonstrations4 ,the cap of this eye-piece is provided with a spiral adjustment for focussing1 the diaphragm being placed in front of the eye-lens1 an essential arrangement for obtaining an accurate focus4 ,the ring seen below the cap1 ,fig4 #ajh1 is graduated so that the rotation for distance of screen may be carefully recorded4 ,illustration3 ,fig4 #ajg4--,the ,compensating ,eye-piece4 ,illustration3 ,fig4 #ajh4--,projection ,eye-piece4 ,schmidt's goniometer positive eye-piece1 for measuring the angles of crystals1 is so arranged as to be easily rotated within a large and accurately graduated circle4 ,in the focus of the eye-piece a single cobweb is drawn across1 and to the upper part is attached a vernier4 ,the crystals being placed in the field of the microscope1 care being taken that they lie perfectly flat1 the vernier is brought to zero1 and then the whole apparatus turned until the line is parallel with one face of the crystal2 the frame-work bearing the cobweb1 with the vernier1 is now rotated until the cobweb becomes parallel with the next face of the crystal1 and the number of degrees which it has traversed may then be accurately read off4 ,goniometer4--,if a higher degree of precision is required1 then1 the double-refracting goniometer invented by the late ,dr4 ,leeson must be substituted4 ,with this goniometer 7,fig4 #aji7 the angles of crystals1 whether microscopic or otherwise1 can be measured4 ,it has removed the earlier difficulties incident to similar instruments formerly in use4 ,among other advantages1 it is capable of measuring opaque and even imperfect crystals1 beside microscopic crystals and those in the interior of other transparent media4 ,it is equally applicable to the largest crystals1 and will measure angles without removing the crystal from a specimen1 provided only the whole is placed on a suitable adjusting stage4 ,the value of the goniometer depends on the application of a doubly refracting prism1 either of ,iceland spar or of quartz1 cut of such a thickness as will partially separate the two images of the angle it is proposed to measure4 ,dr4 ,leeson strongly insisted on the importance of the microscope in the examination of the planes of crystals subjected to measurement1 as obliquity in many cases arises from not only conchoidal fractures1 but also from imperfect lamin elevating one portion of a plane1 and yet allowing a very tolerable reflection when measured by the double refracting goniometer4 ,illustration3 ,fig4 #aji4--,leeson's ,goniometer4 ,microscopes for crystallographic and petrological research are now specially constructed for measuring the angles of crystals4 ,erector eye-pieces and erecting prisms are employed for the purpose of causing the image presented to the eye to correspond with that of the object4 ,they are also helpful in making minute dissections of structure2 the loss of light1 however1 by sending it through two additional surfaces is a drawback1 and impairs the sharpness of the image4 ,nachet designed an extremely ingenious arrangement whereby the inverted image became erect2 he adapted a simple rectangular prism to the eye-piece4 ,the obliquity which a prism gives to the visual rays when the microscope is used in the erect position1 as for dissecting1 is an advantage1 as it brings the image to the eye at an angle very nearly corresponding to that of the inclined position in which the microscope is ordinarily used4 ,the ,achromatic ,objective4 ,illustration3 ,fig4 #aaj4--,pan-aplanatic ,achromatic ,objectives4 ,the ,achromatic ,objective1 of all the optical and mechanical adjuncts to the microscope1 is in every way the most necessary1 as well as the most important4 ,the ideal of perfection aimed at by the optician is a combination of lenses that shall produce a perfect image--that is1 one absolutely perfect in definition and almost free from colour4 ,the method resorted to for the elimination of spherical and chromatic aberration in the lens has been fully explained in a former chapter4 ,it will now be my endeavour to show the progressive stages of achromatism and evolution of the microscope throughout the present century4 ,it is almost as difficult to assign the date of the earliest application of achromatism to the microscope as to that of the inception and many modifications of the instrument in past ages2 indeed1 the question of priority in every step taken in its improvement has been the subject of controversy4 ,among the earlier workers in the first decade of this century will be found the name of ,bernardo ,marzoni1 who was curator of the ,physical ,laboratory of the ,lyceum of ,brescia4 ,he1 an amateur optician1 it has come to light1 in #ahjh constructed an achromatic objective1 and exhibited it at ,milan in #ahaa1 when he obtained the award of a silver medal for its merits1 under the authority of the 8,institute ,reale delli ,scienzo40 ,through the good offices of the late ,mr4 ,john ,mayall one of ,marzoni's objectives1 which had been carefully preserved1 was presented to the ,royal ,microscopical ,society of ,london in #ahij4bj ,this objective is a cemented combination1 with the plane side of the flint-lens presented to the object4 ,this was an improvement of a practical kind1 and of which ,chevalier subsequently availed himself4 ,in #ahbc ,selligue1 a ,french optician1 is credited with having first suggested the plan of combining two1 three1 or four plano-convex achromatic doublets of similar foci1 one above the other1 to increase the power and the aperture of the microscope4 ,fresnel1 who reported upon this invention1 preferred on the whole ,adam's arrangement1 because it gave a larger field4 ,selligue subsequently improved his objective by placing a small diaphragm between the mirror and the object4 ,in this country1 ,tully was induced by ,dr4 ,goring to work at the achromatic objective1 and his first efforts were attended with a success quite equal to that of ,chevalier's4 ,lister on examining these lenses said3--8,the ,french optician knows nothing of the value of aperture1 but he has shown us that fine performance is not confined to triple objectives40 ,amici1 the amateur optician of ,modena1 visited this country in #ahbg and brought his achromatic microscope and objectives1 which were seen to give increase of aperture by combining doublets with triplets4 ,the most lasting improvement in the achromatic objective was that of ,joseph ,jackson ,lister1 ,f4,r4,s41 the father of ,lord ,lister1 and one of the founders of the ,royal ,microscopical ,society of ,london4 ,lister's discoveries at this period 7#ahbi7 in the history of the optics of the microscope were of greater importance than they have been represented to be4 ,that he was an enthusiast is manifest1 for1 being unable to find an optician to carry out his formula for grinding lenses1 he at once set to work to grind his own1 and in a short time was able to make a lens which was said to be the best of the day4 ,lister1 in a paper contributed to the proceedings of the ,royal ,society the same year1 pointed out how the aberrations of one doublet could be neutralised by a second4 ,he further demonstrated that the flint lens should be a plano-concave joined by a permanent cement to the convex crown-glass4 ,the first condition1 he states1 8obviates the risk of error in centring the two curves1 and the second diminishes by one half the loss of light from reflection1 which is very great at the numerous surfaces of every combination40 ,these two conditions then--that the flint lens shall be plano-concave1 and that it shall be joined by some cement 7,canada balsam7 to the convex--may be taken as the basis for the microscopic objective1 provided they can be reconciled with the correction of spherical and chromatic aberration of a large pencil4 ,andrew ,ross was not slow to perceive the value of ,lister's suggestions and in #ahca he had constructed an object-glass on the lines laid down by ,lister1 ,fig4 #aab2 a a representing the anterior pair1 m the middle1 and p the posterior1 the three sets combined forming the achromatic objective1 consisting of three pairs of lenses1 a double-convex crown-glass1 and a plano-concave of flint4 ,illustration3 ,fig4 #aaa4--,lister's double-convex crown and plano-concave flint cemented combination4 ,illustration3 ,fig4 #aab4--;,andrew ,ross's #a_/d-;inch ,objective4 ,lister proposed other combinations1 and himself made an object-glass consisting of a meniscus pair with a triple middle1 and a back plano-convex doublet4 ,this had a working distance of #aa and proved to be so great a success that other opticians--,hugh ,powell1 #ahcd2 ,james ,smith1 #ahci--made objectives after the same formula4 ,the publication of ,lister's data proved of value in another direction3 it stimulated opticians to apply themselves to the further improvement of the achromatic objective4 ,andrew ,ross was one of the more earnest workers in giving effect to ,lister's principles and a short time afterwards found that a triple combination1 with the lenses separated by short intervals1 gave better results4 ,in the accompanying diagram the changes made in the combination of the objective from #ahca1 and extending over a period of about twenty years from this date1 are shown4 ,each objective1 from the #a_/b-;inch to the #a_/ab-;inch1 is seen to be built up of at least six or eight different fronts1 the back combinations being a triplet formed of two double-convex lenses of crown glass with an intermediary double concave lens of flint-glass4 ,illustration3 ,fig4 #aac4--;,combinations of ,early ,dry ,objectives4 ,a1 ,double-convex lens2 ,b1 ,plano-concave2 ,c1 ,bi-convex and plano-concave united2 shown in their various combinations1 as at ,d1 form the #c-;in41 #b-;in4 or #a-a_/b-;in42 at ,e1 #a-;in4 and #b_/c-;in42 and at ,f1 the #a_/b-;in41 #d_/aj-;in41 #a_/d-;in4 and #a_/be-;in4 objectives4 ,combination ,d was for many years known as the ,norfolk ,objective4 ,illustration3 ,fig4 #aad4--,lister's ,correction ,collar1 7in section74 ,no sooner had ,ross constructed #a_/d-;inch achromatic objectives on ,lister's formula than he discovered an error which had hitherto escaped attention1 viz41 that the thinnest cover-glass of an object produced a considerable amount of refractive disturbance4 ,a marked difference was observed in the image when viewed with or without a cover-glass4 ,this difficulty was first met by the addition of a draw-tube to the microscope body4 ,but as this also impaired the image1 ,lister overcame the difficulty by mounting the front lens of the objective in a separate tube made to fit over a second tube carrying the two pairs of lenses4 ,this arrangement led up to his invention of the screw-collar adjustment1 the mechanism for applying which is shown in ,fig4 #aad4 ,the anterior lens a at the end of the tube is enclosed in a brass-piece b containing the combination2 the tube a1 holding the lens nearest the object1 is then made to move up or down the cylinder b1 thus varying the distance1 according to the thickness of the glass covering the object1 by turning the screw ring c1 thus causing the one tube to slide over the other1 and clamping them together when properly adjusted4 ,an aperture is made in the tube a1 within which is seen a mark engraved on the cylinder1 on the edge of which are two marks1 a longer and a shorter1 engraved upon the tube4 ,when the mark on the cylinder coincides with the longer mark on the tube1 the adjustment is made for an uncovered object2 and when the coincidence is with the shorter mark1 the proper distance is obtained to balance the aberrations produced by a cover-glass the hundredth of an inch thick2 such glass covers are now supplied4 ,the adjustment should be tested experimentally by moving the milled edge which separates or closes the combinations1 and at the same time using the fine adjusting screw of the microscope4 ,the difficulty associated with the cover-glass of old has1 by the introduction of the homogeneous immersion system1 been very nearly eliminated4 ,there still remains1 however1 a disturbing amount of residual colour aberration in the achromatic dry objective1 and for the correction of which ,zeiss proposed mounting the several lenses on a method somewhat different to that so long in use in this country4 ,fig4 #aae shows an objective in which the screw-collar ring b b is made to adjust the exact distance between the two back lenses placed at a a4 ,the value of the screw-collar is not questioned4 ,it is difficult to obtain at all times cover-glasses of a perfectly uniform thickness2 they will vary1 and therefore perfect definition must be obtained1 as heretofore1 by adjusting for each separate preparation while the object is under examination4 ,illustration3 ,fig4 #aae4--,the ,continental ,screw-collar ,adjustment4 ,as early as #ahdb the excellence of ,andrew ,ross's achromatic objectives were acknowledged1 and his formula for their construction was generally followed4 ,no doubt many of these early objectives of his manufacture are still regarded as treasures4 ,i possess a #a_/b-;inch and a #a_/d-;inch1 which ,i believe to be comparable with any achromatic objectives of the same apertures of the present day4 ,these ,i have always found most serviceable for histological work4 ,in #ahej ,mr4 ,wenham produced an achromatic objective of considerable achromatic value4 ,this consisted of a single hemispherical front combination1 shown in the accompanying enlarged diagram1 ,fig4 #aaf4 ,wenham's formula seems to have been generally adopted by ,continental opticians1 who sold these lenses at a reduction of price4 ,in ,paris1 ,prazmowski and ,hartnack--,i have had one of ,hartnack's earliest immersions in use for many years--brought this form of objective to greater perfection1 and in #ahfg ,powell and ,lealand adopted the single front combination system in their early water-immersion objective1 whereby the focal distance was said to be 8practically a constant quantity1 while reduction of aperture by making the front lens thinner ensures a much greater working distance without affecting the aberrations1 since the first refraction takes place at the posterior or curved surface of the front lens1 the removal of any portion of thickness at the anterior or plane surface simply cuts off zones of peripheral rays without altering the distance--any space being filled by the homogeneous immersion fluid1 or by an extra thickness of cover-glass40#ba ,illustration3 ,fig4 #aaf4--;,a ,single ,front ,combination formulated by ,wenham for ,messrs4 ,ross 7enlarged74 ,great improvements were brought about by ,r4 ,b4 ,tolles1 of ,boston1 #ahgd1 in the objective1 as well as in the optical and mechanical parts of the microscope1 most of which1 however1 must be ascribed to the criticisms and suggestions of amateur workers skilled in the exhibition of test-objects--the late ,dr4 ,woodward of ,washington1 for example1 whose series of photographs of the more difficult frustules of diatoms have rarely been surpassed4 ,such results were due to improvements made in the optical part of the microscope at his suggestion4 ,he came to the conclusion1 arrived at about the same time by mathematical scientists1 that increase of power in the microscope was only possible in two directions1 the qualitative and the quantitative4 ,it was now that microscopists turned to the late ,professor ,abbe for assistance in perfecting the objective in the dioptric direction4 ,this1 he pointed out1 must be looked for in further improvements in the art of glass-making4 ,a series of experiments ultimately brought to light a mineral substance1 ,fluorite1 which1 when combined in the proper proportion1 one part to two of ,german crown and flint glass1 was found to have the qualities looked for1 and to possess different relations of a dispersive and refractive power4 ,from ,professor ,abbe's researches1 begun in #ahgf1 we have had the aperture of the objective greatly enlarged1 and the homogeneous system brought into general use4 ,previous to this date the best made objective merely approximated to colour correction4 ,undoubtedly the chief object to be obtained was the removal or diminution of the secondary colour aberration4 ,this1 together with other residual errors ,abbe pointed out in #ahhj1 led to the improvement of the optical quality of the glass used in the manufacture of all optical instruments1 the chief difficulties being surmounted in the ,jena glass factory1 whereby a complete revolution was effected in the microscopic objective4 ,the apochromatic glasses of ,zeiss1 ,powell1 ,beck1 ,ross1 ,watson1 ,swift1 and other makers1 in which the secondary spectrum has been totally eliminated1 or only a negligible tertiary spectrum remains--that is to say1 the objectives of these makers--are now corrected for three spectrum rays1 and not two1 as in the older objectives2 and only those who look forward for making further discoveries in the intimate structure of bacilli or for resolving the finest diatom markings can be said to fully appreciate the importance and value of the investigations of the late ,professor ,abbe1 and which have1 so to speak1 entirely changed old empirical views as to the value of high aperture1 and demonstrated that high amplification1 unless associated by proportionally high aperture1 necessarily produces untrue images of minute structures4 ,it was he also who introduced a practically perfect system of estimating apertures1 known as the 8numerical aperture notation10 by which not only can an accurate comparison be made of the relative apertures of any series of objectives1 whether dry or immersion1 but their resolving power under the various conditions of the kind of light employed4 ,their penetrating power and their illuminating power can now be estimated with mathematical exactness4 ,illustration3 ,fig4 #aag4--;,diagram of an ,apochromatic ,combination4 ,the practical advantages1 then1 secured by the adoption of the homogeneous system were1 on the whole1 greater than any before made or believed to be possible1 and when taken into account in connection with the improvement of the eye-piece 7also due to ,abbe71 almost perfect achromatism and homogeneity between objective1 object1 and eye-piece is secured1 together with a sharp definition of the image over the whole visual field4 ,these1 with an increase of working distance between the object and the objective1 and other important results1 have been placed within the reach of the microscopist by men of science1 and the outcome is the general adoption of the homogeneous system1 termed by ,carl ,zeiss1 a fellow-worker with ,abbe1 the#bb apochromatic system of constructing objectives4 ,relative ,merits of the ,english and ,german ,objectives4 ,as to the relative merits of ,german-made objectives1 no superiority can be claimed for them over those made by ,english opticians4 ,the ,continental form of the #a_/ab-;inch oil-immersion objective1 shown in ,fig4 #aah1 on the scale of #f to #a1 consists of four systems of lenses1 namely1 the front1 a deep hemispherical crown lens of high refractive index2 the second front of the system1 an achromatic lens of such a form that it gathers the light from the hemispherical front2 the middle lens1 a single meniscus2 and the back an achromatised lens1 the second front of the back being connected in such a way as to compensate for the spherical and chromatic aberrations of the front lens4 ,the first homogeneous immersion objective which came under my observation was manufactured in the well-known ,jena workshop of ,carl ,zeiss1 ,december1 #ahgg4 ,this had a very considerable increase of numerical aperture1 upwards of #ej per cent42 a clear gain1 as an oil angle of even #aaj proved to be of greater value than an angle of #ahj in air1 while the resolving power of the objective was increased in like proportion4 ,there does not at present appear to be a bar to the construction of objectives of yet higher power1 with increase of aperture4 ,the available course open in this direction is the further discovery of another vitreous material and a suitable immersion fluid with an index of #ah or #ai1 and glass with a corresponding index1 so as to ensure homogeneity of the combination4 ,zeiss asserts that in the more difficult departments of microscopical research the apochromatic lenses will supplant the older objectives1 yet there are many problems in microscopy awaiting solution which do not demand the highest attainable degree of perfection in the objective1 and in the majority of cases the older achromatic objective is all that is needful1 provided it is good of its kind4 ,the achromatic objectives and eye-pieces of the older type have still an advantage1 as1 owing to their simpler construction1 really good lenses of the class required can be purchased at considerably lower prices than the objectives of the new series4 ,these1 from being more complicated in construction1 involve a greater amount of skilled manual labour4 ,illustration3 ,fig4 #aah4--,the ,continental #a_/ab-;in4 ,oil-immersion ,combination 7enlarged diagram74 ,the ,german glasses of to-day afford satisfactory evidence both of skill and workmanship displayed in their production4 ,their cost is greater1 then1 for the reason given1 as will be seen on reference to ,continental catalogues4 ,the dry series of objectives cost somewhat less1 a #a_/b-;inch 7numerical aperture #jcj7 can be had for #a #ajs41 and a #a_/f-;inch 7numerical aperture #jfe7 for #b4 ,on the other hand1 the apochromatic series rapidly increase in price as the numerical aperture approaches the limit of numerical aperture #jdj4 ,the best of ,zeiss's series are the #ab mm4 7#a_/b-;inch7 and the #c mm4 7#a_/h-;inch71 numerical aperture #ad1 both of which possess the optical capacity assigned to them4 ,these objectives are undoubtedly the finest to be met with in the workshop of any optician4 ,achromatic objectives of ,continental manufacture have been as much improved as those of ,english make by the introduction of the newer varieties of glass1 as already explained1 while a new nomenclature has sprung up in consequence4 ,we now have semi-apochromatic and parachromatic4 ,the ,german opticians have followed ,zeiss's lead1 since almost the same series of objectives are given in the catalogues of ,leitz1 ,reichert1 and ,seibert1 while the quality of both dry and immersion objectives is found to be much the same4 ,the low price of ,reichert's immersion objectives should be noted1 as their performance is quite perfect4 ,a #a_/ab-;inch 7numerical aperture #acj7 of ,leitz's1 with which ,i have worked at bacteria1 has given me much satisfaction2 supplied by ,watson and ,baker at #e4 ,a #a_/ab-;inch dry objective by the same maker 7numerical aperture #jhg7 costs #c1 and a water immersion #a_/ab-;inch 7numerical aperture #aaj7 #c #es4 ,leitz reminds me that it requires a good lens of from six to seven hundred magnifying power for the examination of bacteria4 ,for this reason he has constructed a new form of lens1 a #a_/aj-;inch oil-immersion of #be mm4 focus1 for the purpose of adding to the resources of bacteriology4 ,this lens necessarily has a lower magnification than his former #a_/ab-;inch oil-lens1 but as it is less costly to manufacture it is sold at a smaller price4 ,the before-mentioned #a_/ab-;inch1 with a ,no4 #c compensating eye-piece1 gives a magnification of over seven hundred or eight hundred diameters4 ,to secure the best results in using the higher powers of ,leitz's1 from ,no4 #e upwards1 a cover-glass of #jag mm4 in thickness should be used1 and care taken to make the length of the draw-tube equal to #agj mm4 ,this length of tube should be adhered to in the use of this optician's oil-immersion lenses4 ,if the microscope be provided with a nose-piece1 the draw-tube should be drawn out to #afj mm42 in its absence it should be set at #agj mm41 a deviation of #aj mm4 or more from the correct tube-length deteriorates from the value of ,leitz's oil-immersion objectives as of other opticians4 ,it is suggested that the ,german apochromatic combination of three cemented lenses is that adopted by ,steinheil long before1 in the construction of his well-known hand-magnifier 7see page #gg1 ,fig4 #ea74 ,zeiss's #c mm4 objective has a triple front1 balanced by two triple backs--in all nine lenses--a somewhat amplified diagram of which is represented in ,fig4 #aah4 ,the formula for this combination was furnished by ,tolles1 of ,boston1 ,america1 and it at once secured increase of aperture 7the value of this optician's many contributions to microscopy has since his death been generally acknowledged74 ,the metrical equivalent focus assigned by ,zeiss to his series of dry achromatic objectives is given in somewhat ambiguous terms1 which tend to confuse rather than classify them2 for instance1 two lenses of the same aperture--#bd mm4 and #af mm4--corresponding to the ,english #a-;inch and #b_/c-;inch1 each have assigned to them an aperture of #jcj2 a #ab mm4 and #h mm41 corresponding to the ,english #a_/b-;inch and #a_/c-;inch1 have an aperture of #jfe2 while a #f mm4 #a_/d-;inch1 and a #d mm4 #a_/d-;inch and #a_/f-;inch1 have each an aperture of #jie4 ,nachet exhibited at the ,antwerp ,exhibition a fine #a_/aj-;inch oil-immersion1 which was highly praised by the jurors4 ,it is necessary1 to make the fact perfectly clear1 that dry and immersion lenses having the same angular aperture have also a similar defining power4 ,the pencil of rays1 however1 differs in intensity and density as the rays emerging from the cover-glass of the object into air are very considerably deflected1 and the cone suffers a corresponding loss of brightness4 ,on this important point1 then1 ,i believe it will prove of value to interpolate a clear and full exposition of the change brought about by the cover-glass4 ,it is not difficult1 then1 to perceive the importance of ,amici's discovery as to the value of a drop of water inserted between the object and the objective1 and it now seems somewhat surprising it should have been so long neglected by opticians1 since it is at once seen to diminish the reflection which takes place in the incidence of oblique light4 ,the film of water not only gives increased aperture1 but also greater cleanness and sharpness to the image4 ,the film1 then1 as already shown1 collects the straying away of peripheral rays of light1 and sends them on to the eye-piece1 and greatly assists in rendering the image more perfect1 and materially aids in the removal of residuary secondary aberrations2 while with air1 or dry objectives1 a certain amount of aberration takes place1 sufficient to affect the pencils on their passage from the radiant to the medium of the front lens1 adding a considerable ratio to the total spherical aberration with the objective1 which1 in the case of wide angles1 increases disproportionately from the axis outwards4 ,this can only be corrected by a rough method of balancing2 that is1 by introducing an excess of opposite aberration in the posterior lens4 ,an uncorrected residuum1 rapidly increasing with larger apertures1 is then left1 and this appears in the image amplified by the total power of the objective1 so that with a non-homogeneous medium there is a maximum angular aperture which cannot be surpassed without undergoing a perceptible loss of definition1 provided working distance is required4 ,if we abolish the anterior aberration for all colours1 by an immersion fluid which is equal to cover-glass in refractive and dispersive power1 the difficulty is at once overcome4 ,if1 for instance1 we have an objective of #adj in glass 7 #abe ,n4,a47 and water as the immersion fluid1 the aberration in front would affect a pencil of #adj4 ,substituting a homogeneous medium1 the same pencil1 contracted to the equivalent angle in that medium of #aab1 will be admitted to the front lens without any aberration1 and may be made to emerge from the curved surface also without any disturbing aberration1 but contracted to an angle varying from #gj to #ij4 ,the first considerable spherical aberration of the pencil then occurs at the anterior surface of the second lens1 where the maximum obliquity of the rays is already considerably diminished4 ,illustration3 ,fig4 #aai4 ,illustration3 ,fig4 #aai;a4 ,figs4 #aai and #aai;a will doubtless make this clearer4 ,if the objective of #adj works with water 7,fig4 #aai71 there would be a cone of rays extending up to #gj on both sides of the axis1 and this large cone would be submitted to spherical aberration at the front surface a4 ,but with homogeneous immersion 7,fig4 #aai;a7 the whole cone of #aab is admitted to the front lens without any aberration1 there being no refraction at the plane surface2 and as the spherical surface of the front lens is without notable spherical aberration1 the incident pencil is brought from the focus ,f to the conjugate focus ,f1 and contracted to an angle of divergence of #gj-ij without having undergone any spherical aberration at all4 ,the problem of correcting a very wide-angled objective has thus been reduced by the homogeneous oil-immersion system1 both in theory and practice4#bc ,abbe's ,test-plate4 ,abbe designed the test-plate 7,fig4 #abj7 for testing the spherical and chromatic aberrations of objectives1 and estimating the thickness of cover-glasses corresponding to the most perfect correction3 six glasses1 having the exact thickness marked on each1 #jji to #jbd mm41 cemented in succession on a slip1 their lower surface silvered and engraved with parallel lines1 the contours of which form the test4 ,these being coarsely ruled are easily resolved by the lowest powers2 yet1 from the extreme thinness of the silver1 they form also a delicate test for objectives of the highest power and widest aperture4 ,the test-plate in its original size is seen in ,fig4 #abj1 with one of the circles enlarged4 ,illustration3 ,fig4 #abj4--;,abbe's ,test-plate for estimating thickness of glass-covers4 ,to examine an objective of large aperture1 the discs must be focussed in succession1 observing in each case the quality of the image in the centre of the field1 and the variation produced by using1 alternately1 central and very oblique illumination4 ,when the objective is perfectly corrected for spherical aberration1 the outlines of the lines in the centre of the field will be perfectly sharp by oblique illumination1 and without any nebulous doubling or indistinctness of the edges4 ,if1 after exactly adjusting the objective for oblique light1 central illumination is used1 no alteration of the focus should be necessary to show the outlines with equal sharpness4 ,if an objective fulfils these conditions with any one of the discs1 it is free from spherical aberration when used with cover-glasses of that thickness4 ,on the other hand1 if every disc shows nebulous doubling1 or an indistinct appearance of the edges of the line with oblique illumination1 or1 if the objective requires a different focal adjustment to get equal sharpness with central as with oblique light1 the spherical correction of the objective is more or less imperfect4 ,nebulous doubling with oblique illumination indicates over-correction of the marginal zone2 indistinctness of the edges without marked nebulosity indicates under-correction of the zone2 an alteration of the focus for oblique and central illumination points to an absence of concurrent action of the separate zones1 which may be due to either an average under or over correction1 or to irregularity in the convergence of the rays4 ,illustration3 ,fig4 #aba4--,zeiss's ,cover-glass ,gauge4 ,,cover-,,glass ,,gauge4 ,zeiss has gone a step further to lay the microscopist's ghost of the cover-glass4 ,he invented a measurer 7,fig4 #aba7 whereby the precise determination of thickness of glass-covers can be obtained4 ,this measurement is effected by a clip projecting from a circular box2 the reading is given by an indicator moving over a divided circle on the lid of the box4 ,the divisions seen cut round the circumference show #a_/ajjths of a millimeter4 ,this ingenious gauge measures upwards of #e mm4 ,this necessary and important digression has led me away from the consideration of the achromatic objective1 and to which ,i shall now return4 ,english ,immersion and ,dry ,objectives4 ,the homogeneous immersion system met with its earliest as well as its staunchest advocates among ,english opticians4 ,among its more energetic supporters were ,messrs4 ,powell and ,lealand1 who were the first to construct a #a_/h-;inch immersion objective on a formula of their own1 and which was found to resolve test-objects not before capable of resolution by their dry objectives4 ,this encouraged them to make a #a_/af-;inch1 acquired by ,dr4 ,woodward for the ,army ,medical ,department1 ,washington1 and subsequently a #a_/be-;inch2 neither of which surpassed their #a_/h-;inch in aperture1 and a new formula was tried in the construction of their first oil-immersion objective4 ,this had a duplex front1 and two double backs2 but even this did not quite accomplish what was expected of it1 and another change was subsequently made2 the anterior front combination became greater than a hemisphere--a balloon-lens4 ,this at once gave an increase of aperture to a #a_/ab-;inch objective of #adc numerical aperture4 ,after some few more trials a more important change of the formula took place4 ,the front lens was made of flint-glass1 and the combination took the form represented in diagram 7,fig4 #abb74 ,this1 on an enlarged scale1 represents ,powell's #a_/ab-;inch numerical aperture #aej4 ,it is a homogeneous apochromatic immersion of high quality and very flat field4 ,it will be noticed that in this combination the four curves of the lenses are very deep compared with those of other opticians4 ,illustration3 ,fig4 #abb4--,powell and ,lealand's #a_/ab-;in4 ,oil-immersion ,objective1 drawn on a scale of #f-a4 ,messrs4 ,ross have made many important improvements and changes in the construction of their several series of achromatic objectives2 the calculations and formul for which were made exclusively for them by ,dr4 ,schrder4 ,the list is too long to quote1 but most of these lenses are of a high-class character1 and work with admirable precision4 ,among the best of their objectives1 ,i can commend a #a-;inch of #cj and two oil-immersions1 a #a_/h-;inch of #abj and a #a_/ab-;inch of #abe numerical aperture1 each of which bear the highest oculars equally well2 a good test1 as ,i have always maintained1 of excellence4 ,their #a_/aj-;inch has a somewhat larger aperture1 and therefore shows a fine image of the podura scale4 ,the finish of ,ross's several series of objectives fully maintains the high character and reputation of this old-established firm of opticians4 ,messrs4 ,r4 and ,j4 ,beck have bestowed great attention upon the improvement of their dry-objective series1 much in demand for histological work1 especially among the students of city hospitals1 who usually commence their pathological work with the cheaper forms of objectives4 ,in that case an inch objective of about #be air angle1 a #a_/b-;inch of not less than #dj1 and a #a_/d-;inch or #a_/e-;inch magnifying from #ej to #bej diameters1 is quite sufficient for most of their work4 ,for bacteriological research1 ,messrs4 ,beck supply a #a_/f-;inch immersion taken from a series1 having a high aperture and a better finish at a moderate price4 ,their #a_/aj-;inch immersion has in my hands proved a serviceable power for bacteriological research2 it requires a good sub-stage illuminating achromatic condenser to obtain the best results4 ,illustration3 ,fig4 #abc4--a_/f-;in4 ,english ,combination1 largely used4 ,messrs4 ,watson and ,sons have much enhanced their reputation by the marked improvement lately brought about in the manufacture of their whole series of objectives4 ,this probably is chiefly due to the introduction of the ,jena glass into their manufacture1 and which has enabled them to give increase of aperture to one series in particular1 that of the para-chromatic1 all of which in consequence are of very high quality4 ,it is difficult to particularise their several objectives1 the whole having special features in proportion to their magnifying powers1 while much care seems to have been bestowed on them for the elimination of residual colour4 ,a #a_/h-;inch with correction collar is comprised of a single deep and rather thick front lens1 plano-concave flint1 and double convex-crown for the middle and triple combination for the back1 the latter consisting of two crown lenses cemented to a dense flint 7,fig4 #abd7 drawn to scale of #e-a1 with lined portions intended to represent the flint1 and white the crown glass lenses of the combination4 ,the initial magnification of this objective is #hc diameters1 and the numerical aperture #id4 ,this superior objective can be had for the small sum of #b4 ,another remarkably useful and cheap objective1 their #a-;inch numerical aperture #jba1 consists of two achromatic systems forming the front and back with the separation between them of about half an inch1 and may also be especially recommended for students' work4 ,in the accompanying diagram the lenses are drawn on too large a scale1 and therefore the distance between the two combinations should be much greater4 ,among the more useful of ,watson's series1 the #a-;inch1 the #a_/b-;inch1 and the #a_/f-;inch1 together with the #a_/h-;inch dry-objective1 and a #a_/i-;inch1 will be found the most serviceable4 ,illustration3 ,fig4 #abd4--,watson's #a_/h-;in4 ,objective ,para-chromatic ,combination1 scale #e-a4 ,illustration3 ,fig4 #abe4--,watson's #a-;in4 ,achromatic ,combination4 ,messrs4 ,baker have their own series of objectives1 most of which are so very nearly allied to those of the continental opticians2 and what has been said of ,zeiss's and ,leitz's objectives may be taken to apply also to ,baker's1 who have an established reputation for their histological series1 all of which are well suited for students' and class-room work4 ,messrs4 ,swift and ,son have a new series of objectives1 semi-apochromatic and pan-aplanatic1 most of which are excellent in quality and show increased flatness of field together with that of achromatism2 the index of refraction in each series having been correctly determined together with exact radial focal distance1 thus affording more available aperture4 ,i may select for special commendation their #a_/ab-;inch #e #es4 homogeneous immersion objective1 which is in every way suitable for bacteriological work2 its definition is very good1 as is seen in a micro-photograph of podura scale1 given further on4 ,their dry #a_/f-;inch can be had for #a #afs4--a marvel of cheapness4 ,of their general series the most useful for histological work are the #a_/b-;inch1 the #a_/c-;inch at #a #abs41 and their #a_/e-;inch of numerical aperture #jhg at #c4 ,mr4 ,pillischer1 of ,bond ,street1 has manufactured many excellent objectives4 ,a fine homogeneous oil-immersion #a_/ab-;inch numerical aperture #abe is worthy of special notice2 it will be found suitable for bacteriological work2 it has fine definition with a considerable amount of penetration4 ,a more intelligent idea of the magnifying power of the objective combined with the eye-piece will be gained by consulting the table given below2 precision in this respect has long been a desideratum with microscopists4 ,magnifying ,powers of ,eye-,pieces and ,objectives4 ,a ,,typical ,,and ,,initial ,,selection ,,of ,,powers ,,of ,,eye-,,pieces ,,calculated ,,for ,,the #aj-;,,inch ,,tube-,,length4 ,,huyghenian ,,eye-,,pieces4 ,,name ,a ,b ,c ,d ,e ,f ,,of ,,maker4 #j or ,no4 #a #b #c #d #e #f ,baker #f #h #ab #ae -- -- ,diameters4 ,beck1 ,r4 ,j4 #d #h #ae #bj #be not made4 ,leitz #e #f #g #h #aj #ab ,powell ,lealand #e #ge #aj #bj #dj ,reichert #be #ce #d #e #fe #bd ,ross #c #h #ab-a_/b #bj #be #dj #be ,swift ,son #f #i #ab #ae #ah #ba ,watson ,sons #d #f #h #aj #ab #ae ,zeiss #c #d #ee #g #i not made4 ,,compensating ,,eye-,,pieces ,,for ,,use ,,with ,,apochromatic ,,objectives4 ,zeiss #b #d #h #ab #ah #bg ,diameters4 ,this may be taken as a typical set1 further treated of among ,eye-pieces4 ,,initial ,,powers ,,of ,,objectives ,,calculated ,,for ,,the #aj-;,,inch ,,tube-,,length4 ,this is ascertained by dividing the distance of distinct vision #aj inches by the focus of the objective1 thus-- ,focus-inches #d #c #b #a-a_/b #a #b_/c #a_/b #d_/aj #a_/d #a_/e #a_/f #a_/h #a_/ab ,initial magnifying power #be #cc #e #ge #aj #ae #bj #be #dj #ej #fj #hj #abj diameters4 ,a reference to the above table will at once show that the nomenclature of objectives expresses at once the initial magnifying powers1 but as makers have great difficulty in so calculating their formul so as to obtain the exact power1 these figures must be taken as approximate4 ,thus a #a_/d-;inch1 which should magnify #dj diameters if true to its description1 might actually magnify a little more or less4 ,the magnifying powers of ,zeiss's and other apochromatic objectives can be ascertained by dividing the focal length of the objective in millimeters into #bej mm4 7the distance of distinct vision71 thus ,focus millimetres #bd #af #ab #d #c #b #ae ,initial magnifying power #aje #aee #ba #fc #hc #abe #afg diameters4 ,the total magnification1 when any eye-piece is working in conjunction with an objective1 is ascertained by multiplying the initial power of the objective by that of the eye-piece4 ,the above calculations are all for a #aj-;inch tube-length4 ,should1 however1 a shorter or longer length of body be employed1 the magnification can at once be ascertained by a proportion sum4 ,if the magnification be #ahj with #aj-;inch tube-length1 what would it be with a #f-;inch body--#aj 3 #f 33 #ahj #ajh diameters4 ,abbe designed three different forms of eye-pieces3 #a1 the searcher eye-piece2 #b1 the working eye-piece2 and #c1 the projecting eye-piece4 ,the ,searcher is a negative form of low power4 ,the working is both negative and positive1 the positive form of which is constructed on a newer principle2 while the projection is chiefly intended for microphotography1 its field being small and its definition superlatively sharp4 ,these are severally explained among eye-pieces4 ,high-,power ,objectives4 ,points of ,importance for securing the best results with ,high-power ,objectives4--,always give to the body-tube of the microscope the length for which the objective is corrected1 #jafj mm4 for the short continental tube1 and #jbej mm4 for the ,english tube 7#aj-;inch74 ,employ both dry and immersion objectives mounted for correction1 commencing with a numerical aperture of #jge 7that is about #ajj in air74 ,if the graduation is not given in thickness of cover-glass apply to the maker to correct this omission4 ,with the homogeneous oil-immersion objective it is highly necessary to utilise all marginal pencils of light1 to optically unite the upper lens of the condenser with the preparation as well as the front lens of the objective by means of a liquid having the same index of refraction or at least equal to that of the immersion4 ,cedar ,oil has been generally adopted for the purpose mentioned1 the better way of using which is as follows3 place a drop on the centre of the front objective1 or on the top of the cover-glass1 and then lower the objective by means of the coarse adjustment until it comes in contact with the oil1 and carefully bring into focus by the fine adjustment4 ,if the slide is held between the finger and thumb of one hand and moved from side to side1 while the other hand is working the fine adjustment1 there can be no danger of injuring either the objective or the specimen4 ,before putting the microscope away1 take a fine camel-hair brush dipped in ether1 alcohol1 or methylated spirit1 and carefully remove the oil from the objective and the glass cover of the object2 a soft chamois leather or cambric pocket handkerchief will dry it off1 or a piece of fine white blotting paper answers equally well4 ,should the lens come accidentally into contact with the ,canada balsam1 it must be very carefully removed either by ether or alcohol4 ,the former is by far the safest1 as alcohol1 if not very carefully used1 quickly dissolves out the balsam and loosens the cover-glass of the object4 ,achromatic ,condensers4 ,the ,achromatic ,condenser can no longer be classed among the accessories of the microscope1 since it is an absolutely indispensable part of its optical arrangements4 ,its value1 then1 cannot be overrated1 and the corrections of the lenses which enter into the construction of the condenser should be made as perfect as they can be made--in fact1 as nearly approaching that of the objective as it is possible to make them4 ,it may therefore be of interest to know something of the rise and progress of the achromatic condenser4 ,in my first chapter ,i have noticed the earlier attempts made by ,dr4 ,wollaston1 whose experiments led him to fit to the underside of the stage of his microscope a short tube1 in which a plano-convex lens of about three-quarters of an inch focal length was made to slide up and down 7afterwards moved up and down by two knobs72 to improve definition he placed a stop between the mirror and the lens4 ,the stop was found to act better when placed between the lens and the object4 ,from this improvement ,dr4 ,wollaston enunciated that 8the intensity of illumination will depend upon the diameter of the illuminating lens and the proportion of the image to the perforation1 and may be regulated according to the wish of the observer40 ,dujardin in ,france and ,tully in ,england were at work in the same direction4 ,the former a year or two later on contrived an instrument1 which he termed an eclairage1 to remedy the defects of ,wollaston's1 and for illuminating objects with achromatic light4 ,this was submitted for approval to ,sir ,david ,brewster1 who1 when the use of the achromatic condenser was first broached1 used these encouraging words3--8,i have no hesitation in saying that the apparatus for illumination requires to be as perfect as the apparatus for vision1 and on this account ,i would recommend that the illuminating lens should be perfectly free from chromatic and spherical aberration1 and that the greatest care be taken to exclude all extraneous light both from the object and eye of the observer40 ,this far-seeing observer in optical science has borne good fruit1 and the outcome of his views is seen in the great development and improvement of the achromatic condenser4 ,in #ahci ,andrew ,ross made his first useful form of condenser1 and gave rules for the illumination of objects in an article written for the 8,penny ,cyclopdia40 ,these1 epitomised1 read as follows3 #a4 ,that the illuminating cone should equal the aperture of the objective1 and no more4 #b4 ,with daylight1 a white cloud being in focus1 the object has to be placed nearly at the apex of the cone4 ,the object is seen better sometimes above and sometimes below the apex of the cone4 #c4 ,with lamplight a bull's-eye lens is to be used1 to parallelise the rays1 so that they may be similar to those coming from the white cloud4 ,it has been seen that ,mr4 ,lister foreshadowed the sub-stage condenser4 ,the early form of ,ross's condenser consists of two small brass tubes made to slide one in the other4 ,to the outer one is attached a flat brass plate which slides underneath the stage of the microscope1 and by means of a screw the adjustment of the axis of the illuminator is effected4 ,the upper portion of the apparatus carries the achromatic combination1 which by a rack and pinion movement is brought nearer to1 or removed further from the object on the stage4 ,the several parts of the illuminator unscrew1 so that the lenses may be used either combined for high powers1 or separated for low powers4 ,illustration3 ,fig4 #abf4--,original form of ,gillett's ,achromatic ,condenser4 ,messrs4 ,smith ,beck greatly improved upon ,ross's condenser by adding another achromatic lens to the combination1 three being employed when used with high-power objectives and two or even one with the lower1 the adjustment and focussing being made by rack and pinion arrangement beneath the stage4 ,some further changes for the better were made in the condenser by ,powell1 and in #ahej an amateur microscopist1 ,mr4 ,gillett1 fully grasping the value of controlling the cone of rays passing into the microscope1 devised a new form of condenser1 in connection with which a revolving series of diaphragms of different values were made to pass between the achromatic lenses and the source of light4 ,andrew ,ross constructed the first condenser on ,gillett's principle1 and this proved to be one of the most successful pieces of apparatus contrived4 ,gillett's ,condenser consists of an achromatic lens c1 about equal to an object-glass of one quarter of an inch focal length1 with an aperture of #hj4 ,this lens is screwed into the top of a brass tube1 and intersecting which1 at an angle of about #be1 is a circular rotating brass plate a b1 provided with a conical diaphragm1 having a series of circular apertures of different sizes h g1 each of which in succession1 as the diaphragm is rotated1 proportionally limits the light transmitted through the illuminating lens4 ,the circular plate in which the conical diaphragm is fixed is provided with a spring and catch e f1 the latter indicating when an aperture is central with the illuminating lens1 also the number of the aperture as marked on the graduated circular plate4 ,three of these apertures have central discs for circularly oblique illumination1 allowing only the passage of a hollow cone of light to illuminate the object4 ,the illuminator above described is placed in the secondary stage i i1 which is situated below the general stage of the microscope1 and consists of a cylindrical tube having a rotatory motion1 also a rectangular adjustment1 which is effected by means of two screws l m1 one in front1 and the other on the left side of its frame4 ,this tube receives and supports all the various illuminating and polarising apparatus1 and other auxiliaries4 ,directions for using ,gillett's ,condenser4--,in the adjustment of the compound body of the microscope for using with ,gillett's illuminator1 one or two important points should be observed--first1 centricity2 and secondly1 the fittest compensation of the light to be employed4 ,with regard to the first1 place the illuminator in the cylindrical tube1 and press upwards the sliding bar k in its place1 until checked by the stop2 move the microscope body either vertically or inclined for convenient use2 and1 with the rack and pinion which regulates the sliding bar1 bring the illuminating lens to a level with the upper surface of the object-stage2 then move the arm which holds the microscope body to the right1 until it meets the stop1 whereby its central position is attained2 adjust the reflecting mirror so as to throw light up the illuminator1 and place upon the mirror a piece of clean white paper to obtain a uniform disc of light4 ,then put on the low eye-piece1 and a low power 7the half-inch71 as more convenient for the mere adjustment of the instrument2 place a transparent object on the stage1 adjust the microscope-tube1 until vision is obtained of the object2 then remove the object1 and take off the cap of the eye-piece1 and in its place fix on the eye-glass called the 8centring eye-glass10#bf which will be found greatly to facilitate the adjustment now under consideration1 namely1 the centring of the compound body of the microscope with the illuminating apparatus of whatever description4 ,the centring-glass1 being thus affixed to the top of the eye-piece1 is adjusted by its sliding-tube 7without disturbing the microscope-tube7 until the images of the diaphragms in the object-glass and centring lens are distinctly seen4 ,the illuminator should now be moved by means of the left-hand screw on the secondary stage while looking through the microscope1 to enable the observer to recognize the diaphragm belonging to the illuminator1 and by means of the two adjusting screws to place this diaphragm central with the others3 thus the first condition1 that of centricity1 will be accomplished4 ,remove the white paper from the mirror1 and also the centring-glass1 and replace the cap on the eye-piece1 also the object on the stage1 of which distinct vision should then be obtained by the rack and pinion1 or fine screw adjustment1 should it have become deranged4 ,illustration3 ,fig4 #abg4--,the ,ross ,improved ,achromatic ,condenser1 with diaphragm stops4 ,the re-publication of the original directions is given with the view of showing what a clear conception ,gillett had of the value of his invention4 ,the careful directions given for centring must be regarded with interest1 although nearly superseded by the centring screw arrangement in connection with the sub-stage4 ,the best results1 he goes on to say1 will be secured by using the plain mirror and focussing the window-bar on the object1 while a white-cloud illuminator will afford as much light as may be required4 ,it is a mistake to suppose that direct light is more critical than indirect4 ,as a rule1 the student is given to over-illuminate the object4 ,these questions will1 however1 be discussed further on4 ,very many modifications of ,gillett's condenser have1 since #ahej1 become known to microscopists4 ,ross's present improved form 7,fig4 #abg7 is made to drop into the sub-stage of the microscope1 and when adjusted1 is an extremely efficient instrument4 ,the optical part is similar to a #d_/aj-;inch objective4 ,it has two sets of revolving diaphragms1 with apertures and stops for showing surface markings in a perfect manner4 ,abbe's ,condenser4 ,the essential feature of this condenser is its short focus1 which collects the light reflected by the mirror1 so as to form a cone of rays of very large aperture1 having its focus in the plane of the object4 ,illustration3 ,fig4 #abh4--,the ,iris ,diaphragm1 and carrier for ,stops4 ,the full aperture of the illuminating cone should only be used when finely granular and deeply stained particles 7protoplasm1 bacteria1 c47 are being examined with objectives of large aperture4 ,in all cases the cone must be suitably reduced1 either by an iris1 or other form of diaphragm 7central illumination74 ,by placing the diaphragm excentrically1 by means of rack-work attached to the carrier1 the central rays are excluded and a certain extra-axial portion of the illuminating pencil falls upon the object 7oblique illumination74 ,when the diaphragm is thus excentrically placed1 this oblique pencil can be directed from all sides by rotating the carrier round the optic axis4 ,the central stop diaphragm shuts off all the axial and transmits only the marginal rays1 thus producing dark-ground illumination4 ,the iris diaphragm 7,fig4 #abh7 is so shaped that the edge of its smallest opening closely approximates the object-slide on the stage4 ,illustration3 ,fig4 #abi4--,the ,abbe ,condenser1 detached from the ,sub-stage of the ,microscope4 ,the ,abbe condenser is the most popular form in use1 for all purposes4 ,owing to the large aperture of the cone of light which it projects1 it can be employed with the highest powers2 by removing the top lens it can also be used with low powers4 ,dark ground illumination may be obtained with it up to a #a_/d-;inch objective4 ,illustration3 ,fig4 #acj4--,optical ,arrangement of ,abbe ,illuminator1 #ab ,n4,a4 ,illustration3 ,fig4 #aca4--,optical ,arrangement of ,abbe ,illuminator1 #ad ,n4,a4 ,the condenser is made in two forms of #ab and #ad numerical aperture by ,messrs4 ,watson4 ,the lenses are mounted in aluminium4 ,fig4 #acj is in more general use1 but by workers with high powers ,fig4 #aca is preferred1 as it ensures the most oblique illumination with objectives of largest aperture4 ,it is preferred for photo-micrographic purposes4 ,illustration3 ,fig4 #acb4--,the ,optical ,arrangement of ,watson's ,achromatic ,condenser4 ,watson's ,achromatic ,condenser 7,fig4 #acb71 #aj numerical aperture1 shown in section1 although originally designed for use with the micro-spectroscope1 is equally efficient for ordinary purposes4 ,this condenser transmits a larger aplanatic cone of light than ,abbe's4 ,it may therefore be employed with higher power objectives1 and by removing the top lens it is just as useful a condenser for lower powers4 ,being constructed with lenses of an unusually large size1 it is well adapted for use with the micro-spectroscope4 ,it is certainly one of the best all-round condensers in use4 ,the new ,schott glass enters into the construction of the lenses1 and these are mounted in aluminium4 ,illustration3 ,fig4 #acc4--,powell's ,achromatic ,condenser4 ,many microscopists consider on the whole that ,powell's sub-stage apochromatic condenser with collar correction 7,fig4 #acc7 surpasses that of ,abbe4 ,the mechanical arrangement of ,powell's is very simple3 the correction collar is similar to that of an ordinary objective1 it has a steeper spiral slot and only half a revolution of movement2 a long arc is fixed to the collar so that it may conveniently be reached by the finger4 ,it is so constructed as to turn easily and smoothly at the slightest touch4 ,the collar moves only the back lens of the combination1 leaving the mount rigid4 ,the diaphragms are regulated by ,a and ,b4 ,illustration3 ,fig4 #acd4 ,illustration3 ,fig4 #acd;a4 ,illustration3 ,fig4 #acd;b4--,powell's ,apochromatic ,oil ,immersion ,condenser1 ,n4,a4 #adj4 ,the object of the correctional movement is to increase the maximum aplanatic aperture of the condenser by separating the lenses4 ,if the back of a wide-angled objective be examined when an object is illuminated by the full aperture of the condenser1 the edge of the flame being in focus1 it will be noticed that the illuminated portion of the back lens will be oval and pointed instead of circular4 ,also that when the condenser is racked up1 although the external shape of the illuminated portion becomes more circular1 two dark patches will appear on either side of the centre1 showing the operation of the spherical aberration of the condenser4 ,if under these circumstances the lenses are separated by means of the collar adjustment1 the black spots will be closed up1 and a circular and evenly-illuminated disc of illumination of a larger size will result4 ,the wheel of diaphragms1 or a series of graduated diaphragm discs to drop into a holder1 is intended for critical work2 the diaphragm can always be recorded1 and the identical illuminating cone reproduced4 ,hence we have a simple method of graduating apertures between any two contiguous diaphragms2 if1 for example1 we place the lever to the left1 so that the lens may be separated as far as possible1 and use a ,no4 #f diaphragm1 and if1 on examining the object1 it is thought that the illuminating cone is not large enough1 and if when ,no4 #g is turned on it is found too much1 we can go back to ,no4 #f1 and by turning the lever #fj towards the right1 closing the lenses and increasing the power a little1 we shall obtain an aperture somewhere between ,nos4 #f and #g diaphragm4 ,thus we can by means of the correction collar graduate the aperture with the facility as with an iris1 and we can record any particular aperture with a degree of accuracy foreign to the iris4 ,it must be admitted1 however1 that the cone of light transmitted by the condenser is a very small one4 ,powell also supplies an apochromatic oil-immersion condenser1 numerical aperture #adj1 but without collar correction2 ,fig4 #acd shows the sliding tube lowered by arm ,a and cell ,b withdrawn for changing stops1 which can be done without altering the focus of the condenser4 ,fig4 #acd;a shows the cell ,b closed and raised by arm ,a close to the back lens of optical combination4 ,in ,fig4 #acd;b six of the principal stops are shown4 ,powell's dry apochromatic condenser1 of nearly #ji aplanatic cone1 is also very good2 but the high price of all is a bar to their more general use4 ,the speciality of these is the conversion of axis light into condensed oblique incident light by the refraction of the condenser4 ,messrs4 ,r4 ,j4 ,beck have various forms of achromatic condensers1 some of which partake of a somewhat elaborate arrangement2 others are simple and inexpensive1 to suit the students' microscope2 as when the light of the concave mirror proves insufficient for any object requiring intense transmitted light1 an achromatic condenser must be adapted to even the students' form of microscope4 ,the latest form of condenser 7,fig4 #ace7 is fitted with revolving stops and iris diaphragm1 and other appliances for obtaining satisfactory results4 ,illustration3 ,fig4 #ace4--;,beck's newer form of ,achromatic ,condenser4 ,beck's ,compound ,illuminating ,apparatus 7,fig4 #acf74--;,it is useful in working with the microscope to be enabled to rapidly change the illumination1 and for this reason this compound form of condenser has been constructed4 ,it consists of an upper portion ,a1 a wide-angle condenser1 the aperture of which can be reduced at will by an iris diaphragm1 moved by the lever ,b4 ,this can be used for all other purposes4 ,below this diaphragm is a plate ,c1 which can be swung back out of position at will1 as shown in outline4 ,into a cell in this plate the stops ,d can be dropped1 and the condenser can be used for dark field illumination1 or for high powers as an oblique illuminator4 ,a large-size polarising prism ,e1 fastens to the plate ,c1 and can be removed when not required4 ,in this way any of the various modes of illumination may be separately or conjointly obtained4 ,illustration3 ,fig4 #acf4--;,beck's ,compound ,condenser4 ,illustration3 ,fig4 #acg4--;,beck's ,spherical ,achromatic ,condenser4 ,their condenser 7,fig4 #acg7 has a large aperture1 and facilities for rotating the series of diaphragms4 ,it is available for either dry or immersion objectives up to #ac numerical aperture on diatoms1 and wet or dry histological objects4 ,the spherical form of the front is worked by a milled-head that rotates a series of lenses and diaphragms4 ,it also avoids the inconvenience of having the connecting fluid drawn away by capillary attraction1 as would be the case if mounted on a flat surface4 ,it is also less in the way of the sub-stage movements4 ,illustration3 ,fig4 #ach4--,watson's ,parachromatic ,condenser4 ,the ,parachromatic ,condenser of ,messrs4 ,watson 7,fig4 #ach7 was made to meet a demand for a condenser giving a large solid cone of illumination free from colour4 ,the optical part of this condenser consists of a full hemispherical front lens1 and the middle and back combinations of such forms as to produce the necessary corrections4 ,the ,jena phosphate crown and silicate flints are used in its manufacture1 and to these are due its special qualities4 ,the total aperture of the condenser is #aj1 and it yields an aplanatic aperture of #ij numerical aperture4 ,the magnifying power is #b_/gths of an inch4 ,from this it will be seen that it is especially suitable for use with high-power objectives4 ,it can also be employed without the front lens1 when the magnifying power is #d_/ajths of an inch1 and the numerical aperture #ce4 ,it is mounted in an exceedingly convenient manner1 the iris diaphragm being fitted in such a way as to be absolutely central with the optical system4 ,the arc through which the handle controlling the iris travels is divided1 and indicates the aperture at which the condenser may be working at any time4 ,an important feature in this condenser is that it is almost wholly free from colour4 ,as a rule condensers of the same form are found difficult to work with1 because of the small diameter of the field or back lens4 ,this difficulty has been successfully overcome by increasing the size of this lens1 and the whole of which is fully utilised4 ,most ,london opticians have their own especial form of achromatic condenser1 designed for and fitted to their several stands and objectives1 varying from a small price to the more expensively-fitted accessories4 ,illustration3 ,fig4 #aci4--,swift's ,illuminating ,polarising ,apparatus4 ,illustration3 ,fig4 #aci;a4--,swift's ,diaphragms and ,central ,stops4 ,messrs4 ,swift's illuminating apparatus 7,fig4 #aci7 is conveniently supplied with numerous useful appliances4 ,the optical combination ,a is computed to be used as an effective spot lens from a #c-;inch objective up to a sixth4 ,c ,c are two small milled heads by means of which the optical combination ,a is centred to the axis of the objective4 ,the revolving diaphragm ,e has four apertures for the purpose of receiving central stops1 oblique light discs1 and selenite films4 ,d is a frame carrying two revolving cells1 into one of which a mica film is placed1 which can be revolved with ease over either of the selenites below1 whereby changes of colour can be obtained in experimenting with polarised light4 ,the darts and ,p ,a's indicate the position of the positive axis of the mica and selenite films1 and by this means results can be recorded1 etc4 ,either of the revolving cells can be thrown into the centre of the condenser1 and there stopped by means of a spring catch2 when so arranged the mica film1 c41 may be revolved in its place by turning the cell ,d1 as both cells are geared together with fine racked teeth4 ,f is a polarising prism mounted on an eccentric arm1 rendered central when in use1 or thrown out1 as seen1 when out of use4 ,g is the rack dove-tail slide for indicating and focussing the condenser on the object4 ,the advantages associated with this condenser consist in having the polarising prism1 selenite films1 dark-ground1 and oblique light stops1 so that they may be brought close under the optical combination4 ,illustration3 ,fig4 #adj4--;,baker's ,nelson ,achromatic ,condenser4 ,baker's ,nelson ,condenser1 shown in ,fig4 #adj1 is intended for use with their medium instruments4 ,it has1 however1 many pieces of apparatus essential to those of a higher class4 ,it is applicable1 indeed1 to all instruments having sufficient depth beneath the stage to receive it4 ,it comprises an achromatic combination of #ij aperture1 available with all powers up to #a_/h-;inch tinted glass for neutralising the yellow rays of artificial light1 focussing adjustment1 dark-ground illuminator1 large diaphragm with rotating tube to carry oblique light stops1 small wheel of apertures1 polarising prism with two selenite films1 clear aperture1 and oblique light-shutter for low powers4 ,baker's ,students' ,condenser 7,fig4 #ada7 is designed to take the place of ,abbe's1 and costs much less4 ,it transmits a larger aplanatic cone of light1 and can be used either with high or low powers by removing the front lens4 ,it is equally useful for photo-micrographic work4 ,mr4 ,j4 ,mayall's semi-cylinder or prism for oblique illumination 7,fig4 #adb7 is a convenient form1 as it permits of the semi-cylinder being tilted and placed excentrically2 in this manner1 without immersion contact1 and by suitable adjustment1 a dry object can be viewed with any colour of monochromatic light4 ,if placed in immersion contact with the slide1 the utmost obliquity of incident light can be obtained4 ,objects in fluid may be placed on the plane-surface of the semi-cylinder1 and illuminated by ordinary transmitted light1 or rendered 8self-luminous0 in a dark field1 as with the hemispherical illuminator or ,wenham's immersion paraboloid4 ,a concave mirror with a double arm is quite sufficient to direct the illuminating pencil4 ,this semi-cylinder was originally made by ,tolles1 of ,boston1 for measuring apertures1 but1 at ,mr4 ,mayall's suggestion1 ,messrs4 ,ross mounted it as an illuminator4 ,illustration3 ,fig4 #ada4--,optical ,arrangement of ,baker's ,abbe ,condenser4 ,the spiral slot should be fixed close beneath the larger lens of the condenser1 and when properly arranged will be found a convenient mode of obtaining oblique light4 ,illustration3 ,fig4 #adb4--,mayall's ,semi-,cylinder ,illuminator and ,spiral ,diaphragms4 ,the ,webster-,collins ,universal ,condenser 7,fig4 #adc7 is so well known that it scarcely calls for any lengthy description4 ,it is an inexpensive form of condenser1 designed in the first instance for use with the students' microscope4 ,it is fitted into the sub-stage2 has an iris diaphragm as well as a series of revolving diaphragms moved by a milled head screw arrangement4 ,illustration3 ,fig4 #adc4--,the ,webster-,collins ,universal ,condenser4 ,oblique ,illumination4 ,wenham's ,parabolic ,condenser4--,mr4 ,wenham's many useful additions to the microscope and its accessories demand especial notice4 ,when mention is made of the various immersion condensers 7illuminators1 as he preferred to call them71 his original right-angled prism1 his truncated hemispherical lens1 his immersion paraboloid1 and his reflex illuminator1 in which rays beyond the angle of total reflexion are utilised by reflex action from cover-glass on to the surface of the object1 every one of these well-devised inventions will always be spoken of in terms of praise4 ,all in their turn conferred a great service upon the microscope1 and enabled the student to clear up difficulties that stood in the way of developing structure when achromatic lenses and dry-objectives were considered perfect4 ,the superior illumination of the object was wholly due to1 and effected by1 reflected rays from the object to the aperture of the objective1 and obviously1 reflex action could only take place with dry-objectives4 ,this reflex action must be regarded as ,mr4 ,wenham's special discovery4 ,it must be observed1 however1 that it is not the same as the more modern achromatic appliances used for throwing direct rays upon the object1 and which proved the existence of apertures capable of direct transmission up to #bg measured in the body of the front lens4 ,illustration3 ,fig4 #add4--,wenham's ,parabolic ,reflector4 ,the most practical of ,mr4 ,wenham's inventions is probably the hemispherical lens1 since adopted by ,messrs4 ,ross in connection with their excellent ,zentmayer stand1 and which has proved eminently serviceable4 ,but the fact is that devices of the kind for obtaining direct oblique light require a thin stage1 and therefore most of those who possess the earlier-made microscope stand would doubtless hail the appearance of any appliance which will convert axial light into oblique light2 as by so doing the possessors of such instruments1 in which the stage is generally of considerable thickness1 would enjoy the pleasure of seeing the best resolution it is possible to get with their dry-objectives4#bg ,wenham's ,parabolic ,reflector4--,this will be better understood by reference to ,fig4 #ade1 which represents it in section ,a ,b ,c1 and shows that the rays of light r r r1 entering perpendicularly at its surface ,c1 and then reflected by its parabolic surface ,a ,b to a focus at ,f1 can form no part of the largest pencil of light admitted by the object-glass and represented by ,g ,f ,h2 but an object placed at ,f will interrupt the rays and be strongly illuminated4 ,a stop at ,s prevents any light from passing through direct from the mirror4 ,in the microscope the parabolic reflector fits into the cylindrical fitting under the stage1 and the adjustment of its focus upon the object is made by giving it a spiral motion when fitted in--that is1 carefully pushing it up or down at the same time that it is turned round by the milled edge ,b ,b4 ,it must then be focussed by the rack and pinion motion4 ,as the rays of light must be parallel when they enter it1 a flat mirror1 which in this case should be added to the instrument1 is generally used2 daylight will then require only direct reflection1 but the rays from an artificial source will have to be made parallel by placing a side condenser between the light and the mirror1 about #a-c_/d inch from the former and #d-a_/b inches from the latter4 ,nearly the whole surface of the mirror should be equally illuminated2 this may be tested by temporarily placing upon it a card or piece of white paper4 ,parallel rays can also be obtained from the concave mirror1 if the light is placed about #b-a_/b inches from it4 ,dark-ground illumination is not suitable for very transparent objects--that is1 unless there is a considerable difference in their index of refraction1 or they are pervaded by air-cells4 ,illustration3 ,fig4 #ade4--,parabolic ,reflector4 ,one very remarkable example of this may be seen in the tracheal system of insects4 ,if any of the transparent larv of the various kinds of gnat be mounted in gelatine and glycerine jelly1 slightly warmed but not enough to kill the insect outright1 about the third day the fluids circulating in the body will be absorbed and replaced by air4 ,illuminated by the parabolic condenser1 and viewed with a binocular microscope1 and a low power1 the gnat-larva becomes a superb object4 ,the body of the insect is but faintly visible1 and in its place is displayed a marvellous tracheal skeleton1 with the tubes standing out in perspective1 shining brilliantly1 like a structure of burnished silver4 ,unfortunately1 such objects are not permanent1 for when the whole of the water dries up1 the tracheal tubes either collapse or become refilled with fluid4 ,as to the blackness of field1 and luminosity of the object1 this depends upon excess of light from the paraboloid received beyond the angle of aperture of the object-glass4 ,it is found in practice that more and more of the inner annulus of rays from the paraboloid has to be stopped off1 until at last1 with high-angled objectives1 it is scarcely possible to obtain a black field4 ,the light1 on the whole1 most suitable for this method of illumination is lamp1 the rays of which should in all cases be rendered more parallel by means of a large plano-convex lens1 or condenser4 ,illustration3 ,fig4 #adf4--,wenham's ,hemispherical ,lens4 ,wenham's ,immersion ,condenser4--,mr4 ,wenham1 in the year #ahef1 described various forms of oblique illuminators1 one of which was an immersion2 a simple right-angled prism1 connected by a fluid medium of oil of cloves4 ,this1 however1 was abandoned for a nearly hemispherical lens connected with the slide1 and although an improvement1 did not touch the point of excellence ,mr4 ,wenham was looking for4 ,ultimately he adopted a semi-circular disc of glass of the exact form and size represented in the drawing1 ,fig4 #adf1 having a quarter-inch radius1 with a well-polished rounded edge1 the sides being grasped by a simple kind of open clip attached to the sub-stage1 the fluid medium used for connecting the upper surface with the slide being either water1 glycerine1 or oil2 an increase of oblique illumination being obtained by swinging the ordinary mirror sideways4 ,by means of an illuminator of the kind difficult objects mounted in balsam are resolved4 ,this simple piece of glass collects and concentrates light in a marvellous manner1 and is by no means a bad substitute for some of the more costly forms of achromatic condenser4 ,it can be used either in fluid contact with the slide1 or dry1 as an ordinary condenser4 ,mr4 ,wenham subsequently contrived a small truncated glass paraboloid1 for use in fluid contact with the slide2 water1 glycerine1 oil1 or other substance being employed as a contact medium4 ,the rays of light in this illuminator1 being internally reflected from a convex surface of glass1 impinge obliquely on the under surface of the slide1 and are transmitted by the fluid uniting medium1 and internally reflected from the upper surface of the cover-glass to the objective4 ,to use the reflex illuminator efficiently it must be racked up to a level with the stage4 ,the centre of rotation is then set true by a dot on the fitting1 seen with a low power1 a drop of water is then placed on the top1 and upon this the slide is laid4 ,minute objects on the slide must be found either by the aid of a low power1 by their greater brilliancy1 or by rotating the illuminator2 the effect on the podura scale is superb1 the whole scale appearing dotted with bright blue spots in a zig-zag direction4 ,objects for this illuminator should be especially selected and mounted4 ,illustration3 ,fig4 #adg4--,the ,amici ,prism4 ,the ,amici ,prism1 originally designed for oblique illumination1 consists of a flattened triangular glass prism1 the two narrower sides of which are slightly convex1 while the third or broadest side forms the reflecting surface4 ,when properly used1 it is capable of transmitting a very oblique pencil of light4 ,the prism is either mounted1 as in ,fig4 #adg1 for slipping into the fitting of the sub-stage1 or on an independent stand1 as arranged for ,powell's microscope1 page #he1 ,fig4 #ef4 ,method of ,employing the ,achromatic ,condenser to the ,greatest ,advantage4 ,its ,illumination4--,good daylight is the best for general work4 ,the microscope should be placed near a window with a northern aspect4 ,direct sunlight should never be utilised2 the best light is that reflected from a white cloud4 ,a good paraffin lamp is the most serviceable artificial source of light1 and it is quite under control4 ,as an illuminant more often brought into requisition in the smoky atmosphere of towns1 the paraffin lamp is on the whole the handiest and the most useful4 ,if gas-light can be brought into use as suggested for micro-photography1 with the incandescent mantle1 it will be found to be the purest and best form of artificial illumination for the microscope4 ,among paraffin lamps those constructed by ,baker and ,swift are all that can be desired4#bh ,illustration3 ,sectional view of the ,optical ,arrangement of the ,aplanatic ,bull's-eye ,lens1 fitted in gymbal on the front of the lamp4 ,illustration3 ,fig4 #adh4--;,baker's ,microscope ,lamp4 ,as the chimneys of these lamps are made of metal1 and blackened1 no reflected light disturbs the eye4 ,care must be taken to have the wick evenly trimmed2 the metal chimney has a glazed front1 giving exit to the rays of light1 the flat of the flame being used with low powers1 and the image of the flame being reflected by a plane mirror to give equal illumination of the whole field4 ,in working with high powers1 the lamp is turned with the flame edge-wise1 and at the same time the mirror must be dispensed with4 ,by working1 as it is termed1 directly on the edge of the flame1 the illumination is greatly increased1 and a band of light can be concentrated on any part of the preparation it is desired to make a careful study of4 ,to obtain the best results1 time and care must be given to the illumination of the object4 ,the lamp and microscope having been placed in position1 a low power is first used and the smallest diaphragm4 ,on looking through the microscope it will probably be observed that the image of the diaphragm is not in the centre of the field2 by moving the centring screw of the condenser this may be adjusted4 ,the low power is then replaced by a high power1 the largest diaphragm used1 and the bacteria or diatom brought into focus4 ,the diaphragm must now be replaced by one of medium size1 and by racking the condenser up and down1 a point will be arrived at when the image of the edge of the flame appears as an intensely bright band of light4 ,if this is not exactly in the centre of the field the centring screw of the condenser must again be adjusted4 ,with regard to the use of diaphragms1 various sizes should be tried while focussing with the fine adjustment1 at the same time using the correction colour2 in this way we obtain the sharpest possible image4 ,when the condenser has been accurately centred1 it will still be necessary to focus it for each individual specimen1 so as to correct for difference in the thickness of slides and the layers of mounting medium4 ,correction for different thickness of cover-glasses must be made by the aid of the collar adjustment in the following way3 a high-power eye-piece is substituted for the ordinary eye-piece1 and the faults in the image will thereby be intensified4 ,by moving the collar completely round1 first in one direction and then in the other1 while carefully observing the effect of the image1 it will be seen to become obviously worse whichever way the collar is turned4 ,the collar must then be turned through gradually diminishing distances until an intermediate point is reached at which the best image results with the high-power eye-piece1 and on replacing this by the low-power eye-piece the sharpest possible image will be obtained4 ,effect of the ,sub-stage ,condenser4--,the sub-stage condenser gives the most powerful illumination when it has been racked up until it almost touches the specimen4 ,it produces a cone of rays of very short focus1 and the apex of the cone should correspond with the particular bacterium or group of bacterias under observation4 ,the effect of the condenser without a diaphragm is to obliterate what ,koch has termed a structure picture4 ,if the component parts of a tissue section were colourless and of the same refractive power as the medium in which the section is mounted1 nothing would be visible under the microscope4 ,as1 however1 the cells and their nuclei and the tissues do not differ in this respect1 the rays which pass through them are diffracted1 and an image of lines and shadows is developed4 ,if in such a tissue there were minute coloured objects1 and if it were possible to mount the tissue in a medium of exactly the same refractive power1 the tissue being then invisible1 the detection of the coloured objects would be much facilitated4 ,this is exactly what is required in dealing with bacteria which has been stained with aniline dyes1 and the desired result can be obtained by the use of the sub-stage condenser4 ,if we use the full aperture of the condenser the greatly converged rays play on the component parts of the tissue1 light enters from all sides1 the shadows disappear1 and the structure picture is lost4 ,if now a diaphragm is inserted1 so that we are practically only dealing with parallel rays1 the structure picture reappears4 ,as the diaphragm is gradually increased in size the structure picture gradually becomes less and less distinct1 while the colour picture1 the image of the stained bacteria1 becomes more and more intense4 ,when1 therefore1 bacteria in the living condition and unstained tissues are examined1 a diaphragm must be used1 and when the attention is to be concentrated upon the stained bacteria in a section or in a cover-glass preparation the diaphragm must be removed and the field flooded with light--7,crookshank74 ,the wide-angle condenser1 it will be understood1 consists of a combination of lenses1 which concentrate all the light entering them to a small point1 and the condenser must be so accurately focussed that this brilliant cone of light1 when it emerges from the upper lens of the condenser1 falls upon the object from all directions1 forming a wide-angle cone of light1 at the apex of which the object must be placed 7see ,fig4 #adi74 ,that is to say1 the object is illuminated by a cone of rays passing through it in all directions4 ,illustration3 ,fig4 #adi4--;,front ,lens of ,condenser4 ,there are1 however1 objects which require a fully illuminated field1 when the lamp should be turned round and the ,herschel lens condenser 7shown in section1 ,fig4 #adh7 should be used to collect the light and throw it upon the mirror4 ,for moderate powers1 as a four-tenth or one-fifth1 the condenser should be used a little below the focus to give an even illumination over the whole field4 ,moreover1 as to the use of the condenser for defining general objects1 it must be borne in mind that to show different kinds of structure different apertures in the iris diaphragm are necessary1 and that whereas some objects show their structure better with a large angle of light cut down in intensity by the use of blue glass1 others show better with a small pencil of direct rays4 ,for the resolution of diatoms it is often necessary to use oblique light only1 and for this purpose diaphragms with central patches are used1 the iris diaphragm being opened to its full extent4 ,an annular ring of oblique light emerges from the condenser upon the object1 and it is in this manner also that dark-ground illumination is obtained with moderate and low powers4 ,,the ,,diaphragm4 ,illustration3 ,fig4 #aej4--,the ,diaphragm4 ,the early form of diaphragm in use was that shown in ,fig4 #aej4 ,illustration3 ,fig4 #aea4--,shutter ,diaphragm4 ,it consists simply of a circular brass plate with a series of circular openings of different sizes1 arranged to revolve upon another plate by a central pin or axis1 the last being also provided with an opening as large as the largest in the diaphragm-plate1 and corresponding in situation to the axis of the microscope body4 ,the holes in the diaphragm-plate are centred and retained in place by a bent spring in the second plate1 which rubs against the edge of the diaphragm-plate and catches in a notch4 ,the blank space shuts off the light from the mirror when condensed light is about to be used4 ,it is usually made to fit in under the stage of the microscope4 ,this has been almost superseded by the iris diaphragm1 originally designed by ,wales1 of ,america4 ,it was made by this optician for his working students' microscope4 ,an early form of the iris diaphragm is seen in ,fig4 #aea4 ,by pressing upon the lever handle at the side the aperture gradually closes up1 and without for a moment losing sight of the object under examination4 ,the ,mirror4 ,the mode in which an object is illuminated is1 in the words of the late ,andrew ,ross1 8second only in importance to the excellence of the glass through which it is seen40 ,to ensure good illumination the mirror should be in direct co-ordination with the objective and eye-piece2 it must be regarded as a part of the same system1 and tending by a combined series of acts to a perfect result4 ,illumination of the object is recognised as of three kinds or qualities--reflected1 transmitted1 and refracted light4 ,for the illumination of transparent objects1 transmitted light is brought into use2 for opaque objects1 reflected light is needed4 ,the mirror should be about #b-a_/b or #c inches in diameter1 and it must not be fixed1 but made to slide up and down the stem under the stage1 so that the rays of light emanating from it may be brought to a focus4 ,the utility of the mirror is so obvious that it is occasionally passed over in silence by writers4 ,to myself it appears to be an important accessory of the microscope1 and ,i shall therefore proceed to combine theory with practice in what ,i have to say with regard to the mirror4 ,illustration3 ,fig4 #aeb4--,principal ,focus of ,mirror4 ,the microscope mirror should be the segment of a true sphere1 and its centre that of a true curvature4 ,if the mirror has a true circular boundary1 the central point on line ,a 7,fig4 #aeb7 of the reflecting surface1 is the pole of the same4 ,the line ,a ,c is known as its principal axis1 and any other straight line through ,c1 which meets the mirror1 is its secondary axis4 ,when the incident axis is perfectly parallel to the principal axis1 the reflected rays converge to a point ,f1 its principal focus4 ,so much for the theory of the mirror4 ,now we come to its practical use4 ,simple as the mirror of the microscope may appear to be1 if the curve of the surface is not perfect1 it will yield a secondary reflection or double pencil of rays4 ,the plane mirror will occasionally be found to emit more than one reflection of the lamp-flame2 this we find may be corrected by rotating the mirror in its cell4 ,many years ago ,i proposed to meet a difficulty of the kind by arranging a rectangular prism on a separate stand1 shown in ,fig4 #aec1 consisting of a prism ,a ,b1 mounted in gimbal ,c1 ,d1 and ,e1 secured to a brass tube ,g1 fitted to the stem1 and thus made to take the place of the mirror4 ,the direct method of employing the mirror1 that more generally resorted to1 is by reflecting rays from the concave surface2 the plane surface is preferred when the condenser is used4 ,whichever is employed1 it should not be forgotten that the optic axis must be preserved throughout1 and so brought to the centre of the open tube of the microscope4 ,another method is to interpose a bull's-eye lens1 and in this way supply the mirror with a beam of parallel rays of light4 ,the plane side of the bull's-eye lens should be turned towards the lamp1 so that lamp1 bull's-eye1 sub-stage condenser1 and objective1 are brought into an exact line1 the bull's-eye being set at right-angles to the line4 ,a piece of thin white paper held across the bottom of the sub-stage will serve to show whether the rays of light are fairly parallel4 ,the next care is to focus the object on the stage1 and then the sub-stage condenser on the slide2 further correction should be made by means of the centring screws of the sub-stage1 or by moving the bull's-eye lens or lamp slightly1 thus perfecting the arrangements for working with parallel rays of light4 ,illustration3 ,fig4 #aec4--,rectangular ,prism4 ,accessories of the ,microscope4 ,the accessories and appliances of the microscope have become so very numerous1 that any attempt to describe them and explain the uses to which they are put would demand more space than ,i find myself in a position to bestow upon them4 ,i must therefore confine my remarks to those accessories in more general use4 ,illustration3 ,fig4 #aed4--,the ,lieberkhn4 ,having described the method of employing transmitted light1 ,i have a few words to add with regard to the illumination of opaque objects by reflected light4 ,a very early and efficient form of opaque illumination is the well-known ,lieberkhn4 ,this has not been entirely surpassed by more recent inventions4 ,the concave speculum termed a ,lieberkhn1 so named after its celebrated inventor1 directly reflects down upon the object the light received either from the mirror or bull's-eye lens4 ,it consists of a silver cap1 which slides over the objective 7,fig4 #aed71 a indicating the lower part of the compound body1 and b the objective over which slides the ,lieberkhn1 c2 the rays of light are collected to a focus upon the object at d4 ,the object may either be mounted on a slip of glass1 or held by the stage-forceps1 f2 if very small1 or transparent1 it may be gummed to the dark well1 e1 or mounted on a ,beck's opaque disc-revolver4 ,illustration3 ,fig4 #aee4--,stage ,forceps1 for holding objects while under examination4 ,illustration3 ,fig4 #aef4--;,beck's ,disc-holder4 ,this holder will be found useful for the examination of opaque or other objects that cannot be conveniently held by the stage forceps1 the specimen being temporarily attached to it by gum or gold size4 ,the holder is intended to rotate1 so that every portion of the object can be brought into view4 ,in this way it will be found useful in the study of insects1 foraminifera1 c4 ,with the ,lieberkhn1 however1 the illumination of opaque objects must be more or less one-sided1 and therefore1 the silver side-reflector has superseded it for general use 7,fig4 #aeg74 ,to ensure a more perfect illumination of the object1 the bull's-eye lens should also be used4 ,mr4 ,sorby devised a reflector to fit over the objective4 ,it consists of a semi-circular cap2 is1 in short1 a modification of the parabolic reflector4 ,the light from the mirror can1 by slightly varying its inclination1 be brought into use with this reflector4 ,the silver side-reflector is usually made with a ball-and-socket joint1 so that it can be turned in any direction4 ,it is secured to the stage of the microscope by the pin1 which drops into a hole purposely drilled to receive it1 and facility given for turning up and down1 or in any position4 ,if daylight is used the microscope should be placed in such a position that the light from a white cloud falls upon the speculum1 but the light of the lamp is far more manageable for use with the reflector4 ,illustration3 ,fig4 #aeg4--,silver ,side-reflector4 ,the ,lieberkhn is only intended to be used with low powers--a #b-;inch1 #a_/b-;inch and a #b_/c-;inch4 ,such objects as the elytra of the diamond and other beetles are well suited for examination4 ,illustration3 ,fig4 #aeh4--,sorby's ,modification of the ,parabolic ,reflector4 ,while experimenting with a parabolic reflector 7,fig4 #aeh71 ,mr4 ,sorby saw the value of examining objects under every kind of illumination4 ,as on viewing specimens of iron and steel with this reflector he found that1 from the great obliquity of the illumination obtained1 the more brilliantly polished parts of the specimen reflected the light beyond the aperture of the objective1 and these could not be distinguished from those parts which absorbed light1 he thereupon proceeded to place a small flat mirror in front of the objective1 and cover half its aperture1 and at the same time stop off by means of a semi-cylindrical tube the light from the parabolic reflector4 ,this arrangement produced the reverse appearance of that first employed1 and it proved to be a useful aid in determining structure4 ,the ,bull's-eye ,condensing ,lens4 ,this accessory is brought into constant use for the purpose of converging rays from a lamp or mirror2 or1 for reducing the diverging rays of the lamp to parallelism with the parabolic illuminator1 or silver side-reflector4 ,the form in use is a plano-convex lens of about three or four inches in focal length 7,fig4 #aei74 ,it is usually mounted on a brass stand1 so that it may be placed and turned in any direction1 and at any height4 ,when used by daylight1 its plane side should be turned towards the object1 and the same position maintained when used for converging the rays of light from the lamp2 but when used with the side-reflector the plane side must be towards the lamp4 ,much attention has been paid to this very necessary accessory1 the bull's-eye lens4 ,a doublet has been brought into use which has increased the value of the bull's-eye condenser in bacteriological research1 and in micro-photography generally4 ,illustration3 ,fig4 #aei4--;,bull's-eye ,lens4 8,during a recent investigation of the spherical aberration in doublets1 it was believed to be impossible to construct a doublet of the form known as #8,herschel's doublet' free from aberration1 although these doublets figure in many books on optics4 ,in a condenser made by ,baker the aberration is reduced to a minimum1 #bg per cent4 less than ,sir ,john ,herschel's4 ,this doublet1 it appears1 differs from ,herschel's both in the ratio of the radii of the meniscus1 and also in the ratio of the foci of the two lenses2 indeed1 the only point of similarity is in the first lens1 which is crossed4 ,to test this1 project the image of the flat lamp-flame on a piece of white card with a plano-convex lens 7the field-lens of the ,huyghenian eye-piece71 use first the convex side and then the plane side towards the card1 the lamp being placed about #f feet from the lens4 ,focus the lamp-flame as sharply as possible1 and a circular halo of misty light will be seen to surround the lamp-flame2 but when the plane side of the lens is made to face the card this halo of misty light will be seen to be greatly reduced1 and the brightness of the image of the flame proportionately increased4 ,if the lens1 then1 were strictly aplanatic there should be no misty halo1 all the light being concentrated in the image of the lamp-flame1 and the image of maximum brightness4 ,in short1 the diameter of the halo or misty light is the measure of the spherical aberration4 ,if the condenser referred to above1 having the form of minimum aberration for two planes1 be compared in the same manner with an ordinary single bull's-eye of the same focus1 the diameter of the misty halo will be found reduced to a radius of about #a_/e-;inch1 but1 with this new condenser there is a further reduction1 so that the radius of the misty halo measures only #a_/bj-;inch4 ,these experiments are instructive1 because the brightness1 or the mistiness of the microscopical image is an associated phenomenon40#bi ,a sectional view of the optical arrangement of ,baker's aplanatic bull's-eye doublet is shown1 together with lamp1 in ,fig4 #adh4 ,the ,microscope ,lamp4--,the introduction of paraffin into household use has somewhat modified our views with regard to the most suitable artificial source of illumination4 ,good paraffin burns with a whiter and purer flame than colza oil1 and consequently is less liable to fatigue the eyes4 ,the first cost of the lamp is trifling2 for a moderate sum a handy form of lamp can be had1 mounted on an adjustable sliding ring stand1 and with a porcelain1 metal or paper shade1 to protect the eyes from scattered rays of light4 ,all opticians supply accepted forms of lamps4 ,to give the increased effect of whiteness to the light 78white cloud illumination0 as it is termed71 take a piece of tissue paper1 dip it into a hot bath of spermaceti1 and1 when nearly cold1 cut out a circular piece and secure it over the largest opening in the diaphragm plate4 ,this will be found to materially moderate and soften the light4 ,illustration3 ,fig4 #afj4--;,beck's ,complete ,lamp4 ,beck's ,complete ,lamp is constructed especially for delicate microscopical work4 ,it has a burner giving a flat flame2 this can be rotated to enable the edge or the flat of the flame to be used2 likewise a metal chimney with two apertures1 in which #c #a glass slips slide2 either white or coloured glasses may be used4 ,a ,herschel aplanatic condenser is carried on a swinging arm1 which rotates around the lamp flame as a centre1 and can be clamped in any position4 ,the whole lamp has a raising and lowering motion1 with a spring clamp to hold it in any position4 ,the lamp is so designed that at its lowest position the flame is only three inches from the table4 ,here the microscopist is furnished with a lamp which will accomplish all he may require with regard to illumination4 ,illustration3 ,fig4 #afa4--,watson's ,microscope ,lamp4 ,illustration3 ,fig4 #afb4--;,glass ,holder for carrying ,coloured ,glasses4 ,watson's lamp 7,fig4 #afa7 has a metal chimney1 and is somewhat simpler in structure than those already referred to4 ,for the student1 the simpler and cheaper form will answer every purpose4 ,a glass holder for carrying various tinted slips of coloured glass to act as a screen or modifier of the light is much employed1 and assists in determining fine structures 7,fig4 #afb74 ,nose-pieces and ,objective ,changers4 ,a convenient appendage to the microscope is the rotating nose-piece1 invented by ,mr4 ,charles ,brooke1 ,f4,r4,s41 and intended to carry two or more objectives1 whereby a saving of time is effected1 and the trouble of repeatedly screwing and unscrewing is avoided4 ,in the application of the nose-piece attention should be given to centring4 ,messrs4 ,baker's objective changer is intended to facilitate the placing and replacing the nose-piece in position4 ,this adaptation consists of a milled head1 acting on three jaws1 having a universal screw thread1 a decided improvement on the screw4 ,zeiss has adopted a tube-sliding objective changer with centring adjustments4 ,messrs4 ,watson met the difficulty of centring by making the nose-piece a part of the body-tube of their microscopes 7,fig4 #afc74 ,this1 when adapted to the shorter body of the students' microscope1 fully compensates for want of length4 ,illustration3 ,fig4 #afc4--,watson's ,centring ,nose-piece of ,microscope4 ,their triple nose-piece is constructed with much care1 and when in use is found very effective4 ,it is manufactured of that very light metal aluminium1 and which minimises the strain produced by the heavier brass nose-piece4 ,finders4--,the finder affords a necessary and useful means of registering the position of any particular object1 so that it may be readily found again at any subsequent period4 ,in the work of examination the finder will save time when making a special research1 extending over a considerable surface4 ,illustration3 ,fig4 #afd4--,triple ,nose-pieces4 ,that the finder has been of use may be surmised from the number invented and figured in the 8,journal of the ,royal ,microscopical ,society40 ,by far the most useful form is that of graduating the plates of the mechanical stage1 dividing a certain portion into #ajj parts4 ,powell and ,lealand have adopted this system in their ,no4 #a stands1 while ,baker and ,watson have added a graduated scale on silver to #a_/ajjth mm4 as a finder1 and also a stage micrometer in #a_/ajth and #a_/ajjth of a millimetre1 together with a ,maltwood finder for lodging the position of any desired portion of a specimen under examination4 ,the ,maltwood finder 7,fig4 #afe7 can be used with any microscope1 and without a mechanical stage4 ,this useful finder continues to occupy a permanent place among the accessories of the microscope4 ,it consists of a glass slide1 #c #a-a_/d inches1 on which is photographed a scale occupying a square inch2 this is divided by horizontal and vertical lines into #b1ejj squares1 each of which contains two numbers marking its 8latitude10 or place in the vertical series1 and its 8longitude10 or place in the horizontal series4 ,the scale is in each instance an exact distance from the bottom and left-hand end of the glass slide2 and the slide1 when in use1 should rest upon the ledge of the stage of the microscope1 and be made to abut against a stop1 a simple pin1 about an inch and a half from the centre of the stage4 ,illustration3 ,fig4 #afe4--,maltwood's ,finder4 ,dr4 ,pantacsek's finder appears to have some advantage over ,maltwood's1 but it cannot be used with the same facility1 and therefore will not displace an old favourite4 ,the ,amyot finder ,i have long had in use2 it is efficient and inexpensive--can indeed1 if misplaced or lost1 be replaced by the aid of the square and compasses4 ,illustration3 ,fig4 #aff4--;,amyot's ,object ,finder4 ,the ,okeden finder consists of two graduated scales1 one vertical1 attached to the fixed stage-plate1 the other horizontal1 attached to an arm carried by the intermediate plate2 the first of these scales enables the worker to 8set0 the vertically-sliding plate to any determinate position in relation to the fixed plate1 while the second gives the power of setting the horizontally-sliding plate by that of the intermediate4 ,micrometers4--,it is of the utmost importance to have a means of measuring with accuracy the objects1 or part of objects1 under observation4 ,the most efficient piece of apparatus for the purpose is the micrometer eye-piece1 the earlier form of which1 ,jackson's1 has been described under the heading ,eye-pieces 7p4 #add74 ,in the case of micrometers1 as in that of most other accessories1 every optician has his own adaptation and method of employing the same4 ,for the measurement of bacteria1 a stage micrometer should be used with a camera lucida4 ,the stage micrometer consists of a slip of thin glass ruled with a scale consisting of tenths and hundredths of a millimetre4 ,the image is projected on to a piece of paper placed on the table1 and the drawing made1 and the object to be measured can be readily compared with the scale4 ,illustration3 ,fig4 #afg4--,the ,ramsden ,micrometer ,eye-piece4 ,in the ,ramsden micrometer eye-piece1 as previously explained1 two fine wires are stretched across the field of an eye-piece1 one of which can be moved by a micrometer screw4 ,in the field there is also a scale with teeth1 and the interval between them corresponds to that of the threads of the screw4 ,the circumference of the brass head is usually divided into one hundred parts1 and a screw with one hundred threads to the inch is used4 ,the bacterium to be measured is brought into a position in which an edge appears to be in contact with the fixed wire1 and the micrometer screw is turned until the travelling wire appears to be in contact with the other edge4 ,the scale in the field and scale on the milled head1 together1 give the number of complete turns of the screw and the value of a fraction of a turn in separating the wires4 ,in the micrometer eye-piece constructed by ,zeiss1 the eye-piece with a glass plate with crossed lines is carried across the field by means of a micrometer screw4 ,each division on the edge of a drum corresponds to #ja mm4 ,complete revolutions of the drum are counted by means of a figured scale in the visual field4 ,in the micrometer used with ,zeiss's apochromatic objectives and compensating eye-pieces the divisions are so computed1 that1 with a tube-length of #afj mm41 the value of one interval represents1 with each objective1 just as many micra 7#jjja mm47 as there are millimetres in its focal length4 ,a value of tables is therefore not required for these eye-pieces1 since the focus of the lenses indicates their micrometer values within #e per cent4 ,illustration3 ,fig4 #afh4--,the ,wollaston ,camera ,lucida4 ,the ,camera ,lucida will prove an extremely useful adjunct to the micrometer1 and a large number of contrivances have been devised for its employment4 ,there are those which project the image on to the surface of a sheet of paper provided for the drawing1 and those which project the pencil and paper into the field of the microscope4 ,the former method is that usually adopted4 ,to draw an object1 with either a ,wollaston camera lucida or a neutral tint reflector1 such as that of ,beale's1 both of which are made to slide on and take the place of the cap of the eye-piece1 as shown in ,fig4 #afh1 with its flat side uppermost1 the whole instrument must be raised until the edge of the prism is exactly #aj inches from a piece of paper placed upon the table2 with the latter the instrument retains its vertical position1 and the image of the object is thrown on the paper placed in front of the stand4 ,the light must be so regulated that no more than is really necessary is upon the object1 whilst a full light should be thrown upon the paper4 ,only one eye is to be used2 and if one half of the pupil be directed over the edge of the prism1 the object will appear upon the paper1 and can be traced on it by a pencil1 the point of which will also be seen4 ,should any blueness be visible in the field1 the prism is pushed too far on1 and should be drawn back till the colour disappears4 ,illustration3 ,fig4 #afi4--,microscope in position for drawing4 ,illustration3 ,fig4 #agj4--;,beale's ,neutral ,tint ,reflector4 ,the position in which the microscope must be placed is shown in the accompanying illustration 7,fig4 #afi74 ,beale's neutral tint reflector 7,fig4 #agj7 is much in use1 and its advantages are utility1 simplicity1 and inexpensiveness4 ,illustration3 ,fig4 #aga4--,the ,abbe ,model ,camera ,lucida4 ,the ,abbe model of camera lucida has been brought into use because the projected image can be better illuminated1 and is consequently so much brighter4 ,this form is now made in aluminium by ,messrs4 ,watson ,sons4 ,in place of the image being traced by projection on paper1 the reverse is the case1 both the paper and pencil are projected into the field of view4 ,the mirror reflects the paper on to the silvered surface of a prism placed over the eye-lens of the eye-piece of the microscope1 and it is thereby conveyed to the eye4 ,there is a central opening in the silvering through which microscopic vision is obtained4 ,it is fitted in a new manner by means of a cloth-lined adapter1 fitting over the outside of the microscope tube2 this saves all trouble in centring and ensures concentricity4 ,where the instrument has capped eye-pieces1 the camera lucida must be adapted to the eye-piece1 the cap being removed4 ,the apparatus can be disconnected from the fitting adapter by means of a sliding pin1 and readily replaced1 or can be lifted over out of the way1 as shown in the drawing4 ,being made almost entirely in aluminium it is very much lighter than other forms of apparatus1 and does not cause vibration4 ,it can be used with the microscope at any angle1 the only necessity being that the paper on which the sketch is made should be kept at the same angle as the instrument4 ,micro-,photography4 ,micro-photography or photo-micrography1 as it is indifferently termed1 has1 to a very considerable extent1 superseded the use of the camera lucida for the delineation of images seen under the microscope4 ,i may claim to be among the first workers with the microscope 7#ahda7 to prove beyond a doubt that the camera could be made to render invaluable aid to the microscopist1 whereby a great saving of time might be effected1 and a drawing obtained with greater accuracy than that of the pencil of the draughtsman4 ,it was about #ahfd-e that ,dr4 ,woodward's earlier micro-photographs were first seen in ,london4 ,his skill in the manipulation of the microscope had been long known4 ,his first series of photographs of test diatoms created1 ,i remember1 quite a sensation2 they have probably never been surpassed4 ,these were taken by sun-light1 magnesium1 and electric-light4 ,i was the recipient of a series taken at a later date 7#ahgj71 and which1 bound in quarto volume1 are almost as perfect in definition as any of a later date taken by oil-immersion objectives4 ,the objectives used by ,dr4 ,woodward1 throughout1 were a #a_/h-;inch of ,wales's 7new series71 and a #a_/af-;inch immersion1 of ,powell ,lealand's1 especially produced for work with the camera4 ,the magnification varied from #hjj to #c1jjj diameters1 a frustule of ,grammatophora ,marina magnified #b1ejj1 and a scale of podura1 marked #c1jjj in my collection1 are equal in definition to those taken by a high-angle #a_/ab-;inch oil-immersion4 ,pathological specimens taken with lower powers are equally instructive1 a section of epithelial cancer showing both nuclei and cells with distinctness4 ,dr4 ,maddox in #ahfd was also experimentally engaged in the improvement of the processes of photography for the purpose of promoting the work of microscopists4 ,his labours were attended with great success4 ,to him we are indebted for the gelatine dry-plate process1 which gave a remarkable impetus to photography in general4 ,dr4 ,maddox has1 for a period extending over forty years1 diligently and successfully cultivated and promoted micro-photography4 ,among other workers to whom we are indebted for improvements in micro-photography ,i may mention ,wenham1 ,draper1 ,shadbolt1 ,highley1 ,koch1 ,sternberg1 ,pringle1 ,leitz1 and ,pfeiffer4 ,dr4 ,koch justly claims the credit of having extended the application of micro-photography to the delineation of bacteria4 ,a series of instructive micro-photographs were published by him in #ahgg4 ,the importance of the camera has become more manifest as the work of the bacteriologist has progressed4 ,koch strongly advocated micro-photography on the ground that illustrations1 especially of bacteria1 should be as true to nature as possible4 ,dr4 ,edgar ,crookshank holds the same opinion1 and in support of his views we have numerous illustrations of the bacteria given in his valuable 8,text-book of ,bacteriology40 ,but he does not disguise the truth that there are difficulties to be encountered1 the first of which is owing to the fact that the smallest and most interesting bacteria can only be made visible in animal tissues by staining4 ,this drawback has been very nearly overcome by the use of eosin-collodion4 ,with this medium1 and by shutting off portions of the spectrum by coloured glasses1 ,koch succeeded in obtaining photographs of bacteria1 which were stained with blue and red aniline dyes4 ,this method1 however1 introduced a disturbing element of another kind4 ,owing to the longer exposure required1 the results were wanting in definition1 attributable1 it was thought1 to vibrations of the apparatus produced by passing traffic1 or by assistants moving about over the floor of the laboratory4 ,koch nevertheless showed1 at the great meeting of the ,international ,medical ,association in ,london1 #ahha1 a series of micro-photographs of bacteria and tissue sections1 which were the admiration of all who saw them4 ,to meet a difficulty occasioned by the aniline dyes1 ,koch recommended that the preparations should be stained brown2 other experimenters found that preparations stained either yellow or yellowish-brown gave good photographic representations2 but it is by no means an easy matter to find a good differential stain of bacteria in the tissues1 as even ,bismarck brown is not entirely successful4 ,other bacteriologists have encountered similar difficulties at the outset4 ,hauser succeeded in showing the value of micro-photography in the production of pictures of impression preparations and colonies of bacteria in nutrient-gelatine4 ,but to give the general effect1 as well as faithfully reproduce the minute details in these preparations of bacteria by the aid of the pencil1 would in most cases create insurmountable difficulties1 except in the hand of the most accomplished draughtsman4 ,hauser employed ,gerlach's apparatus1 and ,schleusser's dry-plates1 and obtained his illumination by means of a small incandescent lamp1 which gave a strong white light4 ,the preparations so photographed were for the most part stained brown1 and mounted in the ordinary way in ,canada balsam4 ,in #ahhd1 ,van ,ermengen succeeded in photographing preparations of comma-bacilli stained with fuchsine and methyl violet4 ,these pictures afforded the first practical illustration of the value of iso-chromatic plates in micro-photography1 and their introduction marks a distinct era in the progress of micro-photography4 ,the iso-chromatic1 or more properly the ortho-chromatic1 dry-plate process was introduced because in photography blue or violet comes out almost or quite white1 while other colours1 yellow and red1 are represented by a sombre shade or even by black4 ,this is due to the want of equality of strength between the luminous and the actinic or chemical rays of light4 ,in other words1 the violet and blue rays are more chemically active than any other portion of the spectrum4 ,it was found1 then1 that if plates were coloured yellow with turmeric1 the blue and violet rays were intercepted1 and their actinism proportionately reduced4 8,in #ahha1 the so-called iso-chromatic plates were introduced4 ,the emulsion of bromide of silver and gelatine was stained with eosin1 and it was claimed that colours could be represented with their relative intensity2 chlorophyll and other stains have also been tried1 and by such methods the ordinary gelatine dry-plates can be so treated that they will reproduce various colours1 according to their relative light intensity1 and thus be rendered iso-1 or what is now known as ortho-chromatic40 ,apparatus and ,material4 ,apparatus and ,material used in micro-photography have1 from time to time1 been greatly varied by different workers1 some preferring to use the microscope in the vertical position with the camera superimposed or fitted on the eye-piece of the microscope tube2 others1 again1 prefer that both the microscope and the camera should be arrayed horizontally4 ,in another form the ordinary microscope is dispensed with and the objective stage and mirror are adapted to the front of the camera1 together with a suitable arrangement for holding the object4 ,lastly1 the camera is lain aside1 and an operating-room rendered impervious to light1 takes its place1 and the image is projected and focussed upon a ground glass screen held in its place by a separate support4 ,this method has been made practical since the introduction into microscopy by ,zeiss of the projection eye-piece4 ,it is well known that micro-photographs can be produced by employing these projection eye-pieces1 as well as for screen illustrations in the lecture-room4 ,illustration3 ,fig4 #agb4--,swift's ,horizontal ,apparatus4 ,with regard to the position of the microscope and camera1 the horizontal affords greater stability than the vertical1 and is on this account to be preferred4 ,the simplest apparatus consists of a camera fixed upon a base board1 four or five feet in length1 upon which the microscope can be clamped1 and which also carries the lamp and bull's-eye lens 7,fig4 #agb74 ,this arrangement ,i have found economical and useful4 ,no more elaborate arrangement is actually necessary4 ,sunlight is no doubt the best1 but a good paraffin lamp is a handy and available illuminant4 ,with the former1 and rapid plates1 a short exposure of three or four seconds1 even when high powers are used1 is found sufficient2 whereas1 with the paraffin lamp it will vary from three to ten minutes4 ,walmsley gives the following table for exposures with the lamp3-- #a-a_/b-;inch objective #c to #de seconds4 #b_/c-;inch #g to #ij #d_/aj-;inch #a_/b to #c minutes4 #a_/e-;inch #b to #g #a_/aj-;inch #d to #aj ,for micro-photography the following practical rules must be observed4 ,the sub-stage condenser may be dispensed with when low powers are used1 as well as the mirror1 and the lamp so placed that the image of the flat of the flame appears accurately adjusted in the centre of the field of the microscope4 ,the bull's-eye lens is so interposed1 that the image of the flame disappears1 and the whole field becomes equally illuminated with high powers2 the sub-stage achromatic condenser must be used1 and a greater intensity of illumination is obtained by placing the lamp-flame edgeways4 ,it is advisable to begin the practice of micro-photography with low powers1 and a trial experiment should be made with some well-known object as the blow-fly's tongue4 ,dr4 ,crookshank is of opinion that1 in the case of micro-organisms when their biological characters are studied under low powers of the microscope1 photographs are preferable1 because they give a more faithful representation of the object4 ,a micro-organism1 even under the highest powers of the microscope1 is so minute an object1 that to represent it in a drawing requires a very delicate touch1 and it is only too easy to make a picture which gives an erroneous impression to those who have not seen the original4 ,photography enables the scientific worker to record rapid changes1 and it is quite possible as the art advances we may find the film more sensitive than the human retina1 and that it will bring out details in bacteria which would be otherwise unrecognised4 ,the result1 therefore1 of experience is that in research laboratories it will come into more general use as a faithful and graphic method4 ,i cannot better bring these observations to a close than by giving a quotation from ,dr4 ,piersoll's practical method of obtaining micro-photographs4 ,the three essential conditions to ensure success in micro-photography are3--7#a7 ,satisfactory apparatus2 7#b7 good illumination2 7#c7 suitable preparations4 ,with high amplifications 7#a1jjj diameters and over71 the conditions are greatly changed by the approach to the limit both of the shortness of the focus of the objective and of the length of the camera which can be advantageously used2 for the first experience leads to the adoption of the #a_/ab-;inch1 for the second four feet is the limit1 since a given high amplification1 say #b1jjj diameters1 can be more satisfactorily and more conveniently obtained with a superior #a_/ab-;inch connection with suitable optical means to increase the initial magnifying power of the objective1 than with an unaided #a_/be-;inch lens1 and the plate removed to a greater distance4 ,until quite recently the various amplifiers offered the best means of increasing the power of an objective1 but the introduction of the projection-oculars of ,zeiss is an accessory piece of apparatus1 far superior to any older device4 ,these projection-oculars resemble ordinary microscopical oculars or eye-pieces only in general form and name1 being optically a projection-objective in connection with a collecting lens4 ,the new oil-immersion apochromatic lenses1 in combination with these projection-oculars1 form undoubtedly the more efficient equipment for high-power work2 it is as true for high-power photography as for microscopical observation in general1 that the best results are obtained with fine and necessarily expensive1 optical appliances4 ,if for the satisfactory study of the intimate structure of a cell1 or of a micro-organism1 the most improved immersion lenses are necessary1 it is to be expected that1 for the successful photography of the same1 tools at least as good are needed4 ,sunlight certainly affords the most satisfactory illumination whereby good micro-photographs can be obtained1 as well as for recording microscopical images4 ,that by good lamp-light fair impressions of objects under extreme magnification can be secured is encouraging1 but the negatives produced by such illumination seldom1 if ever1 possess the characteristics of a really good sunlight negative1 where the sharpest details are combined with an exquisite softness and harmony of half-tones4 ,if the mirror of the microscope be of good size1 it will only be necessary to make an arm on which to support the removed mirror outside some southerly exposed window1 since it is desirable to have a greater distance between the mirror and the stage than would be possible were the mirror attached in its usual place4 ,where the microscope mirror is too small to be satisfactorily used1 a rectangular wood-framed looking-glass is readily mounted1 with the aid of a few strips of wood1 so as to turn about both axes4 ,the rays from the plane side of the mirror should pass through a condensing lens 7of #h-aj-;inch focus1 if possible71 so placed that they are brought to a focus before reaching the plane of the object4 ,the exact position of the condensing lens is a matter of experience2 usually1 however1 the most favourable illumination is obtained at that point where the field is brilliantly and uniformly illuminated1 just before the rays form the image source of light2 the nearer the focus the less disturbance from diffraction rings4 ,ordinary objectives will require the employment of monochromatic light--produced either by a deep blue solution of ammonia-sulphate of copper1 or by the green glass screen--since the optical and actinic foci do not usually perfectly coincide4 ,powers up to the #c_/d-;inch will require no further condenser2 with the #a_/d or #a_/f-;inch objectives1 the low power 7#a or #c_/d-;inch7 serves with advantage as an achromatic condenser1 when attached to the sub-stage4 ,the ,abbe condenser1 although so important for fine microscopical investigation1 is not adapted to photography unless a very wide cone of light is desired1 which1 for the majority of preparations1 is some advantage2 a low-power objective1 used as a condenser1 is found to be more satisfactory than the ,abbe with a small diaphragm4#cj ,the greatest delicacy in manipulation is necessary1 as in working with a #a_/ab-;inch objective a turn too much of the fine adjustment will cause the image to vanish4 ,with fine preparations of bacteria it is not easy to trace the image1 and hence the advantage of commencing with a well-marked object1 as that of the fly's tongue4 ,the development and fixation of the image must be proceeded with as in the ordinary photographic process4 ,in the text-books of photography full accounts of failures will be found1 their causes and prevention4 ,numerous papers and suggestions for micro-photographic work will also be found scattered throughout the 8,journal of the ,royal ,microscopical ,society40 ,the ,projection ,eye-piece has become an essential part of micro-photography1 and it is so arranged that it may be employed with advantage with objectives of either the apochromatic or ordinary series for photographic purposes1 projecting an exquisitely sharp image of the object on the plate4 ,a diaphragm between the lenses limits the field1 and a sharp image of it should appear on the screen when the eye-piece is adjusted4 ,the adjustment may be effected by revolving the eye-piece cap in a spiral slot1 so that the eye or top lens is either brought closer or removed farther away from the diaphragm1 as may be required1 and divisions and a reader are usually provided for registering positions4 ,such eye-pieces are made to fit any size microscope body4 ,initial magnifying powers3-- ,english length of tube #aj-;in4 #c and #f4 ,continental #f-;in4 #b and #d4 ,illustration3 ,fig4 #agc4--;,baker's ,pringle ,vertical ,micro-photographic ,apparatus4 ,the microscope and camera 7,fig4 #agc7 are here seen to be part of the same instrument4 ,the bellows of the camera have an extension varying from #f in4 to #cj in4 ,the board on which the microscope and limelight jet are fixed is made to turn out of the line of the camera to facilitate adjusting the instrument and radiant1 either limelight1 electric light or paraffin lamp2 when this is done the board carrying the same is turned back to a stop which brings the microscope into a central position with the focussing screen4 ,an adjustment is supplied at the side of the camera1 geared to the slow movement1 for finely focussing the object upon the screen4 ,a light-excluding connection is fitted to the front of the camera and microscope2 immediately behind this1 in the bellows1 is an exposing shutter which is manipulated by means of a small milled head4 ,two focussing screens are usually supplied1 one grey1 and one patent plate1 together with a double dark slide4 ,mr4 ,andrew ,pringle's vertical micro-photographic apparatus is an excellent form2 it consists of a heavy base and brass support1 carrying a quarter-plate camera1 grey and plain glass focussing screen1 double dark back1 camera extending to #bd inches1 and turning aside as shown in ,fig #agc4 ,it is light-tight in all its connections4 ,to secure uniform results in micro-photography1 only thin preparations1 which lie as nearly as possible in one plane1 can be relied upon for good and perfect negatives4 ,illustration3 ,fig4 #agd4--,ross's ,arc ,lamp4 ,an electric arc lamp specially designed for micro-photographic work1 wherever the electric current is available1 is that known as 8the ,ross-,hepworth projection arc lamp40 ,the advantage gained by this form of lamp is not only on account of the ease with which it may be employed1 but also on account of its superior power and quality4 ,it is of primary importance that the lamp employed to convert the electricity into light should be of a good and reliable pattern4 ,it is not essential that it should be automatic in its working--many experienced micro-photographers preferring a simple hand-feed lamp to the one of a more complicated kind1 being so much less difficult to keep in order4 ,a good hand-feed microscope-lamp has the advantage of greater simplicity and portability4 ,the argand gas-light arranged for me many years ago for micro-photography may be employed with advantage4 ,it is clean1 and always ready for use when brought down to the table attached by a piece of india-rubber tubing4 ,the incandescent form of burner enhances its value1 since the light is thereby rendered whiter4 ,the arrangement is shown in the diagrammatic drawing1 ,fig4 #age4 ,over the argand burner ,b1 is a pale-blue glass chimney1 resting on a wire gauze1 stage ,a2 this secures a uniform current of air4 ,the colour of the flame may be still more influenced by a disc of neutral tint1 or other coloured glass1 inserted into the circular opening at ,e1 in a half-cylinder of metal1 ,g1 used to cut off all extraneous light2 can be rotated on the stage by the ivory nob at ,h1 a metallic reflector ,i1 attached to the standard rod1 on being brought parallel to ,f serves to concentrate the light and send it on to the bull's-eye1 and through it to the mirror1 or directly to the photo-microscopic camera4 ,illustration3 ,fig4 #age4--,table ,incandescent ,gas-lamp4 ,by removing the shield ,g1 and bringing the shade ,m over the burner1 it is at once converted into a useful microscopical lamp1 for all ordinary purposes4 ,the screw ,r clamps the lamp-flame at any height1 while the support ,n carries a water-bath ,o1 or a plate ,p1 both of which will be found useful in preparing and mounting objects4 ,a special incandescent gas-lamp is made by ,messrs4 ,r4 ,j4 ,beck4 ,polarisation of ,light4 ,common light moves in two planes at right angles to each other1 while polarised light moves in one plane only4 ,common light may be turned into polarised light either by transmission or reflection2 in the first instance1 one of the planes of common light is got rid of by reflection2 in the other1 by absorption4 ,huyghens was one of the first physicists to notice that a ray of light has not the same properties in every part of its circumference1 and he compared it to a magnet or a collection of magnets2 and supposed that the minute particles of which it was said to be composed had different poles1 which1 when acted on in certain ways1 arranged themselves in particular positions2 and thence the term polarisation1 a term having neither reference to cause nor effect4 ,it is to ,malus1 however1 who1 in #ahjh1 discovered polarisation by reflection1 that we are indebted for the series of splendid phenomena which have since that period been developed2 phenomena of such surpassing beauty as to exceed most ordinary objects presented to the eye under the microscope4 ,certainly no more misleading name could well have been found to describe the causation1 in one particular direction1 of small displacements in the medium1 through which the light waves are made to pass4 ,the effect of 8polarising0 light is simply to alter the directions of the vibrations of light1 and allow of certain waves to pass which are vibrating in one direction only1 vertical1 horizontal1 or oblique1 as the case may be4 ,the most efficient agent discovered for the polarisation of light is that of ,iceland spar1 cut and mounted as a 8,nicol0 prism4 ,by cutting crystals of ,iceland spar into two parts1 at a particular angle1 and cementing them together again in the reverse way1 ,nicol succeeded in showing that one of the two polarising pencils could be totally deflected to one side1 while the other is directly transmitted through the ,nicol prism1 and thereby the beam of light becomes at once 8polarised0 in one plane only4 ,no apparent difference can be seen in the prism on holding it up to the light1 except it be in a very slight loss of brightness2 but if another similarly heated crystal be held before1 and made to revolve around1 a quarter of the circle just where the two cross each other1 total darkness results4 ,this phenomenon alternately recurs at every quadrature of the circle4 ,a pair of ,nicol prisms1 when appropriately mounted1 constitute 8a polarising apparatus0 for the microscope1 one being fitted into the sub-stage1 and the other either immediately above the objective or eye-piece1 where it can be easily rotated1 the object to be examined being placed on the stage of the microscope1 that is1 between the polarising and analysing prisms4 ,illustration3 ,,polariscope ,,objects4 ,tuffen ,west1 del4 ,edmund ,evans4 ,,plate ,,viii4 ,the significance of polarised light centres in the fact that it affords a wider insight into the structure of crystals1 minerals1 and a number of other substances1 and which could not otherwise be obtained without its aid4 ,its usefulness is multifold1 as even glass itself1 when not properly annealed1 exhibits points of fracture1 by a display of ,newton's rings4 ,the knowledge thus acquired is turned to account by glass manufacturers4 ,double refraction4--,when an incident ray of light is refracted into a crystal of any other than the cubic system1 or into compressed or unannealed glass1 it gives rise to two refracted rays which take different paths2 this phenomenon is termed double refraction4 ,attention was called to this in #afgj1 by ,bartolin1 who first observed it in ,iceland spar2 and the laws for this substance were accurately determined by ,huyghens4 ,iceland spar or calc spar is a form of crystallized carbonate of lime4 ,it is composed of fifty-six parts of lime and forty-four parts of carbonic acid1 and is usually found in rhombohedral forms of crystallization4 ,to observe the phenomenon of double refraction1 a rhomb of ,iceland spar may be laid on a page of a printed book1 when all the letters seen through it will appear double2 the depth of the blackness of the letters is seen to be considerably less than that of the originals1 except where the two images overlap4 ,in order to state the laws of the phenomena with precision1 it is necessary to attend to the crystalline form of ,iceland spar1 which has equal obtuse angles4 ,if a line be drawn through one of these corners1 making equal angles with the three edges which meet there1 it1 or any line parallel to it1 is called the axis of the crystal2 the axis being1 properly speaking1 not a definite line but a definite direction4 ,the angles of the crystals are the same in all specimens4 ,if the crystal is of such proportions that these three edges spoken of are equal1 as in the smaller crystal 7,fig4 #agf71 the axis is the direction of one of its diagonals1 as represented4 ,any plane containing 7or parallel to7 the axis is called the principal plane of the crystal4 ,in the next diagram1 ,fig4 #agg1 the line appears double1 as a b and c d1 or the dot1 as e and f4 ,or allow a ray of light1 g h1 to fall thus on the crystal1 it will in its passage through be separated into two rays1 h f1 h e2 and on coming to the opposite surface of the crystal1 will pass out at e f in the direction of i k1 parallel to g h4 ,the plane l m n o is designated the principal section of the crystal1 and the line drawn from the solid angle l to the angle o is where the axis of the crystal will be found2 this is its optic axis4 ,now when a ray of light passes along this axis1 it is undivided1 and there is only one image2 but in all other directions there are two images4 ,illustration3 ,fig4 #agf4--;,axis of ,crystals of ,iceland ,spar4 ,illustration3 ,fig4 #agg4--;,a ,rhomb showing the passage of ,rays of ,light4 ,mr4 ,nicol1 of ,edinburgh first succeeded in making a rhomb of ,iceland spar into a single-image prism4 ,his method of splitting up the crystal into two equal parts was as follows3-- ,a rhomb of ,iceland spar of one-fourth of an inch in length1 and about four-eighths of an inch in breadth and thickness1 is divided into two equal portions in a plane1 passing through the acute lateral angle1 and nearly touching the obtuse side angle4 ,the sectional plane of each of these halves must be carefully polished1 and the two portions cemented firmly together with ,canada balsam1 so as to form a rhomb similar to that before division2 by this management the ordinary and extraordinary rays are so separated that only one is transmitted3 the cause of this great divergence of the rays is considered to be owing to the action of the ,canada balsam1 the refractive index of which 7#aedi7 is that between the ordinary 7#afedc7 and the extraordinary 7#adhcc7 refraction of calcareous spar1 and which will change the direction of both rays in an opposite manner before they enter the posterior half of the combination4 ,the direction of rays passing through such a prism is indicated by the arrow1 ,fig4 #agh4 ,illustration3 ,fig4 #agh4 ,polarised light cannot be distinguished from common light1 as already said1 by the naked eye2 and for all experimental purposes in polarisation1 two pieces of apparatus must be employed1 one to produce polarisation1 and the other to show or an analyse it4 ,the former is called the polariser1 the latter the analyser2 and every apparatus that serves for one of these purposes will also serve for the other4 ,illustration3 ,fig4 #agi4--,polariser4 ,illustration3 ,fig4 #agi;a4--,analyser4 ,polarising ,apparatus for ,students' ,microscope4 ,in all cases there are two positions1 differing by #ahj1 which give a minimum of light1 and the two positions intermediate between these give a maximum of light4 ,the extent of the changes thus observed is a measure of the completeness of the polarisation of light4 ,the two prisms mounted as shown in ,figs4 #agi and #agi;a constitute the apparatus adapted to the microscope4 ,the polariser slips into place below the stage1 and the analyser1 with the prism fixed in a tube1 is screwed in above the objective4 ,the definition is considered by some experimenters as somewhat better if the analyser be used above the eye-piece1 and is certainly more easily rotated4 ,illustration3 ,fig4 #ahj4--,prism mounted as an ,eye-piece4 ,method of employing the ,polarising ,prism 7,fig4 #agi74--;,after having adapted it to slide into a groove on the under-surface of the stage1 where it is secured and kept in place by the small milled-head screw1 the other prism 7,fig4 #agi;a7 is screwed on above the object-glass1 and thus passes directly into the body of the microscope4 ,the light from the mirror having been reflected through them the axes of the two prisms must be made to coincide2 this is done by regulating the milled-head screw until1 by revolving the polarising prism1 the field of view is entirely darkened twice during its revolution4 ,if very minute salts or crystals are submitted for examination then it will be found preferable to place the analyser above the eye-piece1 as in ,fig4 #ahj4 ,thus the polariscope is seen to consist of two parts2 one for polarising1 the other for analysing or testing the light4 ,there is no essential difference between the two parts1 except what convenience or economy may lead us to adopt2 and either part1 therefore1 may be used as polariser or analyser2 but whichever is used as the polariser1 the other becomes the analyser4 ,illustration3 ,fig4 #aha4--,more ,modern ,polariser and ,analyser4 ,opticians have their own methods of adapting the polariser and analyser to their several microscopes4 ,watson's special form of apparatus is represented in ,fig4 #aha1 the polariser being adapted to the sub-stage1 and the analyser to screw into the objective4 ,tourmaline4--,a semi-transparent mineral1 of a neutral or bluish tint1 called tourmaline1 when cut into thin slices 7about #a_/bj-;inch thick7 with their faces parallel to their axes exhibit the same phenomena as the ,nicol prism4 ,the only objection to which is that the transmitted polarised beam is more or less coloured4 ,the tourmaline to be preferred stops the most light when its axis is at right-angles to that of the polariser1 and yet admits the most when in the same plane4 ,make choice of a tourmaline as perfect as possible2 size is of less importance when intended for use with the microscope4 ,transmission of rays through tourmaline is only one of several ways in which light can be polarised4 ,when a beam of light is reflected from a polished surface of glass1 wood1 ivory1 leather1 or any other non-metallic substance1 at an angle of #ej to #fj with the normal1 it is more or less polarised1 and in like manner a reflector composed of any of these substances may be employed as an analyser4 ,in so using it1 it should be rotated about an axis parallel to the incident rays which are to be tested1 and the observation consists in noting whether this rotation produces changes in the amount of reflected light4 ,for every reflected substance there is a particular angle of incidence1 which gives a maximum of polarisation in reflected light4 ,it is called the polarising angle for the substance1 and its tangent is always equal to the index of refraction of the substance2 or1 what amounts to the same thing1 it is that particular angle of incidence which is the complement of the angle of refraction1 so that the refracted rays are at right angles4 ,this important law was discovered experimentally by ,sir ,david ,brewster4 ,tourmaline1 like ,iceland spar1 is a negative uniaxial crystal2 and its use as a polariser depends on the property which it possesses of absorbing the ordinary much more rapidly than the extraordinary ray1 so that a thickness which is tolerably transparent to the latter is almost completely opaque to the former4 ,its pale cobalt blue colour enhances the beauty of certain crystal and mineral substances1 but like ,iceland spar1 the paler and more perfect crystals are becoming scarce4 ,selenite is another mineral of value in polarisation experiments4 ,it is a native crystalline hydrated sulphate of lime4 ,a beautiful fibrous variety called satin-gypsum is found in ,derbyshire4 ,the form of the crystal most frequently met with is that of an oblique rectangular prism1 with ten rhomboidal faces1 two of which are much larger than the rest4 ,it is usually split up into thin lamin parallel to their lateral faces2 each film should have a thickness of from one-twentieth to one-sixtieth of an inch4 ,in the two rectangular directions these films allow perpendicular rays of polarised light to traverse them unchanged1 termed their neutral axes4 ,in two other directions1 however1 which form respectively angles of #de with the neutral axes1 these films have the property of double refraction1 a direction known as the depolarising axis4 ,illustration3 ,fig4 #ahb4--;,darker's ,selenite ,films and ,stage4 ,the thickness of the film of selenite determines the particular tint4 ,if1 therefore1 we use a film of irregular thickness1 different colours are presented by the different thicknesses4 ,these facts admit of very curious and beautiful illustration1 when used under the object placed on the stage of the microscope4 ,the films employed should be mounted between two glasses for protection4 ,some persons employ a large film1 mounted in this way between the plates of glass1 with a raised edge1 to act as a stage for supporting the object1 it is then called the 8selenite stage40 ,the best film for the microscope is that which gives blue1 and its complementary colour yellow4 ,the late ,mr4 ,darker constructed a selenite stage for the purpose 7,fig4 #ahb74 ,with this a mixture of colours will be brought about1 by superimposing three films1 one on the other4 ,by slight variations in their positions1 produced by means of an endless-screw motion1 all the colours of the spectrum can be shown4 ,when objects are thus exhibited1 it should be borne in mind that all negative tints1 as they are termed1 are diminished1 and all positive tints increased2 the effect of which is to mask the true character of the phenomena4 ,for a certain thickness of selenite the ellipse will become a circle1 and we have thus what is called circularly-polarised light1 which is characterised by the property that rotation of the analyser produces no change of intensity4 ,circularly-polarised light is not1 however1 identical with ordinary light2 for the interposition of an additional thickness of selenite converts it into elliptically 7or in a particular case into plane7 polarised light4 ,it is necessary1 for the exhibition of colour in our experiments1 that the plate of selenite should be very thin1 otherwise the retardation of one component vibration as compared with the other will be greater by several complete periods for violet than for red1 so that the ellipses will be identical for several different colours1 and the total non-suppressed light will be sensibly white in all positions of the analyser4 ,two thick plates may1 however1 be so combined as to produce the effect of one thin plate4 ,for example1 two selenite plates of nearly equal thickness may be laid one upon the other1 so that the direction of greatest elasticity in the one shall be parallel to that of least elasticity in the other4 ,the resultant effect in this case will be that due to the difference of their thicknesses4 ,two plates so laid are said to be crossed4 ,illustration3 ,fig4 #ahc4--,red is represented by perpendicular lines2 ,green by oblique4 ,the following experiments will well serve to illustrate some of the more striking phenomena of double refraction1 and will also be a useful introduction to its practical application4 ,take a plate of brass 7,fig4 #ahc7 three inches by one1 perforated with a series of holes from about one-sixteenth to one-fourth of an inch in diameter2 the size of the smallest should be in accordance with the power of the objective1 and the separating power of the double refraction4 ,experiment #a4--,place the brass plate so that the smallest hole shall be in the centre of the stage of the microscope2 employ a low power 7#a-a_/b or #b inches7 objective1 and adjust the focus as for the ordinary microscopic object2 place the double image prism over the eye-piece1 and two distinct images will be seen2 by revolving the prism1 the images will describe a circle1 the circumference of which will cut the centre of the field of view2 one of which is the ordinary1 the other the extraordinary ray4 ,by moving the slide from left to right the larger orifices will appear in the field1 the images seen will not be completely separated1 but will overlap1 as represented in the figure4 ,experiment #b4--;,insert the ,nicol's prism into its place under the stage1 still retaining the double image prism over the eye-piece2 then1 by examining the object1 there will appear in some positions two images1 in others only one image2 it will be seen1 that at #ij this ray will be cut off1 and that which was first observed will become visible2 at #ahj1 or one-half the circle1 an alternate change will take place2 at #bgj1 another change2 and at #cfj1 the completion of the circle1 the first image will reappear4 ,before proceeding to make the next experiment1 the position of the ,nicol's prism should be adjusted1 and its angles brought parallel with the square of the stage4 ,the true relative position of the selenite should also be determined by noticing the natural flaws in the film1 which should run parallel with each other1 and be adjusted at an angle of about #df with the square bars of the stage4 ,experiment #c4--;,if we now take the plate of selenite thus prepared1 and place it under the piece of brass on the stage1 we shall see1 instead of the alternate black and white images1 two coloured images composed of the constituents of white light1 which will alternately change by revolving the eye-piece at every quarter of the circle2 then1 by passing along the brass1 the images will overlap2 and at the point at which they do so1 white light will be produced4 ,if1 by accident1 the prism be placed at an angle of #de from the square part of the stage1 no particular colour will be perceived1 and it will then illustrate the phenomena of the neutral axis of the selenite1 because when placed in the relative position no depolarisation takes place4 ,the phenomena of polarised light may be further illustrated by the addition of a second double image prism1 and a film of selenite adapted between the two4 ,the systems of coloured rings in crystals cut perpendicularly to the principal axis of the crystal are best seen by employing the lowest object-glass4 ,biaxial ,crystals4--,to show perfectly the beautiful series of rings and brushes which biaxial crystals exhibit1 it becomes necessary to convert the microscope1 for the time being1 into 7so to speak7 a wide-angled telescope4 ,illustration3 ,huyghenian ,eye-piece4 ,inner draw-tube4 ,objective in draw-tube4 ,analysing ,prism4 ,objective4 ,specimen under ,examination4 ,sub-stage ,condenser4 ,polarising ,prism1 fixed in sub-stage below4 ,fig4 #ahd4--;,diagrammatic arrangement of the ,polarising ,microscope4 ,in ,sub-stage3 ,p1 polarising prism2 ,c1 sub-stage condenser on stage2 ,m1 mineral or crystal4 ,on nose-piece3 ,o#a1 objective1 #d_/aj-;inch2 ,a1 analysing prism4 ,in ,draw-tube3 ,o#b1 #b or #c inch ,objective2 ,h1 ,huyghenian eye-piece4 ,for the purpose1 screw on a low-power objective to the end of the draw-tube 7,fig4 #ahd74ca ,as the light requires to be passed through the crystals at a considerable angle1 a wide-angled condenser should be employed1 but it need not be achromatic4 ,the objective most suitable is a #d_/aj-;inch1 of #fd numerical aperture1 but a #a_/d-;inch of #ga numerical aperture1 or a #a_/c-;inch of #fe numerical aperture1 will answer the purpose equally well4 ,as the whole of the back lens of the objective should be visible through the analysing ,nicol prism1 the back lens of the objective must not be too large2 thus a #a_/b-;inch of #fe numerical aperture will not be so effective4 ,the analysing prism may be placed either where it is in the drawing1 below the stage1 or above the eye-piece4 ,it works equally well above the objective1 the position it ordinarily occupies in the microscope4 ,for the draw-tube a #b-;inch objective and a ,b ,huyghenian eye-piece answers very well4 ,before screwing the objective on to the end of the draw-tube centre the light in the usual manner1 the ,nicol's being turned so as to give a light field1 then screw the objective on to the end of the aperture1 and put the crystal on the stage1 rack down the body so that the objective on the nose-piece nearly touches the crystal1 then focus with the draw-tube only4 ,the sub-stage condenser should be racked up close to the underside of the crystal4 ,opticians1 however1 have more recently furnished a special form of microscope 7,the ,petrological ,microscope1 ,fig4 #gi1 p4 #aab71 for the use of those students who may desire to prosecute so fascinating a study1 and determine the optic axial angles of crystals4 ,fuess#cb lately introduced a new form of microscope for polarising and viewing biaxial crystals1 which he believes to be needed1 as in the ordinary microscope the opening of the polariser is scarcely a third of that of the condenser2 moreover1 it is not absolutely necessary that the polariser and analyser should be ,nicol's prisms4 ,this fact was discovered by myself many years ago4 ,fuess utilises a bundle of thin glass plates1 as in the older ,nuremberg polariscope4 ,the frame holding plates can be readily adjusted at the proper polarising angle1 the analyser being the ordinary small ,nicol1 screwed above the objective4 ,the illuminator is an ,abbe's triple condenser1 of numerical aperture #adj1 which can be adjusted in the ordinary way4 ,the front lens of this should have a diameter of #aaab mm4 and the lower lens of #cj mm4 ,this increase in the condenser fully compensates for the loss of light by the bundle of glass plates1 and also enables thick sections of crystals to be examined in convergent polarised light4 ,the ocular used should have a large field2 the ,a ,huyghenian answers best4 ,a suggestion to return to the original ,nuremberg polariser is very opportune1 as ,iceland spar is becoming scarce4 ,mr4 ,a4 ,mickel accidentally discovered that an opalescent mirror can be converted into an excellent and inexpensive substitute for the ,nicol-prism polariser4 ,rotation of ,plane of ,polarisation4 ,when a plate of quartz 7rock-crystal71 even of considerable thickness1 cut perpendicular to the axis1 is interposed between the polariser and analyser1 colour is exhibited1 the tints changing as the analyser is rotated2 and similar effects of colour are produced by employing1 instead of quartz1 a solution of sugar enclosed in a tube with plain glass ends4 ,the action thus exerted by quartz and sugar is called rotation of the plane of polarisation1 a name which sufficiently expresses the observed phenomena4 ,in the case of ordinary quartz1 and solutions of sugar-candy1 it is necessary to rotate the analyser in the direction of watch-hands as seen by the observer1 and the rotation of the plane of polarisation is said to be right-handed4 ,in the case of what is called left-handed quartz1 and of solutions of non-crystallisable sugar1 the rotation of the plane of polarisation is in the opposite direction1 and the observer must rotate the analyser against watch-hands4 ,quartz belongs to the uniaxial system of crystals1 and accordingly exhibits one series of rings only1 and no perfect central black cross4 ,on revolving the tourmaline the colour gradually changes1 and passes through all the colours of the spectrum4 ,it can be cut to exhibit either right-handed polarisation or left-handed polarisation and also to exhibit straight lines4 ,calc ,spar4--,a uniaxial crystal showing only one system of rings1 and a black cross1 changing into a white cross on revolving the tourmaline4 ,topaz4--,a biaxial crystal exhibiting only one system of rings with one fringe1 owing to the wide separation of the axes4 ,the fringe and colours change on revolving the tourmaline4 ,borax4--,a biaxial crystal2 the colours are seen to be more intense than in topaz1 but the rings not so complete--only one set of rings can be seen1 owing to their wide separation4 ,rochelle ,salt4--,a biaxial crystal2 the colours are more widely spread out than the former1 and only one set of rings seen at the same time4 ,carbonate of ,lead4--,a biaxial crystal2 axes not so far separated1 and both systems of rings are more widely spread than those of potassium nitrate4 ,aragonite4--,a biaxial crystal2 axes widely separated1 but both systems of rings seen at the same time4 ,a fine crystal for displaying the biaxial system4 ,illustration3 ,fig4 #ahe4--;,crystal of ,potassium ,nitrate4 ,it was long believed that all crystals had only one axis of double refraction2 but ,brewster found that the greater number of crystals which occur in the mineral kingdom have two axes of double refraction1 or rather axes around which double refraction takes place2 in the axes themselves there is no double refraction4 ,potassium nitrate crystallises in six-sided prisms with angles of about #abj4 ,it has two axes of double refraction4 ,these axes are each inclined about #b-a_/b to the axes of the prism1 and #e to each other4 ,if1 therefore1 a small piece be split off a prism of potassium nitrate with a knife driven by a sharp blow of a hammer1 and the two surfaces polished perpendicular to the axes of the prism1 so as to leave the thickness of the sixth or eighth of an inch1 and then a ray of polarised light be transmitted along the axes of the prism1 the double system of rings will be clearly visible4 ,when the line connecting the two axes of the crystal is inclined #de to the plane of primitive polarisation1 a cross is seen on revolving the potassium nitrate2 it gradually assumes the form of two hyperbolic curves1 as in ,fig4 #ahe4 ,but if the tourmaline be again revolved through half a quadrant1 the black cross will be replaced by white spaces1 as in the second figure4 ,these systems of rings have1 generally speaking1 the same colours as those of thin plates1 or as those of a system of rings revolving around one axis4 ,the orders of the colours commence at the centres of each system2 but at a certain distance1 which corresponds to the sixth ring1 the rings1 instead of returning and encircling each pole1 encircle the two poles as an ellipse does its two foci4 ,if the thickness of the plate of nitre be diminished or increased1 the rings are diminished or increased according to the thickness of the crystal4 ,small specimens of various salts may be crystallised and mounted in ,canada balsam for viewing under the stage of the microscope2 by arresting crystallisation at certain stages1 a greater variety of forms and colours will be obtained3 we may enumerate salicine1 asparagine1 acetate of copper1 phospho-borate of soda1 sugar1 carbonate of lime1 potassium chlorate1 oxalic acid1 and all the oxalates found in urine1 with the other salts from the same fluid1 a few of which are shown in ,plate ,,viii4 ,the late ,dr4 ,herapath described a salt of quinine1 remarkable for its polarising properties4 ,the crystals of this salt1 when examined by reflected light1 have a brilliant emerald-green colour1 with almost a metallic lustre2 they appear like portions of the elytr of the cantharides beetle1 and are also very similar to murexide in appearance4 ,when examined by transmitted light1 they scarcely possess any colour1 there is only a slightly olive-green tinge2 but if two crystals1 crossing at right-angles1 be examined1 the spot where they intersect appears perfectly black1 even if the crystals are not more than one five-hundredth of an inch in thickness4 ,if the light be in the slightest degree polarised--as by reflection from a cloud1 or by the blue sky1 or from the glass surface of the mirror of the microscope placed at the polarising angle #fe #de--these little prisms and films assume complementary colours3 one appears green1 and the other pink1 and the part at which they cross is chocolate or deep chestnut-brown1 instead of black4 ,dr4 ,herapath succeeded in making artificial tourmalines large enough to surmount the eye-piece of the microscope2 so that all experiments with those crystals upon polarised light may be made without the tourmaline or ,nicol's prism4 ,the finest rosette crystals are made as follows3--,to a moderately strong solution of ,cinchonidine add a drop or two of ,herapath's test-fluid4#cc ,a few drops of this is placed on the centre of a glass slide1 and put aside until the first crystals are observed to be formed near the margin4 ,the slide should now be placed upon the stage of the microscope1 and the progress of formation of the crystals closely watched4 ,when these are seen to be large enough1 and it is deemed necessary to stop their further development1 the slide must be quickly transferred to the palm of the hand1 the warmth of which will be found sufficient to stop further crystallisation4 ,these crystals attract moisture1 deliquesce1 and should therefore be kept in a perfectly dry place4 ,illustration3 ,fig4 #ahf4--;,in this figure heraldic lines are adopted to denote colour4 ,the dotted parts indicate yellow1 the straight lines red1 the horizontal lines blue1 and the diagonal1 or oblique lines1 green4 ,the arrows show the plane of the tourmaline1 a1 blue stage2 b1 red stage of selenite employed4 ,to render these crystals evident1 it merely remains to bring the glass-slide upon the field of the microscope1 with the selenite stage and single tourmaline1 or ,nicol's prism1 beneath it2 instantly the crystals assume the two complementary colours of the stage3 red and green1 supposing that the pink stage is employed2 or blue and yellow1 provided the blue selenite is made use of4 ,all those crystals at right angles to the plane of the tourmaline produce that tint which an analysing-plate of tourmaline would produce when at right angles to the polarising-plate2 whilst those at #ij to these educe the complementary tint1 as the analysing-plate would also have done if revolved through an arc of #ij4 ,this test is a delicate one for quinine 7,fig4 #ahf1 a and b72 not only do these peculiar crystals act in the way just related1 but they may be easily proved to possess the optical properties of that remarkable salt1 the sulphate of iodo-quinine4 ,illustration3 ,fig4 #ahg4--,polarised ,crystals of ,quinidine4 ,to test for quinidine1 it is merely necessary to allow a drop of acid solution to evaporate to dryness upon the slide1 and to examine the crystalline mass by two tourmalines1 crossed at right angles1 and without the stage4 ,immediately little circular discs of white1 with a well-defined black cross1 start into existence1 should quinidine be present even in very minute traces4 ,these crystals are represented in ,fig4 #ahg4 ,if the selenite stage be employed in the examination of this object1 one of the most gorgeous appearances in the whole domain of the polarising microscope is displayed3 the black cross disappears1 and is replaced by one consisting of two colours1 and divided into a cross having a red and green fringe1 whilst the four intermediate sectors are a gorgeous orange-yellow4 ,these appearances alter on the revolution of the analysing-plate of tourmaline2 when the blue stage is employed1 the cross assumes a blue or yellow tint1 varying according to the position of the analysing plate4 ,these phenomena are analogous to those exhibited by certain circular crystals of boracic acid1 and to circular discs of salicine 7prepared by fusion71 the difference being that the salts of quinidine have more intense depolarising powers than either of the other substances2 the mode of preparation1 however1 excludes these from consideration4 ,quinine prepared in the same manner as quinidine has a very different mode of crystallisation2 but it occasionally presents circular corneous plates1 also exhibiting the black cross and white sectors1 but not with one-tenth part of the brilliancy1 which of course enables us readily to discriminate the two4 ,illustration3 ,fig4 #ahh4--,urinary ,salts1 seen under ,polarised ,light4 a1 ,uric acid2 b1 ,oxalate of lime1 octahedral crystals of2 c1 ,oxalate of lime allowed to dry1 forming a black cube2 d1 ,oxalate of lime as it occasionally appears1 termed the dumb-bell crystal4 ,urinary salts are more readily seen under polarised light than by white light4 ,ice doubly refracts1 while water singly refracts4 ,ice takes the rhomboidic form2 and snow in its crystalline forms may be regarded as the skeleton crystals of this system 7,fig4 #ahi74 ,a sheet of clear ice1 of about one inch thick1 and slowly formed in still weather1 shows circular rings with a cross by polarised light4 ,illustration3 ,fig4 #ahi4--,snow ,crystals4 ,it is probable that the conditions of snow formation are more complex than might be imagined1 familiar as we are with the conditions relating to the crystallisation of water on the earth's surface4 ,a great variety of animal1 vegetable1 and other substances possess a doubly refracting or depolarising structure1 as3 a quill cut and laid out flat on glass2 the cornea of a sheep's eye2 skin1 hair1 a thin section of a finger-nail2 sections of bone1 teeth1 horn1 silk1 cotton1 whalebone2 stems of plants containing silica or flint2 barley1 wheat1 c4 ,the larger-grained starches form splendid objects2 tous-les-mois1 the largest1 may be taken as a type of all others4 ,this presents a black cross1 the arms of which meet at the hilum 7,fig4 #aij74 ,on rotating the analyser1 the black cross disappears1 and at #ij is replaced by a white cross2 another1 but much fainter1 black cross is seen between the arms of the white cross1 no colour being perceptible4 ,but if a thin plate of selenite be interposed between the starch-grains and the polariser1 a series of delicate colours appear1 all of which change on revolving the analyser1 becoming complementary at every quadrant of the circle4 ,west and ,east ,india arrow-root1 sago1 tapioca1 and many other starch-grains1 present a similar appearance2 but in proportion as the grains are smaller1 so are their markings and colourings less distinct4 ,illustration3 ,fig4 #aij4--,potato ,starch1 under ,polarised ,light4 ,molecular ,rotation4 ,for the purpose of studying the various interesting phenomena of molecular rotation1 a few necessary pieces of apparatus must be added to the microscope4 ,first1 an ordinary iron three-armed retort stand1 to the lower arm of which must be attached either a polarising prism or a bundle of glass plates inclined at the polarising angle2 in the upper an analysing prism4 ,the fluid to be examined should be contained in a narrow glass tube about eight inches in height1 and this must be attached to the middle arm4 ,if the prisms be crossed before inserting a fluid possessing rotatory power1 the light passing through the analyser will be coloured4 ,if a solution of sugar be employed1 and the light which passes through the second prism is seen to be red1 but on rotating the analyser towards the right the colour changes to yellow1 and passes through green to violet1 it may be concluded that the rotation is right-handed4 ,if1 on the contrary1 the analyser requires to be turned towards the left hand1 we conclude that the polarisation is left-handed4 ,these phenomena are wholly distinct from those accompanying the action of doubly refracting substances upon plane polarised light4 ,it is not easy to explain in a limited space the course to be followed in ascertaining the amount of rotation produced by different substances4 ,monochromatic light should be used4 ,if we are about to examine a sugar solution with the prisms crossed1 the index attached to the analyser must first be made to point to zero4 ,the sugar is then introduced1 when it will be necessary to rotate the analyser #bc to the right1 in order that the light may be extinguished4 ,this is the amount of rotation for that particular fluid at a given density and that height of column4 ,as the arc varies with increase or decrease of density and height of the fluid1 it is needful to reduce it to a unit of height and density4 ,the following formula is that given by ,biot3--,p quantity of matter in a unit of solution2 d sp4 gr42 l length of column2 a arc of rotation2 m molecular rotation4 ,then m a_/7l p d74 ,the application of the polarising apparatus to the microscope is of much value in determining minute structure4 ,it may also be defined as an instrument of analysis2 a test of difference in density between any two or more parts of the same substance4 ,all structures1 therefore1 belonging either to the animal1 vegetable1 or mineral kingdom1 in which the power of unequal or double refraction is suspected to be present1 are those that should especially be re-investigated by polarised light4 ,some of the most delicate of the elementary tissues of animal structure1 the ultimate fibrill of muscles1 c41 are amongst the most interesting subjects that might be studied with advantage under this method of investigation4 ,the chemist may perform the most dexterous analysis2 the crystallographer may examine crystals by the nicest determination of their forms and cleavage2 the anatomist or botanist may use the dissecting knife and microscope with the most exquisite skill2 but there are still structures in the mineral1 vegetable1 and animal kingdoms which will defy all such modes of examination1 and will yield only to the magical analysis of polarised light4 ,formation and ,polarisation of ,crystals4 ,the inorganic kingdom will afford to the microscopist a never-ending number of objects of unsurpassed beauty and interest4 ,the phenomena of crystallisation in its varied combinations can be made a useful and instructive occupation4 ,although ignorant of the means whereby the great majority of minerals and crystals have been formed in the vast laboratory of ,nature1 we can1 nevertheless1 imitate in a small degree ,nature's handiworks by crystallising out a large number of substances1 and watch their numerous transformations in the smallest appreciable quantities1 when aided by the microscope4 ,among natural crystals we look for the material for the formation of our lenses1 while the varieties of granites present us with the earliest crystallised condition of the earth's crust as it cooled down1 the structure of which is beautifully exhibited under polarised light4 ,in ,plate ,,viii4 various crystalline and other bodies are displayed4 ,in ,no4 #aeh is a section of new red sandstone2 #aei of quartz2 and #afj of granite4 ,special reference is made to others in the following list of salts and other substances which form a beautiful series of objects for study under polarised light3-- ,,salts4 ,alum4 ,asparagine4 ,aspartic ,acid4 ,plate ,,viii4 ,no4 #afh4 ,bitartrate of ,ammonia4 ,boracic ,acid4 ,borax4 ,no4 #afd4 ,carbonate of ,lime4 ,soda4 ,chlorate of ,potash4 ,chloride of ,barium4 ,cobalt4 ,copper and ,ammonia4 ,sodium4 ,cholesterine4 ,chromate of ,potash4 ,cinchonine4 ,cinchonidine4 ,citric ,acid4 ,hippuric ,acid4 ,iodide of ,mercury4 ,potassium4 ,quinine4 ,iodo-disulphate of ,quinine4 ,kreatine4 ,no4 #aff4 ,murexide4 ,nitrate of ,bismuth4 ,barytes4 ,brucine4 ,copper4 ,potash4 ,strontian4 ,uranium4 ,oxalate of ,ammonia4 ,chromium4 ,chromium and ,potash4 ,lime4 ,soda4 ,indurated ,sandstone1 ,howth4 ,indurated ,sandstone1 ,bromsgrove4 ,gibraltar ,rock4 ,granite1 various localities4 ,no4 #afj4 ,hornblend ,schist4 ,labrador ,spar4 ,norway ,rock4 ,quartz ,rock1 various4 ,no4 #aei4 in ,bog ,iron ,ore4 ,quartzite1 ,mont ,blanc4 ,sandstone4 ,no4 #aeh4 ,satin ,spar4 ,selenites1 various colours4 ,tin ,ore1 with ,tourmalin4 ,oxalic ,acid4 ,oxalurate of ,ammonia4 ,permanganate of ,potash4 ,phosphate of ,lead and ,soda4 ,platino-cyanide of ,magnesia4 ,plumose ,quinidine4 ,prussiate of ,potash1 red and yellow4 ,quinidine4 ,santonine4 ,salicine4 ,salignine4 ,no4 #afb4 ,sulphate of ,cadmium4 ,copper4 ,no4 #afa4 ,copper and ,potash4 ,iron4 ,no4 #afc4 ,iron and ,cobalt4 ,no4 #afe4 ,magnesia4 ,nickel and ,potash4 ,soda4 ,zinc4 ,sugar4 ,tartaric ,acid4 ,thionurate of ,ammonia4 ,triple ,phosphate4 ,urate of ,ammonia4 ,soda4 ,urea1 and most urinary deposits4 ,uric ,acid4 ,,minerals4 ,agates1 various4 ,asbestiform ,serpentine4 ,avanturine4 ,carbonate of ,lime4 ,carrara ,marble4 ,,animal ,,structures4 ,cat's ,tongue4 ,no4 #agd4 ,grayling ,scale4 ,no4 #agf4 ,holothuria1 ,spicules of4 ,nos4 #aga-b4 ,prawn ,shell4 ,no4 #age4 ,,vegetable ,,crystalline ,,substances4 ,,cuticle of ,leaf of ,correa ,cardinalis4 ,deutzia scabra4 ,no4 #agc4 ,elagnus4 ,onosma taurica4 ,equisetum4 ,no4 #agj4 ,fibro cells from orchid4 ,no4 #afi4 ,oncidium bicallosum4 ,scalariform ,vessels from ,fern4 ,scyllium ,caniculum4 ,no4 #agg4 ,,silicious ,,cuticles1 various4 ,starches1 various4 ,no4 #afg4 ,the formation of artificial crystal may be readily effected1 and the process watched1 under the microscope1 by simply placing a drop of saturated solution of any salt upon a previously warmed slip of glass4 ,interesting results will be obtained by combining two or more chemical salts in the following manner4 ,to a nearly saturated solution of the sulphate of copper and sulphate of magnesia add a drop on the glass-slide1 and dry quickly4 ,to effect this1 heat the slide so as to fuse the salts in its water of crystallisation1 and there remains an amorphous film on the hot glass4 ,put the slide aside and allow it to cool slowly2 it will gradually absorb a certain amount of moisture from the air1 and begin to throw out crystals4 ,if now placed under the microscope1 numerous points will be seen to start out here and there4 ,the starting points may be produced at pleasure by touching the film with a fine needle point1 so as to admit of a slight amount of moisture being absorbed by the mass of salt4 ,development is at once suspended by applying gentle heat2 cover the specimen with balsam and thin glass4 ,the balsam should completely cover the edges of the thin glass circle1 otherwise moisture will probably insinuate itself1 and destroy the form of the crystals4 ,mr4 ,thomas succeeded in crystallising 8the salts of the magnetic metals0 at very high temperatures1 with very curious results4 ,in ,plate ,,viii4 are seen crystals of sulphate of iron and cobalt1 ,no4 #afc2 and of nickel and potash1 ,no4 #afe1 obtained in the following manner3--,add to a concentrated solution of iron a small quantity of sugar1 to prevent oxidation4 ,put a drop of the solution on a glass slide1 and drive out the water of crystallisation as quickly as possible by the aid of a spirit lamp2 then with a ,bunsen's burner bring the plate to a high temperature4 ,immediately a remarkable change is seen to take place in the form of the crystal1 and if properly managed the 8foliation0 represented in the plate will be fairly exhibited4 ,the slide must not be allowed to cool down too rapidly or the crystals will probably absorb moisture from the atmosphere1 and in so doing the crystals alter their forms4 ,immerse them in balsam1 and cover in the usual way before quite cold4 ,sublimation of ,alkaloids4--,the late ,dr4 ,guy1 ,f4,r4,s41 directed the attention of microscopists to the fact that the crystalline shape of bodies belonging to the inorganic world might be of service in medical jurisprudence4 ,subsequently1 ,dr4 ,a4 ,helwig1 of ,mayence1 investigated this subject1 and found the plan applicable not only to inorganic but also to organic substances1 and especially to poisonous alkaloids4 ,by using a white porcelain saucer ,dr4 ,guy was able to watch the process of crystallisation more minutely1 and to regulate it more exactly4 ,he was1 in fact1 able to obtain characteristic crusts composed of crystals of strychnine weighing not more than #a_/cjjjth or #a_/ejjjth of a grain4 ,morphia affords equally characteristic results4 ,for the examination of these1 ,dr4 ,guy recommended the use of a binocular microscope with an inch object-glass4 ,but it is not to crystalline forms alone that one need trust2 the whole behaviour of a substance as it melts and is converted into vapour is eminently characteristic1 and when once deposited on the microscopical slide1 under the object-glass1 the application of re-agents may give still more satisfactory results4 ,the re-agents1 however1 which are here to be applied are not of the kind ordinarily employed4 ,colour-tests under the microscope are1 comparatively speaking1 useless2 those that give rise to peculiar crystalline forms are rather to be sought after4 ,for instance1 the crystals produced by the action of carbozotic acid on morphia are by themselves almost perfectly characteristic4 ,these experiments should not1 however1 be undertaken for medico-legal purposes by one unskilled in their conduct1 for the effects of the reagents themselves might be mistaken by the uninitiated for the result of their action on the substance under examination4 ,for the special method of procedure1 see ,dr4 ,w4 ,guy1 8,on the ,sublimation of the ,alkaloids40#cd ,the ,micro-spectroscope4 ,spectrum analysis has1 from its first introduction by ,kirschoff in #ahei1 maintained its fascination over men of science throughout the civilised world4 ,microscopists1 astronomers1 and chemists have assigned to the spectroscope a highly important position amongst scientific instruments of research4 ,at quite an early period of its history it appeared to ourselves to promise an extension of the work of the microscope in pathology and microscopy1 and second only to that of astronomy and chemistry4 ,the chief hindrances to the use of the spectroscope were1 in the early days1 of a twofold nature2 a widespread1 but quite erroneous view of the serious difficulties of employing the instrument1 and the want of a first aid to its use4 ,so valuable a means of research has this process of analysis proved to be1 that the discoveries made by the spectroscope appear marvellous4 ,the spectroscope was first made known as a refined instrument for the analysis of light by two ,germans1 a physicist and a chemist1 ,kirschoff and ,bunsen4 ,in #ahfj1 the latter succeeded in detecting and separating two new alkaline bodies from all other bodies from the waters obtained from the ,durkeim springs1 less than #jjjjb part of a milligramme of which can be detected by spectrum analysis4 ,it is to the labours of ,huggins1 ,norman ,lockyer and others that we are indebted for the wonderful discoveries made in astronomy2 and chiefly so to ,brewster1 ,herschel1 and ,talbot1 for showing that certain metals give off light of a high degree of refrangibility2 that distinct bands are situated at a distance beyond the last visible violet ray ten times as great as the length of the whole visible spectrum from red to violet4 ,with regard to the discoveries made in connection with physiological research1 we are indebted to ,f4 ,hoppe1 who in #ahfb first described the absorption bands of human blood4 ,his results were confirmed by the investigations of ,professor ,sir ,george ,gabriel ,stokes1 who1 by adding certain reducing agents to the blood1 found that he could change scarlet blood into purple--8purple cruorine0--and in this way the place occupied by the absorption band in the spectrum could be made to change4 ,he reduced the hmoglobin by robbing the blood of its oxygen4 ,thus1 by ,stokes' and other methods1 we have since arrived at extremely valuable results1 and the explanation of the difference in colour between arterial and venous blood2 and it has also enabled us to show wherein the breathing power of the red corpuscles resides1 and further explains phenomena which before his investigations were inexplicable4 ,illustration3 ,fig4 #aia4--;,frunhofer's ,spectrum ,lines4 ,the spectroscope seems likely to be of almost as great use in medicine as it has already proved to be in solar and terrestrial chemistry1 if we may form an opinion from the large amount of literature which has appeared on the subject4 ,the inception of this magical instrument arose on the instance of a discovery made by ,dr4 ,wollaston in #ahjb1 who1 on making a slit in the shutter of his room1 instead of a round hole1 the spectrum of sunlight1 instead of being composed of a number of coloured discs1 was now a band of pure colours1 each colour being free from admixture with the next to it4 ,moreover1 he found that this colour band was not continuous1 as ,newton described it1 but interrupted here and there by fine black lines4 ,in #ahad1 ,frunhofer1#ce a ,german optician1 discovered these lines quite independently1 and mapped out #egf of them1 calling the more prominent of them ,a1 ,b1 ,c1 ,d1 ,e1 ,f1 ,g1 ,h1 which lines he used as marks of comparison4 ,he also found that the distances of these lines from each other may vary according to the nature of the substance composing the prism2 thus1 their relative distances are not the same in prisms of flint-glass1 crown-glass1 and bisulphide of carbon1 but they always occupy the same position relatively to the colours of the spectrum4 ,kirschoff and ,angstrm had mapped out in #ahhj no less a number than #b1jjj ,frunhofer lines1 a portion of which are correctly shown in the accompanying chart 7,fig4 #aia74 ,in #ahcj1 ,simms1 a ,london optician1 made an improvement in the construction of the spectroscope by placing a lens in front of the prism1 so arranged that the slit was in the focus of the lens4 ,this lens turns the light1 after it has passed through the slit1 into a cylindrical beam before entering the prism4 ,another lens1 also introduced by him1 receives the circular beam emerging from the prism1 and compels it to throw an image of the slit1 which may be magnified at pleasure for each ray4 ,the lens between the prism and the slit is termed the collimating lens4 ,thus the following are the essential parts of a chemical spectroscope3--7#a7 a slit1 the edges of which are two knife-edges of steel very truly ground1 and exactly parallel to each other1 and in a direction parallel to the refracting edge of the prism1 to admit a pencil of rays4 7#b7 ,a collimating lens2 a convex lens with the slit at its principal focus1 which renders the rays parallel before entering the prism4 7#c7 ,a prism of dense glass1 in which the rays are refracted and dispersed4 7#d7 ,an observing telescope constructed like an astronomical refractor of small size1 and placed so that the rays shall traverse it after emerging from the prism4 ,such are the essentials of a one-prism chemical spectroscope4 ,the form of instrument in use with the microscope is the 8direct vision0 spectroscope1 consisting of two prisms of flint-glass1 placed between three of crown-glass cemented together by ,canada balsam2 the spectrum being viewed directly by the eye4 ,the earliest constructed form of micro-spectroscope is shown in ,fig4 #aib1 the ,browning-,huggins4 ,it was1 however1 ,mr4 ,sorby who suggested that the prism should be made of dense flint-glass and of such a form that it could be used in two different positions1 and that in one it should give twice the dispersion that it would in the other1 but that the angle made by the incident and emergent rays should be the same in both positions4 ,illustration3 ,fig4 #aib4--,the ,browning-,huggins ,micro-spectroscope4 ,illustration3 ,fig4 #aic4 ,illustration3 ,fig4 #aic;a4 ,figs4 #aic and #aic;a represent prisms of the kind arranged to use in two different positions1 i and i being the same angle as ,i and ,i4 ,for most absorption-bands1 particularly if faint1 the prism should be used in the first position1 in which it gives the least dispersion2 when greater dispersion is required1 so as to separate some particular lines more widely1 or to show the spectra of the metals1 or ,frunhofer's lines in the solar spectrum1 then the prism must be used as in ,fig4 #aic;a4 ,this answers well for liquids or transparent objects1 but it is1 of course1 not applicable to opaque objects4 ,to combine both purposes1 some form of direct vision-prisms that maybe applied to the body of the microscope is required4 ,fig4 #aid represents an arrangement of direct vision-prisms1 invented by ,herschel4 ,the line ,r ,r shows the path of a ray of light through the prisms1 where it would be seen that the emergent ray ,r is parallel and coincident with the incident ray ,r4 ,illustration3 ,fig4 #aid4 ,illustration3 ,fig4 #aid;a4 ,another very compact combination is shown in ,fig4 #aid;a4 ,any number of these prisms 7,p ,p ,p7 may be used1 according to the amount of dispersion required4 ,they are mounted in a similar way to a ,nicol's prism1 and are applied directly over the eye-piece of the microscope4 ,the slit ,s ,s is placed in the focus of the first glass 7,f7 if a negative1 or below the second glass if a positive eye-piece be employed4 ,one edge of the slit is movable1 and1 in using the instrument1 the slit is first opened wide1 so that a clear view of the object is obtained4 ,the part of the object of which the spectrum is to be examined is then made to coincide with the fixed edge of the slit1 and the movable edge is screwed up1 until a brilliant coloured spectrum is produced4 ,the absorption-bands will then be readily found by slightly altering the focus4 ,this contrivance answers perfectly for opaque objects1 without any preparation2 and1 when desirable1 the same prism can be placed below the stage1 and a micrometer used in the eye-piece of the microscope1 thus avoiding a multiplicity of apparatus4 ,illustration3 ,fig4 #aie4--,the ,sorby-,browning ,micro-spectroscopic ,eye-piece4 ,a later and better form of instrument is the ,sorby-,browning eye-piece 7,fig4 #aie71 shown in section 7,fig4 #aif7 ready for inserting into the body-tube of the microscope1 the prism of which is contained in a small tube1 removable at pleasure4 ,below the prism is an achromatic eye-piece1 having an adjustable slit between the two lenses1 the upper lens being furnished with a screw motion to focus the slit4 ,a side slit1 capable of adjustment1 admits1 when required1 a second beam of light from any object whose spectrum it is desired to compare with that of the object placed on the stage of the microscope4 ,this second beam of light strikes against a very small prism1 suitably placed inside the apparatus1 and is reflected up through the compound prism1 forming a spectrum in the same field with that obtained from the object on the stage4 ,illustration3 ,fig4 #aif4--,sectional view of bright-line ,spectroscope2 the letters also apply to the standard spectrum scale 7,fig4 #aih74 ,a is a brass tube1 carrying the compound direct vision prism2 ,b1 a milled head1 with screw motion to adjust the focus of the achromatic eye lens ,c1 seen in the sectional view as a triple combination of prisms4 ,another screw at right angles to ,c1 which from its position cannot be well shown in the figure1 regulates the slit horizontally4 ,this screw has a larger head1 and when once recognised cannot be mistaken for the other4 ,d ,d is a clip and ledge for holding a small tube1 so that the spectrum given by its contents may be compared with one from an object on the stage4 ,e is a round hole for a square-headed screw1 opening and shutting a slit1 admitting the quantity of light required to form the second spectrum4 ,a light entering the round hole near ,e strikes against the right-angled prism1 which is placed inside the apparatus1 and is reflected up through the slit belonging to the compound prism4 ,if any incandescent object be placed in a suitable position with reference to the round hole1 its spectrum will be obtained4 ,f shows the position of the field lens of the eye-piece4 ,the tube is made to fit the microscope to which the instrument is applied4 ,to use this instrument insert ,f as an eye-piece in the microscope tube1 taking care that the slit at the top of the eye-piece is in the same direction as the slit below the prism4 ,screw on to the microscope the object-glass required1 and place the object whose spectrum is to be viewed on the stage4 ,illuminate with the stage mirror if it be transparent2 with mirror1 ,lieberkhn1 and dark well1 by side reflector1 or bull's-eye condenser if opaque4 ,remove ,a1 and open the slit by means of the milled-head1 not shown in figure1 but which is at right angles to ,d ,d4 ,when the slit is sufficiently open the rest of the apparatus acts as an ordinary eye-piece1 and any object can be focussed in the usual way4 ,having focussed the object1 replace ,a1 and gradually close the slit till a good spectrum is obtained4 ,the spectrum will be much improved by throwing the object a little out of focus4 ,illustration3 ,figs4 #aig and #aig;a4--,the ,beck-,sorby ,micro-spectroscope ,eye-piece1 drawn on a scale of one half size4 ,every part of the spectrum differs a little from adjacent parts in refrangibility1 and delicate bands or lines can only be brought out by accurately focussing that particular part of the spectrum4 ,this can be done by the milled-head ,b4 ,disappointment will occur in any attempt at delicate investigation if the directions given be not carefully followed out4 ,opposite ,e a small mirror is attached4 ,it is like the mirror below the stage of a microscope1 and is mounted in a similar manner4 ,by means of this mirror light may be reflected into the eye-piece1 and in this way two spectra may be procured from one lamp4 ,method of using the ,micro-,spectroscope4 ,a beginner with the micro-spectroscope should first make himself fully acquainted with the spectroscope by holding it up to the sky and noting the effects of opening and regulating the slit1 by rotating the screw ,c1 ,figs4 #aie and #aig4 ,the lines will be well seen on closing down the opening4 ,this screw diminishes the length of the slit1 when the spectrum is seen as a narrow ribbon of prismatic colours4 ,the screw ,e regulates the admission of light through the aperture above ,d4 ,the better objects with which to commence the study of the absorption bands are1 aniline dye1 much diluted1 madder1 permanganate of potash1 and blood4 ,as each colour varies in refrangibility1 the focus must be adjusted by the screw ,e4 ,when it is desired to view the spectrum of a very minute object1 the prisms should be removed by withdrawing the tube containing them1 the slit set open1 and the object brought into the centre of the field2 the vertical and horizontal slits must then be partially closed up1 and the prisms replaced1 when a suitable objective is employed to examine the spectrum4 ,for ordinary observations a magnifying power of an inch and a half or two inches will be suitable1 but for small quantities of material a higher power must be employed1 when a single blood corpuscle can be made to show its characteristic absorption band4 ,after having obtained the best image of any object on stage1 throw it slightly out of focus1 and substitute the micro-spectroscopic eye-piece for the ,huyghenian4 ,opaque objects should be examined by reflected light1 by means of the bull's-eye condenser1 or side reflector4 ,mr4 ,sorby uses a binocular microscope1 which enables him to regulate the focussing and throwing out of focus of the object4 ,in examining crystals or other small objects1 a small cardboard diaphragm should be placed beneath them2 and when examining the spectra of liquids in cells1 slip a small cap with a perforation of #a_/aj-;inch in diameter over the tube containing the #a_/b-;inch or #b-;inch objective4 ,substances which give absorption bands or lines in the red are best seen by artificial light1 while those which show bands in the violet are better seen by daylight4 ,by following rules of the kind we are less likely to mix the bands of the absorption spectrum with the ,frunhofer lines4 ,for example1 if the edge of a band happens to coincide with a ,frunhofer line1 the observer is apt to imagine that the band is better defined and more abruptly shaded on one side than it really is4 ,illustration3 ,standard ,spectrum ,scale4 ,cells for use with ,spectroscope4 ,fig4 #aih4 ,cells and ,tubes4--,these are either supplied ready-made by the optician1 or can be formed out of small pieces of barometer tubing1 with the edges ground down and cemented on ordinary glass slips4 ,in ,fig4 #aih is seen the several kinds of cells and tubes usually employed1 while the little flat tubes commonly in use as bouquet holders will be found of use1 with the side stage reflecting spectrum as comparison tubes2 being of different diameters they allow of two or more depths of colour in the fluid intended for examination4 ,in the case of many other fluids the sloping form of cell 7,fig4 #aih7 will be useful1 as different shades of fluids can be examined without removal from the stage of the microscope4 ,the deeper cells are cut from a piece of barometer tubing of about half to an inch long1 one end being cemented to a piece of flatted glass1 and the other covered over temporarily or permanently with a thin piece of glass on the top1 held in its place by capillary attraction1 thus admitting of the tube being turned upside down4 ,re-agents required4--,a diluted solution of ammonia1 citric acid1 double tartrate of potash and soda 7the last being used to prevent the precipitation of oxide of iron71 and the double sulphate of the protoxide of iron and ammonia 7employed to deoxidise blood1 etc474 ,in some special cases1 dilute hydrochloric acid1 purified boric acid1 and sulphate of soda are required4 ,the character of stains of blood varies with age and with the nature of the substance with which it happens to be combined4 ,this is important to remember in connection with ,jurisprudence1 when the micro-spectroscope is brought into use for the detection of blood stains4 ,the spectrum used in important cases of the kind should have a compound prism1 with enough1 but not too great dispersive power1 otherwise the bands become1 as it were1 diluted1 and less distinct4 ,if the blood stain is quite recent1 the colouring matter will be hmoglobin only4 ,this easily dissolves out in water1 and when sufficiently diluted gives the spectrum of oxy-hmoglobin1 which on the addition of ammonia1 together with a small quantity of the double tartrate1 a small piece of ferrous salt1 and stirring carefully without the admission of air1 changes the spectrum of reduced hmoglobin4 ,when stirred again1 so as to expose the solution as much as possible to air1 the two bands reappear2 on gradually adding citric acid in small quantities the colour begins to change1 and the bands are seen to gradually fade away2 if there should have been much blood present1 a band appears in the red2 the further addition of ammonia makes all clear again1 but does not restore the original bands1 because the hmoglobin has been permanently changed into hmatin4 ,this reaction alone distinguishes blood from most other colouring matters1 since other substances after being changed by acids are restored by alkalies to their original state4 ,there are many other curious facts connected with the spectroscopic analysis of blood1 which are fully explained and illustrated by ,dr4 ,maemunn in his book on 8,the ,use of the ,spectroscope in ,medicine10 and also in ,dr4 ,thudicum's#cf reports and charts1 which are the most complete4 ,sir ,george ,stokes1 ,f4,r4,s41 was one of the first to show the essential value of the spectral phenomena of hematine1 and who proved1 after ,hoppe had first drawn attention to the fact1 that this colouring matter is capable of existing in two states of oxidation1 and that a very different spectrum is produced according as the substance1 which he termed cruorine1 is in a more or less oxidised condition4 ,the chart appended to his paper#cg affords an imperfect representation of the changes seen in the spectrum4 ,illustration3 ,no4 #a4--;,arterial ,blood1 ,scarlet ,cruorine4 ,no4 #b4--,venous ,blood1 ,purple ,cruorine4 ,no4 #c4--;,blood treated with ,acetic ,acid4 ,no4 #d4--,solution of ,hmatin4 ,fig4 #aii4--,sir ,george ,stokes' ,chart of the ,absorption ,bands of ,blood4 ,proto-sulphate of iron1 or proto-chloride of tin1 causes the reduction of the colouring-matter1 but1 on exposure to air1 oxygen is absorbed1 and the solution again exhibits the spectrum characteristic of the more oxidised state4 ,the different substances obtained from blood colouring-matter produce different bands4 ,thus1 hmatin gives rise to a band in the red spectrum ,d2 hmato-globulin produces two bands1 the second twice the breadth of the first in the yellow portion of the spectrum between the lines ,d and ,e1 ,no4 #a4 ,the absorption-bands differ according to the strength of the solution employed1 and the medium in which the blood-salt is dissolved2 but an exceedingly minute proportion dissolved in water is sufficient to bring out very distinct bands4 ,b represents the red end of the spectrum and ,g the green as it approaches the violet end4 ,mapping the ,spectra4--,in the sectional view given of the micro-spectroscope 7,fig4 #aif71 the internal construction of the instrument is shown1 and the arrangement made for throwing a bright point on to the surface of the upper prism is clearly seen4 ,the mapping out is accomplished by means of a photographic scale fixed as a standard spectrum 7,fig4 #aih71 in the position of ,a ,a1 illuminated by the small mirror at ,r1 and focussed by a small lens at ,c1 so that on looking into the instrument one can see the spectrum accurately divided into one hundred equal parts1 and scale readings can be made at once2 the only precaution needed is to be sure the ,d 7or the sodium line1 if ,d cannot be got7 always stands at the same number on the scale4 ,to map absorption spectra on this scale we have to lay down a line1 as many millimetres long as there are divisions in the scale1 and mark the position of the bands on this line4 ,mr4 ,browning supplies scales printed off ready for use4 ,but the mapping out of spectra1 as ,mr4 ,sorby pointed out1 requires some consideration2 since the number of divisions depends on the thickness of the interference-plate1 it becomes necessary to decide what number should be adopted4 ,ten it was thought would be most suitable2 but1 on trial1 it appeared to be too few for practical work4 ,twenty is too many1 since it then becomes extremely difficult to count them4 ,twelve is as many as can well be counted2 it is a number easily remembered1 is sufficiently accurate1 and has other practical advantages4 ,with twelve divisions the sodium-line #j comes very accurately at #c-a_/b2 thus1 by adjusting the plate so that a bright sodium-light is brought into the centre of the band1 when the ,nicol's prisms are also crossed accurately at #c-a_/b1 parallelism is secured1 together with a wider field of observation4 ,the general character of the scale will be best understood from the following figure1 in which the bands are numbered1 and given below the principal ,frunhofer lines4 ,the centre of the bands is black1 and they are shaded off gradually at each side1 so that the shaded part is about equal to the intermediate bright spaces4 ,taking1 then1 the centres of the black bands as #a1 #b1 #c1 c41 the centres of the spaces are #a-a_/b1 #b-a_/b1 #c-a_/b1 c41 the lower edges of each #c_/d1 #a-c_/d1 c41 and the upper #a-a_/d1 #b-a_/d1 c41 we can easily divide these quarters into eighths by the eye3 and this is as near as is required in the subject before us1 and corresponds as nearly as possible to #a_/ajjth part of the whole spectrum1 visible under ordinary circumstances by gaslight and daylight4 ,absorption-bands at the red end are best seen by lamp-light1 and those at the blue end by daylight4 ,illustration3 #j #a #b #c #d #e #f #g #h #i #aj #aa #ab 7,red end47 7,bue end47 ,a ,b ,c ,d ,e b ,f ,g ,fig4 #bjj4-- ,on this scale the position of some of the principal lines of the solar spectrum is about as follows3-- ,a #c_/d ,b #a-a_/b ,c #b-c_/h ,d #c-a_/b ,e #e-aa_/af b #f-c_/af ,f #g-a_/b ,g #aj-e_/h ,at first plates of selenite1 which are easily prepared1 were used1 because they can be split to nearly the requisite thickness with parallel faces2 but their depolarising power varied much with temperature4 ,even the ordinary atmospheric changes alter the position of the bands4 ,however1 quartz cut parallel to the principal axis of the crystal is but slightly affected1 and is not open to the same objection2 but this is prepared with some difficulty4 ,the sides should be perfectly parallel1 the thickness about #jdc-;inch1 and gradually polished down with rouge until the sodium-line is seen in its proper place4 ,this must be done with care1 since a difference of #a_/ajjjj-;inch in thickness would make it almost worthless4 ,the two ,nicol's prisms and the intervening plate are mounted in a tube1 and attached to a piece of brass in such a manner that the centre of the aperture exactly corresponds to the centre of any of the cells used in the experiments1 and must be made to correspond with equal care1 so that any of them1 or this apparatus in particular1 may be placed on the stage and in proper position without further adjustment1 whereby both time and trouble are saved4 ,absorption ,spectrum of ,chromule4 ,in #ahfi ,i published in the ,journal of the ,royal ,microscopical ,society#ch a paper on results obtained by the spectrum analysis of the colouring-matter of plants and flowers1 some of which were of considerable interest in many respects4 ,my examinations extended to several hundred different specimens1 from which ,i was led to conclude that the chromule of flowers is1 for the most part1 due to the chemical action of the actinic rays of light over the protoplasm of the plant1 more so than to that of soil4 ,but as certain roots of plants1 as those of the alkanet1 yield their colouring-matter to oil1 and in a much smaller degree to spirit or water1 it follows then that conclusions of any kind can only be drawn after a long and careful study of the question4 ,some of the results obtained were1 however1 of some interest at the time1 that1 for example1 seen in three different solutions of the chlorophyll of ,cinchona succirubra1 one of three solutions in alcohol1 scarcely coloured1 having in fact only a faint tinge of green colour1 and the spectrum of which much astonished me at the time4 ,it gave four well-marked absorption-bands2 one deep sharp line in the red2 another1 rather narrower1 in the orange1 coincident with ,d1 or the sodium-line2 one in the green1 about b1 coincident with the ,thallium green band2 and a fourth on the blue line ,f1 nearly as broad as that in the red4 ,the ethereal solution gave different results4 ,it showed only three bands of absorption1 nearly the same as in the last case 7though all of them fainter72 but the fourth in the blue was not apparent1 the whole of that end of the spectrum being absorbed a little beyond the green line b4 ,this solution was deep emerald-green1 and even dilution did not alter the phenomena4 ,the acid alcoholic solution was as deeply green as the last1 but gave only the sharp broad absorption-band in the red1 and two very faint ghostly bands in the position described above of the ,d and b lines respectively4 ,further additional researches on the chlorophyll of plants furnished curious results1 the chlorophyll being dissolved out by alcohol1 digested for some hours1 and without heat2 some plants being fresh1 and others dried4 ,five classes of phenomena exhibited themselves1 but all agreed in having the red absorption-band broad1 sharp1 and well defined1 some having this one band only1 the ,lilac being of this type4 ,there are two classes in which two absorption-bands occur4 ,one has the red and the orange bands1 of which the ,fuchsia1 ,guelder-rose1 and ,tansy are examples2 another1 in which the red and the green bands are alone co-existent4 ,ivy is the type of the class1 and it is immaterial whether we take last year's leaves or those of the early spring2 the results are the same4 ,the fourth class consists of the two former spectra superposed4 ,three lines occur1 the red1 the orange1 and the green bands1 at ,c1 ,d1 and b1 as before4 ,this is by far the largest class1 and ,i have thirty or forty examples of it4 nothera biennis1 ,laurestinus1 c41 are types with the ethereal solution of the leaves of ,red ,bark4 ,the fifth class consists of those having properties similar to the alcoholic solution of ,red ,bark described4 ,but ,i only found eight of these1 and not all equal in colour power1 namely3 ,berberry1 ,sloe1 ,tea1 ,hyoscyamus1 ,digitalis1 ,senna1 and ,red ,bark4 ,the results obtained appeared at the time to be well worth following up to a more practical conclusion than that arrived at4 ,it should be noted that in the preparation of vegetable colouring matters for the micro-spectroscope1 care must be taken to employ only a small quantity of spirits of wine to filter the solution1 and evaporate it at once to dryness at a very gentle heat1 otherwise if we attempt to keep the colouring matters in a fluid state they quickly decompose4 ,it is necessary also to employ various re-agents in developing characteristic spectra4 ,the most valuable re-agent is sulphite of soda4 ,this admits of the division of colours into groups4 ,it is better to use a dilute alcoholic solution for the extraction of colour from plants1 and to observe the spectrum in a column of about three-quarters of an inch in height4 ,by this means it is quite possible to ascertain that the spectrum of chlorophyll presents seven distinct absorption bands4 ,for further information on this interesting subject ,i must refer the reader to ,mr4 ,sorby's paper 8,on a ,definite ,method of ,qualitative ,analysis of ,vegetable and ,animal ,colouring ,matter by means of the ,spectrum ,microscope10 8,proc4 ,roy4 ,soc410 ,no4 #ib1 #ahfg4 ,,chapter ,,iv4 ,practical ,microscopy3 ,manipulation1 and ,mode of ,using the ,microscope4 ,in this chapter it will be my aim to discuss the best practical methods of employing the microscope and its appliances to the greatest advantage4 ,first1 the student should select a quiet room for working in1 with1 if possible1 a northern aspect1 free from all tremor occasioned by passing vehicles4 ,the table selected for use should be firm1 and provided with drawers1 in which his several appliances can be kept ready to hand4 ,the microscope must be placed at such an inclination as will enable him to work in comfort1 and without putting strain on the muscles of the neck or fatiguing the eyes4 ,the next important point is that of light4 ,daylight1 in some respects1 is an advantage2 this should come from a white cloud on a bright day1 but as a rule more satisfactory results will be obtained by using a well-made lamp1 as this can be controlled with ease1 and used at a proper height and distance from the microscope4 ,to have a good form of lamp is as much to be desired for the student as for those engaged in the more advanced work of microscopy4 ,whatever the source of light we must on no account over-illuminate4 ,the object having been placed on the stage of the microscope1 the body should be racked down to within a quarter or half an inch of the specimen1 and then1 while looking through the eye-piece1 should be slowly withdrawn until a sharp image comes into view4 ,the fine adjustment may now be used for the more delicate focussing of the several parts of the field4 ,accurate adjustment of focus is required when using a #a_/d-;inch objective2 details of the object1 as stri1 being brought into view when a stronger light is thrown obliquely upon them from the mirror4 ,if a #a-;inch objective is used the light often proves to be in excess of what is required1 and this must be regulated by the aid of the diaphragm4 ,the iris diaphragm1 made to drop into the under-stage1 is more generally employed1 as when racked up to the object it affords every necessary graduation of illumination4 ,illustration3 ,fig4 #bja4--;,bull's-eye ,lens4 ,to illuminate opaque objects the light should be thrown upon them from above by the bull's-eye lens 7,fig4 #bja74 ,the focus of such a lens and the lamp placed at four inches from it1 is about three inches for daylight1 or two inches for artificial light4 ,a large object may be placed upon the stage of the microscope at once1 but smaller objects are either laid on a glass slide or held in the stage forceps4 ,when illuminating objects from above all light from the mirror1 or that which might enter the objective from below the stage1 should be carefully excluded4 ,dark-field illumination is a means of seeing a transparent object as an opaque one4 ,the principle1 however1 is that all the light shall be thrown from below the object1 but so obliquely that it cannot enter the object-glass unless interrupted by the object2 this is best accomplished by ,wenham's ,parabola4 ,glass of any kind requires occasional cleaning2 a piece of soft washed chamois leather should be used for this purpose4 ,the fronts of the objectives may be carefully wiped1 but not unscrewed or tampered with2 a short thick-set camel's hair brush may be passed down to the back lens1 and all dust removed without doing any harm4 ,if the objective is an immersion1 carefully remove the fluid from the front lens1 as even distilled water will leave a stain behind4 ,for removing oil see special directions given at page #aga4 ,when cleaning the eye-pieces1 which should be done occasionally1 the cells containing the glasses must be unscrewed and replaced one at a time1 so that they may not be made to change places4 ,any dirt upon the eye-pieces may be detected by turning them round whilst looking through the instrument2 but if the object-glasses are not clean1 or are injured1 it will1 for the most part1 only be seen by the object appearing misty4 ,the object-glasses1 when in use but not on the microscope1 should be stood upon the table with the screw downwards1 to prevent dust getting into the lenses1 and they should always be put into their brass cases when done with4 ,a large bell-glass shade will be found the most useful cover for keeping dust from the instrument when not in use4 ,when looking through the eye-piece be sure to place the eye in close proximation to the cap1 otherwise the whole field will not be perfectly visible2 it should appear as an equally well-illuminated circular disc4 ,if the eyelashes are reflected from the eye-glass1 the observer is looking upon the eye-piece1 and not through it4 ,the ,mirror4--,the working focal distance of the mirror is that which brings the images of the window-bars sharply out upon the object resting upon the stage4 ,in other words1 the focus of the mirror is that which brings parallel rays to a correct focus on the object-glass4 ,if employing artificial light1 then the flame of the lamp should be distinguishable2 a slight change in the inclination of the mirror will throw the image of the lamp-flame out of the field4 ,the strongest light is reflected from the concave side of the mirror1 that from the flat side is more diffuse and less intense4 ,oblique light can be obtained by turning the mirror on one side and then adjusting it so as to illuminate the field from that position4 ,all the necessary mechanism of the microscope is easily and quickly learned4 ,the object-glasses or objectives are1 as previously explained1 designated according to the focal distance of a single lens of the same magnifying power4 ,thus a #b-;inch objective is understood to be a combination which has the magnifying power of a single lens whose focal point is two inches from the object1 and so on with reference to other powers4 ,by the aid of different eye-pieces an extensive range of magnifying power can be obtained2 for example1 the #b-;inch objective with a deep eye-piece will give the same amplification as the quarter objective with the ordinary eye-piece4 ,indeed1 for certain observations1 the combination of a wide-angled low-power objective1 with a deep eye-piece1 or compensating eye-piece1 is considered to have an advantage4 ,it has been already explained that two objectives1 one of much greater power than the other1 but both having only the same numerical aperture1 will show only the same amount of detail2 the higher power on a larger scale4 ,that is1 supposing with a #a_/d-;inch objective of #aj numerical aperture certain structure is resolved1 then a #a_/h-;inch substituted with exactly the same numerical aperture1 but with double the magnification1 no more resolving power will be found in the latter objective than in the former4 ,for this reason a doubt has been expressed as to whether high-power objectives--especially the more expensive oil-immersions1 made to transmit large pencils of light through their larger apertures--are so well adapted for ordinary research as the best series of dry achromatic objectives1 or even1 in some instances1 the medium aperture lenses2 undoubtedly1 for histological 7physiological and pathological7 work1 the latter will be found to meet the students' requirements quite as well as the former4 ,the student or amateur will do well to commence with moderate or medium powers1 a #b-;inch1 a #a-;inch1 a #a_/b-;inch1 a #d_/aj-;inch1 or #a_/d-;inch4 ,these1 together with the ,a and ,b eye-pieces1 will give a range of magnification from #cj to #bej diameters4 ,penetration in the objective is a quality for consideration1 as the adjustment of high powers is a work of delicacy1 and in some cases their penetration is impaired by the arrangement made to obtain finer definition4 ,the value1 however1 of penetration in an objective is always considered to be of more or less importance4 ,it is a quality whereby1 under certain conditions1 a more perfect insight into structure is obtained4 ,as a rule1 the objective having the largest working distance possesses the better penetration4 ,theoretically1 the penetration of an objective decreases as the square of the angular aperture increases4 ,for this reason the medical student will be justified in choosing the objectives ,i have named1 since these will be better adapted to his work and pursuits4 ,the penetration of the objective is a relative quality assessed at a different value by workers whose aims are widely different4 ,but for the observation of living organisms1 the cyclosis within the cell of the closterium or valisneria1 for instance1 preference will undoubtedly be in favour of the objective with good penetration4 ,resolving ,power4--,this is a quality highly prized by the bacteriologist4 ,in the case of the high-angled apochromatic oil-immersion1 with its compensating eye-piece1 its resolution is found to be of very considerable advantage1 because of its capacity to receive and recombine all the diffraction spectra that lie beyond the range of the older achromatic objective1 with its smaller angular aperture4 ,the actual loss of resolving power consequent upon the contraction of aperture from #ahj to #abh-a_/b is ten per cent41 if not more4 ,resolution depends1 then1 upon the quality and quantity of the light admitted1 the power of collecting the greatest number of rays1 and the perfection of centring4 ,in other words1 upon the co-ordination of the illuminating system of the microscope--mirror1 achromatic condenser1 objective and eye-piece4 ,if diatoms are employed as test-objects1 it should not be forgotten that there are great differences1 even in the same species1 in the distances their lines are apart4 ,for this reason ruled lines of known value1 as ,nobert's lines1 are to be preferred4 ,the following example will suffice to show the value of a dry #a_/h-;inch objective of #abj in defining the rulings of a #ai-;band plate1 which is equivalent to the #a_/fgjjjth of an inch4 ,this objective1 with careful illumination1 showed them all2 but when cut down by a diaphragm to #aaj1 the eighteenth line was not separable2 further cut down to #ajj the seventeenth was the limit1 to #hj the fourteenth1 and to #fj the tenth was barely reached4 ,flatness of ,field4--,this quality in the objective has1 by the introduction of the immersion system1 lost much of the importance formerly attached to it4 ,some writers assume it to be an 8optical impossibility40 ,the compensating eye-piece has had the effect of contracting the visual field1 consequently the peripheral imperfections of the objective are of a less disturbing character4 ,it has1 however1 not been made perfectly clear whether the highest perfection of the two primary qualities of a good objective1 defining power and resolving power1 can be always obtained in one and the same combination of lenses4 ,doubtless1 defining power can be more satisfactorily determined by the examination of a suitable object1 and the perfection of the image obtained2 to assist in securing which1 a solid axial cone of light equal to about three-fourths of the aperture of the objective must be employed4 ,to sum up1 then1 8the focal power of all objectives depends in their perfect definition1 a property on which their converging power depends1 and in turn their magnifying action is dependent2 again1 focal power is the curvature imprinted by the lens on a plane wave1 and is reciprocal of the true focal length4 ,it is appropriately expressed in terms of the proper unit of focal curvature1 the dioptric2 a unit of curvature40#ci ,illustration3 ,fig4 #bjb4--,seiler's ,test ,slide4 ,it may be taken as an axiom with microscopists that 8neither the penetrating power nor the high-power defining objective is alone sufficient for every kind of work4 ,the larger the details of ultimate structure1 the narrower the aperture--and the converse2 the minuter the dimensions of elementary structure1 the wider must be the aperture of the objective40 ,every worker with the microscope must have satisfied himself of the truth of this statement1 when engaged in the study of the movements of living organisms1 or defining the intimate structure of the minuter diatoms1 or of the podura scale4 ,test for ,illumination4--,dr4 ,c4 ,seiler recommends the human blood corpuscle as the best test of good illumination4 ,he prepares the object in the following manner3 ,take for the purpose a clean glass slide of the ordinary kind1 and place near its extreme edge a drop of fresh blood drawn by pricking the finger with a needle4 ,then take another slide of the same size1 with ground edges1 and bring one end in contact with the drop of blood1 as shown in ,fig4 #bjb1 at an angle of #de2 then draw it evenly and quickly across the underslide1 and the result will be to spread out the corpuscles evenly throughout4 ,blood discs being lenticular bodies1 with depressed centres1 act like so many little glass-lenses1 and show diffraction rings if the light is not properly adjusted4#dj ,errors of ,interpretation4--,to be in a position to draw an accurate conclusion of the nature and properties of the object under examination is a matter of great importance to the microscopist4 ,the viewing of objects by transmitted light is of quite an exceptional character1 rather calculated to mislead the judgment as well as the eye4 ,it requires1 therefore1 an unusual amount of care to avoid falling into errors of interpretation4 ,among test objects the precise nature of the structural elements of the ,diatomace have given rise to great divergence of opinion4 ,then1 again1 the minute scales of the podura ,springtails1 one of the ,collembola1 and their congeners ,lepisma saccharina1 the structure of which is equally debatable4 ,mr4 ,r4 ,beck1 in an instructive paper published in the 8,transactions of the ,royal ,microscopical ,society10 says that the scales of the ,lepisma can be made to put on an appearance which bears little resemblance to their actual structure4 ,illustration3 ,fig4 #bjc4--,portions of ,scales of ,lepisma4 ,in the more abundant kind of scales the prominent markings appear as a series of double lines4 ,these run parallel and at considerable intervals from end to end of the scale1 whilst other lines1 generally much fainter1 radiate from the quill1 and take the same direction as the outline of the scale when near the fixed or quill end2 but there is1 in addition1 an interrupted appearance at the sides of the scale1 which is very different from the mere union1 or 8cross-hatchings10 of the two sets of lines 7,fig4 #bjc1 ,nos4 #a and #b1 the upper portions74 ,the scales themselves are formed of some truly transparent substance1 for water instantly and almost entirely obliterates their markings1 but they reappear unaltered as the moisture leaves them2 therefore the fact of their being visible at all1 under any circumstances1 is due to the refraction of light by superficial irregularities1 and the following experiment establishes this fact1 whilst it determines at the same time the structure of each side of the scale1 which it is otherwise impossible to do from the appearance of the markings in their unaltered state3-- 8,remove some of the scales by pressing a clean and dry slide against the body of the insect1 and cover them with a piece of thin glass1 which may be prevented from moving by a little gum at each corner4 ,no4 #c may then be taken as an exaggerated section of the various parts4 ,a ,b is the glass slide1 with a scale1 ,c1 closely adherent to it1 and ,d the thin glass-cover4 ,if a very small drop of water be placed at the edge of the thin glass1 it will run under by capillary attraction2 but when it reaches the scale1 ,c1 it will run first between it and the glass slide1 ,a ,b1 because the attraction there will be greater1 and consequently the markings on that side of the scale which is in contact with the slide will be obliterated1 while those on the other side will1 for some time at least1 remain unaltered3 when such is the case1 the strongly marked vertical lines disappear1 and the radiating ones become continuous4 7,see ,no4 #a1 the lower left-hand portion47 ,to try the same experiment with the other1 or inner surface of the scales1 it is only requisite to transfer them1 by pressing the first piece of glass1 by which they were taken from the insect1 upon another piece1 and then the same process as before may be repeated with the scales that have adhered to the second slide1 the radiating lines will now disappear1 and the vertical ones become continuous4 7,see ,no4 #b1 left portion47 ,these results1 therefore1 show that the interrupted appearance is produced by two sets of uninterrupted lines on different surfaces1 the lines in each instance being caused by corrugations or folds on the external surfaces of the scales4 ,nos4 #a and #b are parts of a camera lucida drawing of a scale which happened to have opposite surfaces obliterated in different parts4 ,no4 #d shows parts of a small scale in a dry and natural state2 at the upper part the interrupted appearance is not much unlike that seen at the sides of the larger scales2 but lower down1 where lines of equal strength cross nearly at right angles1 the lines are entirely lost in a series of dots1 and exactly the same appearance is shown in ,no4 #e to be produced by the two scales at a part where they overlie each other1 although each one separately shows only parallel vertical lines40 ,illustration3 ,fig4 #bjd4--,outer ,membrane of ,upper ,plane of ,red ,beads thrown by each alternate hole of grating2 on lowering the focus white interspaces turn into blue beads4 ,illustration3 ,fig4 #bjd;a4--,outer ,membrane of ,lower ,plane of ,beads thrown from remaining holes of grating2 on raising the focus white interspaces turn into red beads4 ,objective used1 ,zeiss's apochromatic #a_/ab-;inch oil-immersion1 numerical aperture #adj1 magnifying power #a1gej diameters4 ,a well-known skilled observer of test objects#da says3 8,practically the resolving power of our achromatic objectives on lined objects reached their maximum in the late ,dr4 ,woodward's hands4 ,amphipleura pellucida was then1 as now1 the finest known regular structure of the diatoms4 ,there appeared then nothing more to be gained in resolution when one of the apochromatic #a_/ab-;inch objectives of ,zeiss1 with its entire absence of colour1 passed into my hands1 and ,i soon became convinced that it possessed the power of separating the different layers of structure in the valve1 beyond the grasp of the dry-objective4 ,the result of this increase of power enabled me to split up1 as it were1 the one plate of silex forming the valve of ,pleurosigma formosum into three layers1 and which had never before appeared to be possible2 proving1 in fact1 that magnification without corresponding aperture is of little or no account40 8,the intimate structure of these test objects10 says ,mr4 ,smith1 8is built up on one plan1 each being composed of two or more layers1 7#a7 a valve with two layers1 as in ,pleurosigma balticum2 7#b7 two layers with a grating and secondary markings placed diagonally1 as in ,pleurosigma formosum2 7#c7 with two layers of a net-like structure1 as in ,pleurosigma angulatum1 the fineness of the stri or gratings of which measure the #a_/ejjjjth of an inch4 ,five other diatoms afford evidence of this compound structure4 ,the presence of beads or hemispheres in one of the focal planes1 and depressions or pits in another1 are emphasised in the micro-photograph itself2 reduced portions of the valve are represented in ,figs4 #bjd and #bjd;a40 ,a portion of a diatom valve1 ,pleurosigma angulatum1 micro-photographed on a higher scale of magnification1 #d1ejj diameters1 is given further on4 ,illustration3 ,fig4 #bje4--,sections of an old-fashioned ,glass ,tumbler1 from photographs by the late ,mr4 ,r4 ,beck4 ,errors of interpretation arise either from the small cones of illumination afforded by the dry-objective1 or the oblique illumination formerly resorted to for the resolution of these difficult test objects1 and several of the lights and shadows resulting from the refractive power of the object itself4 ,but the most common error is that produced by the reversal of the lights and shadows resulting from the refractive powers of the object itself4 ,to make this clear1 ,i reproduce two reduced photographs of a small section of an old-fashioned glass tumbler1 covered externally with numerous hemispheres1 illuminated by transmitted light 7,fig4 #bje74 ,this illustration well emphasises the difficulty there is in determining structure under precisely similar conditions to those we are accustomed to of examining valves of diatoms under the microscope4 ,if these photographs be held in front of a strong light1 they at once convey different impressions to the mind1 the hemispheres appearing depressions in the one1 and raised beads in the other4 ,both are prints from the same negative1 but in mounting are reversed2 and therefore the apparent dissimilarity is due to a slight inequality of illumination1 which the mind accepts as light and shade4 ,very similar appearances to those described will result if a thin plate of glass were studded with minute1 equal1 and equi-distant plano-convex lenses1 the foci of which would very nearly lie in the same plane4 ,if the focal surface1 or plane of vision1 of the objective be made to coincide with this plane1 a series of bright points will result1 from the excess of light falling on each lens4 ,if the plane of vision be next made to coincide with the surfaces of the lenses1 these points would appear dark1 in consequence of the rays being refracted towards points now out of focus4 ,lastly1 if the plane of vision be made to coincide with the plane beneath the lenses that contain their several foci1 so that each lens may be1 as it were1 combined with the object-glass1 then a second series of bright points will result from the accumulation of the rays transmitted at those points4 ,moreover1 as all rays capable of entering the objective are concerned in the formation of the second series of bright focal points1 the first series being formed by the rays of a cone of light only1 it is evident that the circle of least confusion must be much less1 and therefore the bright points better defined in the first than in the last series4 ,there are no set of objects which have given rise to more discussion as to their precise character than the scales of the podura 7,lepidocyrtus cervicollis71 to the intimate structure of which ,mr4 ,smith turned his attention1 and succeeded1 ,i am inclined to think1 in his attempt to settle the structure of these very minute scales1 and which heretofore have been described as 8notes of exclamation40 ,by the aid of the same power as that employed in the examination of the pleurosigma formosum1 the old conventional markings have disappeared1 and well-defined 8featherlets0 have taken their place4 ,by careful focussing up and down1 a series of whitish pin-like bodies is to be seen1 with an intervening secondary structure4 ,a micro-photograph of a portion of a scale taken by ,mr4 ,smith shows that these pin-like bodies are inserted in a fold of the basement membrane1 which1 in his opinion1 furnish unmistakable evidence of the fact that these projecting bodies are real1 and must no longer be looked upon as mere ghosts4 ,quite recently1 a micro-photograph of a portion of a podura scale was placed in my hands1 taken by ,mr4 ,j4 ,w4 ,gifford with a ,swift's #a_/ab-;inch apochromatic objective1 of numerical aperture #adj1 and a deep eye-piece1 having a combined magnifying power of #c1hbg diameters4 ,fig4 #bjf shows a portion of the photograph which1 it will be admitted1 supports ,mr4 ,smith's view of the structure of the podura scale4 ,illustration3 ,fig4 #bjf4--,podura ,scale1 taken with a #a_/ab ,swift's ,immersion #c1hbg4 ,many other errors of interpretation are not unknown to the experienced operator with the microscope1 arising1 for the most part1 from an influence exerted by peculiarities in the internal structure of certain objects2 for example1 that offered by the human hair1 and which1 when viewed by transmitted light1 presents the appearance of a flattened-out band1 with a darkish centre1 due to the refractive influence of the rays of light transmitted through the hair4 ,that it is a solid or tubular structure is proved by making a transverse section of the hair-shaft1 when it is seen filled up by medullary matter1 the centre being somewhat darker than the outer part4 ,it is1 in fact1 a spiral outgrowth of the epithelial scales1 overlapping each other1 imparting a striated appearance to the surface4 ,a cylindrical thread of glass in balsam appears as a flattened1 band-like streak1 of little brilliancy4 ,another instance of fallacy arising from diversity in the refractive power of the internal parts of an object is furnished by the mistakes formerly made with regard to the true character of the lacun and canaliculi of bone structure4 ,these were long supposed to be solid corpuscles1 with radiating opaque filaments proceeding from a dense centre2 on the contrary1 they are minute chambers1 with diverging passages--excavations in the solid osseous structure4 ,that such is the case is shown by the effects of ,canada balsam1 which infiltrates the osseous substance4 ,air bubbles are a perplexing source of trouble4 ,the better way of becoming accustomed to deceptive appearances of the kind is to compare the aspect of globules of oil in water with bubbles of air in water1 or ,canada balsam4 ,the molecular movements of finely divided particles1 seen in nearly all cases when certain objects are first suspended in water1 or other fluids1 are a frequent cause of embarrassment to beginners4 ,if a minute portion of indigo or carmine be rubbed up with a little water1 and a drop placed on a glass slide under the microscope1 it will at once exhibit a peculiar perpetual motion appearance4 ,this movement was first observed in the granular particles seen among pollen grains of plants1 known as fovilla1 and which are set free when the pollen is crushed4 ,important vital endowments were formerly attributed to these particles1 but ,dr4 ,robert ,brown showed that such granules were common enough both in organic and inorganic substances1 and were in no way 8indicative of life40#db ,professor ,jevons succeeded in throwing light on these curious movements4 ,he showed that they were not due to evaporation1 as some observers contended1 as they continue when all possibility of evaporation is cut off1 when the fluid is surrounded by a layer of oil1 and enclosed in an air-tight case3 but as ,professor ,jevons pointed out1 these movements are greatly affected by the admixture of various substances with water1 being increased by a small quantity of gum1 and checked by a drop of sulphuric acid1 or a few grains of some saline substance1 which increases the conducting power of water for electricity4 ,the ,brownian movement1 now termed pedesis1 much depends upon the size of the particles1 their specific gravity1 and the nature of the liquid in which they are immersed4 ,the correct conclusions to be drawn by the microscopist regarding the nature of an object will necessarily depend upon previous experience in microscopic observations1 a knowledge of the class of bodies brought under observation1 and the skill of the observer in the use of the instrument--that is1 in securing the best focus possible with any objective brought into use4 ,i am indebted to ,messrs4 ,beck for the following series of illustrations1 showing the effect of under and over correction of the objective4 ,,directions ,,for ,,finding ,,the ,,best ,,focus4 ,the method of finding and determining when the screw-collar adjustment of the high-power objective has arrived at a point of perfect definition and magnification is as follows3-- ,select any dark speck of dust1 or an opaque portion of the object1 and carefully focus this small particle by working the screw of the fine adjustment1 move the screw up and down until you are satisfied the image is the sharpest and blackest that can be obtained1 then once more test the focus a little above and a little below while closely scrutinising the effect on the image4 ,it will now be seen that whereas in focussing on one side of the best focus the object disappears in a fog1 by focussing on the other side it remains in view for a longer period1 but alters its appearance2 it is now no longer a black dot1 but a bright dot of light surrounded by a black margin4 ,the effects being thus dissimilar on different sides of the best focus1 show that the objective is not perfectly adjusted for the cover-glass in use4 ,the next step is to find out whether the bright image is above or below the best focus1 as on this depends the direction in which the adjustment-collar should be turned4 ,to determine this it is only necessary to ascertain which way the slow-motion milled head of the microscope turns when moving the objective upwards4 ,in the case under consideration1 the bright image will be above the best focus1 which shows that the cover-glass in use is thicker than that for which the objective is adjusted1 consequently the adjustment-collar must be moved in the opposite direction4 ,illustration3 ,fig4 #bjg4--,podura ,scale ,test4 ,if the collar be turned too far in the opposite direction1 it will be found that the bright image is below the best focus1 and the cover-glass is then thinner than that for which the objective is adjusted4 ,the collar must then be turned back again until the effect on each side of the best focus is exactly similar4 ,this effect in the case of a circular speck of dust will be that the object disappears equally rapidly on either side1 and does not instantly vanish into fog1 on either side presenting the bright spot appearance1 though not in so marked a degree on either side4 ,when the object is in perfect adjustment the expansion of the outline is exactly the same1 both within and without the focus4 ,a different indication1 however1 is afforded by such test-objects as the finer diatoms1 and the podura scale1 in which we have to do with a set of distinct dots and other markings4 ,if the dots have a tendency to run into lines when the object is without the focus1 the glasses should be brought closer together2 on the contrary1 if the lines appear when the object is within the focal point1 the glasses should be farther separated4 ,the adjustment of the objective by the screw-collar in the case of the podura scale should be carried out in the way described1 when the following effects will be observed to take place1 usually in the order of their arrangement4 ,fig4 #a shows the appearance of a podura scale when the adjustment of the object-glass is correct1 and ,fig4 #b shows the effect produced on each side of the exact focus4 ,fig4 #c shows the way in which the markings individually divide when all the adjustments are correct1 and when the focus is altered the least possible amount only each way4 ,figs4 #d and #e show the two appearances on one and the other side of the best focus when the adjustment is incorrect1 ,fig4 #f showing the appearance of the same at its best focus4 ,the scales are magnified #a1cjj diameters1 and each square measures #jja of an inch4 ,this method1 however1 of finding the best focus of an objective can scarcely be accomplished without a sub-stage condenser4 ,it may therefore be of service to the student1 and to those who are not disposed to purchase expensive forms of condensers1 to know that either an inch or an inch and a half objective1 or convex-lens mounted on a simple wooden ring with a flange1 can be arranged to slip in the place of the diaphragm under the stage4 ,this kind of condenser will prove to be of considerable value with a #a_/b-;inch1 a #d_/aj-;inch1 and a #a_/d-;inch2 while a still more excellent achromatic condenser can be made out of a ,steinheil's aplanatic-loup arranged to drop into the central fitting of the sub-stage4 ,as without a condenser of some kind it is hardly possible to enter upon any course of histological or scientific research4#dc ,working ,accessories4 ,,troughs--,,live-,,cages--,,compressors 4 ,a glass plate with a ledge1 and some pieces of thin glass1 although applicable for many purposes1 are specially designed for objects in fluid4 ,thus a drop of fluid containing the object sought for is placed upon the slide and covered by a piece of thin glass2 or1 the object being put upon the glass slide and the thin glass over it1 the fluid is applied near one side1 and runs under by capillary attraction4 ,illustration3 ,fig4 #bjh4--,varley's ,live-box4 ,troughs and ,live-box4--,these are made of various materials1 glass1 vulcanite1 brass1 c41 expressly for examining infusoria and live animals4 ,they should be so constructed as to admit of the use of a medium power1 a #a_/b-;inch at least1 under the microscope4 ,they should also admit of being easily cleaned and repaired when broken2 matters rarely thought of by those who construct them4 ,an early devised live-box 7,varley's1 ,fig4 #bjh7 consists of two circular pieces of brass tubing1 one sliding over the other carrying a disc of glass and fitting over another glass with bevelled edges to prevent the fluid flowing away4 ,illustration3 ,fig4 #bji4--,ross's ,compressorium4 ,the ,compressorium is used for similar purposes4 ,by a graduated pressure the fluid is thinned out and a higher power can be employed for the examination of the object4 ,ross's early compressorium consists of a plate of brass about three inches long1 having in its centre a circle of glass like the bottom of the live-box4 ,this piece of glass is set in a frame1 ,b1 which slides in and out so that it can be removed for the convenience of preparing any object upon it--under water if desirable4 ,the upper movable part1 ,d1 is attached to a screw-motion at ,c2 and at one end of the brass plate1 ,a1 which forms the bed of the instrument1 is an upright piece of brass grooved so as to receive a vertical plate1 to which a downward motion is given by a single fine screw1 surrounded by a spiral spring1 which elevates the plate as soon as the screw-pressure is removed4 ,illustration3 ,fig4 #baj4--;,beck's ,parallel-plate ,compressor4 ,beck's ,parallel-plate ,compressor 7,fig4 #baj7 affords a more exact means of regulating the pressure1 and can be used for a variety of purposes4 ,it is also easily cleaned4 ,illustration3 ,fig4 #baa4--,rousselet's ,compressorium4 ,rousselet's ,compressorium 7,fig4 #baa7 is a very effective form for general use4 ,it is so arranged that the student has perfect control over the pressure to which the specimen should be subjected4 ,the cover-glass is large in comparison with that beneath2 being bevelled causes evaporation to go on very slowly while the pressure between the two glass surfaces is kept perfectly parallel4 ,illustration3 ,fig4 #bab4--;,botterill's ,live-trough4 ,botterill's ,live-trough 7,fig4 #bab7 consists of two brass plates screwed together by binding screws1 and holding between them two plates of thin glass1 which are maintained at a proper distance by inserting a semicircular flat disc of india-rubber4 ,illustration3 ,fig4 #bac4--;,glass ,trough4 ,glass troughs for chara and polypes 7a sectional view of one shown at ,fig4 #bac7 are made of three pieces of glass1 the bottom being a thick strip1 and the front 7a7 of thinner glass than the back 7b72 the whole is cemented together with ,jeffery's marine-glue4 ,the method adopted for confining objects near the front glass varies according to circumstances4 ,the most convenient is to place in the trough a piece of glass wide enough to stand across diagonally1 as at c2 then1 if the object be heavier than water1 it will sink until stopped by the glass plate4 ,at other times1 when used to view chara1 the diagonal plate may be made to press it close to the front by means of a wedge of glass or cork4 ,when using the trough the microscope should be placed in a nearly horizontal position4 ,illustration3 ,fig4 #bad4--,weber's ,slip with ,convex ,cell for use as a ,live-trough4 ,illustration3 ,fig4 #bae4--;,current-slide ,live-cell4 ,cells for viewing living objects1 and watching their movements1 take many forms1 usually determined by the makers for the purposes they are required to serve4 ,the smaller glass troughs 7,figs4 #baf1 #baf;a7 are made for examining the small infusoria1 rotifers1 c41 some of which take special forms1 as the double or divided trough 7,fig4 #bag7 intended for viewing the circulation of the blood in the tail of a small fish1 and at the same time keep up a supply of water and air4 ,illustration3 ,fig4 #baf4 ,illustration3 ,fig4 #baf;a4 ,the ,frog-plate consists of a strip of plate-glass1 or wood1 pierced with holes on either side1 through which tapes are passed to secure the frog in its place4 ,at the extreme end is a shallow glass trough1 made to hold a sufficient quantity of water to keep the web of the foot moist while under examination4 ,in this way a continuous view of the circulation of the blood of the animal is obtained4 ,illustration3 ,fig4 #bag4 ,growing ,cells have received more attention from those who devote attention to the lower forms of life1 the construction of which1 for the purpose of maintaining a continuous supply of fresh water to objects under observation1 and for sustaining their vital energy for a long period1 is of some importance4 ,the employment of live-cells is resorted to by microscopists1 as doubtless there is much to be discovered concerning the metamorphoses which some of the lower micro-organisms1 both of plant and animal life1 pass through4 ,illustration3 ,fig4 #bah4--;,frog-plate4 ,holman's life slide consists of a #c #a inch glass slide1 with a deep oval cavity in the middle to receive the specimen for observation4 ,a shallow oval is ground and polished around the deep cavity1 forming a bevel4 ,from this bevel a fine cut extends1 to furnish fresh air to the living low forms of life which invariably seek the bevelled edge of the cavity1 thus bringing them within reach of the highest powers4 ,he also contrived a convenient form of 8moist chamber10 or animalcule-cage 7,fig4 #bbj71 for the purpose of studying the growth of minute organisms1 without in any way disturbing them for a lengthened period4 ,this is also found useful as a dry chamber for holding minute insects4 ,illustration3 ,fig4 #bai4--;,holman's ,life ,slide4 ,full size4 ,illustration3 ,fig4 #bbj4--;,holman's ,moist ,chamber4 ,zentmayer's ,holman ,syphon ,slide is used either as a hot or cold water cell4 ,it should be deep enough to hold a small fish or newt1 and retain it without any undue pressure4 ,when in use it is only necessary to place the animal into it 7as shown in ,fig4 #bba71 with some water1 and secure it with a glass cover2 then immerse the upper tube in a jar of water1 while another1 at a lower level1 maintains a current4 ,when the slide is on the stage of the microscope1 one jar should stand on a lower level than the other1 the slide being made the highest part of the syphon4 ,the pressure of the atmosphere is sufficient to keep the cover-glass in its place4 ,the examination of the various kinds of infusorial life--rotifers1 for instance--is facilitated by the addition of the smallest particle of colouring matter1 either carmine or indigo4 ,a small quantity of either of these colours should be rubbed up in a little water in a watch-glass1 and a portion taken up on the point of a brush1 and the brush run along the edge of the cover-glass2 sufficient will be left behind to barely tinge the water with the colour1 and this gradually distributes itself over the rotifers4 ,under the microscope this minute quantity will be seen like a rising cloud of dust1 and as it approaches a rotifer it is whirled round in different curves1 showing at once the action of its wonderfully rapid cilia4 ,this colouring matter appears to be devoured1 as it may be traced from the mouth to the digestive canal4 ,monads may be detected by this means1 and the smaller forms of alg1 ,euglena viridis and ,protococcus pluvialis4 ,illustration3 ,fig4 #bba4--;,holman's ,syphon ,slide4 ,dipping-tubes4--,in dealing with infusorial or monad life it is convenient to keep a stock-bottle ready for their reception1 and in a light favourable to health4 ,when a live specimen is required for examination1 the dipping-tube is brought into requisition4 ,these tubes are open at both ends1 and vary in length and diameter4 ,their ends should be nicely rounded off in the flame of a blow-pipe2 in form either straight1 or bent and drawn out to a fine point1 as represented in ,fig4 #bbb4 ,when any special specimen is required for examination1 then one of the tubes must be passed down into the water1 the upper orifice having been previously closed by the forefinger1 and kept tightly pressed1 until its lower orifice comes in contact with the object4 ,on the finger being removed1 the water rushes up and carries the creature sought for with it4 ,the finger is once more replaced at the top of the tube2 it is then lifted out1 and the contents deposited in one or other of the glass cells described4 ,tubes with india-rubber covers can be had4 ,illustration3 ,fig4 #bbb4--;,dipping-tubes4 ,illustration3 ,fig4 #bbc4--,stock-bottle4 ,moist and ,warm ,stages4--,in addition to the moist cells and chambers described it is often found necessary in working out the histories of minute organisms to keep them for some time under observation1 and as far as possible in an undisturbed condition1 and it is equally necessary to prevent evaporation of the water in which they are immersed4 ,one of the best warm stages is that known as ,maddox's growing stage2 this can be had of any optician4 ,more elaborate adaptions are required for the study of special organisms1 and for experimental research4 ,illustration3 ,fig4 #bbd4--;,bartley's ,warm ,stage4 ,in that case ,bartley's ,warm ,stage 7,fig4 #bbd7 is recommended4 ,there are other forms of warm stages in use1 many of an inexpensive kind and readily adaptable to any stage4 ,bartley's has proved useful2 it consists of a vessel1 ,e1 three parts filled with water and supported on a ring stand4 ,this may be kept at any temperature by the small spirit-lamp1 ,c2 a syphon tube d conveys the warm water along f1 and through the bent tubing which surrounds the object under observation on the stage1 ,d1 and then passes off through the open end1 ,c1 into the receptacle1 ,b1 placed to receive the overflow4 ,steam can be used for heating1 or iced water for observing the effects of cold upon the organism4 ,a simple form of warm stage may be made of an oblong copper plate1 two inches long by one wide1 from one side of which a rod of the same material projects4 ,the plate has a round aperture1 the centre half an inch in diameter1 and is fastened to an ordinary slide with sealing-wax4 ,the drop or object to be examined is placed on a large-sized cover-glass and covered over with a smaller one4 ,olive oil or vaseline is painted round the edge of the smaller one to prevent evaporation1 and the preparation is placed over the aperture in the plate4 ,the slide bearing the copper plate is clamped to the stage of the microscope4 ,the flame of the spirit-lamp is applied to the extremity of the rod1 and the heat is conducted to the plate and thence transmitted to the specimen4 ,in order that the temperature of the copper plate may be approximately that of the body1 the lamp is so adjusted that a fragment of cacao butter and wax placed close to the preparation is melted4 ,professors ,stricker and ,schfer have constructed warm stages for accurate observations1 and which fully answer every purpose4 ,illustration3 ,fig4 #bbe4--,stricker's ,warm ,stage4 ,stricker's ,stage 7,fig4 #bbe7 consists of a rectangular box with a central opening1 ,c1 permitting the passage of light through the specimen under examination4 ,the water makes its exit and entrance at the side tubes ,b ,b1 and the temperature is indicated by a thermometer in front4 ,in this apparatus either warm or cold water can be continuously used4 ,illustration3 ,fig4 #bbf4--,schfer's ,warm ,stage4 ,schfer's apparatus 7,fig4 #bbf7 consists of a vessel filled with water 7seen near the stage7 which has been first boiled to expel the air1 and then heated by means of a gas flame4 ,the warm water ascends the india-rubber tubing to the brass box on the stage4 ,the box is pierced by a tubular aperture to admit light to the object1 and has an exit tube by which the cooled water from the stage returns by another piece of tubing to be reheated by the gas flame4 ,there is a gas-regulator1 by means of which any temperature can be maintained4 ,methods of ,preparing1 ,hardening1 ,staining and ,section ,cutting4 ,numerous methods are employed for the preparation1 hardening1 staining1 and section cutting of animal and vegetable tissues for the microscope1 the details of which are modified1 or varied as may be found needful1 from time to time1 by those whose intimate acquaintance with the subject entitles them to make innovations and changes in this very important department of microscopy4 ,in the hands of the original worker1 formul and methods will only be regarded as finger-posts pointing out a means of saving time in turning over pages to find this or that special method of staining4 ,for this particular reason ,i have collected all the most accredited formul together in an ,appendix at the end of the book1 and arranged them alphabetically for ready reference4 ,as to section cutting1 the student will do well to practise himself in making dissections1 thick and thin sections1 of vegetable and animal substances4 ,the medical student will require no advice on this point1 as the use of the scalpel1 and those instruments needed for microscopical work1 form an important part of his education4 ,of all the instruments contrived for delicate dissections1 none are more serviceable than those which the student may make for himself out of ordinary needles4 ,these may be fixed in handles as represented in ,fig4 #bbi1 in addition to which1 a pair of scissors and forceps1 and a few small knives1 such as those used in eye-operations1 will prove most suitable4 ,the double-bladed scissors represented in ,fig4 #bbg1 with curved blades1 are brought into use for cutting vegetable and other soft structures1 the disadvantage attendant upon the use of which is owing to the curvature of the blades2 when dealing with flat surfaces1 the middle of the section is left too thick to exhibit structure4 ,the double-bladed knife of ,professor ,valentin was formerly held in high estimation by the microscopist1 but this has been almost superseded by the microtome1 which has taken the place of all other instruments1 since by its aid uniform series of nearly all substances can be cut4 ,the standard unit of a perfect section cutter1 of any kind1 has been fixed by the ,royal ,microscopical ,society at the one-thousandth of a millimetre4 ,illustration3 ,fig4 #bbg4--,section ,scissors and ,forceps4 ,the use of the razor for cutting sections has not been wholly abandoned1 the method of using which is as follows3--,take the tissue between the thumb and finger of the left hand1 hold the finger horizontally1 so that its upper surface may form a rest for the razor to glide upon1 take the razor firmly1 and keep the handle in a line with the blade1 then draw it through the tissue from heel to point and towards yourself4 ,while cutting keep the razor well wetted with diluted methylated spirit4 ,illustration3 ,fig4 #bbh4--;,dissecting ,knives4 ,some preparation is required for cutting sections with the single microtome4 ,the substance to be cut must be embedded in some other material1 as carrot1 turnip1 potato1 alder pith1 paraffin1 or thick gum1 with either of which the cylinder or well of the microtome must be so nearly filled as to leave only an excavation in the centre for the specimen to be operated upon to occupy4 ,the various forms of microtomes in use1 and the selection of the most suitable1 is therefore a matter of some difficulty4 ,i must content myself by particularising two or three typical forms in general use4 ,as all the substances intended for cutting require preparation1 it will be first necessary to attend to the following directions given by one experienced in section cutting1 ,mr4 ,m4 ,j4 ,cole#dd3--7a7 ,always use fresh tissues4 7#b7 ,cut the organs into small pieces with a sharp knife4 7#c7 ,never wash a specimen in water2 when it is necessary to remove any matter1 allow some weak salt solution to flow over the surface of the tissue1 or wash it in some hardening re-agent4 7#d7 ,all specimens should be hardened in a large quantity of the re-agent2 too many pieces should not be put into the same bottle1 and keep them in a cool place4 7#e7 ,in all cases the hardening process must be completed in spirits4 7#f7 ,label the bottles1 stating the contents1 the hardening fluid used1 and when changed4 ,attention to details is necessary1 as if hardening is neglected1 good sections cannot be made4 ,embedding in ,paraffin ,wax or ,lard4--,melt together1 by the aid of gentle heat1 four parts of solid paraffin and one part of lard4 ,a quantity of this may be made and kept ready for use4 ,melt the paraffin mass over a water bath1 take the specimen1 and dry it between the folds of a cloth to remove the spirit1 so that the paraffin may adhere to its surface1 place it in a small chip-box1 in the desired position1 and pour in enough melted paraffin to cover it1 then set aside to solidify2 when quite cold break away the box1 and cut sections from the embedded mass with a sharp razor4 ,to infiltrate a tissue with paraffin1 place the specimen in absolute alcohol or chloroform for an hour or two1 then transfer to a bath of melted paraffin1 at its melting point 7about #aaj ,f471 and keep it at this temperature for several hours1 so that the paraffin may penetrate to the middle of the tissue4 ,then remove the specimen from the paraffin and put it into a small chip-box1 pour in enough paraffin to cover it1 and set aside to cool4 ,when quite cold1 make sections as before1 with a razor1 or fix it into a microtome1 with a little melted paraffin4 ,the sections when cut must be placed in turpentine to remove the paraffin1 and then into absolute alcohol to remove the turpentine1 and finally in distilled water to remove the alcohol1 when they may be forthwith stained4 ,it is often found better to stain the tissue in bulk before embedding4 ,in this case the sections will only require the turpentine to dissolve away the paraffin1 and may then be mounted in ,canada balsam4 ,hardening and ,preparing ,animal ,tissues for section cutting and microscopical examination4--,fresh tissues are not well suited for microscopical examination1 but it is sometimes advisable to observe the appearances of a fresh specimen1 especially if it is suspected to contain amaloid bodies or parasites4 ,it will then be necessary to tease out a small portion of the tissue immersed in a weak solution of salt and water by the aid of a pair of fine needles 7,fig4 #bbi7 and the dissecting microscope 7,fig4 #bcj74 ,illustration3 ,fig4 #bbi4--,needles for teasing out ,sections4 ,illustration3 ,fig4 #bcj4--;,dissecting ,microscope4 ,the most important point in connection with an instrument of this kind is1 that it affords firm and convenient rests for the hands1 and should not be raised too high from the table4 ,the stage should either be made of glass1 or provided with a glass dish for dissecting under water1 or preservative fluid4 ,a pair of aplanatic lenses1 mounted on a focussing bar as shown in ,fig4 #bcj1 will be found the most convenient to work with4 ,investigations of this nature should be always carried out in the manner described1 but preparations of the kind cannot be preserved any length of time1 unless properly hardened in spirit or ,formalin solution4 ,the method of teasing out under the light of a condensing lens is shown in ,fig4 #bca4 ,illustration3 ,fig4 #bca4--,method of teasing out ,muscular ,fibre1 c41 in a fluid medium under ,condensed ,light4 ,it may be as well to state at the outset that physiological and pathological tissues can be hardened by immersion in methylated spirit alone1 or a saturated solution of picric acid in methylated spirit in about a week1 and it is said to yield satisfactory results1 even some of the tissues being ready in twenty-four hours4 ,the only drawback is that sections thus quickly hardened must be stained with picro-carmine4 ,but1 whatever method of hardening adopted1 the tissue should be washed by means of a stream of water for half an hour1 to remove all traces of the hardening agent1 and on its removal pressed between folds of cotton cloth or fine ,swedish filtering paper4 ,the principal hardening re-agents usually kept in bulk ready for use are the following3-- ,absolute ,alcohol4--,this is suitable for the internal organs of animals1 glands1 c4 ,these organs must be perfectly fresh1 and should be cut into small pieces1 so that the alcohol may penetrate them as quickly as possible4 ,the hardening is usually complete in a short time4#de ,chromic ,acid and ,spirit4--,chromic acid one-sixth per cent41 water solution two parts1 and methylated spirit one part4 ,this reagent hardens in about ten days4 ,then transfer to methylated spirit1 which should be changed every day until all colour is discharged from the tissue4 ,this is a suitable reagent for the preparation of cartilage1 nerve trunks1 heart1 lips1 blood vessels1 trachea1 lungs1 tongue1 intestines1 and gullet4 ,potassium ,bichromate4---,make a two per cent4 water solution of this salt4 ,this will harden specimens in about three weeks4 ,then transfer the preparation to methylated spirit1 and change it every day until all colour is discharged4 ,this is suitable for spinal cord1 medulla1 cerebellum1 and cerebrum4 ,mller's ,fluid4--,bichromate of potash #cj grains1 sulphate of soda #ae grains1 distilled water #c-a_/b ounces4 ,this hardens in from three to six weeks4 ,then transfer1 as before1 to methylated spirits1 and change it every day until colour ceases to appear4 ,most suitable for lymphatic glands1 eye-ball and its internal structures1 as well as for tendons1 and thymus gland4 ,methylated ,spirit may be generally employed1 but it has a tendency to shrink some tissues too much2 it hardens in about ten days4 ,it is usual to change the spirit daily1 for the first three days at least4 ,skin1 mammary gland1 supra-renal glands1 tonsils1 and all injected organs may be hardened in it4 7,see note on the adulteration of methylated spirit with rack-oil1 which utterly spoils it for use47 ,decalcifying solution for bones and teeth4 ,take one-sixth per cent4 watery solution of chromic acid1 and to every measured ounce add five drops of nitric acid4 ,this reagent will soften the femur of any small animal in about three weeks2 larger require a longer time4 ,change the fluid several times1 and test its action by running a needle through the thickest part of the bone4 ,should it not pass through easily1 then continue the process until it does4 ,when soft enough transfer to water1 let it soak for an hour or two1 then pour off the water and add ten per cent4 solution of carbonate of soda1 and soak for twelve hours to remove all trace of acid4 ,wash again in water1 and transfer to methylated spirit until required4 ,teeth require a large quantity of the decalcifying solution for softening4 ,microtomes4--,the simplest form of 8hand-cutting machine0 is that worked by a screw1 which raises the preparation1 and at the same time regulates the fineness of the section4 ,when a number of sections are required1 or when a complete series of sections of an organ is desired1 ,cole's simple microtome 7,fig4 #bcc7 is in every way adapted4 ,illustration3 ,fig4 #bcb4--;,hand ,section ,cutter4 ,illustration3 ,fig4 #bcc4--;,cole's ,section ,cutting ,microtome4 ,the method of using it is as follows3--,screw the microtome firmly to the table1 and with the brass tube supplied with the microtome1 punch out a cylinder of carrot to fit into the well4 ,cut this in half longitudinally1 and scrape out enough space in one half of the carrot to take the specimen2 then place the other half of carrot in position1 and make sure that the specimen is held firmly between them1 but it must not be crushed4 ,now put the cylinder of carrot and specimen into the well of the microtome and commence cutting the section4 ,a good razor will do1 but it is better to use the knife which ,messrs4 ,watson supply with the microtome4 ,while cutting keep the knife and plate of the microtome well wetted with dilute methylated spirit1 and as sections are cut place them in a saucer of dilute spirit4 ,a number of sections may be cut and preserved in methylated spirit until required for examination or mounting4 ,when a specimen has a very irregular outline1 it cannot be very successfully embedded in carrot2 paraffin will then be found to be more suitable4 ,place the tissue in the well of the microtome in the proper position1 pour in enough melted paraffin to cover it1 and put it by to get cold and hard before attempting to cut sections4 ,illustration3 ,fig4 #bcd4--,the ,cambridge ,rocking ,microtome4 ,cambridge ,rocking ,microtome4--,this new pattern ,cambridge ,rocking ,microtome 7,fig4 #bcd7 possesses advantages over other instruments in use for cutting flat sections1 and not parts of a cylindrical surface4 ,the tube containing the paraffin is #cj millimetres in internal diameter instead of #bj millimetres1 as in the earlier forms4 ,the forward movement is also increased1 so that an object #ab millimetres long can be cut throughout its whole length4 ,it is provided with a dividing arc for reading off the thickness of the section in thousandths of a millimetre4 ,the razor may be fixed either with its edge at right angles to the direction of motion of the object1 or diagonally1 for giving a slicing cut4 ,the object can also be raised and fixed in position clear of the razor4 ,this microtome has both steadiness and stiffness in its geometrical arrangement and bearings1 while the simplicity and efficiency of its mechanism for advancing the section between each stroke of the razor is remarkable4 ,although it may appear more complicated at first sight1 it is found not to be so when brought into use4 ,illustration3 ,fig4 #bce4--;,cathcart's ,microtome4 ,illustration3 ,fig4 #bce;a4--,section ,cutting ,holder for ,microtome4 ,cathcart's ,freezing ,microtome4--,this is a convenient and useful microtome for freezing purposes4 ,since its first introduction it has been much improved4 ,the clamping arrangements give steadiness1 and the principal screw is more effective2 the freezing-plate is circular1 and the arrangements made for preventing the ether from reaching the upper plate secures the object in view4 ,this instrument can now be used for embedding as well as freezing4 ,the directions for freezing are as follows3-- #a4 ,place a few drops of mucilage 7one part gum to three parts water7 on the zinc plate4 #b4 ,take a piece of the tissue to be cut1 of about a quarter of an inch in thickness1 and press it into the gum4 #c4 ,fill the ether bottle with anhydrous methylated ether1 and push the spray points into their socket4 ,all spirit must of course have been previously removed by soaking for a night in water4 ,the tissue should afterwards be soaked in gum for a like time before being cut4 ,work the spray bellows briskly until the gum begins to freeze2 after this work more gently4 ,be always careful to brush off the frozen vapour which1 in a moist atmosphere1 may collect below the zinc plate4 ,if the ether should tend to collect in drops below the plate1 work the bellows slower4 #e4 ,raise the tissue by turning the milled head1 and cut by sliding the knife along the glass plates4 #f4 ,after use1 be careful to wipe the whole instrument clean4 #g4 ,should the ether point become choked1 clear by means of the fine wire provided for the purpose4 #h4 ,the instrument is intended for use with methylated sulphuric ether4 #i4 ,in clamping the instrument to a table1 or other support1 care should be taken that the zinc plate is in a horizontal position4 ,if the plate be not horizontal1 the gum will tend to run to one side4 ,the arrangement made for cutting and embedding sections consists of a cylindrical tube 7,fig4 #bce;a7 fitting into the principal well of the microtome1 within which is a hinged plate1 upon which the screw acts1 as in an ordinary vice4 ,to bring this into use the freezing apparatus must be first removed1 and the embedding tube placed in the well1 and firmly pressed into place4 ,staining ,animal ,structures4 ,specific stains are chiefly employed to assist the eye in distinguishing one elementary tissue from another4 ,it is therefore necessary to stain all structures1 as certain parts are seen to have a special affinity for one colouring agent rather than another1 whereby they become more deeply stained1 and consequently more clearly differentiated4 ,for staining animal structures1 borax1 carmine1 and hmatoxylin are more frequently employed than others4 ,the formul for each will be found in the ,appendix 8,formul and ,methods40 ,staining ,process4--,place the section in distilled water to wash away the alcohol2 place a little of the carmine in a watch glass1 and immerse the section in it for four or five minutes2 then remove it to a solution composed of methylated spirit five parts1 hydrochloric acid one part2 shake well together4 ,this solution should be kept ready for use4 ,immerse the section in this solution and leave it to soak for about five or ten minutes if over-stained1 until the desired tint has been obtained4 ,sections of skin and fibrous tissue may be left until nearly all colour is removed1 the glands and hair follicles will then be brought out more clearly4 ,the section must be transferred to methylated spirit to remove all traces of acid1 then to oil of cloves contained in a watch glass1 lift the section from the methylated spirit by one of the lifters 7,fig4 #bej71 and carefully float it on the oil1 in which it should be allowed to remain for about five minutes4 ,this is the clearing process1 the object of which is to remove the spirit and prepare the section for mounting in ,canada balsam4 ,first1 however1 place the section in filtered turpentine to wash away the oil of cloves2 this is found to answer better than another plan adopted1 that of removing the section from the oil of cloves and mounting it in balsam direct4 ,the oil1 however1 has a tendency to darken the balsam4 ,logwood or ,hmatoxylin ,stains 7see ,appendix for the several formul74 ,staining by this agent is effected as follows3-- ,after the specimen has been hardened in any of the chromic acid solutions in use1 transfer it to a seven per cent4 watery solution of bicarbonate of soda for about five minutes1 then wash well in distilled water4 ,spirit prepared preparations do not require to be transferred to the soda solution1 but all sections must be washed before they are transferred to the logwood stain4 ,to a watch glass nearly full of distilled water add ten or twenty drops of the logwood stain1 in which it should remain for twenty or thirty minutes4 ,wash well with the ordinary tap water1 which will fix the dye and cause it to become blue4 ,dehydrate in methylated spirit1 clear in clove oil1 and mount in dammar or ,canada balsam4 ,double-staining with ,hmatoxylin and ,rosin4--,stain the section as directed above1 then place it in an alcoholic solution of rosin1 about one gramme of rosin to an ounce of methylated spirit1 and let it soak for a few minutes2 wash well in methylated spirit1 clear in oil of cloves1 and mount in balsam4 ,canada balsam should be prepared for use as follows3--,one ounce of dried balsam to one fluid ounce of pure benzole2 dissolve1 and keep in an outside stoppered bottle4 ,clear the section in clove oil1 and place it in turpentine1 clean a cover-glass and slide1 place a few drops of balsam on the centre of the latter1 take the section from the turpentine on a lifter1 allow the excess of turpentine to drain away1 and with a needle-point lift the section on to the balsam slide4 ,now take up the cover-glass with a pair of forceps 7,fig4 #bcf71 and bring its edge in contact with the balsam1 ease it down carefully as shown in ,fig4 #bcg1 so that no air bubbles are enclosed1 and with the needle point press the surface of the cover until the section lies quite smoothly and flat1 and the excess of balsam is pressed out4 ,the slide should now be transferred to the warm-chamber1 and there allowed to remain for a day or two1 or until set and hardened4 ,illustration3 ,fig4 #bcf4--;,forceps for ,mounting4 ,any exuded balsam may be washed away with benzole and a soft camel's hair brush2 then dry the slide with an old piece of linen cloth1 and apply a ring of cement or ,japanner's gold size4 ,other methods for staining and mounting will be found to answer quite as well--that of ,beneke's is a useful one for staining connective tissue4 ,illustration3 ,fig4 #bcg4--,mode of placing ,glass ,cover on ,object4 ,for staining connective tissue a modification of ,weigert's method of staining fibrine is resorted to4 ,portions of tissue that have been fixed in alcohol having been embedded in paraffin and cut1 the sections are detached and placed on glass slides1 and stained for ten or twenty minutes with gentian violet1 ten parts1 well shaken with water #ajj parts2 filter1 and add five to ten parts of a concentrated alcoholic gentian violet solution4 ,afterwards treat for one minute with lugol solution1 of a port wine tint1 dry with filter paper and decolourise with aniline xylol 7aniline oil two parts and xylol three parts74 ,decolourisation having been stopped at the right point 7judged from experience7 mount the sections in xylol balsam4 ,the fibres of the connective tissue should appear stained of various shades of violet4 ,double ,staining nucleated blood corpuscles4 ,two kinds of staining agents are required4 ,stain ,a3 dissolve five grammes of rosin in half an ounce of distilled water1 and add half an ounce of rectified alcohol4 ,stain ,b3 dissolve five grammes of methyl green in an ounce of distilled water4 ,place a drop of frog's blood on a glass slide1 and with the edge of another slide spread it evenly over the centre of the slip1 and put it away to dry2 when quite dry flood the slide with stain ,a for three minutes1 and wash with water1 now flood the slide with ,stain ,b for five minutes1 wash again with water1 and allow the slide to dry4 ,apply a drop of the prepared ,canada balsam and a cover-glass4 ,illustration3 ,fig4 #bch4--,shadbolt's ,turn-table4 ,the blood of such mammals as are non-nucleated should be treated in a slightly different way4 ,spread a drop or two of blood on a slide and dry it quickly2 then put the slide on ,shadbolt's turn-table 7,fig4 #bch7 and run a ring of cement around it2 allow this time to dry1 and then apply a second coating1 and before this becomes quite dry place on it a clean glass cover1 and press it down gently with one of the fine needles 7,fig4 #bbi71 until firmly adherent4 ,epithelium4--,remove from the mouth of a frog by scraping some squamous epithelium2 the columnar must be taken from the stomach2 place it in glycerine1 or ,farrant's solution on the slide2 apply a cover-glass1 and with the point of the needle press it down until the epithelium cells are separated and spread evenly over the slide4 ,set this aside for a day or two1 then wash away any of the medium which may have escaped2 dry the slide1 and run a ring of cement around the edges1 on the turn-table4 ,portions of the intestine of a rabbit or other animal may be treated in the same way4 ,if it is wished to make permanent specimens of such structures1 the intestine must be hardened in a two per cent4 solution of bichromate of potash for a couple of days1 then washed until all colour is discharged1 and removed to a solution of picro-carmine for twenty-four hours1 after which allow the stain to drain away1 when it will be ready for mounting4 ,by the aid of the handy little spring clip 7,fig4 #bci71 objects of delicacy when mounted may be left to dry and harden for any length of time4 ,illustration3 ,fig4 #bci4--,spring-clip for ,mounting4 ,striped muscular fibre1 taken from the pig1 must be teased out in a two per cent4 solution of bichromate of potash1 in which it should remain for two or three weeks1 when it may be transferred to methylated spirit1 and allowed to remain until required for mounting4 ,soak a piece in water to remove the spirit1 place a small fragment on a slide in a few drops of water1 and with a couple of needles tease the tissue up1 so as to separate the fibres4 ,drain away the water1 and apply a drop or two of ,farrant's medium and a cover-glass1 which cement down as before directed4 ,fibrous tissue may be served in the same way4 ,yellow elastic tissue must be first placed in a solution of chromic acid and spirit for ten days1 and then treated as directed for muscular fibre4 ,non-striated ,muscle4--,a piece of the intestine of a rabbit should be steeped in chromic acid and spirit for ten days1 then washed in water2 strip off a thin layer of the muscular coat1 and stain in hmatoxylin solution4 ,well wash in ordinary water until the colour changes to blue1 when it will be fit for mounting4 ,place a fragment on a slide and a drop of water1 and carefully separate the fibres with a pair of needles4 ,drain off the water1 as it is now ready for mounting1 place on slide1 and add a drop or two of ,farrant's medium1 and place on the cover-glass4 ,nerve ,tissue4--,dissect out the large sciatic nerve from a frog's thigh1 and stretch it on a small piece of wood1 to which pin both ends of the nerve1 and transfer it to a one per cent4 solution of osmic acid for an hour or two4 ,wash in distilled water2 tease up a small fragment on a slide 7as shown in ,fig4 #bdj71 and apply a drop or two of ,farrant's solution and cover-glass4 ,tissues containing air should be soaked in water that has been boiled for ten minutes2 this will displace the air4 7,for ,farrant's medium1 see ,appendix47 ,glycerine ,jelly4--,dissolve one ounce of ,french gelatine in six ounces of distilled water1 and melt together in a hot-water bath4 ,when quite dissolved1 add four ounces of glycerine1 and a few drops of creosote or carbolic acid4 ,filter through white filtering paper while warm1 and keep in a capped bottle4 ,this may be used instead of ,farrant's solution4 ,illustration3 ,fig4 #bdj4--,method of ,teasing out ,tissue4 ,nitrate of silver darkens by exposure2 it is used in a half per cent4 watery solution4 ,specimens to be acted upon should be washed in distilled water1 to remove every trace of sodium chloride1 and then steeped in the silver solution for some two or three minutes1 after which they should be again washed until they cease to turn milky2 then place them in glycerine and expose them to the action of light until they assume a dark brown colour1 when they should be mounted in glycerine or glycerine jelly4 ,by means of this stain the endothelial cells of the lymphatics1 blood vessels1 c41 and the nodes of ,ranvier1 constrictions in medullary nerves1 are rendered visible4 ,sections of any of these may subsequently be stained by logwood or carmine4 ,several methods have been adopted for staining with gold chloride4 ,dr4 ,klein's and ,professor ,schfer's are among the best4 ,dr4 ,klein's method of showing the nerves of the cornea is as follows3--,remove the cornea within fifteen minutes of death2 place it in a half per cent4 chloride of gold solution for half an hour1 or an hour2 wash in distilled water1 and expose to the light for a few days2 in the meantime occasionally change the water4 ,then immerse it in glycerine and distilled water1 in the proportion of one to two2 lastly1 place it in water1 and brush gently with a sable pencil to remove any precipitate1 when it will be fit for mounting in glycerine4 ,the colour of the cornea should be grey-violet4 ,schfer adopts another method--a double chloride of gold and potassium solution4 ,osmic acid1 first used by ,schultze1 is useful for the demonstration of fatty matters1 all of which it colours black2 it is also valuable for certain nerve preparations4 ,specimens should be allowed to remain in a one or two per cent4 aqueous solution of the acid from a quarter to twenty-four hours1 when the staining will be completed2 but if it is desired to harden specimens at the same time1 they should remain in it for some few days4 ,osmic acid does not penetrate very deeply1 therefore small portions should be selected for immersion4 ,this is a useful stain for infusorial animals4 ,chloride of palladium1 another of ,schultze's staining fluids1 is used to stain and harden the retina1 crystalline lens1 and other tissues of the eye1 the cornified fat and connective tissues remaining uncoloured4 ,the solution should be used very weak3--,chloride of palladium1 one part2 distilled water1 #a1jjj parts4 ,specimens should be mounted in glycerine at once1 or further stained with carmine4 ,dr4 ,schfer employs a silver nitrate and gelatine solution for demonstrating lung epithelium2 this is made as follows3--,take of gelatine ten grammes1 soak in cold water1 dissolve1 and add warm water to #ajj cc4 ,dissolve a decigramme of nitrate of silver in a little distilled water1 and add to the gelatine solution4 ,inject this with a glass syringe into the lung until distension is pretty complete4 ,leave it to rest in a cool place until the gelatine has set2 then cut sections as thin as possible1 place them on a slide with glycerine1 and expose to light till ready for mounting4 ,of the double stains ,mr4 ,groves prefers only those where the double colour is produced by a single process--or stains in which one colour is first employed1 and then another4 ,single stains are picro-carmine1 carmine and indigo carmine1 aniline blue and aniline red4 ,picro-carmine is specially useful for staining sections hardened in picric acid4 ,it is prepared in several ways3-- #a4 ,add to a saturated solution of picric acid in water a strong solution of carmine in ammonia to saturation4 #b4 ,evaporate the mixture to one-fifth its bulk over a water bath1 allow it to cool1 filter from deposit1 and evaporate to dryness1 when picro-carmine is left as a crystalline powder of red-ochre colour4 ,sections can be stained in a one per cent4 aqueous solution1 requiring only ten minutes for the process2 wash well in distilled water1 and transfer them to methylated alcohol1 then to absolute alcohol1 after which they are rendered transparent by immersing in oil of cloves or benzole1 before mounting in balsam or dammar4 ,to summarise ,mr4 ,groves' recommendations3-- #a4 ,let the material be quite fresh4 #b4 7a7 ,take care that the hardening or softening fluid is not too strong4 7b7 ,use a large bulk of fluid in proportion to the material4 7c7 ,change the fluid frequently4 7d7 ,if freezing be employed1 take care that the specimen is thoroughly frozen4 #c4 7a7 ,always use a sharp razor4 7b7 ,take it with one diagonal sweep through the material4 7c7 ,make the sections as thin as possible2 and 7d7 ,remove each one as soon as cut1 for if sections accumulate on the knife or razor they are sure to get torn4 #d4 7a7 ,do not be in a hurry to stain1 but 7b7 ,remember that a weak colouring solution permeates the section better1 and produces the best results2 and 7c7 ,that the thinner the section the better it will take the stains4 #e4 7a7 ,always use glass slips and covers free from scratches and bubbles1 and chemically clean4 7b7 ,never use any but extra thin circular covers1 so that the specimens may be used with high powers4 7c7 ,always use cold preservatives1 except in the case of glycerine jelly1 and never use warmth to hasten the drying of balsam or dammar1 but run a ring of cement round the cover4 #f4 ,label specimens correctly2 keep them in a flat tray1 and in the dark4 ,double and ,treble ,staining4 ,dr4 ,w4 ,stirling#df furnishes a brief but useful account of the methods he has employed with much success4 ,osmic ,acid and ,picro-carmine4--,mix on a glass slide a drop of the blood of newt or frog and a drop of a one per cent4 aqueous solution of osmic acid1 and allow the slide to stand by4 ,this will fix the corpuscles without altering their shape4 ,at the end of five minutes remove any excess of acid with blotting-paper1 add a drop of a solution of picro-carmine1 and a trace of glycerine to prevent evaporation1 and set aside for three or four hours to see that no overstaining takes place4 ,at the end of this time the nucleus will be found to be stained red1 and the perinuclear part yellow4 ,picric ,acid and ,picro-carmine4--,place a drop of the blood of a frog or newt on a glass slide1 and add a drop of a saturated solution of picric acid3 put the slide aside and allow it to remain for five minutes2 at the end of that time1 when the acid has fixed the corpuscles 7that is1 coagulated their contents71 any excess of acid should be removed as before4 ,a drop of solution of picro-carmine should now be added1 and a trace of glycerine1 and the preparation set aside for an hour4 ,at the end of that time remove the picro-carmine solution by means of a narrow slip of blotting-paper1 and add a drop of ,farrant's solution of glycerine and apply glass-cover4 ,the perinuclear part of the corpuscles will be seen to be highly granular and of a deep orange colour1 whilst the nucleus is stained red4 ,some of the corpuscles will appear of a delicate yellow colour1 and threads are seen extending from the nucleus to the envelopes4 ,the preparation should be preserved and mounted in glycerine4 ,picro-carmine and ,aniline ,dye4--,for glandular tissue1 none of the aniline dyes answer so well as iodine green1 used in the form of a one per cent4 watery solution4 ,stain the tissue in picro-carmine1 wash it in distilled water acidulated with acetic acid1 and stain it in a solution of iodine green4 ,as it acts rapidly1 care must be taken not to overstain4 ,wash the section in water1 and then transfer it to alcohol2 finally clear with oil of cloves4 ,the washing should be done rapidly1 as the spirit dissolves out the green dye4 ,all preparations stained with iodine green must be mounted in dammar4 ,picro-carmine and ,iodine ,green4--,stain a section of the cancellated head of a very young bone 7ftal bone7 in picro-carmine1 wash it in distilled water1 and stain it with iodine green1 and mount in dammar4 ,all newly-formed bone is stained red2 that in the centre of the osseous trabecul1 the residue of the calcified cartilage in which the bone is deposited1 is stained green4 ,many of the bone corpuscles are also stained green4 ,ossifying cartilage1 the back part of the tongue1 ,peyer's ,patches1 solitary-glands1 trachea1 and bronchus1 may all be treated in the same way4 ,in preparing the skin1 take a vertical section from the sole of the foot of a ftus4 ,the cuticle and superficial layers of the epithelium are dyed yellow1 the rete ,malpighii green2 and the continuation of these cells can be traced into the ducts of the sweat-glands1 which are green1 and form a marked contrast to the red stained connective tissue of the cutis vera1 through which they have to ascend to reach the surface4 ,the outer layer of the grey matter of the cerebellum with ,purkinge's cells is1 when double stained1 red1 while the inner or granular layer is green4 ,logwood and iodine green stains the mucous glands of the tongue green1 and the serous glands1 lilac logwood stain4 ,eosin and ,iodine ,green4--,eosin is used as the ground colour4 ,stain the tissue in an alcoholic solution of eosin1 which will colour it very rapidly1 usually in a few seconds4 ,wash the section thoroughly in water acidulated with acetic or hydrochloric acid1 a one per cent4 solution1 and stain with iodine green4 ,this will double stain bone and cerebellum2 but if logwood is substituted for the latter1 the cerebrum and general substance become stained by the eosin1 while the logwood colours the nerve-cells a lilac4 ,gold ,chloride and ,aniline ,dyes4--,the tissue must be impregnated with chloride of gold1 and then stained with either aniline blue1 iodine green1 or rosin4 ,the tail of a young rat1 containing as it does so many different structures1 is an excellent material for experimenting upon4 ,remove the skin from the tail1 and place pieces half an inch long into the juice of a fresh lemon for five minutes1 wash it to get rid of the acid4 ,the fine tendons swell up under the action of the lemon acid1 and permit of the more ready action of the chloride of gold solution4 ,place the piece for an hour or more in a one per cent4 solution of gold1 remove it and wash it thoroughly1 and then place it in a twenty-five per cent4 solution of formic acid for twenty-four hours4 ,this reduces the gold4 ,during the process of reduction the preparation must be kept in the dark4 ,the osseous portion has then to be decalcified in the ordinary way1 with a mixture of chromic and nitric acid4 ,after decalcification preserve the whole in alcohol4 ,transverse sections of the decalcified tail are made1 and may be stained with a red dye1 as rosin1 and afterwards with a watery solution of iodine green4 ,mount in dammar4 ,injecting ,small ,animal ,bodies4 ,illustration3 ,fig4 #bda4--;,injecting ,syringe4 ,illustration3 ,fig4 #bdb4--,water ,bath and ,melting ,vessels4 ,the injection of animal bodies practised by the older anatomists1 to render the vascular system more apparent1 has not been superseded by the more modern methods of staining4 ,the method of injecting even small bodies requires some skill1 and a few pieces of apparatus made expressly for the purpose4 ,first1 a special form of brass syringe of such a size that it may be grasped with the right hand1 the thumb at the same time covering the button at the top of the piston-rod when drawn out to the full4 ,in ,fig4 #bda the piston rod is seen withdrawn1 a is the body1 with a screw at the top for firmly screwing down the cover1 b1 after the piston1 c1 is replaced2 e is a stop-cock1 to the end of which either of the smaller cannul1 g1 is affixed4 ,the transverse wires are for securing them tightly with thread to the vessels into which they are to be inserted4 ,in addition to the syringe1 two or three tinned vessels are required to contain size1 injecting fluid1 and hot water4 ,the size must be kept hot by the aid of a water bath2 if a naked fire be used there is danger of burning it4 ,a convenient form of apparatus for melting the size1 and afterwards keeping it at a proper temperature1 is ,fig4 #bdb4 ,illustration3 ,fig4 #bdc4--;,artery ,needle4 ,a pair of strong forceps for seizing the vessel1 and a small needle 7,fig4 #bdc7 is also necessary for passing the thread round the vessel into which the injection pipe has been inserted4 ,these complete the list of apparatus4 ,to prepare the material for opaque injections1 take one pound of the finest and most transparent glue1 break it into small pieces1 put it into an earthen pot1 and pour on it three pints of cold water2 let it stand twenty-four hours1 stirring it now and then with a stick2 set it over a slow fire for half an hour1 or until all the pieces are perfectly dissolved1 skim off the froth from the surface1 and strain through a flannel for use4 ,isinglass and cuttings of parchment make an excellent size1 and are preferable for particular injections4 ,if gelatine be employed an ounce to a pint of water will be sufficiently strong1 but in very hot weather it is necessary to add a little more gelatine4 ,it must be first soaked in part of the cold water until it swells up and becomes soft1 when the rest of the water1 made hot1 is to be added4 ,the size thus prepared may be fixed with finely levigated vermilion1 chrome-yellow1 blue salts1 or flake white4 ,to prepare the subject1 the principal points to be attained are3 to dissolve the fluids and completely empty the vessels2 relax the solids2 and prevent the injection from coagulating too soon4 ,for this purpose it is necessary to place the animal1 or part to be injected1 in warm water1 as hot as the operator's hand will bear4 ,this should be kept at nearly the same temperature for some time by occasionally adding hot water4 ,the length of time required is in proportion to the size of the part and the amount of its rigidity4 ,injecting the systems of ,vessels with different colours3 ,carmine and ,gelatine ,injection4--,carmine #cj grains1 strong liquid ammonia #fj drops1 glacial acetic acid #dc drops1 gelatine solution 7one ounce in six ounces of water7 two ounces1 water one ounce3 dissolve the carmine in the ammonia and water in a test tube1 and mix it with one half of the warm gelatine1 add the acid to the remaining half of gelatine1 and drop it little by little into the carmine mixture1 stirring it well with a glass rod during the mixing2 filter through flannel1 and add a few drops of carbolic acid to make it keep4 ,it is very important that the stain should be quite neutral1 the test of which is the colour and smell of the fluid4 ,it should be a bright red1 and all trace of smell of ammonia must be removed4 ,prussian or ,berlin ,blue and ,gelatine4--,take #a-a_/b ounces of gelatine1 place it in a vessel and cover it with water2 allow it to stand until all the water is absorbed and the gelatine is quite soft1 then dissolve in hot water4 ,dissolve one drachm 7#fj grains7 of ,prussian or ,berlin blue in six ounces of water1 and gradually mix it with the gelatine solution1 stirring well with a glass rod during the mixing2 then filter as before4 ,watery ,solution of ,berlin ,blue4--,dissolve #b-a_/b drachms of the blue in #ah ounces of distilled water1 and filter4 ,this staining fluid is used for injecting the lymphatic system4 ,directions for ,injecting4--,the animal to be injected must be first killed by chloroform1 and injected while still warm2 to secure this place the body in a water bath1 at a temperature of #ajd ,fahrenheit4 ,expose the main artery of the parts to be injected1 clear a small portion of it from the surrounding tissues1 and place a ligature of thin tissue or silk round it1 by means of the small artery needle 7,fig4 #bdc74 ,with a pair of sharp-pointed scissors make an oblique slit in the wall of the vessel1 insert the cannula1 and tie the ligature firmly over the artery behind the point of the cannula1 into which put the stop-cock4 ,fill the syringe with injection fluid1 which must not be too warm1 and take care not to draw up any air-bubbles2 insert the nozzle of the syringe into the stop-cock and force in a little fluid2 remove the syringe so that the air may escape1 re-insert the syringe1 repeat the process until no air-bubbles escape1 and then proceed slowly with the injection4 ,half an hour will be required to complete the process in an animal the size of a rabbit4 ,to judge of the completeness of the injection1 examine the vascular parts of the lips1 tongues and eyes2 if satisfactory1 tie the ligature round the artery and withdraw the syringe2 place the animal in cold water for an hour to consolidate the injection fluid4 ,when cold dissect out the organs1 cut them up1 and place them in methylated spirit to harden4 ,change the spirit every twenty-four hours for the first three days4 ,the hardening process will be complete in ten days4 ,to inject lymphatics by the puncture process1 a small-sized subcutaneous syringe should be used1 filled with a watery solution of the prepared stains4 ,thrust the nozzle into the pad of the foot1 7or tongue71 and then rub the limb to cause the injection fluid to flow along the lymphatic vessels into the glands4 ,when the blue stain is used add a few drops of acetic acid to the spirit while the hardening process is going on4 ,of ,injecting ,different ,systems of ,vessels with ,different ,colours4--,it is often desirable to inject different systems of vessels distributed to a part with different colours1 in order to ascertain the arrangement of each set of vessels and their relation to each other4 ,a portion of the gall-bladder in which the veins have been injected with white lead1 and the arteries with vermilion1 forms an attractive preparation4 ,each artery1 even to its smallest branches1 is seen to be accompanied by two small veins1 one lying on either side of it4 ,by this method four different sets of tubes have been injected--the artery with vermilion1 the portal vein with white lead1 the duct with ,prussian blue1 and the hepatic vein with lake4 ,there are also opaque colouring matters which may be employed for double injections4 ,injecting the ,lower ,animals4--,the vessels of fishes are exceedingly tender1 and require great caution in filling them4 ,it is often difficult or quite impossible to tie the pipe in the vessel of a fish1 and it will generally be found a much easier process to cut off the tail of the fish1 and put the pipe into the divided vessel which lies immediately beneath the spinal column4 ,in this simple manner beautiful injections of fish may be made4 ,mollusca 7slug1 snail1 oyster1 c474--,the tenuity of the vessels of the mollusc often renders it impossible to tie the pipe in the usual manner4 ,the capillaries are1 however1 usually very large1 so that the injection runs very readily4 ,in different parts of the bodies of these animals are numerous lacun or spaces1 which communicate directly with the vessels4 ,now1 if an opening be made through the integument of the muscular foot of the animal1 a pipe may be inserted1 and thus the vessels may be injected from these lacun with comparative facility4 ,insects4--,injections of insects may be made by forcing the injection into the general abdominal cavity1 when it passes into the dorsal vessel and is afterwards distributed throughout the system4 ,the superfluous injection is then washed away1 and such parts of the body as may be required removed for examination4 ,natural injection of ,medus may be effected without injuring the vessels1 with an opening at the side remote from it4 ,the medusa must be placed in a glass vessel1 with the bell downwards1 and a bell-jar ending in a narrow tube above is placed over it and made air-tight2 the medusa is then covered with the injection-mass1 the air in the glass is exhausted1 and as the sea-water runs out by slits in the lower side of the annular canal1 the coloured fluid runs in4 ,in the case of leeches and large species of earthworms1 the natural injection is made from the ventral sinus4 ,in all cases a glass tube is used1 with a finely drawn-out point4 ,the injection is complete when the injection issues from the counter-opening4 ,besides the animals mentioned1 large caterpillars1 beetles1 and larv of various kinds are favourable objects for injection2 the glass cannula being introduced into the posterior end of the dorsal vessel1 and the counter-opening made in the ventral vessel1 and vice vers4 ,staining ,living ,protoplasm with ,bismarck ,brown4--,henneguy having treated ,paramcium aurelia with an aqueous solution of aniline brown 7known as 8,bismarck ,brown071 found that they assumed an intense yellow-brown colour4 ,the colour first appears in the vacuoles of the protoplasm1 and then in the protoplasm itself1 the nucleus generally remaining colourless1 and becoming more visible than in the normal state4 ,if a yellow-tinted paramcium be compressed so as to cause a small quantity of the protoplasm to exude1 it is seen that it really is the protoplasmic substance which becomes coloured4 ,all the ,infusoria may be stained with ,bismarck brown1 but no other aniline colour employed exhibits the same property--they merely stain the ,infusoria after death1 and are in fact poisonous4 ,living protoplasm does not as a rule absorb colouring matters1 and as ,infusoria are chiefly composed of protoplasm1 attempts have been made to ascertain whether protoplasm in general1 of animal or vegetable origin1 behaved in the same way in the presence of aniline brown4 ,a tolerably strong solution of ,bismarck brown was therefore injected under the skin of the back of several frogs4 ,after some hours the tissues became uniformly tinted a deep yellow2 the muscular substance especially had a very marked yellow tint4 ,the frogs did not appear in the least incommoded4 ,small fry of trout placed in a solution stained rapidly and continued to swim about4 ,finally1 a guinea-pig1 under whose skin some powder of ,bismarck brown had been introduced1 soon presented a yellow staining of the buccal and anal mucous membranes and of the skin4 ,seeds of cress sown on cotton soaked with a concentrated solution of the ,bismarck brown sprouted1 and the young plants were strongly stained brown2 but on crushing the tissues and examining them under the microscope1 it was ascertained that the protoplasm of the cells was very feebly coloured3 the vessels1 on the contrary1 showed a deep brown stain up to their termination of the leaf4 ,the mycelium of a mould developed in a solution of ,bismarck brown was clearly stained after having been washed in water1 whilst it is known that the mycelium1 which frequently forms in coloured solutions1 picro-carmine1 hmatoxylin1 c41 remained perfectly colourless4 ,other aniline colours injected under the skin of frogs stained the connective tissue as deeply as did the ,bismarck brown2 but the stri of muscle remained colourless4 ,we may conclude1 then1 that ,bismarck brown possesses the quality of colouring living protoplasm both in plants and in animals4 ,cutting1 ,grinding1 and ,mounting ,hard ,structures4 ,take the femur of cat1 or rabbit1 remove as much of the muscle as possible and macerate it in water until quite clean2 on removal hang it up to dry4 ,with a fine saw make transverse and longitudinal sections4 ,file the section down until flat1 and smooth4 ,take some ,canada balsam1 place a piece on a square of glass and warm gently over a lamp until the balsam is plastic enough to allow of the section being pressed into it1 and set it aside to consolidate4 ,take a hone 78,water-of-,ayr0 stone71 moisten it with water1 and rub one side of the section upon it until quite smooth1 then place the glass slip1 with the section still attached1 into methylated spirit1 and in a very short time the section will be separated2 wash it and remount it on the reverse side1 and proceed to rub it down on the hone until it appears to be thin enough for mounting4 ,polish both sides on a polishing strop with ,tripoli powder1 and mount in ,canada balsam4 ,illustration3 ,fig4 #bdd4--,small ,lathe for cutting and polishing ,sections of ,teeth4 ,teeth4--,the enamel of the teeth is a much harder structure than that of bone1 consequently it is found necessary to have recourse to a cutting machine4 ,hand machines have been introduced for this purpose1 but the small lathe described in the earlier editions of my book has in no way been superseded by later cutting machines4 ,fig4 #bdd represents the small lathe used for cutting and polishing every kind of hard substance4 ,with regard to the teeth1 two sections should be made perpendicular to one another through the middle of the crown and fang of the tooth from before backwards1 and from right to left1 which will show the peculiar structure of the enamel4 ,the section must be cemented to the carrier of the stock of the lathe1 or to the metal plate a1 and kept in position by the steel holder b2 the wheel being set in motion by the first treadle4 ,the embedding materials in use are either gum-shellac or ,canada balsam4 ,the former is more generally employed by the lapidary and grinder of lenses than the latter4 ,as the enamel is liable to fracture under the saw1 it will be necessary to lessen the friction by dripping water on the saw as it is made to revolve4 ,thick sections can be quickly ground down against the corrondum wheel4 ,the final polishing of the section may be done on the lathe1 or by rubbing the flattened surface with water upon a 8,water-of-,ayr0 stone1 and ultimately set up in ,canada balsam1 which must not be too fluid1 or it will penetrate the lacun and canaliculi1 fill up the interspaces1 and cause them to become quite invisible4 ,as the flatness of the polishing surfaces is a matter of importance1 the stones themselves should be tested from time to time1 and when found to present an uneven surface must be rubbed down on a granite stone with fine sand1 or on a lead plate with emery powder4 ,if it is decided to use ,canada balsam as the embedding material1 this must be prepared in the following manner3--,the section of tooth or bone must be attached to a slip of well-annealed glass by hardened ,canada balsam1 and its adhesion effectually secured by placing the slide on the cover of a water bath1 or in the hot-chamber 7,fig4 #bef71 when the balsam1 a thick drop of which should be used1 will spread out by liquefaction4 ,the slide should then be removed and allowed to cool in order that the hardness of the balsam may be tested4 ,if too soft1 as indicated by its readily yielding to the pressure of the thumb-nail1 the heating process must be repeated1 care being taken not to cause it to boil and form bubbles2 if too hard1 which will be shown by its chipping1 it must be remelted and diluted with fluid balsam1 and then set aside as before4 ,when it is found to be of the right consistence1 the section must be laid upon its surface with the polished side downwards2 the slip of glass is next to be gradually warmed until the balsam is softened1 care being taken to avoid the formation of bubbles1 then press the section gently down with a needle upon the liquefied balsam1 the pressure being just applied on one side rather than over the whole surface1 so as to drive the superfluous balsam towards the opposite side2 finally1 an equable pressure over the whole will secure a perfect attachment of the section without air bubbles4 ,if1 however1 these should present themselves in drying1 and they cannot otherwise be expelled by pressure1 it will be found better to take the section off and relay it as before4 ,the thickness of the layer of balsam may be reduced by rubbing it down before applying the glass-cover4 ,rock ,sections4--,small pieces of rock may be ground down by the aid of the lathe1 or on a zinc plate1 with emery powder and water1 until one side is rendered smooth and flat4 ,then fasten the polished side of the section to a square of glass on the metal holder of the lathe1 with dried ,canada balsam1 as directed for bone1 and allow it time to become consolidated4 ,when moderately thin take a piece of plate-glass and some fine emery or putty-powder and rub the section down as thin as possible4 ,when found to be thin enough wash it well in water1 and put it aside to dry1 or warm it over a spirit-lamp1 and with a needle push the section off the glass into a watch-glass of benzole or turpentine1 and allow it to soak until all the balsam is dissolved out4 ,wash again in turpentine1 and mount in ,canada balsam1 with or without a cover-glass4 ,sections of echinus spines1 shells1 stones of fruits1 c41 are prepared in the same way as those of bones and teeth2 but when the grinding is finished1 the sections must be passed through alcohol into oil of cloves1 after which they should be mounted in ,canada balsam4 ,if tolerably thin1 sections of these substances can be cut in the lathe2 in the first instance1 there will be no actual occasion to attach them to glass at all1 except for the purpose of obtaining a hold upon the specimen for polishing1 but the surface thus attached must afterwards be completely removed in order to bring into view a stratum which the ,canada balsam may not have penetrated4 ,with regard to smaller bodies1 these can scarcely be treated in any other way than by attaching a number of them to slips of glass at once1 and in such a way as to make them mutually support each other4 ,thus in making horizontal and vertical sections of foraminifera1 it would be impossible to slice them through unless they were laid close together in a bed of hardened ,canada balsam1 and first grinding away one side and then turning and rubbing down the other4 ,my friend1 ,dr4 ,wallich1 many years ago communicated to me the ingenious plan adopted by himself when mounting and turning a number of these minute objects together4 ,the specimens being cemented with ,canada balsam1 in the first instance1 to a thin film of mica1 and then attached to a glass slide by the same means1 when ground down to the thinness desired1 the slide must be gradually heated just sufficiently to allow of the detachment of the mica-film and the specimen it carries2 a clean slide with a thin layer of hardened balsam having been prepared1 the mica-film is transferred to it with the ground surface downward4 ,its adhesion by drying having been complete1 the grinding and polishing should be proceeded with2 and as the mica-film will yield to the stone without any difficulty1 the specimen now reversed in position may be further reduced to the requisite thickness for mounting as a permanent object4 ,staining and ,mounting ,vegetable ,tissues4--,bacteria ,i propose to treat of in a separate section4 ,vegetable tissues generally will first receive attention1 and their differentiation is based on the employment of delicate gradations of colour stains4 ,the more striking results are obtained by ,multiple ,staining1 while the cell contents are rendered more palpable4 ,on this account colouring media have been divided into nuclear1 plasmic1 and specific4 ,the first are chiefly valued in proportion as they prove to have a selective affinity for the nuclei of cells1 and leaving the protoplasm comparatively unstained4 ,such stains are needful for fresh and young tissues4 ,on the other hand1 plasmic stains colour tissue uniformly1 and are used to give a ground colour by way of contrast2 and specific stains are chiefly employed to distinguish certain elementary structures from the mass of cellulose which forms the basis of vegetable tissue1 and which is also met with to a slight extent in animal membranes4 ,cellulose1 as it occurs in plant life1 presents a variety of physical properties3 sometimes it is soft1 as in young plants1 and again quite dense in older structures4 ,this fact accounts for the varying results obtained when cellulose is subjected to the action of staining fluids1 and whether the cellulose occurs in a nearly pure form1 as in cotton fibre1 or in the modified form of lignine or woody-fibre4 ,stains which readily attack young tissue have little or no effect upon it in its maturer form4 ,it is of much importance1 then1 in the staining of fibres1 as well as sections for the microscope1 that the cellulose should take the stain uniformly4 ,the staining of tissues may be effected in four ways4 ,first1 when the stain has sufficient affinity for the tissue to be retained by it without the intervention of any outside agent4 ,second1 when the stain and mordant are mixed and applied to the tissue in one solution4 ,these two are the simplest and easiest methods of staining4 ,third1 when the tissue is first immersed in the staining liquid and then transferred to some other liquid which shall fix the colour upon the tissue4 ,fourth1 when the tissue is first impregnated with the mordant1 or fixing agent1 and then immersed in the stain4 ,the last method is the one usually followed in commercial works1 and it is to be recommended in the staining of microscopical preparations which do not readily take the stain4 ,nuclear ,stains4--,as in both vegetable and animal sections it is generally the nuclei which form the landmarks of the structure1 so the most important class of reagents which are used in any of the branches of microscopical work are the 8nuclear stains40 ,there are several of these stains1 the most important of which is the hmatoxylin1 and when proper solutions are used the results are very satisfactory4 ,many formul have been given1 but there are three only reliable1 ,delafield's1 ,kleinenberg's1 and ,ehrlich's1 in all of which alum is present as an ingredient2 the idea being that the alumina forms with the colouring matter an insoluble lake1 and so acts as a mordant4 ,in ,delafield's solutions a large proportion of alum to hmatoxylin is used1 and methylic alcohol 7wood-spirit in the place of rectified spirit74 ,for ,kleinenberg's solution many different formul exist4 ,squire's improved formul for both stains is given in the ,appendix1 8,formul and ,methods40 ,hmatoxylin solutions stain the nuclei violet1 and in order to change this into blue1 the sections should be transferred to water taken from the house supply1 not distilled water2 but as the alkalinity of the water varies in different localities1 a better and more uniform result is obtained by using a weak solution of bicarbonate of sodium 7half a grain to the ounce74 ,carmine is also much in vogue as a nuclear stain1 and the two solutions more generally employed are ,greenacher's alcoholic borax carmine1 and ,orth's lithium carmine4 ,under ordinary circumstances they act as general stains1 affecting the ground tissue as well as the nuclei4 ,by subsequent treatment with acidulated alcohol or acidulated glycerine the colour is discharged from the ground tissue without seriously affecting the nuclei4 ,used in this way1 carmine becomes a good nuclear stain4 ,it should be remembered that the sections must not be washed in pure water1 as the colour will to a great extent be discharged2 nor in acidulated water1 as the carmine will be precipitated4 ,alum carmine and alum cochineal are useful nuclear stains1 not requiring after-treatment4 ,picro-carmines are also largely used4 ,the following formul will be found the most useful3-- ,ammonia ,picro-carmine4--,carmine1 one gramme2 strong solution of ammonia1 three cc42 distilled water1 five cc4 ,dissolve the carmine in the ammonia and water with a gentle heat1 then add saturated aqueous solution of picric acid1 #bjj cc42 heat to boiling1 and filter4 ,picro-,lithium ,carmine4--,the following is generally preferred for use--,lithium carmine solution1 #ajj cc42 saturated solution of picric acid1 #bgj cc4 ,there are several aniline dyes which are used for nuclear staining3 methylene blue1 methyl green1 safranine1 gentian violet1 vesuvine1 fuchsine1 and ,hoffmann's blue4 ,the usual process is to stain in #a_/d or #a_/b per cent4 aqueous solutions and wash in methylated spirit4 ,methylene blue and methyl green have the reputation of being so readily washed out in the methylated spirit as to be worthless4 ,this is obviated by washing the sections 7when removed from the stain7 in distilled water1 previous to the differentiation in methylated spirit4 ,treated in this manner1 the nuclear staining is very beautiful4 ,this also applies to ,hoffmann's blue and partly to vesuvine2 with the latter1 however1 it is not a necessity4 ,safranine and gentian violet worked better by transferring the sections directly from the stain into #ij per cent4 alcohol4 ,contrast ,stains4--,very frequently other stains are used to dye the ground a colour which is in contrast to that employed for the nuclei4 ,brown1 orange1 or pink are used after nuclear blue or green4 ,carmine is generally counterstained yellow or indigo-blue2 and fuchsine red1 as in tubercle bacilli1 is counterstained with nuclear blue4 ,it is important that the ground stain should be made weaker than the principal stain1 so that the whole tissue may be shown without detracting from the nuclei4 ,the following colours are used as counterstains for animal sections1 but they prove less useful for vegetable sections3 benzo-purpurine1 eosin1 erythrosine1 orange1 acid rubin1 and picric acid4 ,examples of specific stains are fuchsine1 methylene blue1 and gentian violet for bacteria2 osmic acid for fatty elements2 victoria blue and rose bengale1 for demonstrating elastic tissue2 methyl violet1 iodine1 and safranine1 for amyloid degeneration4 ,methylene blue is one of the most useful of aniline dyes1 and one of the most variable in composition4 ,iodine green1 or methyl green1 has long been in use as a reagent for amyloid1 starchy matters1 in ignorance of the fact that the reaction is due to the methyl violet1 contained as an impurity in the iodine green4 ,it is exceedingly difficult to obtain a green quite free from violet4 ,as nuclear stains they are identical1 and the amyloid reaction1 being dependent wholly upon the contained violet1 varies1 not with the formula of the green1 but with the extent to which it has been purified4 ,cellulose reactions4--,after the nuclear stains1 the most important reagents to the botanist are those which affect cellulose and its several modifications4 ,pure cellulose is coloured yellow by iodine1 the colour being changed to a blue on the addition of slightly dilute sulphuric acid1 or a strong solution of zinc4 ,solutions containing iodine1 iodide of potassium1 and chloride of zinc1 give a violet reaction with unaltered cellulose1 and yellow with lignine4 ,schulze's zinc re-agent must be used with a certain amount of caution1 as the chloride of zinc and potassium undergo decomposition4 ,the formula now in use is as follows3 ,take of zinc chloride solution 7sp4 gr4 #ahe7 #gj cc41 potassium iodide #aj grammes1 iodine #ja gramme2 but this solution can only be employed as a re-agent and not as a dye1 and structures stained with it cannot be mounted in any of the ordinary media1 and the only fluid for ringing them down is caoutchouc cement4 ,cellulose can be stained permanently by carmine1 hmatoxylin1 nigrosine1 methylene blue1 safranine1 and fuchsine4 ,the aniline dyes are used in dilute aqueous solutions containing one-eighth or one-fourth per cent4 of dye4 ,when the cellulose undergoes the change known as lignification its reactions are altered4 ,it is coloured yellow by chloro-zinc iodine1 red by phloroglucin1 yellow by aniline chloride4 ,the two latter are much assisted by hydrochloric acid4 ,the results of these reactions also cannot be preserved in the usual mounting media4 ,sections containing mixed tissue1 partly unaltered cellulose and partly lignified1 give striking results with aniline dyes1 and with this additional advantage can be preserved for years4 ,double ,staining4--,when a section is passed through methyl green solution and afterwards one of carmine1 the lignified portion is coloured green and the unlignified red4 ,acid green may be used in the place of methyl green1 with a similar result4 ,when picric acid is used with carmine1 ingrosine1 or ,hoffmann's blue1 the picric acid dyes the ligneous portion and the others colour the unlignified structure1 red1 black1 and blue respectively4 ,eosin stain is the most useful for sieve-tubes and plates4 ,make a strong solution of eosin in equal parts of water and alcohol1 and stain the section for five or ten minutes4 ,wash well in methylated spirit1 dehydrate1 clean in oil of cloves1 and mount in ,canada balsam4 ,bleaching ,process4--,the bleaching and clearing of vegetable structures before staining is a very necessary process1 especially so if starch be present in any quantity4 ,clearing agents are of two kinds--those which act by virtue of their property of strongly refracting light1 and those which disintegrate and dissolve the amyloid cell contents4 ,to the first class belong the essential oils1 as oil of cloves1 ,canada balsam1 glycerine1 and other similar bodies2 to the second class1 solutions of potash1 phenol1 and chloral hydrate4 ,the actual value of some of these agents is questionable4 ,the process usually preferred is as follows3 ,place the sections in a fresh clear solution of chlorinated lime1 allowing them to remain until quite bleached1 say from two to four or five minutes2 then gently warm in a test-tube for a few seconds1 and quickly replace the solution with distilled water and boil for two or three minutes2 repeat the treatment with boiling water three times2 wash with a one per cent4 solution of acetic acid1 and finally with distilled water4 ,the sections are then quite ready for staining operations4 ,when the stem is hard and brown1 a solution of chloride of lime should be used--a quarter of an ounce of chloride dissolved in a pint of water1 well shaken and stood by to settle down1 then pour off the clear fluid for use4 ,for hard tissues this solution answers well1 but it is not suitable for leaves1 as they require not only bleaching1 but the cell contents should be dissolved out to render them transparent4 ,a solution of chlorinated soda answers well for both stems and leaves4 ,it is prepared as follows3-- ,to one pint of water add two ounces of fresh chloride of lime1 shake or stir it well two or three times1 then allow it to stand till the lime has settled4 ,prepare meanwhile a saturated solution of carbonate of soda--common washing soda4 ,now pour off the clear supernatant fluid from the chloride of lime1 and add to it1 by degrees1 the soda solution1 when a precipitate of carbonate of lime will be thrown down2 continue to add the soda solution till no further precipitate is formed4 ,filter the solution1 and keep it in a well-stoppered bottle in the dark1 otherwise it speedily spoils4 ,sections bleached in chlorinated soda must1 when white enough1 be washed in distilled water1 and allowed to remain in it for twenty-four hours1 changing the water four or five times1 and adding a few drops of nitric acid1 or at the rate of eight or ten drops to the half-pint1 to the water employed before the final washing takes place4 ,from water transfer them to alcohol1 in which they must remain for an hour or more4 ,although alkaline glycerine has been recommended for several purposes in micro-technique1 it is not so well known as it should be how serviceable it is as an extempore mounting solution in vegetable histology4 ,the best mixture for general use is composed of glycerine #b ozs41 distilled water #a-a_/b oz41 solution of potash1 ,b4,p41 #a_/b oz4 ,this combines the refringent property of the glycerine with the clearing action of the caustic potash1 while the swelling action of the potash is considerably diminished4 ,cutting ,sections of ,hard ,woods4--,the lathe and circular saw will be found as useful for cutting sections of the harder kinds of woods1 as for bone structure4 ,it may be necessary to subject the older and consequently harder pieces of wood to the action of steam for a few hours to soften them1 and afterwards transfer them to methylated spirit1 before making an attempt to cut sections4 ,but the more open woods1 of one1 two1 or three years' growth1 will show all that may be required1 and these can be cut by hand1 or with the microtome1 as already described4 ,with a little practice the finest and thinnest possible slices may be cut by hand4 ,it is usual to take off the first slice to give a smooth and even surface to the specimen4 ,then turn the screw to raise it a little1 sprinkle the surface with spirit and water1 and cut with a light hand4 ,remove the cut sections with a fine camel's-hair brush or a section lifter 7,fig4 #bej7 to a small vessel containing water1 when the thinnest will float on the surface1 and remove to methylated spirit and water1 where they should remain until they can be mounted4 ,sections of hard woods1 and those containing gum-resins1 or other insoluble material1 must first be kept in methylated spirit or alcohol1 and finally transferred to oil of cloves1 to render them sufficiently transparent for mounting in ,canada balsam4 ,if the structure of an exogenous wood is required to be examined1 the sections should be made in at least three different ways3 the transverse1 the longitudinal1 and the oblique1 or1 as they are sometimes called1 the horizontal1 vertical1 and tangential1 each of which will exhibit different appearances1 as seen in ,fig4 #bde3 b is a vertical section through the pith of a coniferous plant1 and exhibits the medullary rays known to the cabinet-maker as the silver grain2 e is a magnified view of a part of the same2 the woody fibres are seen with their dots l1 and the horizontal lines k indicating the medullary rays cut lengthwise2 c is a tangential section1 and f a portion of the same2 the medullary rays m m1 and the woody fibres with vertical slices of the dots1 are shown4 ,instructive preparations will be secured by cutting oblique sections of the stem4 ,the sections seen are made from the pine4 ,all exogenous stems1 however1 exhibit three different appearances1 according to the direction in which the section is made4 ,illustration3 ,fig4 #bde4--,sections of ,wood4 ,bacteria ,cultivation1 ,sterilising1 and ,preparing for ,microscopical ,examination4 ,that branch of mycology which is now looked upon as a separate department of science1 termed bacteriology1 took shape in the years #ahge-i1 when its founder1 the veteran botanist ,cohn1 who recognised that the protoplasm of plants corresponded to the animal sarcode1 published his exact mode of studying bacteria4 ,but it was a pupil of his1 ,dr4 ,koch1 who a year later discovered that a specific cattle disease1 anthrax1 was due to a bacillus1 and it was he also who gave us the useful modification of gelatine as a medium in which to grow bacteria2 he hit upon the method of pouring melted gelatine containing distributed germs on to plates1 and thus isolating the colonies and ensuring the further isolation of the spores1 and so facilitate the preparation of pure cultures on a large scale1 and with great saving of time4 ,the difficulty of isolating a bacterium and tracing its life history under the microscope must at first sight appear great4 ,a further objection that such work is slow and difficult has no more weight here than in any other department of science1 as will be seen on proceeding to follow out the directions ,i am about to furnish for the use of the student4 ,apparatus1 ,material1 and ,reagents employed in ,bacteriological ,investigations4 ,a good microscope with a wide-angled sub-stage condenser1 and objectives of an inch1 #a_/d-;inch1 or #a_/f-;inch1 and a #a_/ab-;inch homogeneous oil-immersion4 ,a large bell-glass for covering the same when fuming acids are in use in the laboratory4 ,about a square foot of blackened plate-glass4 ,a white porcelain slab1 or a shallow photographic dish of some size4 ,glass bottles with ground stoppers for alcoholic solutions and aniline dyes4 ,glass bottles with funnels for filtering solutions of stains1 with pipettes4 ,a specialised form of pipette for the micro-chemical filtration of solutions 7,fig4 #bdf74 ,a small stoppered bottle of cedar oil 7,fig4 #bdg74 ,set of small glass dishes or watch-glasses for section staining4 ,stock of glass slides sterilised1 together with round thin glass-covers1 in boxes 7,fig4 #bdh74 ,needle holders and platinum needles1 with a packet of ordinary sewing needles 7,fig4 #bdi74 ,platinum1 or plated copper section-lifters 7,fig4 #bej74 ,glass rods1 drawn out to a fine point1 for manipulating sections when acids are employed4 ,illustration3 ,fig4 #bdg4--;,bottle and ,dipper for ,cedar ,oil4 ,illustration3 ,fig4 #bdf4--,pipette for ,micro-chemical ,filtration4 ,illustration3 ,fig4 #bdh4--;,box for keeping ,glass-covers4 ,illustration3 ,fig4 #bdi4--,needle ,holders1 fine ,lifter and ,hook for ,manipulating ,structure4 ,illustration3 ,fig4 #bej4--,section ,lifters4 ,illustration3 ,fig4 #bea4--,spring ,flat ,forceps4 ,illustration3 ,fig4 #bea;a4--,forceps with fine ,points4 ,a pair of small spring steel platinum-pointed forceps for holding glass-covers 7,fig4 #bea74 ,one or two pairs of fine-pointed forceps 7,fig4 #bea;a74 ,collapsible tubes for containing ,canada balsam and dammar4 ,soft rags or old pocket handkerchiefs for removing cedar oil from lenses and cover-glasses4 ,chamois leather for wiping lenses and removing dust4 ,reagents1 alcohol1 bergamot oil1 celloidin1 dissolved in equal parts of ether and alcohol4 ,ebner's solution4 7,see ,appendix47 ,formalin1 glycerine1 gelatine1 ,klebs' and ,kleinenberg's solutions4 7,see ,appendix47 ,the latter consisting of a watery solution of picric acid #ajj parts2 strong sulphuric acid two parts2 filter1 and add distilled water #cjj parts4 ,muller fluid4 7,see ,appendix47 ,osmic acid1 a five per cent4 solution4 ,paraffin1 spermaceti and xylol1 acetic acid1 hydrochloric acid1 a one per cent4 solution with alcohol4 ,ammonia liquid1 ether1 picro-lithium carmine1 potash solution4 ,safranine1 concentrated alcoholic solution of1 and a watery solution4 ,turpentine1 vesuvin1 water distilled and sterilised4 ,aqueous solutions of the several dyes may be kept in bottles ready for use4 ,to both aqueous and alcoholic solutions a few drops of phenol1 or a crystal of thymol1 should be added as a preservative4 ,for the rapid staining of cover-glass preparations1 it is convenient to have the most frequently used stains--fuchsine1 methyl-violet1 c4--in bottles provided with pipette stoppers4 ,clearing ,agents4--,oils of cedar wood1 cloves1 origanum1 aniline1 terebene1 toluol and xylol1 benzol and spirits of turpentine4 ,mounting ,media4--,acetate of potash solution concentrated1 benzole1 balsam1 glycerine jelly1 ,fanant's medium1 dammar and mastic1 ,canada balsam in xylol1 ,hollis's glue1 zinc white4 ,cement for fixing small specimens temporarily to a glass slide4 ,remove all traces of moisture1 place upon it a drop or two of a medium prepared as follows3--,dissolve over a water bath #ae grammes of white lac in #ajj grammes of absolute alcohol1 decant off the clear liquid1 and stand it by for a while4 ,as the alcohol evaporates from the warmed surface of the glass slide a hard transparent coating is left4 ,this may be slightly softened at any time by means of a drop of oil of lavender4 ,after arranging the objects the heat of a spirit-lamp will cause the oil to evaporate1 leaving them firmly attached4 ,objects may be mounted on cover-glasses in a similar way4 ,a resinous mounting medium may then be employed in the usual manner4 ,if glycerine or glycerine jelly is the mounting medium employed1 collodion diluted with two or three times its volume of oil of lavender may be found preferable as the fixing agent4 ,the section should be placed in position before the preparation dries and the oil is evaporated4 ,methylated spirit is often so largely adulterated with rock-oil as to render it unsuitable for technical purposes4 ,even to varnishes it imparts a fluorescent appearance as it dries off4 ,illustration3 ,fig4 #beb4--;,iron ,box for holding ,sterilised ,instruments and ,glass ,plates4 ,the needles and instruments used must not be passed through a ,bunsen burner flame1 which is most destructive1 but enclosed in a sheet-iron box made for the purpose 7,fig4 #beb71 and placed in the hot-air steriliser for an hour at #aej;,c4 ,the box can be opened at the side1 and each instrument withdrawn with a pair of sterilised forceps when required for use4 ,glass plates are sterilised in the same iron box1 and the platinum needles for inoculating nutrient media1 examining cultivations1 c41 are served in the same manner before being used4 ,the needles consist of two or three inches of platinum wire fixed to the end of a glass rod4 ,several of these needles should be made by fixing pieces of wire into a glass rod about six inches long4 ,the glass rod must be heated at the extreme end in the flame of a ,bunsen burner1 or blow-pipe1 and the platinum wire held near one extremity with forceps1 and fused into the end of the glass rod4 ,some of these rods should be straight1 and some bent1 and others provided with a loop1 and kept especially ready for inoculating test-tubes of nutrient jelly4 ,illustration3 ,fig4 #bec4--;,damp ,chamber for ,plate-cultivations4 ,glass ,dishes4--,several shallow glass dishes are required for preparing damp chamber cultivations1 the upper covers fitting over the under 7as in ,fig4 #bec71 in the centre of which culture-plates are stacked one above the other1 and when necessary placed in the incubator4 ,apparatus for ,incubation and ,cultivations in ,liquid ,media4 ,lister's ,flasks4--,lister devised a globe-shaped flask with two necks1 a vertical and a lateral one1 the lateral being a bent spout1 tapering towards the extremity4 ,when the vessel is restored to the erect position after pouring out some of its contents1 a drop of liquid remains behind in the end of the nozzle1 and thus prevents the regurgitation of air through the spout4 ,a cap of cotton-wool is tied over the orifice1 and the residue left in the flask for future use4 ,the vertical neck of the flask is plugged with sterilised cotton-wool in the ordinary way4 ,illustration3 ,fig4 #bed4--,pasteur's ,bulb ,pipette4 ,illustration3 ,fig4 #bee4--,storing ,cultivation ,tube4 ,sternberg advocates the use of a glass bulb1 provided with a slender neck drawn out to a fine point and hermetically sealed4 ,special forms of tubes1 bulbs1 and pipettes were devised by ,pasteur1 and are still in use at the ,bacteriological ,institute1 ,paris1 and known as the ,pasteur's bulb pipette 7,fig4 #bed74 ,others are provided with lateral or with curved arms1 one of which is drawn out to a fine point1 and the slender neck plugged with cotton-wool1 as in ,fig4 #bee4 ,,the ,,warm ,,chamber1 ,,steriliser1 ,,and ,,incubator4 ,illustration3 ,fig4 #bef4--,pfeiffer's ,warm ,chamber4 ,the ,warm ,chamber4--,this is an accessory of importance in bacteriological work4 ,for the continuous heating of specimens during cultivation it is an absolute necessity4 ,pfeiffer's warm chamber 7,fig4 #bef7 is suitable for microscopical work generally4 ,it consists of a hard-wood box1 made air-tight1 with doors and glass windows to allow of the specimen being moved from time to time1 and kept under constant observation4 ,the box is mounted on a metal plate tripod stand1 and is heated from below by a small gas burner1 with a thermo-regulator4 ,a paraffin lamp will do as well1 so long as it maintains a temperature of from #be to #de;,c41 and without danger of injury to the stand and lenses of the microscope4 ,a thermometer is placed in the air space to mark the temperature4 ,illustration3 ,fig4 #beg4--;,crookshank's ,incubator4 ,hot-air ,incubators and ,sterilisers are usually made of sheet-iron1 in the form of a cubical chest1 with double walls1 supported on four legs1 as that of ,dr4 ,crookshank's 7,fig4 #beg74 ,they are heated by gas or a lamp from below1 while the temperature is indicated by a thermometer inserted through a hole in the top1 as in that of the ,hearson's incubator4 ,test-tubes1 flasks1 funnels1 cotton-wool1 c41 must be sterilised by exposure to a temperature of #aej;,c4 for an hour or more4 ,wire ,cages or crates are used for containing test-tubes1 especially when they are to be sterilised in the hot-air steriliser1 or for lowering tubes of nutrient jelly into the steam steriliser4 ,all instruments1 needles1 scalpels1 c41 before using must be carefully sterilised4 ,illustration3 ,fig4 #beh4--;,dr4 ,koch's ,steam ,steriliser4 ,steam ,sterilisers are made either of iron or tin1 jacketed with thick felt1 and provided with a conical cap or lid perforated at the apex to receive a thermometer 7,fig4 #beh74 ,inside the vessel is an iron grating or diaphragm about two-thirds of the way down1 which divides the interior into two chambers1 the upper or steam chamber1 and the lower or water chamber4 ,a gauge outside marks the level of the water in the lower chamber2 this should be kept about two-thirds full4 ,the apparatus stands upon three legs1 and is heated from below with a ,bunsen burner or a lamp4 ,it is employed for sterilising nutrient media in tubes or flasks1 for cooking potatoes or hastening the filtration of agar-agar4 ,when the thermometer indicates #ajj ,c4 the lid is removed1 and test-tubes are lowered in a wire-basket by means of a hook and string1 and the lid quickly replaced4 ,potatoes or small flasks are lowered into the cylinder in a tin receiver with a perforated bottom1 which rests upon the grating1 and admits of the contents being exposed to the steam generated4 ,one of the most efficient forms of incubators introduced into the bacteriological laboratory is that known as ,hearson's 7,fig4 #bei74 ,this consists of a chamber surrounded by a water-jacket1 with water space below1 to afford room for the pipe1 ,l1 which conveys the heated products from the flame of the lamp1 ,t1 through the water and back again to the lantern4 ,a is the water-jacket surrounding the chamber containing the cultures2 ,o1 the pipe through which the water supply is admitted2 ,n1 the tap for employing the same2 ,m1 the overflow pipe2 ,s1 the capsule in a case attached by a tube to the lower plate outside2 ,d1 a lever pivoted on the left1 carrying at its free end a damper1 ,f1 which1 when resting on the chimney1 ,v1 effectually closes it2 ,p1 a screw for adjusting the damper when starting the apparatus2 ,h1 a lead weight for bringing more pressure on the capsule2 ,k1 a thermometer1 the bulb of which is inside and the scale outside the chamber4 ,illustration3 ,fig4 #bei4--,the ,baird-,hearson ,biological ,incubator4 ,the treated products of combustion move in the direction indicated until the water and chamber are sufficiently heated to distend the capsule4 ,when this point is reached the wire between ,s and ,p is pushed up by the capsule1 and the lever causes the damper to rise more or less off the chimney1 ,v1 and on examining the thermometer the inside of the chamber is at length found to remain steadily at the required temperature4 ,when the thermometer registers the desired temperature1 the lead weight must be damped to the lever by means of the milled-head screw which goes through it4 ,after having been once adjusted the heat in the interior will remain constant1 notwithstanding the utmost changes of temperature occurring in these latitudes1 nor will very great alterations in the size of the lamp-flame seriously interfere with the results4 ,the milled-head screw1 ,p1 must be turned1 after the first adjustment1 during the whole time that the incubator is in use4 ,observe the temperature before opening the door2 observations taken afterwards are worthless4 ,preparation of ,nutrient ,media--,separation1 and ,cultivation of ,bacteria4 ,illustration3 ,fig4 #bfj4--,plate ,cultivation ,showing ,colonies4 ,to cultivate micro-organisms artificially they must be supplied with the proper nutrient material1 perfectly free from pre-existing organisms4 ,the secret of ,koch's methods greatly depends upon the possibility1 in the case of starting with a mixture of micro-organisms1 of being able to isolate them completely one from another1 and to obtain an absolutely pure growth of each cultivable species4 ,when sterile nutrient gelatine has been liquefied in a test-tube and inoculated with a mixture of bacteria in such a way that the individual micro-organisms are distributed throughout it1 and the liquid is poured out on a glass plate and allowed to solidify1 the individual bacteria1 instead of moving about freely as in a liquid medium1 are fixed to one spot1 where they develop their own species4 ,in this way colonies are formed1 each possessing its own biological characteristics and morphological appearances 7,fig4 #bfj74 ,to maintain individuals isolated from each other during growth1 and free from contamination1 it is only necessary to thin out the cultivation to protect the plates from the air1 and to have facilities for examining them from time to time1 and observing the characteristic microscopical appearances4 ,the colonies on nutrient gelatine examined with a low power 7,fig4 #bfj71 if micro-organisms such as ,bacillus anthraces and ,proteus mirabilis1 the naked eye appearances in test-tubes of the growth of the bacilli of anthrax and tubercle1 and the brilliant growth of micro-coccus prodigiosus1 may be given as examples in which the appearances are often very striking and sometimes quite characteristic4 ,i must1 however1 first direct attention to a well-recognised fact1 that bacteriology only touches animal pathology at a few points1 and that so far from bacteria being synonymous with disease germs1 the majority of these remarkable organisms appear to be beneficent rather than inimical to man4 ,this is of immense importance to science1 as ,i shall attempt to show further on2 although even a brief description of all the useful ferments due to bacteria and brought into use would occupy a volume to themselves1 and call for a school of bacteriology quite apart from that involved in the medical aspect of the question1 for the purpose of fully investigating problems raised by the agriculturist1 the forester1 the gardener1 the dairyman1 brewer1 dyer1 tanner1 and other industries1 which open up vistas of practical application1 and to some extent are already being taken advantage of in commerce4 ,the ,preparation of ,nutrient ,gelatine and ,agar-agar4--,take half a kilogramme 7one pound7 of beef as free as possible from fat1 chop finely1 transfer to a flask or cylindrical vessel1 and shake up well with a litre of distilled water4 ,place the vessel in an ice-pail1 or ice-cupboard1 or in winter in a cold cellar1 and leave for the night4 ,next morning commence with the preparation of all requisite apparatus4 ,thoroughly wash and rinse with alcohol about #ajj test-tubes1 and allow them to dry4 ,plug the mouths of the test-tubes with cotton-wool1 place them in their wire cages in the hot-air steriliser1 to be heated for an hour at a temperature of #aej;,c4 ,in the same manner cleanse and sterilise several flasks1 and a small glass funnel4 ,in the meantime1 the meat infusion must be well shaken1 and the liquid portion separated by filtering and squeezing through a linen cloth or a meat press4 ,the red juice thus obtained must be brought up to a litre by transferring it to a large measuring glass and adding distilled water4 ,it is then poured into a sufficiently large and strong beaker1 and set aside after the addition of ten grammes of peptone1 five grammes of common salt1 and #ajj grammes of best gelatine4 ,in about half an hour the gelatine is sufficiently softened1 and subsequent heating in a water bath causes it to be completely dissolved4 ,the next process requires the greatest care and attention4 ,some micro-organisms grow best in a slightly acid1 others in a slightly alkaline1 medium4 ,for example1 for the growth and characteristic appearances of the comma bacillus of ,asiatic cholera a faintly alkaline soil is absolutely essential4 ,this slightly alkaline medium will be found to answer best for most micro-organisms1 and may be obtained as follows3--,with a clean glass rod dipped in the mixture1 the reaction upon litmus-paper may be obtained1 and a concentrated solution of carbonate of soda must be added drop by drop until red litmus-paper becomes faintly blue4 ,if it is too alkaline1 it can be neutralised by the addition of lactic acid4 ,finally1 the mixture is heated for an hour in the water-bath4 ,ten minutes before the boiling is completed the white of an egg beaten up with the shell is added1 and the liquid is then filtered while hot4 ,during filtration the funnel should be covered over with a plate of glass1 and the process of filtering must be repeated1 if necessary1 until a pale straw-coloured1 perfectly transparent filtrate results4 ,the sterilised test-tubes are filled to about a third of their depth by pouring in the gelatine carefully and steadily4 ,the object of this care is to prevent the mixture touching the part of the tube with which the plug comes into contact2 otherwise1 when the gelatine sets1 the cotton-wool adheres to the tubes and becomes a source of embarrassment to subsequent procedures4 ,as the tubes are filled they are placed in a basket1 and then sterilised4 ,they are either lowered into the steam steriliser1 when the thermometer indicates #ajj cc41 for twelve minutes1 for four or five successive days1 or they may be transferred to the test-tube water-bath1 and heated for an hour or two for three successive days4 ,if the gelatine shows any turbidity after1 it must be poured back into a flask1 boiled for ten minutes1 and filtered again1 and the process of sterilisation repeated4 ,nutrient ,agar-agar is a substance prepared from seaweed which grows on the coasts of ,japan and ,india1 and is supplied in long crinkled strips4 ,it boils at #ij ,c41 and remains solid up to a temperature of about #de ,c4 ,it is therefore substituted for gelatine in the preparation of a jelly for the cultivation of those bacteria which will grow best in the incubator at the temperature of the blood1 and also at ordinary temperature for bacteria which lignify gelatine4 ,the preparation is conducted on much the same principles as those already described4 ,instead1 however1 of #ajj grammes of gelatine1 only about twenty grammes of agar-agar 7#ae to #b per cent471 and to facilitate the solution it must be allowed to soak in salt water overnight4 ,flannel is substituted for filter paper4 ,the hot-water apparatus is invariably employed4 ,the final results1 when solid1 should be colourless and clear2 but if slightly milky1 it may still be employed4 ,wort-gelatine is used in studying the bacteria of fermentation4 ,it is made by adding from five to ten per cent4 of gelatine to beer-wort4 ,glycerine ,agar-agar4--,this is made by adding five per cent4 of glycerine to nutrient agar-agar1 after the boiling and before the filtration4 ,illustration3 #a #b #c #d #e #f ,yellow4 ,yellow4 ,red4 ,orange4 ,green4 ,brown4 ,fig4 #bfa4--,pure ,cultivation in ,tubes 7,crookshank74 ,test-tube ,cultivations4--,to inoculate test-tubes containing nutrient jelly1 the cotton-wool plug is removed4 ,a sterilised needle1 charged1 for example1 with blood or pus containing bacteria1 is thrust once in the middle line into the nutrient jelly1 and steadily withdrawn4 ,the tube should be held horizontally or with its mouth downwards1 and the plug replaced as quickly as possible1 and an india-rubber cap fitted over the mouth of the tube4 ,the appearance produced by the growths in the test-tubes can be in most cases sufficiently examined with the naked eye 7,fig4 #bfa74 ,in some cases the jelly is partially liquefied1 while in others it remains solid4 ,the growths may be abundant or scanty1 coloured or colourless4 ,when liquefaction slowly takes place in the needle tracts1 the appearances which result are often very delicate and in some very characteristic4 ,the appearance of a simple white thread with branching lateral filaments1 of a cloudiness1 or of a string of beads in the track of the needle1 may be given as examples4 ,in some cases much may be learnt by means of a magnifying-glass4 ,beneke recommends that gelatine culture tubes should be inoculated by making a puncture quite at the side of the medium1 close to the glass4 ,the advantage of this method over the plan of inoculating the mass in the middle is that the growing culture can be microscopically examined from the outside1 and various details made out1 such as the nature of the growth1 the comparative appearance of colonies near the surface and those situated more deeply1 and the presence of one or more distinct organisms4 ,if the tubes used have the opposite sides flat and parallel1 such examinations will be still further facilitated4 ,plate ,cultivations4--,by this method a mixture of bacteria1 whether in fluids1 excreta1 or in cultivations on solid media1 can be so treated that the different species are isolated one from the other1 and perfectly pure cultivations of each of the cultivable bacteria in the original mixture established in various nutrient media4 ,we are enabled also to examine under a low power of the microscope the individual colonies of bacteria4 ,the same process1 with slight modification1 is also employed in the examination of air1 soil1 and water4 ,in order to spread out the liquid jelly evenly on the surface of a glass plate1 and to hasten its solidification1 it is necessary to place the plate upon a level and cool surface4 ,the glass plates are sterilised in an iron box placed in the hot-air steriliser1 at #aej ,c41 from one to two hours4 ,the damp chambers for the reception of the inoculated plates are prepared by cleansing and washing out with one in twenty carbolic acid the shallow glass dish and bell-cover 7,fig4 #bec74 ,a piece of filter-paper should cover the bottom of dish1 moistened with the same solution4 8,in a glass-beaker with pad of cotton-wool at bottom place tube containing cultivation1 the three tubes to be inoculated1 three glass rods which have to be sterilised1 and a thermometer4 ,liquefy the gelatine in the three tubes by placing them in a beaker containing water #cj ,c4 ,keep the tubes1 both before and after the inoculation1 in the warm water to maintain the gelatine in a state of liquefaction4 ,remove the plug from the culture and also the plug of test-tube with liquefied jelly4 ,with the needle take up a droplet of the cultivation and stir it round in the liquefied jelly4 ,replace both plugs1 and set aside the cultivation4 ,hold the freshly-inoculated tube almost horizontally1 then raise it to the vertical1 so that the liquid gelatine gently flows back4 ,by repeating this motion1 and rolling the tube1 the micro-organisms which have been introduced are distributed throughout the gelatine4 ,any violent shaking1 and consequent formation of bubbles1 must be carefully avoided4 ,inoculate the second tube1 and also third1 in the same way1 but with three droplets from a sterilised needle4 ,the next process consists in pouring out the gelatine on glass plates and allowing it to solidify4 8,remove cover of box containing sterilised plates1 withdraw a plate with sterilised forceps1 and rapidly transfer it to the filter-paper under the bell-glass and quickly replace cover of box4 ,remove plug from the test-tube which was first inoculated1 and the contents are poured out on the plate4 ,with a glass rod the gelatine must be then rapidly spread out in an even layer within about half an inch of the margin of the plate1 the bell-glass is replaced1 and the gelatine is allowed to set4 ,meanwhile a glass bench is placed in damp chamber1 upon which the plate is placed when the gelatine is quite solid2 precisely the same process is repeated with the other tubes4 8,the colonies will be found to develop in the course of a day or two1 the time varying with the temperature of the room4 ,the lower plate will contain a countless number of colonies1 which1 if the micro-organisms liquefy gelatine1 speedily commingle1 and produce in a very short time a complete liquefaction of the whole gelatine4 ,on the middle plate the colonies will also be very numerous1 but retain their isolated positions for a longer time2 while on the uppermost plate the colonies are completely isolated from one another1 with an appreciable surface of gelatine intervening4 8,the microscopical appearances of the colonies are best studied by placing the plate on a slab of blackened glass1 or on a porcelain slab if the colonies are coloured4 ,a small diaphragm is used1 and the appearances studied principally with a low power4 ,a much simpler method of plate-cultivation is to pour the liquefied jelly into shallow flat dishes2 they take up much less room1 and in many ways are more convenient4 8,nutrient agar-agar can also be employed for the preparation of plate-cultivations1 but it is much more difficult to obtain satisfactory results40 ,microscopical ,examination of ,bacteria4 ,bacteria in ,liquids1 ,cultures1 and ,fresh ,tissues4--,in conducting bacteriological researches1 the importance of absolute cleanliness cannot be too strongly insisted upon4 ,all instruments1 glass vessels1 slides1 and cover-glasses should be thoroughly cleansed before use4 ,the same applies to the preparation and employment of culture media2 any laxity in the processes of sterilisation1 or insufficient attention to minute technical details1 will be followed with disappointing results by contamination of the cultures1 resulting in the loss of much time4 ,for the preparation of microscopical specimens it will be found convenient to use a platinum inoculating needle1 sterilised1 as before directed1 in the sheet-iron box2 in a few moments it will be cool enough not to destroy the bacteria with which it is brought into contact4 ,unstained ,bacteria4--,the bacteria in liquids1 such as blood and culture-fluids1 can be investigated in the unstained condition by transferring a drop with a looped platinum needle1 or a capillary pipette1 to a slide1 covering it with a clean cover-glass1 and examining without further treatment4 ,if it is desirable to keep the specimen under prolonged observation1 a drop of sterilised water or salt solution must be run in at the margin of the cover-glass to counteract the tendency to dry4 ,cultures on the solid media can be examined by transferring a small portion with a sterilised needle to a drop of sterilised water on a slide1 thinning it out1 and covering with cover-glass as already described4 ,tissues in the fresh state may be teased out with needles 7,fig4 #bdi7 in sterilised salt solution1 and pressed out into a sufficiently thin layer between the slide and cover-glass4 ,glycerine may in many cases be substituted for salt solution1 especially for such as actinomyces and mould fungi4 ,very small bacilli and micro-cocci are distinguished from granular matter or fat-crystals1 or vice vers1 by the fact that the latter are altered or dispersed by the addition of acetic acid1 and changed by solution of potash2 ether dissolves out fatty particles1 while micro-organisms remain unaffected4 ,baumgarten demonstrated tubercle bacilli in sections by treating them with potash1 which clarified the tissues and brought the bacilli clearly into view4 ,in examining unstained bacteria the iris-diaphragm should be used1 and the sub-stage condenser carefully centred and focussed4 ,his's ,method of ,staining4--,a slide is prepared as for bacteria in the fresh state2 the reagents are then applied by placing them with a pipette drop by drop at a margin of the cover-glass1 and causing them to flow through the preparation by means of a strip of filter-paper placed at the opposite margin4 ,babs' ,method is as follows3 ,a little of the growth spread out on a cover-glass into as thin a film as possible2 when almost dry1 apply a drop or two of a weak aqueous solution of methyl-violet from a pipette to the film2 any excess of the stain must be removed by gentle pressure with a strip of filter-paper4 ,cover-glass ,preparations4--,a cover-glass is smeared with the substance to be examined spread out into a sufficiently thin layer2 in the case of cultures on solid media1 diffuse the bacteria in a little sterilised water4 ,by means of another cover-glass the juice or fluid is squeezed out from between them into a thin layer1 and on sliding them apart each cover-glass bears on it a thin film of the material4 ,the cover-glass is then placed with its film side upwards and allowed to dry4 ,after a few minutes it is passed from above downwards through the flame of a ,bunsen burner three times4 ,apply two or three drops of an aqueous solution of fuchsine or methyl-violet to cover the film1 wash away any surplus stain after a few minutes with distilled water4 ,the cover-glass is then allowed to dry1 when the preparation may be mounted in ,canada balsam1 or while still wet1 turned over on a slide1 and the excess of water removed with filter-paper4 ,if necessary to apply stain for a much larger period1 pour staining solution into a watch glass and allow cover-glass to swim on surface with prepared side downwards4 ,crookshank1 instead of watery solutions of aniline dyes1 prefers to use stronger solutions1 and to reduce the staining by a momentary immersion in alcohol4 ,the method is as follows3 cover-glass preparations are stained with carbolised fuchsine 7,neelsen's solution7 for about two minutes1 rinsed in alcohol for a few seconds1 and quickly washed in water4 ,this method is specially valuable for sarcin and streptococci4 ,gram's ,method4--,the whole film is first stained violet with gentian-violet1 fixed by a solution of iodine1 in iodide of potassium in the bacilli1 but not in any dbris1 pus cells1 or tissue elements present4 ,transfer cover-glass to alcohol1 the bacilli alone remain stained1 the violet colour being changed to blue4 ,by employing a contrast colour1 such as eosin1 a double staining is obtained4 ,for staining preparations with gentian-violet ,crookshank employs the following useful method3--,place four or five drops of pure aniline in a test-tube1 add distilled water to three-quarters full1 close mouth with thumb1 shake thoroughly4 ,filter the emulsion twice1 pour filtrate into watch-glass4 ,to the perfectly clear aniline water thus obtained1 add1 drop by drop1 a concentrated alcoholic solution of gentian-violet till precipitation commences4 ,cover-glasses must be left in this solution ten minutes1 transferred to iodine-potassic-iodide until the film becomes uniformly brown1 then rinsed in alcohol4 ,the decolourisation may be hastened by dipping the cover-glass in clove oil and returning to alcohol4 ,again immerse cover-glass in clove oil1 dry by gently pressing between two layers of filter-paper1 and mount in ,canada balsam4 ,double-staining of cover-glass preparations4--,they can be treated by ,ehrlich's method for staining tubercular sputum1 or by ,neelsen's modification1 or by staining with eosin after treatment by the method of ,gram4 ,ehrlich's ,method is as follows3 ,five parts of aniline oil are shaken up with one hundred parts of distilled water1 and the emulsion filtered through moistened filter-paper4 ,a saturated alcoholic solution of fuchsine1 methyl-violet1 or gentian-violet1 is added to filtrate in watch-glass1 drop by drop1 until precipitation commences4 ,cover-glass preparations are floated in this mixture for fifteen minutes to half an hour1 then washed for a few seconds in dilute nitric acid 7one part of nitric acid to two of water71 then rinsed in distilled water4 ,neelsen's ,solution and ,methylene ,blue4--,ziehl suggested the use of carbolic acid as a substitute for aniline blue4 ,neelsen recommended a solution of carbolic acid1 absolute alcohol and fuchsine4 7,see ,appendix47 ,gram's ,solution and ,eosin4--,after using ,gram's method as above and decolourising in alcohol1 the cover-glass is placed in a weak solution of eosin for two or three minutes1 washed in alcohol1 immersed in clove oil1 dried1 and mounted in balsam4 ,staining of ,spores4--,the cover-glass preparation must be heated to #baj ,c4 for half an hour1 or passed about twelve times through the flame of a ,bunsen burner1 or exposed to the action of strong sulphuric acid for several seconds1 then a few drops of a watery solution of aniline dye applied in the usual way4 ,to double-stain spore-bearing bacilli the cover-glass preparation must be floated from twenty minutes to an hour on ,ehrlich's fuchsine-aniline-water1 or on the ,ziehl-,neelsen solution4 ,the stain must be heated until steam arises4 ,staining of ,flagella4 ,koch first stained flagella by floating the cover-glass on a watery solution of hmatoxylin1 transferring them to a five per cent4 solution of chromic acid1 or to ,mller's fluid1 by which they obtained a brownish-black coloration4 ,lffler's ,method4--,add together aqueous solutions of ferrous-sulphate and tannin 7twenty per cent47 until the mixture turns a violet-black colour1 then add three or four cc4 of a one-in-eight aqueous solution of logwood2 a few drops of carbolic acid may be added before transferring to a stoppered bottle2 that is the mordant4 ,the dye consists of #a cc4 of a one per cent4 solution of caustic soda1 added to #ajj cc4 of aniline water1 in which four or five grammes of either methyl-violet1 methylene blue1 or fuchsine1 are dissolved4 ,a cover-glass preparation is made in the usual way1 then the film is covered with mordant1 and cover-glass held over flame until steam rises1 the mordant is then washed off with distilled water4 ,the stain is filtered and a few drops allowed to fall on film1 after a few minutes the cover-glass is again warmed until steam rises4 ,the stain is then washed off with distilled water1 and the preparation is ready to be mounted for examination4 ,as ,lffler's process is somewhat complicated1 a modification has been said to afford more satisfactory results4 ,a specimen is taken from a recent gelatine culture and diluted with water4 ,a little of the fluid is then transferred to a warm cover-glass by means of a pipette and allowed to dry1 after which a drop of the following mordant is applied3--,aqueous solution of tannin 7twenty per cent471 ten cc42 cold saturated solution of ferrous sulphate1 five cc42 saturated solution of fuchsine in absolute alcohol1 one cc4 ,the cover is next heated gently for a short time until vapours are given off1 then washed carefully4 ,this process is repeated two or three times1 and the specimen washed after each application4 ,subsequently1 staining is effected by means of ,ziehl's fuchsine solution1 the cover is afterwards warmed once or twice for about fifteen seconds1 then washed1 and the specimen examined in water to ascertain if the colour is sufficiently intense4 ,if satisfactory1 the preparation may then be dried and finally mounted in ,canada balsam or dammar4 ,preservation of ,preparations4--,after examining a cover-glass preparation with an oil-immersion objective the cedar oil must be carefully wiped off1 and the slide set aside for the ,canada balsam to set4 ,at a convenient time these preparations should be sealed with a ring of ,hollis's glue4 ,bacteria in ,sections of ,tissues4 ,method of ,hardening and ,decalcifying ,tissues4--,to harden small organs1 such as the viscera of a mouse1 they should be placed on a piece of filter-paper at the bottom of a small wide-mouthed glass jar1 and covered with about twenty times their volume of absolute alcohol4 ,larger organs are treated in the same way1 but must be cut up into small pieces4 ,mller's fluid1 methylated spirit1 or formalin may be used4 ,teeth1 or osseous structures1 must first be placed in a decalcifying solution1 as ,kleinenberg's4 ,when sufficiently softened1 soak in water1 to wash out picric acid1 and transfer to weak spirit4 ,ebner's solution gives good results4 ,methods of embedding1 fixing1 and cutting4--,crookshank finds that after hardening1 the pieces of tissue are embedded in a mixture of ether and alcohol for an hour or more1 then transferred to a solution of celloidin in equal parts of ether and alcohol1 and left there for several hours4 ,the piece of tissue is then placed in a glass capsule1 and some of the celloidin solution poured over it4 ,the capsule can be placed bodily in #fj to #hj per cent4 alcohol1 and left there until the following morning4 ,the celloidin should be of the consistency of wax4 ,the piece of tissue is next cut out1 and after trimming is put into water until it sinks1 then transferred to gum1 and cut with the freezing microtome4 ,sections of fresh tissues are to be floated in #h per cent4 salt solution1 and then carefully transferred by a platinum lifter to a watch-glass containing absolute alcohol4 ,staining ,bacteria in ,tissue ,sections4--,weigert's method is as follows3--,place sections for from six to eighteen hours in a one per cent4 watery solution of any of the basic aniline dyes4 ,to hasten1 place the capsule containing solution in the incubator1 or heat it to #de ,c41 or a stronger solution may be used4 ,in the latter case the sections must be treated with a half-saturated solution of carbonate of potash1 as they are easily over-stained4 ,in either case the sections are next washed with distilled water1 passed through sixty per cent4 alcohol into absolute alcohol4 ,when almost decolourised1 spread out on a platinum lifter and transfer to clove oil1 or stain with picro-carmine solution 7,weigert's7 for half an hour1 wash in water1 alcohol1 and treat with clove oil1 and transfer to clean glass slide4 ,gram's ,method4--,sections are stained for ten minutes in a capsule containing aniline-gentian-violet solution1 then placed in the iodine and iodide solution until uniformly brown1 then placed in absolute alcohol1 and washed by carefully moving sections in the liquid with a glass rod4 ,when completely decolourised1 they are transferred to clove oil and then to a slide4 ,double-staining is obtained by transferring the sections after decolourisation to eosin1 ,bismarck brown1 or vesuvin 7,crookshank74 ,formalin is an excellent preservative fluid2 one part to #bj1jjj is sufficient to prevent fermentation4 ,for the preservation of vegetable sections1 a one per cent4 solution is required2 even the fresh appearance of vegetable structures is preserved for some time when immersed in it4 ,in the nutrient gelatine for biological specimens1 if used early1 will arrest the liquefaction of the gelatine by bacteria4 ,for hardening it saves time1 and is even better than alcohol1 chromic acid1 pot4 bich41 and many others4 ,it does not cause shrinkage of the cells4 ,tissue #a_/b to #c_/d inch thick hardens in twenty-four hours in pure formalin2 five to ten per cent4 is best for loose tissue4 ,in another method1 by which time can be saved1 instead of placing the specimen in the formalin and afterwards in mucilage1 prior to cutting sections1 make the mucilage with two per cent4 7or stronger7 formalin water1 and it will then answer both purposes at the same time4 ,preparing1 ,mounting1 ,cementing and ,collecting ,objects4 ,various materials are required for preparing and mounting microscopic objects1 as slips of glass1 patent flatted plate measuring #c #a inch1 thin glass covers1 glass cells1 preservative media1 varnishes1 cements1 a glazier's diamond1 and a ,shadbolt's turn-table4 ,the glass slides and covers1 although sent out packed ready for use1 should be immersed in an alkaline solution to ensure perfect freedom from any greasiness derived from touching by the fingers4 ,dr4 ,seller recommends a particular solution for this purpose4 7,see ,formul1 ,appendix47 ,varnishes and cements must be selected with care1 as these are not only expected to adhere firmly to the glass slide1 but also to resist the action of the preservative fluid in which the specimen may be mounted4 ,among the numerous preparations employed1 ,i may enumerate ,canada balsam1 gum dammar1 ,venice turpentine1 ,japanners' gold size1 used for closing up cells1 asphalte varnish1 ,brunswick black1 shellac1 glue and honey1 ,hollis' liquid glue1 and marine glue4 ,to give a finish to the mounted specimen1 coloured varnishes are sometimes resorted to4 ,a red varnish of sealing-wax is made by digesting powdered sealing-wax in strong alcohol4 ,filter1 and place the solution in a dish1 and evaporate by means of a sand bath to reduce it to a proper consistency4 ,this is said to resist the action of cedar oil4 ,for white1 zinc1 cement is the best4 ,this is made of benzole1 gum dammar1 oxide of zinc1 and turpentine4 ,cole gives another formula1 but either of these may be obtained of ,squire1 who supplies every kind of staining and mounting material4 ,illustration3 ,fig4 #bfb4--,walmsley's ,cell-making ,turn-table4 ,cells for ,mounting4--,the minuter forms of life should be mounted in thin cells1 which may be readily made with ,japanners' gold size1 dammar or asphalte1 and a ,shadbolt or ,walmsley's turntable4 ,the glass slide being placed under the metal springs in such a manner that its two ends shall be equi-distant from the centre 7a guide to the position is afforded by the circles traced out on the brass71 take a camel's hair pencil and dip it into the ,japanner's gold-size1 holding it firmly between the finger and thumb1 and set the wheel in motion1 when a perfect circle will be formed2 put it aside to dry1 or place it in the warm chamber to harden4 ,to cut cover-glasses place a sheet of thin glass under the brass springs1 and substitute for the pencil a cutting diamond4 ,a cutting diamond is not only useful to the microscopist for the above purpose1 but also for writing the names of mounted objects on one end of the slide4 ,it will be found convenient to make a number of such cells1 and keep a stock ready for use4 ,there are many objects whose structure is very transparent4 ,these should be mounted dry4 ,scales from the wings of butterflies and moths1 of the podura and lepisma1 and some of the diatomace are of this class4 ,all that is necessary in preparing objects for dry mounting is to take care that they are free from extraneous matter1 and fix them permanently in the position in which their structure will show to the best advantage4 ,for mounting specimens of greater thickness it is desirable to use deeper cells4 ,it will then be found convenient to make a second or a third application of the gold-size1 allowing sufficient time between applications for the varnish to dry4 ,cells of a still deeper kind are made up by cementing rings of glass or metal to the glass-slides with marine glue or ,brunswick black4 ,the latter will be rendered more durable by mixing in a small quantity of indiarubber varnish 7made by dissolving small strips of caoutchouc in gas-tar74 ,the process of mounting in glass-cells is similar to that employed in making varnish-cells1 except that a somewhat larger quantity of cementing medium is required4 ,objects mounted in this way should be kept for a time in the horizontal position1 and a little fresh varnish must be applied if the cement shows a tendency to crack4 ,in mounting objects in balsam1 care must be taken to have the specimen quite dry before transferring it to turpentine4 ,objects mounted in cells should become perfectly saturated with the mounting fluid before being finally cemented down4 ,illustration3 ,fig4 #bfc4--;,glass-cells for ,mounting4 ,it is preferable to mount and preserve specimens of animal tissues in shallow cells1 to avoid undue pressure on the preparation4 ,cells intended to contain preparations immersed in fluid must be made of a substance impervious to the fluid used1 such as here represented 7,fig4 #bfc74 ,the surface of the fixed glass-circle should be slightly roughened before applying the cement4 ,different modes of mounting may be employed with advantage2 for instance1 entomological specimens1 as legs1 wings1 spiracles1 trache1 ovipositors1 stings1 tongues1 palates1 corne1 should be mounted in balsam2 the trachea of the house-cricket1 however1 should be mounted dry4 ,sections of bone may either be mounted dry or in a fluid4 ,other objects1 as sections of wood and stones of fruit1 exhibit their structure best in ,canada balsam4 ,in mounting entomological specimens1 the first thing1 of course1 is the dissection of the insect4 ,this is best accomplished by the aid of a dissecting microscope1 a pair of small brass forceps1 and finely-pointed scissors2 the parts to be prepared and mounted should first be carefully detached from the insect with the scissors1 then immersed in a solution of caustic alkali 7liquor potass7 for a few days1 to soften and dissolve out the fat and soft parts4 ,the length of time necessary for their immersion can only be determined by experience1 but1 as a general rule1 the objects assume a certain amount of transparency when they have been long enough in the alkali2 when this is ascertained1 the object must be placed in a proper receptacle and put by to soak for two or three hours in soft or distilled water4 ,it should then be placed between two slips of glass1 and gently pressed till the softer parts are removed4 ,should any adhere to the edge of the object1 it will be necessary to wash the specimen carefully in water1 a process that will be much assisted by the delicate touches of a camel's-hair brush4 ,place the object now and then under the microscope to see that all extraneous matter is removed1 and when this is accomplished take the specimen up carefully with the camel's-hair brush1 or a lifter1 and place it on a piece of very smooth paper 7thick ivory note is the best for the purpose71 arrange it carefully with the brush and a finely pointed needle1 place a second piece of paper over it1 and press it flat between two slips of glass1 and compress it by a small spring clip 7,fig4 #bfd74 ,a dozen clips may be had for a few pence4 ,when thoroughly dry 7which it will probably be in about twenty-four hours1 if in a warm room71 separate the glasses1 and gently unfold the paper2 then1 with a little careful manipulation1 the object may be readily detached1 and placed in a little spirit of turpentine1 where it should be allowed to remain until rendered transparent and fit for mounting4 ,the time during which it should remain in this liquid will depend on the structure2 some objects1 such as wings of flies1 will be quickly permeated1 while horny and dense objects require an immersion of a fortnight or even longer4 ,a pomatum pot with a concave bottom and well-fitting lid will answer admirably for conducting the soaking process in2 and it is well1 in preparing several specimens at a time1 to have two pots1 one for large and medium1 the other for very small objects1 otherwise the smaller will adhere to the larger4 ,illustration3 ,fig4 #bfd4--,spring ,clip for ,mounting4 ,in mounting objects in fluid1 the glass cover should come nearly1 but not quite1 to the edge of the cell1 a slight margin being left for the cement1 which should project slightly over the edge of the cover1 in order to secure it to the cell4 ,media for ,preserving ,alg4--,the most useful preservative media for alg are chrome-alum1 formalin1 and camphor water4 ,the solution should consist of one per cent4 of chrome-alum and one per cent4 of formalin2 this will render the gelatinous sheath and matrix form clear1 while it will retain the colour of the alg in most cases4 ,the ,chlorophyce do well in any of these media2 but other species1 as ,ulva ,lactuca1 are rendered somewhat brittle4 ,for such use formalin alone4 ,the ,phophyce should be placed while fresh in the formalin2 the larger forms are better fixed by placing them for an hour or two in chrome-alum solution4 ,the ,floride do well in any of the three solutions1 but the more delicate species1 ,griffithsia1 require a two per cent4 formalin solution in sea-water2 the plant preserves its natural appearance in this medium4 ,to preserve and mount diatomace in as nearly as possible a natural condition1 they should be first well washed in distilled water and mounted in a medium composed of one part of spirits of wine to seven parts of distilled water4 ,the siliceous coverings of the diatoms1 however1 which show various beautiful forms under the higher powers of the microscope1 require more care in preparation4 ,the guano1 or infusorial earth containing them1 should first be washed several times in water till the water is colourless1 allowing sufficient time for precipitation between each washing4 ,the deposit must then be put into a test tube and nitro-hydrochloric acid 7equal parts of nitric and hydrochloric acids7 added to it1 when a violent effervescence will take place4 ,when this has subsided1 the whole should be subjected to heat1 brought nearly to the boiling point for six or eight hours4 ,the acid must now be carefully poured off1 and the precipitate washed in a large quantity of water1 allowing some three or four hours between each washing1 for the subsidence of some of the lighter forms4 ,the sediment must be examined under the microscope with an inch object-glass1 and the siliceous valves of the diatoms picked out with a coarse hair or bristle4 ,dr4 ,rezner's ,mechanical ,finger 7,fig4 #bfe7 for selecting and arranging diatoms1 adaptable to any microscope1 is made to slip on to the objective far enough to have a firm bearing1 and so that the bristle point can be brought into focus when depressed to its limit4 ,it is clamped in its place by a small thumb-screw4 ,the bristle holder slides into its place1 and is carefully adjusted to the centre of the field4 ,when using the finger1 the bristle is first raised by means of the micrometer screw till so far within focus as to be nearly or quite invisible1 then the objective is focussed on to the slide1 and the desired object sought for and brought into the centre of the field2 the bristle point is then lowered by the screw until it reaches the object1 which usually adheres to it at once1 and can then be examined by rotating the bristle wire by means of the milled head4 ,illustration3 ,fig4 #bfe4--,rezner's ,mechanical ,finger4 ,the medium used for mounting diatomace is of considerable importance1 inasmuch as their visibility is either diminished or much increased thereby4 ,professor ,abbe1 experimenting with the more minute test objects1 diatoms1 c41 found monobromide of naphthaline gave increased definition to most of them4 ,this liquid is colourless1 somewhat of an oleaginous nature1 and is soluble in alcohol4 ,its density is #aeee1 and refractive index #af4 ,its index of visibility is about twice that of ,canada balsam4 ,taking the refractive index of air as #aj1 and diatomaceous silex as #adc1 the visibility may be expressed by the difference #dc4 ,the following table may be constructed 3-- ,refractive indices ,visibility of silex 7taken approximately74 7,refr4 index #adc74 ,water #acc #aj ,canada balsam #aed #aa ,bisulphide of carbon #afh #be ,sol4 of sulphur in bisulph4 #age #cb phosphorus #baa #fg ,these data relating to visibility must be taken in connection with the numerical aperture of the objectives and of the illuminating pencil4 ,the effect produced on diatoms is very remarkable1 the markings on their siliceous frustules being visible under much lower powers4 ,so that the visibility of the diatom mounted in phosphorus as compared with balsam is as sixty-seven to eleven2 in other words1 the image is six times more visible4 ,mr4 ,stephenson's phosphorus medium is composed of a solution of solid or stick phosphorous dissolved in bisulphide of carbon4 ,great care is required in preparing the solution owing to the very inflammable nature of the materials4 ,so small a quantity of the bisulphide of carbon is required to dissolve the phosphorus that the diatom may be said to be mounted in nearly pure phosphorus4 ,remarkable enough1 this medium has the reverse effect upon such test-objects as podura and lepisma scales4 ,these lose their characteristic markings4 ,for mounting minute objects1 carbolic acid solution will be found a useful medium--the purest crystals of carbolic acid dissolved in just sufficient water to render them fluid4 ,no more should be dissolved than may be wanted for the time being1 as if left standing exposed to the light it changes colour4 ,small crustacean foraminifera1 the palates of moluscs1 after boiling a short time in liquid potash and well washing to remove all traces of alkali1 may be preserved in carbolic acid solution4 ,should the specimens appear cloudy gently warm the slide over a spirit lamp4 ,preserving and ,killing ,rotatoria with cilia in situ4--,mr4 ,c4 ,rousselet's method of preserving and mounting the ,rotatoria#dg has been attended with so much success that the old difficulty attendant upon the preservation of these various beautiful forms of infusorial life has been practically overcome4 ,the process resorted to consists of four stages1 namely1 narcotising1 killing1 fixing1 and preserving4 ,in dealing with rotifers hitherto1 the difficulty has been that of successfully killing them with their rotating organs fully extended4 ,it has been found needful to have recourse in the first instance to a narcotising agent1 and one that acts slowly4 ,the most suitable is a weak solution of the hydrochlorate of cocaine1 a one per cent4 solution1 or even weaker4 ,this was first proposed by ,mr4 ,weber for keeping these active little bodies quiet while under observation4 ,mr4 ,rousselet carries this agent further2 he applied it to narcotise them prior to killing1 and this it does most effectually4 ,the rotifers are seen to sink to the bottom of the live-cell1 and the cilia gradually to slacken in motion1 and the time for killing has arrived4 ,this is effected by ,flemming's chromo-aceto-osmic acid4 ,a rather weak solution must be employed--consisting of #a per cent4 solution of chromic acid1 #ae parts2 #b per cent4 osmic acid1 #d parts2 glacial acetic acid1 #a part--which is at the same time a killing and fixing medium4 ,the word 8fixing0 must not be taken to imply simply fixing1 as it includes rapidly killing and hardening and preventing further change in the tissues of the rotifers by subsequent treatment1 as mounting4 ,the animal1 therefore1 must remain quietly for a few minutes1 and then taken out and washed in five or six changes of distilled water1 and hence transferred to the preservative fluid4 ,all this must be effected with great care4 ,the best preservative fluid is simply distilled water1 rendered antiseptic by a trace of the fixing solution 7about eight drops to an ounce of water7 giving the slightest tinge of yellow to the solution4 ,this slight tinge of colour is imparted to the rotifers1 otherwise they remain transparent and unchanged1 while the nervous tissue throughout the body is brought out to perfection4 ,some slight difference in treatment is required by certain species1 as that of ,asplanchna priodonta2 after the application of the cocaine solution1 which should be added slowly1 that is1 by letting a few drops trickle down the side of the live-trough2 this1 being heavier than water1 sinks to the bottom1 thus narcotising the rotifers1 and assisting to kill them with the cilia fully expanded4 ,they should be left quietly for fifteen minutes1 then thoroughly washed with distilled water4 ,on further experimenting1 ,mr4 ,rousselet found that a weaker solution of osmic acid alone1 #a_/d per cent41 answers quite as well as1 if not better than1 ,flemming's fluid2 even this must be allowed to act for only a very short time--a minute at most2 the rotifers then remain white and transparent1 excepting the ova1 in which a fat-like substance1 lecithene1 is secreted4 ,if they become too much stained1 they may be decolourised by passing them through peroxide of hydrogen4 ,for narcotising the following solution has been found most useful3--,take a #b per cent4 solution of cocaine hydrochlorate1 #c parts2 methylated spirit of wood naphtha1 #a part2 and distilled water1 #f parts4 ,this must be added as before directed1 drop by drop1 watching the effect upon the rotifers under the microscope4 ,all the rotatoria may be killed and preserved in the same way4 ,for mounting1 ,mr4 ,rousselet prefers a slightly hollowed-out glass cell1 the advantage of which is that the rotifers are kept to the centre1 and cannot move to the edge4 ,a little difficulty at first presents itself to exclude air-bubbles1 but this1 with a little care1 can be overcome by placing a drop of a two or three per cent4 solution of formalin1 just sufficient to fill the cell4 ,then transfer the rotifers with a dipping pipette to the cell1 and lower the cover-glass down very gently1 removing any excess of fluid by blotting-paper4 ,the best cement for the cover-glass is gold-size4 ,method of ,cementing4--,after many years' experience1 ,i have arrived at the conclusion that for cementing down the cover-glass there is nothing better than either gold size or gum dammar varnish4 ,the latter1 for some preparations1 will be improved by the addition of a small proportion of indiarubber dissolved in naphtha4 7,see ,appendix47 ,should glycerine be preferred1 carefully wash away any surplus quantity by gently syringing2 then apply a ring of waterproof cement round the cover-glass4 ,an inexpensive one can be made by dissolving ten grains of gum-ammoniac in an ounce of acetic acid1 and adding to this solution two drachms of ,cox's gelatine4 ,this liquid flows easily from the brush and is waterproof1 rendered more so if subsequently brushed over with a solution of ten grains of bichromate of potash in an ounce of water4 ,an especial recommendation to this cement is its adhesiveness to glass1 even should there be a little glycerine left behind on the cover4 ,after the gelatine ring is thoroughly dry any kind of cement may be employed4 ,a useful cement for fixing minute objects1 diatoms1 c41 temporarily to thin glass covers1 before permanently mounting them in ,canada balsam1 is made as follows3--,dissolve1 without heat1 two or three grains of gum arabic in one ounce of distilled water1 then add glacial acetic acid1 three minims1 and the least trace of sugar4 ,filter carefully through filter paper1 and repeat this in the course of three or four weeks4 ,this cement will be unaffected by the balsam4 ,mounting ,chara4--,it is often found difficult to preserve and mount the fruit of chara1 but this can be successfully accomplished in glycerine jelly1 by taking the following precautions4 ,after cleaning the specimen place it in #ib per cent4 of alcohol for several hours1 then transfer it to a mixture of equal parts of spirit and glycerine for several hours longer1 pour off nearly all the mixture1 and add pure glycerine at intervals till the glycerine becomes concentrated4 ,the specimen is then mounted in glycerine jelly in a cell just deep enough to take it without pressure4 ,there are some objects much more difficult to prepare than others1 and which tax the patience of the beginner in a manner which can hardly be imagined by any one who has never made the attempt4 ,the structure of many creatures is so delicate as to require the very greatest care to prevent mutilation1 and consequent spoliation1 of the specimen4 ,the beginner1 therefore1 must not be discouraged by a few failures in commencing1 but should persevere in his attempts1 and constant practice will soon teach him the best way of managing intricate and difficult objects4 ,the room in which he operates should be free from dust1 smoke1 and intrusion1 and everything used should be kept scrupulously clean1 since a very small speck of dirt1 which may be almost invisible to the naked eye1 will assume unpleasant proportions under the microscope1 and not only mar1 but possibly spoil a fine and delicate preparation4 ,few students on commencing to work with the microscope will fully realise the fact that under medium or high powers the natural appearance of almost all objects is changed by the refractive nature of the fluid medium in which they are immersed and which enters more or less into their composition4 ,the remarkable changes effected by the law of diffusion1 when alkaloid substances enter into their composition1 show the necessity of taking every precaution in the employment of preservative fluids4 ,glycerine affords an example of the chemical change induced1 should the preparation have been passed through an alkaline solution4 ,air ,bubbles are a constant source of annoyance both in preparing and mounting4 ,these may be removed from the specimen by gently warming the under part of the slide over a spirit lamp1 or placing the slide in the warm chamber1 when the bubbles will move towards the edge of the cover-glass and ultimately disappear4 ,the air-pump is preferred by many microscopists4 ,collection of ,objects4 ,infusorial ,life1 with all its fascinations1 was fully unveiled to naturalists by the celebrated ,ehrenberg4 ,it was he who termed it infusorial1 because he first met with the more interesting forms of minute life in infusions of hay and other vegetable substances4 ,since his day it is a well-known experience of those who take up the microscope that the most interesting objects to commence with are infusorial living creatures of sufficient dimensions to be easily understood and seen with moderate magnifying powers4 ,moreover1 infusoria are more readily found in almost any pool or running stream of water1 either near the surface or clinging to the under surfaces of aquatic plants4 ,at one time all the small shallow pools in the neighbourhood of ,london--,hampstead ,heath1 ,clapham1 ,wandsworth1 and other commons--abounded in the most interesting forms of life1 were famous hunting grounds for the marvellous volvox1 the charming dismid and diatom1 the wonderful budding and self-dividing hydra4 ,a few hours' ramble furnished the microscopist with a bountiful supply of these and many other forms of life4 ,now all is changed2 our commons have been devoted to other purposes1 and with the general levelling up all the little pools have disappeared1 and the microscopist has been warned off and driven further afield1 or seeks the good offices of a country friend for an occasional peep into pond life4#dh ,a teaspoonful1 however1 judiciously taken from a well-chosen locality will often be found to contain a variety of living forms1 every one of which will deserve a careful and patient study4 ,of the microscopic organisms1 the collection of which requires no other methods than those ordinarily pursued by the naturalist1 most of them must be sought for in pools or running waters1 basking in the sunshine1 clinging to leaves and rootlets of all aquatic plants2 some freely moving about1 others clinging to stones or pieces of wood at the bottom4 ,dismids congregate in shallow waters or rise to the surface in a quiet nook1 while the diatomace are seen covering the bottom of clear water1 to which they give a yellowish-brown tinge of colour4 ,infusorial animal life1 as vorticell1 stentors1 rotifers1 and various polyzoa1 cling1 as also do hydra1 in colonies to vallisneria1 duck-weed1 frogbit1 or small branches dipping down under water2 and if some of the water-weed is brought home the little creatures will live and thrive for several weeks4 ,no waters1 however1 are so full of minute animal life as the sphagnum bog4 ,a number of species of diatoms1 as well as protozoids and the smaller molluscs1 will be found in all peat bogs4 ,it is remarkable1 too1 that the same species1 everywhere1 are associated with this kind of moss4 ,lord ,sidney ,godolphin ,osborn supplied his friends with moss growing in a damp part of the garden walk of his rectory2 this always furnished the same species of rotifers4 ,these proved to be most interesting objects to my friends1 and in an early communication ,i described them as indestructible1 since they will bear any amount of desiccation2 nevertheless1 they were revived when a drop of water was introduced into the glass-cell4 ,illustration3 ,fig4 #bff4--;,collecting ,stick1 ,bottle1 ,hook1 and ,net4 ,the ,thames mud always furnishes a number of beautiful forms of triceratum4 ,lower down the river1 as brackish water is reached1 greater varieties of diatoms appear4 ,but to secure them the collector must be provided with a collecting stick4 ,a convenient form is furnished by ,messrs4 ,baker 7,fig4 #bff74 ,this consists of an ordinary walking-stick1 together with a lengthening rod1 a cutting hook to clear away weeds1 ringed bottles with screw tops1 and a net with a glass tube attached4 ,their uses are too obvious to need further description4 ,the siliceous skeletons of diatoms are met with in the fossil state4 ,among the first discovered of the infusorial strata were the polishing slates of ,bilin and ,tripoli1 the berg-mehl or mountain meal1 the entire mass of which is composed of the siliceous skeletons of different species of diatoms4 ,richmond1 ,virginia1 is rich in the same organisms1 while the great mass of our chalk cliffs are composed of foraminiferous shells1 xanthidi1 c4 ,one remarkable fact in connection with fossil infusoria is that most of the forms are still found in the recent state4 ,the beautiful engine-turned discs1 ,coscinodisci1 so abundant in the ,richmond earth1 may be met with in our own seas1 and in great profusion in the deposits of guano on the ,african and ,american coasts1 and in the stomachs of the oyster1 scallop1 and other salt-water molluscous animals common to our shores4 ,a great number of infusorial earths may be mounted as dry objects1 while others require careful washing and digesting in appropriate media4 ,the finer portions of the sediments will be found to contain the better and more perfect siliceous shells4 ,preparing and ,mounting ,apparatus4 ,illustration3 ,fig4 #bfg4--,mounting ,apparatus4 #a4--,ross's instrument for cutting thin covering-glass for objects4 ,this apparatus consists of a bent arm supporting the cutting portion of this apparatus1 which consists of a vertical rod with a soft cork at one end4 ,a brass arm at right angles carries the diamond parallel with and close to the main rod4 #b4--;,covering-glass measurer4 ,to measure the thickness of covering-glass1 place it between the brass plate and the steel bearing2 the long end of the lever will then indicate the thickness on the scale1 to #a_/ej-th1 #a_/ajj-th1 or #a_/ajjj-th inch4 #c4--;,brass table on folding legs1 with lamp for mounting objects4 #d4--,whirling table with eccentric adjustment for making cells and finishing off slides4 #e4--;,air-pump with glass receiver1 #c-a_/b-;inch brass plate for mounting objects and withdrawing air-bubbles4 #f4--;,improved table with knife for cutting soft sections4 ,this consists of an absolutely flat brass table1 with a square hole to receive the wood1 or other matter1 on a movable screw1 which adjusts the thickness of the section4 #g4--,smith's holder with spring and screw for adjusting pressure when mounting objects4 #h4--;,cutting diamonds for cell-making and cutting slips of glass4 #i4--,writing diamonds for cutting thin covering-glass and naming objects4 #aj4--,page's wooden forceps1 for holding glass slips or objects when heated1 during mounting4 ,,part ,,ii4 ,,chapter ,i4 ,microscopic ,forms of ,life--,thallophytes--,pteridophyta1 ,phanerogam--,structure and ,properties of the ,cell4 ,the time has long since passed by since the value of the microscope as an instrument of scientific research might have been called in question4 ,by its aid the foundation of mycology has been securely laid1 and cryptogamic botany in particular has1 during the last quarter of a century1 made surprising progress in the hands of those devoted to pursuits which confer benefits upon mankind4 ,little more than thirty years ago practically nothing was known of the life history of a fungus1 nothing of parasitism1 of infectious diseases1 or even of fermentation4 ,our knowledge of the physiology of nutrition was in its infancy2 even the significance of starches and sugars in the green plant was as yet not understood1 while a number of the most important facts relating to plants and the physiology of animals were unknown and undiscovered4 ,when we reflect on these matters1 and remember that bacteria were regarded merely as curious animalcul1 that rusts and smuts were supposed to be emanations of diseased states1 and that spontaneous generation still-survived among us1 some idea may be formed of the condition of cryptogamic botany and the lower forms of animal life some eight or ten years after my book on the microscope made its first appearance 7#ahed74 ,indeed1 long prior to this time1 dating from that of even the earliest workers with the microscope1 it was known that the water of pools and ditches1 and especially infusions of plants and animals of all kinds1 teem with living organisms1 but it was not recognised definitely that vast numbers of these microscopic living beings 7and even actively moving ones7 are plants1 growing on and in the various solid and liquid matters examined1 and as truly as visible and accepted plants grow on soil and in the air and water4 ,perhaps the most important discovery in the history of cryptogamic botany was initiated here4 ,the change1 then1 that has come over our knowledge of microscopic plant life during this last busy quarter of a century has been almost entirely due to the initiation and improvement1 first in methods of growing them1 and in the methods of 8,microscopic ,gardening02 and secondly1 to the greater knowledge gained in the use of the microscope4 8,if we look at the great groups of plants from a broad point of view1 it is remarkable that the fungi and the phanerogams occupy attention on quite other grounds than do the alg1 mosses1 and ferns4 ,alg are especially a physiologist's group1 employed in questions on nutrition1 reproduction1 and cell division and growth2 the ,bryophyta and ,pteridophyta are1 on the other hand1 the domain of the morphologist4 ,fungi and ,phanerogams1 while equally or even more employed by specialists in morphology and physiology1 appeal widely to general interest on the ground of utility4 8,it is very significant that a group like the fungi should have attracted so much scientific attention1 and aroused so general an interest at the same time4 ,but the fact that fungi affect our lives directly has been driven home2 and whether as poisons or foods1 destructive moulds or fermentation agents1 parasitic mildews or disease germs1 they occupy more interest than all other cryptogams put together1 the flowering plants alone rivalling them in this respect4 ,a marked feature of the period in which we live will be the great advances made in our knowledge of the uses of plants1 for1 of course1 this development of economic botany has gone hand in hand with the progress of geological botany1 the extension of our planting1 and the useful applications of botany to the processes of home industries40#di ,the intimate organic structure of the vegetable world is seen to consist of a variety of different materials indeterminable by unassisted vision1 and for the most part requiring high magnification for their discrimination4 ,chemical analysis had1 however1 shown that vegetables are composed of a few simple substances1 water1 carbonic acid gas1 oxygen1 nitric acid1 and a small portion of inorganic salts4 ,out of these simple elements the whole of the immense variety of substances produced by the vegetable kingdom are constructed4 ,no part of the plant contains fewer than three of these universally distributed elements1 hence the greater uniformity in their chemical constituents4 ,it will be seen1 then1 that the methods of plant chemistry are of supreme interest both to the chemist and the physiologist1 or biologist4 ,plants1 while they borrow materials from the inorganic1 and powers from the physical world1 whereby they are enabled to pass through the several stages of germination1 growth1 and reproduction1 could not accomplish these transformations without the all-important aid of light and heat1 the combined functions of which are indispensable to the perfect development of the vegetable world4 ,light1 then1 enables plants to decompose1 change into living matter1 and consolidate1 the inorganic elements of carbonic acid gas1 water1 and ammonia1 which are absorbed by the leaves and roots from the atmosphere and earth2 the quantity of carbon consolidated being exactly in proportion to the intensity of the light4 ,nevertheless1 light in its chemical character is a deoxidising agent1 by which the numerous neutral compounds common to vegetables are formed4 ,it is the principal agent in preparing the food of plants1 and it is during the chemical changes spoken of that the specific heat of plants is slowly evolved1 which1 though generally feeble1 is sometimes very sensibly evolved1 especially so when flowers and fruits are forming1 on account of the increase of chemical energy at this period4 ,the action of heat is measurable throughout the whole course of vegetable life1 although its manifestations take on various forms--those suited to the period and circumstances of growth4 ,upon the heat generated depends the formation of protein and nitrogenous substances1 which abound more directly in the seed buds1 the points of the roots1 and in all those organs of plants which are in the greatest state of activity4 ,the whole chemistry of plant life1 in fact1 is manifest in this production of energy for drawing material from its surroundings2 therefore the organising power of plants bears a direct ratio to the amount of light and heat acting upon them4 ,the living medium1 then1 which possesses the marvellous property of being primarily aroused into life and energy1 and which either forms the whole or the greater portion of every plant1 is in its earliest and simplest form nothing more than a microscopic cell1 consisting of one or two colourless particles of matter1 in closest contact1 and wholly immersed in a transparent substance somewhat resembling albumen 7white of egg71 termed protoplasm1 but differing essentially in its character and properties4 ,this nearly colourless organisable matter is the life-blood of the cell4 ,it is sufficiently viscid to maintain its globular form1 and under high powers is seen to have a slightly consolidated film enclosing semi-transparent particles1 together with vacuoles which are of a highly refractive nature4 ,these small bodies are termed nuclei1 and they appear to be furnished with an extremely delicate enveloping film4 ,in a short time the nuclei increase in number and split up the parent body4 ,the protoplasmic mass1 however1 is undoubtedly the true formative material1 and is rightly regarded as 8the physical basis of life0 of both the vegetable and animal kingdoms4 ,there are1 however1 certain members of the vegetable kingdom which somewhat resemble animals in their dependence upon receiving organic compounds already formed for them1 being themselves unable to effect the fixation of the carbon needed to effect the first stage in their after chemical transformations4 ,such is the case with a large class of flowering plants1 among ,phanerogams1 and the leafless parasites which draw their support chiefly from the tissues of their hosts4 ,it is likewise the case with regard to the whole group of fungi2 the lower cryptogams1 which derive the greater portion of their nutritive materials from organic matter undergoing some form of histolysis2 while others belonging to this group have the power of originating decomposition by a fermentative 7zymotic7 action peculiarly their own4 ,there are many other protophytes which live by absorption1 and which appear to take in no solid matter1 but draw nourishment from the atmosphere or the water in which they exist4 ,with regard to motion1 this was at one time considered the distinctive attribute of animal life1 but many protophytes possess a spontaneity of power and motion1 while others are furnished with curious motile organs termed cilia1 or whip-like appendages1 flagella1 by which their bodies are propelled with considerable force through the water in which they live4 ,henceforth this protoplasmic substance was destined to take an important position in the physiological world4 ,it is1 then1 desirable to enter somewhat more fully into the life history of so remarkable a body4 ,it has a limiting membrane1 composed of a substance somewhat allied to starch1 termed cellulose1 one of the group of compounds known as carbo-hydrates4 ,the mode of formation and growth of this cell wall is not yet definitely determined2 nevertheless1 it is the universal framework or skeleton of the vegetable world1 although it appears to play no special part in their vital functions4 ,it merely serves the purpose of a protecting membrane to the globular body called the 8primordial cell10 which permanently constitutes the living principle upon which the whole fundamental phenomena of growth and reproduction depend4 ,sometimes this protoplasmic material is seen to constitute the whole plant2 and so with regard to the simplest known forms of animal life--the amba1 for example4 ,that so simple and minute an organism should be capable of independent motion is indeed surprising4 ,dujardin1 a ,french physiologist1 termed this animated matter sarcode4 ,on a closer study of the numerous forms of animal life it was found that all were alike composed of this sarcode substance1 some apparently not having a cell wall4 ,the same seemed to hold good of certain higher forms of cells1 the colourless blood corpuscles for instance1 which under high powers of the microscope are seen to change their shape1 moving about by the streaming out of this sarcode4 ,at length the truth dawned on histologists that the cell contents1 rather than the closing wall1 must be the essential structure4 ,on further investigation it became apparent that a far closer similarity existed between vegetables and animals than was before supposed4 ,ultimately it was made clear that the vegetable protoplasm and the animal sarcode were one and the same structure4 ,max ,schultz found this to be the case1 and to all intents and purposes they are identical4 ,we have now to retrace our steps and look somewhat more closely into the discovery of that important body1 the cell-nucleus4 ,it was an ,english botanist1 ,dr4 ,robert ,brown1 who1 in #ahcc1 during his microscopical studies of the epidermis of orchids1 discovered in their cells 8an opaque spot10 to which soon afterwards he gave the name of nucleus4 ,schleiden and ,schwann's later researches led them to the conclusion that the nucleus is the most characteristic formative element in all vegetable and animal tissues in the incipient phase of existence4 ,it then began to be taught that there is one universal principle of development for the elementary parts of all organisms1 however different1 and that is the formation of cells4 ,thus was enunciated a doctrine which was for all practical purposes absolutely new1 and which opened out a wide field of further investigation for the physiologist1 and led up to a fuller knowledge of the cell contents4 ,in fact1 it became a question as to whether the cell contents rather than the enclosing wall should not be considered the basis of life1 since the cell at this time had by no means lost its importance1 although it no longer signified the minute cavity it did when originally discovered by ,schwann4 ,it now implied1 as ,schultz defined it1 8a small mass of viscid matter1 protoplasm1 endowed with the attributes of life40 ,the nucleus was once more restored to its original importance1 and with even greater significance4 ,in place of being a structure generated de novo from non-cellular substance1 and disappearing as soon as its function of cell formation is accomplished1 the nucleus is now known as the central permanent feature of every cell1 and indestructible while the cell lives1 and the parent1 by division of its substance1 of other generations of nuclei and cells4 ,the word cell has at the same time received its final definition as 8a small mass of protoplasm supplied with a nucleus40 ,in short1 all the activities of plant and animal life are really the product of energy liberated solely through histolysis1 or destructive processes1 amounting to the combustion that takes place in the ultimate cells of the organisms4 ,but there are other points of especial interest involved in the question of cell formation beside those already mentioned4 ,the cell and its contents collectively are termed the endoplasm1 or when coloured1 as in alg1 endochrome4 ,with regard to the outer layer of the cell and its growth nothing satisfactory has been clearly determined and finally accepted4 ,the cell as a whole is a protoplasmic mass1 and not an emulsion1 as some observers would have us suppose4 ,it is1 in fact1 a reticulated tissue of the most delicate structure1 made up of canaliculate spiral fibrils with hyaline walls capable of expansion and contraction4 ,these fibrils are probably composed of still finer spirals4 ,the visible granulated portion of the protoplasm1 the only part that takes a stain under ordinary circumstances1 is simply the contents of these canals4 ,it is the chromatin of ,flemming1 and is capable of motion within the canals4 ,the nucleus1 then1 is probably nothing more than a granule of the extra-cellular net1 and is formed by the junction of the several bands of wall-threads which traverse it in different directions4 ,the cell wall of plants possesses the same structure as protoplasm1 and is probably protoplasm impregnated by cellulose4 ,it is this portion of the protoplasmic mass that is now recognised under the term octoplasm1 or primordial utricle1 and is of so fine and delicate a nature that it is only brought into view when separated from the cell wall either by further developmental changes1 or by reagents and certain stains or dyes4 ,it was1 in fact1 discovered to be a slightly condensed portion of the protoplasmic layer corresponding to the octosare of the lower forms of animal life4 ,the octoplasm and cell wall can only be distinguished from each other by chemical tests4 ,both nucleus and nucleoli are only rendered visible in the same way1 that is1 by staining for several hours in a carmine solution1 and washing in a weak acetic acid solution4 ,with the enlargement of the cell by the imbibition of water1 clear spaces1 termed vacuoles1 are seen to occupy a small portion of the cell1 while the nucleus and nucleoli lie close to the parietal layer4 ,the interesting phenomenon of cyclosis1 to which ,i shall have occasion to refer further on1 is now believed to be due to the contractility of certain wall-threads stretching from the nucleus to the outermost layers of the cell4 ,an intimate relationship is thereby established between the nucleus1 the nucleolus1 and the parietal layer4 ,this much has been made clear by the more scientific methods of investigation pursued in the use of the microscope4 ,nevertheless a large and important class of cells1 forming a kind of borderland between the vegetable and animal kingdoms1 still remains to be dealt with1 in which the cell contents are only imperfectly differentiated1 while numerous other unicellular organisms1 owing to their extreme minuteness1 tenuity1 and want of all colour1 are apparently devoid of any nucleus1 and when present can only be differentiated by a resort to a specially conducted method of preparation and staining4 ,there is1 however1 a remarkable feature in connection with many micro-organisms--that certain of these protophytes possess motive organs1 cilia or flagella1 bodies at one time supposed to be characteristic of1 and belonging to1 the protozoa4 ,this being the case1 the methods of plant chemistry are of supreme interest1 the more so because physiologists are in a position to isolate a single bacterial cell1 grow it in certain media1 and thus devote special attention to it1 and keep it for some time under observation4 ,in this way it has become possible to further grasp facts in connection with cell nutrition and the nature of its waste products4 ,we have1 then1 arrived at a stage when the history of the chemical changes brought about by bacteria can be more definitely determined1 as we have here to do with the vegetable cell in its simplest form4 ,the chemical work performed by these micro-organisms has as yet occupied only a few years2 nevertheless1 the results have been of the most remarkable and encouraging character4 ,at an earlier period an interesting discovery in connection with the pathogenic action of these bodies was1 by the labours of ,schenlein1 ,robin1 and others1 brought to the notice of the medical profession1 viz41 that certain diseases affecting the human body were due to vegetable parasites4 ,in #ahef an opportunity offered itself for a thorough investigation1 and the microscopical part of the work fell into my hands1 with the result that ,i was able to add considerably to ,schenlein's list of parasitic skin diseases4 ,my observations were in the first instance communicated to the medical journals4 ,but the generalisation arrived at was that 8,if there be any exceptions to the law that parasites select for their sustenance the subjects of debility and decay1 such exceptions are rarely to be found among the vegetations belonging to fungi1 which invariably derive nutrition from matter in a state of lowered vitality1 passing into degeneration1 or wherein decomposition has already taken place to a certain extent4444 ,it scarcely admits of a doubt that all diseases observed of late years among plants have been due to parasites of the same class favoured by want of vigour of growth and atmospheric conditions1 and that the cause of the various murrains of which so much has been heard is also due to similar causes40#ej ,herein1 then1 is to be found the solution of a difficulty that so long surrounded the question1 but which subsequently culminated in the specialisation and scientific development of bacteriology1 due to the unceasing labours of ,pasteur1 whose solid genius enabled him to overcome the prejudices of those who were at work on other lines1 and who had no conception of the functions that parasitic organisms fulfil in nature4 ,going back to my earlier experimental researches to determine the part taken by saccharomycetes and saprophytes in fermentation1 ,i find1 from correspondence in my possession1 that in #ahei ,i demonstrated to the satisfaction of ,dr4 ,bell1 ,f4,r4,s41 the then head of the chemical laboratory of ,somerset ,house1 that a very small portion of putrefactive matter taken from an animal body1 a parasitic fungus 7,achorion ,schenleinii71 a mould 7,aspergillus or ,penicillium71 and a yeast 7,torula cerevisi7 would in a short time1 and indifferently1 set up a ferment in sweet-wort and transform its saccharine elements into alcohol1 differing only in degree 7quantitative71 and not in kind or quality4 ,this1 then1 was the first step in the direction towards proving symbiotic action between these several parasitic organisms4 ,the only apparent difference observed during the fermentative processes was that putrefactive 7saprophytic7 action commenced at a somewhat earlier stage1 and that the percentage of alcohol was also somewhat less4#ea ,in #ahef1 also1 the robic bacteria attracted my attention1 and1 together with the late ,rev4 ,lord ,sidney ,godolphin ,osborne1 ,i exposed plates of glass 7microscopical slides71 covered with glycerine and grape sugar1 in every conceivable place where we thought it possible to arrest micro-organisms4 ,the result is known1 viz41 that fungoid bodies 7moulds and bacterial7 were taken in great numbers1 and varying with the seasons4 ,the air of the hospital and sick-room likewise engaged attention1 each of which proved especially rich in parasitic bodies4 ,during the cholera visitation of #aheh the air was rich in robic and anrobic bacteria1 while a blue mist which prevailed throughout the epidemic yielded a far greater number than at any former period 7represented in ,plate ,i41 ,no4 #ac74 ,this blue mist attracted the especial attention of meteorologists4 ,at a somewhat later period a more remarkable fungoid disease1 the fungus foot of ,india1 mycetoma1 came under my observation1 a detailed description of which ,i contributed to the medical journals1 and also1 with further details1 to the 8,monthly ,microscopical ,journal0 of #ahga4 ,interlacing mycelia1 ending in hyph1 in this destructive form of parasitic disease were seen to pervade the whole of the tissues of the foot1 the bony structures being involved1 and it was only possible to stay the action of the parasite by amputation4 ,so far1 then1 the study of parasitic organisms had at an early period shared largely in my microscopical work1 extending over several years1 and with the result that these micro-organisms were found to exhibit on occasions great diversity of character1 and that different members of the bacteria in particular flourish under great diversity of action1 and often under entirely opposite conditions2 that they feed upon wholly different materials1 and perform an immense variety of chemical work in the media in which they live4 ,the study of the chemistry 7chemotaxis7 of bacteria has1 however1 greatly enlarged our conception of the chemical value and power of the vegetable cell1 while it is obvious that no more appropriate or remunerative field of study could engage the attention of the microscopist1 as well as the chemist1 than that of bacterial life1 and which is so well calculated to enlarge our views of created organisms1 whether belonging to the vegetable or animal kingdom4 ,pathogenic ,fungi and ,moulds4 ,it is scarcely necessary to go back to the history of the parasitic fungi to which diseases of various kinds were early attributable4 ,the rude microscopes of two and a half centuries ago revealed the simple fact that all decomposable substances swarmed with countless multitudes of organisms1 invisible to ordinary vision4 ,leuwenhoek1 the father of microscopy1 and whose researches were generally known and accepted in #afge1 tells of his discovery of extremely minute organisms in rain-water1 in vegetable infusions1 in saliva1 and in scrapings from the teeth2 further1 he differentiated these living organisms by their size and form1 and illustrated them by means of woodcuts2 and there can be no doubt that his figures are intended to represent leptothrix filaments1 vibrios1 and spirilla4 ,in other of his writings attempts are made to give an idea of the size of these 8animalcules02 he described them as a thousand times smaller than a grain of sand4 ,from his investigations a belief sprung up that malaria was produced by 8animalcules10 and that the plague which visited ,toulon and ,marseilles in #agba arose from a similar cause4 ,somewhat later on the natural history of micro-organisms was more diligently studied1 and with increasing interest4 ,mller1 in #aghf1 pointed out that they had been too much given to occupy themselves in finding new organisms1 he therefore devoted himself to the study of their forms and biological characters1 and it was on such data he based a classification4 ,thus the scientific knowledge gained of these minute bodies was considerably advanced1 and the subject now entered upon a new phase3 the origin of micro-organisms4 ,it further resolved itself into two rival theories--spontaneous generation1 and development from pre-existing germs--the discussion over which lasted more than a century4 ,indeed1 it only ended in #ahga1 when the originator of the ,abiogenesis theory withdrew from the contest1 and the more scientific investigations of ,pasteur 7#ahfa7 found general acceptance4 ,this indefatigable worker had been investigating fermentation1 and studying the so-called diseases of wines and a contagious disease which was committing ravages among silkworms4 ,pasteur in time was able to confirm the belief that the 8muscadine disease0 of silkworms was due to the presence of micro-organisms1 discernible only by the microscope4 ,the oval1 shining bodies in the moth1 worm1 and eggs had been previously observed and described by ,ngeli and others1 but it was reserved for ,pasteur to show that when a silkworm whose body contained these organisms was pounded up in a mortar with water1 and painted over the leaves of the tree upon which healthy worms were fed1 all took the disease and died4 ,illustration3 ,,plate ,,ix4 ,,after ,d,r ,,crookshank ,j4 ,t4 ,balcomb4 del4 ,,typical ,,forms ,,of ,,bacteria1 ,,schizomycetes1 ,,or ,,fission-,,fungi4 ,as the contagious particles were transmitted to the eggs1 the method adopted for preventing the spread of the disease was as follows3--,each female moth was kept separate from the others1 and allowed to deposit her eggs1 and after death her body was crushed up in a mortar as before1 and a drop of the fluid examined under the microscope4 ,when any trace of muscadine was found present1 the whole of the eggs and body were burnt4 ,in this way the disease was combated1 and ultimately stamped out4 ,pasteur also pointed out that one form or cause of disease must not be confounded with another4 ,for example1 muscadine1 a true fungus 7,botrytis bassiana71 should not be confounded with another disease known to attack silkworms1 termed pebrin1 this being caused by a bacterium1 and1 according to the more recent researches of ,balbiani1 by a ,psorospermia4 ,botrytis is a true mould1 belonging to the ,oomycetes1 and allied to the potato fungus1 ,peronospora4 ,it is propagated by spores1 which1 falling on a silkworm1 germinate and penetrate its body4 ,a mycelium is then developed1 which spreads throughout the body4 ,hyph appear through the skin1 and bear white chalky-looking spores2 these become detached1 and float in the air as an impalpable dust-like smoke4 ,damp further develops the fungus4 ,insects suffer much from the ravages of fungi4 ,the house-fly sticking to the window-pane is seen to be surrounded by the mycelia of ,penicillium racemosum 7,sporendonema musc1 or ,saprolegnia fer74 ,in other cases ,cordiceps attacks certain caterpillars belonging to the genera ,cossus and ,hepialus when they are buried in the sand and before their metamorphosis into chrysalides2 they are killed by the rapid development of hyph and mycelium in their tissues4 ,sphria miletaris1 a parasite of ,bombyx pilyocarpa1 the caterpillar of which is found on pine-trees1 is one of the few fungi which may be regarded as beneficial to man1 since it aids in the destruction of multitudes of these caterpillars1 which otherwise would devour the young shoots and pine needles4 ,giard specialises other parasites of insects1 which he terms ,entomophore4 ,others1 ,e4 rimosa1 attack grasshoppers and the diptera1 enveloping them in a dense coating of mycelium and spores1 which speedily kills the victim4 ,the study1 then1 of the life-history of germs1 microbes1 micro-organisms1 or bacteria 7as they are indifferently termed71 opened up a new science1 that of ,bacteriology4 ,by the more recent advances in this science we are enabled to understand the very important part these minute organisms fill in the great scheme of ,nature1 for almost exclusively by their agency the soil is supplied with the requisite nutritive material for plant life4 ,and1 as already pointed out1 wherever organic matter is present--that is1 the dead and useless substances which are the refuse of life--such material is promptly seized upon by micro-organisms1 by means of which histolysis is rapidly accomplished4 ,bacteria require a power of from #fjj to #a1jjj diameters or more for the determination of the species to which they belong4 ,the number of species has been so much increased of late that a bulky volume is found to be insufficient for their enumeration4 ,i am1 however1 by the courtesy of ,professor ,crookshank1 enabled to present my readers with the typical forms of thirty-nine species of ,bacteria1 ,schizomycetes1 or fission-fungi1 a selection1 it will be seen1 chiefly taken from among pathogenic organisms--those believed to originate disease4 ,but many of the supposed ,saprophytic forms often described as originating disease are merely accidental associates1 that is1 living in companionship for a time4 ,size4--,in ordinary terms of measurement1 bacteria are on an average from #a_/bejjjth to about #a_/ejjjth of an inch long4 ,these measurements do not convey a definite impression to the mind4 ,it is calculated that a thousand million of them could be contained in a space of #a_/beth of an inch4 ,the best impression of the size of the bacteria is1 perhaps1 obtained when it is stated that a #a_/be-;inch immersion objective gives a magnification of nearly #b1bjj diameters1 and that under this power the bacteria appear to be about the size of very small print4 ,the standard of measurement accepted by bacteriologists is the micro-millimeter4 ,one millimeter is equal to about #a_/bejjjth an ,english inch4 ,the number of micrococci in a milligramme of a culture of ,staphylococcus pyogenes aurens has been estimated by ,bujwid by counting at eight thousand millions4 ,not only do various species differ in dimensions1 but considerable differences may be noted in a pure culture of the same species4 ,on the other hand1 there are numerous species which so closely resemble each other in size and shape that they cannot be differentiated by microscopic examination alone1 and we have to look to other characteristics1 as colour1 growth in various culture media1 pathogenic power1 chemical products1 c41 in order to decide the question of identity4 ,reproduction4--,the reproduction of bacteria takes place for the most part by fission and by spore formation4 ,fission is a process of splitting up or division1 whereby an organism divides into two or more parts1 each of which lives and divides in its turn4 ,if certain organisms are watched under the microscope1 a coccus or bacillus will be seen to elongate and at the same time become narrower1 until its two halves become free1 the two individual organisms again dividing and subdividing in their turn4 ,this kind of reproduction is more readily seen in a higher class of unicellular organisms1 the desmids4 ,if1 however1 the new organisms do not break away from each other1 but remain connected in groups or clusters1 they are termed ,staphylococci2 if they remain connected in the form of a chain1 or like a string of beads1 they are termed ,streptococci4 ,if the division takes place in one plane1 ,diplococci are formed2 if in two directions ,tetracocci1 or ,tablet-cocci1 are formed4 ,on account of this multiplication by fission1 the generic name of ,schizomycetes1 or fission-fungi1 has been given to bacteria4 ,spores4--,a second method by which bacteria propagate is by spores4 ,these bodies are distinguished by their remarkable power of resistance to the influence of temperature and the action of chemical reagents4 ,some of them will resist their immersion in strong acid solutions for many hours2 also freezing and very high temperatures4 ,spore formation may take place in two ways3 firstly1 by 8endogenous spores0 7internal spores72 secondly1 by 8arthrospores40 ,endogenous ,spores4--,when the formation of the spores takes place in the mother-cell1 the protoplasm is seen to contract1 giving rise to one or more highly refractive bodies1 which are the spores4 ,the enclosing membrane of the organism then breaks away1 leaving the spores free4 ,arthrospores4--,when the spore is not formed in the parent bacillus1 but when entire cells 7owing to lack of favourable conditions of growth7 become converted into spores1 the formation is known as 8arthrogenous10 the single individual being called an arthrospore4 ,when the conditions are again favourable1 spores germinate1 giving rise to new bacilli4 ,the germinating spore becomes elongated1 and loses its bright appearance1 the outer membrane becomes ruptured1 and the young bacillus is set free4 ,certain conditions1 such as the presence of oxygen in the case of the anthrax bacillus1 give rise to the formation of spores2 while various kinds of bacteria secure continuous existence by developing spores when there is lack of proper food material4 ,with reference to the incredible rapidity with which the bacteria multiply under conditions favourable to the growth and development1 ,cohn writes as follows3--8,let us assume that a microbe divides into two within an hour1 then again into eight in the third hour1 and so on4 ,the number of microbes thus produced in twenty-four hours would exceed sixteen and a half millions2 in two days they would increase to forty-seven trillions2 and in a week the number expressing them would be made up of fifty-one figures4 ,at the end of twenty-four hours the microbes descended from a single individual would occupy #a_/djth of a hollow cube1 with edges #a_/beth of an inch long1 but at the end of the following day would fill a space of twenty-seven cubic inches1 and in less than five days their volume would equal that of the entire ocean40 ,again1 ,cohn estimated that a single bacillus weighs about #jjjj1jjj1jjj1jbd1bdc1fgb of a grain2 forty thousand millions1 #a grain2 #bhi billions1 #a pound4 ,after twenty-four hours the descendants from a single bacillus would weigh #a_/bfffth of a grain2 after two days1 over a pound2 after three days1 sixteen and a half million pounds1 or #g1cff tons4 ,it is quite unneccessary to state that these figures are purely theoretical1 and could only be realised if there were no impediment to such rapid increase4 ,fortunately1 however1 various checks1 such as lack of food and unfavourable physical conditions1 intervene to prevent unmanageable multiplication of these bodies4 ,these figures show1 however1 what a tremendous vital activity micro-organisms do possess1 and it will be seen later at what great speed they increase in water1 milk1 broth1 and other suitable media4 ,the following bacilli1 among others1 have numerous flagella distributed over the whole of the organism3 the bacillus of blue milk 7,bacillus cyanogenus7#eb2 the bacillus of malignant dema2 the hay bacillus 7,bacillus subtilis72 ,proteus vulgaris1 c4 ,the following have only one or two flagella at the poles3 the ,bacillus pyocyaneus1 the ,spirillum finkleri1 the ,spirillum choler ,asiatic1 c4 ,the ,spirillum undala1 ,spirillum rubrum1 ,spirillum concentricum1 and ,sarcin1 pocket-cocci1 have several flagella4 ,micrococcus agilis have also several flagella2 these possibly arise from one point4 ,as ,i have already pointed out1 the classification of the bacteria is one of great difficulty1 since new kinds are being constantly discovered1 and at present any attempt made in this direction can only be considered as quite of a provisional nature4 ,the difficulties which stand in the way may be surmised from the fact that ,sarcin1 pocket-cocci1 were originally believed to be a single species1 described by me1 under the name of ,sarcina ventriculi1 in the fourth edition of my book1 8as remarkable bodies invading the human and animal stomach1 and seriously interfering with its functions40 ,illustration3 ,fig4 #bfh4--,sarcin4 ,the original woodcut of these curious parasites is reproduced in ,fig4 #bfh1 also in ,plate ,,ix41 ,no4 #g1 and which evidently belong to a different species1 numbering thirty-nine altogether4 ,quite recently ,mr4 ,g4 ,h4 ,broadbent1 ,m4,r4,c4,s41 ,manchester1 sent me a supply of these interesting bodies lately discovered by him in an infusion of cow manure4 ,on examining a drop with a power of #aejj diameters they were discovered moving over the field of the microscope with a gyrating motion by the aid of flagella projecting from each corner of the pocket4 ,after some days1 having attained their full growth of four1 eight or sixteen in a pocket1 they break up1 and recommence the formative process4 ,sarcin are certainly pathogenic in their nature4 ,cocci in groups1 or asso-cocci1 are similarly associated4 ,these several forms of spiro-bacteria are enclosed in a transparent cell-wall1 and are sometimes described as zoogla4 ,of bacteria the most characteristic groups are bacillus1 bacterium1 and a species of clostridium1 a bottle-shaped bacillus4 ,it is1 however1 difficult to draw a sharp line between so-called species4 ,spiro-bacteria1 or spirilla1 possess short or long filaments1 rigid or flexible1 and their movements are accordingly rotatory1 or in the long axis of the filaments4 ,these bodies are again divided into comma bacilli1 or vibrios--a name invented by the older microscopists who first described them--some species of which have a flagellate appendage1 to which their movements are due4 ,anthrax1 ,splenic ,fever1 has been long known to be prevalent among cattle at certain seasons of the year1 and is believed to originate from peculiar conditions of climate and soil4 ,this view of splenic fever on microscopical examination proved an entire fallacy4 ,bollinger in #ahgb discovered that the blood of the affected animal was still virulent after death1 owing to the presence of the spores of the bacillus1 and that the soil also became infected and impregnated by the disease germs wherever the fever first broke out4 ,in #ahgg ,dr4 ,koch made a more careful investigation into the source of the disease1 and was able to give a complete demonstration of the life-history of the splenic fever bacillus1 and to offer definite proofs of its pathogenic properties4 ,he pointed out that the rods grew in the blood and tissues by lengthening and by cross division4 ,further1 that they not only grew into long leptothrix filaments but they produced enormous numbers of seeds or spores4 ,he watched the fusion of the rods to the formation of spores and the sprouting of fresh rods4 ,he furthermore inoculated a mouse1 watched the effect through several generations1 and fully demonstrated that in the blood and swollen spleen of the animal the same rods were always present4 ,pasteur and ,paul ,bret pursued the same course of investigations1 which were always followed with precisely similar results4 ,it was1 however1 principally due to the researches of ,koch that the doctrine of contagium vivum was placed on a scientific basis4 ,subsequently ,koch formulated methods of cultivation1 and dictated the microscopical apparatus needful4 ,furthermore1 he furnished postulates for proving beyond doubt the existence of specific pathogenic micro-organisms4 8,the chain of evidence regarded by ,dr4 ,koch as essential for proving the existence of a pathogenic organism is as follows3--#a4 ,the micro-organism must be found in the blood1 lymph1 or diseased tissue of man or animal suffering from1 or dead of the disease4 #b4 ,the micro-organism must be isolated from the blood or tissue1 and cultivated in suitable media--i4e41 outside the animal body4 ,these pure cultivations must be carried on through successive generations of the organism4 #c4 ,pure cultivation thus obtained must1 when introduced into the body of a healthy animal1 produce the disease in question4 #d4 ,in the inoculated animal the same micro-organism must again be found4 ,the chain of evidence will be still more complete if1 from artificial culture1 a chemical substance is obtained capable of producing the disease quite independently of the living organism4 ,it is not enough to merely detect1 or even artificially cultivate1 a bacterium associated with disease4 ,an endeavour must be made to establish the exact relationship of the bacteria to disease processes4 ,in many instances disease bacteria regarded as the actual contagia have been found1 on a further searching inquiry1 to be entirely misleading4 ,it is almost needless to remind the enthusiast that the actual contagion of the disease must be fully demonstrated40 ,illustration3 ,fig4 #bfi4--,micro-,photograph of ,typhoid ,fever ,bacteria4 ,magnified #ajjj 4 ,taken by ,leitz's oil immersion #a_/ab-;inch ocular ,no4 #d1 and sunlight exposure of one minute4 ,typhoid ,bacillus 7,fig4 #bfi74--,rods #a to #c in length1 and #e to #h in breadth1 and threads4 ,spore-formation has not been observed1 but the protoplasm may be broken up1 producing appearances which may be mistaken for spores4 ,actively motile1 provided1 some with a single and others with very numerous flagella1 which are from three to five times as long as the bacillus itself4 ,they stain readily in aqueous solutions of aniline dyes2 and grow rapidly at a temperature of about #fj ,fahr4 ,in plate cultivations minute colonies are visible in thirty-six to forty-eight hours2 they are circular or oval1 with an irregular margin4 ,on agar they form a whitish transparent layer1 and they flourish in milk4 ,illustration3 ,fig4 #bgj4--,plague ,bacillus1 ,bombay1 #ahig4 ,magnified #abjj 4 ,the ,plague 7,pestis ,bacillus74--,the ,bombay plague of #ahig-ih will ever be remembered as one of the most appalling visitations ever known4 ,the number of deaths will never be accurately determined1 as the native population1 among whom the disease chiefly prevailed and became so fatal1 concealed their dead or carried them away by night4 ,the outbreak from the first proved to be most infectious1 its incubation lasting from a few hours to a week only4 ,it prevailed in all the over-crowded native quarters of the city4 ,the rats and mice that infested the dwellings of the poor were found to be equally susceptible with human beings1 and these vermin also died by hundreds4 ,those that survived left their holes and made off1 in this way helping to spread the infective virus4 ,on examining the bodies of dead rats1 they were found to have swollen legs1 the blood being filled by bacilli and curious monads1 with whip-like appendages4 ,the bacillus of plague was discovered by ,kitasato in #ahid2 it is characterised by short rods with rounded ends1 and a clear space in the middle4 ,the bacilli stain readily with aniline dyes1 and when cultivated on agar1 white transparent colonies are formed which present an iridescent appearance when examined by reflected light4 ,in addition to the bubonic swellings1 the neighbouring lymphatic glands were also swollen and blocked by bacilli4 ,illustration3 ,fig4 #bga4--,monads in ,rat's ,blood1 #a1bjj 4 7,crookshank47 a4 ,monad threading its way among the blood-corpuscles2 b4 ,another with pendulum movement attached to a corpuscle2 c4 ,angular forms2 d4 ,encysted forms2 e and f4 ,the same seen edgeways4 ,my illustration 7,fig4 #bgj7 is from a micro-photograph taken in #ahig1 when the death rate stood very high4 ,the general distribution of the bacilli1 together with phagocytes and the contents of swollen lymphatic glands1 magnified #a1bjj 1 is from a preparation made in hospital4 ,the monads from the rat's blood1 #abjj 1 seen threading their way among the blood corpuscles of a rat1 and represented in ,fig4 #bga1 are somewhat larger than those found in the ,bombay rats1 but the flagella in the latter were quite as marked1 while the encysted forms were wholly absent and the blood corpuscles less crenated4 ,the white bodies 7,fig4 #bgj7 were in some preparations1 together with the lymphatic bodies1 more numerous and more swollen4 ,with regard to the conditions of life of the bacteria1 they may be divided broadly into two classes4 ,when the organisms draw their nourishment from some living body or 8host10 they are known as 8parasites40 ,these are further termed 8obligate0 parasites if they exclusively live on their 8host40 ,if the bacteria draw their nourishment from dead organic matter1 they are called 8saprophytes40 ,these are also divided into 8obligate0 and 8facultative0 saprophytes4 ,thus it will be apparent that a parasite under certain circumstances may readily become a saprophyte4 ,some of the more important saprophytes are those organisms which play an important and useful part in our every-day life1 such as1 for instance1 in the phenomena associated with fermentation1 and putrefaction agents which transform dead and decomposing organic matter into their simpler elements1 thus completing the great life cycle1 and rendering the dead and effete matter again ready for the vital processes4 ,among other life manifestations of certain bacteria may be mentioned those which have the property of generating colouring matter1 though not chlorophyll4 ,the bacteria themselves are colourless and transparent1 and the pigment is merely formed as a product of their metabolism1 especially under the influence of light4 ,many of the bacteria give rise to various gases and odours1 particularly the anrobic organisms1 which originate those foul putrefactive gases 7ammonia1 sulphuretted hydrogen1 c474 ,the blood-rain1 ,micrococcus prodigiosus1 gives off an odour resembling trimethylamin4 ,micro-organisms have the property of producing various changes in the medium on which they are grown4 ,in many cases albuminous bodies are peptonized and gelatine is liquefied4 ,many bacteria have the faculty of resolving organic bodies into their simplest elements2 others1 again1 have the property of converting ammonia into nitric and nitrous acid4 ,certain microbes have the property of becoming phosphorescent in the dark4 ,these phosphorescent bacteria are often seen on decaying plants and wood2 sometimes in tropical climates the sea becomes luminous owing to the presence of countless numbers of these organisms4 ,again1 they are frequently seen on the surface of dead fish1 particularly mackerel1 which often become so bright as to strongly illuminate the cupboard in which they lie4 ,the particular class of fungi that produce disease in man and the higher animals are generally known as 8pathogenic40 ,these pathogenic organisms may exert their pernicious power in several ways4 ,they may be injurious on account of their abstracting nourishment from the blood or tissues1 or for the purely mechanical reason of their stopping up the minute capillaries and blood-vessels by their excessive multiplication4 ,but the poisonous action of most of the pathogenic bacteria is due to the chemical products secreted by the organisms1 and it is to the circulation and absorption within the body of these poisons that the disturbances of the animal system1 which characterise disease1 decay1 and dissolution of every organism1 must be traced4 ,parasitic ,diseases of ,plants4 ,the subject of fungoid diseases and fungus epidemics are of worldwide interest1 if only because of the annual losses to agriculturists from parasitic diseases of plants1 amounting to millions of pounds sterling4 ,the history of wheat-rust1 and that of oats and rye1 each equally susceptible to the ravages of the same ,rufus1 can be traced back to ,genesis4 ,a description of it was given in #ahje by ,sir ,joseph ,banks4 ,he suggested that the germs entered the stomata1 and he warned farmers against the use of rusted litter1 and made important experiments on the sowing of rusted wheat-grains4 ,a great discussion on the barberry question followed1 ,fries particularly insisting on the difference between cidium berberidis and ,puccinia graminis4 ,tulasne confirmed the statement made by ,henslow that the uredo and puccinia stages belong to the same fungus1 and are not mixed species4 ,de ,bary's investigations in #ahfj-fd proved that the sporidia of some ,uredinie 7e4g41 ,coleosporium7 will not infect the plant which bears the spores1 and that the cidia of certain other forms are stages in the life-history of species of ,uromyces and ,puccinia4 ,furthermore1 ,de ,bary in #ahfd attacked the question of wheat rust1 and by means of numerous sowings of the telentospores on barberry proved that they bring about the infection4 ,this led to the discovery of the phenomenon of ,hetercism 7colonisation71 introducing a new idea1 and clearing up many difficulties4 ,in #ahij the rust question entered on a new phase3 it was taken up by men of science all over the world1 and active inquiries were set on foot4 ,the result has been the confirmation of ,de ,bary's results1 but with the further discovery that our four common cereals are attacked by no less than ten different forms of rust belonging to five separate species or 8form species10 and with several physiological varieties1 capable of turning the table upon the barberry by infecting it4 ,some of these are found to be strictly confined to one or other of the four common cereals1 infecting two or more of them1 while others can infect various kinds of our common wild grasses4 ,illustration3 ,fig4 #bgb4--,puccinia1 displaying uredospores and telentospores4 a4 ,aregma speciosum2 b4 ,xenodochus paradoxus2 c4 ,p4 ,amorph2 d4 ,triphmium dubens2 e4 ,younger spores2 f4 ,p4 lateripes2 magnified #dej diameters4 ,the fact is1 that what has usually gone by the name of ,puccinia graminis is an aggregate of several species1 and that varietal forms of this exist so especially adapted to the host1 that1 although no morphical differences can be detected between them1 they cannot be transferred from one cereal to another1 pointing to physiological variations of a kind met with among bacteria and yeasts1 but hitherto unsuspected in these higher parasitic fungi4 ,it now appears we must be prepared for similar specialisation of varietal forms among ,ustilagine as well as among ,uredine4 ,moreover1 it has been found that different sorts of wheat1 oats1 barley1 and rye are susceptible to their particular rusts in different degrees1 at the bottom of which1 it is suggested1 there must be some complex physiological causes4 ,de ,bary gave proof1 in #ahhf1 that ,peziza 7,plate ,i41 ,nos4 #a1 #d1 #e1 #f7 succeeds in becoming parasitic only after saprophytic culture to a strong mycelium1 and that its form is altered thereby--probably by the excretion of a poison4 ,professor ,marshall ,ward showed that similar results took place in the case of the lily disease4 ,reinhardt1 in #ahib1 showed that the apical growth of a peziza is disturbed and interrupted if the culture solution is employed concentrated2 and ,bsgen1 in #ahic1 showed that ,botrytis cinerea excretes poison at the tips of the hyph1 thus confirming ,professor ,ward's results with the lily disease in #ahhh1 and of later years1 that a similar excretion occurs in rust-fungus4 ,he further found that the water contents of the infected plant exercises an influence1 as in the case of ,botrytis attacking chrysanthemums and other plants in the autumn1 and that cold increases the germinating capacity of the spores4 ,pfeiffer1 in his work on 8,chemotaxis10 shows that bacteria will congregate in the neighbourhood of an algal cell evolving oxygen4 ,he also found that many motile antherozoids1 zoospores1 bacteria1 c41 when free to move in a liquid1 are attracted towards a point whence a given chemical substance is diffusing4 ,he was concerning himself less with the evolution of oxygen or movements of bacteria than with a fundamental question of stimulation to movement in general4 ,he found the attractive power of different chemical substances vary with the organism1 and that various other bodies beside oxygen attract bacteria--peptone1 dextrose1 potassium salts1 c42 that swarm spores of the fungus ,saprolegnia are powerfully attracted towards the muscles of a fly's leg placed in the water in which they are swimming about2 also1 that in many cases where the hyph of fungi suddenly and sharply bend out of their original course to enter the body of a plant or animal1 the cause of the bending lies in a powerful chemotropic action1 due to the attraction of some substance escaping from the body4 ,professor ,ward has seen zoospores of a ,pythium suddenly dart out on to the cut surface of a bean-stem1 and there fix themselves4 ,this will be better understood by referring to the course pursued by these bodies generally4 ,when the spore of a parasitic fungus settles on a plant1 it frequently behaves as follows3--,the spore germinates and forms a slender tube of delicate consistency1 blunt at the end1 and containing colourless protoplasm1 as shown1 highly magnified in ,fig4 #bgb1 and in ,figs4 #bgc and #bgd much less magnified4 ,de ,bary long ago showed that such a tube--the germinal-hypha--only grows for a short time along the surface of the organ1 and its tip soon bends down and enters the plant1 either through one of the stomata or by boring its way directly through the cell-walls4 ,professor ,ward says these phenomena suggested to himself that the end of the tube is attracted in some way1 and by some force which brings its tip out of the previous direction1 and ,de ,bary has suggested that this attraction is due to some chemical substance excreted by the host plant4 ,it is remarkable with what ease the tube penetrates the cell-walls1 and which ,ward believes to be due to the solvent action of an enzyme1 capable of dissolving cellulose4 8,miyoshi carried these observations a step further when1 in #ahid1 he showed that if a leaf is injected with a substance such as ammonium-chloride1 dextrine1 or cane-sugar 7all substances capable of exerting chemotropic attraction on fungus-hyph71 and spores of a fungus which is not parasitic are then sown on it1 the hyph of the fungus penetrate the stomata and behave exactly as if the fungus were a true parasite4 8,so surprising a result lets in a flood of light on many known cases of fungi1 which are1 as a rule1 non-parasitic1 becoming so1 in fact1 only when the host plant is in an abnormal condition1 e4g41 the entry of species of ,botrytis into living tissues when the weather is cold and damp and the light dull2 the entry of ,mucor into various fruits1 tomatoes1 apples1 pears1 c41 when the hyph meet with a slight crack or wound1 through which the juices are exposed4 ,it is exceedingly probable that the rapid infection of potato leaves in damp weather in ,july is traceable not merely to the favouring effect of the moisture on the fungus1 but that the state of super-saturation of the cell-walls of the potato leaf--the tissues of which are now unduly filled with water and dissolved sugars1 c41 owing to the dull light and diminished transpiration--is the primary factor which determines the easy victory of the parasite1 and1 as ,professor ,ward suggested some time ago1 that the suppressed life of ,ustilagine in the stems of grasses is due to the want of particular carbo-hydrates in the vegetative tissues1 but which are present in the grain4 ,a year later ,miyoshi carried proof to demonstration1 and showed that a fungus-hypha is actually so attracted by substances on the other side of a membrane1 and that its tip pierces the latter2 for the hyph were made to grow through films of artificial cellulose1 of collodion1 of cellulose impregnated with paraffin1 of parchment paper1 and even the chitinous coat of an insect1 simply by placing the intact films on gelatine impregnated with the attracting substance1 and laying the spores on the opposite side of the membrane4 8,now this is obviously a point of the highest importance in the theory of parasitism and parasitic diseases1 because it suggests at once that in the varying conditions of the cells1 the contents of which are separated only by membranous walls from the fungus-hyph1 whose entrance means ruin and destruction1 there may be found circumstances which sometimes favour and sometimes disfavour the entrance of the hyph2 and it is1 at least1 a remarkable fact that some of the substances which experiments prove to be highly attractive to such hyph--e4g41 sugars1 the sap of plums1 phosphates1 nitrates1 c4--are just the substances found in plants2 and the discovery that the action depends upon the nature of the substance as well as on the kind of fungus1 and is affected by its concentration1 the temperature1 and other circumstances1 only confirms us in this idea40 ,moreover1 there is one other fact which it is important to notice1 viz41 that there are substances which repel instead of attract the hyph4 ,is it not1 then1 asks ,professor ,ward1 natural to conclude that the differences in behaviour of different parasites towards different host-plants1 and towards the same host-plant under different conditions1 probably depend on the chemotropic irritability of the hyph towards the substance formed in the cells on the other side of the membranous cell-walls8 ,and when1 as often happens1 the effusion of substances1 such as the cells contain1 to the exterior is facilitated by over-distension and super-saturation1 or by actual wounds1 we cannot be surprised at the consequences when a fungus1 hitherto unable to enter the plant1 suddenly does so4 ,to this proposition my answer is emphatically in the affirmative1 since in my investigations into the 8fungus-foot disease0 78,mycetoma071 #ahga1 of ,india1 the entry of the fungus was in almost every case shown to be through an abrasion of the skin or a direct open wound2 the majority of the cases reported were among the agricultural classes4 ,when1 then1 as often happens1 the effusion of substances1 such as the cells contain1 to the exterior is facilitated by over-distension and super-saturation1 or by actual wounds1 we cannot be surprised at the consequences when a fungus1 hitherto unable to enter the plant1 suddenly does so4 ,nevertheless1 it must be admitted that the knowledge gained of parasites does not satisfactorily account for epidemic visitations over large areas4 ,habitat of ,fungi and ,moulds4 ,illustration3 ,fig4 #bgc4--;,fungi and ,moulds4 ,description of ,figures4--a4 ,fungi ,spores1 taken in a sick chamber2 b4 ,aspergillus glaucus2 c4 ,yeast1 recent state2 d4 ,exhausted yeast1 budding2 e4 ,penicillium spores more highly magnified2 g4 ,aerobic spores and mould mycelium2 h4 ,aspergillus spore1 grown on melon4 ,habitat1 ,specialised ,forms of ,parasites4 ,habitat4--,the habitat of vegetable parasitic fungi is extremely variable4 ,fungi are found everywhere1 living and flourishing on all the families of the vegetable and animal kingdoms4 ,they attack our houses1 foods1 clothes1 utensils of every kind1 wall papers and books1 the paste of which1 to my astonishment1 affords a sufficient supply of nourishment4 ,members of the parasitic tribe of bacteria1 by a combined effort of countless myriads1 have given rise to a sense of supernatural agency4 ,bacillus prodigiosus1 described also as ,palmella mirifica and ,zoogalactina imetropia1 from its attacking milk and other alimentary substances1 the spores of which are often of a deep red colour1 have been found to cover whole tracts of country in a single night with what is called a 8gory dew10 changing in daylight to a deep green colour4 ,this was at one time regarded with superstitious awe as a miracle1 as it has been known to attack bread and even the sacred wafer1 and which in medival ages was described as the 8bleeding-host40 ,this parasitic plant belongs to anrobic bacteria1 and is only developed in the dark4 ,the nitrogen required for nutrition must be derived from the air4 ,an algal form gives rise to the red scum seen in ponds and reservoirs in the autumn4 ,the discharge from wounds is coloured blue by ,bacterium pyocyanine4 ,there are many other forms1 some of which have an orange colour1 and the genus is recognised as 8chromogenic microbes40 ,illustration3 ,fig4 #bgd4--;,fungi and ,moulds4 ,description of ,figures4--d4 ,puccinia graminis on wheat2 c4 ,polycystis spore of rye-smut2 f4 ,alder fungus spores1 ,microspheria penicellula2 g4 ,dactylium roseum1 rose-coloured mould2 h4 ,verticillium distans1 whorled mould found on herbaceous plants2 i4 ,botrytis1 vine and lily fungus2 j1 j4 ,peronospora infestans1 potato fungus2 k4 ,p4 gangliformis1 mould of herbaceous plants2 l4 ,various ,penicillium and other spores taken in a bean-field4 ,a cryptogam belonging to anrobic bacteria1 described as ,protococcus invalis1 on being set aside in a bottle1 and a little rain water added1 was seen to set up spontaneous fermentation1 and in a very short time exhibited remarkable activity4 ,the colour of the infusion changed1 it assumed a delicate pink hue in direct light1 which deepened to a red in reflected light4 ,the fluid contents were now observed to be dichoric1 and the spectroscopic appearance subsequently presented was one of much interest4 ,the spectrum was a well-marked one1 and might be taken to determine the presence of a nitrogenous element or of glucose4 ,among all the various plants known to suffer from the attacks of parasites1 the vine has been the greatest sufferer4 ,the odium1 or ,erysiphe ,tuckeri1 so called from the name of the discoverer by whom it was first described1 has been longest known to the vine grower4 ,this really belongs to the group ,ascomycetes1 and appears to have been brought from ,america in #ahde1 whence it was passed on to ,france1 where it soon threatened to entirely destroy the vineyards4 ,this was followed by another parasite1 belonging in this instance to the animal kingdom1 ,phylloxera vastatrix4 ,this odium appears on the grape in the form of greyish filaments1 terminating in an enlarged head1 which contains an agglomeration of spores1 not free or in a chaplet1 as in ,aspergillus 7,fig4 #bgc74 ,these spores when ripe burst from the capsule as fine dust1 and are diffused by the air in all directions1 thus spreading the disease far and away4 ,another of the parasitic moulds1 ,peronospora viticola1 is a kind of mildew1 differing from odium4 ,the hyph penetrate more deeply than that of odium4 ,on the upper surface of the leaf brown patches appear2 these branch out and ramify as seen in the potato-fungus1 ,p4 infestans 7,fig4 #bgd74 ,the parasite destroys the tissue of the leaf1 and it withers and dies4 ,there are other well-known parasites1 the black-rot1 ,phomauvicola1 belonging to the ,ascomycetes4 ,this appears in early shoots in the form of round black spots1 and gradually spreads over leaves and young fruit4 ,this same rot1 one year1 devastated the ,american vineyards4 ,illustration3 ,fig4 #bge4--;,fungi1 ,moulds4 a4 ,clustered ,spores1 ,gonatobotrys simplex2 b4 ,spore of ,puccinia coronata1 the mildew of grapes2 c4 ,barley smut2 d4 ,puccinia altha2 e4 ,penicillium glaucum2 m4 ,ixodes farin1 found in damaged flour together with smut4 ,cereals1 wheats and grasses1 suffer from other well-known forms of microscopic fungi termed rusts and smuts1 which cover the blades or infect the full ear of the fruit4 ,the name given indicates their colour1 and these belong1 for the most part1 to the genus ,uredo and the family of the ,basidiomycetes4 ,they have no endogenous spores but as many as four forms of exogenous4 ,this is also the case with wheat and barley1 whereby they are distinguished as ,uredo or ,puccinia graminis 7see ,figs4 #bgc and #bgd1 and ,plate ,i41 ,nos4 #ai and #bb1 cidium berberidis74 ,for a long time it was believed that ,uredo linearis and ,puccinia graminis were so many distinct species1 but it is now known that there are only three successive phases of the developmental stages of a single species--that1 as a matter of fact1 puccinia presents the phenomenon of alternation of generations1 that is1 that the complete development of the fungus is only effected by its transference from one plant to another4 ,other uredines1 ,ustilago and ,tilletia smuts1 are more apt to affect the ears of wheat1 rye1 and other grasses than puccinia4 ,bread made from wheat affected by smut has an acrid and bitter taste1 while that made from rye flour often produces a serious form of disease4 ,the propagation of either1 then1 should be stopped as quickly as possible by destroying all barberry bushes growing near or within the vicinity of corn fields1 and by other means4 ,the ergot of rye is due to distinct species of fungi having endogenous spores enclosed in a sac or ascus1 hence the name of the family1 ,ascomycetes or ,tuberace1 which are reproduced by the spores contained in these asci4 ,truffles belong to this family4 ,but other members of the same family have several forms of spores1 and these again present us with the phenomenon of alternation of generations4 ,illustration3 ,fig4 #bgf4--;,fungi1 ,moulds4 p4 ,spores of ,tilletia caries2 q4 ,spores of ,tilletia caries1 when germinating1 produce a ftid olive-coloured spore in cereal grains2 r4 ,telentospores of ,puccinia graminis2 s4 ,crystopus candidus1 spores growing in chains2 t4 ,petronospora infestans1 mildew of turnips1 c42 u4 ,a transverse section of ergot of rye1 showing spores in masses2 v4 ,claviceps purpur1 associated with ergoted rye4 ,ergot of rye is used in medicine1 but if not used with care it will produce a dangerous disease4 ,this parasitic fungi consists of minute microscopic masses of spores1 which cover the young flower of the rye with a white flocculent mass1 formerly termed sphacelium4 ,the mycelium formed spreads over the ear of corn in thick felt-like masses1 termed sclerotis4 ,the sphacelium changes its form in the following spring4 ,other changes are brought about1 and it seems to pass through a cycle of alternations of generations4 ,bread made from rye so infested is known to produce grave consequences1 soon to become fatal if not detected in time4 ,the disease is termed ergotism1 and gangrene of the extremities takes place among people of the north of ,france and ,russia1 who consume bread made from rye flour4 ,ergot of maize will also cause similar diseases4 ,fowls and other animals fed upon this cereal become in a short time poisoned1 and the cause of death is not rightly suspected4 ,there is another fungus belonging to the same group of ,ascomycetes1 known as ,eurotium repens1 which appears upon leather when left in a damp place1 and also upon vegetable or animal substances if badly preserved1 and gradually destroys it4 ,this mould is of a darkish green colour4 ,the minute spores display themselves as rows of beads when fully ripe on the erect mycelium4 ,aspergillus glaucus represents the white exogenous spores of the sphacelium of the ergot of rye2 and those subsequently produced in the yellow balls correspond with the asci developed in sclerotis1 the endogenous species4 ,many of the parasitic species belonging to the genera ,erysiphe1 ,sphria1 ,sordaria1 ,penicillium1 c41 have a similar mode of propagation1 and affect a large number of plants4 ,parasitic ,fungi of ,men and ,animals4 ,in the microscopical examinations especially given to the elucidation of parasitic diseases of the skin1 previously referred to1 ,i discovered more varieties of spores and filaments of certain cryptogamic plants associated with a larger number of specific forms of fungi than any previous observer4 ,i did not1 however1 feel justified in concluding1 with ,kchenmeister1 ,schnlein1 and ,robin1 that these fungoid growths were the primary cause of the diseases referred to4 ,indeed1 the foremost dermatologists of the period utterly refused to entertain the specific germ theory of the ,german investigators4 ,nevertheless1 ,i contended1 8the universality of their distribution is in itself a fact of very considerable importance1 and one pointing to the belief that they are scavengers ever ready to fasten on decaying matter1 and1 on finding a suitable soil1 spread out their invisible filaments in every direction in so persistent a manner as to arrest growth and overwhelm the plant in destruction40#ec ,special forms of fungi are given in ,plate ,i41 ,nos4 #aj-ad1 and those of the ascomycetes in ,nos4 #ag-ba4 ,illustration3 ,fig4 #bgg4--;,healthy fresh ,yeast1 from a large ,brewery1 in an active stage of formation1 #djj4 ,odium albicans affects both animals and plants4 ,it often attacks the mucous membrane of the mouths of young children4 ,the spores become elongated and converted into hyph1 and ramify about in all directions1 producing a troublesome form of disease4 ,this parasitic fungus is better known under another name1 ,saccharomyces mycoderma4 ,odium resemble alg in their mode of life1 as they are mostly found in a liquid media4 ,the structure of all ferments is very simple3 each plant is composed of a single cell1 either of a spherical1 elliptical1 or cylindrical form1 varying in size1 and filled with protoplasmic and nucleated matter4 ,this grows1 and is seen to bud out and divide into two or more parts1 all resembling the mother cell4 ,fig4 #bgg represents the healthy cells of yeast1 ,saccharomyces cerevisi1 freshly taken from a brewer's vat1 and in an active stage of growth4 ,the mode of multiplication continues as long as the plant remains in a liquid favourable to its nutrition4 ,the changes from one stage to another are rapid1 as will be noticed on reference to the consecutive formative processes the cells are known to pass through1 ,fig4 #bgh 7#ahei74 ,if the development of the plant is arrested by want of a saccharine or nitrogenous substance1 and the liquid dries up1 the protoplasm contained in the cell contracts1 and the spores1 or endogenous reproductive organs1 of the plant will remain in a state of rest1 become perfectly dry1 and yet retain life4 ,they are not easily killed1 even when subjected to a very high or low temperature1 they do not lose the power of germination when favourable conditions present themselves1 and at once take on a new birth4 ,there are1 however1 many other ferments besides that of beer-yeasts1 such as alcoholic and wine ferments1 the commonest of which1 according to ,pasteur1 is ,saccharomyces ellipsoideus4 ,illustration3 ,fig4 #bgh4--;,development of ,yeast ,cells4 #a4 ,when first taken2 #b4 ,one hour after introducing a few cells into sweet-wort2 #c4 ,three hours after2 #d4 ,eight hours2 #e4 ,forty-eight hours1 when the cells become elongated4 ,but yeast-fungi and mould-fungi1 like bacteria or fission-fungi1 are micro-organisms1 belonging to two specific orders1 the ,saccharomycetes and the ,hyphomycetes1 which are intimately related to each other1 but quite distinct from bacteria4 ,their germs occur widely distributed in air1 soil1 and water4 ,many species are of hygienic1 while others are of pathological interest and importance in being either accidentally associated with1 or the cause of1 disease processes1 while others are fermentations of very essential service in various industrial processes4 ,the making of beers1 wines1 and spirits1 as we understand them1 constitutes but a small part of the province of fermentation4 ,the life activities of ferments open out a study of vast importance to mankind1 and while they have only been regarded in their worst aspect--that of a bane--they are1 nevertheless1 a boon to mankind4 ,the first clear view we obtained of this was that of ,reess1 who in #ahgj showed there were several species or forms of the yeast-fungus4 ,hansen followed up this discovery in #ahhc1 and1 taking advantage of the strict methods of culture introduced by bacteriologists1 found that by cultivating yeast on a solid media from a single spore it was quite possible to obtain constant types of pure yeasts1 each possessing its own peculiar properties4 ,one consequence of ,hansen's labours was that it now became possible for every brewer to work with a yeast of uniform type instead of with haphazard mixtures1 in which serious disease forms might predominate and injure the beer4 ,among other things made clear was that a true yeast may have a mycelial stage of development4 ,furthermore1 there is the influence exercised by the nucleus of the yeast cell4 ,many other points of interest arose out of these investigations2 one was1 that many higher fungi can assume a yeast-like stage of development if submerged in fluids1 as1 for instance1 various species of ,mucor1 ,ustilago1 ,exoascus1 and numerous others4 ,ascomycetes1 and ,basidiomycetes as well1 are known to form budding cells1 and it was thought that the yeasts of alcoholic fermentation are merely reduced forms of these higher fungi1 which have become habituated to the budding condition--a conclusion supported by ,hansen's discovery that a true ,saccharomyces can develop a feeble1 but a true1 mycelium4 ,illustration3 ,fig4 #bgi4--,saccharomyces and ,moulds4 #a4 ,section from a tomato1 showing spores growing from cuticle2 #b4 ,portion detached to show budding-out process2 #c4 ,lateral view of spore sac with oospores issuing forth2 #d4 ,apiculated ferment spores2 #f and #g4 ,mycoderma cerivisi in different stages of growth1 as seen on wine bottles2 #h and #i4 ,torul diabetic1 torul and fission spores4 8,this view has been entirely confirmed by an inquiry into the mode of brewing sak by the ,japanese1 by the aid of the ,aspergillus fungus4 ,further researches established the fact that other forms of fungi1 e4g41 those on the surface of fruits1 developed endogenous spores1 which cause alcoholic fermentation4 ,more recently1 and by further experimental inquiry1 partly by pure cultures of separate forms1 and partly by well-devised cultures on ripening fruits still attached to the plant but imprisoned in sterilised glass vessels1 it has been found that yeast and moulds are separate forms1 not genetically connected1 but merely associated in nature1 as are so many other forms of yeasts1 bacteria1 and moulds4 ,further1 ,hansen has discovered that several yeasts furnish quite distinct races or varieties in different breweries in various parts of the world1 so that we cannot avoid the conclusion that their race characteristics have been impressed on the cells by the continued action of the conditions of culture to which they have so long been exposed--they are1 in fact1 domesticated races40 ,the environments of yeasts are peculiar4 ,sauer found that a given variety of yeast1 whose activity is normally inhibited when the alcohol attains a certain degree of concentration in the liquid1 can be induced to go on fermenting until a higher degree is attained by the addition of a certain lactic acid bacterium4 ,the latter1 indeed1 appears to prepare the way for the yeast4 ,it has been shown1 also1 that damage may be done to beers and wines by allowing plant germs to gain access with the yeast2 there are1 too1 several forms of yeast that are inimical to the action of the required fermentation4 ,other researches show that associated yeasts may ferment better than any single yeast1 and such symbiotic action of two yeasts of high fermenting power has given better results than either alone4 ,english ginger-beer furnishes a curious symbiotic association of two organisms--a true yeast and a true bacterium--so closely united that the yeast cells become imprisoned in the gelatinous meshes of the bacterium2 and it is a curious fact that this symbiotic union of yeast and bacterium ferments is far more energetic than either when used alone1 and the product is different1 large quantities of lactic and carbonic acids being formed1 and little or no alcohol4 ,many years ago ,i gave an account of similar curious symbiotic results obtained by introducing into a wort-infusion a small proportion of ,german yeast1 an artificial product composed of honey1 malt1 and a certain proportion of spontaneously-fermented wheat flour4 ,this1 to my astonishment1 produced ten per cent4 more alcohol than any of its congeners1 and did not so soon exhaust itself as brewer's yeast4#ed ,in the hephir used in ,europe for fermenting milk1 another symbiotic association of yeast and a bacterium1 it is seen that in this process no less than four distinct organisms are concerned4 ,i have already instanced the fermentation of rice to produce sak1 which is first acted upon by an ,aspergillus that converts the starch into sugar and an associated yeast1 and this is also shown to be a distinct fungus1 symbiotically associated in the conversion4 8,starting1 then1 from the fact that the constitution of the medium profoundly affects the physiological action of the fungus1 there can be nothing surprising in the discovery that the fungus is more active in a medium which has been favourably altered by an associated organism1 whether the latter aids the fungus by directly altering the medium1 or by ridding it of products of excretion1 or by adding gaseous or other body4 ,it is not difficult to see1 then1 that natural selection will aid in the perpetuation of the symbiosis1 and in cases like that of the ginger-beer plant it is extremely difficult to get the two organisms apart1 a difficulty similar to that in the case of the soredia of lichens40 ,buchner discovered that by means of extreme pressure a something can be extracted from yeast which at once decomposes sugar into alcohol and carbon-dioxide4 ,this something is regarded as a kind of incomplete protoplasm--a body1 as we have already seen1 composed of proteid--and in a structural condition somewhere between that of true soluble enzymes like invertin and a complete living protoplasm4 ,this reminds me of an older experiment of mine1 the immediate conversion of cane-sugar into grape-sugar4 ,if we take two parts of white sugar and rub it up in a mortar with one part of a perfectly dry solid1 the ,german yeast before spoken of1 it is immediately transformed as if by magic into a flowing liquid mass--a syrup4 ,this process of forming 8invert sugar0 can be watched under the microscope2 the liberation of carbonic acid gas in large bubbles is seen to go on simultaneously with the assimilation of the dextrose1 and the breaking up of the crystals of sugar2 the cell at the same time increasing in size as well as in refractive power2 a curious state of activity appears to be going on in the small mass1 which is very interesting to watch throughout4 ,however1 the enzymes of ,buchner are probably bits off the protoplasm1 as it were1 and so the essentials of the theory of fermentation remain1 the immediate agent being not that of protoplasm itself1 but of something made by or broken off from it4 ,enzymes1 or similar bodies1 are known to be very common in plants1 and the suspicion that fungi do much work with their aid is abundantly confirmed4 ,it seems1 indeed1 that there are a whole series of these bodies which have the power of carrying over oxygen to other bodies1 and so bringing about oxidations of a peculiar character4 ,these curious enzymes were first observed owing to studies on the changes which wine and plant juice undergo when exposed to the action of the oxygen of the air4 ,the browning of cut apples is known to be due to the action of an oxydase1 that is1 an oxygen carrying ferment1 and the same is claimed for the deep colouring of certain lacs obtained from the juice of plants1 such as ,anacardiace1 which are pale and transparent when fresh drawn1 but which gradually darken in colour on exposure to the air4 ,oxydases have been isolated from beets1 dahlia1 potato-tubers1 and several other plants4 ,this fact explains a phenomenon known to botanists1 and partly explained by ,schnbein as far back as #ahfh1 that if certain fungi 7e4g41 ,boletus beridies7 are broken or bruised1 the yellow or white flesh at once turns blue2 this action is now traced to the presence in the cell sap of an oxydase4 ,it is the diastatic activity of ,aspergillus which is utilised in the making of sak from rice1 and in the preparation of soy from the soja bean in ,japan4 ,katz has recently tested the diastatic activity of ,aspergillus1 of ,penicillium1 and of ,bacterium megatherium1 in the presence of large and small quantities of sugar1 and found all are able to produce not only diastase1 but also other enzymes2 as the sugar accumulates the diastase formed diminishes1 whereas the accumulation of other carbo-hydrates produces no such effect4 ,harting's investigation on the destruction of timber by fungi derives new interest from the discovery of an emulsion-like enzyme in many such wood-destroying forms1 which splits up glucosides1 amygdalin1 and other substances into sugar1 and that hyph feed on other carbo-hydrates4 ,the fact1 also1 that ,aspergillus can form inverts of the sucrase and maltase types1 as well as emulsin1 inulate1 and diastase1 according to circumstances of nutrition1 will explain why this fungus can grow on almost any organic substance it may happen to alight upon4 ,the secretion of special enzymes by fungi has a further interest just now1 for recent investigations promise to bring us much nearer to an understanding of the phenomena of parasitism than it was possible when ,i was at work upon them some forty or fifty years ago4 ,it was ,de ,bary who impelled botanists to abandon older methods1 and he who laid the foundation of modern mycology4 ,later on he pointed out that when the infecting germinal tube of a fungus enters a plant-cell1 two phenomena must be taken into account1 the penetration of the cell-walls and tissues1 and the attraction which causes the tips of the growing hypha to face and penetrate these obstacles1 instead of gliding over them in the lines of apparent least resistance4 ,the further development of these two factors shows that in the successful attack of a parasitic plant on its victim or host these fungi can excrete cellulose-dissolving enzymes1 and that they have the power of destroying lignine4 ,zopf has also furnished examples of fungi which can consume fats4 ,there is1 however1 one other connection in which these observations on enzymes in the plant-cell promise to be of considerable importance1 viz41 the remarkable action of certain rays of the solar light on bacteria4 ,it has been known for some time past that if bacteria in a nutrient liquid are exposed to sunlight they quickly die4 ,the further researches of ,professor ,marshall ,ward and other workers in the same direction have brought out the fact that it is really the light rays1 and not high temperatures1 that it is especially the blue-violet and ultra-violet rays1 which exert the most effective bactericidal action4 ,this proof depended upon the production of actual photographs in bacteria of the spectrum itself4 ,apart from this1 the ,professor demonstrated that just such spores as those of anthrax1 at the same time pathogenic and highly resistant to heat1 succumb soonest to the action of these cold light-rays1 and that under conditions which preclude their being poisoned by a liquid bath4 ,it is in all probability the action of these rays of light upon the enzymes1 which abound in the bacterial cells1 that bring about their death4 ,the sun1 then1 is seen to be our most powerful scavenger1 and this apparently receives confirmation in connection with ,martinaud's observations1 that the yeasts necessary for wine-making are deficient in numbers and power on grapes exposed to intense light1 and to this is due that better results are obtained in central ,france as contrasted with those in the south4 8,when we reflect1 then1 that the nature of parasitic fungi1 the actual demonstration of infection by a fungus spore1 the transmission of germs by water and air1 the meaning and significance of polymorphism1 hetercism1 symbiosis1 had already been rendered clear in the case of fungi1 and that it was by these studies in fermentation1 and in the life-history of the fungus ,saccharomyces1 that the way was prepared for the tiology of bacterial diseases in animals1 there should be no doubt as to the mutual bearings of these matters40 ,industrial uses of ,fungi and ,saccharomycetes4 ,there are many industrial processes which are more or less dependent for success on bacterial fermentations4 ,the subject is young1 but the results already obtained are seen to be of immense importance from a scientific point of view1 and to open up vistas of practical application already being taken advantage of in commerce1 while problems are continually being raised by the forester1 the agriculturist1 the gardener1 the dairyman1 the brewer1 dyer1 tanner1 and with regard to various industries1 which will eventually confer great advantages in their economic application4 ,the remarkable discovery made by ,alvarez of the bacillus1 which converts a sterilised decoction of the indigo plant into indigo sugar and indigo white1 the latter then oxidising to form the valuable blue dye1 whereas the sterile decoction itself1 even in presence of oxygen1 forms no indigo1 plainly proves how these minute organisms may be turned to a good account4 ,there are1 however1 important points to be determined as to the action of the fermentation brought about by these enzymes1 and the appearance of certain mysterious diseases in the indigo vats4 ,again1 certain stages in the preparation of tea and tobacco leaves are found to depend upon very carefully regulated fermentations1 which must be stopped at the right moment1 or the product will be spoilt4 ,regarding the possible rle of bacteria1 the ,west ,indian tobacco has a special bacterium1 which has been isolated and found to play a very important part in its flavour4 ,every botanist knows that flax and hemp are the best fibres of ,linum and ,cannabis respectively1 separated by steeping in water until the middle lamella is destroyed and the fibres isolated2 but it is not so well known that not every water is suitable for this 8retting0 or steeping process2 and for a long time this was as much a mystery as why some waters are so much better than others for brewing4 ,quite recently ,fribes has succeeded in isolating the bacillus upon which the dissolution of the middle lamella depends4 ,this investigation brought out other interesting details as to the reaction produced by living micro-organisms1 and which can be utilised in deciding questions of plant chemistry too subtile for testing with ordinary re-agents4 ,one other important fact connected with these researches is that botanists have now discarded the view that the middle lamella of the plants referred to is composed of cellulose1 and know that it consists of pectin compounds4 ,fribes' anrobic bacillus is found to dissolve and destroy pectins and pectinates1 but does not touch cellulose or gum4 ,it is well known that the steeping of skins in water in preparation for tanning involves bacterial action1 owing to which the hair and epidermal coverings are removed1 but it also appears that in the process of swelling the limed skins1 the gases evolved in the substance of the tissues1 and the evolution of which causes the swelling and loosens the fibre so that the tanning solutions may penetrate1 are due to a particular fermentation caused by a bacterium1 which1 according to some investigators1 is identical with a lactic ferment introduced by the pine bark1 and which is responsible for the advantageous acidification of the tanning solutions4 ,hay is made in different ways1 and in those where a 8spontaneous0 heating process is resorted to the fermentation is no doubt dependent upon the presence of thermogenic bacteria4 ,but probably no other subject has attained to so much importance as the bacteriology of the dairy3 the study of the bacteria found in milk1 butter1 and cheese in their various forms4 ,of milk1 especially1 much has been written and said as a disease-transmitting medium1 and with every good reason1 and1 if the statement of a ,continental authority may be accepted that each time we eat a slice of bread and butter we devour a number of bacteria equal to the population of ,europe1 we have sure grounds for seeking for further information as to what these bacteria are and what they are doing4 ,and similarly so with cheese1 which teems with millions of these minute organisms4 8,some few years ago it was found that the peculiar aroma of butter was due to a bacterium4 ,there are two species of bacteria1 one of which develops an exquisite flavour and aroma1 but the butter keeps badly1 while the other develops less aroma1 but the butter keeps better4 ,in ,america1 however1 they have isolated and distributed pure cultures of a particular butter bacillus which develops the famous #8,june' flavour1 hitherto only met with in the butter made in a certain district during a short season of the year4 ,this fine-flavoured butter is now constantly manufactured in a hundred ,american dairies2 and the manufacture of pure butter with a constant flavour has become a matter of certainty4 8,properly considered1 the manufacture of cheese is a form of #8microscopic gardening' even more complex and more horticultural in nature than the brewing of beer4 ,from the first moment1 when the cheesemaker guards and cools his milk1 till his stock is ready he is doing his best to keep down the growth of micro-organisms rushing about to take possession of his milk4 ,he therefore coagulates it with rennet--an enzyme of animals1 but also1 as we have seen1 common in plants--and the curd thus prepared is simply treated as a medium1 on which he grows certain fungi and bacteria1 with every needed precaution for favouring their development1 and protecting them against the inroads of other pests and against unsuitable temperature1 moisture1 and access of light4 ,having succeeded in growing the right kind of plants on his curd1 his art then demands that he shall stop their growth at the critical moment1 and his cheese is ready for market4 8,furthermore1 the particular flavour and peculiar odours of cheeses1 as ,camembert1 ,stilton1 and ,roquefort1 have to be obtained1 and this is secured1 for instance1 by cultivating a certain fungus1 ,penicillium1 on bread1 and purposely adding it to ,roquefort4 ,this is found to destroy the lactic and other acids1 and so enables certain bacteria in the cheese to set to work and further change the medium2 whereas in another kind of cheese the object is to prevent this fungus paving the way for these bacteria4 ,another kind of bacillus has been discovered which gives a peculiar clover aroma to certain cheeses4 8,it is thought that more definite results will be obtained by the investigation of the manufacture of the vegetable cheeses of ,china and ,japan1 which are made by exposing the beans of the leguminous plant1 ,glycine--termed soja-beans--to bacterial fermentations in warm cellars with or without certain mould-fungi4 ,several kinds of bean-cheeses are made in this way1 known by special names4 ,they all depend upon the peculiar decompositions of the tissues of the cotyledons of the soja-beans1 which contain #ce to #dj per cent4 of proteids and quantities of fatty matter4 ,the softened beans are first rendered mouldy1 and the interpenetrating hyph render the contents accessible to certain bacteria1 which peptonise and otherwise alter them4 ,there is the further question of the manufacture of vinegar by fermentation1 of the preparation of soy from a brine extract of mouldy and fermented soja-beans1 of bread-making1 and other equally interesting manufactures40 ,results of ,de ,bary's ,investigations in ,parasitism4 8,when the idea of parasitism was rendered definite by the fundamental distinction drawn by ,de ,bary between a parasite and a saprophyte1 it soon became evident that some further distinction must be made between obligate facultative parasites and saprophytes respectively4 ,de ,bary1 when he proposed these terms for adoption1 was clearly alive to the existence of transitions which we now know to be numerous and so gradual in character that we can no longer define any such physiological groups4 ,twenty years ago penicillium and mucor would have been regarded as saprophytes of the most obligate type1 but we now know that under certain circumstances these fungi can become parasites1 and the borderland between facultative parasites and saprophytes on the one hand1 and between the former and true parasites on the other1 can no longer be recognised40 ,in #ahff the germ of an idea was sown which has taken root and extended4 ,de ,bary pointed out that in the case of lichens we have either a fungus parasite on an alg1 or else certain organisms hitherto accepted as alg are merely incomplete forms4 8,in #ahgi the same observer definitely launched the new hypothesis of symbiosis4 ,the word itself is due to ,frank1 who1 in a valuable paper on the biology of the thallus of certain lichens1 very clearly set forth the existence of various stages of life in common among all the lower forms of plants4 ,the details of these matters are now principally of historical interest4 ,we now know that lichens are dual organisms1 composed of various alg1 symbiotic with ,ascomycetes1 with ,basidiomycetes1 and1 as ,massee has shown1 even with ,gastromycetes4 ,the soil contains also bacterio-lichens4 ,hence arose a new biological idea--that a fungus may be in such nicely-balanced relationship with the host from which it derives its sustenance1 that it may be attended with nearly equal advantage to both4 8,in the humus of forests we find the roots of beeches and other ,cupulifer 7willows1 pines1 and so forth7 clothed with a dense mantle of hyph1 and swollen into fleshlike masses of mycorhiza4 ,in similar soils1 and in moorlands1 which abound in the slowly decomposing root-fibres and other vegetable remains so characteristic of these soils1 the roots of orchids1 heaths1 gentians1 c41 are similarly provided with fungi1 the hyph of which penetrate further into the tissues1 and even send haustoria into the living cells1 but without injuring them4 ,as observations multiplied it became clear that the mycorhiza1 or fungus-root1 was not to be dismissed as a mere case of roots affected by parasites1 but that a symbiotic union1 comparable to that of the lichens1 exists1 and we must assume that both tree and fungus derive benefit from the connection4 ,illustration3 ,fig4 #bhj4--;,fine ,section through ,truffle4 a4 ,asci filled with spores2 b4 ,mycelia1 #bej4 8,frank stated1 as the result of his experimental research1 that seedling forest-trees cannot be grown in sterilised soil1 where their roots are prevented from forming mycorhiza2 and he concluded that the fungus conveys organic materials to the roots1 which it obtains by breaking down the leaf-mould and decaying plant remains1 together with water and minerals from the soil1 and plays the especial part of a nitrogen-catching apparatus4 ,in return for this import service the root pays a tax to the fungus by sparing it certain of its tissue contents4 ,it is a curious fact then that the mycorhiza is only formed where humus or vegetable mould abounds40 ,these instructive investigations offer an intelligible explanation of the growth of that well-known subterranean fungus1 the truffle 7,tuber cibarium71 the microscopic appearances of a section of which formed the subject of a paper ,i contributed to 8,the ,popular ,science ,review0 some years ago 7#ahfb74 ,the fungus1 as will be seen by the fine section cut through a truffle1 ,fig4 #bhj1 consists of flocculent filaments1 which in the first instance cover the ground at the fall of the leaf in autumn1 under oak or beech trees1 the hyph of which penetrate the ground1 through the humid soil to the root-hairs of the tree4 ,filaments 7mycelia7 are again given off which terminate in asci or sacs filled with minute spores of about #a_/bejjth of an inch in size1 while the interspaces are filled up by mycelia1 that become consolidated into a firm nut-like body4 ,what happens1 then1 is this3 ,trees and plants with normal roots and root-hairs1 when growing in ordinary soil1 can adapt their roots to life in a soil heavily charged with humus only by contracting symbiotic association with the fungus and paying the tax demanded by the latter in return for its supplies and services4 ,if this adaptation is impossible1 and no other suitable variation is evolved1 such trees cannot grow in such soils4 ,the physiological relations of the root to the fungus must be different in details in the case of non-green1 purely saprophytic1 plants1 ,neottia1 ,monotropa1 c41 and in that of green plants like ,erica1 ,fagus1 and ,pinus4 ,it is1 however1 a well-known fact that ordinary green plants cannot utilize vegetable dbris directly1 and forest trees do so in appearance only1 for the fungi1 yeasts and bacteria there are actively decomposing the leaves and other remains4 ,a class of pseudo-symbiotic organisms are1 however1 being brought into the foreground1 where the combined action of two symbionts results in the death of or injury to a third plant1 each symbiont alone proving harmless4 ,some time ago ,vuillemin showed that a disease in olives results from the invasion of a bacillus 7,b4 ole71 which can1 however1 only obtain its way into the tissues through the passages driven by the hyph of a fungus 7,chtophoma74 ,the resulting injury is a sort of burr4 ,this observer also observed the same bacillus and fungus in the canker burrs of the ash4 ,among many similar cases well worth further attention are the invasion of potato-tubers by bacteria1 these making their way down the decaying hyph of pioneer fungi4 ,professor ,marshall ,ward has seen tomatoes infected by similar means1 and other facts show that many bacteria which quicken the rotting of wood are thus led into the tissues by fungi4 ,probably no subject in the whole domain of cryptogamic botany has wider bearings on agricultural science than the study of the flora and changes on and in manure and soil4 ,nitrifying bacteria play a very important part by providing plant life with a most necessary food4 ,they occur in the soil1 and two kinds have been described--the one kind converting ammonia into nitrous acid1 and the other changing nitrous into nitric acid4 ,we are principally indebted to ,winogradsky for our knowledge of these bacteria2 he furnishes instances of the bearing of bacteriological work on this department of science1 and explains1 not only the origin of nitre-beds and deposits1 but also the way the ammonia compounds fixed by the soil in the neighbourhood of the root-hairs are nitrified1 and so rendered directly available to plant life4 ,the investigations of other observers show that the nitrifying organism is a much more highly-developed and complex form than had been suspected2 that it can be grown on various media1 and that it exhibits considerable polymorphism--i4e41 it can be made to branch out and show other characteristics of a true fungus4 8,i have10 writes ,professor ,ward1 8for some time insisted on the fact that river water contains reduced forms of bacteria--i4e41 forms so altered by exposure to light1 changes of temperature1 and the low nutritive value of the water1 that it is only after prolonged culture in richer food media that their true nature becomes apparent40 ,strutzer and ,hartleb show that the morphological form of the nitrifying organism can be profoundly altered by just such variations of the conditions described by ,ward1 and that it occurs as a branched mycelial form2 as bacilli or bacteria2 or as cocci of various dimensions1 according to the conditions4 8,these observations1 and others made on variations in form 7polymorphism7 in other fungi and bacteria1 open out a vast field for further work1 and must lead to advancement in our knowledge of these puzzling organisms2 they also help us to explain many inconsistencies in the existing systems of classification of the so-called #8species' of bacteria as determined by test-tube culture40 ,alg4--,the algals have a special charm for microscopists4 ,i am free to confess my interest in these organisms1 and for several reasons4 ,in this humid climate of ours they are accessible during the greater part of the year2 they can be found in any damp soil1 in bog1 moss1 and in water--indeed1 wherever the conditions for their existence seem to be at all favourable for development4 ,should the soil dry up for a time1 when the rain returns alg are seen to spring into life and give forth their dormant spores1 which once more resume the circle of formation and propagation4 ,in the earliest stage of development the spore or spore cell is so very small when in a desiccated state1 that any number may be carried about by the slightest breath of air and borne away to a great distance4 ,to all such organisms ,i originally gave the name of rozoa2 now recognised as robic and anrobic organisms 7,fig4 #bha74 ,illustration3 ,fig4 #bha4--robic ,spores #bjj4 #a4 robic fungi caught over a sewer2 #b4 ,fragments of ,penicillium spores2 #c4 robic fungi taken in the time of the cholera visitation1 #ahed4 ,with reference to the robic bacteria ,i have only to add that in addition to the simple mode of taking them on glass slides smeared over with glycerine1 special forms of roscopes are now in use for the purpose1 consisting of a small cylinder in which a current of air is produced by an aspirator and diffused through a glass vessel containing a sterilised fluid4 ,these are in constant use in all bacteriological laboratories4 ,the results obtained are transferred to sterilised flasks or tubes as those shown in a former chapter4 ,miquel1 who has given considerable attention to the subject of robic and anrobic bacteria1 reckons that the number of spores that find their way into the human system by respiration1 even should health be perfectly sound1 may be estimated at #cjj1jjj a day4 ,one of the most commonly met with forms of micro-organisms is ,leptothrix buccalis4 ,it chiefly finds its nutritive material in the interstices of the teeth1 and is composed of short rods and tufted stems of vigorous growth1 to which the name of ,bacillus subtilis has been given 7,fig4 #bhb74 ,among numerous other fungoid bodies discovered in the mouth1 ,sarcin have been found4 ,see ,plate ,,ix41 ,no4 #g4 ,illustration3 ,fig4 #bhb4--,section of the ,mucous ,membrane of the ,mouth1 #cej4 ,showing3 a4 ,the denser connective tissue2 b4 ,teased out tissue2 c4 ,muscular fibre2 d4 ,leptothrix buccalis1 together with minute forms of bacteria and micrococci2 e4 ,ascomycetes and starch granules4 ,the ,beggiatoa1 a sewage fungus1 found by me in the river ,lea water of #ahhd growing in great profusion1 consists chiefly of mycelial threads and a number of globular1 highly refractive bodies1 and may be regarded as evidence of the presence in the water of an abnormal amount of sulphates which set free a gas1 sulphuretted hydrogen1 of a dangerous and offensive character4 ,another curious body closely allied to ,beggiatoa alba is ,cladothrix2 this assumes a whitish pellicle on the surface of putrefying liquids4 ,these saprophytes obtain nourishment from organic matter2 nevertheless they are not true parasites in the first stage of their existence1 during which they live freely in the water or in damp soil2 they1 however1 become pathogenic parasites when they penetrate into the tissues of animals1 and necessarily live at the expense of their host4 ,illustration3 ,,fungi1 ,,alg1 ,,lichens1 ,,etc4 ,tuffen ,west1 del4 ,edmund ,evans4 ,,plate ,i4 ,bacteria1 as ,i have said1 were for a long time classed with fungi under the name of ,schizomycetes4 ,but the more recent researches into their organisation1 and more especially into their mode of reproduction1 show that they rather more resemble a group of alg devoid of chlorophyll4 ,zopf asserts that the same species of algals may at one time be presented in the form of a plant living freely in water1 or in damp ground1 in association with chlorophyllaceous protoplasm1 and at another in the form of a bacterium devoid of green colouring matter1 and receiving nourishment from organic substances previously elaborated by plants or animals1 thus accommodating itself1 according to circumstances1 to two very different modes of existence4 ,that widely-distributed single-cell plant1 the ,palmogla macrococca of ,ktzing1 that spreads itself as a green slime over damp stones1 walls1 and other bodies1 affords an example4 ,if a small portion be scraped off and placed on a slip of glass1 and examined with a half or a quarter-inch power1 it will be seen to consist of a number of ovoid cells1 having a transparent structureless envelope1 nearly filled by granular matter of a greenish colour4 ,at certain periods this mass divides into two parts1 and ultimately the cell becomes two4 ,sometimes the cells are united end to end1 just as we see them united in the actively-growing yeast plant2 but in this case the growth is accelerated1 apparently1 by cold and damp4 ,another plant belonging to the same species1 the ,protococcus pluvialis1 is found in every pool of water1 the spores of which must be always floating in the air1 since they appear after every shower of rain4 ,protococcus pluvialis is furnished with motile organs--two or more vibratile flagella passing through perforations in the cell-wall--whereby1 at certain stages1 they move rapidly about4 ,the flagella are distinctly seen on the application of the smallest drop of iodine4 ,the more remarkable of the several forms presented by the plant is that of naked spores1 termed by ,flotow ,hmatococcus porphyrocephalus4 ,these minute bodies are usually seen to consist of green1 red1 and colourless granules in equal proportions1 and occupying different portions of the cell4 ,they seem to have some share in the after subdivision of the cell 7,fig4 #bhc74 ,there are also still-cells1 which sub-divide into two1 while the motile cells divide into four or eight4 ,it is not quite clear what becomes of the motile zoospores1 ,b1 but as they have been seen to become encysted1 they doubtless have a special function1 or become still-cells under certain circumstances4 ,it appears that both longitudinal and transverse division of the primordial cell takes place2 and that the vibratile flagella of the parent cell retain to the last their function and their motion after the primordial cell has become detached and transformed into an independent secondary cell 7,fig4 #bhc1 ,g74 ,illustration3 ,fig4 #bhc4--;,cell ,development4 7,protococcus pluvialis47 ,protococcus pluvialis1 ,ktzing4 ,hmatococcus pluvialis1 ,flotow4 ,chlamidococcus versatilis1 ,a4 ,braun4 ,chlamidococcus pluvialis1 ,flotow and ,braun4 ,a4 ,division of a simple cell into two1 each primordial vesicle having developed a cellulose envelope2 ,b4 ,zoospores1 having escaped from a cell2 ,c4 ,division of an encysted cell into segments2 ,d4 ,division of another cell1 with vibratile flagella projecting through cell-wall2 ,e4 ,an encysted flagellate cell2 ,f4 ,division of an encysted nucleated cell into four parts1 with vibratile filaments projecting2 ,g4 ,fission of a young cell4 ,the most striking of the vital phenomena presented by ,protococcus is that of periodicity4 ,certain forms--for instance1 encysted zoospores1 of a certain colour1 appear in a given infusion1 at first exclusively1 then they gradually diminish1 become more and more rare1 and finally disappear altogether4 ,after some time their number again increases1 and this may be repeated4 ,thus1 a cell which at one time presented only still forms at another contained only motile ones4 ,the same may be said with respect to segmentation4 ,if a number of motile cells be transferred from a larger vessel into a smaller one1 in the course of a few hours most of them will have subsided to the bottom1 and in the course of the day observed to be on the point of sub-division4 ,on the following morning division will have become completed2 on the next day the bottom of the vessel will be found covered with a new generation of self-dividing cells1 which1 again1 will produce another generation4 ,this regularity1 however1 is not always observed4 ,the influence of every change in the external conditions of life upon the plant is very remarkable4 ,it is only necessary to pour water from a smaller into a larger or shallower vessel to at once induce segmentation of cells4 ,the same phenomenon occurs in other algals2 thus ,vaucheria almost always develops zoospores at whatever time of year they may be brought from their natural habitat into a warm room4 ,light is conducive to the manifestation of vital action in the motile spores2 they usually collect in great numbers on the surface of the water1 and at that part exposed to the strongest light4 ,but in the act of propagation1 on the contrary1 and when about to pass into the still condition1 the motile ,protococcus cell seems to shun light1 and falls to the bottom of the vessel4 ,too strong sunlight1 as when concentrated by a lens1 quickly kills the young zoospores4 ,a temperature of undue elevation is injurious to the development of their vital activity and the formation of the zoospores4 ,frost destroys motile1 but not still zoospores4#ee ,stephanosphra pluvialis is a conspicuous variety of the fresh-water algals1 described by ,cohn4 ,it consists of a cell containing eight primordial cells filled with chlorophyll1 uniformly arranged 7see ,plate ,i41 ,no4 #bd d74 ,the globular mother-cell rotates1 somewhat in the same way as the volvox1 by vibratile flagella1 two of which are seen projecting from each cell and piercing the transparent outer cell wall4 ,every cell divides first into two1 then four1 and lastly eight cells1 each one of which again divides into a number of micro-gonidia1 which have a motion within the mother-cell1 and ultimately escape from it4 ,under certain circumstances each of the eight young cells is observed to change places in the interior of the cell2 eventually they escape1 lose their flagella1 form a thicker membrane as at b1 and for a time remain motionless1 and sink to the bottom of the vessel in which they are contained4 ,if the vessel is permitted to become thoroughly dry1 and then again has water poured into it1 motile cells reappear2 from which circumstance it is probable that these represent the resting spores of the plant4 ,when in the condition of greatest activity its division into eight is perfected during the night1 and early in the morning light the young cells escape and pass through similar changes4 ,it is calculated that in eight days1 under favourable circumstances1 #af1ggg1baf families may be formed from one resting-cell of ,stephanosphra4 ,in certain of the cells1 and at particular periods1 remarkable amboid bodies 7,plate ,i41 ,no4 #bd c7 make their appearance4 ,there is a marked difference between ,stephanosphra and ,chlamydococcus1 for while in the latter the individual portions of a primordial cell separate entirely from one another1 each developing its own enveloping membrane1 and ultimately escaping as a unicellular individual2 in the former1 on the other hand1 the eight portions remain for a time living in companionship4 ,volvocine4--,a fresh-water unicellular plant of singular beauty and interest to the microscopist is the ,volvox globator 7,plate ,i41 ,no4 #ae74 ,no4 #af represents a portion of another cell1 with brownish amboid bodies enclosed in the protoplasmic web4 ,it is common to our fresh-water pools1 and attains a diameter of about #a_/bjth or #a_/cjth of an inch4 ,its movement is peculiar1 a continued roll onwards1 or a rotation like that of a top2 at other times it glides along smoothly4 ,when examined under a sufficiently high power1 it is seen to be a hollow sphere1 studded with green spots1 and traversed by green threads connecting each of the spots or spores with the maternal cell4 ,from each of the spores proceed two long flagella1 lashing filaments1 which keep the globular body on the move4 ,after a time the sphere bursts1 and the contained sporules issue forth and speedily pass through a similar stage of development4 ,these interesting cells were long taken to be animal bodies4 ,ehrenberg described them as ,monads1 possessing a mouth1 stomach1 and an eye4 ,the setting free of the young volvox is essentially a process of cell division1 occurring during the warmer periods of the year1 and1 as ,professor ,cohn shows1 is a considerable advance upon the simpler conjugation of two smaller cells in desmids2 it more closely resembles that which prevails among the higher alg and a large number of cryptogams4 ,as autumn advances the volvox spherules usually cease to multiply by the formation of zoosporanges1 and certain of their ordinary cells begin to undergo changes by which they are converted1 some into male or sperm-cells1 others into germ-cells1 but the greater number appear to remain sterile4 ,both kinds of cells at first so nearly resemble each other that it is only when the sperm cells begin to undergo sub-division that they are seen to be about three times the size of the sterile cells4 ,then the primary cell resolves itself into a cluster of peculiar secondary cells1 each consisting of an elongated body containing an orange-coloured endochrome and a pair of long flagella1 as seen in the antherozoids of the higher cryptogams4 ,as the sperm-cells approach maturity the clusters may be seen to move within them2 the bundles then separate and show an independent active movement while still within the cavity of the primary cell1 and finally escape through a rupture in the cell-wall1 rapidly diffusing themselves as they pass through the cavity4 ,the germ-cells continue to increase in size without undergoing sub-division1 at first showing large vacuoles in their protoplasm1 but subsequently becoming filled with a darker coloured endochrome4 ,the form of the cell also changes from its flask-like shape to the globular1 and at the same time seems to acquire a firmer envelope4 ,over this the swarming antherozoids diffuse themselves and penetrate the substance to the interior1 and are then lost to view4 ,the product of this fusion1 ,cohn tells us1 is a reproductive cell1 or 8oospore10 which speedily becomes enveloped in another membrane with a thicker external coat1 beset with conical-pointed processes2 and now the chlorophyll of the young cell gives place1 as in ,palmogl1 to starch and reddish or orange-coloured1 and a more highly refractive1 fluid4 ,as many as forty of such oospores have been counted in a single sphere of volvox1 which then acquires the peculiar appearance observed by ,ehrenberg1 and described by him under the name of ,volvox stellatus4 ,the further history of this wonderful spheroid unicellular plant has been traced out by ,kirchner1 who found that their germination commences in the early months of the year--in ,february--with the liberation of the spherical endospore from its envelope and its division into four cells4 ,a remarkable phenomenon has been observed by ,dr4 ,braxton ,hicks--the conversion of an ordinary volvox cell into a moving mass of protoplasm that bears a striking resemblance to the well-known amba4 8,towards the end of the autumn the endochrome mass of the volvox increases to nearly double its ordinary size1 but instead of undergoing the usual sub-division so as to produce a macrogonidium1 it loses its colour and regularity of form1 and becomes an irregular mass of colourless protoplasm1 containing a number of brownish granules40 ,the final change and the ultimate destination of these curious amboid bodies have not been satisfactorily made out1 but from other observations on the protoplasmic contents of the cells of the roots of mosses1 which in the course of two hours become changed into ciliated bodies1 it is believed that this is the mode in which these fragile structures are enabled to retain life and to resist all the external conditions1 such as damp1 dryness1 and the alternations of heat and cold4 ,it would be quite impossible to deny the great similarity there is between the structure of volvox and that of the motile cell of ,protococcus pluvialis4 ,the influence of reagents will sometimes cause the connecting processes of the young cells1 as in ,protococcus1 to be drawn back into the central mass1 and the connecting threads are sometimes seen as double lines1 or tubular prolongations of the membrane4 ,at other times they appear to be connected by star-like prolongations to the parent cell 7,plate ,i41 ,no4 #ae71 presenting an almost identical appearance with ,pediastrum pertusum4 ,another body designated by ,ehrenberg ,sphrosira volvox is an ordinary volvox in a different stage of development2 its only features of dissimilarity being that a large proportion of the green cells1 instead of being single1 are double or quadruple1 and that the groups of flagellate cells form by their aggregation discoid bodies1 each furnished with a single flagellum4 ,these clusters separate themselves from the parent cell1 and swim off freely under the forms which have been designated ,uvella and ,syncrypta by ,ehrenberg4 ,mr4 ,henry ,carter1 ,f4,r4,s41 who made a careful investigation of unicellular plants1 described ,sphrosira as the male1 or spermatic form of volvox4 ,among other organisms closely allied to volvox and included in ,volvocine1 affording the microscopist many interesting transitional forms in their various modes of fructification1 are the ,eudorina1 still-water organisms that pass through a similar process of reproduction as the volvox4 ,in the ,pandorina morum1 its reproduction is curiously intermediate between the lower and the higher types2 as within each cell is a mulberry-like mass1 composed of cells possessing a definite number of swarm spores1 sixteen usually1 which rupture the mother cell1 and swim off furnished with a pair of flagella4 ,a similar process takes place in some of the ,confervace and other fresh-water alg4 ,the ,palmella1 again1 consist of 7,plate ,i41 ,no4 #ba7 minute organisms of very simple structure1 which grow either on damp surfaces or in fresh water4 ,the stonework of some of our churches is often seen to be covered with a species of ,palmella1 that take the form of an indefinite slimy film4 ,the 8red snow0 of ,arctic or ,alpine regions1 considered to be a species of ,protococcus1 is frequently placed among ,palmella4 ,a more characteristic form of the ,p4 cruenta is the ,hmatococcus sanguinis1 the whole mass of which is sub-divided by partitions enclosing a larger or smaller number of cells1 which diffuse their granular contents through the gelatinous mass in which their several changes take place4 ,the albuminoid envelope of these masses is seen to contain parasitic growths1 which have given rise to some discussion1 especially when their filaments are observed to radiate in various directions4 ,the ,oscillariace constitute a genus of ,confervace which have always had very great interest for the microscopist in consequence of their very remarkable animal-like movements1 and from which they derive their generic name4 ,for more than a century these ,bacillaria have excited the curiosity of all observers without any one having derived more than an approximate idea of their remarkable rhythmical movements4 ,the frustule consists of a number of very fine short threads attached together by a gelatinous sheath1 in one species all of equal length4 ,their backward and forward movement is of a most singular character2 the only other conferva in which ,i have seen a motion of a similar kind is the ,schizonema4 ,in this species the frustules are packed together in regular series1 the front and side views being always in the same direction4 ,these several bodies move along within the filamentous sheath without leaving their respective places4 ,on carefully following the movement1 it is seen at first much extended1 and then more compressed1 while the frustules become more linear in their arrangement1 and present a closer resemblance to ,bacillaria paradoxa1 augmented by the circumstance that the frustules are seen to move in both directions4 ,a frustule of ,schizonema can move independently of the sheath1 and so will a detached frustule of bacillaria4 ,this peculiar and exceptionally anomalous phenomenon as that of the movements of bacillaria can hardly be confined to a solitary species4 ,the movements of the frustules are much accelerated by warmth and light4 ,the longer filaments of other minute species only slightly exhibit any motion of the kind1 but have peculiar undulating motions4 ,illustration3 ,fig4 #bhd4--;,confervace4 #a4 ,volvox globator2 #b4 ,a section of volvox1 showing the flagellate margin of the cell2 #c4 ,a portion more highly magnified1 to show the young volvocina1 with their nuclei and thread-like attachments2 #d4 ,spirogyra1 near which are spores in different stages of development2 #e4 ,conferva floccosa2 #f4 ,stigeoclonium protensum1 jointed filaments and single zoospores2 #g4 ,staurocarpus gracilis1 conjugating filaments and spores4 ,confervace are a genus of algals4 ,the species consist of unbranched filaments composed of cylindrical or moniliform cells1 with starch granules4 ,many are vesicular1 and all multiply by zoospores generated in the interior of the plant at the expense of the granular matter4 ,they are1 for the most part1 found in fresh water attached or floating1 some in salt water1 and a few in both1 in colour usually green1 but occasionally olive1 violet1 and red4 ,the ,confervace proper are often divided into four families3 #a4 ,hydrodictid2 #b4 ,zygnemid2 #c4 ,confervid2 #d4 ,chtophorid4 ,to the microscopist all the plants of this genera are extremely interesting as subjects for the study of cell multiplication4 ,the process usually takes place in the terminal cell1 the first step in which is the division of the endochrome1 and then follows a sort of hour-glass contraction across the cavity of the parent cell1 whereby it is divided into two equal parts4 ,this is better seen in some of the desmids than in ,fig4 #bhd1 ,nos4 #d1 #e1 and #f4 ,some species are characterised by a different mode of reproduction2 these possess a number of nuclei1 and multiply by zoospores of two kinds1 the largest of which have either two or four cilia1 which germinate directly the smaller are biciliated2 conjugation has been seen to take place in a few instances4 ,allied to the ,confervace is an interesting plant1 ,sphroplea annulina1 which has received careful attention from ,cohn4 ,the oospores of this plant are the product of a process partaking of a sexual nature1 and when mature are filled with reddish fat vesicles which divide by segmentation4 ,the dogoniace also closely resemble ,confervace in habits of life1 but differ in some particulars1 especially so in the mode of reproduction 7only a single large zoospore being set free from each cell7 and by the almost complete fission of the cell-wall or one of the rings which serve as a hinge4 ,the zoospores are the largest known among algals1 and each is described as having a red eye-spot4 ,the ,chtophorace form an interesting group of confervoid plants1 and are usually found in running streams1 as they prefer pure water4 ,one of the characteristics of the group is that the extremities of the branches are prolonged into an acute-shaped termination1 as represented in ,fig4 #bhd1 ,no4 #f4 ,a very pretty object under the microscope is ,draparnaldia glomerata1 belonging to this species4 ,it consists of an axis composed of a row of cells1 and at regular intervals whorls of slender prolongations1 containing chlorophyll or endochrome of a deeper green2 these attain to an extraordinary length4 ,the ,batrachosperm bear a strong resemblance to frog-spawn1 from which they derive their name1 and are chiefly a marine group of algals allied to the ,rhodesperme or red seaweeds4 ,the late ,dr4 ,a4 ,hassall first described them2 they have since received more careful attention from ,m4 ,sirodot4 ,they are reddish-green1 extremely flexible1 and nothing can surpass the grace of their movements in water2 but when removed from their element they lose all form1 and resemble a jelly-like substance without a trace of organisation2 but if allowed to remain quiet they regain their original shape4 ,the presence of the cell-membrane will be best demonstrated by breaking up the filaments1 either by moving the thin glass cover1 or by cutting through a mass of them in all directions with a fine dissecting knife4 ,on now examining the slide1 in most instances many detached empty pieces of the cell-membrane1 with its stri1 will be seen1 as well as filaments partly deprived of protoplasm4 ,on the application of iodine all these appearances become more distinguishable in consequence of the filament turning red or brown1 while the empty cells remain either unaffected1 or present a slight yellowish tint1 as is frequently the case with cellulose when old4 ,illustration3 ,fig4 #bhe4--,mesoglia vermicularis4 ,with regard to the contents of the cell1 the endochrome is coloured in the ,oscillatori1 and is distinguishable by circular bands or rings around the axis of the cylindrical filament4 ,iodine stains them brown or red1 and syrup and dilute sulphuric acid produce a beautiful rose colour4 ,as to their mode of propagation1 nothing positive is known4 ,if kept for some time they gradually lose their green colour2 a portion of the mass1 becoming brown1 sinks to the bottom of the vessel1 and presents a granular layer4 ,mesoglia vermicularis 7,fig4 #bhe7 consists of strings of cells cohering and held together by their membranous covering4 ,in the lowly organised plant ,vaucheria 7,plate ,i41 ,no4 #bc1 ,v4 sessilis7--so named after its discoverer ,vaucher1 a ,german botanist--a genus of ,siphonace1 we have an example of true processes of sexual generation4 ,the branching filaments are often seen to bear at their sides peculiar globular bodies or oval protuberances1 nipple-shaped buddings-out of the cell-wall1 filled with a dark-coloured endochrome and distributed in pairs1 one of which curves round to meet the other1 when conjugation is seen to take place4 ,near these bodies others are found with pointed projections1 which have been described as 8horns10 but these1 ,pringshelm says1 are 8antherids which produce antherozoids in their interior10 while the capsule-like bodies constituting the oospores become1 when fertilised1 a new generation1 which swarm out through a cavity or aperture in the parent cell-wall4 ,the fruit of fresh-water and most olive-green algals is enclosed in spherical cavities under the epidermis of the frond1 termed conceptacles1 and may be either male or female4 ,the zoids are bottle-shaped and have flagella2 the transparent vesicle in which they are contained is itself enclosed in a second of similar form4 ,in moncious and dicious algals the female conceptacles are distinguished from the male by their olive colour4 ,the spores1 when developed1 are borne on a pedicle emanating from the inner wall of the conceptacle4 ,they rupture the outer wall at its apex2 at first the spore appears simple1 but soon after a series of changes takes place1 consisting in a splitting up of the endochrome into six or eight masses of spheroidal bodies4 ,a budding-out occurs in a few hours' time1 and ultimately elongates into a cylindrical thread4 ,the ,vaucheria present a double mode of reproduction1 and their fronds consist of branching tubes resembling in their general character that of the ,bryophyta1 from which indeed they differ only in respect of the arrangement of their green contents4 ,in that most remarkable plant ,saprolegnia ferox1 which is structurally so closely allied to ,vaucheria1 though separated from them by the absence of green colouring matter1 a corresponding analogy in the processes of development takes place4 ,in the formation of its zoospores1 an intermediate step is presented between that of the alg and a class of plants formally placed among fungi4 ,the ,ulvace4--,the typical form of seaweeds is the ,ulva lactuca1 well known from its fronds of dark-green 8laver0 on every coast throughout the world4 ,ulv are seen to differ but little from the preceding group of fresh-water algals4 ,the specific difference is that the cells1 when multiplied by binary subdivision1 not only remain in firm connection with each other but possess a more regular arrangement4 ,the frond plane of the algal is either more simple or lobed1 and is formed of a double layer of cells closely packed together and producing zoospores4 ,the whole group is chiefly distinguished from ,porphyra by their green colour1 the latter being roseate or purple4 ,ulv are mostly marine1 with one or two exceptions4 ,one species 7,u4 thermalis7 grows in the hot springs of ,gastein1 in a temperature of about #aag ,fahr4 ,the development of ,ulv is seen in ,fig4 #bhf4 ,the isolated cells1 ,a1 resemble in some points those of the ,protococcus2 these give rise to successive subdivisions determining the clusters seen at ,b and ,c1 and by their aggregation to the confervoid filament shown at ,d4 ,these filaments increase in length and breadth by successive additions1 and finally take the form of fronds1 or rows of cells4 ,illustration3 ,fig4 #bhf4--,successive ,stages of ,development of ,ulv4 ,a4 ,isolated spores2 ,b and ,c4 ,clusters of cells2 ,d4 ,cells in the filamentous stage4 ,illustration3 ,fig4 #bhg4--,sphacelaria cirrhosa1 with spores borne at the sides of the branchlets4 ,the marine greenish-olive alg present a general appearance which might at first sight be mistaken for plants of a higher order of cryptogams4 ,their fronds have no longer the form of a filament1 but assume that of a membranous expansion of cells4 ,the cells in which zoospores are found have an increased quantity of coloured protoplasm accumulated towards one point of the cell-wall2 while the zoospores are observed to converge with their apices towards the same point4 ,in some alg1 which seem to be closely related in form and structure to the ,bryophyta1 we notice this important difference1 that the zoospores are developed in an organ specially destined for the purpose1 presenting peculiarities of form and distinguishing it from other parts of the branching tubular frond4 ,in the genus ,derbesia distinct spore cases develop1 a young branch of which1 when destined to become a spore case1 instead of elongating indefinitely1 begins1 after having arrived at a certain length1 to swell out into an ovoid vesicle1 in the cavity of which a considerable accumulation of protoplasm takes place4 ,this is separated from the rest of the plant1 and becomes an opaque mass1 surrounded by a distinct membrane4 ,after a time a division of the mass takes place1 and a number of pyriform zoospores1 each of which is furnished with flagella1 are set free4 ,illustration3 ,,desmidiace1 ,,diatomace1 ,,alg4 ,tuffen ,west1 del4 ,edmund ,evans4 ,,plate ,,ii4 ,illustration3 ,fig4 #bhh4--;,cutleria dichotoma4 ,section of lacinia of a frond1 showing the stalked eight-chambered oosporanges growing on tufts with intercalated filaments4 ,magnified #ej diameters4 ,in ,cutleria 7,fig4 #bhh7 we have a special feature of interest with two kinds of organs1 seemingly opposed to each other with regard to their reproductive functions4 ,the sporangia not only differ from those of other species1 but the frond consists of olive-coloured irregularly-divided flagella1 on each side of which tufts 7sori7 consisting of the reproductive organs1 intermixed with hair-like bodies1 are scattered4 ,the zoospores are divided by transverse partitions into four cavities1 each of which is again bisected by a longitudinal median septum4 ,when first thrown off they are in appearance so much like the spores of ,puccinia that they may be mistaken for them1 although so very much larger than those of other olive-coloured alg4 ,floride1 the red alg 7,plate ,,ii471 present many varieties of structure1 although less appears to be known of their reproductive processes than of lower forms of cryptogamic plants4 ,these are1 however1 of three kinds4 ,the first1 to which the term polyspore has been applied1 is that of a gelatinous or membranous pericarp or conceptacle1 in which an indefinite number of zoospores are contained4 ,this organ may be either at the summit or base of a branch1 or it may be concealed in or below the cortical layer of the stem4 ,in some cases a number of spore-bearing filaments emanate from a kind of membrane at the base of a spheroidal cellular perisporangium1 by the rupture of which the zoospores formed from the endochrome of the filaments make their escape4 ,other changes have been observed2 however1 they all agree in one particular1 namely1 that the zoospore is developed in the interior of a cell1 the wall of which forms its perispore1 and the internal protoplasmic membrane endochrome1 the zoospore itself1 for the escape of which the perispore opens out at its apex4 ,illustration3 ,fig4 #bhi4--;,dasya kutzingiana1 with seed vessel and two rows of tetraspores4 ,magnified #ej diameters4 ,the second form is more simple1 and consists of a globular or ovoid cell1 containing a central granular mass2 this ultimately divides into four quadrate-shaped spores2 these1 on attaining maturity1 escape by rupture of the cell-wall4 ,another organ1 called a tetraspore1 takes its origin in the cortical layer4 ,the tetraspores are arranged either in an isolated manner along the branches1 or in numbers together2 in some instances the branches that contain them are so modified in form they look like special organs1 and have been called stichidia2 as1 for example1 in ,dasya 7,fig4 #bhi74 ,of the third kind of reproductive organ a difference of opinion exists as to the signification of their antheridia2 although always produced in precisely the same situations as the tetraspores and polyspores1 they are agglomerations of little colourless cells1 either united in a bunch1 as in ,griffithsia1 or enclosed in a transparent cylinder1 as in ,polysiphonia1 or covering a kind of expanded disc of peculiar form1 as in ,laurencia4 ,according to competent observers1 the cells contain spermatozoids4 ,ngeli describes the spermatozoid as a spiral fibre1 which1 as it escapes1 lengthens itself in the form of a screw4 ,thuret1 on the contrary1 says the contents are granular1 and offer no trace of a spiral filament1 but are expelled from the cells by a slow motion4 ,the antheridia appear in their most simple form in ,callithamnion 7,plate ,,ii41 ,nos4 #cb and #cd71 being reduced to a small mass of cells composed by numerous little bunches which are sessile on the bifurcations of the terminal branches4 ,the spores are simpler structures than the tetraspores1 and mostly occupy a more important position4 ,they are not scattered through the frond1 but grouped in definite masses1 and generally enclosed in a special capsule or conceptacle1 which may be mistaken for a tetraspore case4 ,the simplest form of the spore fruit consists of spherical masses of spores attached to the wall of the frond1 or imbedded in its substance1 without a proper conceptacle2 such a fruit is called a favellidium1 and occurs in ,halymenia2 the same name is applied to the fruits of similar structures not perfectly immersed1 as those of ,gigartina1 ,gelidium1 c41 where they form tubercular swellings on the lobes4 ,in some1 the tubercles present a pore at the summit1 through which the spores emerge forth4 ,in other cases1 as in ,ceramium 7,plate ,,ii41 ,nos4 #bg and #cg71 the spores occupy a more conspicuous place2 a characteristic species is ,delessaria 7,plate ,,ii41 ,no4 #ci71 the coccidium either occurring on lateral branches1 or is sessile on the face of the frond1 when it consists of a case filled with angular-shaped spores attached to the wall of the case4 ,the general external appearance of the red alg is very varied1 but it seems to attain to its deepest colouring in the ,red ,sea1 which1 it is said1 is entirely due to the peculiarly vivid red seaweed4 ,they are all exquisite objects for the microscope1 as may be surmised from the few varieties presented in ,plate ,,ii4 ,the ,floride of the warmer seas exhibit most elegantly formed fronds1 as will be seen on reference to the 8,phycologia ,australica0 of the late ,dr4 ,william ,harvey1 ,f4,r4,s4 ,the ,charace may be placed among the highest of the algals1 if only for the complexity of their reproductive organs1 which certainly offer a contrast in their simplicity of structure4 ,chara vulgaris1 stonewort1 is a simple fresh-water plant1 preferring still freshwater ponds or slow-moving rivers running over a chalky soil4 ,it thus derives the calcareous matter found in the axis of the plant1 together with a small portion of silica4 ,its filaments 7or branches1 as some botanists prefer to call them7 are given off in whorls4 ,the ,charace are a small family of acrogens1 consisting of only two or three at most4 ,they are moncious and dicious1 the two kinds of fruit being often placed close together4 ,they may easily be grown in a tall glass jar for observation4 ,all that is necessary is to put the jar occasionally under the house tap and let the water run slowly over the top for a short time1 thus renewing the contents without disturbing the plant4 ,the hard water supplied to ,london suits chara better than softer water4 ,both chara and nitella are objects of great interest to microscopists1 since in the former the important fact of vegetable circulation was first observed4 ,a portion of the plant of the natural size is shown in ,fig4 #bij1 ,no4 #a4 ,charace4 ,illustration3 ,fig4 #bij4--;,diagrammatic sketch of ,chara4 #a4 ,a stem of ,chara vulgaris1 natural size2 #b4 ,magnified view 7arrows indicating the course taken by the chlorophyll72 #c4 ,a limb1 with buds protruding2 #d4 ,portion of a leaf of ,vallisneria spiralis1 showing cyclosis of chlorophyll granules4 ,each plant is composed of an assemblage of long tubiform cells placed end to end1 with fixed intervals1 around which the branchlets are disposed with great regularity4 ,in nitella the stem and branches are composed of simple cells1 which sometimes attain to several inches in length4 ,each node1 or zone1 from which the branches spring1 consists of a single plate1 or layer1 of small cells1 which are a continuation of the cortical layer of the internode 7,fig4 #bij1 ,no4 #c7 as an outgrowth4 ,each cell is partially filled with chlorophyll granules1 and it is these that are seen under the microscope taking the course shown by the arrows 7,fig4 #bij1 ,no4 #b74 ,the rate of movement of the granules is accelerated by moderate warmth and retarded by cold4 ,it is in viewing the circulation in water plants that the warm stage of the microscope is brought into use4 ,borne along with the protoplasmic stream are a number of solid particles consisting of starch granules and other matters4 ,the method of viewing the circulation is by cutting sections off a portion of the plant with a very sharp knife1 and arranging them in a growing cell with a few drops of water1 and covering over with a thin cover-glass4 ,illustration3 ,fig4 #bia4--,the ,fructification of ,chara fragilis4 ,a4 ,portion of filament containing 8antheroids02 ,b4 ,a group of antheridial filaments1 composed of a series of cells1 within each of which antherozoids are formed2 ,c4 ,the escape of mature antherozoids1 with whip-like prolongations1 about to swim off2 ,d4 ,antherid supported on flask-shaped pedicle2 ,e4 ,nucule enlarging1 and seen to contain oospores2 ,f4 ,spores and elaters of ,equisetum2 ,g4 ,spores surrounded by elaters of ,equisetum4 ,the reproductive process of ,chara is effected by two sets of bodies1 both of which are placed at the base of the branches 7,fig4 #bia1 ,e and ,d7 either on the same or different plants1 one set known as globules or antherids1 and the other as nucules1 containing the oospores or archegones4 ,these are often of a bright red colour1 and have covering plates1 or shields 7,b and ,e71 curiously marked1 and the central portion is composed of a number of filaments rolled up 7as in ,e7 or free 7as seen at ,b71 projecting out from the centre of the sphere4 ,the antherid is supported on a short flask-shaped pedicle1 which projects into the interior4 ,at the apex of each of the eight manubria is a roundish hyaline cell1 termed a capitulum1 and at its apex again six smaller or secondary capitula4 ,the long whip-shaped filaments are divided by transverse septa into a hundred or more compartments1 every one of which is filled with an antherozoid 7as at ,a71 consisting of a spiral thread of protoplasm packed into two or three coils2 these escape and become free 7as seen at ,c71 each having two long fine flagella4 ,the young antherozoid swims off with a lashing action1 and the whole field appears for a time filled with life4 ,they swim about freely1 but their motion gradually ceases1 and soon they arrive at a state of inaction4 ,nitella appears to have a somewhat different mode of fructification to that of its congener4 ,it puts forth a long filamentous branch from one of its joints1 which1 on reaching the surface of the water1 terminates in a whitish fruit-like cluster4 ,it is even a more delicate and less robust algal than chara1 and every care should be taken to imitate the still water in which it grows4 ,it delights in shady woods and in calcareous open pools4 ,similar care is requisite with regard to ,vallisneria2 and a more equal temperature is better suited to the growth of this aquatic plant4 ,it should be planted in the middle of the jar or aquarium1 about two inches deep in mould1 closely pressed down1 then gently fill the jar with water4 ,when the water requires changing1 a small portion only should be run off at a time4 ,it appears to thrive in proportion to the frequency of changing the water1 and taking care that the water added rather increases the temperature than lowers it4 ,the natural habitat of the ,frog-bit1 another water-plant of much interest1 is found on the surface of ponds and ditches2 in the autumn its seeds fall1 and become buried in the mud at the bottom during the winter2 in the spring these plants rise to the surface1 produce flowers1 and grow throughout the summer4 ,chara may be found in many places around ,london1 and in the upper reaches of the ,thames4 ,anacharis alsinastrum4--,this remarkable plant is so unlike any other water-plant that it may be at once recognised by its leaves growing in threes round a slender stem4 ,it is also known as 8,waterthyme10 from a resemblance it bears to that plant4 ,the colour of the plant is deep green2 the leaves are nearly half an inch long1 by an eighth wide1 egg-shaped at the point1 with serrated edges4 ,its powers of increase are prodigious1 as every fragment is capable of becoming an independent plant1 producing roots and stems1 and extending itself indefinitely in every direction4 ,the specific gravity of it is so nearly that of water1 that it is more disposed to sink than float4 ,a small branch of the plant is represented1 with a hydra attached to it1 in a subsequent chapter4 ,the special cells in which the circulation is most readily seen are the elongated cells around the margin of the leaf and those of the midrib4 ,on examining the leaf with polarised light1 the cells are observed to contain a large proportion of silica1 and present a very interesting appearance4 ,a bright band of light encircles the leaf1 and traverses its centre4 ,in fact1 the leaf is set1 as it were1 in a framework of silica4 ,by boiling the leaf for a short time in equal parts of nitric acid and water1 a portion of the vegetable tissue is destroyed1 and the silica rendered more distinct1 without changing the form of the leaf4 ,it is necessary to make a thin section or strip from the leaf of ,vallisneria for the purpose of exhibiting the circulation in the cells1 as shown in ,fig4 #bij1 ,no4 #d4 ,among the cell granules1 a few of a more transparent character than the rest1 are seen to have a nucleolus within4 ,the phenomenon of cell cyclosis occurs in other plants beside those growing in water4 ,the leaf of the common plantain or dock1 ,plantago1 furnishes a good example1 the movement being seen both in the cells of the plant and hairs of the cuticle torn from the midrib4 ,cell-division4--,in order to study the process of cell-division the hairs on the stamens of ,tradescantia should be taken4 ,remove one from a bud on a warm day and let a drop of a one per cent4 sugar solution fall upon it1 and cover it with a thin glass cover4 ,place it for a short time in a moist-chamber 7,fig4 #bef71 and then examine it with a magnifying power of #ejj diameters4 ,the nucleus of the cell will be seen1 near its terminal position1 to gradually elongate in the direction of the longer axis of the cell and become more granular1 while the protoplasm moves towards the extreme end2 the nucleus at the same time will present a striated appearance1 with the fibrilla arranged parallel to the longer axis of the nucleus1 and at length approach each other at the poles4 ,a nuclear spindle will now be produced1 and the fibres ruptured in the equatorial plane1 so that two nuclei will be found in place of the one4 ,the best preparations of nuclei are obtained by making thin longitudinal sections of actively-growing plants 7young rootlets of ,pinus1 for example71 and staining them with hmatoxylin in the manner described in a former chapter4 ,desmidiace and ,diatomace4 ,the two groups of ,desmidiace and ,diatomace differ so little in their general characters that they may be spoken of as members or representative families of microscopic and unicellular alg alike in their remarkable beauty and bilateral symmetry1 and of such peculiar interest as to call for special notice4 ,desmids differ from diatoms chiefly in colour1 in lacking a non-silicious skeleton1 and in their generative process1 which for the most part consists in the conjugation of two similar cells4 ,diatoms1 on the other hand1 have dense silicious skeletons and a general absence of green colouring matter4 ,ralfs1 in his systematic monograph1 enumerates twenty genera of desmids4 ,the limiting membrane is alike firm and flexible1 since it exhibits some elasticity and resistance to pressure1 and is not readily decomposable4 ,traces of silica are found in only a few of the desmids1 while the frustule of the diatom is chiefly composed of this substance2 both have an external membranous covering1 so transparent and homogeneous in structure as to be in danger of being entirely overlooked1 unless some staining material is used1 together with a high-power objective possessing considerable penetration4 ,in some species1 however1 the mucous covering is more clearly defined1 as in ,staurastrum and ,didymoprium ,grevelli4 ,openings occur in the outer membrane of other species1 as the ,closterium4 ,illustration3 ,,plate ,x4 ,,desmidiace4 ,many species of desmids have a power of motion1 the cause of which must be due either to cilia or a flagellate organ4 ,this1 however1 is denied by some observers1 who regard their movements as due to an exudation of the mucilaginous contents of the cell1 to exosmose1 or diffusion1 neither of which hypotheses will at all help us to understand the gliding movements of the ,oscillari or the sharp jerky movement of the ,schizonema4 ,the movements of desmids are especially exerted when in the act of dividing1 and by sunlight1 towards which they are always observed to move4 ,the force with which some diatoms move about is very great1 and this can only be satisfactorily explained by admitting a specialised organ4 ,the appearance of the ,desmidiace 7,plate ,x47 is much modified by their eminences1 depressions1 and processes1 as well as that of the surface1 the margin of the fronds1 and the depth and width of the central constriction4 ,the surfaces may be dotted over irregularly1 the dots themselves being elevated or depressed points in their structural character4 ,the margins of some have a dentate appearance1 as in ,cosmarium4 ,in the elongated forms1 such as ,penium1 the puncta are disposed in lines parallel to the length4 ,in several these lines are either elevations or furrows1 it is not always easy to say which2 they are peculiar1 however1 to the elongated forms of ,closterium4 ,when the lines are fine they produce a striation of the surface1 but in order to discover this the fronds should be viewed when empty and by a fairly good power4 ,the modification of surface in several genera seems to be due1 not to mere simple appendages1 but to expansion of the limiting membrance into thickened processes1 and which may terminate in spines1 as in ,xanthidium and ,staurastrum 7,plate ,x41 ,nos4 #h-ai and #bb74 ,a general distribution over the surface is characteristic of the former1 but in ,euastrum the surfaces are very irregular1 and therefore described as 8swellings or inflations40 ,micrasterias has its margin deeply incised into lobes1 which in some have a radiating arrangement2 when the lobes on the margin are small they constitute crenations or dentations4 ,the fronds of ,euastrum binatum are bicrenate on the sides1 as are those of ,desmidium and ,hyalotheca and other species4 ,another variety of margin exists1 known as undulating or wavy1 while the general concavity or convexity of the margins furnish other specific characteristics4 ,pediastre 7,plate ,x41 ,nos4 #bd-bi74--,the members of this family formerly included the ,micrasterias and ,arthrodesmius of ,ehrenberg4 ,from their arrangement of cells in determinate numbers and definite forms1 it has been thought by some observers that they should be removed from the desmids to a special or sub-family4 ,the points of difference consist in the firmness of the outer covering1 in the frequent interruptions on the margin of the cells1 and in the protrusion of 8horns10 or rather a notch more or less deep4 ,it is true that the cells are not made up of two symmetrical halves1 and that they are in aggregation1 which is not 7except in the ,scenedesmus1 a genus that distinctly connects this group with desmids7 in linear series1 but in the form of discoidal fronds4 ,they1 however1 divide into #h1 #af1 or #cb gonidia1 and these move about for some time before the formation of a new frond4 ,it was ,ngeli who first instituted a sub-genus of ,pediastrum1 under the designation of ,anomopedium1 the chief characteristic of which is the absence of bilobed peripheral cells4 ,in ,clastrum the cells are hexangular1 the central ones very regularly so2 in ,sorastrum they are wedge-shaped1 or triangular1 with rounded-off angles4 ,viewed laterally the cells appear oblong4 ,the cells of ,pediastrum are considerably compressed1 so that when aggregated they form a flattened tubular structure2 in figure they are polygonal1 frequently hexagonal1 a shape owing1 in all probability1 to mutual lateral pressure during growth4 ,there is a pervading uniformity in the contents of the cells of the different genera1 which consist of protoplasmic endochrome4 ,at first the colour is pale green1 but it becomes deeper with full maturity1 while the decaying cells are seen to change to a deep reddish-yellow or brown4 ,the protoplasm is also clear and homogeneous1 but in time granules appear1 enlarge1 and multiply in number2 moreover1 each cell presents a single bright green vesicle1 around which are collected clear circular spaces or globules1 recalling those of ,closterium1 and varying in number from two to six or more1 their position not being regulated by the partition wall as in ,palmell1 but by the centre of the entire frond4 ,oil globules are also contained in the cells2 their presence is indicated by the addition of a drop of tincture of iodine4 ,on one occasion ,ngeli saw in ,pediastrum boryanum the endochrome disposed in a radiating manner1 an arrangement which often obtains in algals and in other vegetable cells with a central nucleus4 ,the cells of ,pediastre are always united together in compound fronds1 as represented in ,plate ,x41 ,nos4 #bd and #bi4ef ,the differences pointed out in no way constitute a claim to remove ,pediastre from among ,desmidiace1 certainly not to rank as a distinct species4 ,reproduction of ,desmidiace4--,a true reproductive act is presented by the conjugation or coupling of two fronds1 and by the resulting development of a sporangium and subsequent interchange of the contents of the two cells4 ,at another time self-division is frequently seen to take place in all respects as in the cells of other alg4 ,the proceeding is varied in some essential particulars by the form of the fronds and by other circumstances2 as in fission of ,euastrum1 for instance 7seen in ,plate ,x41 ,nos4 #a1 #b1 and #ab71 when the narrow connecting bands between the two segments of the fronds are rapidly pushed aside by growth and finally divide4 ,two modes of conjugation of fronds are represented in ,plate ,x41 ,nos4 #be and #cc1 in ,closterium and ,penium4 ,the act of conjugation admits of variations in character1 as shown in ,staurastrum and ,microsterias2 the contents of both fronds are discharged into a delicate intermediate sac2 this gradually thickens and produces spines 7,plate ,x41 ,nos4 #h and #ai74 ,in ,didymoprium the separate joints unite by a narrow process pushed out from each other1 often of considerable length1 through which the endochrome of one cell is transferred to the other1 and thus a sporangium is produced within one of two cells1 just as in the conjugat 7,no4 #e74 ,in ,penium ,jennereri the conjugation takes a varied form2 the fronds do not open and gape at the suture1 but couple by small but distinct cylindrical tubes 7,no4 #bg74 ,among those enumerated1 the compressed and deeply constricted cells of ,euastrum offer the more favourable opportunities for studying the manner of their division2 for although the frond is really a single cell1 in all its stages it appears like two1 the segments being always distinct1 from the earliest stage4 ,the segments1 however1 are separated by a connecting link1 which is subsequently converted into two somewhat round hyaline bodies4 ,these bodies gradually increase and acquire colour1 and as they grow the original segments are further divided1 and at length become disconnected1 each taking a new segment to supply the place of that from which it is separated4 ,it is curious to trace the progressive development of the newer portions1 which at first are devoid of all colour2 but as they become larger a faint green tint is observed1 which gradually darkens1 and then assumes a granular appearance4 ,soon the new segments attain their normal size1 while the covering in some species shows the presence of puncta4 ,in ,xanthidium1 ,plate ,x41 ,nos4 #i1 #aj1 and ,staurastrum1 ,nos4 #ae-ah1 the spines and processes make their appearance last1 beginning as mere tubercles1 and then lengthening until they attain their perfect form and size1 armed with set2 but complete separation frequently occurs before growth is fully completed4 ,this singular process is repeated again and again1 so that the older segments are united successively1 as it were1 with many generations4 ,when the cells approach maturity1 molecular movements may be at times noticed in their contents1 precisely similar to what ,agardh and others aptly term 8swarming40 ,meyen describes this granular matter as starch4#eg ,closterium1 early in the spring1 when freshly secured and exposed to light1 presents a wonderful appearance1 these bodies being kept continually in motion at both ends of the frustule by the ciliary action within the cell1 and the whole frond is seen brilliantly glittering with active cilia4 ,when a gleam of stronger light is allowed for a moment to fall on the frond1 the rapid undulations of the cilia produce a series of most delicate prismatic ,newton's rings4 ,the action and distribution of the cilia1 together with the cyclosis of the granular bodies in the frond1 are better seen by the aid of ,wenham's parabola or a good condenser with a central stop4 ,one of the wide angular objectives shows the circulation around the marginal portions of the whole frond4 ,the stream is seen to be running up the more external portion1 internal to which is another stream following a contrary direction2 this action1 confined to the space between the mass of endochrome and the outer portion of the cell-wall1 is seen to pass above or around the space in which cyclosis of the spores is taking place4 ,during the summer of #ahed1 the late ,rev4 ,lord ,sidney ,godolphin ,osborne and myself became much interested in the remarkable family of ,closteria4 ,fig4 #bib is a highly magnified view of ,closterium lunula which ,i drew by the aid of the camera-lucida at the time4 ,there could be no doubt about the ciliary action within the frond3 it was in every way similar to that of the branchi of the muscle1 the same wavy motion1 which gradually became slower as the death of the desmid drew near4 ,this was brought about earlier when the cell was not kept supplied with fresh water4 ,illustration3 ,fig4 #bib4--;,closterium lunula4 ,in diagram ,a1 line b points to a cluster of ovoid bodies2 these are seen at intervals throughout the endochrome within the investing membrane4 ,these bodies are attached to the membrane by small pedicles1 and are occasionally seen in motion about the spot1 from which they eventually break away1 and are carried off1 by the circulating fluid1 to the chambers at the extremities of the frond2 there they join a crowd of similar bodies1 in constant motion within the chambers1 when the specimen is quite fresh4 ,that the action of these free granules or spores is 8,brownian10 as surmised by some writers1 is in my opinion entirely fallacious4 ,it is doubtless in a measure due to the current brought about by the ciliary motion of the more fluid contents of the cell4 ,the circulation1 when made out over the centre of the frond1 for instance at a1 is in appearance of a wholly different nature from that seen at the edges4 ,in the latter the matter circulated is that of granules1 passing each other in distinct lines1 but in opposite directions2 in the circulation as seen at a1 the streams are broad1 tortuous1 of far greater body1 and passing with much less rapidity4 ,to see the centre circulation1 use a ,gillett's illuminator and a #a_/hth or a #a_/ajth immersion2 work the fine adjustment so as to bring the centre of the frond into focus1 then almost lose it by raising the objective2 after this1 with great care1 work the milled head until the darker body of the endochrome is clearly brought out4 ,at ,b is an enlarged sketch of one extremity of the frond4 ,the arrows within the chamber pointing to b denote the direction of a strong current of fluid1 which can be occasionally followed throughout4 ,it is acted upon by cilia at the edges of the chamber1 the greater impetus appearing to come from the centre of the endochrome4 ,the fluid is here acting in positive jets1 that is1 with an almost arterial action2 and according to the strength with which it is propelled at the time1 the loose floating bodies are sent to a greater or less distance from the end of the frustule2 the fluid is thus impelled from a centre1 and kept in activity by the lateral cilia1 that create a rapid current and give a turning motion to the free bodies4 ,the line--a1 in this diagram1 denotes the outline of the membrane which encloses the endochrome2 on both sides cilia can be seen4 ,the circulation exterior to it passes and repasses in opposite directions1 in three or four distinct courses2 these1 when they arrive at--c1 seem to encounter a stream making its way towards an aperture at the apex of the chamber2 then they appear to be driven back again by a stronger force4 ,some1 however1 do occasionally enter the chamber1 but very rarely will one of the bodies escape into the outer current1 and should it do so1 is carried about until it becomes adherent to the side wall of the frond4 ,with regard to the propagation of the ,c4 lunula1 ,i have never seen anything like conjugation2 but ,i have repeatedly seen self-division 7shown at ,d a a74 ,this act is chiefly the work of one half of the frond4 ,having watched for some time1 one half is seen to remain passive1 while the other has a lateral motion from side to side1 as if moving on an axis at the point of juncture2 the motion increases1 is more active1 until at last with a jerk one segment separates itself from the other1 as seen at ,e4 ,it will be noticed that each end of the segment is perfectly closed before separation finally takes place2 there is1 however1 only one perfect chamber1 that belonging to the extremity of the original entire frond4 ,the circulation continues for some time previous to and after subdivision1 in both fronds1 and by almost imperceptible degrees increases in volume4 ,from the end of the endochrome symptoms of elongation of the frond take place1 the semi-lunar form gradually changes1 elongates1 and is more defined1 until it takes the form and outline of the fully-formed frustule at the extremity4 ,the obtuse end--b of the other portion of frond is at the same time elongating and contracting1 and in a few hours from the division of the one segment from the other the appearance of each half is that of a nearly perfect frustule1 the chamber at the new end is complete1 the globular circulation exterior to it becomes affected by the circulation from within the said chamber1 and1 shortly afterwards1 some of the free bodies descend1 and become exposed to the current already going on in the chamber4 ,e is a diagram of one end of a ,c4 didymotocum1 in which the same process was well marked1 and completed while it was under observation4 ,it will appear to most observers that if the continuation of the widely-spread family of ,desmidiace was wholly dependent upon conjugation and subdivision of their frustules1 a process requiring several hours for its completion1 the whole species must have long ago disappeared4 ,it may be presumed then that some other mode of reproduction must prevail4 ,in the fresh-water alg the two more general methods of multiplication are clearly governed by the conditions of the seasons2 the resting-spores securing continuity of life during the winter1 the swarm-spores spreading the plant profusely during the warmer portion of the year1 when rapid growth is possible4 ,i therefore regard the actively swarming bodies seen in continuous motion at the two extreme portions of the frustule of ,closterium lunula as being either oospores or zoospores1 by means of which reproduction takes place4 ,diatomace1 commonly called brittleworts1 ,plate ,,xi41 are chiefly composed of two symmetrical valves1 narrow and wand-like1 navicular1 miniature boat-shaped1 hence their name ,navicula 7little ship74 ,hitherto they have excited the deepest interest among microscopists because of their wonderfully minute structure1 and the difficulty involved in determining their exact nature and formation4 ,each individual diatom has a silicious skeleton1 spoken of as a frustule1 frond1 or cell1 having a rectangular or prismatic form1 which mostly obtains in the whole family1 the angles of the junction of the two united valves being1 as a rule1 acute1 and enclosing a yellowish-brown endochrome4 ,deeply-notched frustules1 like those of the ,desmidiace1 do not occur1 and the production of spines and tubercles so common in that family is rare in the ,diatomace4 ,great variety of outline prevails1 so much so that no rule in this respect can be formulated4 ,the frustules1 however1 are usually composed of two equal and similar halves1 but exceptions to this are found in the ,actinomthe1 ,cocconcid1 and one or two other families4 ,the extremities of some species1 e4g41 ,nitzshia and ,pleurosigma1 are extremely elongated1 forming long1 filiform1 tubular processes2 in ,biddulphia and ,rizoselenia1 short tubular processes from their margins4 ,great variety of outline may prevail in a genus1 so considerable indeed that no accurate definition can be given1 the characteristics shading off through several species until the similarity to an assumed typical form is much diminished1 which may again be modified by accidental circumstances that surround the development of the silicious frustule4 ,it must not be forgotten that the figure is greatly modified or entirely changed by the position of the valves1 whether seen in one position or another1 as already explained in connection with 8,errors of ,interpretation40 ,again1 in the genera ,navicula1 ,pinnularia 7,plate ,,ii41 ,nos4 #cc1 #ch1 and #dj71 and others1 the frustules are in one aspect boat-shaped1 but in the other either oblong with truncated ends1 or prismatic4 ,in the genus ,triceratium 7,plate ,,xi41 ,no4 #aj71 the difference of figure is very remarkable as the front or side view is examined4 ,the sudden change in appearance presented to the eye as the frustule is seen to roll over is rather peculiar4 ,as a rule1 therefore1 we must examine all specimens in every aspect1 to accomplish which very shallow cells should be selected1 say of #a_/ajjth of an inch deep1 and covered with glass #a_/bejth of an inch thick4 ,a good penetrating objective should be used1 and careful illumination obtained4 ,the ,diatomace are perhaps more widely distributed than any other class of infusorial life2 they are found in fresh1 salt1 and brackish water2 many grow attached to other bodies by a stalk 7,plate ,,ii41 ,no4 #cc1 ,licmophora and ,achnanthidium72 while others1 as ,pleurosigma1 ,no4 #dj1 swim about freely4 ,illustration3 ,,plate ,,xi4 ,,diatomace1 ,,recent ,,and ,,fossil4 ,there are a considerable number of ,diatomace which1 when in the young state1 are enclosed in a muco-gelatinous sheath2 while others are attached by stipes or stalk to alg4 ,it would be vain1 in a limited space1 to attempt a description of this numerous and extensive family4 ,ngeli and other observers describe a 8mucilaginous pellicle on the inner layer of the valves10 while1 as ,menghine observes1 8an organic membrane ought to exist both inside and outside1 for the silica could not become solid except by crystallizing or depositing itself on some pre-existing substance40 ,the surface of the frustules is generally very beautifully sculptured1 and the markings assume the appearance of dots 7puncta71 stripes 7stri71 ribs 7cost71 pinnules 7pinn71 of furrows and fine lines2 longitudinal1 transverse1 and radiating bands2 canals or canaliculi2 and of cells or areol2 whilst all present striking varieties and modifications in their form1 character1 and degree of development4 ,again1 the fine lines or stri of many frustules are resolvable into rows of minute dots or perforations1 as occur in ,pleurosigma angulatum1 delineated in the accompanying microphotograph 7,fig4 #bid71 taken for the author purposely to show the markings on this especially selected test diatom4 ,illustration3 ,fig4 #bic4 #a4 ,pleurosigma attenuatum2 #b4 ,pleurosigma angulatum2 #c4 ,pleurosigma ,spencerii4 ,magnified #dej diameters4 ,the nature of the markings on the diatom valves is one of considerable interest1 and attempts have been made to produce them artificially1 but without success4 ,illustration3 ,fig4 #bid4--,pleurosigma angulatum1 magnified #dejj diameters4 7,from a microphotograph taken by ,zeiss with the #b mm4 aprochromatic objective1 #acj numerical aperture1 and projection eye-piece1 ,no4 #d47 ,professor ,max ,schultze devoted a great amount of time to the investigation of the subject1 and has recorded in a voluminous paper#eh the results of his observations4 ,he says1 8,most of the species of the ,diatomace are characterised by the presence on their outer surface of certain differences of relief1 referable either to elevations or to depressions disposed in rows4 ,the opinions of microscopists with respect to the nature of these markings are still somewhat divided4 ,whilst in the larger forms1 and those distinguished by their coarser dots1 the appearance is manifestly due to the existence of thinner spots in the valve1 we cannot so easily explain the cause of the striation or punctation in ,pleurosigma angulatum and similar finely-marked forms40 ,dr4 ,r4 ,zeiss some time ago furnished me with a microphotograph of a frustule magnified #dejj diameters that seemed to confirm ,mr4 ,t4 ,f4 ,smith's view of the structure of these valves4 ,dr4 ,van ,heurck has also made a study of this diatom1 and concludes that the valves consist of two membranes of thin films1 and of an intermediate layer1 the outer being pierced with openings4 ,the outer membrane is1 he believes1 8so delicate that it is easily destroyed by acid or by friction1 and the several processes employed in cleaning and preparing it for microscopical examination4 ,when the openings or apertures of the internal portion are arranged in alternate rows they assume the hexagonal form2 when in straight rows1 the openings are seen to be square or oblong40 ,a description hardly in accord with ,fig4 #bid4 ,movements of ,diatoms4 ,the late ,professor ,smith1 in his 8,synopsis of ,diatoms10 refers to their movements in the following terms3 8,i am constrained to believe that the movements observed in the ,diatomace are due to forces operating within the frustule1 and are probably connected with the endosmotic and exosmotic action of the cells4 ,the fluids which are concerned in these actions must enter1 and be emitted through the minute foramina at the extremities of the silicious valves40 ,schultze's researches1 which were made at a later date1 carried this debatable question somewhat further4 ,he is of opinion 8that a sarcode 7protoplasmic7 substance envelops the external surface of the diatoms1 and its movements are due to this agent exclusively40 ,his investigations were mainly confined to ,p4 angulatum1 and to the larger ,p4 attenuatum 7,fig4 #bic1 #a and #b71 as the transverse markings on the frustule do not impede to so great an extent the observation of what is going on within4 ,the living specimen of ,p4 angulatum under the microscope usually has its broad side turned to view1 with one long curved 8raphe0 uppermost1 and the other in contact with the glass cover 7,fig4 #bic74 ,within the frustule the yellow colouring matter1 8endochrome10 fills the cavity more or less completely4 ,in the broader part of the frustule these bands of endochrome describe one or two complicated windings4 ,it is only possible in those specimens in which the bands are narrow to properly trace their foldings1 and determine their number4 ,the next objects which strike the eye on examining a freshly-gathered ,pleurosigma are numerous highly refractive oil-globules4 ,these are not1 however1 all in the same place1 and one globule appears nearer the observer than the other2 their relative position is best seen when a view of the narrow side of the frustule can be obtained1 so that one raphe is to the left and the other to the right4 ,the blue-black colour which is assumed by these globules after treating with acid demonstrates their oleaginous nature4 ,the middle of the cavity of the frustule is occupied1 in the larger navicula1 by two large oil-globules 7seen in the diagrammatic ,fig4 #bie71 and by a colourless finely granular mass1 whose position in the body is not so clearly seen in the flat view as in the side view4 ,besides the central mass1 the conical cavities at either end of the frustule are seen to enclose granular substance1 and two linear extensions from each of three masses are developed1 closely underlying the raph4 ,in the side view1 therefore1 they appear attached to the right and left edges of the interior of the frustule4 ,this colourless granular substance carries in its centre1 near the middle part of the diatom1 an imperfectly developed nucleus which is not very easy to see1 but may be demonstrated by the application of an acid4 ,the colourless substance is protoplasm1 and encloses numerous small refractive particles2 this1 on adding a drop of a one per cent4 solution of osmic acid1 is coloured blue-black1 and proves to be fat4 ,it is1 however1 exceedingly difficult to determine the exact limitations of the protoplasm1 on account of the highly refractive character of the silicious skeleton1 and the obstruction to the light presented by the endochrome4 ,at a short distance the protoplasm reappears1 contracted into a considerable mass1 within the terminal ends of the frustule4 ,schultze observed in this part of the protoplasm a rapid molecular movement1 8cyclosis10 such as occurs in ,closterium1 and also a current of the granules of the protoplasm along the raphe4 8,pleurosigma angulatum #8crawls1' as do all diatoms possessing a raphe1 along this line of suture4 ,to crawl along1 it must have a fixed support40 8,there is obviously10 adds ,schultze1 8but one explanation2 it is clear that there must be a band of protoplasm lying along the raphe1 which causes the particles of colouring matter to adhere1 and gives rise to a gliding movement4 ,for there is but one phenomenon which can be compared with the gliding motion of foreign bodies on the ,diatomace1 and that is1 the clinging to and casting off of particles by the pseudopodia of the rhizopod1 as observed1 for instance1 on placing a living ,gromia or ,miliolina in still water with finely-powdered carmine4 ,the nature of the adhesion and of the motion is in both cases the same4 ,and since1 with diatoms as unicellular organisms1 protoplasm forms a large part of the cell 7in many cases two distinctly moving protoplasms71 this implies that the external movements are referable to the movements of the protoplasm40 ,it is quite evident to those who have studied the movements of diatoms that they are surrounded by a sarcode structure of a more pellucid character than that of ,amba4 ,six years before ,schultze's observations were published1 ,i wrote in a third edition of my book1 page #cjg1 8,the act of progression favours the notion of contractile tentacular filaments--pseudopodia--as the organs of locomotion and prehension40 ,since my former observations on the movements of diatoms1 ,i have given much attention to two forms1 ,p4 angulatum and ,pinnularia4 ,the powers used were ,hartnack's ,no4 #h1 and ,gunlack's #a_/af-;inch immersion2 ,gillett's condenser illumination1 with lamp flame edge turned to mirror and bull's-eye lens2 a perforated slide with a square of thin glass #jjf cemented to it1 and a cover-glass of #jje4 ,so far as ,i could satisfy myself1 no terminal space1 as in the ,closteria1 could be seen1 otherwise the course of the gemmules is as freely traced as in that form4 ,they are more minute than the ,closterium lunula granules1 more steadily or slowly seen to pass up and down one half the frustule towards the extremity1 one half of the current seeming to turn round upon its axis and descending towards the other4 ,the granules were thickly scattered at the apex1 but gradually became fewer1 and the ascending and descending current tapered away towards the central nodule1 which became more filled up or closed in4 ,illustration3 ,fig4 #bie4--,outline sketches of ,pinnulari1 showing vesicles4 ,illustration3 ,fig4 #bif4--;,gomphonema constrictum4 7,from a microphotograph47 ,this beautiful sight was not confined to one frustule1 but was exhibited in all that were in a healthy condition4 ,i examined several1 and watched them for a long time4 ,the phenomenon described depends much upon the healthy condition of the frustule at the time2 as the movements of the diatoms became sluggish1 the circulation gradually slackens and then ceases altogether4 ,i also saw a somewhat similar action in the more active specimens of ,p4 hippocampus and ,navicula cuspidata1 but the coarser markings and thickness of the wall of these diatoms seemed to place greater difficulties in the way of observation than the finer valves of the ,p4 angulatum4 ,one thing ,i believe is certain1 that the circulation described is precisely similar to that seen in the ,closteria1 or1 on a much larger scale1 in ,chara and the leaf of the ,anacharis1 bearing in mind also that in the ,closterium the cell is divided by a transverse suture1 and in ,p4 angulatum by a longitudinal one 7,plate ,,ii41 ,nos4 #ch-dj74 ,about the same time some very lively specimens of the ,pinnulari were sent to me1 and the movements of these frustules were more closely observed4 ,one or two of the more active would attack a body relatively larger than itself1 it would also force its way into a mass of granular matter1 and then recede from it with a jerky motion4 ,in more than one instance a cell of ,palmogla was seized and carried away by the ,pinnularia1 the former at the time being actively engaged in the process of cell division4 ,other diatoms present among my specimens were also in an active condition1 and the circulation of granular matter in all was distinctly visible4 ,in the ,pinnulari two large colourless vesicles were seen on either side of the median nodule1 each having a central nucleus1 as represented in the accompanying sketch1 made while under observation in two positions4 ,the central portion of each frustule was closely packed with a rich yellowish-brown coloured endochrome1 interspersed with a few fat globules4 ,the phenomenon of cyclosis was not seen in any of these diatoms1 but ,i have satisfied myself1 by staining1 of the presence of a delicately fine external protoplasmic covering in many diatoms4 ,that their movements resemble the gliding movements exhibited by the ,amba can scarcely be doubted4 ,numerous forms of ,diatomace are found growing on or attached to water-plants or pieces of detached stalks1 which1 although generally simple1 are sometimes compound1 dividing and subdividing in a beautiful ramous manner4 ,pinnulari1 ,nitzschia1 c41 are seen adherent by one extremity1 about which they turn or bend themselves as on a hinge4 ,by the process of cell-division1 groups of ,synedr become attached by a point1 in a fan-like form4 ,the fan-like collection of frustules is said to be flabellate1 or radiate4 ,in ,licmophora1 ,achnanthes and other species 7,plate ,,ii41 ,nos4 #bi-cc7 the double condition of union of frustules and of attachment by a pedicle are illustrated4 ,when a stipe branches it does so normally in a dichotomous manner1 each new individual being produced by a secondary pedicle4 ,this regular dichotomy is seen in several genera3 ,cocconema and ,gomphonema1 the latter more perfectly in ,fig4 #bif1 from a microphotograph1 in which a branching1 or rather longitudinal1 rupture of the pedicle takes place at intervals1 and the entire organism presents a more or less complete flabella1 or fan-like cluster1 on the summit of the branches1 and imperfect or single frustules irregularly scattered throughout the whole length of the pedicle4 ,isthmia enervis 7,fig4 #big74--,the unicellular frustule of this species is extremely difficult to define1 owing to the large areolations of the valves2 it has a remarkable internal structure4 ,the olive-brown cell contents are found collected1 for the most part1 into a central mass1 from which radiating1 branched1 granular threads extend to and unite with the periphery4 ,when viewed by a magnifying power of #fjj or #gjj diameters1 these prolongations are seen to be composed of aggregations of ovate or spindle-shaped corpuscles1 held together by protoplasmic matter4 ,these bodies are sometimes quiescent1 but more often travel slowly to and fro from the central mass4 ,the general aspect under these conditions so nearly corresponds to the characteristic circulation in the frustules of unicellular plants and of certain rhizopoda1 that it is difficult to realise that the object when under examination is an elegant marine diatom4 ,illustration3 ,fig4 #big4--;,isthmia enervis4 ,microphotograph4 ,there is a large section of diatoms in which the frustules are diffused throughout a muco-gelatinous envelope in a definite manner4 ,histologically this is homologous with the pedicles and connecting nodules thrown out during the act of self-division1 and in some species 7,cocconeis1 ,fragillaria1 c47 it often persists after that act is complete4 ,diatomace1 ,recent and ,fossil4 ,illustration3 ,fig4 #bih4--;,fossil ,diatoms from ,springfield 7,barbadoes74 #a1 ,achnanthidium2 #b1 ,diatoma vulgare1 side view and front view2 #c1 ,biddulphia2 #d1 #e1 #f1 #g1 ,amphitetias antediluviana1 front view1 with globular and oval forms2 ,gomphonema elongatum and capitatum4 ,fossilised ,diatomace4--,dr4 ,gregory was of opinion that a large number of diatoms separated into species are only transition forms1 and more extended observations have proved that form and outline are not always to be trusted in this matter4 ,species-making is a modern invention1 and can hardly apply to the indestructible fossilised forms of the frustules of ,diatomace1 with their beautiful sculpturings and geometrical constructions1 which have not been materially changed since they were first deposited4 ,startling and almost incredible as the assertion may appear to some1 it is none the less a fact established beyond all question1 that some of the most gigantic mountain-ranges1 as the mighty ,andes1 towering into space #be1bej feet above the level of the sea1 their base occupying vast areas of land2 as also massive limestone rocks2 the sand that covers boundless deserts2 and the soil of many wide-extended plains1 are each and all principally composed of ,diatomace4 ,and1 as ,dr4 ,buckland once observed3 8,the remains of such minute animals have added much more to the mass of materials which compose the exterior crust of the globe than the bones of elephants1 hippopotami1 and whales40 ,in #ahda the late ,mr4 ,sollitt1 of ,hull1 discovered the beautiful longitudinal and transverse stri 7markings7 on the ,pleurosigma hippocampus4 ,a curved graceful line runs down the shell1 in the centre of which is an expanded oval opening4 ,near to the central opening the dots elongate crossways1 presenting the appearance of small short bands4 ,in the vicinity of this town many interesting varieties of ,diatomace have been found1 the beauty of the varied forms of which are constantly under investigation2 at the same time some of them are highly useful1 as forming that class of test objects which are better calculated than many others for determining the excellence and powers of certain objectives4 ,mr4 ,sollitt carefully measured the markings on some of the frustules and found they ranged between the #a_/cjjjjth and #a_/acjjjjth of an inch2 the ,pleurosigma strigilis having the strongest markings1 and the ,pleurosigma acus the finest4 ,mr4 ,j4 ,d4 ,sollitt not only first proposed their use1 but he also furnished the measurements of the lines of the several members of this family1 as follows3-- ,amphipleura pellucida1 or ,acus1 #acj1jjj in the inch1 cross lines4 sigmoidea1 #gj1jjj in the inch4 ,navicula rhomboides1 #aaa1jjj in the inch1 cross lines4 ,pleurosigma fasciola1 fine shell1 #hf1jjj in the inch1 cross lines4 strong shell1 #fd1jjj in the inch1 cross lines4 strigosum1 #gb1jjj in the inch1 diagonal lines4 angulatum1 #ea1jjj in the inch1 diagonal lines4 quadratum1 #ej1jjj in the inch1 diagonal lines4 ,spencerii1 #ej1jjj in the inch1 cross lines4 attenuatum1 #db1jjj in the inch1 cross lines4 ,balticum1 #dj1jjj in the inch1 cross lines4 formosum1 #cb1jjj in the inch1 diagonal lines4 strigilis1 #cj1jjj in the inch1 cross lines4 ,illustration3 ,,plate ,,xii4 ,,micro-,,photograph ,,of ,,test ,,diatoms4 ,lichenace4 ,the lichens are a family of autonomous plants1 an intermediary group of algals or cellular cryptogams1 drawing their nourishment from the air through their whole surface medium1 and propagating by spores usually enclosed in asci1 and always having green gonidia in their thallus4 ,their gonidia1 bright coloured globular cells1 form layers under the cortical covering of the thallus1 and generally develop in the form of incrustations1 which cover stones1 wood1 and the bark of trees1 or penetrate into the lamell of the epidermis of woody plants4 ,the gonidia of lichens partake of both the character of vegetative and reproductive cells4 ,the thallus in the fructicose group attaches itself by a narrow base1 growing in the form of a miniature shrub4 ,another group is met with in a slimy condition--the gelatinous lichens4 ,these species1 for the most part1 furnished dyes before the discovery of the coal-tar dyes4 ,in many of the ,palmella cruenta1 commonly found growing on the walls and roofs of houses1 a colourless acid liquid is found1 which1 on being treated with alkali1 produces a bright yellow colour2 and another1 ,avernia vulpina1 furnishes a brown dye2 the ,rocella fuciformis and ,r4 tinctoria yield the purple dye substance known as orchil1 or archil1 from which the useful blue paper of the chemist for testing acidity is manufactured4 ,usnic acid1 combined with green and yellow resins1 seems to be more or less a constituent of many lichens4 ,a vertical section of ,palmella stellata is given in ,plate ,i41 ,no4 #bf1 in which the emission of the ripe spores of the lichens is seen to be not unlike that which takes place in some of the fungi1 ,peziz1 ,sphri1 c4 ,if a portion of the thallus be moistened and placed in a common phial1 with the apotheca turned toward one side1 in a few hours the opposite surface of the glass will be found covered with patches of spores1 easily perceptible by their colour2 or if placed on a moistened surface1 and one of the usual glass slips laid over it1 the latter will be covered in a short time4 ,as to the powers of dissemination of these lowly organised plants1 an observation led to the conclusion that the gonidia of lichens have greater powers in this direction than was formerly supposed4 ,it is found that by placing a clean sheet of glass in the open air during a fall of snow1 and receiving the melting water in a tube or bottle1 quantities of what has been looked upon as a 8unicellular plant0 can be taken1 the cells of which may be kept in a dormant condition for a long time during cold weather1 but upon the return of spring warmth and moisture they begin to increase1 by a process of subdivision1 into two1 four or eight portions2 these soon assume a rounded form1 and burst the parent cell-wall open2 these secondary cells then begin to divide and subdivide again1 and the process may go on without much variation for a long time4 ,the phenomena described may be watched by taking a portion of the bark of a tree on which ,chlorococcus has been deposited1 and placing it under a glass to keep it in a moderately moist atmosphere2 the only difference being a change in colour1 caused by the growth of the fibres1 as may be seen on microscopical examination4 8,and this10 says ,dr4 ,hicks1 who first observed this phenomenon in plant life1 8is an instructive point1 because it will be found that the colour varies notably according to the lichen prevalent in its neighbourhood40#ei ,he believes there can be no doubt that what has been called ,chlorococcus is nothing more than the gonidia of a lichen2 and that under suitable conditions1 chiefly drought and warmth1 the gonidium often throws out from its external envelope a small fibre1 which1 adhering and branching1 forms a 8soridium40 8,the soridia remain dormant for a very long time1 and do not develop into thalli unless in a favourable situation1 in some cases it may be for years4 ,it will be perceived that the soridium contains all the elements of a thallus in miniature2 in fact1 a thallus does frequently arise from one alone1 and the fibres of neighbouring soridia interlace2 thus a thallus is matured very rapidly4 ,this is one of the causes of the variation of appearance so common in many species of lichens1 more readily seen towards the centre of the parent thallus4 ,when the gonidia remain attached to the parent thallus1 the circumstances are1 of course1 more favourable1 and they develop into secondary thalli1 attached more or less to the older one1 which1 in many instances1 decays beneath them4 ,this process being continued year after year gives an apparent thickness and spongy appearance to the lichen1 and is the principal cause of the various modifications in the external aspect of the lichens which caused them formerly to be misunderstood and wrongly classified40#fj ,the erratic lichens are found among the genus ,palmella1 some of which grow among boulders of the primary and metamorphic formations1 curled up into a ball1 and only fixed to their matrix by a slender thread4 ,the globular ,lecanora esculenta will at times suddenly cover large tracts of country in ,persia and ,tartary1 where it is eaten by the cattle4 ,during a scarcity of food a shower of these lichens1 ,mr4 ,berkeley tells us1 fell at ,erzeroum1 and saved the cattle from starvation4#fa ,another group of the ,palmella1 or ,peltigeri1 so named from the target-like discs on their surface1 spread their foliaceous fronds over the ground1 and as the fruit is marginal1 it gives the thallus a digitate appearance4 ,these are often spotted over by a little red fungus4 ,the ,lecidinei contains numerous species of the most varied habits1 and always crustaceous1 and so closely adherent to the hard rocks and stones on which they grow1 that at length they disintegrate them4 ,from this low species a higher form arises1 with erect branching stems1 and clothed with foliaceous1 brightly-coloured scales4 ,the ,coccocarpei is mainly distinguished by having orbicular discs entirely deprived of the cortical envelope called an excipulum4 ,the discs spring at once from the medullary stratum1 and contain asci and sporidia similar to those of the minute fungi ,sphri4 ,some of the lichens are themselves parasitic1 and begin existence under the thick skin of the leaves of tropical plants1 and spread encrusting thallus over their surface1 the excipulum and perithecia being black2 but in most cases these are beautifully sculptured1 and are interesting objects for the microscope4 ,indeed1 the sphere-bearing lichens1 with upright stems bearing globular fruit at the extremity of their branches1 are at first indicated by a swelling1 but in time the outer layer bursts and exposes sporidia1 which are beautiful objects under the microscope on account of their spherical form and more or less deep blue tint4 ,humble and lowly as lichens may appear to be1 they have been divided into fifty-eight or more genera and #b1ejj species4 ,the brothers ,tulasne1 ,de ,bary1 the ,rev4 ,mr4 ,berkeley1 and others1 devoted great attention to the peculiarities of their structure and natural history4 ,hepatic4--,an intermediary group of much interest to the microscopist are the ,hepatic 7liverworts74 ,these are found growing on damp rocks in the neighbourhood of springs and dripping banks4 ,the scale-moss1 the ,marchantia polymorphia 7,fig4 #bii71 may be taken as typical of this little group1 with its gemmiparous conceptacles and lobed receptacles1 bearing archegones on transparent glass-like fruit stalks1 carrying on their summits either round shield-like discs or radiating bodies with a striking resemblance to a wheel without its tyre4 ,illustration3 ,fig4 #bii4--,marchantia polymorphia4 ,the liverworts are closely allied to the mosses1 and as much difficulty was experienced in dividing the two1 ,hooker placed the whole under one genus1 the ,jungermannia4 ,more recently1 however1 they have been divided into those with a stem and leaves confluent in a frond1 ,marchantia2 those with stem and leaves distinct1 ,jungermannia2 and those with a solitary capsule1 filiform1 bivalved1 stalked1 with a free central placentation1 ,anthocotace4 ,some botanists have further divided them1 but they are all extensively propagated by gemm4 ,the fronds carry the male organs1 or antherids1 and the disc1 in the first instance1 bears the female organs1 or archegones1 and after a time gives place to the sporanges1 or spore cases4 ,it is these bodies which are of so much interest to microscopists2 if the plant is brought into a warm room1 they suddenly burst open with some violence the moment a drop of water is applied to them1 and the sporanges are dispersed in a small cloud of brownish dust4 ,if this dust is examined under a medium power1 it is seen to consist of a number of chain-like bodies1 somewhat like the spring of a small watch2 and if the process of bursting be closely watched1 these minute springs will be found twisting and curling about in every direction4 ,the structure of the frond itself will be seen to be interesting when cut in the vertical direction and placed under the microscope4 ,illustration3 ,fig4 #cjj4--;,gemmiparous conceptacle of ,marchantia polymorphia1 expanding and rising from the surface of a frond4 ,in the interior are seen gopidial gemm already detached by the splitting of the epiderm4 ,the gemm of ,marchantia polymorphia are produced in elegant membranous cups1 with a toothed margin growing on the upper surface of the frond1 especially in very damp courtyards between the stones1 or near running water1 where its lobed fronds are found covering extensive tracts of moist soil4 ,at the period of fructification the fronds send up stalks1 which carry at their summit round shield-like radiating discs1 which bear upon their surface a number of little open basket-shaped 8conceptacles40 ,these again expand into singularly graceful cups 7as in ,fig4 #cjj71 and are found in all stages of development4 ,when mature1 the basket contains a number of little green round or oblong discs1 each composed of two or more layers of cells2 the wall itself being surmounted by a glistening fringe of teeth1 whose edges are themselves regularly fringed with minute outgrowths4 ,the cup seems to be formed by a development of the superior epidermis1 which is raised up1 and finally bursts and spreads out1 laying bare the seeds4 ,the archegones of ,marchantia are very curious bodies1 while the elater and spores are even still more so4 ,these are elongated cells1 each containing a double spiral fibre coiled up in the interior4 ,it is the elasticity of this which tears apart the cell-membrane1 and sends forth the spores with a jerk1 and thus assists in their dispersion4 ,marchantia is the type of the malloid ,hepatic4 ,musci1 ,bryophyta4 ,mosses are a beautiful class of non-vascular cryptogams4 ,linnus called them servi1 servants or workmen1 as they seem to labour to produce vegetation in places where soil is not already formed4 ,the ,bryophyta form three natural divisions3 the ,bryin1 or true mosses2 the ,sphagnace1 or peat-mosses2 and the ,hepatic1 or liverworts4 ,the two first are commonly united4 ,in these the sexual organs consist of antheridia and archegonia1 but they are of simpler structure than will be found in ferns2 and the first generation from the spore is asexual4 ,illustration3 ,fig4 #cja4--,screw-moss4 ,the common or wall screw-moss 7,fig4 #cja7 grows almost everywhere1 and if examined closely1 is seen to have springing from its base numerous very slender stems1 each terminating in a dark brown case1 which encloses antheroids4 ,if a patch of the moss is gathered when in this state1 and the green part of the base is put into water1 the threads of the fringe will uncoil and disentangle themselves in a most curious and beautiful manner2 from this circumstance the plant takes its popular name of screw-moss4 ,the leaf usually consists of either a single or a double layer of cells1 having flattened sides1 by which they adhere one to another4 ,the leaf-cells 7,fig4 #cjb7 of the ,sphagnum or bog-moss exhibit a curious departure from the ordinary type2 they are large1 polygonal1 and elongated1 and contain spiral fibres loosely coiled in their interior4 ,the young leaf does not differ from the older2 both are evolved by a gradual process of differentiation4 ,illustration3 ,fig4 #cjb4--,section of leaf of ,sphagnum moss1 showing large cells of spiral fibres and connecting apertures4 ,mosses1 like liverworts1 possess both antheridia and pistillida1 which are engaged in the process of fructification4 ,the fertilized cell becomes gradually developed into a conical body elevated upon a footstalk1 the walls of the flask-shaped body carrying the higher part upwards as a calyptra or hood upon its summit1 while the lower part remains to form a kind of collar round the base4 ,these spore-capsules are closed on their summit by opercula or lids1 and their mouths when laid open are surrounded by a beautiful toothed fringe1 termed the peristome4 ,this fringe is shown in ,fig4 #cjc1 in the centre of a capsule of ,funaria1 with its peristome in situ4 ,the fringes of teeth are variously constructed1 and are of great service in discriminating the genera4 ,in ,neckera antipyretica the peristome is double1 the inner being composed of teeth united by cross bars1 forming a very pretty trellis4 ,the seed spores are contained in the upper part of the capsule1 where they are clustered round the central pillar1 termed the columella2 and at the time of maturity1 the interior of the capsule is almost entirely occupied by spores4 ,illustration3 ,fig4 #cjc4--,mouth of ,capsule of ,funaria1 showing ,peristome4 ,illustration3 ,fig4 #cjd4--;,hair-moss in ,fruit4 ,the undulating hair-moss1 ,polytrichum undulatum 7,fig4 #cjd71 is found on moist1 shady banks of pools and rivulets4 ,the seed-vessel has a curious shaggy cap2 but in its construction it is very similar to that of the screw-moss1 except that the fringe around its opening is not twisted4 ,the reproductive organs of mosses are of two kinds2 the capsule containing minute spores1 archegonia1 and the antheridia1 or male efflorescence4 ,the capsule1 theca1 or sporangium1 is lateral or terminal1 sessile1 or on a fruit stalk 7seta7 of various shapes1 indehiscent1 or bursting by four valves at the sides1 or more commonly by a deciduous cup1 operculum4 ,when this falls the mouth of the capsule becomes exposed4 ,the rim is crowned with tooth-like or cilia-like appendages in sets of four or multiples of that number--peristome4 ,these are often brightly coloured and hydroscopic4 ,by simply breathing upon them they suddenly fly open1 and are endowed with motion1 that is1 if they contain spores4 ,the spores on germination produce a green confervoid-like mass of threads1 from which the young plant arises4 ,the ,sphagnace1 or 8bog mosses10 have been separated from true mosses from the marked differences they present4 ,the stem is more widely differentiated1 and throughout its structure a rapid passage of fluid takes place4 ,it has the power of absorbing moisture from the atmosphere1 so that if a plant be placed dry in a glass of water with its rosette of leaves hanging over the edge1 it acts like a syphon1 and the water will drop from it until the glass is emptied4 ,as may be supposed1 the leaf is composed of large open cells1 and it absorbs more water than the root4 ,the antherids or male organs of ,sphagnace resemble those of liverworts1 rather than those of mosses1 both in form and arrangement2 they are grouped in 8catkins0 at the tips of the lateral branches1 each of the imbricated perigonal leaves enclosing a single globose antherid on a slender foot-stalk1 and surrounded by long branched paraphyses of cobweb-like tenuity4 ,the female organs1 or archegones1 do not differ materially in structure from those of mosses2 they are grouped together in a sheath of deep green leaves at the end of the shorter lateral branchlets at the side of the rosette or terminal crown of leaves4 ,the sporange is very uniform in all the species1 and the spores are in groups of fours1 as in mosses1 around a hemispherical columella4 ,these plants grow so rapidly that they soon cover a pool with thin matted bundles of branches1 and as they decay they fall to the bottom1 and become the foundation of the future bog or peat moss4 ,felices4--,of all the spore-bearing families the ferns are the more universally known4 ,they constitute an exceedingly numerous genera and species1 and vary from low herbaceous plants of an inch in height to that of tree ferns1 which attain a height of fifty or more feet1 terminating in a graceful coronet of fronds or leaves4 ,of whatever size a fern may be1 its spores are1 for the most part1 microscopic1 produced within the sporangium by cell division1 and are therefore free and variously shaped4 ,the true mode of development of ferns from their spores was that furnished by ,ngeli1 who announced the existence of antheridia4 ,on the spore starting into life it sends out from the cell-wall of its outer coat a white tubular projection1 or root fibre 7,fig4 #cje1 ,a1 ,b1 and ,c71 which passes through the cell-wall of its outer coat4 ,this attracts sufficient moisture to burst open the outer1 and then it begins to increase by the subdivision of its cells1 until the primary green prothallus ,d is formed4 ,this falls to the ground1 and1 being furnished on its under side with thread-like fibres1 fixes itself to the earth1 and thus is developed the rhizome1 or root of the future plant4 ,in each of the antheridia1 which are numerous1 a cell is formed1 chiefly filled with albuminous matter and free spores1 each having attached a flat ribbon-like filament1 or stermatoid1 curled in a spiral manner4 ,these are ultimately set free by the rupture of the cell-wall1 and commence revolving rapidly by the agency of the whip-like appendage at the larger end4 ,illustration3 ,fig4 #cje4--;,development of the ,globular ,antheridium and ,spermatoids of ,pteris serrulata4 ,a4 ,spores2 ,b1 ,c4 ,early stages of development2 ,d4 ,prothallus with radial fibres2 a1 a and a1 b are stermatoids2 and h1 h4 ,enclosed antheridia4 ,the sporangia1 or spore-cases1 are1 for the most part1 globular in form1 and are nearly or quite surrounded by a strong elastic ring1 which in some cases is continued to form a stalk4 ,when the spores are ripe1 this ring1 by its elastic force1 tears open the sporangia and gives exit to a quantity of microscopic filaments1 curled in corkscrew-like fashion 7,figs4 #cje and #cjg74 ,the ring assumes various forms2 in one group it passes vertically up the back of the sporangium1 and is continued to a point termed the stomata1 where the horizontal bursting takes place4 ,this form is seen in ,fig4 #cjf1 a1 b4 ,in other groups it is vertical1 as in c1 c2 in others transverse1 as in d2 or apical1 as at e2 and in a few instances it is obsolete1 as in f4 ,these are the true ferns1 and their systematic arrangement is chiefly founded on the peculiarity of the sori and sporangia1 characters which become quite intelligible by the aid of the microscope4 ,illustration3 ,fig4 #cjf4--,sporangia of ,polypodiaceous ,ferns4 a1 b4 ,polypodiace2 c4 ,cyantheine2 d4 ,gleichenine2 e4 ,schizeine2 f4 ,osmundine4 ,illustration3 ,fig4 #cjg4--,spores of ,deparia prolifera4 ,the beautiful ringed sporangium of the fern 7,fig4 #cjg7 when ruptured gives exit to the dust-like spores2 these1 examined under a moderate power1 are seen to be sub-globose and pyramidal1 the outer coat or exospore being a coloured hyaline cell with nuclei similar to the spores of mosses1 but in which chlorophyll soon begins to form1 and from this little green embryonic growth the organs of reproduction are formed4 ,in all ferns the pistillidia or archegonia are analogous to the ovules or nascent seeds of flowering plants1 and contain1 like them1 a germinal vesicle1 which becomes fertilized through the agency of the spiral filaments1 and then gradually develops into an embryo plant possessing a terminal bud4 ,this bud begins at once to unfold and push out leaves with a circinate vernation1 of a very simple form at first1 and growing up beneath the prothallium1 coming out at the notch2 single fibrous roots are at the same time sent down into the earth1 the delicate expanded prothallium withers away1 and the foundation of the perfect fern plant is laid4 ,when a fern acquires a considerable stem1 as in a tree fern1 it consists of cellular tissue and an external cortical portion forming fibro-vascular bundles1 scalariform ducts1 and woody fibre4 ,fig4 #cjh1 b1 shows an oblique section of the footstalk of a fern leaf with its bundle of scalariform ducts4 ,these observations on ferns have acquired increased interest from subsequent investigations made on the allied ,cryptogams1 and on the processes occurring in the impregnation of the ,conifers4 ,not only have later researches furnished a satisfactory interpretation of the archegonia and antheridia of the mosses and liverworts1 but they have made known and co-ordinated the existence of analogous phenomena in the ,equisetace1 ,lycopodiace1 and ,rhizocarpe1 and prove1 moreover1 that the bodies described by ,dr4 ,brown in the ,conifers under the name of 8corpuscles0 are analogous to the archegonia of the ,cryptogams2 so that a link is hereby formed between these groups and the higher flowering plants4 ,illustration3 ,fig4 #cjh4--;a4 ,vertical section of ,fern-root1 showing spiral tissue and cells filled with granular bodies2 b4 ,section of ,footstalk4 ,equisetace4--,the development of ,horse-tails 7,fig4 #cji71 the name by which they are commonly known1 corresponds in some respects with that of ferns4 ,they comprise a little group1 and the whole of their structure is composed in an extraordinary degree by silex1 so that even when the organic portion has been destroyed by prolonged maceration in strong acid1 a consistent skeleton still remains4 ,it is this flinty material that constitutes their chief interest for microscopists4 ,a portion of their silicious particles is distributed in two lines1 arranged parallel to the axis of the plant1 others are grouped into oval forms1 and connected by a chain as in a necklace4 ,the form and arrangement of the crystals are better seen under polarised light4 ,plate ,,viii41 ,no4 #agj1 a portion of the epidermis1 forms an extremely beautiful object4 ,sir ,david ,brewster pointed out that each silicious particle has a regular axis of double refraction4 ,what is usually said to be the fructification of the ,equisetace forms a cone or spike-like extremity to the top of the stem 7,fig4 #cji71 the whole resembling a series of spike-like branches 7the real stem being a horizontal rhizome71 and a cluster of shield-like discs1 each of which carries a circle of sporanges that open by longitudinal slits to set free the spores which are attached to it in two pairs of elastic filaments 7shown in ,fig4 #bia1 ,f1 ,g71 elaters2 these are at first coiled up around the spore in the manner represented at ,g1 but on their liberation they extend themselves as shown at ,f4 ,the slightest moisture will close them up again1 and their purpose having been served in the distribution of the spores1 they are no longer required4 ,if a number of spores be spread out on a glass-slip under the microscope and1 while watching1 a bystander breathes upon them1 they immediately respond1 are set in motion1 presenting a curious appearance1 but as soon as the hydroscopic effect has passed off they return to their previous condition4 ,these spores can be mounted in a cell with a movable cover1 and made to exhibit the same effect over and over again4 ,illustration3 ,fig4 #cji4--;,equisetum giganticum4 a4 ,fragment of stem showing mode of branching out2 b4 ,cone or spike of fructification2 c4 ,scale detached from cone2 d4 ,spore with elastic filaments2 e4 ,vertical section of stem2 f4 ,transverse section showing hexagonal cells4 ,the vascular tissue of the ,equisetace 7,fig4 #cji1 e1 f7 shows them to be of a higher grade than the ferns4 ,more recently discovered ,horse-tails1 of ,brazil1 grow to a gigantic size1 but even these are comparatively small when compared with the ,calamites1 and other fossil ,equisetace of the coal measures and new red sandstone4 ,they all require a calcareous flinty soil for growth4 ,a spring water-course making its way to the sea1 as in the ,chines of the ,isle of ,wight1 is very favourable1 the author having gathered them more than once in ,bramble ,chine4 ,nearly allied to ferns is a little group of small aquatic plants1 the ,rhizocarpe 7pepperworts71 which either float on the water or creep along shallow bottoms4 ,these are chiefly curious from having two kinds of spores produced from separate sporanges2 smaller and larger 8microspores0 undergoing progressive sub-division without the formation of a distinct prothallium2 each cell giving origin to an antherozoid1 a generative process said to belong exclusively to flowering plants1 corresponding indeed to the pollen grains of higher plants4 ,structure of ,phanerogami or ,flowering ,plants4 ,the two great divisions of the vegetable kingdom are known as ,cryptogamia and ,phanerogamia4 ,it does not follow1 however1 that there is any abrupt break between the two1 as will appear from the context4 ,although it is customary to speak of the flowering plants as a higher grade of life1 yet there is an intermediary class of ,phanerogami in which the conspicuous parts of the generative system partake of a condition closely resembling those of the higher ,cryptogami1 observed in ,gymnosperms1 ,conifer1 and ,cycad4 ,so it may be said the distinctive character of the former is that of reproduction by seeds rather than flowers4 ,the progress of botanical science during the latter half of the ,victorian reign has been quite as remarkable as that of histology2 while the comparative physiology and morphology of plants have perhaps advanced even more rapidly because the ground was newer4 ,the consequence is that the specialisation of botanical science has been brought about con-currently with a more comprehensive nomenclature4 ,the chief cause in this instance of modern specialisation is utility4 8,if we look at the great groups of plants from a broad point of view1 it will be seen that the fungi and the phanerogams occupy public attention on other grounds than do the alg1 mosses and ferns4 ,alg are especially a physiologist's group1 employed in questions on nutrition1 reproduction1 and cell division and growth4 ,the ,bryophyta and ,pteridophyta1 are1 on the other hand1 the domain of the morphologist concerned with such questions as the alternations of generations and the evolution of the higher plants4 8,fungi and phanerogams1 while equally or even more employed by specialists in morphology and physiology1 appeal widely to general interest1 and evidently so on the ground of utility4 ,without saying that this enhances the importance of either group1 it certainly attracts scientific attention to them4 ,however1 the histology of the minute cell1 in addition to its importance from an academical point of view1 has a special interest for the microscopist40 ,it would be impossible to find anything more remarkable in histology than the detailed agreement in the structure and behaviour of the nucleus in the higher plants and the higher animals1 an agreement which is conspicuously manifest in those special divisions which take place during the maturation of the sexual cells4 ,so with regard to the question of 8alternation of generations40 ,we have known since the important discoveries of ,hofmeister that the development of a large part of the vegetable kingdom involves a regular alternation of two distinct generations1 the one which is sexual being constantly succeeded1 so far as the normal cycle is concerned1 by the other which is asexual4 ,this alternation is most marked in the mosses and ferns4 ,in the ,bryophyta the ordinary moss or liverwort plant is the sexual generation of the ovum1 which1 when fertilised1 gives rise to the moss-fruit1 and represents the asexual stage4 ,the latter is once more seen to form spores from which the sexual plant is again developed4 ,in the ,pteridophyta the alternation is equally regular1 but the relative development of the two generations is totally different1 the sexual form being the insignificant prothallus1 while the whole fern-plant1 as we ordinarily know it1 is the asexual generation4 ,the thallus of some of the lower ,bryophyta is quite comparable with the prothallus of a fern1 so as regards the sexual generation there is no difficulty in seeing the relation of the two classes2 but when we come to the asexual generation or sporophyte the case is totally different4 ,there is no appreciable resemblance between the fruit of any of the ,bryophyta and the plant of any vascular ,cryptogam4 8,it is now known that in the higher plants a remarkable numerical change takes place in the constituents of the nucleus of the cell shortly before fertilisation4 ,in angiospermous plants a reduction of the chromosomes occurs shortly before differentiation of the sexual cells4 ,thus1 in the case of the lily1 fertilisation is not the simple fusion of nuclear bodies4 ,these spheres are seen to fuse in pairs1 and then by position to determine the plane of first cleavage of the ovum2 agreeing1 in fact1 closely with what is observed to take place in the animal kingdom40 ,in the higher grades of plants it will be evident that the several tissues that compose their bodies are not found in the root1 stem1 and leaf without definite order and purpose1 but that they are grouped into systems for the performance of different kinds of work4 ,in all flowering plants at least three different systems may be clearly distinguished4 ,these are the epidermal or boundary tissue system1 the fundamental or ground tissue system1 and the fibro-vascular or conducting system4 ,all three systems of tissue originate from meristem cells1 located at the growing point of the stem and root4 ,although these systems characterise the higher types of plants1 the elementary tissues 7represented in ,plate ,,xiii4 and in other figures7 enter alike into the several component parts of nearly all plants4 ,the stem1 the branch1 and the root1 are alike constituted of an outer coating which affords a mechanical support1 and once formed takes no further share in the economy of the plant1 excepting that of assisting to convey fluid from the roots to the branches and leaves1 an action more of a capillary nature than vital4 ,the nourishment of the plant is brought about by other material structures1 as the pith1 the cortex1 the cambium1 and so forth1 all of which greatly assist in the formative process4 ,the woody portion of the plants is especially concerned in furnishing support to the softer pulpy textures1 while the tissues of leaves and flowers are chiefly composed of cells compactly held together by protoplasmic or albuminoid matter4 ,water1 of course1 enters largely into the constituents of all plants4 ,beneath the epidermis is another layer of importance1 the parenchymatous1 which becomes more or less solid with the growth of the pith and cellular wall4 ,in the pulpy substance of some leaves the epidermis presents a thin lamina of palisade-tissue1 the bulk of the mesophyll consisting of spongy parenchyma or sclerenchymatous fibres 7seen in ,fig4 #caj71 which also serve to show the disposition of the several layers about to be brought under notice4 ,development of the ,tissue ,systems4--,in the growing plant the embryonic cells soon become differentiated into three primary meristem layers1 known as dermatogen1 periblem1 and phloem1 from which are developed respectively the primary cortex1 epidermis1 and the stele or vascular cylinder4 ,the dermatogen forms the outermost layer of cells at the growing point1 and when present always develops into true epidermal tissue4 ,in stems the dermatogen is always single-layered1 while in roots it consists of several layers and develops a many-layered epidermis4 ,illustration3 ,fig4 #caj4--,section of ,leaf of ,piper4 c4 ,cortex2 ep4 ,epidermis2 pal4 ,palisade-tissue2 scl f4 ,sclerenchymatous fibres of pericycle2 o4 ,oil gland4 ,the periblem occurs immediately beneath the dermatogen1 forming a hollow cylinder of tissue1 which surrounds the phloem4 ,from the periblem is developed the fundamental tissue of the primary cortex4 ,when no dermatogen is present in the growing-point 7stems of vascular cryptogams7 the external layer of the periblem develops cells which perform epidermal functions4 ,the phloem occupies the centre of the growing-point1 and consists of a solid mass of somewhat elongated cells4 ,from the phloem are developed the fibro-vascular and fundamental tissues of the vascular-cylinder or stele4 ,illustration3 ,,plate ,,xiii4 ,,elementary ,,plant ,,tissues4 ,epidermal or ,boundary ,tissue ,system4--,this system constitutes the external covering of the plant1 and is commonly called the epidermis4 ,it includes1 besides the ordinary epidermal cells1 the guard-cells of the stomata and water pores1 the plant hairs or trichomes1 and the epidermal or external glands4 ,the epidermal tissues are chiefly protective in function1 serving to prevent excessive evaporation from the interior tissues of the plant4 ,illustration3 ,fig4 #caa4 a4 ,epidermis1 reticulated ducts1 and conjunctive palisade cells2 b4 ,vertical section of alder root1 woody layer1 and boundary ducts4 ,in stems the external layer of cells1 whatever its origin1 is known as the epidermis1 while in roots it is called the epiblema4 ,the epidermis usually consists of a single layer of cells1 but in some cases it is two or three-layered1 as in the leaves of figs and begonias4 ,in land plants the epidermis is usually strongly cutinised1 while in submerged plants it is never cutinised4 ,the epidermis of land plants is also often waxy1 the wax occurring on the surface as minute grains1 rods or flakes1 constituting the so-called bloom of leaves and fruits1 and giving to them their glaucous appearance4 ,chlorophyll bodies are usually absent from the ordinary epidermal cells of land plants1 while they commonly occur in the epidermal cells of aquatic plants4 ,ordinary epidermal cells are usually thin-walled and transparent1 and contain a nucleus and colourless watery protoplasm1 but are destitute of both chlorophyll-bodies and starch-grains4 ,the external layers of the outer walls constitute the cuticle of the plant1 while the internal layers and the radial and inner walls are composed of cellulose4 ,the cells of the epidermis are always very compactly arranged1 having their walls so closely adherent that the intercellular spaces are entirely obliterated except at the stomata and water-pores4 ,illustration3 ,fig4 #cab4 #a4 ,vertical section of leaf of ,iris germanica2 a1 a4 ,elongated cells of the epiderm2 b4 ,stomata cut through longitudinally2 c1 c4 ,green cells of the parenchyma2 d1 d4 ,colourless tissue of the interior of the leaf4 #b4 ,portion of leaf torn from its surface2 a4 ,elongated cells of the cuticle2 b4 ,cells of the stomata2 c4 ,cells of the parenchyma2 d4 ,limiting wall of the epidermic cell2 e4 ,lacun or openings in the parenchyma corresponding to the stomata4 ,there are exceptions to this rule1 as1 for example1 in ,cinchona calisaya1 which shows no trace of epidermis1 this being replaced by a corky layer of tubular cells4 ,where this occurs in a plant to any extent1 the whole of the outer tissues are displaced1 and the bark consists exclusively of phloem tissues4 ,this1 although of constant occurrence in ,c4 calisaya1 is not so common in other species1 as ,c4 succirubia1 the middle structure of which consists of parenchyma in which appear more or less numerous isolated store-cells1 and when these are absent there is a formation of rhytidoma and displacement of the tissues containing the store-cells and ducts4 ,the chlorophyll of ,c4 succirubia is very marked1 and its spectrum presents seven distinct absorption bands4 ,the epidermal system of plants in general includes other tissues than those already named1 as the guard-cells of the stomata1 the water-pores1 plant-hairs or trichomes1 and the external or epidermal glands1 all of which are but modifications of ordinary epidermal tissue4 ,the ,stomata or ,breathing ,pores are apertures in the epidermal which lie over large intercellular spaces 7,fig #cab1 #b1 b74 ,these are usually bordered by two modified epidermal cells1 called guard-cells4 ,stomata are formed in the following manner3 ,a young epidermal cell divides into two equal portions by the formation of a septum across its middle1 each half developing into a guard-cell2 the septum now splits lengthwise and separates the guard-cells1 leaving an aperture or stoma between them4 ,in the higher plants the guard-cells of the stomata are crescent-shaped and occur in pairs1 the concave sides of the cells facing each other with the aperture between1 while in mosses the stomata possesses but a single annular guard-cell which surrounds the aperture4 ,the guard-cells of stomata usually contain chlorophyll-bodies in addition to the ordinary protoplasm4 ,they have the power of increasing or diminishing the size of the aperture under the influence of light and moisture1 thus regulating the amount of evaporation from the internal tissues of the plant4 ,water ,pores or ,water ,stomata are apertures in the epidermis1 similar in structure to ordinary stomata1 but differ from them both in function and distribution4 ,water-pores excrete water in the form of drops1 and have their guard-cells fixed and immovable4 ,they always occur at the ends of vasal bundles1 and are found on the margin and at the apex of leaves4 ,plant ,hairs or ,trichomes are modified epidermal cells prolonged externally1 and may be either unicellular or multicellular4 ,each hair consists of a basal portion1 or foot1 which is embedded among the ordinary epidermal cells1 and an apical portion or body1 which is prolonged externally4 ,ordinary epidermal hairs are usually thin-walled1 the inner layers of the wall being composed of cellulose1 while the outer layer is more or less strongly cutinised4 ,the walls may become hardened by deposits of lime-salts or silica4 ,sometimes the cells become glandular and secrete oily1 resinous1 or irritating matters1 as in stinging-nettle hairs 7,plate ,,xiii41 ,no4 #ai71 when they are known as glandular hairs4 ,the development of resin-passages may be observed in transverse sections of the stem of the ivy 7,hedera helix7 cut from a young succulent stem1 and mounted in glycerine4 ,the resin is seen scattered through the cortex and pith1 and in the soft bast which lies outside the cambium in various stages of development1 starting from a group of four cells without intercellular spaces4 ,root hairs spring from the epiblema and are never cutinised1 but are frequently more or less mucilaginous4 ,the root-hairs are the principal absorbing organs of the plant1 and are confined to the younger roots1 occurring just above their tips4 ,root-hairs are never present in aquatic plants1 and are absent from the roots of certain of the ,conifer4 ,it is a curious fact with regard to bell-heather growing in higher latitudes1 that the plants possess a peculiar root structure as a protection against droughts4 ,in most of them the sustentation of life depends upon the formation of a number of long thin filaments on their roots resembling root-hairs1 which penetrate the root1 forming nodular masses within it4 ,these filaments belong to a fungus entirely parasitic to the root1 and yet different from a common parasite1 inasmuch as the plant in this way obtains so much of its nourishment1 and when the fungus is not present1 or is removed1 the plant can no longer live on a peaty soil4 ,the leaf-blade of the coarse moorland grass ,nardus is likewise endowed with a singular property--that of rolling up cylindrically and spreading out again to adapt itself to the dry and wet weather of the moorlands of ,scotland4 ,illustration3 ,fig4 #cac4 a4 ,section of the testa of ,gourd ,seed1 showing communicating cells filled with colouring matter2 b4 ,section of stem of ,clematis1 three pores separated and more highly magnified2 c4 ,transverse section of same1 showing medullary rays4 ,fundamental or ,ground ,tissue ,system4--,this system constitutes the groundwork of plants1 and is the system through which the vasal bundles are distributed4 ,the fundamental tissues are composed largely1 though not wholly1 of parenchyma1 and are chiefly concerned in the metabolic work of plant life4 ,ground tissue includes1 besides ordinary parenchyma1 collenchyma1 selerenchymatous parenchyma1 fibrous tissue1 cork1 laticiferous and glandular tissues4 ,to the fundamental system also belongs the chlorophyll cells of leaves1 the thin-walled cells of the pith and medullary rays1 the cells of the cortex of stems and roots1 and most of the soft cellular tissues in all plants4 ,the lower plants consist almost entirely of fundamental tissue4 ,in the herbaceous forms of the higher plants the ground tissues largely predominate1 while in woody plants they are present in much smaller proportion1 the vascular tissues being the most abundant4 ,in aquatic plants generally1 the fundamental tissues constitute the principal system4 ,the hypoderma occurs immediately beneath the epidermis1 and consists of several layers of cells4 ,a collenchymatous hypoderma is found in the stems and petioles of most herbaceous dicotyls1 and frequently occurs next the mid-rib of leaves1 where it forms a strengthening tissue4 ,a sclerenchymatous hypoderma occurs either as a continuous layer beneath the epidermis1 as in the stems of some ferns1 ,pteris aquilina1 and in leaves of the pine2 or it may form numerous isolated strands beneath the epidermis1 as in the stems of horsetails and in certain ,umbellifer4 ,illustration3 ,fig4 #cad4 a4 ,tangential section of ,taxus baccata 7,yew71 showing the woody fibre2 b4 ,vertical section of same1 spiral fibres1 and ducts2 c4 ,vertical section of ,elm1 showing ducts and dotted cells4 ,the endodermis is the innermost layer of the extra-stelar fundamental tissues1 and always abuts on the stele or steles4 ,in monocotyls it marks the boundary between the cortex and the central cylinder1 and it is sometimes spoken of as the nucleus sheath4 ,in stems the endodermal cells are usually thin-walled and unlignified1 having a suberous thickening band extending round the upper1 lower and lateral surfaces1 which in cross-section appears as a black dot on the radial wall 7,fig4 #cad1 c47 ,according to its position in the stele1 the conjunctive tissue is divided into three principal portions1 viz41 that portion which invests the vasal bundles1 the pericycle2 that portion which lies between the bundles of the stele1 the interfascicular conjunctive tissue2 and that which occupies the centre of the stele1 the medullary conjunctive tissue4 ,the pericycle1 formerly called the pericambium1 is the outermost layer of the conjunctive tissue of the stele4 ,the bundle-sheath of the young stem is more easily recognised than in the older stem4 ,it is1 in fact1 a continuous layer of cells1 whose radial walls have a characteristic dark spot on each radial wall4 ,the bundle-sheath lies immediately outside the vascular bundles1 curving slightly towards the centre of the stem in the spaces between the bundles4 ,it is more prominent in the stem when very young1 as the cells are then filled with starch granules4 ,this layer of cells will be readily seen in sections treated with iodine4 ,in dicotyls and gymnosperms the medullary rays consist essentially of interfascicular ground tissue4 ,the medullary conjunctive tissue occupies the centre of the stele1 constituting the so-called pith1 and usually consists of parenchymatous cells1 but may contain1 in addition1 either stone cells1 sclerenchyma fibres1 laticiferous or glandular tissues4 ,the ,fibro-vascular or ,conducting ,tissue ,system4--,this system constitutes the fibrous framework of the plant1 and is the system by means of which fluids are conducted from one part of the plant to another4 ,its function is partly to give strength and support1 but principally to conduct the crude and elaborated juices to and from the leaves4 ,it is found only in the higher plants1 constituting the tough and stringy tissues in stems and roots1 and the system of veins in leaves4 ,the fibro-vascular system consists essentially of vascular tissue 7ducts1 tracheids1 and sieve-tubes71 and forms long strands--the fibro-vascular bundles--which extend vertically through the fundamental tissues of the plant4 ,the term 8fibro-vascular10 as applied to the conducting system1 is not strictly correct1 since fibres do not always accompany the vascular elements1 hence this system is often spoken of as the vascular system1 and the bundles as vascular1 or more briefly as vasal bundles4 ,that the arrangement1 and course of the vascular bundles in dicotyledous stems are connected with those of the leaves is an obvious fact4 ,it may be seen in sections of ,helianthus1 but is more markedly shown in plants with regularly decussate leaves1 as ,cerastium1 ,clematis1 c4 ,still1 the arrangement of the bundles may differ radically from that of the leaves1 and is1 to a certain extent1 independent of them4 ,this will be noticed in sections of ,iberis amara1 where the bundles do not run longitudinally1 but in tangential spirals4 ,these1 as ,ngeli pointed out1 have no direct relation with the leaves2 and he recommends a series of types for investigation1 in which it will be seen how closely the arrangement of the bundles is connected with the arrangement of the leaves1 and the number of bundles entering the stem from each leaf3 ,iberis amara1 leaves alternate1 leaf-trace with one bundle2 ,lupinus1 leaves alternate1 leaf-trace with three bundles2 ,cerastium1 leaves opposite1 leaf-trace with one bundle2 ,clematis1 leaves opposite1 leaf-trace with three bundles2 ,stachys1 leaves opposite1 leaf-trace with two bundles4 ,illustration3 ,fig4 #cae4 #a4 ,transverse section of the stem of ,cedar1 showing xylem or wood2 #b4 ,section of stem of ,conifer1 the phloem and zones of annual growth2 #c4 ,section of an ,ivory ,nut1 cells1 and radiating pores2 #d4 ,section of the outer or ligneous portion of same1 with radiating cells4 ,the connection of the leaf and stem will be best seen by cutting longitudinal sections through a young node of ,helianthus1 so as to include the median plane of the leaf1 or of both leaves if opposite to each other1 as they often are2 steep them in dilute potash for twenty-four hours and mount in glycerine4 ,a medium power will serve for their examination4 ,the course of the vascular bundles will appear dark through the more transparent parenchyma4 ,the continuity of the tissues of the stem and petiole if followed will be seen to have no definite boundary between the two parts2 the bundles from the petiole pass into the stem1 and no bundle of the upper internode lies in the same vertical plane as that which enters from the petiole between two successive bundles of the vascular ring4 ,every complete vasal bundle consists of xylem or wood and phloem or bast4 ,the former consists essentially of trachery tissue 7ducts and tracheids71 and may contain in addition both wood fibres and wood parenchyma4 ,the phloem or bast consists essentially of sieve tissue1 and usually contains some ordinary parenchyma4 ,in angiosperms companion-cells always accompany the sieve-tubes in the phloem1 while in gymnosperms they are absent4 ,according to the relative positions of the xylem and phloem elements1 there are two principal kinds of conjoint bundles--the collateral and the concentric4 ,of these again there are three varieties1 but the experiments with leaves bring out parallel facts2 that in ordinary stems the staining of the wood by an ascending coloured liquid is due1 not to the passage of the coloured liquid up the substance of the wood1 but to the permeability of its ducts and such of its pitted cells as are united into regular canals2 and the facts showing this at the same time indicate with tolerable clearness the process by which wood is formed1 for what in these cases is seen to take place with dye may be fairly presumed to take place with sap4 ,taking it1 then1 as a fact that the vessels and ducts are the channels through which the sap is distributed1 the varying permeability of their walls1 and consequent formation of wood1 is due to the exposure of the plant to intermittent mechanical strains1 actual or potential1 or both1 in this way4 ,if a trunk1 a bough1 shoot1 or a petiole is bent by a gust of wind1 the substance of its convex side is subject to longitudinal tension1 the substance of its concave side being at the same time compressed4 ,this is the primary mechanical effect4 ,the secondary is when the tissues of the convex side are stretched1 and also produce lateral compression4 ,in short1 the formation of wood is dependent upon transverse strains1 such as are produced in the aerial parts of upright plants by the action of the wind4 ,illustration3 ,fig4 #caf4--,termination of ,vascular ,system4 #a4--;,absorbent organ from the leaf of ,euphorbia neriifolia4 ,the cluster of fibrous cells forming one of the terminations of the vascular system is here embedded in a solid parenchyma4 #b4--;,a structure of analogous kind from the leaf of ,ficus elastica4 ,here the expanded terminations of the vessels are embedded in the network parenchyma1 the cells of which unite to form envelopes for them4 #c4--;,end view of an absorbent organ from the root of a turnip4 ,it is taken from the outermost layer of vessels4 ,its funnel-shaped interior is drawn as it presents itself when looked at from the outside of this layer1 its narrow end being directed towards the centre of the turnip4 #d4--,shows on a larger scale one of these absorbents from the leaf of ,panax ,lessonii4 ,in this figure is clearly seen the way in which the cells of the network parenchyma unite into a closely-fitting case for the spiral cells4 #e4--;,a less-developed absorbent1 showing its approximate connection with a duct4 ,in their simplest forms these structures consist of only two fenestrated cells1 with their ends bent round so as to meet4 ,such types occur in the central mass of the turnip1 where the vascular system is relatively imperfect4 ,besides the comparatively regular forms of these absorbents1 there are forms composed of amorphous masses of fenestrated cells4 ,it should be added that both the regular and irregular kinds are very variable in their numbers3 in some turnips they are abundant1 and in others scarcely to be found4 ,possibly their presence depends on the age of the turnip4 #f4--,represents a much more massive absorbent from the same leaf1 the surrounding tissues being omitted4 #g4--,similarly represents1 without its sheath1 an absorbent from the leaf of ,clusia flava4 #h4--;,a longitudinal section through the axis of another such organ1 showing its annuli of reticulated cells when cut through4 ,the cellular tissue which fills the interior is supposed to be removed4 ,in concentric bundles one of the elements1 either the xylem or the phloem1 occupies the centre1 and is more or less surrounded by the other1 as seen in ,fig4 #caj4 ,meristem tissue is never present1 hence concentric bundles are always closed4 ,they1 however1 occur in the stems of most ferns1 and are always surrounded by a pericycle and endodermis1 and should be regarded as steles4 ,concentric bundles with a central phloem occur in the rhizomes of some monocotyles1 as ,calamus1 ,iris1 ,convallaria1 c4 ,illustration3 ,fig4 #cag4--,vertical section of ,sugar-cane ,stem showing parachyma and crystalline cells1 #bjj diameters4 ,the ,stele1 or ,vascular ,cylinder1 is developed from the phloem of the growing plant1 and consists of one or more vasal bundles imbedded in fundamental tissue1 the whole being enclosed by a pericycle and an endoderm4 ,the typical stele includes all the tissues evolved by the endodermis1 which1 however1 forms no part of the vascular cylinder itself1 but merely surrounds it4 ,the pericycle is always the outermost layer of the tissues of the stele1 while the endodermis is the innermost layer of the extra-stelar tissues4 ,the arboreus type of stem can be best followed by making sections of a twig of the elm 7,ulmus campestris71 which will be found to be cylindrical hirsute1 green or brown according to age1 the latter colour being due to the formation of cork4 ,small brown excrescences are scattered over its surface2 these are termed lenticels4 ,the cork will be seen to lie immediately below the epidermis1 and to consist of cubical cells1 with little or no cell contents2 they are arranged in radial rows1 without intercellular spaces4 ,the walls of these cork cells will stain yellowish-brown with ,schultze's solution4 ,treat a thin section with sulphuric acid and the walls will swell out and gradually lose their sharpness of outline1 with the exception of the cuticularised outer wall of the epidermis and the cork4 ,this material is occasionally found developed in the twigs of the elm1 so that it can be separated as thick radial plates of tissue4 8,by comparing sections of twigs cut of various ages1 the following information may be gleaned3 ,that cork cambium1 or phellogen1 appears as a layer of cortical cells below the epidermis1 and that these divide parallel to the surface of the stem4 ,the result of successive divisions in this direction is the formation of secondary tissue1 which develops externally as cork1 internally as phelloderm4 ,the true cork cambium consists of only a single cell in each radial row1 from which1 by successive division1 all these secondary tissues are derived--i4e41 cambium of vascular bundles4 ,as stems grow older1 layers of cork appear successively further and further from the external surface2 not only the cortex1 but also the outer portions of the phloem are thus cut off from physiological connection with the inner tissue4 ,the term bark is applied to tissues thus cut off1 together with the cork which forms the physiological boundary4 ,the stem of ,vitis affords a good example of such successive layers of cork40 ,illustration3 ,fig4 #cah4 #a4 ,laticiferous ,tissue2 #b4 ,vertical section of a ,leaf of the ,india-rubber ,tree1 with a central gland2 #c4 ,vertical cast of spiral tubes of ,opuntia4 ,for the study of sieve-tubes take the vegetable marrow1 in which they are of extraordinary size4 ,cut transverse sections of the stem and stain with eosin1 and mount them in glycerine4 ,the general arrangement will be seen to differ from that of most other herbaceous plants4 ,below the epidermis a thick walled band of sclerenchyma with lignified walls will be seen distinct from the vascular bundles1 which readily take a stain4 ,the vascular bundles are separate and distinct1 and the structure of the bundle is abnormal1 there being in each a separate central mass of xylem1 with the phloem masses lying1 the one central1 the other in the peripheral side4 ,between the xylem and the phloem masses is the cambium layer4 ,the structure being the same in both will serve for the study of the punctate sieve-plates2 these are readily stained with eosin1 as shown in ,sach's text-book4 ,laticiferous ,tissues 7,fig4 #cah74--;,in cutting sections of latex care must be taken to at once transfer them to alcohol so as to prevent the flow of the latex from the cells1 otherwise the laticiferous vessels will be much less easily traced4 ,the better method is to plunge the root of the dandelion 7,leontodon taraxacum71 after cleaning1 into alcohol1 and there let it remain until it has become hardened2 then cut thin tangential sections from the phloem1 and longitudinal sections through the cambium1 and mount them in potash and glycerine4 ,the laticiferous vessels appear circular in the transverse sections with brown contents2 these are distributed in groups round the central xylem4 ,observe in such sections the presence of sphere crystals of inulin4 ,these are formed quite irrespective of the cell-walls4 ,laticiferous cells are readily seen in the cortex of ,euphorbia splendens1 cut just outside the vascular ring4 ,long tubes will be seen to run through the cortical parenchyma1 with thick cellulose walls and granular contents4 ,these are the laticiferous cells1 the branching of which distinguishes them from the preceding structure4 ,included in the granular contents are starch grains of a peculiar dumb-bell form4 ,leaf or ,petiole4--,the general morphology of leaf tissue is essentially the same as that of the stem from which it proceeds4 ,in the typical monostotic stem of ,phanerogam each leaf receives a portion of the stele or central cylinder of the stem4 ,such portion is termed a meristele1 and may be either entire or split up into a number of schizosteles4 ,the microscopical structure of leaves should be studied in the whole organ1 and by the aid of isolating elements4 ,the whole or portion of a leaf should be soaked in chloral hydrate solution2 this will render it transparent1 whereby the internal structure can be studied as a whole4 ,sections should be prepared from fresh leaves1 or dried ones softened by soaking in water4 ,cut them transversely1 both in the direction of the mid-rib and at right angles to it4 ,this is best effected by placing the material between two pieces of elder pith or fresh carrot4 ,sections of the whole are made and transferred to a dish of water4 ,leaf sections are easily made for examination by macerating the leaves in solution of caustic potash varying in strength from one to five per cent4 ,the epidermis on both sides may be detached1 and the elements of the mesophyll and vascular bundles isolated for separate examination4 ,potassium permanganate proves to be a useful reagent4 ,a weak solution causes the protoplasmic structures to swell up1 thus assisting in the observation of the structure of the chromatophores4 ,this solution may also be employed as a macerating fluid4 ,beautiful preparations are obtained in this way of the sieve-tubes of ,vitis4 ,special structural peculiarities are to be observed in the leaves of various plants in which the epidermis consists of more than a single layer of cells 7e4g41 the leaves of ,ficus1 ,peperace1 ,begoniace1 c471 cystoleths in the cells of the epidermis of ,urtica2 glandular structure in ,ruta1 ,psorales2 the coriaceous leaves of the ,cherry ,laurel1 and the cylindrical leaves of ,stonecrop 7,sedum acre74 ,reproductive ,organs4--,the development of the rudiments of flowers is of an extremely interesting nature1 and the complete flower should be carefully studied4 ,median sections are best suited for the purpose4 ,in the large majority of plants the calyx is developed first1 then the corolla1 and next the stamens4 ,preparations should be made from materials hardened in alcohol1 or first fixed with a strong solution of picric acid and then hardened in alcohol4 ,pollen-grains4--,microspores are found lying free in sections made of the reproductive organs2 these may be transferred to a glycerine fluid and examined under a high power4 ,they are mostly spherical1 with granular protoplasmic contents1 in which with much difficulty two nuclei can be made out4 ,mount and examine1 as types of the various forms of granules1 the pollen of ,helianthus1 ,altha1 ,cucurbita1 nothera1 ,orchis1 ,mimosa1 ,tulipa1 c4 ,mount any of these pollen-grains in a weak solution of cane-sugar 7about five per cent471 examine with a high power1 and note the configuration of their walls with a medium power under polarised light4 ,if transverse sections be made from very young buds1 the development of the anther and the pollen may be traced4 ,the material should be preserved in strong alcohol1 and the sections treated with equal parts of alcohol and glycerine1 and exposed in a watch-glass that the alcohol may evaporate4 ,by this method sections may be prepared for illustrating the formation of the tapetum1 special mother-cells1 and division of the nucleus4 ,illustration3 ,fig4 #cai4--,pollen ,grains4 ,a4 ,pollen-grain of ,clove-pink2 ,b4 ,poppy2 ,c4 ,passion-flower 7,passiflora crulea72 ,d4 ,coba scandens4 ,starch ,granules4--,one of the most universally distributed materials found in plants is starch composed of two substances1 granulose1 which constitutes by far the largest part1 and a skeleton of farinose4 ,it is only the former of these that stains blue with iodine solutions2 the latter partially assumes a brownish colour4 ,the structure of starch granules is not of equal density throughout2 the hilum or nuclear portion is most conspicuous1 around which the rest of the material is deposited in layers1 indicative of stratification4 ,the several layers next to the hilum are less dense than those farthest from it4 ,the position of the hilum determines the form of the grain1 a few being rounded1 others oval or elongated4 ,the grain also contains different proportions of water2 this conveys the appearance of concentric lines or curves about the nucleus4 ,the latter is more conspicuous in the potato starches1 as seen in ,plate ,,xiii41 ,nos4 #f-ae4 ,starch grains1 in nearly all cases1 are formed by the agency of proteid bodies1 either chloroplasts or amyloplasts1 and under the action of sunlight are gradually broken up and employed in the process of growth4 ,there are some plants1 however1 notably the ,composite1 in which another carbohydrate1 inulin1 takes the place of starch from the first1 and is used as a reserve food material4 ,for this reason we look in vain for starch in the cells of ,inula1 ,taraxacum1 c4 ,from the whole group of fungi starch is absent2 this seems to explain the fact that chlorophyll1 or colouring matter1 is rarely met with in the fungi1 hence their inability to utilize1 like green plants1 carbon-dioxide as food4 ,illustration3 ,fig4 #cbj4--,swollen ,potato ,starch1 after the application of potassium hydrate4 7,magnified #baj diameters47 ,the tissues which most commonly contain starch1 or which contain it in largest quantity1 are those of the parenchymatous series1 though it sometimes occurs in the latex of laticiferous tissues1 and even in ducts and tracheids4 ,in the stems of ,dicotyledons it occurs chiefly in the parenchyma of the middle and inner bark1 in the medullary ray cells1 and in the cells of the pith4 ,in the roots of these plants it has a similar distribution1 being for the most part confined to the middle or inner bark and the medullary rays1 pith not being present in these organs4 ,in succulent stems and roots1 of course1 it also commonly occurs in the xylem tissues of the fibro-vascular bundles4 ,a study of the various kinds of starches is important1 since this material is very largely used as an adulterant4 ,other than microscopical means of detecting frauds are practically useless2 assaying is tedious and expensive1 while the microscope is always available and at hand4 ,the limits of variation should be studied in starches from the same species of plants2 the variations are not very wide1 but in most cases characteristic1 so that the discrimination is at all times an easy task4 ,the reagents required are simply iodine and dilute potassium hydrate1 aided by polarised light4 ,illustration3 ,fig4 #cba4 a a a4 ,granules and cells of cocoa2 b b b4 ,arrowroot1 ,tous-les-mois2 c c c4 ,tapioca starch4 7,magnified #cjj diameters47 ,the starch grains of the potato are the best to study in the first instance on account of their large size 7,fig4 #cbj74 ,in arrowroot starch 7,fig4 #cba7 the stratification is almost as distinct as in that of the potato2 the grains much resemble each other4 ,although somewhat smaller1 the grains of arrowroot are more uniform in size4 ,the starches are much used as an adulterant of drugs and various articles sold as cocoas4 ,wheat-starch 7,fig4 #cbb7 consists of circular flattened grains varying much in size1 the central nucleus and stratification of which are very difficult to distinguish4 ,in the smaller starches the hilum becomes more indistinct1 and without stratification1 as in rice-starch1 the latter being angular in shape4 ,the hilum in other leguminous plants forms a longitudinal cleft2 white rye-starch exhibits distinct cracks4 ,compound grains are occasionally met with1 as in the oat4 ,in ,plate ,,xiii4 will be found small groups of starches taken under the same medium power for the sake of comparison4 ,in the microscopical examination of starches first use a #b_/c-;inch or a #a_/b-;inch and then a #a_/f-;inch objective4 ,illustration3 ,fig4 #cbb4 a4 ,husks of ,wheat-starch1 swollen by reagents and heat2 b4 ,a portion of cellulose2 c4 ,rice-starch1 magnified #dbj diameters4 ,the bran of the husk of wheat when broken by grinding is seen to be composed of two coats of hexagonal cells1 the outer of which is detached by the roasting process4 ,the hexagonal cell layer is1 however1 so little altered as to be perfectly distinguishable under the microscope4 ,thus even a small admixture of roasted corn with coffee or chicory can be detected without much difficulty4 ,as to whether starch granules should be regarded as crystalline or colloid bodies1 a difference of opinion still prevails4 ,there are1 however1 reasons for believing that the polarisation effects produced by starch grains are not due to crystalline structure but to stress or strain1 of the same nature as the polarisation of glass when it is subject to strain4 ,the polarising phenomena are precisely such as would be induced in any transparent solid composed of layers1 the inner of which being kept in a state of stress by the compression exerted by the outer layers4 ,moreover1 when by use of a swelling reagent1 such as caustic potash solution1 the outer wall of the starch is made to expand by the imbibition of water1 the polarisation effects immediately disappear4 ,were the solid particles of crystal thus forced apart by water each particle would still exhibit polarisation phenomena4 ,want of space will not permit me to further enlarge upon other micro-chemical substances that enter into the composition of plants2 as1 for example1 the oil secreting glands4 ,these when present take the place of starch4 ,there is1 however1 one product among the cell contents of plants of some interest to the microscopist--those extremely fine crystals known as raphides1 composed of calcium-phosphate and oxalate4 ,mr4 ,gulliver insisted upon the value of raphides as characteristic of several families of plants4 ,schleiden states that 8needle-formed crystals1 in bundles of from twenty to thirty in a cell1 are present in almost all plants10 and that so really practical is the presence or absence of raphides1 that by studying them he has been able to pick out pots of seedling ,onagrace1 which had been accidentally mixed with pots of other seedlings of the same age1 and at that period of growth when no other botanical character would have been so readily sufficient4 ,if we examine a portion of the layers of an onion 7,plate ,,xiv41 ,no4 #c71 or a thin section of the stem or root of the garden rhubarb 7,no4 #d71 we shall find many cells in which either bundles of needle-shaped crystals or masses of a stellate form occur1 not strictly raphides4 ,raphides were first noticed by ,malpighi in ,opuntia1 and subsequently described by ,jurine and ,raspail4 ,according to the latter observer1 the needle-shaped or acicular are composed of phosphate1 and the stellate of oxalate of lime4 ,there are others having lime as a basis1 in combination with tartaric1 malic1 and citric acids1 all of which are destroyed by acetic acid2 others are soluble in many of the fluids employed in mounting4 ,these crystals vary in size from the #a_/djth of an inch1 while others are as small as the #a_/ajjjth4 ,they occur in all parts of the plant2 in the stem1 bark1 leaf1 petals1 fruit1 root1 and even in the pollen1 and occasionally in the interior of cells4 ,in certain species of aloe1 as ,aloe verrucosa1 we are able to discern small silky filaments2 these are bundles of the acicular form of raphides1 and probably1 as in sponges1 act as a skeleton support to the internal soft pulpy mass4 ,illustration3 ,,plate ,,xiv4 ,,stellate ,,and ,,crystalline ,,tissue ,,of ,,plants4 ,in portions of the cuticle of the medicinal squill 7,scilla maritima7 large cells are found full of needle-shaped crystals4 ,these cells1 however1 do not lie in the same plane as the smaller cells of the cuticle4 ,in the cuticle of an onion every cell is occupied either by an octahedral or a prismatic crystal of calcium oxalate4 ,in some specimens the octahedral form predominates2 in others1 even from the same plant1 the crystals are prismatic and arranged in a stellate form1 as in that of the grass 7,pharus cristatus74 7,plate ,,xiv41 ,no4 #f47 ,raphides of peculiar figure are found in the bark of certain trees4 ,in the hickory 7,carya alba7 may be observed masses of flattened prisms having both extremities pointed4 ,in vertical sections from the stem of ,elagnus angustifolia1 numerous raphides of large size are embedded in the pith1 and also found in the bark of the apple-tree1 and in elm seeds1 every cell containing two or more minute crystals4 ,in the ,graminace1 especially the canes2 in the ,equisetum hyemale1 or ,dutch rush2 in the husk of rice1 wheat1 and other grains1 silica in some form or other is abundant4 ,some have beautifully-arranged masses of silica with raphides4 ,the leaves of ,deutzia scabia1 ,no4 #g1 are remarkable for their stellate hairs1 developed from the cuticle of both their upper and under surfaces2 forming most interesting and attractive objects examined under polarised light4 7,plate ,,viii41 ,no4 #agc47 ,silica is found in the structure of ,rubiace both in the stem and leaves1 and1 if present in sufficient thickness1 depolarises light4 ,this is especially the case in the glandular hairs on the margins of the leaves4 ,one of the order ,composit1 a plant popularly known as the 8sneezewort0 7,archill ptarmica71 has a large amount of silica in the hairs found about the serratures of its leaves4 ,all plants are provided with hairs2 some few with hairs of a defensive character4 ,those in the ,urtica dioica1 commonly called the ,stinging-nettle1 are glandular hairs1 developed from the cuticle1 and contain an irritating fluid2 in other hairs a circulation is visible3 examined under a power of #ajj diameters1 they present the appearance seen at ,plate ,,xiii41 ,no4 #ai4 ,illustration3 ,fig4 #cbc4 ,a4 ,cotton2 ,b4 ,fibres of ,flax2 ,c4 ,filaments of ,silk2 ,d4 ,wool of ,sheep4 ,the fibrous tissue of plants is of great value in many manufactures4 ,it supplies material for our linens1 cordage1 paper1 and other industries4 ,this tissue is remarkable for toughness of fibre1 and exhibits an approach to indestructibility1 in the use it is put to in connection with the electric light4 ,it is of importance1 then1 to be able to distinguish it from other fibres with which it is often mixed in various manufactures4 ,here the use of the microscope is found of considerable importance4 ,in flax and hemp1 in which the fibres are of great length1 there are traces of transverse markings at short intervals4 ,in the rough condition in which flax is imported into this country1 the fibres have been separated1 to a certain extent1 by a process termed hackling1 and further subjected to hackling1 maceration1 and bleaching1 before it can be reduced to the white silky condition required by the spinner and weaver1 and finally assumes the appearance of structureless tubes1 ,fig4 #cbc ,b4 ,china-grass1 ,new ,zealand flax1 and some other plants produce a similar material1 but are not so strong1 in consequence of the outer membrane containing more lignine4 ,it is important to the manufacturer that he should be able to determine the true character of some of the textures employed in articles of clothing2 this he may do by the aid of the microscope4 ,in linen we find each component thread made up of the longitudinal1 unmarked fibres of flax2 but if cotton has been mixed1 we recognise a flattened1 more or less rounded band1 as in ,fig4 #cbc ,a1 having a very striking resemblance to hair1 which1 in reality1 it is2 since1 in the condition of elongated cells1 it lines the inner surface of the pod4 ,these1 again1 should he contrasted with the filaments of silk1 ,fig4 #cbc ,c1 and also of wool1 ,fig4 #cbc ,d4 ,the latter may be at once recognised by the zigzag transverse markings on its fibres4 ,the surface of wool is covered with furrowed and twisted fine cross lines1 of which there are from #b1jjj to #d1jjj in an inch4 ,on this structure depends its felting property1 in judging of fleeces1 attention should be paid to the fineness and elasticity of the fibre--the furrowed and scaly surface1 as shown by the microscope1 the quantity of fibre in a given surface1 the purity of the fleece1 upon which depend the success of the scouring and subsequent operations4 ,in the mummy-cloths of the ,egyptians flax only was used1 whereas the ,peruvians used cotton alone4 ,by the many improvements introduced into manufacturing processes1 flax has been reduced to the fineness and texture of silk1 and even made to resemble other materials4 ,illustration3 ,fig4 #cbd4 #a4 ,woody ,fibre from the root of the ,elder1 exhibiting small pores2 #b4 ,woody fibre of fossil wood1 showing large pores2 #c4 ,woody fibre of fossil wood1 bordered with pores and spiral fibres2 #d4 ,fossil wood from coal4 ,fossil ,plants4--,it is well known that the primordial forests furnish a number of families of plants familiar to the modern algologist4 ,the cord-like plant1 ,chorda filium1 known as 8dead men's ropes10 from its proving fatal at times to the too adventurous swimmer who gets entangled in its thick wreaths1 had a ,lower ,silurian representative1 known to palontologists as ,palochorda1 or ancient chorda1 which existed1 apparently1 in two species1--a larger and a smaller4 ,the still better known ,chondrus crispus1 the ,irish moss1 or ,carrageen moss1 has likewise its apparent1 though more distant representative1 in chondritis1 a ,lower ,silurian algal1 of which there seems to exist at least three species4 ,the fucoids1 or kelpweeds1 appear to have also their representatives in such plants as ,fucoides gracilis1 of the ,lower ,silurians of the ,malverns2 in short1 the ,thallogens of the first ages of vegetable life seem to have resembled in the group1 and in at least their more prominent features1 the alg of the existing time4 ,and with the first indications of land we pass from the thallogens to the acrogens--from the seaweeds to the fern-allies4 ,the ,lycopodiace1 or club-mosses1 bear in the axils of their leaves minute circular cases1 which form the receptacles of their spore-like seeds4 ,and when high in the ,upper ,silurian system1 and just when preparing to quit it for the ,lower ,old ,red ,sandstone1 we detect our earliest terrestrial organisms1 we find that they are composed exclusively of those little spore-receptacles4 ,the existing plants whence we derive our analogies in dealing with the vegetation of this early period contribute but little1 if at all1 to the support of animal life4 ,the ferns and their allies remain untouched by the grazing animals4 ,our native club-mosses1 though once used in medicine1 are positively deleterious2 horsetails 7,equisetace71 though harmless1 so abound in silex1 which wrap them round with a cuticle of stone1 that they are rarely cropped by cattle2 while the thickets of fern which cover our hill and dell1 and seem so temptingly rich and green in their season1 scarce support the existence of a single creature1 and remain untouched1 in stem and leaf1 from their first appearance in spring until they droop and wither under the frosts of early winter4 ,the flora of the coal measures was the richest and most luxuriant1 in at least individual productions1 with which the fossil botanist has formed an acquaintance4 ,never before or since did our planet bear so rank a vegetation as that of which the numerous coal seams and inflammable shales of the carboniferous period form but a portion of the remains--the portion spared1 in the first instance1 by dissipation and decay1 and in the second by denuding agencies4 ,nevertheless almost all our coal--the stored-up fuel of a world--is not1 as it is often said to be1 the product of destroyed forests of conifers and flora of the profuse vegetation of the earliest periods in the history of our globe4 ,later investigations show that our coal measures are the compressed accumulations of peat-bogs which1 layer by layer1 have sunken down under the superimposed weight of the next4 ,the vertical stems of coniferous trees became imbedded by a natural process of decay1 and were subsequently overwhelmed in the erect position in which they are found4 ,the true grasses scarcely appear in the fossil state at all4 ,for the first time1 amid the remains of a flora that seems to have had but few flowers--the ,oolitic ages--do we detect1 in a few broken fragments of the wings of butterflies1 decided traces of the flower-sucking insects4 ,not1 however1 until we enter into the great ,tertiary division do these become numerous4 ,the first bee makes its appearance in the amber of the ,eocene1 locked up hermetically in its gem-like tomb--an embalmed corpse in a crystal coffin--along with fragments of flower-bearing herbs and trees4 ,her tomb remains to testify to the gradual fitting up of our earth as a place of habitation for creatures destined to seek delight for the mind and eye1 as certainly as for the proper senses1 and in especial marks the introduction of the stately forest trees1 and the arrival of the charmingly beautiful flowers that now deck the earth4#fb ,,chapter ,,ii4 ,the ,sub-kingdom ,protozoa4 ,the consideration of the whole special group of organisms forming the subject matter of this chapter1 under the heading of ,protozoa1 were formerly included among ,infusoria1 which also embraced every kind of microscopical aquatic body1 whether belonging to the vegetable or animal series4 ,a more critical survey of the organisation and affinities of ,infusoria and the members which constituted the group led to a re-arrangement1 which has been very generally accepted as forming a sub-kingdom1 ,protozoa4 ,this may be defined as embracing all those forms of life1 referable to the lowest grade of the animal kingdom1 whose members for the most part are represented by organisms possessing a single cell or aggregation of cells 7and also included under the general term of unicellular organisms7 the whole of which are engaged in feeding1 moving1 respiring1 and reproducing by segmentation or fission much in the same way as that of the unicellular plants described in a previous chapter4 ,following out this sub-division of the entire series of ,protozoa1 the several groups range themselves into four readily distinguishable sections4 ,in the first1 the most lowly organised and most abundant have no oral orifice in the literal meaning of the word1 food being intercepted at any point of the surface of the body4 ,this most simple elementary type of structure of the ,protozoa is represented in the ,amba and ,actinophrys1 the various representatives of the ,foraminifera1 and certain ,flagellata1 as ,spumella and ,anthrophysa4 ,next in the ascending scale is a group of ,protozoa1 in which1 though differentiation has not proceeded so far as to arrive at the constitution of a distinct oral aperture1 the inception of food substance is limited to a discoidal area occupying the anterior extremity of the body and is associated with the special food-arresting apparatus4 ,to this section of the ,protozoa are relegated the minuter flagellate1 8collar-bearing0 animals1 and also the entire group of sponges or ,porifera4 ,illustration3 ,,gregarinida1 ,,polycystina1 ,,foraminifera1 ,,rotifera1 ,,etc4 ,tuffen ,west1 del4 ,edmund ,evans4 ,,plate ,,iii4 ,in the third section the highest degree of organisation is arrived at4 ,here is represented a single1 simple1 often highly-differentiated oral aperture or true mouth4 ,associated with this section are found the majority of those organisms that collectively constitute the class ,infusoria in the proper acceptation of the term1 and it embraces the majority of the ,ciliata1 the ,cilio-flagellata1 as ,euglena1 ,chilomonas1 c41 in which the presence of a distinct and circumscribed oral aperture is clearly seen4 ,with the fourth and remaining section of ,protozoa1 the oral or inceptive apparatus exhibits a highly characteristic structural modification4 ,this is not restricted to a definite area1 nor is it associated with the entire surface of the body1 but it consists of a number of flexible1 retractile1 tentacle-like organs radiating from diverse and definite regions of the periphery1 each of which subserves as a tubular sucking-mouth1 or for the purpose of grasping food4 ,these may be literally described as many-mouthed1 and have been appropriately designated ,polystomata4 ,the true zoological position of the ,spongida or ,porifera is not finally settled1 the members of this important section having been formerly regarded as a subordinate group of the ,rhizopoda or an independent class of the ,protozoa2 consequently a tendency has been shown to assign to them a position more nearly approximating to that of the ,clenterata1 or zoophytes and corals1 or place them among the more highly organised tissue-constructed animals1 the ,metazoa1 these being characterised by groups of cells set apart to perform certain functions for the whole animal4 ,a division of labour is seen to be marked in these lower animals as the organism becomes more specialised1 and the number of functions a cell performs becomes more and more limited as the body becomes more complex4 ,it has been found convenient to adopt the following definition of the ,infusoria as one more generally acceptable4 ,the ,protozoa in their adult condition are furnished with prehensile or locomotive organs1 that take the form of cilia1 flagella1 or of adhesive or suctorial tentacula1 but not of simple pseudopodia2 their zooids are essentially unicellular1 free swimming or sedentary2 they are either naked1 loricate1 or inhabit a simple1 mucilaginous matrix2 single or united in aggregations1 in which the individual units are distinctly recognisable2 not united and forming a single gelatinous plasmodium1 as in ,mycetozoa1 nor immersed within and lining the interior cavities of a complex protoplasmic and mostly spiculiferous skeleton1 as in the ,spongida1 their food substances being intercepted by a single distinct oral aperture1 or by several apertures through a limited terminal region or through the entire area of the general surface of the body4 ,they increase by simple longitudinal or transverse fission1 by external or internal gemmation or division1 preceded mostly by a quiescent or encysted state1 into a greater or less number of sporular bodies4 ,sexual elements1 as represented by true ova or spermatozoa1 are entirely absent1 but two or more zooids frequently coalesce as an antecedent process to the phenomena of open formation4#fc ,the infusorial body in its simplest type of development1 as in ,amba1 exhibits a structural composition substantially corresponding with that of the lowest organised tissue cell4 ,there is no distinct bounding membrane1 or cell-wall1 and it is throughout1 and apart from the nucleus or endopart1 one continuous mass of granular matter1 but otherwise homogeneous and undifferentiated protoplasm4 ,professor ,greef1 who has made a study of the ,amba1 describes motor fibrils in the exoplasm which are active and large in ,a4 terricola4 ,these are readily seen by staining with osmic acid1 and1 after washing this out with water1 immersing in a weak alcoholic solution4 ,in ,amba so prepared and examined with a high power1 the whole body will be seen to be surrounded by a distinct double integumentary layer4 ,highly refractive bodies may also be seen in the interior1 connected together by extremely fine filaments4 ,professor ,greef concludes that here we have to do with muscular fibrill1 which traverse the contractile outer zone in a radial direction and there terminate for the time being4 ,by a similar method1 axial filaments can be demonstrated in ,heliozoa2 these1 it is believed1 are the true motors of their pseudopodia1 and also the axial structures of the ,acineta1 a marine animal related to ciliate infusoria4 ,in the ,amba1 at one time well known as the ,proteus animalcule1 ,fig4 #cbe1 the marvellous body creeps onward in a flowing manner1 occasionally and languidly emitting a single pseudopod first on one side1 then on the other4 ,more commonly it puts on a dendroid or palmate form2 then again it assumes more or less grotesque shapes in which almost any conceivable image may be imagined4 ,the body1 as will be seen in this highly-magnified figure1 is full of granules 7with the exception of a thin clear outer hyaline zone71 and near the centre is a globular or discoid body known as the nucleus1 composed of slightly denser material than that which surrounds it4 ,the division of the body into two is preceded by a division of this nucleus4 ,near the latter is a clear spherical space--the contractile vacuole--which gradually expands1 and then rather suddenly collapses and reappears at the same spot1 the systole and diastole being slow and continuous4 ,the contractile vacuole contains a clear liquid which is expelled on the collapse of the vacuole4 ,this organ probably serves the double function of respiration and excretion4 ,the ,amba is omnivorous1 chiefly a vegetarian1 and1 therefore1 found on the ooze of ponds or on the under surface of the leaves of aquatic plants1 especially among ,conferv4 ,it can be readily produced by placing a few fibres of fresh meat in an infusion of hay4 ,illustration3 ,fig4 #cbe4--;,amba1 ,proteus animalcule2 magnified #fjj diameters4--7,warne74 ,the ,gregarin consist of a remarkable group of organisms1 but these1 although unicellular1 are1 for the most part1 confined to the intestinal tract of worms and of the higher animals1 and will therefore be described among internal parasites4 ,tho fungus-animals1 ,mycetozoa1 have already been referred to in a previous chapter4 ,the best known species1 however1 is found in tan yards in the form of creeping masses of naked protoplasm1 termed ,plasmodia4 ,cakes of protoplasm become segregated from the main mass1 and break up into ,amba-like spores1 which unite again to form ,plasmodia4 ,illustration3 ,fig4 #cbf4--,rhizopoda lobosa4 ,a4 ,difflugia proteiformis2 ,b4 ,difflugia oblonga2 ,c1 ,d4 ,arcella acuminata and dentata ,the ,rhizopoda1 or root-footed class of animals1 are among the most interesting simple organisms with which the microscope has made us acquainted4 ,in the living state they have the power of protruding pseudopodia from the body1 by which they creep about1 or cling to plants when in search of food4 ,this group1 in fact1 includes ,amba1 ,foraminifera1 ,sun-animalcules1 and ,radiolarians4 ,in the first the pseudopodia are simple and lobose2 in the second they are slender1 confluent and reticulate2 while in the two last they are simple1 radiating and somewhat stiff1 and partake of a calcareous formation4 ,of the ,lobosa1 we may take a well-known representative of the group1 the ,protomyxa1 found at the bottom of fresh-water pools1 especially those near bog-moss1 where its minute orange-coloured particles of jelly-like substance are seen creeping over stones or shells4 ,if quietly watched the pseudopodia1 some of which are broad and others slender1 become quiescent spheres1 which break up into numerous portions1 each of which becomes a new animal4 ,this group is divided into the shell-less 7,nuda7 and shell-formed 7,testacea74 ,the brown1 horny covering is often finely faceted1 and is either shaped like a dome1 semi-circular1 or flat as a box1 through which they protrude their few or many pseudopodia 7seen in ,fig4 #cbf74 ,illustration3 ,,plate ,,xv4 ,,gromia4 ,in the ,difflugia the lorica or shell is strengthened by the addition of silicious particles2 in ,euglypta it is sac-shaped1 with a jagged free margin1 the surface being covered by overlapping scales2 while ,arcella are capable of secreting vesicles of air in their interior1 whereby they are enabled to rise to the surface4 ,on some parts of our coast1 if the sea sand be carefully looked over with a pocket lens1 there will often be found minute grains of a porcelain oval kind1 belonging to the ,miliolina1 segmented or strung together not quite in the same plane4 ,illustration3 ,fig4 #cbg4--,section of ,rotalia4 a1a1 ,radiating interceptal canals2 b1 ,internal bifurcations2 c1 ,transverse branch2 d1 ,tubular wall of chambers4 ,illustration3 ,fig4 #cbh4--,rosalina varians or ,discorbina globularia1 with pseudopodia protruding4 ,the ,foraminifera are rhizopods1 whose simple protoplasmic bodies send forth1 through perforations in the membrane or outer covering of calcium carbonate and silica1 branching rays of pseudopodia4 ,the order is divided into two groups1 the ,imperforata and the ,perforata2 in the former the shell or harder structure possesses only one or more apertures1 whereas in the latter1 in addition to the main opening1 the shell has its walls perforated throughout1 which admits of minute pseudopodia or fine threads being protruded 7,fig4 #cbh74 7,see also ,plate ,,iii41 ,nos4 #ge-he47 ,the vast majority of ,perforata form their shells1 or rather skeletons1 of calcium carbonate and silica1 which renders them almost indestructible4 ,consequently the form is preserved through ages1 and they present objects of the greatest interest to the microscopist4 ,a curious and interesting feature of the ,foraminifera--often an element of difficulty to the student--is the tendency of modifications of types comprising the larger groups to run into parallel isomorphous series4 ,thus1 if the entire class be roughly divided1 as it sometimes has been1 into three orders1 comprising respectively the forms characterised by porcellaneous1 arenaceous1 and hyaline 8tests10 the same general conformation and arrangement of chambers will be found in each of the three series4 ,the most remarkable example1 even among the smaller groups1 is the ,rotaliid1 of which three or four genera may be arranged in parallel lines1 and in more or less closely isomorphous series4 ,in the report appended to the 8,challenger0 scheme of classification many examples are enumerated4 ,in ,arenacea we have a small family of ,foraminifera1 the external surfaces of which present a ridge and furrow arrangement1 and the incrustations are entirely of a sandy nature held together by a cement secreted by the animal4 7,plate ,,xv41 ,no4 #a1 ,astrorhiza limicola47 ,gromia4--,among the more remarkable of the ,perforata group the ,gromia have a foremost place4 ,they are very minute globular or oval-shaped bodies1 about one-twenty-fourth of an inch in length1 found in fresh1 brackish1 and salt water4 ,the forms brought up in ,dr4 ,wallich's deep sea soundings of #ahfj were taken attached to pieces of corallines1 or found loose among ,globigerina ooze4 ,at first there appears to be nothing peculiar about these tiny specks of matter resembling the ova of a zoophyte1 but presently1 at the smaller end1 a very fine thread is protruded1 and then another1 dividing into finer branches1 and1 ultimately1 a complete network of filaments extends on all sides1 and become attached to the side of the glass jar that contains them4 ,now1 on employing magnifying power1 every thread exhibits a circulatory motion1 an up and down stream or cyclosis of granules suspended in a fluid mass4 ,it is by means of these pseudopodia1 as the threads are termed1 that the ,gromia moves its body along and clings to the glass4 ,we may surmise1 then1 that these pseudopodia are either gelatinous1 glutinous1 or terminate in sucker-like processes4 ,increase in the 8test10 integument1 is brought about1 as in ,difflugia1 by the secretion of calcareous matter or by cementing fine silicious particles to the outer wall1 as the protoplasm is seen to flow over the test1 so that when it comes in contact with a diatom it is thereby drawn towards the oral opening and slowly digested4 ,some considerable time elapsed between the discovery of ,gromia by ,mr4 ,w4 ,archer1 ,f4,r4,s41 and the demonstration of a nucleus and contractile vesicle by ,dr4 ,wallich4 ,it was thought that in the whole of the ,monozoa the nucleus was absent1 but it is now known that this important body is embedded in the protoplasmic substance1 and the reproduction of these curious animals is thereby secured4 ,among the better known species of ,gromia is ,g4 ,dujardinii1 chiefly distinguishable by the darker colour of the 8test10 by the greater quantity of silica that enters into the formation of its pseudopodia1 and by the formation of isogamous zoospores1 two of which are seen in conjugation in ,plate ,,xv41 ,no4 #b4 ,an excess of protoplasm must also be secreted to admit of so large a protrusion outside the testa4 ,g4 ,lieberkhnia 7of ,claparde and ,lachman71 ,no4 #e1 differs in formation4 ,its shape is pyriform1 and the opening whence the pseudopodia streams out is situated in a lateral depression about midway in the testa1 c1 o4 ,hence a trunk branch is seen to issue forth1 and from this a ramification of threads1 psdp1 extends to a considerable distance in all directions4 ,the ,micro-gromia of ,hertwig1 ,no4 #d1 is the minutest form of the genus yet discovered1 and differs from those already described in the mode of reproduction4 ,the individual takes the shape of a water bottle with a short neck1 whence issue forth a limited number of very slender threads4 ,the test is quite transparent1 and it was in this species that the nucleus and contractile vesicle1 which lie embedded near the mouth1 were first clearly made out4 ,the zoospores of ,micro-gromia have a curious habit of uniting with their neighbours to form a colony1 ,no4 #d4 ,their colonisation is apparently intended to facilitate multiplication4 ,reproduction is carried on somewhat after the manner of ,volvox4 ,the globular bodies formed sink to the bottom of the glass vessel1 and there remain for a time in a quiescent state4 ,in the course of a day or two the mass assumes a motive appearance1 increases in bulk1 becomes more ovoid in shape1 and ultimately the nucleus shows the first sign of division4 ,vertical segmentation takes place1 as at ,a1 into two equal parts2 each half is seen to possess its fair share of the nucleus and contractile vesicle4 ,it then turns in the horizontal direction1 and now there appears to be an upper and a lower division1 the uppermost having a neck-like attachment1 and this is making its way to the narrow oral opening in the parent testa1 as at ,b4 ,here it is seen pressing forward1 and at ,c the neck is protruding some distance1 and the second half assumes a bottle shape2 at ,d the greater part of the animal is nearly set free1 and after a short rest it fully launches forth4 ,it finally pulls itself together1 as at ,e1 and either develops a pair of flagella and swims off1 or assumes the form of an ,actinophrys4 ,in either case1 and in a very short space of time1 the separated young animal is quite ready to re-unite1 as at ,f1 and assist in forming a new colony of the species4 ,the ,polymorphina belong to a low genus of the ,foraminifera4 ,they consist of a number of forms and exhibit a rather extensive series of variations1 although consisting of a few simple types1 and showing transitions between forms which at first seem to be distinct4 ,the majority of species keep to the sea bottom2 some few are pelagic1 and occur in abundance on the surface of the ocean4 ,among the latter are the ,globigerina3 its shell is about one-fortieth of an inch in diameter1 and usually composed of seven globular chambers arranged spirally in such a manner that all are visible from above1 each chamber opening by a crescentic-shaped orifice into a depression in the middle of the next4 ,perfect specimens bristle with long slender spines1 the pores affording passage to pseudopodia1 which stream out along the spines4 ,the more carefully-conducted deep-sea investigations have brought to light the fact that the floor of the ocean1 at great depths1 and over a vast area1 is formed of these white or pinkish coloured bodies1 all containing on an average about #fj per cent4 of calcium carbonate4 ,it is a question whether the ,globigerinid which make up the bulk of the ooze actually live at the bottom as well as the surface of the sea4 ,this question has given rise to much discussion4 ,dr4 ,murray came to the conclusion that pelagic species do not live near the ocean floor4 ,this opinion is partly based on the fact that the area of the ,globigerina ooze coincides with the area of surface of temperature at which these bodies are found to exist4 ,when the surface water is too cold for them1 they are not to be found1 neither are they found below4 ,major ,s4 ,r4 ,j4 ,owen1 while dredging the surface of mid-ocean--the ,indian1 and the warmer portion of the ,atlantic--found attached to his nets a number of these interesting bodies1 and which always made their appearance just about sunset4 ,in ,plate ,,iii41 ,nos4 #dc-eb1 a number of these interesting and variously-formed bodies are given1 and an attempt is also made to show the richly-tinted colour appearances presented by the sarcode or protoplasm of the ,globigerina4 ,illustration3 ,fig4 #cbi4--;,globigerina and other bodies taken in deep sea soundings 7,atlantic74 8,many of the forms10 writes ,major ,owen1#fd 8have hitherto been claimed by the geologist1 but ,i have found them enjoying life in this their true home1 the silicious shells filled with coloured sarcode1 and sometimes this sarcode in a state of distension somewhat similar to that found projecting from the ,foraminifera1 but not in such slender threads4 ,there are no objects in nature more brilliant in their colouring or more exquisitely delicate in their forms and structure4 ,some are of but one colour1 crimson1 yellow1 or blue2 sometimes two colours are found on the same individual1 but always separate1 and rarely if ever mixed to form green or purple4 ,in a globular species1 whose shell is made up of the most delicate fretwork1 the brilliant colours of the sarcode shine through the little perforations very prettily4 ,in specimens of the triangular and square forms 7,plate ,,iii41 ,nos4 #dc1 #dd1 #de and #df71 the respective tints of yellow and crimson are vivid and delicately shaded2 in one the pink lines are concentric2 while another is of a stellate form1 the points and uncoloured parts being bright clear crystal1 while a beautiful crimson ring surrounds the central portion4 ,a globular form resembles a specimen of the ,chinese ball-cutting--one sphere within another2 this1 however1 appears to belong to a distinct species4 ,illustration3 ,fig4 #ccj4--;,globigerina and other bodies taken in deep sea soundings1 #ahef 7,atlantic74 8,the shells of some of the globular forms of these ,polycystina1 whose conjugation ,i believe ,i have witnessed1 are composed of a fine fretwork1 with one or more large circular holes2 and ,i suspect the junction to take place by the union of two such apertures4 ,that the figures of these shells become elongated1 lose their globular form after death1 and present a disturbed surface is seen in some of the figures represented in ,plate ,,iii41 ,nos4 #hb-he40 ,those without internal chambers have been described as ,orbulina universa1 ,plate ,,iii41 ,fig4 #gh1 while ,nos4 #ge and #gf1 although members of the same family1 have been separated1 but all should certainly be united under ,globigerina4 8,the minute silicious shells of ,polycystina present wonderful beauty and variety of form2 all are more or less perforated1 and often prolonged into spines or other projections1 through which the sarcode body extends itself into pseudopodial prolongations resembling those of ,actinophrys4 ,when seen disporting themselves in all their living splendour1 their brilliancy of colouring renders them objects of unusual attraction4 ,it will appear that they wish to avoid the light1 as they are rarely found on the surface of the sea in the daytime2 it is after sunset and during the twilight that they make their appearance40 ,many forms of ,globigerina and ,foraminifera are represented in ,figs4 #cbi and #ccj4 ,these varied and beautiful forms were dredged up with soundings made in #ahef for the purpose of ascertaining the depth of the ,atlantic1 prior to the laying down of the electric telegraph wire from ,england to ,america1 and taken at a depth of #b1jgj fathoms4 ,heliozoa4--,actinophrys-,sol1 8sun-animalcules10 belong to this group2 most of them inhabit fresh water 7,plate ,,iii41 ,no4 #ff74 ,the chief characteristic1 and the one to which they owe their name1 is the possession of long1 slender1 somewhat stiff pseudopodia2 these radiate from all parts of the body4 ,the living animal usually contains green-coloured particles within a minute translucent spherical globule of about #a_/bejth of an inch in diameter4 ,it is1 therefore1 variously designated the green sun-animalcule1 ,acanthocystis1 or ,actinophrys-,sol4 ,it is commonly found amongst the weeds in clear pools of water1 where desmids abound4 ,the pseudopodia appear to be stiff2 they are1 however1 quite flexible1 and the body contains more than one clear vesicle with a nucleus2 reproduction is secured by the simple division commencing in the nucleus4 ,the little animal can move over a hard surface by the alternate relaxation and stiffening of its pseudopodia2 when one of these touches a small organism1 it is believed to paralyse it1 then envelop1 and deliberately digest it4 ,in another species1 the lattice-animalcule 7,cathrulina71 the pseudopodia or silicious threads are arranged tangentially4 ,it grows on a long flexible stalk1 attached to an aquatic plant1 the total length of which is about #a_/bjjth an inch4 ,the globular body is perforated in all directions1 through which the fine stiff pseudopodia are thrust out2 it is often known to form colonies4 ,in this order may well be placed the ,radiolaria2 they are1 however1 usually separated4 ,but ,radiolarians1 whether seen alive or in their skeleton form1 are surpassingly beautiful4 ,by the favour of ,messrs4 ,warne1 ,i am enabled to append a frontispiece plate to this volume taken from their 8,royal ,natural ,history40 ,these bodies are all marine1 and live in zones of several thousand fathoms1 and like their congeners1 the ,globigerina1 they avoid a strong light1 and only appear after sunset4 ,their bodies are supposed to emit a phosphorescent glow1 but more is known of their silicious skeletons than of their living forms2 yet it is not this feature that separates them from other orders of rhizopods1 but the possession of a membranous central capsule enclosing the nucleus4 ,the body substance outside this capsule is highly vacuolated in some species1 especially in surface forms4 ,a few are without a skeleton1 and these consist of oval masses of protoplasm1 with slender pseudopodia4 ,in a few species the skeleton is formed of a glassy horny substance1 termed acanthin1 arranged in the form of radiating spines4 ,radiolarians secrete a silicious skeleton1 which assumes a variety of forms1 as trellis-work1 boxes joined by radiating spines1 helmets1 baskets1 bee-hives1 discs1 rings1 and numerous other forms4 ,haeckel has described upwards of four thousand species1 and possibly as many more could be added to this number4 ,radiolaria are divided into two groups4 ,in the one there is either no skeleton or one of silex2 in the other the skeleton is formed of radiating spines of a horny nature4 ,these are again subdivided according to the characters of the central capsule4 ,in those forms with a silicious skeleton the geometrical pattern conforms more or less to the shape of the central capsule1 being either spherical or conical4 ,the central capsule is regarded as being homologous with the calcareous shell of ,globigerina4 ,reproduction takes place by simple division into two1 or by the body breaking up into spores1 each provided with a flagellum1 or two spores may fuse together1 and the result will be an adult ,radiolarian4 ,certain yellow corpuscles present in the outer part of their body-surface change into unicellular parasitic algals2 these can be separated and cultivated independently of their host4 ,the ,radiolarians live floating at all depths from #a1jjj to #b1ejj fathoms1 and are distributed over areas in the central ,pacific and the south-eastern part of the ,indian ,ocean1 the ooze forming the ocean bed being made up of their skeletons to an extent of #hj per cent4 of the deposit2 hence it has become known as ,radiolarian ooze4 ,the chalky-looking ,barbadoes earth1 a ,tertiary formation1 is composed almost entirely of their skeletons4 ,somewhat similar deposits exist in the ,nicobar ,islands1 in ,greece1 and in ,sicily4 ,it will have been noticed that by far the greater number of ,foraminifera are of marine origin1 and these occur in such widespread profusion that the finest calcareous particles which constitute the seashore in some places consist almost wholly of their microscopic remains4 ,at former periods of the earth's history they appear to have existed even in greater profusion than at the present time4 ,this is evidenced by their remains forming the principal constituent of our largest geological formations4 ,moreover1 during the ,canadian ,geological ,survey large masses of what appeared to be a fossil organism were discovered in rocks situated near the base of the ,laurentian series of ,north ,america4 ,sir ,william ,dawson1 of ,montreal1 referred these remains to an animal of the foraminiferal type2 and specimens were sent by ,sir ,w4 ,logan to the late ,dr4 ,carpenter1 requesting him to subject them to a careful examination4 ,as far back as #aheh ,sir ,w4 ,logan had suspected the existence of organic remains in specimens from the ,grand ,calumet limestone1 on the ,ottawa ,river1 but a casual examination of the specimens was insufficient to determine the point4 ,similar forms being seen by ,sir ,w4 ,logan in blocks from the ,grenville bed of the ,laurentian limestone were in their turn tried1 and ultimately revealed their true structure to ,sir ,william ,dawson and ,dr4 ,sterry ,hunt1 who named the structure ,eozoon ,canadense4 ,the masses of which these fossils consist are composed of layers of serpentine alternating with calc spar4 ,it was found by these observers that the calcareous layers represented the original shell1 and the silicious layers the softer parts of the once living ,foraminifera4 ,the results were arrived at through comparison of the appearance presented by the ,eozoon with the microscopic structure which ,dr4 ,carpenter had previously shown to characterise certain members of the ,foraminifera4 ,the ,eozoon not only exceeded other known ,foraminifera in size to an extent that might have easily led observers astray1 but1 from its apparently very irregular mode of growth and general external form1 no help was derived in its identification1 and it was only by microscopical examination of its minute structure that its true character was ascertained4 ,dr4 ,carpenter wrote3--8,the minute structure of ,eozoon may be determined by the microscopic examination either of thin transparent sections1 or of portions which have been subjected to the action of dilute acids1 so as to remove the calcareous portion1 leaving only the internal casts1 or models1 in silex1 of the chambers and other cavities originally occupied by the substance of one animal40 ,subsequently he found portions of minute structure so perfect that he was able to say that 8delicate pseudopodial threads were originally put forth through openings in the shell wall of less than #a_/ajjjjth of an inch in diameter0 7,plate ,,iii41 ,nos4 #fd1 #fe74 ,in a paper read at the meeting of the ,geological ,society he stated that he had since detected ,eozoon in a specimen of ophicalcite from ,bohemia1 in a specimen of gneiss from near ,moldau1 and in specimens of serpentine limestone sent to ,sir ,c4 ,lyell by ,dr4 ,gmbel1 of ,bavaria4 ,these also were found to be parts of the great formation of the 8fundamental0 gneiss1 considered by ,sir ,roderick ,murchison as the equivalent of the ,laurentian rocks of ,canada4#fe ,if the remains of ,foraminifera be dissolved in dilute hydrochloric acid1 an organic basis is left1 after the removal of the calcareous matter1 accurately retaining the form of the shell with all its openings and pores4 ,the earthy constituent is mainly calcium carbonate2 but there is also a small amount of phosphate of lime in the shells of many of them4 ,illustration3 ,fig4 #cca4 #a4 ,separated prisms from outer layer of ,pinna shell2 #b4 ,skeletons of ,foraminifera from limestone2 #c4 ,recent shell of ,polystomella crispa2 examined under dark-ground illumination4 ,infusoria4 ,we are now brought face to face with animals which possess considerable variation of structure1 ,infusorial animalcules1 as they are termed4 ,it was ,ehrenberg who attributed to them a highly complex organisation1 but later observations negatived these views and showed them to be animals formed of one or more cells1 or colonies of so-called individuals4 ,it is true that this cell or united protoplasm may show a wonderful amount of differentiation1 what with its nucleus and vacuole1 mouth and gullet1 its variously-arranged cilia or flagella1 its contractile fibres1 its separation into an outer denser and a more fluid inner protoplasm1 and its horny cup and stalks4 ,in these few lines we have a condensed summary of the special qualities of minute forms of life that afford much interesting work for the microscope4 ,illustration3 ,fig4 #ccb4--;,acineta1 magnified #fjj diameters 7,warne74 ,among those widespread1 and in some respects heterogeneous1 forms of life associated under the comprehensive title of ,infusoria1 we encounter types that not only differ very widely from one another1 but which occupy a different rank or position1 so to speak1 with regard to the relation they bear to each other1 and also to the outlying representatives of the series--differences that permeate throughout the ranks of this extensive group4 ,furthermore1 a considerable number of ,infusorial animalcules foreshadow or typify1 in a corresponding degree1 the separate or associated cell elements out of which higher tissue structures--metazoic organisms--are built up4 ,we may take the well-known example ,euglena viridis 7,plate ,,iii41 ,no4 #fg71 or ,paramecium 7,no4 #gd71 and their allies2 these would appear to be the prototypes of ,turbellaria4 ,another more lowly organised group of the ,ciliata exhibits a distinct and highly-interesting affinity to the ,opalinid4 ,there are many other species 7,acineta1 ,plate ,,iii41 ,no4 #fh1 for instance71 which at first sight would seem to stand by themselves and present no marked agreement with any metazoic type4 ,indeed1 the function of these and other polypites consists simply in seizing food and conveying it through perforations at the extremity of each separate tentaculum to its interior4 ,in ,acineta certain of the tentacles only are suctorial1 and these1 being the inner ones1 fulfil the ingestive function1 while the peripheral series are prehensile4 ,this stalked club-shaped body 7,fig4 #ccb71 which fixes itself to seaweeds or ,bryozoa1 is seen to have a nucleus1 and also clear vesicles in the body-substance2 its embryos are ciliated4 ,it is an object of considerable interest even among curious marine animalcules2 one or two species inhabit fresh water4 ,the spiral-mouthed ,spirostomum are among the largest of the class1 and in sunlight are visible to the naked eye as slender golden threads of about #a_/ajth of an inch in length4 ,the mouth slit1 extending half the length of the body1 is bordered on one side by cilia4 ,the body is cylindrical and the surface covered with rows of cilia4 ,its multiplication takes place by transverse fission through the middle4 ,flagellate ,infusoria4--,the characteristic of this group1 as its name implies1 is the possession of one or more flagella or whip-like appendages1 at the base of which is an opening in the denser surface layer of protoplasm1 and in the interior a nucleus and one or more contractile vacuoles1 and not infrequently a brilliant red spot of pigment known to microscopists as the eye-spot4 ,the ,monads1 which constitute the simplest members of the group1 are commonly found in fresh-water pools and vegetable infusions4 ,the typical form consists simply of a spherical or oval cell provided with a flagellum4 ,the ,volvox was formerly placed in this group1 but as it contains chlorophyll it is properly claimed by the botanist4 ,the collared group possesses cup-like collars1 and these frequently secrete horny receptacles or cups1 and form elegant tree-like colonies4 ,the mail-coated group are of very varied form1 the body being often prolonged into spiny processes4 ,they have two long flagella which fit into grooves purposely provided4 ,but the most interesting and remarkable are the phosphorescent animalcules 7,noctiluca71 whose beautiful bluish-green luminosity on the surface of the sea has attracted attention from very early periods4 ,it was1 however1 not until the first half of the present century that the luminosity was discovered to be due to the presence of multitudes of these minute jelly-like spheres4 ,illustration3 ,fig4 #ccc4--,noctiluca miliaris2 magnified #aej diameters4 ,illustration3 ,fig4 #ccd4--,pyrocystis2 magnified #aej diameters4 ,the body of the ,noctiluca 7,fig4 #ccc7 is a nearly globular-shaped cyst1 enclosed in a tough membranous wall1 from a grooved opening in which a striated muscular flagellum or proboscis is projected forth1 and it is by means of this the animal swims away even in rough seas4 ,a fine whip-like flagellum is also located in the same groove4 ,at the apex of the funnel there is a mass of protoplasm which extends itself as a widely-meshed1 highly-vacuolated network to the inner wall of the cyst1 whence it is believed the phosphorescent light emanates4 ,it multiplies by self-division1 first becoming encysted after withdrawing its flagellum1 and then breaking up into numerous ciliated helmet-shaped swarm spores4 ,frequently two organisms fuse into one and then divide into spores4 ,noctiluca mainly confines itself to the shallower seas1 but there are related forms met with in the warmer open seas2 these belong to the genus ,pyrocystis 7,fig4 #ccd74 ,in one variety the body is perfectly spherical and without the big flagellum or proboscis4 ,professor ,butschli1 however1 regards this species as an encysted or resting phase of the commoner and better-known form4 ,the late ,mr4 ,philip ,gosse1 ,f4,r4,s41 was the first microscopist to describe the ,noctiluca4 ,after careful observation1 he wrote in his 8,naturalist's ,rambles0 as follows3--8,i had an opportunity of becoming acquainted with the minute animals to which a great portion of the luminousness of the sea is attributed4 ,one of my large glass vases of sea-water ,i had observed to become suddenly at night1 when tapped with the finger1 studded with minute but brilliant sparks at various points on the surface of the water4 ,i set the jar in the window1 and was not long in discovering1 without the aid of a lens1 a goodly number of the tiny jelly-like globules of ,noctiluca miliaris swimming about in various directions4 ,they swam with an even gliding motion1 much resembling that of the ,volvox globator of our fresh-water pools4 ,they congregated in little groups1 and a shake of the vessel sent them darting down from the surface4 ,it was not easy to keep them in view when seen1 owing rather to their extreme delicacy and colourless transparency than to their minuteness4 ,they were1 in fact1 distinctly appreciable by the naked eye1 measuring from #a_/ejth to #a_/cjth of an inch in diameter40 ,among the numerous fresh-water members of the flagellate infusoria1 there is one which especially calls for notice1 ,codosiga1 discovered by the late ,professor ,h4 ,j4 ,clark4 ,this minute body bears a delicate funnel-shaped protoplasmic expansion or collar1 common to the several members of this organic series4 ,the flagellum is placed at the base of the oral opening1 and within the circumscribed area of the collar1 which is of such extreme tenuity that its true form and nature can only be determined by a very careful adjustment of the achromatic condenser and accessory apparatus employed1 together with a wide-angled objective4 ,it is seen to greater advantage by supplying the animal with very fine particles of colouring matter4 ,in this way it is found that the infundibuliform cup consists of protoplasm1 through which the flagellum is protruded and withdrawn into the general substance of the ,monad's body 7,fig4 #cce74 ,as many as twenty or more zooids are attached to the extremity of a slender footstalk4 ,the length of the body1 exclusive of the collar1 is #a_/bejjth to the #a_/abjjth of an inch4 ,the habitat of these bodies is fresh water4 ,mr4 ,saville ,kent in #ahfi discovered some of these interesting infusoria in the ,london ,docks4 8,the more exact significance of the special organ1 the collar1 is manifest by the circulatory currents or cyclosis induced1 and there can be no room for doubt that this structure finds its precise homologue in the pseudopodia of the foraminiferous group of the ,rhizopoda1 in which a similar circulation or cyclosis of the constituent sarcode is exhibited4 ,the whole of this highly-interesting flagellate order1 a comparatively small one as yet1 are remarkable for their pale glaucous green or florescent hue1 such colour assisting materially in their recognition1 even when the magnifying power employed is insufficient for the detection of the very characteristic collar with its enclosed flagellum40#ff ,illustration3 ,fig4 #cce4--;,codosiga umbellata2 a few colonies of ,zooids diverging from the parent foot-stalk with flagella extended1 magnified #fej diameters4 ,ciliata4--,types of ,ciliata obtained from hay infusions are very numerous4 ,ehrenberg's animalcules were mainly of a large size1 and of those belonging to the higher order of the ,ciliata1 pertaining to such genera as ,paramecium1 ,colpoda1 ,cyclidium1 ,oxytricha1 and ,vorticella4 ,these1 however1 represent but an insignificant minority of the hosts of flagellate forms which abound in our humid climate1 and in hay infusions in particular4 ,in such infusions1 watched from day to day and produced from hay obtained from different localities1 the number of types developed in regular sequence is found to be perfectly marvellous1 commencing with the ,monas proper1 ,amphimonas and ,heteromita2 while ,bacteria1 in their motile and quiescent forms1 are invariably present and furnish an abundant supply of material for the microscope4#fg ,vorticellid constitute one of the most numerous families of the ciliate infusoria4 ,all its members are at once recognised by their normal stationary condition1 and by the structure of their oral system4 ,in but few of the genera is there any marked divergence from this formula1 and when any exists it is made manifest by an increase in development of some one of its elements at the expense of another4 ,for instance1 in the genus ,spirochona1 the external edge of the encircling border or peristome is suppressed1 while the inner portion is abnormally developed into a transparent and highly elevated spiral membrane4 ,the bell-animalcules usually possess stalks1 and are either solitary or form branching colonies4 ,conichilus vorticella 7,plate ,,iii41 ,no4 #hj7 is a well-known member of the colony stock1 all the zooids of which are united on a slender branching pedicle1 which consists of a central contractile cord enclosed within a tubular hyaline sheath4 ,there are many other shrub-like colonies all variously modified in form and character4 ,the ,epistylis opercularia1 or nodding-bell animalcule1 is an interesting member of a numerous host of solitary short-stalked forms 7,fig4 #ccg74 ,when the animal is disturbed1 the heads drop down towards the stalk4 ,this animalcule has been found to form a colony2 and another1 ,carchesium1 whose tiny branched tree-like colonies resemble little white globular masses of moulds1 are seen at once to drop down towards the base of the colony with a jerky movement if the cell be touched4 ,by a process of encysting1 all the ,vorticell and many of the more highly-organised ciliata have the means of what may be termed self-preservation4 ,should the water dry up in which they have been living1 the little animal encases itself in mud at the bottom of the pool4 ,should this be baked by the sun not the least injury arises1 for at this stage it crumbles into dust1 and is carried by the wind to long distances1 but the first shower of rain calls it back to active life1 and soon after it is seen to issue forth as a free swimming bud4 ,illustration3 ,fig4 #ccf4--,vorticella microstoma4 ,thuricola valvata 7,plate ,,iii41 ,no4 #gb7 possesses a hinge-like process which closes up like a door when the animal contracts itself into its case4 ,this very effectually protects it from assault4 ,both portions of the valve are capable of extension4 ,another group of ciliate infusoria also possess a limited number of cilia1 but these1 although restricted to the under surface of their bodies1 have an unrestricted range of motion4 ,the group are all free swimmers1 belonging to the genus ,oxytricha4 ,they possess two separate alimentary orifices1 neither of which are situated at the extremities or encased by a dense integument4 ,their locomotive organs consist either of set1 vibratile cilia1 or non-vibratile styles or uncini1 variously situated1 and all serving to make these infusorial animals very active 7,plate ,,iii41 ,nos4 #gc and #gg74 ,a typical species is the mussel-animalcule 7,stylonychia1 ,fig4 #cch71 common in all infusions and pools of water4 ,its body is oval and flattened1 and about #a_/ajjth of an inch in length4 ,at one end a funnel-shaped depression or mouth1 with a ciliated margin1 leads to the inner part of the body1 in which are two oval bodies1 a nucleus and a contractile vacuole1 which is seen to contract rhythmically4 ,the creature can also stalk along by means of its cilia or set1 and set up currents to the mouth4 ,plate ,,iii41 ,nos4 #gj1 #ga1 #gb1 #gc1 and #gd1 are types of these interesting bodies4 ,illustration3 ,fig4 #ccg4--,nodding-bell animalcule 7,epistyles operculata7 #bej 7,warne74 ,illustration3 ,fig4 #cch4--,mussel-animalcule 7,stylonychia mytilus7 under surface4 a4 ,mouth2 b4 ,contractile vacuole2 c4 ,nucleus4 7,magnified #aej diameters47 ,dr4 ,balbini believes a true sexual generation occurs among these organisms1 but1 with the exception of the ,paramecium1 this has not been seen to take place2 even ,gruber's more recent investigations appear to be inconclusive on this point4 ,conjugation1 however1 it is said takes place among some attached forms1 as in the ,stentors4 ,these have been seen to put forth a bud from the body base1 and soon after become free swimming bodies4 ,the trumpet-animalcule 7,stentor71 a conspicuous member of the ciliata1 is comparatively large1 being about the #a_/beth of an inch in length when extended to the full size4 ,it is usually found attached to the under sides of duckweed1 and is continually changing its form from that of a small knob when contracted1 to the trumpet shape seen in ,fig4 #cci1 ,no4 #f1 when fully extended1 and from which it derives its name4 ,the long cilia projected from the upper part form a spiral within the margin of the open mouth leading to the digestive sac4 ,a contractile vacuole lies to the right of the oral opening4 ,new individuals are produced by the process of budding1 and in the form of ciliated embryos from the nucleus4 ,stentors are commonly met with in fresh water1 and are usually of a brilliant green colour4 ,these little bodies will bear cutting up3 if only a fragment of the nucleus be included in the section1 the injury is soon repaired4 ,rotifera1 or ,wheel-animalcules 7,fig4 #cci74--;,in this group we have a higher type of animal1 with a more complex organisation than those previously noticed4 ,the great majority inhabit fresh water1 and are readily developed in hay infusions1 in bog-moss1 in house-top gutters1 everywhere if looked for after a shower of rain4 ,the rotating organs from which these fascinating animalcula derive their name consist of two disc-like bodies whose margins are fringed with rows of cilia1 which create currents toward the oral aperture1 and which have given rise to the optical delusion of rotating wheels4 ,the disposition of the cilia is so arranged as to bring food to the rotifer and conduct it to the mastax or digesting apparatus--a muscular bulb moved by a series of muscles--the gastric glands and stomach4 ,the great transparency of the whole structure permits of the animal economy being easily studied4 ,the body is covered with a horny envelope of two layers1 and is divided into segmental divisions1 which slide into each other telescopic fashion4 ,consequently1 as the water dries up1 the animal is for a long time rendered indestructible and capable of resisting varying temperatures and the action of caustic reagents4 ,rotifers are oviparous1 and their eggs are conspicuous and of three kinds4 ,the common soft-shelled eggs produce females1 the smaller and more spherical produce males4 ,the ephippial1 or summer eggs1 are often beset with spines or bosses2 these have only a membranous covering1 and are hatched soon after they are laid1 or before leaving the ova sac4 ,the male rotifer is but a third of the length of the female1 often without cilia1 and appears to have no alimentary tract2 indeed1 the only internal organ is a large sperm sac4 ,rotifers have been divided by ,dr4 ,hudson and the late ,mr4 ,gosse in their charming work on these very interesting 8,wheel-animalcules0 into four orders1 according to their powers of locomotion1 as follows3--7#a7 ,rhizota1 the rooted2 7#b7 ,bdelloida1 the leech-like1 that swim and creep like a leech2 7#c7 ,ploma1 the sea-worthy1 that only swim with their ciliary wreath2 7#d7 ,scirtopoda1 the skippers1 that swim with their cilia and skip with arthropodous limbs4 ,these1 again1 are subdivided into families4 ,with such hardy creatures as ,philodina1 ,adineta1 ,brachionus1 c41 creatures to whom extremes of cold1 heat1 and drought are the ordinary conditions of life1 nothing can be easier to keep going throughout the year4 ,mr4 ,c4 ,f4 ,rousselet1 who has so thoroughly succeeded in mounting ,rotifers with their cilia fully extended1 recently exhibited at one of the evening meetings of the ,royal ,microscopical ,society1 ,london1 no less than four hundred specimens in a natural and perfect condition1 the nervous system being seen more clearly from its successful staining throughout the body than in the living rotifer4 ,illustration3 ,fig4 #cci4 #a4 ,rotifer vulgaris with its cilia2 b4 rotating2 c4 horn2 d4 sophagus2 f4 outer case2 g4 ova1 foot protruding through outer case4 #b4 ,same in the contracted state and at rest1 showing the segmentation of the body and development of young4 #c4 ,pitcher-shaped ,brachionus1 furnished with two horny projections2 a4 mastax2 b4 shell2 c4 cilia1 rotating disc2 d4 foot4 #d4 ,baker's ,brachionus1 with six horny set2 these are retracted when the cilia are in action2 the letters relate to the same internal organs as in the former2 the ova sac seen filled with eggs4 #e and #f4 ,b4 ovalis1 closed1 and with cilia displayed4 ,there is also a family of ,rotatoria with a single rotatory organ1 disposed around the margin of the case4 ,this comprises at present a very small group4 ,the cistes is a member of the family 7,plate ,,iii41 ,no4 #fi74 ,a single ciliary wreath leads to the alimentary canal1 and a pharyngeal bulb or mastax comprises the apparatus of nutrition4 ,the visual organs are red1 as in other rotifers1 and the ovarium contains several ova1 shown in ,no4 #fi4 ,the envelope is a gelatinous transparent sheath1 into which the animalcule can withdraw itself1 its attachment to the bottom being by the end of the foot-like tail4 ,the most interesting among this genus are the ,floscularians4 ,these creatures may undoubtedly be described as among the most beautiful and interesting of infusorial animals4 ,the ,stephanoceros1 8crowned animalcule10 as it is termed1 is about #a_/cfth of an inch in length1 and enclosed in a transparent cylindrical flexible case1 beyond which it protrudes five long arms in a graceful manner4 ,these1 touching at their points1 give a form from which it derives its name4 ,these arms are furnished with several rows of short cilia1 which seize the food brought within their grasp until it can be swallowed4 ,in addition to the rotatory organs1 they have short flexible processes1 or cornu1 attached to the outside of one or more of their lobes4 ,the water vascular system consists of two canals arising from a small pyriform contractile vesicle1 situated below the stomach4 ,the ova1 after leaving the ova sac1 remain quiescent until their cilia are developed4 ,floscularians1 like ,melicertans1 have a certain affinity in form with ,vorticellians and ,stentors1 and also with ,campanulari1 among polypes4 ,their cilia are less regular when in action than in other ,rotatoria4 ,when they retreat into their transparent cells they appear to fold themselves up4 ,their internal structure can be seen through the external case1 and ova are observed enclosed in an ova sac2 when thrown off they remain quiescent until the formation of their cilia4 ,the whole family furnish interesting objects for microscopic investigation4 ,melicerta ringens 78beaded ,melicerta074--,of all the ,melicerta1 or 8horny floscularia10 this is the most beautiful4 ,its crystalline body is enclosed in a pellucid covering1 wider at the top than the bottom1 of a dark yellow or reddish-brown colour1 which gradually becomes encrusted by zones of a variety of shapes1 cemented together with a peculiar secretion that hardens in water4 ,it derives its name from these pellets1 which have the appearance of rows of beads4 ,mr4 ,gosse furnished an excellent account of the architectural instincts of ,melicerta ringens3 8,an animalcule so minute as to be with difficulty appreciable by the naked eye1 inhabiting a tube composed of pellets1 which it forms and lays one by one4 ,it is a mason who not only builds up his mansion brick by brick1 but makes his bricks as he goes on1 from substances which he collects around him1 shaping them in a mould which he carries on his body4 8,the pellets composing the case are very regularly placed in position2 in a fine specimen1 about the #a_/cjth of an inch in length1 when fully expanded1 as many as fifteen longitudinal rows of pellets were counted1 which gave about thirty-two rows in all4 ,as it exposes itself more and more1 suddenly two large rounded discs are expanded1 around which1 at the same instant1 a wreath of cilia is seen performing surprising motions4 8,on mixing carmine with the water1 the course of the ciliary current is readily traced1 and forms a fine spectacle4 ,the particles are hurled round the margin of the disc1 until they pass off in front through the great sinus1 between the larger petals4 ,if the pigment be abundant1 the cloudy torrent for the most part rushes off1 and prevents our seeing what takes place2 but if the atoms be few1 we see them swiftly glide along the facial surface1 following the irregularities of outline with beautiful precision1 dash round the projecting chin like a fleet of boats doubling a bold headland1 and lodge themselves1 one after another1 in the little cup-like receptacle beneath4 ,mr4 ,gosse1 believing that the pellets of the case might be prepared in the cup-like receptacle1 watched the animal1 and presently had the satisfaction of seeing it bend its head forward1 as anticipated1 and after a second or two raise it again2 the little cup having in the meantime lost its contents4 ,it immediately began to fill again2 and when it was full1 and the contents were consolidated by rotation1 aided probably by the admixture of a salivary secretion1 it was again bent down to the margin of the case1 and emptied of its pellet4 ,this process he saw repeated many times in succession1 until a goodly array of dark-red pellets were laid upon the yellowish-brown ones1 but very irregularly4 ,after a certain number were deposited in one part1 the animal would suddenly turn itself round in its case1 and deposit some in another part4 ,it took from two-and-a-half to three-and-a-half minutes to make and deposit a pellet40 ,melicerta may be found in clear pools1 mill-ponds1 and other places through which a current of water gently flows4 ,if a portion of water-weed be brought home and placed in a small glass zoophyte-trough1 and carefully examined with a magnifying power of about fifty diameters1 a few delicate-looking projections of a reddish-brown colour will probably be seen adhering to the plant2 these are the tubular cases of ,melicerta1 which1 after a short period of rest1 will be seen to be animals of #a_/abth of an inch or more in length4 ,porifera4 ,spongiad4 ,illustration3 ,fig4 #cdj4--,spongia panicea4 ,bread-crumb ,sponge1 showing currents entering surface a1 and leaving by oscules b4 ,sponges4--,the term ,porifera1 or 8canal-bearing zoophytes10 was applied by the late ,dr4 ,grant to designate the remarkable class of organisms known as sponges1 met with in every sea1 and numbering about two thousand species1 varying in size from a pin's head to masses several feet in height2 and weighing from a few grains to over a hundred pounds4 ,sponges assume an endless variety of shapes1 as cups1 vases1 spheres1 tubes1 baskets1 branched-like trees1 but often as shapeless masses4 ,when living they are all colours and all consistences1 soft and gelatinous1 fleshy1 leathery or stony4 ,a fuller knowledge of sponges was gained in #ahbe1 when ,dr4 ,robert ,grant examined a fragment of living sponge under the microscope4 ,on bringing it to the side of the glass cell in which he had preserved it1 he beheld this living fountain pouring forth a torrent of liquid matter in rapid succession1 and he was at once convinced that a current flowed out of the larger orifices4 ,he introduced a small portion of fine chalk1 and saw particles driven into the interior1 and pass out again by different ways4 ,to determine the cause of the currents1 it was necessary to make a closer examination of the anatomy of the sponge4 ,for this purpose he cut or peeled off thin sections1 and saw that the whole substance was divided into flagellated chambers1 enclosing spherical and other bodies1 and perforated by pores4 ,each chamber proved to be about #a_/ejjth of an inch in diameter1 groups of them opening by a wider orifice into a common space1 or canaliculus1 and joining others to form canals terminating in larger oscular canals4 ,the walls throughout are lined with flat cells1 but in the flagellated chambers the living cells are more or less cylindrical1 and each is provided at the free end with a whip-like appendage1 or flagellum4 ,furthermore the upper margin was seen to be expanded into a thin hyaline collar1 so that the whip appeared to have its origin in the centre of a basin or funnel4 ,the currents of water traversing the body of the sponge are kept up by the movements of the flagella of the collar-cells4 ,these beat the water in the flagellated chambers into the rootlets of the canals leading to the oscules4 ,to replace this1 water flows into the flagellated chambers from the rootlets of the canals passing down from the groups of pores in the skin4 ,the currents entering the sponge bring in oxygenated sea-water and minute food particles1 such as diatoms and infusorial organisms2 the currents from the oscules contain an excess of carbonic acid of waste products1 resulting from vital activity and indigestible remains4 ,the cells lining the canals effect the exchange of gases1 and take up food particles4 ,illustration3 ,fig4 #cda4--;,a section of a flagellate chamber of a ,fresh-water ,sponge1 showing collar-cells 7,vosmaer74 ,professor ,grant's careful and instructive researches were begun on the smaller kind of ,british sponges hanging down from rocks 7,spongia coalita71 and on which he gazed for 8twenty-five minutes1 until obliged to withdraw his eyes from fatigue40 ,this sponge fixes itself by a root2 and the currents enter through the stem and body1 and leave principally by oscules placed on the branches4 ,illustration3 ,fig4 #cdb4--;,an ,ascon ,sponge4 ,a4 ,magnified #bj diameters2 ,b4 #hj diameters2 ,c4 ,transverse section2 ,d4 ,collar-cells1 #gjj diameters4 ,the embryo1 an extremely minute oval cyst1 is furnished with a flagellum for swimming2 in the third it assumes an amboid form 7,warne47 ,at present too little is known as to the physiology of digestion in sponges to permit of a definite statement on the subject4 ,in specimens fed upon carmine the collar-cells have been found loaded with granules2 in others1 again1 the flat cells lining the subdermal cavities have been found gorged with colour granules4 ,from ,bowerbank's monograph on the ,british ,spongiad 7#ahfd and #ahgd7 nothing of importance can be gained on the subject2 in fact1 it relates almost entirely to the structure and organisation of sponges in their dried or preserved condition1 and therefore is only of value for purposes of specific identification4 ,one of the simplest of living sponges1 the microscopic structure of which it is possible to trace1 ,ascetta primordialis1 is found on seaweeds in the ,mediterranean4 ,in its simple unbranched condition it forms a minute white sac about one twenty-fifth of an inch in height1 opening above by a wide round oscule and narrowing below to a stalk 7,fig4 #cdb74 ,the walls are very thin and perforated by pores1 through which the water passes into the interior4 ,the walls of the sac are composed of two layers1 an inner lining of collar-cells1 and an outer layer consisting of a gelatinous matrix containing amboid bodies and transparent three-rayed spicules4 ,these serve to support the walls and as a frame-work for the pores1 as in all the sponges4 ,by eliminating the spicular skeleton1 and by supposing the tube to be more globular1 the 8olynthus form0 will be obtained1 which has been regarded as the hypothetical ancestor of all sponges4 ,a canal system arises when the walls grow thick or form folds1 or give off pouches or tubes4 ,from these channels arise incipient in-current canals1 between the inside or lumen of the folds and that forming the out-current canal system4 ,there is a common ciliated ,sycon found on seaweed round the ,british coast2 it has the appearance of a white sac about an inch in height1 with a crown of glassy spicules around the orifice4 ,the vertical cavity of the sac is surrounded by a wall of closely-packed horizontal tubes1 opening at their inner ends into the central cavity1 but externally ending blindly4 ,the central cavity of the sac is surrounded or lined with flat-cells1 and the radial tubes with collar-cells1 and the walls of the tubes are perforated4 ,here the spaces between and outside the densely-packed tubes are the in-current canals4 ,in an equally common ,british sponge1 ,grantia1 which forms small flat white bags1 a rudimentary cortex covers the outer ends of the tubes4 ,in ,grantiopois1 the cortex becomes quite thick2 as the radial tubes in this species become more branched and the mesoderm thicker1 so the passages or in-current canals become more complicated4 ,common silicious1 sponges develop in a different manner from the calcareous ones1 namely1 from a hollow conical sac open at the top and with a flat base2 the spherical flagellated chambers at a very early stage forming a mammillated layer in the walls4 ,plakina1 one of the simplest silicious sponges1 encrusts stones with a fleshy crust1 consisting of a sac with a flat base attached to the stone in sucker-like fashion1 and with the rest of the walls forming simple folds4 ,the spaces between and outside the folds form the in-current1 and those in the lumen of the folds the out-current1 channels4 ,each of the flagellated chambers in the walls of the folds communicates with the in-current spaces through several pores1 and opens into the out-current spaces by one large pore1 the currents of water passing out by the central oscule4 ,here we have a general idea of the formation of all the commoner forms of sponges4 ,in the more delicate species1 as that of ,venus' flowerbasket1 the cells are formed by a trellis work of large spicules of silica4 ,groups of cells congregate in the ground substance and secrete a network of cylindrical fibres and spicules1 which1 although they remain to a certain extent separate1 are always beautifully adapted for purposes of support4 ,in addition to the support these afford1 the skeleton spicules afford a means of defence against the attacks of small animals4#fh ,a fairly good idea will be gained of the internal structure of sponges from the section made of a ,geodia ,barretti1 ,fig4 #cdc4 ,illustration3 ,fig4 #cdc4--;,geodia ,barretti 7,bowerbank74 ,a tangential section of geodia sponge exhibiting the radial d isposition of the fasciculi of the skeleton1 and a portion of the mesoderm of the sponge1 magnified #ej diameters2 a4 intermarginal cavities2 b4 a basal intermarginal cavity2 c4 ova imbedded in the dermal crust of the sponge2 d4 large patentoternate spicula1 the heads of which form areas for the valvular bases of the intermarginal cavities2 e4 recurvo-ternate defensive and aggressive spicula within the summits of the intercellular spaces of the sponge2 f4 portion of the interstitial membrane of sponge1 crowded with minute stellate spicula2 g4 portions of the secondary system of external defensive spicula4 ,reproduction4--,as regards the modes of reproduction1 both male and female cells are found in the mesoderm4 ,the male cells generally give rise by division of the nucleus to masses of spermatozoa1 each of which possesses a conical head and a long vibratile filament4 ,the ova appear as large round cells1 and when conglomerated in masses1 resemble those of ,micro-gromia1 which1 after fertilisation1 undergo segmentation or division1 first into two cells1 and again dividing and sub-dividing1 until a cluster or mass of cells results 7as seen in ,fig4 #cdc74 ,the outer layer of the egg-shaped embryo becomes more cylindrical in shape1 and is now provided with cilia1 and soon appears as an independent minute oval body4 ,if a bread-crumb sponge be cut open in the autumn1 the embryos will be seen as bright yellow spots within the body-substance4 ,by keeping specimens in a vessel of water1 the embryos will be seen to escape from the oscules1 and swim freely about with the broad end forwards4 ,after twenty-four hours of independent existence1 the embryo remains stationary1 and fixes itself by its broad end1 which becomes flattened out4 ,by a remarkable transformation1 the larger granular cells of the interior burst out and grow over the outer flagellate layer of cells1 and the latter become the collar-cells of the adult sponge4 ,a minute sponge with one oscule results from the development of the fertilised ovum4 ,an extensive crust with numerous oscules may be regarded either as a colony in which each oscule represents an individual1 or simply as one individual in which the growth of the body necessitates the formation of new channels for the conveyance of food materials4 ,the embryos of some of the fresh-water sponges 7,spongillid7 living in ponds1 canals1 lakes and rivers all over the world1 as soon as they become fertilised undergo segmentation1 and form oval ciliated bodies1 in appearance somewhat resembling the gastrula of ,monoxenia1 one of the simplest kinds of corals4 ,fresh-water sponges are green in colour1 due to the granular bodies which crowd the cells near the surface of the sponge2 that this colour is not due to the formation of chlorophyll is seen on keeping them in a shady place1 when they become pale grey or yellowish-brown1 and if kept quite in the dark they entirely lose all colour4 ,illustration3 ,,plate ,,xvi4 ,,skeletons ,,and ,,spicula ,,of ,,sponges4 ,a few sponges possess no skeleton whatever1 excepting the gelatinous ground substance2 in some specimens the skeleton is mainly or entirely composed of foreign particles of sand or the remains of ,foraminifera4 ,others are composed of calcium carbonate1 and form the class ,calcarea1 the spicules of which are white1 and opaque in mass2 but on placing portions in hydrochloric acid1 the skeleton is dissolved away with effervescence1 and the spicules are left behind transparent and glassy4 ,a great variety is seen in the different species1 as will be gathered from the few typical forms shown in ,plate ,,xvi41 and which even in their fossilised state remain unaltered1 the silica which enters so largely into their composition being indestructible1 the calcareous matter alone becoming separated in exposure to the action of air1 or by boiling in hydrochloric acid4 ,the only perceptible difference noticed is an increase in transparency1 and this1 on mounting them in ,canada balsam1 adds to their beauty when examined by polarised light4 ,hyalonema1 the 8glass-rope0 sponge of ,japan1 consists of a bundle of from #bjj to #cjj threads of transparent silica1 glistening with a satiny lustre like the most brilliant spun glass2 each thread is about eighteen inches long1 in the middle the thickness of a knitting-needle1 and gradually tapering towards either end to a fine point2 the whole bundle coiled like a strand of rope into a lengthened spiral1 the threads of the middle and lower portions remaining compactly coiled by a permanent twist of the individual threads2 the upper portions of the coil frayed out1 so that the glassy threads stand separate from each other4 ,the spicules on the outside of the coil stretch its entire length1 each taking about two and a half turns of the spiral4 ,one of these long needles is about one-third of a line in diameter in the centre1 gradually tapering towards either end4 ,the spirally-twisted portion of the needle occupies rather more than the middle half of its entire length4 ,in the lower portion of the coil1 which is embedded in the sponge1 the spicule becomes straight1 and tapers down to an extreme tenuity1 ultimately becoming so fine that it is scarcely possible to trace it to its termination4 ,within the mesoderm1 and in oscule1 was noticed a deep brownish-orange coloured shrunken membrane2 this was traced to a parasitic polyp4 ,since this was first observed on an early specimen of the ,japanese glass-sponge1 the same parasite has always been found growing on and in all these curious sponges4 ,the surface of the stalk above the portion embedded in the mud is seen to be covered with a warty crust of parasitic polyps4 ,all the specimens of ,hyalonema in the ,european museums in #ahfj had their stalks overgrown with ,palythoa1 while many had their bodies also covered with another parasite1 and which1 fortunately for the sponge1 did not form a sandy crust4 ,the polyps1 having no skeleton1 dry up entirely1 and leave behind no trace except the stain first referred to4 ,unlike a parasite1 however1 the polyps do not feed upon the juices and soft parts of the sponge1 nor indeed do they share its food1 but simply settle upon the sponge and feed upon any food that may chance to come within their reach4 ,the dredgings of the ,challenger brought to the surface many entirely new forms of glass-sponges and from great depths4 ,one of the most beautiful1 known as ,carpenter's glass-sponge 7,pheronema71 is composed of concentric lamin of silica deposited around a fine central axial canal4 ,these form a gauze-like network throughout1 but with no regularity of structure4 ,clion4--,not the least wonderful circumstance connected with the history of sponges is the power possessed by certain species of boring into substances1 the hardness of which might be considered as a sufficient protection against such apparently contemptible foes4 ,shells 7both living and dead71 coral1 and even solid rocks are attacked by these humble destroyers1 gradually broken up1 and1 no doubt1 finally reduced to such a state as to render substances which would otherwise remain dead and useless in the economy of nature available for the supply of the necessities of other living creatures4 ,these boring sponges constitute the genus ,cliona of ,dr4 ,grant4 ,they are branched in form1 or consist of lobes united by delicate stems1 and after having buried themselves in shells or other calcareous objects1 preserve their communication with the water by means of perforations in the outer wall of the shell4 ,the mechanism by which a creature of so low a type of organisation contrives to produce effects so remarkable is still doubtful1 from the great difficulties which lie in the way of coming to any satisfactory conclusions upon the habits of an animal that works so completely in the dark as the ,cliona celata4 ,mr4 ,hancock1 in his valuable memoir upon the boring sponges1 attributes their excavating power to the presence of the multitude of minute silicious crystalline particles adhering to the surface of the sponge2 these he supposes are set in motion by ciliary action4 ,in whatever way this action may be produced1 however1 there can be no doubt that these sponges are constantly and silently effecting the disintegration of submarine calcareous bodies--the shelly coverings1 it may be1 of animals far higher in organisation1 and in many instances they prove themselves formidable enemies even to living molluscs1 by boring completely through the shell4 ,in this case the animal whose domicile it so unceremoniously invades has no alternative but to raise a wall of new shelly matter between himself and his unwelcome guest1 and in this manner generally succeeds in barring him out4 ,from a close examination of the structural and developmental characters of the ,spongide1 it must be conceded that they belong rather to the flagellata ,protozoa than to any other order4 ,this was the view held by the late ,professor ,clark1 and ,mr4 ,saville ,kent quite concurs in it4#fi ,summing up the entire evidence adduced1 scarcely a shadow of doubt is admissible concerning the intimate relationship that subsists between the ,choano-flagellata and other flagellate ,protozoa and that of sponges4 ,the primary and essential element of the apparently complex sponge stock is the assemblage of collared flagellate zooids that inhabit its interstitial cavities under various plans of distribution4 ,individually these collared zooids correspond structurally and functionally in every detail with the collared units of such genera as ,codosiga1 ,salpingca1 and ,proto-spongia4 ,the collar in either case presents the same structure and functions1 exhibits the same circulatory currents or cyclosis1 and acts in the same way for the capture of food4 ,the body contains an identical centrally located spheroidal nucleus or endoplast1 and a corresponding series of rhythmically pulsating contractile vesicles4 ,the developmental reproductive phenomena are also strictly parallel4 ,both originate as simple ,amba or simple flagellate ,monads1 exhibiting no trace in their earliest stage of the subsequently acquired characteristic collar4 ,both again after a time withdraw their collar and flagellum1 and assume the amboid state2 then1 coalescing1 enter upon a quiescent or encysted condition1 and break up into a number of sporular bodies1 and thus provide for the further existence and distribution of the species4 ,the whole process again is much akin to that which obtains in the protophytic type1 ,volvox globator1 which liberates from its interior free swimming gemmules that take the form of spherical aggregation of biflagellate daughter-cells4 ,in their isolated state1 on the other hand1 the swarm gemmules of the sponge stock are directly comparable with the free swimming subspheroidal colony stock of the flagellate infusoria ,synura1 ,syncrypta1 and ,uroglena1 or with the attached subspheroidal clusters of ,codosiga and ,anthophysa4 ,illustration3 ,,echinodermata1 ,,hydrozoa1 ,,polyzoa1 ,,helminthoida4 ,tuffen ,west1 del4 ,edmund ,evans4 ,,plate ,,iv4 ,,chapter ,,iii4 ,zoophytes1 ,clenterata1 ,medus1 ,corals1 ,hydrozoa4 ,illustration3 ,fig4 #cdd4--;,gorgonia ,nobilis4 ,a study of the earliest growth of the ,clenterata has shown that their internal cavities are nothing more than regular radiate out-growths of the internal structures4 ,the result of this development is a condition which does not occur again in the whole of the animal kingdom4 ,there is a system of cavities all in open communication one with another1 no closed blood vascular system1 and no specialised respiratory apparatus4 ,again1 all the animals that constitute this large group are radiate in structure1 that is1 when viewed from above they are typically star-shaped1 and if cut across1 every horizontal section shows a symmetrical arrangement of the several parts around a centre4 ,there are other radiate animals1 as the ,echinoderms1 but while in these five is the fundamental number of rays1 in the ,clenterata the rays are a multiple of four1 six and upwards4 ,the skeleton or framework of each differs1 and when the ,clenterata form calcareous structures1 these are quite different from the tests of the sea-urchins2 and in all cases the anterior portion of the body is crowned with one or more circles of tentacles1 which remain perfectly flexible and flower-like4 ,the most highly-developed of the free forms are the sea-anemones and the jelly-fish4 ,these have no hard or calcareous skeleton whatever1 but withal they are1 in the opinion of naturalists and microscopists1 the most beautiful objects among ,zoophytes4 ,in spite of their variety of forms1 the ,clenterata seem to be as incapable of higher development as do the ,echinoderms1 and they have failed to make headway in fresh water1 but it is not improbable that some of the simplest forms of the whole group may have given rise to higher animal forms1 while the sea anemones1 corals1 c41 being those descendants of the primitive simple form1 have retained the original type of organization almost unchanged4 ,illustration3 ,fig4 #cde4--;,hydra viridis1 adhering to a stalk of ,anacharis alsinastrum4 ,the type of the group is the ,hydra1 a fresh-water polyp1 commonly found attached to the leaves and stems of many aquatic plants1 or floating pieces of stick4 ,two species are well known to microscopists1 the ,h4 viridis1 or green polyp1 and the ,h4 vulgaris1 somewhat darker in colour1 probably dependent upon the nature of its food4 ,the third1 less common species1 the ,h4 fasca1 is distinguished from both by the length of its tentacles1 which1 when fully extended1 greatly exceed those of either of the before-mentioned4 ,the fresh-water group measures from one-eighth to the one-third of an inch in length1 and form simple stocks of one1 two or more branches4 ,they almost exactly resemble in form the polyps of the ,hydractinia1 which are provided with a circle of tentacles4 ,when placed in a vessel of water and left undisturbed they often attach themselves to the side1 where they may be examined with a moderate power at leisure4 ,they are then seen to spread out their tentacles like fine threads1 and seize upon any small creature that may come in their way1 and by the same means convey it to a mouth capable of great extension4 ,all ,hydra possess stinging-cells1 by means of which they paralyse their prey4 ,many ,hydra attain to a large size1 and shoot out long poisonous filaments2 they also possess smaller kinds of smooth cells1 which appear to be employed for an entirely different purpose1 but for what is not positively known4 ,hydra usually multiply by means of buds1 an out-growth from the body1 and these remain attached to the mother stalk for some time1 often long enough to give rise to one or two smaller buds4 ,single eggs are also developed in the ectoderm beneath capsules1 or wart-like prominences4 ,the adult animal can be cut to pieces1 and from each piece a new individual will be developed4 ,this method of reproduction was first tried by the naturalist ,trembley in #agci1 whose experiments in this direction excited the greatest interest among the naturalists of the middle of the last century4 ,hydra fusca in various stages of development is given in outline in ,fig4 #cdf4 ,illustration3 ,fig4 #cdf4 #a1 #b1 #c4 ,hydra in various stages of development2 #d4 ,group of ,stentor polymorphus1 many-shaped ,stentor2 #e4 ,englena2 #f4 ,monads4 ,in the polyps belonging to this family the body-structure for the most part consists of a homogeneous aggregation of vesicular granules1 held together by an intercellular sarcode1 and capable of great extension and contraction1 so that these animals can assume a variety of forms and extend their body and tentacles until the latter become almost invisible4 ,it was the resemblance in this respect to the fabled ,hydra that originated the name4 ,its organ of prehension is termed the hasta2 this consists of a sac or opening at the terminal end of the tentacle1 within which is seen a saucer-shaped vesicle1 supporting a minute ovate body1 which carries a sharp calcareous piece termed a sagitta or arrow4 ,although the fresh-water ,hydra may be regarded as typical of this group of animals1 marine fauna furnish a far more extensive group in the corals1 jelly-fish1 and sea-anemones4 ,a smaller group1 the ,ctenophora1 although members of this sub-kingdom1 have not yet found their true position2 nevertheless they are interesting glassy1 transparent creatures1 either shaped like apples1 melons1 or ,phrygian caps1 or else forming bands of some considerable length2 all are wonderfully transparent1 with the single exception of the ,bero4 ,these inhabit the open sea1 and are only seen inshore when driven in by currents or strong winds4 ,their position in the water is usually more or less vertical1 the mouth being turned downwards4 ,the portion from which this group derives its name is the ribs1 which are symmetrically arranged1 and consist of rows of short transverse combs1 each forming rows of cilia1 which1 as they wave to and fro1 constitute a swimming or rowing plate1 their activity in the water depending upon the will of the animal4 ,they are also provided with an oral umbrella1 and capturing filaments or tentacles with hair-like branches4 ,these tentacles1 attached to the sides of the animal1 are capable of erection or withdrawal into pockets4 ,great variety is seen in these accessory organs of locomotion2 for instance1 the ,cydippid 7,plate ,,xvii47 have only arms1 but these are remarkable for their length1 and serve for the purpose of capturing food as well as for steering4 ,the most interesting1 if not the most beautiful of the ,ctenophora1 are the ,beroid2 it is this family that bear a resemblance to the ,phrygian cap 7,plate ,,xvii41 e74 ,the mouth is wide1 but it appears to have no capturing tentacles1 and yet their habits are carnivorous2 they will even devour their own relations4 ,many of the genus are phosphorescent1 and in place of stinging-cells have small spherical knobs beset with sticky globules1 in which their food becomes entangled1 and these are apparently in constant use4 ,illustration3 ,,plate ,,xvii4 ,,zoophytes1 ,,asteroids1 ,,nudibranchis1 ,,acaleps1 ,,echinoids1 ,,ctenophora1 ,,tunicata1 ,,and ,,crustaceans4 ,the ,stinging ,series1 ,cnidaria1 comprise sea-anemones1 corals1 jelly-fish among marine animals1 and ,hydra among the fresh-water ,clenterata2 and derive their name from a remarkably curious feature1 the so-called stinging capsules4 ,these are not only offensive1 but also defensive weapons with all the animals belonging to this group2 the possession of which has converted the bell-like jelly-fish into a simple ,cnidarian4 ,the principal change is in the gelatinous layer between the outer wall and the inner digesting layer of the ectoderm4 ,but without entering further into their structure and relations1 the stinging-cells and batteries claim especial attention4 ,these cells vary considerably in size without their characteristics being essentially changed4 ,the protoplasm of the cell is modified into a tolerably firm substance1 enclosing an oval or cylindrical vesicle4 ,closely associated with this is a pointed process1 standing up far above the level of the outer covering1 known as the cnidocil4 ,within the vesicle is found1 either spirally rolled up or in an irregular tangle1 a long filament or hollow tube1 a prolongation of the vesicle1 but turned outside in4 ,this tube is more than twenty times as long as the cell1 is pointed at the tip1 and beset with two rows of fine spirally-arranged barbed hooks4 ,when the cnidocil is touched or irritated1 this filament is violently shot out1 being then turned inside-out1 like the fingers of a glove4 ,so long as the thread remains rolled up within the vesicle the barbed hooks remain in their tube1 but when shot out1 they change to the outside4 ,the rolled-up filament appears to be filled with some poisonous material1 which is ejected when the tube is shot out1 and where the point strikes a wound is inflicted1 so that unless the prey is stronger than the attacker it cannot escape4 ,the greater the struggle1 the larger the number of capsules discharged in order to kill4 ,illustration3 ,fig4 #cdg4--,the ,stinging ,capsules of ,cnidaria4 #a and #b4 ,retracted filaments2 #c4 ,partly protruded2 #d4 ,fully protruded4 ,magnified #fjj4 7,warne47 ,polypomedus4--,among the higher development of the stinging group is the jelly-fish4 ,the ,siphonophora1 as represented by the ,portuguese man-of-war1 are in their turn the highest development of swimming-bells1 and exhibit many modifications and combinations of individuals4 ,the tentacles of the ,physalia1 the best known1 are stiff with batteries of stinging-capsules1 the sting of which is more like the shock of the electric current4 ,the ,challenger soundings brought to light some remarkably interesting forms1 and these have furnished much work for the microscope1 as all their larval forms are extremely curious4 ,among the ,hydromedus there are many different life histories4 ,take the jelly-fish1 the eggs of which have given up forming stocks1 and are hatched out at once as ,medus4 ,there are others1 the eggs of which form stocks2 others1 again1 in which the sexual individuals do not swim away as jelly-fish4 ,the last were at one time described under a new name1 because of one or two curious forms being taken creeping on the ground4 ,this creeping ,medusa 7,clavatella prolifera7 has six arms1 the tips of which are provided with true suckers1 and on these it walks as on stilts1 while from each arm a short stalk arises1 the swollen end of which is beset with stinging capsules4 ,it has an extensile mouth-tube1 and feeds upon small crustaceans found on seaweeds4 ,illustration3 ,fig4 #cdh4--,plumularia primata4 ,doris tuberculata seen clinging to a fucus4 ,among the forms that swim away as jelly-fish a very curious example is presented in ,corymorpha mutans4 ,these swim about for a time1 and then firmly attach themselves by numerous thread-like appendages1 forced into the sand1 and where the young prepare for their next metamorphosis4 ,as an example of the stocks of those representatives which do not swim away as jelly-fish1 take the beautifully-feathered1 plant-like creatures found erect along the seashore1 the ,sertularia 7,fig4 #ceh1 ,no4 #ab7 and ,plumularia4 ,plumularia primata1 ,fig4 #cdh4 ,other members of these groups will be found in ,plate ,,iv41 ,nos4 #ie-ii4 ,illustration3 ,fig4 #cdi4--;,group of female stock of ,hydractinia echinata4 a1 a4 ,nutritive individuals2 b1 b4 ,female individuals and groups of eggs4 ,highly magnified4--7,warne47 ,in addition to the nutritive individuals1 there are the egg-bearing2 these do not become free-swimming individuals4 ,one small family is neither branched nor feathered--the ,hydractinia echinata1 found in the ,north ,sea and on the ,norwegian coasts1 where it attaches itself to the shells of gastropods1 selecting those inhabited by hermit crabs4 ,the part of the stock common to all the individuals is the skin-like portion which adheres to the surface of the shell4 ,in some spiny processes are produced1 and the nutritive canals running down the stems of the polyps are continued into the membrane belonging to the stock1 as seen in ,fig4 #cdi4 ,the nutritive individuals are distinguished by long tentacles1 mouths1 and digestive canals4 ,the females have no mouths1 and are supplied with food through the system of canals running to them from the nutritive males4 ,these reproductive members are furnished with stinging threads instead of tentacles for the protection of their ova4 ,the ciliated larv1 in a very short time1 swim off to found new colonies4 ,illustration3 ,fig4 #cej4--,medus1 ,jelly-fish4 ,the free-swimming jelly-fish 7,fig4 #cej1 and ,plate ,,xvii41 c and d7 belong to the order ,scyphomedus4 ,these are characterised by their delicate colouring1 and from the arrangement of their nervous system1 which can only be made out by staining4 ,some new and curious forms were dredged from a depth of more than #f1jjj feet off the coast of ,new ,zealand1 varying in size from an inch to twenty inches2 many having from four to eight or ten eyes arranged along the margin4 ,anthozoa4--,from the free-swimming we turn to a group of permanently fixed polyp forms1 the sea-anemones and corals4 ,the development of ,monoxenia commences with the egg1 repeatedly dividing into many parts 7,fig4 #cea1 ,c1 ,d1 and ,e71 by a process common to the animal kingdom1 termed egg-segmentation1 in this particular instance proceeding from an apparently hollow sphere1 ,a1 enclosing a single layer of cells1 ,g4 ,each cell sends out a long cilia1 or whip-like process1 ,f1 by means of which the larva turns about and swims in the body fluid of the parent polyp4 ,one half of the sphere now becomes enfolded into the other half1 ,h1 and forms what is termed a gastrula1 ,i1 ,k4 ,the gastrula stage of ,monoxenia is of the simplest kind1 the larva forming a sac1 with walls consisting of two layers1 an outer1 or ectoderm1 and an inner1 or endoderm4 ,the transition from the flat dish shape1 ,h1 to the sac with a narrow mouth is at once clear1 and the knowledge that all the ,clenterates proceed from similar larv1 and that all the complications of their various systems are developed from a simple gastrula1 throws much light on their anatomy4 ,during these transitions the endoderm1 whose cells multiply1 continues as an uninterrupted lining to the stomach and its appendages1 while the ectoderm yields the cuticular elements4 ,illustration3 ,fig4 #cea4--,stages in development of ,monoxenia ,darwinii1 #fjj4--7,warne47 ,a third intermediate gelatinous layer1 the mesogla1 arises between the two layers in which muscles and connective interstitial tissue appear4 ,in the mesogla of one species of coral calcification takes place2 this internal calcification has but a small share in the work of the great rock-making corals1 their most important calcification being external4 ,in ,monoxenia1 although the transition from the gastrula larva to the adult animal has not been seen1 there can be no doubt as to how this is carried out1 the transformations having been watched throughout in other species4 ,the larva attaches itself with the end opposite the mouth1 the cilia disappear1 and after the mouth-tube has been formed by the folding in of the anterior end along the longitudinal axis of the body1 and has thus become marked off from the stomach1 eight hollow tentacles rise round the mouth as outgrowths of the body cavity1 or as direct continuations of the stomach4 ,like all other corals1 ,monoxenia periodically multiply by means of eggs1 which are formed either in the walls of the radiating partitions or septa1 or along the free edges4 ,these are ejected through the oral opening4 ,as a rule1 the polyps are either male or female2 but in stock-forming species individuals of the two sexes are often mixed4 ,monoxenia may be taken as the simplest type of the regularly radiate polyps2 in all the different organs being repeated in regular rings round a central axis2 the mouth also is circular4 ,from this interesting account1 drawn by ,haeckel1 of a simple polyp1 it will be at once seen what kind of radiate animal it is that builds up the coral reefs4 8,no garden on earth can match the gardens of the sea that circle the northern part of ,australia4 ,as the tide ebbs in azure sunset1 coral-reefs peer out symmetrically arranged in beds and intersected by emerald pathways coursing through corals of all hues and tints fathoms deep in the channels40 ,in a growing polyp-stock the individuals usually remain in organic connection2 that is to say1 each first provides for itself and then shares its superfluity with others1 sometimes by means of a continuous reticulated system of canals perforating the calcareous substance which often separates the members of one stock from another4 ,the whole colony may thus be physiologically one creature with many mouths4 ,there are others that remain single1 as the inverted pyramidal-looking bodies1 ,fungid1 commonly called 8,sea-mushrooms10 found in great variety4 ,the colour of the polypidom is white1 of a flattened round shape1 made up of thin plates or scales1 imbedded in a translucent jelly-like substance1 and within is concealed a polyp2 the footstalk1 by means of which the animal is attached to the rock1 is of a calcareous nature 7,fig4 #ceb1 ,no4 #a74 ,illustration3 ,fig4 #ceb4--,sea-,anemones4 #a4 ,actinia rubra1 tentacles displayed and retracted2 #b4 ,heticictis bellis2 #c4 ,h4 bellis1 seen from above4 ,hexactinia 7six-rayed polyps7 are not limited to six rays1 as the name given them may seem to imply2 they are1 in fact1 very numerous in some of the largest and most gorgeous of the sea-anemones4 ,all are distinguished by their solitary manner of life1 their size1 and their vivid and variedly beautiful colouring4 ,the endoderm is firm1 and when the animal withdraws its tentacles and shuts its body substance in1 there is some difficulty in penetrating to the interior4 ,it does not1 however1 secrete a calcareous skeleton inside or out1 as do the true coral polyps4 ,among the ,hexactinia the sea-anemone 7,fig4 #ceb7 takes the first place4 ,these beautifully coloured creatures are1 for the most part1 found attached to the spot selected by the larv2 a few species bore into the sand with the posterior part of the body1 or build a sheath1 which they inhabit4 ,they are voracious feeders1 and devour large pieces of flesh1 and even mussel and oysters1 sucking them in by means of their long grasping tentacles4 ,well-fed anemones change their skin frequently1 during which process they remain closely retracted2 the shed skin forms a loose girdle around the base4 ,actinia bellis not infrequently attach themselves to the shells of crabs and whelks1 and are thus carried to pastures new4 ,illustration3 ,fig4 #cec4--,larv of ,sea-,anemones1 ,actinia effta1 highly magnified4 ,on account of the ease with which anemones are kept in captivity1 their mode of reproduction can be closely observed4 ,with but few exceptions they develop from eggs1 and in the course of a few weeks are hatched into ciliated infusorial larv1 presenting most curious and exquisite representations of jugs and jars1 with cover lids 7as seen in ,fig4 #cec1 ,actinia effta74 ,these evince the handiwork of a master hand in the ceramic art4 ,they are1 however1 of so translucent a nature as to permit of the internal structure being seen to consist of nerves and vessels1 and which are rendered more apparent by staining4 ,these settle down in a week or ten days1 and then shed their cilia1 the first tentacle appearing during the process of attachment4 ,in some species the young ,actini are seen to pass through their whole development within the body cavity of the parent4 ,most anemones are provided with several circles of more or less cylindrical tentacles1 and there are a few specially beautiful species which1 besides tentacles of the usual form1 have1 either within or without the ordinary circle of tentacles1 lobed or leaf-like tactile and seizing organs4 ,these belong to the family of the beautiful ,crambactis of the ,red ,sea4 ,below these grasping tentacles comes a circle of thicker arms unlike the former1 being spindle shaped4 ,all the tentacles of the sea-anemones are hollow with a fine aperture at the tip1 through which1 on closing rapidly1 it is seen to expel a jet of water4 ,true ,corals4--,it will have been noticed in the foregoing remarks that in the soft body-division of the ,hexactinia there are both single individuals and colonies joined together to form stocks4 ,the same diversity in this respect will be found among corals proper1 with this difference1 that the skeleton-forming polyps1 by combining1 build up substantial structures in the most secure and advantageous positions4 ,now it so happens that all the corals found about our coasts are generally small and solitary dwellers1 one of the best known of which is the scarlet crisp coral1 ,flabellum1 and is characterised by the slit-like form of the mouth4 ,viewed sideways it resembles a small fan fastened along the edges1 and just inside a row of fully developed tentacles is seen protruding4 ,an interesting form of budding occurs in these corals3 the buds fall off1 and in this budding condition the coral might pass1 and indeed has been described as a different species of ,flabellum4 ,the colour of the coral is a beautifully transparent red4 ,remarkable as the solitary corals are1 they are surpassed both in number and in form by those which form compound stocks1 that is to say1 in which the buds do not fall off1 but go on building up coral islands and barrier reefs in the warmer seas4 ,some very few typical forms only are given in the group accompanying1 shown in ,fig4 #ceh4 ,a different kind of stock is developed in a number of forms1 some producing many buds1 as in the ,madrepores1 in which selected polyps spring up above the rest1 their sides also becoming covered with small buds1 each one of which is a living1 feeding1 coral animal surrounded by a crown of tentacles4 ,these ,madrepores play a very important part in the building up of coral reefs4 ,illustration3 ,fig4 #ced4 ,developmental stages of ,larv1 ,astroides calycularis1 #dj4 ,another massive coral1 the ,astroides calycularis1 has a different mode of growth1 the tubes not being fused together4 ,when seen standing out these yellowish-red polyps have been mistaken for small anemones4 ,the larv of this coral leave the egg while still in the large chambered body cavity of the parent1 where they swim about for a time1 till they escape through the mouth4 ,they are worm-like in form1 and swim by means of cilia1 which are thicker at the foremost end4 ,the mouth first appears after leaving the parent1 but as they soon become exhausted by the effort they assume a contracted form1 and attach themselves1 as do anemones1 by pressing the thicker end of the body against a rock1 the whole contracting into a thick round disc1 while longitudinal furrows become visible at the upper part where the mouth sinks in4 ,at the end of these furrows twelve tentacles appear4 ,the accompanying illustration shows the various stages through which the larv pass in rapid succession 7,fig4 #ced72 at the same time it has already commenced to secrete its calcareous skeleton4 ,this is not formed as a connected whole but from a number of separate centres of secretion formed between the polyp and the substance to which it has attached itself1 and which become gradually fused into a perfect skeleton4 ,a section of the polyp at this stage forms an interesting microscopical object4 ,the so-called eight-rayed corals consist of the one genus ,tubipora1 the members of which are few in number and not varied in form 7,fig4 #ceh1 ,no4 #aj74 ,in the structure1 however1 of skeletons they are unique among extant corals4 ,each individual secretes a smooth-walled tube without calcification of the vertical septa4 ,these tubes1 like the pipes of an organ1 stand almost parallel1 and are united to form a stock by means of transverse platforms4 ,the formation of buds does not appear to take place in this family4 ,another of the eight-rayed corals is ,gorgoniid4 ,these are permanently fixed to the spot on which they are found1 and form a bush-like growth1 giving no idea of the living coral1 as it rises in graceful branching colonies1 in deep water1 and represents a portion of ,gorgonia nobilis with polyps expanded 7,figs4 #cdd and #ceh1 ,no4 #i74 ,other corals present numerous other departures from the types we have been considering1 but so far modified in form as that of the ,sea-pen1 ,veretillum 7,fig4 #cee71 the stock part of which is surrounded by polyps continued down a portion of the cylindrical stalk4 ,the best known of the species is ,pennatula phosphorea of the ,mediterranean4 ,illustration3 ,fig4 #cee4 #a4 ,pennatula phosphorea2 #b4 ,synapta chirodata2 #c4 ,anchor-shaped spiculum and plate from the ectoderm of same4 ,pennatulid4--,this family derives its name from penna1 a quill4 ,their spicula also resemble a penholder in appearance1 shown in ,fig4 #ceh1 ,no4 #c4 ,the polyps are without colour1 provided with eight rather long retractile tentacula1 beautifully ciliated on the inner aspect with two series of short processes1 and strengthened by these crystalline spicula1 a row being carried up the stalk1 together with a series of ciliated processes4 ,the mouth1 occupying the centre of the tentacula1 is somewhat angular4 ,the ova lie between the membranous part of the pinn2 these are globular1 of a yellowish colour1 and by pressure can be made to pass through the mouth4 ,dr4 ,grant wrote3--8,a more singular and beautiful spectacle could scarcely be conceived than that of a deep purple ,pennatula phosphorea1 with all its delicate transparent polyps expanded and emitting their usual brilliant phosphorescent light1 sailing through the still and dark abyss1 by the regular and synchronous pulsations of the minute fringed arms of the polyps40 ,the spicula are seen to be a continuous series of cones fitting into each other4 ,bryozoa1 ,moss-animals4 ,the exact position in which the ,bryozoa1 or moss-animals1 should be placed in the animal kingdom has not been finally determined4 ,they were at one time associated with corals2 then with sponges2 but1 on further acquaintance1 it became evident that they did not belong to either4 ,naturalists also claimed them as ,rotifers and ,ciliata1 but this claim met with no better reception4 ,since they appear to have no settled classification1 there can be no objection to linking them once more to corals1 as they apparently resemble these animals by always living in colonies1 the individual members of which are joined in a number of different ways to form stocks1 the individuals themselves1 however1 being very much smaller than those of corals proper4 ,the advantage is that the structure of the ,bryozoans can be more readily studied1 as many of them live in transparent chambers or cells1 the walls of which1 although somewhat firmly agglutinated together1 are flexible enough to fold up1 as the animals instantly withdraw their bodies and close up the top on the slightest alarm 7,fig4 #cef74 ,illustration3 ,fig4 #cef4--,paludicella1 tentacles expanded and cell closed4 ,illustration3 ,fig4 #ceg4--,sea-moss1 ,flustra1 the body having been withdrawn from its cell4 ,the general structure of the ,bryozoan individual1 figured attached by its footstalk to a stem of wood1 consists of a mouth at the anterior part of the body opening into a muscular pharynx in the alimentary canal1 together occupying a considerable amount of space4 ,the terminal portion turns upon itself towards the oral opening1 its chief attachment being a short strand of tissue termed the funiculus 7shown in ,fig4 #ceh1 ,no4 #aa74 ,in all adults two masses of cells are found attached to the wall of the chamber2 the upper yields the eggs1 within the lower the male elements are developed4 ,moss-animals are hermaphrodite1 fertilisation being effected by the two elements mingling together in the body fluid4 ,these are the essential points in the structure of the whole seventeen hundred species4 ,among the larger colonies a number of fresh-water genera are found attached to the roots and branches of aquatic plants1 most of which1 however1 are inconspicuous4 ,the beauty of these minute bodies can only be seen under the microscope4 ,many consist of delicate branching growths1 the ,sea-mats 7,flustra71 for instance2 others again appear as attractive lace corals1 between the open meshes of which multitudes of minute apertures crowned with tentacles are displayed4 ,the several individuals of the genus ,lepralia are arranged in rows1 and further distinguished by the animals being developed only on one side of the stock4 ,the marvellous variety of forms presented by these small animals is in a measure determined by the particular manner of their buddings4 ,the greater number of fresh-water moss-animals belong to the order ,phylactolmata1 so called because the mouth is provided with a tongue-shaped lid4 ,the crown of tentacles is furnished with rows of cilia1 and is horseshoe-shaped1 the whole being surrounded at its base by an integument forming a kind of cup1 which is either soft or horny4 ,those belonging to the wandering types 7,cristatella1 ,plate ,,iv41 ,nos4 #ie-ih7 form flattened elliptical colonies1 some of which creep or move about on a kind of foot4 ,a nervous system pervades the mass of polyps1 while in each separate polyp a nerve ganglion is seen to be situated between the sophagus and the posterior part of the alimentary canal4 ,the colony nerve system regulates the movements of the stock4 ,illustration3 ,fig4 #ceh4--,typical forms of ,corals4 #a4 ,fungia agariciformis2 #b4 ,alcyonium1 ,cydonium ,mulleri2 #c4 ,cydonium1 polyps protruding and tentacles expanded1 others closed2 #d4 ,a stock viewed from above2 #e4 ,madrepore abrotanoide2 #f4 ,madrepore1 slightly magnified1 showing oral opening2 #g4 ,corallid2 #h4 ,coral1 polyps protruding from cells2 #i4 ,gorgonia nobilis1 with polyps expanded2 #aj4 ,tubipora musica2 #aa4 ,tubes of same1 with polyps expanded1 one cut longitudinally to show internal structure2 #ab4 ,sertularia1 polyps protruded1 and withdrawn into their polypidoms4 ,illustration3 ,fig4 #cei4 #a4 ,coryne stauridia2 #b4 ,a tentacle detached and magnified #bjj diameters4 ,there are many beautifully formed freshwater polyps deserving of more than a passing notice1 as the slender ,coryne 7,coryne stauridia71 found adhering to the footstalk of a ,rhodymenia 7,fig4 #cei71 about which it creeps in the form of a white thread4 ,on placing both under the microscope1 the thread-like body of the little animal appears cylindrical and tubular1 perfectly transparent1 and permeated by a central core1 apparently cellular in texture1 hollow1 and within which a rather slow circulation of globules is perceived4 ,the parent ,coryne sends off numerous branches1 the terminal head of which is oblong1 cylindrical1 and at the extreme end there are arranged four tentacles1 long and slender1 each being furnished with a nodular head4 ,a magnified view of one detached is shown erect 7,fig4 #cei1 ,no4 #b74 ,this polyp is much infested by parasites1 vorticella growing on it in immense numbers1 forming aggregated clusters here and there1 individuals of the parasitic colony adhering to each other1 and projecting outwards in every direction4 ,alcyonella1 another fresh-water polyp1 is found in the autumn of the year in all the ,london ,docks adhering to pieces of floating timber4 ,a4 stagnorum partakes of the character of a sponge rather than that of a polyp4 ,it is usually found in gelatinous colonies1 and when stood aside for a short time these put forth a number of ciliated tentacles 7shown in ,fig4 #cfj1 magnified #ajj diameters74 ,the ova contained within the sac1 and viewed by transmitted light1 appear as opaque spheres surrounded by a thin transparent margin2 these increase in thickness as the ova is developed1 and such of the ova as lie in contact seem to unite and form a statoblast4 ,a rapid current in the water around each animal1 drawing with it loose particles and floating animalcules1 is seen moving with some velocity as in other ciliated bodies2 and a zone of very minute vibrating cilia surrounds the transparent margin of each tentacle4 ,illustration3 ,fig4 #cfj4--;,alcyonella fluviatella4 ,dr4 ,percival ,wright discovered on the western coast of ,ireland a new genus of ,alcyonid1 which he named after the well-known naturalist ,harte1 ,hartea elegans 7,plate ,,iv41 ,no4 #hf74 ,this polyp is solitary1 the body cylindrical1 and fixed by its base to the rock2 it has eight ciliated tentacles1 which are knobbed at their base and most freely displayed4 ,it is a very beautiful polyzoon of a clear white colour1 and when fully expanded stands three-quarters of an inch high4 ,lophopus crystallinus 7,plate ,,iv41 ,no4 #ih7 displays beautiful plumes of tentacles arranged in a double horseshoe-shaped series4 ,when first observed these polyps resemble in many respects masses of the water snail ova1 for which they are often mistaken4 ,on placing these jelly-like masses into a glass trough with some of the clear water taken from the stream in which they are found1 delicate tubes are seen to cautiously protrude1 and the beautiful fringes of cilia are quickly brought into play4 ,the organisation of ,l4 crystallinus is simple1 although it is provided with organs of digestion1 circulation1 respiration1 and generation4 ,the nervous#gj and muscular systems are well developed4 ,this polyp increases both by budding and by ova1 both of which conditions are shown in ,plate ,,iv41 ,no4 #ih4 ,the ova are enclosed in the transparent case of the parent4 ,in ,lophopus and some other fresh-water genera1 ,cristatella1 ,plumatella1 and ,alcyonella1 the neural margin of the ,lophopore is extended into two triangular arms1 giving it the appearance of a deep crescent4 ,another family presents a contrast3 there is no lid to the mouth1 and the tentacles are arranged in a circle on a disc4 ,an important rise in organisation is found in the ,gymnolmata1 especially in the lip-mouthed forms2 the individuals belonging to this order vary in structure and fulfil different physiological functions4 ,there are structures known as zocia1 stolons1 avicularia1 vibracula1 and ovicells1 some of which are merely modified individuals4 ,the zocia are the normal individuals of the colony1 fully developed for most of the functions of life2 the stolons have a much humbler function1 but are indispensable--they are the root-like outgrowths of the stock1 and serve for attaching the colony to foreign objects4 ,the most remarkable are those known as avicularia1 so called because they resemble the head of a bird4 ,this process acts as a pair of forceps1 the large upper blade of which is very like the skull and upper jaw of a bird1 and the smaller lower blade 7like the lower jaw7 constantly opens and shuts by means of a complicated arrangement of muscles 7shown in ,fig4 #cfa74 ,these avicularia are movably attached by short muscles to the neck1 and are found near the entrance to a zocium4 ,they turn from side to side1 snapping in all directions1 catching at every particle of food that may come near2 at length the morsel is drawn into the mouth by the cilia on the tentacles4 ,from this very peculiar structure the ,chilostomata were originally named bird's-head corallines1 then specifically shepherd's-purse corallines1 ,notamia bursaria4 ,equally interesting1 again1 are the vibracula1 long thread-like structures1 attached by short footstalks4 ,these keep up a constant whip-like motion1 the object of which is not quite clear4 ,the ovicells1 or egg receptacles1 are found at the lower ends of the zocia in the form of shields1 helmets1 or vesicles4 ,in ,plate ,,iv41 ,nos4 #ie and #if1 a front and edge view of the statoblast is shown highly magnified4 ,illustration3 ,fig4 #cfa4 #a4 ,notamia bursaria1 shepherd's-purse ,bryozoa2 #b4 ,polyp magnified and withdrawn into its cell2 #c4 ,portion of a colony of ,hydroid polyps4 ,another sub-order consists of the ,cyclostomata1 or round-mouthed ,bryozoans1 of which the ,tubulipora is the typical form4 ,the stocks are cup-shaped incrustations1 the individuals radiating outwards1 as in ,plate ,,iv41 ,no4 #ib4 ,tubularia dumortierii is a very interesting form1 the germinal bodies1 statoblasts1 being formed as cell masses on the strand1 or funiculus1 which also maintains the stomach in its place4 ,they are round or oval in shape1 and brown or yellow in colour1 and consist of two valves fitted one upon the other like watch glasses1 as shown in ,no4 #if4 ,a number of other statoblasts are shown1 ,nos4 #ig1 #ih1 and #ii4 ,the edge running round ,no4 #ie is seen to have barbed tips2 the ring itself contains small air chambers1 and is termed the swimming belt4 ,it is1 in fact1 a perfect hydrostatic apparatus1 giving support to the winter buds or statoblasts on the surface of the water4 ,the barbed hooks apparently act as anchors1 and by their means they catch on at points suitable for their development during the coming spring4 ,as soon as the time comes1 the two halves split apart and the germinal mass emerges forth4 ,out of these winter buds and statoblasts asexually produced individuals arise1 which reproduce themselves sexually1 their descendants again yielding winter germs4 ,in short1 an alternation of generations is a continually recurring process4 ,illustration3 ,fig4 #cfb4--,lingula pyramidata4 ,brachiopoda4--,here again we have to do with an enigmatical class of arm-footed animals1 of which the ,lamp-shells may be regarded as typical4 ,these have remained unaltered from the earliest geological epochs4 ,brachiopods are divided into two orders3 those having shells without hinges1 and those with shells hinged together4 ,on the whole they possess less interest for the microscopists than many other animals1 except in their earliest developmental stages of existence4 ,one of the most interesting of the hinge-class group1 living chiefly near the shores of the warmer seas1 is the ,lingulid4 ,the valves are almost exactly similar1 but are not hinged together1 and have no processes for the support of the thick fleshy spiral arms of the animals4 ,in ,l4 pyramidata1 found around the ,philippine ,islands 7,fig4 #cfb71 the stalk is nine times longer than the body4 ,the animal does not attach itself by this1 but moves about like a worm1 making tubes out of sand1 into which it can withdraw itself and disappear4 ,the cilia at the mantle edge form a fine sieve1 thus preventing foreign particles from entering the gills4 ,its internal structure possesses points of interest1 and the parasitic growths covering the cartilaginous structure1 miscalled a shell1 are curious1 and excite the attention of the naturalist4 ,another bivalve so unlike a crustacean1 among which it has been placed1 ,i may venture to describe among ,lamp-shells4 ,i refer to the barnacle 7,lepas7 generally met with covering the bottoms of ships4 ,these1 as in the former genus1 are more interesting to the microscopist in the early stage of existence1 and also for the curious parasites known to infest them4 ,the barnacle protrudes through its two valves six pairs of slender1 bristly1 two-branched filamentous limbs1 which keep up a constant sweeping motion1 and whereby it secures its supply of food 7,fig4 #cfc74 ,when first hatched the young are in the ,nauplius stage1 being furnished with a median eye and three pairs of flagellated appendages4 ,after enjoying a free life the larva moults and passes into a second stage1 in which with its two eyes and compressed carapace 7shown in ,fig4 #cfd7 it so nearly resembles a ,daphnia4 ,before these thoracic appendages entirely disappear they first change places1 and then each is seen to be provided with a sucker2 by this means the larva fixes itself to its permanent resting-place1 while a cement gland pours out a secretion that glues it firmly to the point of attachment chosen4 ,these ,cirripedes are not true parasites1 inasmuch as they do not extract nourishment from the body to which they are attached4 ,illustration3 ,fig4 #cfc4 #a4 ,spat of oyster1 some ciliated2 #b4 ,barnacles attached by footstalks4 ,one species1 the ,proteolepas1 is in the adult stage a maggot-like1 limbless1 shell-less animal found living within the mantle chamber of other members of the same order1 while the root-headed ,cirripedes 7,peltogaster curvatus1 as ,fig4 #cfd1 ,no4 #a7 live parasitically upon higher crustaceans4 ,echinodermata4--,this sub-kingdom includes the star-fishes1 stone-lilies1 sea-urchins1 feather-stars1 and sea-cucumbers1 some of which have been already alluded to1 and are so well known that they need no lengthy description1 while of the fossil sea-urchins of our chalk formations1 the ,pentremites and ,crinoids1 whose silicious remains are so abundant and so familiar to naturalists and geologists1 but little remains to be said4 ,they are chiefly interesting to the microscopist from their calcareous and silicious appendages1 known as spicula4 ,in the sea-urchin1 brittle-star1 or feather-star1 the outer body surface consists almost wholly of a deposit of calcium carbonate1 combined in the form of little plates built up into a rigid 8test10 whereas in the star-fish it usually forms a kind of scaffolding1 between the layers of which there stretches a firm leathery skin4 ,among the sea-cucumbers1 the living specimens of which present extraordinary variations both in form and character1 the deposit consists chiefly of small spicules which grate when the skin is cut with a knife4 ,if a thin section of the skin is examined under the microscope1 the spicules are seen to be profusely distributed in the middle layer4 ,the same deposit takes place in the stalked column of a crinoid and in sea-urchins 7,echinodermata71 which has tended to preserve them in the fossilised state4 ,fig4 #cfe is selected as exhibiting to perfection the ,medusa-headed ,pentacrinoid4 ,this echinoderm differs in two characters3 first1 its microscopic structure is that of a meshwork deposited in the spaces of a network of soft tissue2 secondly1 that each element1 whether a spicule or a plate1 is1 despite its trellised structure1 deposited around regular lines of crystallisation 7shown in ,plate ,,iv41 ,nos4 #hi and #ij74 ,owing to these characteristics the minutest portion of an echinoderm skeleton is readily recognised1 even when fossilised1 under the microscope4 ,even the species of the sea-cucumber can be determined by the shape of their spicules4 ,illustration3 ,fig4 #cfd4--,parasitic ,barnacles4 #a4 ,peltogaster curvatus2 #b4 ,nauplius larva of ,parthenopea2 #bjj4 ,another noticeable feature in the radiate structure is that in many cases it gives to the animal a star-shape1 to which the names of star-fish and brittle-star are given 7see ,plate ,,iv41 ,no4 #ia1 and ,plate ,,xvii41 f and n74 ,the ordinary five-rayed star-fish is found everywhere around the ,english coasts4 ,this constant arrangement of organs holds good in the majority of the echinoderms2 it can be detected in the ,holothurians1 where1 beside the feathery tentacles of the head1 rows of shorter sucker-like processes will be found1 which in some instances extend the whole length of the body1 the fixed number of rows being also five in their internal organs4 ,hence these animals were formerly grouped under ,radiata4 ,but if a sea-cucumber or sea-urchin be dissected1 a marked distinction will be found between them1 in one portion of the organism in particular3 the intestine is shut off from the rest of the body-cavity1 often coiling round inside4 ,examine a star-fish or sea-urchin on the under-surface of the rays1 and1 passing in five bands from top to bottom1 a number of small cylindrical processes are seen gently waving about2 these lie in two rows with a clear space between them1 and are termed in consequence ambulacrum4 ,they end in sucker-like discs1 which enable the animal to attach itself1 or pull itself against strong currents4 ,illustration3 ,fig4 #cfe4--,medusa-headed ,pentacrinoid4 a4 ,crown and part of stem2 b4 ,upper surface of body1 the arms broken away1 showing the food grooves passing to the central mouth4--7,warne47 ,just one other special feature should be noticed3 radial canals pass along under the ambulacra1 and join a ring-canal around the mouth1 well supplied by nerve cells4 ,illustration3 ,fig4 #cff4 #a4 ,transverse section of a branch of ,myriapore2 #b1 and the others ,section of the stem of ,virgularia mirabilis2 #c1 ,spiculum from the outer surface of ,sea-pen2 #d1 ,spicula from ,isis hippuris2 #e1 from ,gorgonia elongata2 #f1 from ,alcyonium2 #g1 and from ,gorgonia umbraculum2 #h1 ,calcareous remains of a ,crinoid4 ,crinoids 7stone-lilies71 on the other hand1 are formed of a series of flat rings1 pierced through by a narrow canal4 ,the ossicles1 as they are termed1 are joined by ligaments passing through their solid substance and endowed with muscular power2 the central part serves for the passage of blood-vessels1 and is surrounded by a sheath of nervous tissue that controls the movements of the stem1 the latter being encrusted by a number of fine rootlets4 ,the stems possess a limited power of bending4 ,in the words of ,professor ,agassiz1 8,the stem itself passes slowly from a rigid vertical attitude to a curved or even a drooping position2 the cirri move more rapidly than the arms1 and the animal uses them as hooks to catch hold of objects1 and on account of their sharp extremities they are well adapted to retain their hold of prey40 ,the rosy-feather star-fish is often found clinging to a tube of the ,sabella worm2 the food of crinoids consists of foraminifera1 diatoms1 and the larv of crustaceans4 ,there are so many curious features in connection with the ,echinodermata that my readers may with advantage consult 8,the ,challenger ,reports0 and ,warne's 8,natural ,history0 on other points of interest4 ,holothuroidea 7sea-cucumbers7 are elongated slug-like creatures1 the skin being in structure similar to that of the slug1 with a comparatively small amount of calcareous matter4 ,usually this occurs in small spicules1 which assume very definite shapes1 as the anchors of ,synapta 7,plate ,,iv41 ,no4 #hg1 and in ,fig4 #cee74 ,there are also rings of calcareous plates around the gullet1 five of which have the same relation to the radial water-vessels as the auricles round the jaws of a sea-urchin1 and which likewise serve for the attachment of muscles4 ,these plates are seen in ,plate ,,viii41 ,nos4 #aga and #agb1 as they appear coloured by selenite films under polarised light4 ,around the mouth in ,cucumaria is a fringe of branched tentacles connected with the water-vascular ring2 these appear to be used as a net to intercept floating organisms4 ,correlated with the star-fishes is a small family based on the character of their pincer-like organs1 called pedicellari1 on the surface of the test 7shown in ,plate ,,iv41 ,nos4 #ic and #id1 magnified #be74 ,movable spines cover the surface of these echinoderms1 varying in size from minute bristle-like structures to long rods4 ,the pedicellari are1 it is believed1 derived from the smaller spines1 and two of them are united at the base by muscles1 slightly curved1 and made to approach each other at their extremities4 ,there is a gradual modification of this type through the whole series4 ,many uses have been assigned to them1 as the holding of food1 as they have been seen to hold to the fronds of seaweed and keep them steady until the spines and tube feet can be brought into action4 ,the inner surface of the pedicellari are known to be the most sensitive1 and the blades close on the minutest object touching the inner surface4 ,beside these peculiar bodies the surface of the skin has small tubular processes1 and tubular feet with suckers at the end4 ,at the extremity of each arm is a single tube-foot with an impaired tentacle1 and above this again is a small eye coloured by red pigment4 ,passing by many other points of interest in the ,echinoid1 the spines are seen to be attached to the test or shell by a ball and socket joint and well-arranged muscles1 whereby the spines can be moved in any direction4 ,the tubercles1 however1 do not cover the whole test1 but are disposed chiefly in five broad zones extending from one pole to another4 ,when a transverse section of a spine is examined by a medium power it is seen to be made up of a series of concentric and radiating layers 7shown in ,plate ,,xviii41 ,nos4 #a and #b71 the centre being occupied by reticulated structure and structureless spots arranged at equal distances2 these may be termed ribs or pillars4 ,passing towards the margin are other rows conveying the impression of a beautiful indented reticulated tissue4 ,many of the spines present no structure1 while others exhibit a series of concentric rings of successive growth1 which strongly remind one of the medullary rays of plants4 ,when a vertical section of a spine is submitted to examination1 it is seen to be composed of cones placed one above the other1 the outer margin of each cone being formed by the series of pillars4 ,in certain species of ,echinus the number of cones is very considerable1 while in others there are seldom more than one or two to be found2 from these1 transverse sections may when made show no concentric rings1 only the external row of pillars4 ,the skeleton of echinoderms contains but a small amount of organic matter1 as will be seen on dissolving out the calcareous portion in dilute nitric or hydrochloric acids4 ,the residuum structure will appear to be meshes or areol1 bounded by a substance having a fibrous appearance1 intermingled with granulous matter2 in fact1 it bears a close resemblance to the areolar tissue of higher animals1 and the test may be considered as formed1 not by the consolidation of the cells of the ectoderm1 as in the mollusc1 but by the calcification of the fibro-areolar tissue of the endoderm4 ,this calcification of a simple fibrous tissue by the deposit of a mineral substance1 not in the meshes of areol but in intimate union with the organic basis1 is a condition of much interest to the physiologist2 it presents an example of a process which seems to have an important share in the formation and growth of bone1 namely1 in the progressive calcification of the fibrous tissue of the periosteum membrane covering of the bone4 ,the development of the sea-urchin from the fertilised egg first divides and then sub-divides1 and in a short time the embryo issues forth with a small tuft of cilia1 by means of which it swims off freely4 ,the larv1 in its full development1 measures about one millimetre in diameter1 and is a curious and remarkable creature4 ,the sub-kingdom ,mollusca comprises some fifty thousand species1 and fresh forms are being constantly discovered1 the number of the aquatic genera being more than double that of the terrestrial species1 for it matters not to what depth of ocean the dredge is let down1 some new form is certain to be gathered4 ,the ,challenger expedition has enriched our knowledge of the deep-sea fauna to an enormous extent2 so much so1 that fifty volumes have already been published descriptive of animals brought to the surface4 ,nevertheless1 we are told that the great coast lines of ,south ,america1 ,africa1 ,asia1 and parts of ,australia have been but imperfectly explored for smaller kinds of ,mollusca4 ,molluscs are soft-bodied1 cold-blooded animals1 without any internal skeleton1 but this is compensated for by the external hardened shell1 which at once serves the purpose of bones1 and is a means of defence4 ,these bodies are not divided into segments like those of worms and insects1 but are enveloped in a muscular covering or skin1 termed the mantle1 the special function of which in most species is the formation and secretion of the shell4 ,the foot1 which serves the double purpose of locomotion and burrowing in the sand or rock1 is an organ particularly characteristic of most molluscs4 ,there are many departures from this rule1 as1 for instance1 in the group ,chitonid1 where the shell takes the form of a series of eight adjacent plates2 and in another1 the ,pholadid1 there are one or more accessory pieces in addition to the two principal valves4 ,some are bivalved1 others univalved1 and concealed beneath the skin4 ,all shells are mainly composed of carbonate of lime1 with a small admixture of animal matter4 ,their microscopic examination reveals a great diversity of structure1 as we shall presently see1 and they are accordingly termed porcellaneous1 nacreous1 glassy1 horny1 and fibrous4 ,most molluscs have the power of repairing injuries to their shells2 many exhibit an outer coat of animal matter1 termed the peristracum1 the special function of which is to preserve the shell from atmospheric and chemical action of the carbonic acid in the water in which they dwell4 ,the shells of gastropods are enlarged with the growth of the mollusc by the addition of fresh layers to the margin4 ,in some species the periodic formation of spines occurs2 a typical case will be found among ,muricid4 ,the varied colours of shells are due to glands situated on the margin of the mantle1 and beneath the peristracum2 occasionally the inner layer of porcellaneous shells is of a different colour to the outer1 as1 for example1 in the helmet-shells 7,cassis71 much used by carvers of shell cameos4 ,light and warmth1 as in the vegetable kingdom1 are the great factors in the production of brilliant colours4 ,in cold climates land snails bury themselves in winter time in the ground or beneath decaying vegetable matter1 and in hot seasons they close up the aperture of the shells with a temporary lid1 called an epiphragm4 ,these exhibit great tenacity of life1 as1 for instance1 in the ,egyptian desert-snail1 ,helix desertorum4 ,the reproductive system is in all cases effected by means of eggs4 ,the ova are usually enclosed in capsules1 and deposited in masses1 and the number of eggs contained in the squid and the whelk have been stated to be thirty or forty thousand4 ,the ova of molluscs may be gradually developed into the adult1 or there may be a free-swimming ciliated larval stage1 or a special larval form1 as in the fresh-water mussel4 ,most are provided with a more or less distinct head2 both cephalopods and gastropods are furnished with eyes4 ,in land snails these are found placed on projecting stalks4 ,in most cases the utility of molluscs far outweighs the injury occasioned by a few species1 as1 for instance1 the ,teredo1 and the burrowing habits of the ,pholas and ,saxicava1 compact marble having been found bored through by them4 ,mr4 ,j4 ,robertson wrote me in #ahff3--8;,having1 while residing here 7,brighton71 opportunities of studying the ,pholas dactylus1 ,i have endeavoured during the last six months to discover how this mollusc makes its hole or crypt in the chalk--by a chemical solvent8 by absorption8 by ciliary currents8 or by rotatory motions8 ,my observations1 dissections1 and experiments set at rest controversy on this point4 ,between twenty and thirty of these creatures have been at work in lumps of chalk in sea water in a finger glass and a pan1 at my window for the last three months4 ,the ,pholas dactylus makes its hole by grating the chalk with its rasp-like valves1 licking it up when pulverised with its foot1 forcing it up through its principal or branchial siphon1 and squirting it out in oblong nodules4 ,the crypt protects the ,pholas from ,conferve1 often found growing parasitically not only outside the shell but even within the lips of the valves1 thus preventing the action of the siphons4 ,in the foot there is a spring1 or style1 which when removed is found to possess great elasticity1 and this seems to be the mainspring of the motion of the ,pholas40 ,illustration3 ,fig4 #cfg4--;,hexabranchus4 ,i must pass by many groups and orders to more aberrant types1 represented by the naked-gilled orders1 ,opisthobranchiata and ,nudibranchiata4 ,these gastropods constitute a large sub-order of extremely beautiful molluscs1 remarkable in shape1 and often brilliant in colour4 ,the distinguishing character of these typical forms consists in the peculiar nature and situation of their breathing organs1 which are exposed on the back of the animal or around the anterior part1 and are not protected by the mantle4 ,but the situation is varied1 and the gills are sometimes placed on each side of the body1 respiration being effected by the ciliated surface of the whole4 ,for these and other reasons they have been placed in four groups4 ,nudibranchs are found in all parts of the world1 and are most abundant in depths where the choicest seaweeds and corallines abound4 ,their fecundity is very great1 as many as sixty thousand eggs being deposited by a single female at one time4 ,they are eaten as a luxury where they most abound4 ,illustration3 ,fig4 #cfh4--,longitudinal section of ,pleurobranchus aurantiacus1 showing circulation and gills or branchi4--7,warne47 ,in the ,opisthobranchs the branched veins as well as the auricle are placed behind the ventricle of the heart4 ,they differ from ,nudibranchs inasmuch as they are usually furnished with a pair of tentacles and labial palpi1 or an expansion of the skin like the veil of the larval form4 ,to clearly understand the character of the internal organisation of these curious animals1 the longitudinal section given in ,fig4 #cfh must be consulted3 p is the foot2 a the mouth1 covered above with the veil-like expansion1 over which are the tentacles1 c2 the branchial veins1 v1 carry the blood to the gills1 from which it flows into the heart at h4 ,this disposition is the opposite of that which characterises the ,prosobranchus4 ,another anatomical peculiarity1 which may here be referred to1 is the direct communication of the system of blood vessels with the surrounding medium2 a characteristic common to most other molluscs1 and on which depends the changeable external appearance of the animal4 ,in the illustration of ,pleurobranchus here given1 g indicates the opening of the duct which conveys water direct to the blood1 and through which the blood vessels permeate the back and foot4 ,like the holes in the sponges1 it can be filled or emptied at the will of the animal4 ,although this1 in the main1 is the principle of the circulation in most of this order1 one branch possesses no special breathing organs1 respiration being carried on throughout the naked skin of the body4 ,with regard to the ,nudibranchiata1 the group having the most symmetrical form is the extensive family ,doridid1 characterised by differences in the branchi1 the relative proportion of the mantle to the foot1 and variations in the radula and jaws4 ,the general aspect of the genus ,doris1 although drawn on a small scale1 is represented in ,plate ,,xvii41 ,fig4 b4 ,the whole sub-order of ,nudibranchs has become more generally known and admired since the publication of ,alder and ,hancock's monograph with its many attractive coloured illustrations4 ,these gastropods can be kept alive for some time in a small aquarium if the precaution is observed of often changing the water and adding a little fresh seaweed4 ,numerous curious microscopic forms of life may be found adhering to them4 ,illustration3 ,fig4 #cfi4--;,aplysia dipilans4 ,tunicata4--,the most remarkable group of animals belonging to this sub-order are the ,ascidians4 ,they derive their name from the test or tunic1 a membranous consistence1 in which they dwell1 and which often includes calcareous spicules4 ,the test has two orifices1 within which is the mantle4 ,few microscopic spectacles are more interesting than the circulation along this network of muslin-like fabric1 and that of the ciliary movement by which the fluid is kept moving4 ,in the transparent species1 as ,clavelina and ,perophora1 the ciliary movement is seen to greater advantage4 ,the animals are found adhering to the broad fronds of fuci near low water-mark4 ,they thrive in tanks1 and multiply both by fission and budding4 ,two species are figured in ,plate ,,xvii41 ,figs4 i and k1 the zooids of which were found arranged in clusters1 as represented4 ,aplysiid 7sea-hares71 so called on account of a slight resemblance to a crouching hare4 ,the body form is elongated with a partially developed neck and head1 oral and dorsal tentacles1 and furnished beneath the mantle with a shelly plate to protect the branchi4 ,the mouth is provided with horny jaws1 and the gizzard is armed with spines1 to prepare the food for digestion4 ,the side lobes are thin and large1 and are either folded over the back or used in swimming4 ,fig4 #cfi is a reduced drawing of ,a4 dipilans4 ,the ,pectinibranchs are known as violet sea-snails1 ,ianthinid and ,scalariid4 ,the radula consists of numerous rows of pointed teeth arranged in cross series1 forming an angle in the middle4 ,there is no central or rachidian tooth1 and they have thin trochiform shells adapted for a pelagic life4 ,they are mostly of a violet colour1 from which they derive their name1 the colour being more vivid on the underside1 which is turned up towards the light when the animal is swimming near the surface of the sea 7,fig4 #cgj74 ,illustration3 ,fig4 #cgj4--;,ianthinia1 ,violet ,sea-snail4--7,warne47 ,the bubble b1 drawn somewhat too large1 is about to be joined to the anterior end of the float2 c4 ,shell2 l4 ,float2 p4 ,foot2 t4 ,head4 ,the most interesting feature in connection with these oceanic snails is the curious float which they construct to support their egg-capsules4 ,it is a gelatinous raft1 in fact1 enclosing air-bubbles1 which is attached to the foot1 the egg capsules being suspended from its under-surface4 ,they are unable to sink so long as they are in connection with their floats1 and are therefore often cast on shore during storms1 and furnish an endless series of microscopic specimens4 ,the violet snails feed on various kinds of jelly-fish1 and occur in shoals4 ,pond ,snails4--,the three families1 ,limnid1 ,physid1 and ,chilinid1 form a special group of the pulminate1 sessile-eyed fresh-water snails4 ,the larger family of these belongs to the genus ,limna1 having a compressed and triangular head with two tentacles and eyes placed at their inner base4 ,they are prolific and gregarious1 and their ova are enclosed in transparent gelatinous capsules1 deposited in continuous series1 and firmly glued to submerged stems and leaves of aquatic plants4 ,l4 stagnalis is common in all ponds1 marshes and slow-running rivers of ,great ,britain4 ,illustration3 ,fig4 #cga4--,ova and young of ,limnus stagnalis4 ,one of the species1 ,l4 trancatula1 is the host of the liver-fluke so fatal to sheep4 ,the fluke parasite passes one stage of its existence in the intestine of the pond snail4 ,each ova-sac of ,limna contains from fifty to sixty ova 7represented in ,fig4 #cga1 at a74 ,if examined with a low power soon after the eggs are deposited1 they appear to consist simply of a pellucid protoplasmic substance4 ,in about twenty-four hours a very minute yellowish spot1 the nucleus1 is discovered near the cell-wall4 ,in another twenty-four hours the nucleus referred to is seen to have assumed a somewhat deeper colour and to contain within it a minute spot--a nucleolus4 ,on the fourth day the nucleus has changed its position1 and is enlarged to double the size2 a slightly magnified view is seen at b4 ,on a closer examination a tranverse fissure is seen2 this on the eighth day divides the small mass as at c1 and the outer wall is thickened4 ,the embryo becomes detached from the side of the cell1 and moves with a rotatory motion around the interior2 the direction of this motion is from the right to the left1 and is always increased when sunlight falls upon it4 ,the increase is gradual up to the eighteenth day1 when the changes are more distinctly visible1 and the ova crowd down to the mouth of the ova-sac1 as at d4 ,by employing a higher magnifying power a minute black spec1 the future eye 7e7 and tentacles of the snail1 is quite visible4 ,upon closely observing it1 a fringe of cilia is noticed in motion near the edge of the shell4 ,it is now apparent that the rotatory motion first observed must have been in a great measure due to this2 and the current kept up in the fluid contents of the cell by the ciliary fringes4 ,for days after the young animal has escaped from the egg1 this ciliary motion is carried on1 not alone by the fringe surrounding the mouth1 but by cilia entirely surrounding the tentacles themselves1 which whips up a supply of nourishment1 and at the same time aeration of the blood is effected4 ,from the twenty-sixth to the twenty-eighth day it appears actively engaged near the side of the egg1 using force to break through the cell-wall1 which at length it succeeds in accomplishing2 leaving its shell in the ova-sac1 and immediately attaching itself to the side of the glass its ciliary action recommences1 and it appears to have advanced a stage1 as at f4 ,it is still some months before the embryo grows to the perfect form1 ,fig4 #cgb2 the animal is here shown with its sucker-like foot adhering closely to the glass of the aquarium4 ,a single snail will deposit from two to three of these ova-sacs a week1 producing1 in the course of six weeks or two months1 from #ijj to #a1jjj young4 ,illustration3 ,fig4 #cgb4--,limnus stagnalis 7natural size74 ,the shell itself is deposited in minute cells1 which take up a circular position around the axis2 on its under-surface a hyaline membrane is secreted4 ,the integument expands1 and at various points an internal colouring-matter or pigment is deposited4 ,the increase of the animal goes on until the expanded foot is formed1 the outer edge of which is rounded off and turned over by condensed tissue in the form of a twisted wire2 this encloses a network of small vessels filled with a fluid in constant and rapid motion4 ,the course of the blood or fluid1 as it passes from the heart1 may be traced through the larger branches to the respiratory organs1 consisting of branchial-fringes placed near the mouth2 the blood may also be seen returning through other vessels4 ,the heart1 a strong muscular apparatus1 is pear-shaped1 and enclosed within a pericardium or extremely thin and pellucid enveloping membrane4 ,the heart is seen to be furnished with muscular bands of considerable strength1 the action of which appears like the alternate to-and-fro motion occasioned by drawing out a band of indiarubber1 and which1 although so minute1 are clearly analogous to the muscular fibres of the mammal heart2 it beats or contracts at the rate of about sixty times a minute1 and is placed rather far back in the body1 towards the axis of the shell4 ,the nervous system is made up of ganglia1 or nervous centres1 and distributed throughout the various portions of the body4 ,the singular arrangement of the eye cannot be omitted2 it appears at an early stage of life to be within the tentacle1 and consequently capable of being retracted into it4 ,in the adult animal the eye is situated at the base of the tentacle2 and although it can be protruded at pleasure for a short distance1 it seems to depend much upon the tentacle for protection as a coverlid--it invariably draws down the tentacle over the eye when that organ needs protection4 ,the eye itself is pyriform1 somewhat resembling the round figure of the human eye-ball1 with its optic-nerve attached4 ,in colour it is very dark1 having a central pupillary-opening for the admission of light4 ,the tentacle1 which is cylindrical in the young animal1 becomes flat and triangular in shape in the adult4 ,the tentacles serve in some respect to distinguish species4 ,in ,limna they are1 as ,i have said1 compressed and triangular1 with the eyes at their inner base4 ,in ,physa they are cylindrical and slender and without lateral mantle lobes4 ,the development of the lingual membrane is delayed2 consequently1 the young animal does not early take to a vegetable sustenance3 in place of teeth it has two rows of cilia1 as before stated1 which drop off when the teeth are fully formed4 ,the lingual band bearing the teeth1 or the 8tongue10 as it is termed1 consists of several rows of cutting spines1 pointed with silica4 ,it is a fact of some interest1 physiologically1 to know that if the young animal is kept in fresh water alone1 without vegetable matter of any kind1 it retains its cilia1 and arrest of development follows1 and it more slowly acquires gastric teeth1 and attains to perfection in form or size4 ,if1 at the same time1 it is confined within a narrow cell or space1 it grows only to such a size as will enable it to move about freely2 thus it is made to adapt itself to the necessities of a restricted state of existence4 ,some young animals in a narrow glass-cell1 at the end of six months1 were alive and well2 the cilia were seen to be retained around the tentacles in constant activity1 whilst other animals of the same brood and age1 placed in a situation favourable to growth1 attained their full size1 and produced young1 which grew in three weeks to the size of their elder relations4#ga ,my experimental investigations were further extended to the development of the lingual membrane1 or teeth1 of ,gastropoda1 as well as the jaw and radula4 ,in ,limna1 the teeth when fully developed resemble those of ,helix2 that is to say1 in the fully grown animal are found several rows or bands of similar teeth1 with simple obtuse cusps and a much suppressed central tooth4 ,in the young snail a high power of the microscope is required to make them out4 ,the dental band1 however1 in most ,mollusca is disposed in longitudinal series1 but varies a good deal in this respect1 as will be seen on reference to my several papers1 with illustrations of upwards of a hundred different species1 published in 8,linnan ,transactions0 of #ahff1 and in the 8,microscopical ,society's ,transactions0 of #ahfh4 ,by way of example ,i may say1 in the ,pulmonata the lingual band usually consists of a single median row1 the laterals on each side being broad and similar4 ,but in many other groups the teeth are arranged in three1 five1 or seven dissimilar series4 ,taking ,nerita as a type1 the broad teeth on each side of the median are termed laterals2 and the numerous small teeth on the outside of the band1 known as the pleur1 are termed uncini4 ,since the investigations of ,lovn into the lingual dentition of the ,mollusca1 various observers have studied the subject1 with great advantage to our knowledge of the affinities of these animals4 ,that these investigations have proved of value is shown by the light which has been shed on the true position of many species4 ,when once we have ascertained the homology of a genus1 whose relations were otherwise somewhat doubtful1 it is surprising how other characteristics1 even of the shell1 probably misunderstood before1 concur to bear out the affinities indicated by the lingual band4 ,these tooth-bearing membranes1 armed with sharp cutting points1 admirably adapted for the division of the food on which they feed1 are most of them beautiful objects for the microscope4 ,illustration3 ,fig4 #cgc4 #a4 ,palate of ,buccinum undatum1 common ,whelk1 seen under polarised light2 #b4 ,palate of ,doris tuberculata1 ,sea-slug4 ,the two ends of each longitudinal row of teeth are connected with muscles attached to the upper and lower surfaces of cartilaginous cushions2 the alternate contractions and extensions of the muscles cause the bands of teeth to work backwards and forwards1 after the fashion of a chain-saw1 or rather of a rasp1 upon any substance to which it is applied1 and the resulting wear and tear of the anterior teeth are made good by a development of new teeth in the secreting sac in which the hinder end of the band is lodged4 ,besides the chain-saw-like motion of the band the lingual membrane has a kind of licking or scraping action as a whole4 ,with the constant growth of the band new teeth are developed1 when the teeth on the extreme portion of the band differ much in size and form from those in the median line4 ,as ,i have shown in the papers already referred to1 that as each row is a repetition of the first1 the arrangement of teeth admits of easy representation by a numerical formula1 in which1 when the uncini are very numerous1 they are indicated by the sign 7infinity71 and the others by the proper figure4 ,thus1 #e #a #e 1 which1 in the genus ,trochus1 signifies that each row consists of one median1 flanked on both sides by five lateral teeth1 and these again by a large number of uncini4 ,when only three areas are found1 the outer ones must be considered the pleur1 inasmuch as there is frequently a manifest division in the membrane between them and the lateral areas4 ,most of the ,cephalopod molluscs are provided with well-developed teeth1 and they are1 as we know1 carnivorous4 ,the teeth of the cuttle-fish1 ,sepia officinalis 7,plate ,v41 ,no4 #aaa71 resemble those of the ,pteropoda1 and have the same formula1 #c #a #c4 ,sepia are also furnished with a retractile proboscis1 and a prehensile spiny collar1 apparently for the purpose of seizing and holding prey while the teeth are tearing it to pieces4 ,in the squid ,loligo 7,plate ,v41 ,no4 #aac7 the median teeth are broad at the base1 approach the tricuspid form with a prolonged acute central cusp1 while the uncini are much prolonged and slightly curved4 ,the lingual band increases in breadth towards the base1 sometimes to twice that of the anterior portion4 ,this band1 mounted dry1 forms an attractive object for black-ground illumination4 ,in another family1 that of the rock-limpet1 ,patella radiata1 the lingual band 7,plate ,v41 ,no4 #aaf7 well serves to distinguish it from the better-known common limpet4 ,it is furnished with a remarkable long ribbon1 studded by numerous rows of strong dark-brown tricuspid teeth4 ,the lingual membrane when not in use lies folded up in the abdominal cavity4 ,the teeth of ,acma are somewhat differently arranged 7,plate ,v41 ,no4 #aag72 their formula is #c #a #c4 ,testacella maugei1 belonging to ,pulmonifera1 is slug-like in appearance1 and subterranean in its habits1 chiefly feeding on earth-worms4 ,during winter and in dry weather it forms a kind of cocoon1 and thus completely encloses itself in an opaque white mantle2 in this way it protects itself from frost and cold4 ,its lingual membrane is large1 and covered with about fifty rows of divergent teeth1 gradually diminishing in size towards the median row2 each tooth is barbed and pointed1 broader towards the base1 and with an articulating nipple set in the basement membrane4 ,a few rows are represented slightly magnified 7,plate ,v41 ,no4 #aba74 ,their formula is #j #j #a #j #j4 ,illustration3 ,,tongues1 ,,etc41 ,,of ,,gasteropods4 ,tuffen ,west1 del4 ,w4 ,f4 ,maples1 ad4 nat4 del4 ,edmund ,evans4 ,,plate ,v4 ,the boat-shell1 ,cymba olla1 belonging to the ,velutinid1 formula #j #a #j1 or #a #a #a4 ,the lingual band 7,plate ,v41 ,no4 #aah7 is narrow and ribbon-like in its appearance1 with numerous trident-shaped teeth set on a strong muscular membrane4 ,the end of the band and its connection with the muscles at the extremity of the cartilaginous cushion is shown in the drawing4 ,the blueish appearance is produced by a selenite film and polarised light4 ,in ,scapander ligniarius the band 7,plate ,v41 ,no4 #aai7 is also narrow1 but the teeth are bold and of extraordinary size2 their formula is #a #j #a4 ,this mollusc is said to be eyeless4 ,pleurobranchus plumula belongs to the same family2 its teeth are simple1 recurved1 and convex1 and arranged in numerous divergent rows1 the medians of which are largest4 ,the mandible 7,plate ,v41 ,no4 #abb7 presents an exceedingly pretty tesselated appearance1 and the numerous divergent rows of teeth are tricuspid4 ,the velvety-shell1 ,velutina lvigata1 formula #c #a #c4 ,the teeth 7,plate ,v41 ,no4 #ajh7 are small and fine2 medians recurved1 with a series of delicate denticulations on either side of the central cusp1 which is much prolonged3 #ast laterals1 denticulate1 with outer cusp prolonged2 #bnd and #crd laterals1 simple curved or hooked-shaped4 ,the mandible 7,no4 #aji71 divided in the centre1 forms two plates of divergent denticulations4 ,the ear-shell1 ,haliotis tuberculatus1 is a well-known beautiful shell1 much used for ornamental purposes4 ,the lingual band 7,plate ,v41 ,no4 #aad71 is well developed4 ,the medians are flattened-out1 recurved obtuse teeth2 #ast laterals1 trapezoidal or beam-like2 uncini numerous1 about sixty1 denticulate1 the few first pairs prolonged into strong pointed cusps4 ,the top-shell1 ,turbo marmoratus4 ,after the outer layer of shell is removed1 it presents a delicate pearly appearance4 ,its lingual band 7,no4 #abc7 closely resembles ,trochus2 it is long and narrow1 the median teeth are broadest1 with five recurved laterals1 and numerous rows of uncini1 slender and hooked4 ,a single row only is represented in the plate4 ,cyclotus translucidus1 a family of operculate land-shells1 belongs to the ,cyclostomatid4 ,the teeth shown in ,no4 #aaj1 formula #c #a #c1 are arranged in slightly divergent rows on a narrow band2 they are more or less subquadrate1 recurved1 with their central cusps prolonged4 ,cistula catenata1 one of the family ,cyclophorid2 its band 7,no4 #aae7 formula1 #b #a #b4 ,its teeth resemble those of ,littorina4 ,the lingual band of ,cyclostomatid points out a near alliance to the ,trochid2 but this question can only be determined by an examination of several species1 when it may1 perhaps1 be decided to give them rank as a sub-order4 ,they are numerous enough2 the ,west ,indian islands alone furnish #bjj species4 ,the length of the lingual band1 and number of rows of teeth borne on it1 vary greatly in different species4 ,but it is among the ,pulmonifera we meet with the most astonishing instances of large numbers of teeth4 ,limax maximus possesses #bf1hjj1 distributed through #ahj rows of #afj each1 the individual teeth measuring only one #aj1jjjth of an inch4 ,helix pomatia has #ba1jjj1 and its comparatively dwarfed congener1 ,h4 absoluta1 no less than #ae1jjj4 ,structure of the ,shell of ,mollusca4--,in my opening sketch of the sub-order ,mollusca an idea may have been gathered of the general character of the shell covering of these animals4 ,the simplest form of shell occurs in the rudimentary oval plate of the common slug1 ,limax rufus4 ,it is embedded in the shield situated at the back1 near the head of the animal4 ,in the ,chitons1 a small but singular group of molluscs allied to the univalve limpets1 we have an ovoid shell1 made up of eight segments1 or movable plates1 which give them a resemblance to enormous woodlice4 ,these have been regarded as forming a transition series--a link between one division and the other4 ,the shell in by far the greater portion of all the molluscs is developed from cells that in process of growth have become hardened by the deposition of calcareous matter in the interior4 ,this earthy matter consists principally of calcium carbonate deposited in a crystalline state2 and in certain shells1 as in that of the oyster 7,plate ,,xviii41 ,fig4 #h71 from the animal cell not having sufficiently controlled the mode of deposition of the earth particles1 they have assumed the form of perfect rhomboidal crystals4#gb ,illustration3 ,,plate ,,xviii4 ,,sections ,,of ,,shell-,,structure4 ,the shell of the wing-shells1 ,pinna ingens 7,plate ,,xviii41 ,no4 #g71 is composed of hexagonal cells1 filled with partially translucent calcareous matter1 the outer layer of which can be split up into prism-like columns4 ,figs4 #c and #f are horizontal sections of the ,haliotis splendens1 with stellate pigment in a portion of the section1 and wavy lines1 as in the dentine of the human tooth1 and of ,terebratulata rubicuna1 showing radiating perforations4 ,nos4 #d and #e1 sections of the shell of a crab1 show pigment granules beneath the articular layer and the general hexagonal structure of the next layer4 ,some difference of opinion has been expressed with regard to the formation of pearls1 but it is now generally understood to be a diseased condition4 ,pearls are matured on a nucleus1 consisting of the same matter as that from which the new layers of shell proceed at the edge of the mussel or oyster4 ,the finest kinds are formed in the body of the animal1 or originate in the pearly-looking part of the shell4 ,it is from the size1 roundness1 and brilliancy of pearls that their value is estimated4 ,the microscope discloses a difference in the structure of pearls3 those having a prismatic cellular structure have a brown horny nucleus1 surrounded by small imperfectly-formed prismatic cells2 there is also a ring of horny matter1 followed by other prisms1 and so on1 as represented in ,fig4 #cgd2 and all transverse sections of pearls from oysters show the same successive rings of growth or deposit4 ,illustration3 ,fig4 #cgd4 #a4 ,a transverse section of a ,pearl from ,oyster1 showing its prismatic structure #b4 ,a transverse section of another ,pearl1 showing its central cellular structure1 with outside rings of true pearly matter4 7,magnified #ej diameters47 ,in a segment of a transverse section of a small purple pearl from a species of ,mytilus 7,fig4 #cge71 all trace of prismatic structure has disappeared1 and only a series of fine curved or radiating lines is seen4 ,this pearl consists of a beautiful purple-coloured series of regular lamin1 many of which have a series of concentric zones1 and are of a yellow tint4 ,the most beautiful sections for microscopic examination are obtained from ,scotch pearls4 ,preparation of the ,teeth and ,shell of ,mollusca for ,microscopical ,examination4--,the method of preparing lingual membranes of ,mollusca is as follows3 ,under a dissecting microscope1 and with a large bull's eye lens1 cut open and expose to view the floor of the mouth2 pin back the cut edges throughout its length1 and work out the dental band with knife and forceps4 ,the band being detached1 place it in a watch-glass1 and boil in caustic potash solution for a few minutes4 ,having by this process freed the tongue from its integuments1 remove it1 wash it well1 and place it for a short time in a dilute acid solution1 either acetic or hydrochloric4 ,wash it well and float it upon a slide2 with a fine sable brush open it out flat1 and remove whatever dirt or fibre may be adhering to it4 ,lastly1 place it in weak spirit and water1 and there let it remain for a few days before mounting in formalin4 ,canada balsam renders them rather too pellucid1 and the finer teeth are thereby lost4 ,illustration3 ,fig4 #cge4 #a4 ,transverse section of a small ,pearl from a ,mytilus2 #b4 ,horizontal section magnified #bdj diameters to show prismatic structure and transverse stri4 ,the preparation of shell structure must be proceeded with with some amount of care and caution1 or the delicate reticulated network membrane will be destroyed4 ,if any acid solvent be used to remove the calcareous structure it should be much diluted1 so that the action may proceed slowly rather than hastily4 ,in the young hermit-crab1 for example1 where the calcareous and membranous portions of the shell are continuous1 and the calcium carbonate in a relatively small proportion1 a strong acid solution would entirely destroy the specimen4 ,in the case of nacreous shells the process of cutting and grinding must also be proceeded with with some amount of caution4 ,the operation should be examined as the process proceeds1 and under polarised light4 ,sections of shell structure are usually mounted in ,canada balsam4 ,under the heading ,technique much useful information on this and kindred subjects will be found in the 8,journal of the ,royal ,microscopical ,society40 ,annulosa1 ,worms1 and ,entozoa4 ,the ,annulosa of ,huxley embraces the lowest grade of articulated animals1 most of which are now grouped with ,metazoa1 while some writers place them in a sub-kingdom ,vermes4 ,it appears to me then only possible to describe this heterogeneous group of worm-like animals among those which resemble each other in certain negative features1 but not possessing any of the distinctive characters of those previously described4 ,there are numerous species among ,entozoa1 every one of which is of the highest interest to mankind in general1 and to animal life as a whole4 ,to these ,i shall devote some attention1 from the wide-spread importance attached to them4 ,they are characterised by having a soft absorbent body with little or no colour1 in consequence of being excluded from light1 living within the bodies of animals and absorbing their vital juices1 thereby inflicting a large amount of injury and death upon the whole vertebrate kingdom4 ,they bear in this respect a close analogy to parasitic ,fungi in the nature of their destructive action upon plant life1 which ,i have fully discussed in a previous chapter4 ,the relations which obtain between parasites and their hosts are in all respects conditioned by their natural history2 and without a detailed knowledge of the organisation1 the development1 and the mode of life of the different species1 it is impossible to determine the nature and extent of the pathological conditions to which they give rise1 and at the same time find means of protection against guests in every way so unwelcome4 ,the nutritive system of the entozoa must be regarded as in the lowest state of development1 yet there are some among them of a higher grade1 as will be seen as we proceed4 ,all are remarkable alike for their vast productiveness and for their peculiar metamorphoses4 ,for example1 the greater number of the ,tnia begin their lives as sexless1 encysted larv1 and on entering their final abode1 segments are successively added1 until the worm has finally reached the adult stage4 ,again1 the tapeworm of the cat has its origin in the encysted larv found in the livers of the mouse and rat4 ,another species of entozoa inhabit the stomach of the stickle-back1 and only attain their perfect form in the stomachs of aquatic birds that feed exclusively on fish4 ,another infests the mantle of pond-snails1 and through their agency1 the embryos pass into the stomach of sheep4 ,an almost endless number of similar transformations take place in other genera4 ,the simplest form among internal parasites is the ,gregarin1 formerly grouped among ,protozoa4 ,they consist of a simple limiting membrane1 with a mass of granular matter enclosed and surrounding a nucleus 7,plate ,,iii41 ,no4 #ec74 ,these parasites pass through a crystoid stage in the body of one of the lower animals1 usually the earthworm1 ,lumbricus agricola4 ,in the more mature organism an envelope1 differentiated from the protoplasm within1 can be made out 7,no4 #ed72 this affords an indication of greater differentiation in the subjacent layer of protoplasm4 ,an anterior portion is in many cases separated by a constriction from the cylindrical or band-like body 7,no4 #ef74 ,gregarin multiply when encysted1 and divide into a multitude of minute pseudo-navicula1 so named from their resemblance in shape to a well-known form of ,diatomace4 ,when a young pseudo-navicule escapes it behaves somewhat like an amba1 and if perchance it is swallowed by an appropriate host1 it develops at once into the higher stage4 ,the various forms are represented in ,plate ,,iii41 ,nos4 #ec--fa4 ,miescher1 in #ahdc1 described suchlike bodies1 taken from the muscles of a mouse4 ,a good account of specimens obtained from the muscles of a pig was published by the late ,mr4 ,rainey in the 8,philosophical ,transactions10 #aheg4 ,he regarded them as cestoid entozoa4 ,they have been described under a variety of names1 as worm-nodules1 egg-sacs1 eggs of the fluke1 young measles1 c4 ,m4 ,lieberkhn carefully traced the pseudo-navicul after leaving the perivisceral cavity of the earth-worm2 he found large numbers of small corpuscles1 exhibiting amba-like movements1 as well as pseudo-navicul1 containing granules1 formed in an encysted ,gregarin4 ,he imagines that these latter bodies burst1 and that their contained granules develop into the ambiform bodies which subsequently become ,gregarin4 ,professor ,ray ,lankester made a careful examination of more than a hundred worms for the purpose of studying these questions1 but he succeeded in arriving at no other conclusion than that certain forms may be the by-products of encysted ,gregarin4 ,the ,g4 lumbricus is one of those forms which are unilocular4 ,the vesicle is not always very distinct1 and is sometimes altogether absent2 occasionally it contains no granules1 sometimes several1 one of which is generally nucleated4 ,in other of these cysts a number of nucleated cells may be seen developing from the enclosed ,gregarina1 which gradually become fused together and broken up1 until the entire mass is converted into nucleated bodies1 often seen in different stages of development1 assuming the form of a double cone1 as that presented by certain species of ,diatomace4 ,at length the cyst contains nothing but pseudo-navicul1 sometimes enclosing granules2 these gradually disappear1 and finally the cyst bursts4 ,encystation seems to take place much more rarely among the bilocular forms of ,gregarin than in the unilocular species found in the earthworm and other ,annelids4#gc ,dr4 ,j4 ,leidy published in the 8,transactions of the ,philadelphia ,society10 #ahec1 the results of his examinations of several new species of ,gregarin4 ,he described a double membrane 8within the parietal tunic of the posterior sac1 this being transparent1 colourless1 and marked by a most beautiful set of exceedingly regular parallel longitudinal lines40 ,professor ,r4 ,leuckart is the latest writer on the parasites of animals1 and to him we are indebted for a more systematic account of the whole group1 and their life-history1 than to any previous investigator4 ,i can only attempt to give a mere outline of the developmental stages of a few typical forms of parasites1 commencing with the cystic tapeworm1 ,tnia4 ,these worms are ribbon-like in appearance1 and are divided throughout the greater part of their length into segments1 and their usual habitation is the intestinal cavity of vertebrate animals4 ,the anterior extremity of a tnoid worm is usually called the head1 and bears the organ by which the animal attaches itself to the mucous membrane of the creature which it infests4 ,these organs are either suckers1 or hooks1 or both conjoined4 ,in ,tnia1 four suckers are combined with a circlet of hooks1 disposed around a median terminal prominence4 ,the embryo passes through certain stages of development--viz41 four forms or changes3 but the embryo itself is very peculiar1 consisting of an oval non-ciliated mass1 provided with six hooks1 three upon each side of the middle line4 ,tnia are found enclosed in various situations besides that of the alimentary canal3 the eye1 the brain1 the muscular tissues1 the liver1 c41 of animals4 ,the following cystic worms are usually included in this genera1 ,cysticercus ,anthocephalus1 ,cnurus1 and ,t4 ,echinococcus4 ,plate ,,iv41 ,no4 #ajj1 shows an adult specimen of the latter with rostellum suckers1 and three successive segments1 the last of which is the ova sac4 ,the water-vascular system is represented coloured by carmine4 ,this parasite infests the human body as frequently as many other species4 ,my accurately-drawn figure is copied from ,cobbold's 8,introduction to the ,study of ,entozoa40 ,cysticercus fasciolaris is developed within the liver of white mice2 ,cysticercus cellulos in the muscles of the pig2 hence we have the diseased state of pork familiarly known as 8measly pork40 ,should a lamb become infested with ,tnia the final transformation will be different2 within a fortnight symptoms of a disease known as 8staggers0 manifest themselves1 and in the course of a few weeks the ,cnurus cerebralis will be developed within the brain4 ,von ,siebold pointed out the bearing of this fact upon the important practical problem of the prevention of 8staggers40 ,others belonging to the same class of parasites are quite as remarkable in their preference for the alimentary canal of fishes4 ,the ,echinorhynchus is developed in the intestinal canal of the flounder1 ,trinophorus nodulus in the liver of the salmon4 ,thus1 by careful and repeated observation with the microscope1 a close connection is found to exist between the cystic and cestoid entozoa4 ,the ,echinococcus 7,plate ,,iv41 ,no4 #aja7 infests the human liver4 ,these parasites are always found in cysts1 and in closed cavities in the interior of the body4 ,they are united in fours by a very short stalk or pedicle1 common to the whole4 ,by an increase of magnification the contents of a cyst present the several structures represented in ,fig4 #cgf4 ,echinorhynchus1 or spiny-headed threadworms1 constitute a group of entozoa which undergo a metamorphosis hardly1 perhaps1 less remarkable than that known to take place in other ,nematode worms4 ,leuckart instituted1 in #ahfa1 a series of experiments with the ova of ,echinorhynchus proteus found parasitic upon the ,gammarus pulex4 ,the ova of ,e4 proteus resemble in form and structure those of allied species4 ,they are of a fusiform shape1 surrounded with two membranes1 an external of a more albuminous nature1 and an internal chitinous one4 ,when the eggs reach the intestine the outer of these membranes is absent1 being in fact digested1 while the inner remains intact until ruptured by the embryo4 ,illustration3 ,fig4 #cgf4--;,cystic ,disease of ,liver 7,human74 a4 ,cyst with ,echinococcus enclosed2 b4 detached hooklets from the head of ,echinococcus1 magnified #bej diameters2 c4 crystals found in cyst1 chiefly cholesterine2 d4 cylindrical epithelium1 some enclosed in structureless vesicles2 e4 ,puro-muculent granules1 fat and blood corpuscles4 ,the typical ,threadworm belonging to the order ,nematoidea infest the intestines of children1 and are a source of much suffering4 ,the egg is elliptical1 and contains a mass of granular protoplasm1 the external wall of which soon becomes marked out into a layer of cells4 ,the mouth of the worm appears as a depression at the end of the blunt head4 ,when the muscular system and alimentary canal are developed the embryo hatches out1 some few of which are free living forms2 most of them lead a parasitic life4 ,their reproduction is enormous1 representing thousands of eggs and embryos4 ,of the non-parasitic species of thread-worm1 the common vinegar eel1 ,anguillula1#gd affords an example4 ,this is found in polluted water1 bog-moss1 and moist earth1 as well as in vinegar2 also in the alimentary canal of the pond-snail1 the frog1 fish1 c4 ,another species is met with in the ears of wheat affected with a blight termed the 8cockle02 another1 the ,a4 glutinis1 in sour paste4 ,if grains of the affected wheat are soaked in water for an hour or two before they are cut open1 the so called 8eels0 will be found4 ,the paste-eel makes its appearance spontaneously just as the pasty mass is turning sour2 the means of securing a supply for microscopical examination consists in allowing a portion of the paste in which they show themselves to dry up1 and laying it by for stock2 if at any time a portion of this is introduced into a little fresh-made paste1 and the whole kept warm and moist for a few hours1 it will be found to swarm with these wriggling little worms4 ,a small portion of paste spread over the face of a ,coddington lens is a ready way of viewing them4 ,trichina spiralis4--,one of the smallest and most dangerous of all human internal parasites is ,t4 spiralis1 since it finds its way into the muscles throughout the human body4 ,the young animal presents the form of a spirally-coiled worm in the interior of a minute oval-shaped cyst 7,plate ,,iv41 ,no4 #ajd71 a mere speck scarcely visible to the naked eye4 ,in the muscular structure it resembles a small millet seed1 somewhat calcareous in composition4 ,the history of the development of ,trichina in the human muscle is briefly that in a few hours after the ingestion of infected pork1 ,trichina1 disengaged from the muscle1 will be found in the stomach3 hence they pass into the small intestine1 where they are further developed4 ,continuing their migrations1 they penetrate far into the interior of the primitive muscular fasciculi1 where they will be found1 in about three days after ingestion1 in considerable numbers1 and so far developed that the young entozoa have almost attained a size equal to that of the full-grown ,trichina 7,plate ,,iv41 ,no4 #aje74 ,they quickly advance into the interior of the muscular fasciculi1 where they live and multiply in continuous series1 while the surrounding structures as well as the muscular tissue undergo a process of histolysis4 ,the destructive nature of the parasite is very great4 ,the number of progeny produced by one female may amount to several thousands1 and as soon as they leave the egg they either penetrate through the blood-vessels1 or are carried on by the circulation1 and ultimately become lodged in the muscles situated in the most distant parts of the body4 ,here1 as already explained1 they become encysted4 ,illustration3 ,fig4 #cgg4--,monads in ,rat's ,blood1 stained with methyl violet1 showing membrane under different aspects2 blood-corpuscles1 some crenated and others with stained discs 7 #a1bjj74--7;,crookshank47 ,professor ,virchow draws the following conclusions3--8#a4 ,the ingestion of pig's flesh1 fresh or badly dressed1 containing ,trichin1 is attended with the greatest danger1 and may prove the proximate cause of death4 #b4 ,the ,trichin maintain their living properties in decomposed flesh2 they resist immersion in water for weeks together1 and when encysted may1 without injury to their vitality1 be plunged in a sufficiently dilute solution of chromic acid for at least ten days4 #c4 ,on the contrary1 they perish and are deprived of all noxious influence in ham which has been well smoked1 kept a sufficient length of time1 and then well boiled before it is consumed40 ,a more minute ,filarian worm has been detected in the human blood-vessels1 known as ,filaria sanguinis hominis4 ,this worm carries on its work of destruction throughout the night2 during the day it remains perfectly passive4 ,it increases rapidly1 and produces swellings of the glandular structures of the body1 somewhat after the nature of those characteristic of the ,bombay plague1 with a slight difference1 that after death the swellings are seen to be due to the vast accumulations of the ,filaria sanguinis blocking the blood-vessels4 ,the accompanying ,fig4 #cgg shows a similar infiltration of monads in the blood of rats dying of plague in ,bombay4 ,trematode ,worms4--,in the order ,trematoda1 to which the fluke belongs1 the body is unsegmented1 and to the naked eye smooth throughout1 with a blood circulatory system1 and two suctorial discs at the hinder end4 ,there is a distinct digestive canal1 usually forked1 furnished with only one aperture1 the mouth4 ,the excretory organs open out as in tape worms1 and the male and female organs co-exist in the same individual4 ,the ,fluke 7shown in ,plate ,,iv41 ,no4 #ajc7 is cone-shaped1 and is the ,amphistome conicum of ,rudolphi4 ,this parasite is common in oxen1 sheep1 and deer1 and it has also been found in the ,dorcas antelope4 ,it invariably takes up its abode in the first stomach1 or rumen1 attaching itself to the papillated folds of the mucous membrane4 ,in the full-grown1 adult stage1 it rarely exceeds half an inch in length4 ,it is certainly one of the most remarkable in form and organisation of any of the internal parasites4 ,the larger fluke 7,fasciola hepatica7 often attains to an inch or more in size4 ,it is not only of frequent occurrence in all varieties of grazing cattle1 but has likewise been found in the horse1 the ass1 and also in the hare and rabbit and other animals4 ,its occurrence in man has been recorded by more than one observer4 ,the oral sucker forming the mouth leads to a short sophagus1 which very soon divides into two primary stomachal or intestinal trunks1 the latter in their turn sending off branches2 the whole together forming that attractive dendritic system of vessels so often compared to plant-venation4 ,this remarkably-formed digestive apparatus is represented in ,plate ,,iv41 ,nos4 #ajf and #ajg1 ,fasciola gigantea of ,cobbold1 and should be contrasted with the somewhat similarly racemose character of the water-vascular system4 ,let it be expressly noted1 however1 that in the digestive system the majority of the tubes branch out in a direction obliquely downwards1 whereas those of the vascular system slope obliquely upwards4 ,a further comparison of the disposition of these two systems of structure1 with the same systems figured and described as characteristic of the ,amphistoma1 will at once serve to demonstrate the important differences which subsist between the several members of the two genera1 if we turn to the consideration of the habits of ,fasciola hepatica1 which1 in so far as they relate to excitation of the liver disease in sheep1 acquire the highest practical importance4 ,intelligent cattle-breeders1 agriculturists1 and veterinarians have all along observed that the rot1 as this disease is commonly called1 is particularly prevalent after long-continued wet weather1 and more especially so if there have been a succession of wet seasons2 and from this circumstance they have very naturally inferred that the humidity of the atmosphere1 coupled with a moist condition of the soil1 forms the sole cause of the malady4 ,co-ordinating with these facts1 it has likewise been noticed that the flocks grazing in low pastures and marshy districts are much more liable to the invasion of this endemic disease than are those pasturing on higher and drier grounds2 a noteworthy exception occurring in the case of those flocks feeding in the salt-water marshes on our eastern shores4 ,plate ,,iv41 ,no4 #ajf1 ,fasciola gigantea3 the anterior surface is exposed to display oral and ventral suckers1 and the dendriform digestive apparatus injected with ultra-marine2 ,no4 #ajg shows the dorsal aspect of the specimen and the multiramose character of the water-vascular system1 the vessels being injected with vermilion4 ,in their larval condition the ,amphistoma live in or upon the body of the pond-snail4 ,this we infer from the circumstance that the larv1 or cercari1 of a closely-allied species1 the ,amphistoma subclavatum1 are known to infest the alimentary canal of frogs and newts1 and have also been found on the body of the ,planorbis by myself4 ,the cercari larv are taken1 it is believed1 by the sheep and the cattle while drinking4 ,the earliest embryotic stage in which ,i have found the embryo fluke is represented at ,fig4 #cgh1 ,no4 #a4 ,in the year #ahed1 whilst observing the habits of ,limna and other water-snails1 ,i brought home specimens from the ornamental water in the ,botanic ,gardens2 upon these were discovered thousands of minute thread-like worms1 subsequently met with on other embryos1 and at first taken to be simple infusorial animals1 but upon placing them in a glass vessel these minute bodies were observed to detach themselves and commence a free-swimming existence4 ,a fringe of cilia was seen to surround the flask-shaped body 7,no4 #a74 ,illustration3 ,fig4 #cgh4--;,forms of ,cercaria2 stages in the development of the ,fluke4 #a4 ,an infusorial embryo2 #b4 a ,trematode embryo having quite recently escaped from the egg2 #c4 embryo cercaria2 #d4 fully-formed cercaria1 showing alimentary canal and sucker-like head2 #e4 encysted form of same2 #f4 ,cercaria furcata1 with the nervous system and forked tail displayed2 #g4 in the act of breaking up2 #h4 tail portion half an hour after division2 #i4 parasitic worm of another species of ,trematoda4 7,magnified from #aj to #be diameters47 ,the study of these embryos throws a flood of light upon the obscure history of ,cercari4 ,after a short period of wandering1 their embryos fasten upon the water-snail1 and compel it to act as a wet-nurse1 and prepare it for a further and higher stage of life4 ,the earliest condition in which ,i have discovered them concealed about the body of the water-snail is shown at ,no4 #b2 in appearance1 a simple elongated sac filled with ova or germs1 and which in a short time develop into the caudate worms already spoken of2 their tails gradually attaining to the length of the mature embryos1 ,nos4 #c and #d1 the latter being a full-grown ,cercaria ephemera4 ,diesing described no less than twelve species of ,cercari1 some of the most curious of which live on the puddle-snail1 in colonies of thousands4 ,all throw off their tails at the moment of changing into a fluke4 ,on placing some ,cercaria furcata 7,nos4 #f and #g7 under the microscope1 they were seen to plunge about in frantic attempts to escape from confinement4 ,suddenly ,i saw them shed their tails and their bodies divide into two parts1 each half swimming about as vigorously as before1 quite indifferent as to the severance1 and apparently dying from exhaustion4 ,those represented in ,nos4 #f and #g have a highly-organised nervous system1 forming a continuous circuit throughout the body and tail4 ,the mouth is furnished with a sucker and hooklets1 which can be projected out some distance1 while a digestive apparatus and ventral opening or sucker can be differentiated4 ,the tail is bifurcated and articulated with the body by a sort of ball-and-socket joint1 and when broken off1 the convexity of one part is seen to accurately fit into the concavity of the other2 it lashes about this appendage with considerable dexterity1 rarely attaching itself to any of the small aquatic plants4#ge ,there is yet another ,filarian worm1 a pest to the poultry-yard1 the ,gape-worm1 ,sclerostoma syngamus4 ,this parasite is widely distributed1 and is invested with special interest1 since it produces disease1 and kills annually thousands of young chickens1 pheasants1 partridges1 and many of the larger kinds of wild birds4 ,the worms find their way into the windpipe or trache1 through the drinking water1 while in the embryotic or cercarian stage of existence1 and their increase is so rapid1 the birds quickly die of suffocation4 ,the female gape-worm often attains to a considerable size1 and when full grown resembles the well-known mud-worm of the ,thames 7,gordius aquaticus74 ,she measures full six-eighths of an inch in length1 while the male only measures one-eighth4 ,so insignificantly small is he that the female carries him about tucked into a side pocket4 ,the ova sac occupies a considerable portion of the internal body space1 and is always found loaded with eggs in all stages of development1 numbering some five hundred or a thousand4 ,in shape these are ovoid4 ,on cutting open the windpipe of chicken and partridges1 ,i have found their trache literally swarming with the gape-worm4#gf ,a remarkable form of the ,trematode worm is ,bilharzia hmatobra of ,cobbold1 ,distomia hmatobium of other authors 7,plate ,,iv41 ,no4 #ajb74 ,this genus of fluke1 discovered by ,dr4 ,bilharz in the human portal system of blood vessels1 gives rise to a very serious state of disease among the ,egyptians4 ,so common is the occurrence of this worm1 that this physician expressed his belief that half the grown-up population of ,egypt suffer from it4 ,griesinger conjectures that the young of the parasite exist in the waters of the ,nile1 and in the fish which abound4 ,dr4 ,cobbold thinks 8it more probable that the larv1 in the form of cercari1 redi1 and sporocysts1 will be found in certain gasteropod mollusca proper to the locality40 ,the anatomy of this fluke is fully described by ,kchenmeister in his book on parasites1 by ,leuckart1#gg and by ,cobbold4 ,the eggs and embryos of ,bilharzia are peculiar in possessing the power of altering their forms in both stages of life2 and it is more than probable that the embryo form has been mistaken for some extraordinary form of ciliated infusorial animal1 its movements being quick and lively4 ,we cannot fail to notice the curious form of the male animal1 and1 unlike the ,filarian previously described1 it is he who carries the female about and feeds her4 ,the whip-like appendage seen in the figure is a portion of the body of the female4 ,the disease produced by this parasite is said to be more virulent in the summer months1 probably owing to the greater abundance of cercarian larv at this period of the year4 ,illustration3 ,fig4 #cgi4--,the double parasitic worm 7,diplozoum paradoxum74 ,there are also double parasitic worms1 which may be described as a sub-order of ,trematoda1 differing very much from those previously described4 ,these live on the gills of several species of fresh-water fish1 the gudgeon and minnow1 for instance4 ,among them is a most remarkable creature well deserving the name of ,diplozoum paradoxum which has been bestowed upon it4 ,it consists of two complete mature similar halves1 each possessing every attribute of a perfect animal 7a74 ,each of the pointed front ends has a mouth aperture1 and close to it two small sucking discs2 while each individual has a separate intestine1 consisting of a medium tube and innumerable side-branches4 ,at the hinder end of the body are two suckers sunk in a depression1 and protected by four hard buckle-shaped organs4 ,the eggs are elongated1 and provided at one end with a fine thread-like appendage 7b74 ,in this egg the young 7c7--which at the time of hatching is only about one-hundredth of an inch--takes about a fortnight to develop4 ,it is covered with cilia1 has two eyes and two suckers2 after quitting the egg1 the larv are very lively and restless in their movements1 gliding about and then swimming off with rapidity4 ,if unable to find the fish into which they are destined to live1 they grow feeble and perish1 but if successful they grow into the ,diporpa 7d71 which is flattened and lancet-shaped1 and bears a small sucking disc on the under surface and a conical excrescence on the back4 ,after living in this state for some weeks1 and gaining nourishment by sucking the blood from the fish's gills1 the worms begin to join together in pairs1 one specimen seizing the conical excrescence of another by its ventrical sucker2 then1 by a truly acrobatic feat1 the second twists itself to the dorsal excrescence of the first1 and in this state an inseparable fusion takes place between the suckers and the excrescences involved in the adhesion4#gh ,in the group ,vermes1 the more highly-organised ,annelida must be included4 ,these1 for the most part1 live either in fresh or salt water4 ,the ,annelids are various1 while the ,planaria1 a genus of ,turbellaria1 are very common in pools1 and resemble minute leeches2 their motion is continuous and gliding1 and they are always found crawling over the surfaces of aquatic plants and animals1 both in fresh and salt water4 ,the body has the flattened sole-like shape of the ,trematode entozoa 7,fig4 #cgh1 ,no4 #i71 the mouth is surrounded by a circular sucker2 this is applied to the surface of the plant from which the animal draws its nourishment2 it is also furnished with a rather long proboscis1 which is probably employed for a similar purpose4 ,planari multiply by eggs1 and by spontaneous fissuration in a transverse direction1 each segment becoming a perfect animal4 ,professor ,agassiz believes that the infusorial animals1 ,paramcium and ,kolpoda1 are simply planarian larv4 ,hirudinid1 the leech tribe1 are usually believed to form a link between the ,annelida on the one hand1 and the ,trematoda on the other2 their affinities place them closer with the latter than the former4 ,although deprived of the characteristic set of the ,annelida1 and exhibiting no sectional divisions1 they are provided with a sucker-like mouth possessed by ,trematoda1 but they present no resemblance to them in their reproductive organs4 ,on the other hand1 in the arrangement of the nervous system and in their vascular system1 the ,hirudinid resemble ,annelida4 ,the head in most of the ,annelida is distinctly marked1 and furnished with eyes1 tentacles1 mouth1 and teeth1 and in some instances with auditory vesicles1 containing otolithes4 ,the nervous system consists of a series of ganglia running along the ventral portion of the animal1 and communicating with a central mass of brain4 ,hirudina medicinalis puts forth a claim for special attention on the ground of services rendered to mankind4 ,the whole of the family live by sucking the blood of other animals2 and for this purpose the mouth of the leech is furnished with a number of strong horny teeth1 by which they cut through the skin4 ,in the common leech three rows of teeth exist1 arranged in a triangular1 or rather triradiate form1 a structure that accounts for the peculiar appearance of leech bites4 ,the most interesting part of the anatomy of the leech to microscopists is certainly the structure of the mouth 7,fig4 #chj74 ,this is a muscular dilatable orifice1 within which three beautiful little semi-circular saws are situated1 arranged so that their edges meet in the centre4 ,it is by means of these saws that the leech makes the incisions whence blood is to be procured1 an operation which is performed in the following manner4 ,no sooner is the sucker firmly fixed to the skin1 than the mouth becomes slightly everted1 and the edges of the saws are thus made to press upon the tense skin1 a sawing movement being at the same time given to each1 whereby it is made gradually to pierce the surface1 and cut its way to the capillary blood-vessels beneath4 ,illustration3 ,fig4 #chj4--,mouth of ,leech4 ,in ,clepsinid the body is of a leech-like form1 but very much narrowed in front1 and the mouth is furnished with a prehensile proboscis4 ,these animals live in fresh water1 where they may often be seen creeping over aquatic plants4 ,their prey is the pond-snail4 ,tubicola4--,the worms belonging to this series of branchiferous ,annelida are all marine1 and distinguished by their invariable habit of forming a tube or case1 within which the soft parts of the animal can be entirely retracted4 ,this tube is usually attached to stones or other submarine bodies4 ,externally it is composed of various foreign materials1 sand1 crystalline bodies1 and the dbris of shells2 internally it is lined with a smooth coating of sarcode1 sometimes of a harder consistency4 ,the ,tubicola generally live in societies1 winding their tubes into a mass which often attains a considerable size2 only a few are solitary in their habits4 ,they retain their position in their cases by means of tufts of bristles and spines2 the latter1 in the tubicular ,annelids1 are usually hooked1 so that by applying them to the walls of the case1 the animal is enabled to oppose a considerable resistance to any effort made to withdraw it4 ,in the best known family of the order 7,sabellia71 the branchi are placed in the head1 and form a circle of plumes1 or a tuft of branched organs4 ,the ,serpulid form irregularly twisted calcareous tubes1 and often grow together in large masses1 when they secure themselves to shells and similar objects2 other species1 ,terebellid1 which build their cases of sand and stones1 appear to prefer a life of solitude4 ,the best known form is ,terebella littoralis4#gi ,the curious little spiral shells seen upon the fronds of seaweeds are formed by an animal belonging to the ,spirorbis4 ,illustration3 ,fig4 #cha4--,serpula with extended tentacles and body protruding from calcareous case4 ,if the animals be placed in a vessel of sea-water a very pleasing spectacle will soon be witnessed4 ,the top part of the tube is seen to open1 and the creature cautiously protrudes a fringe of tentacles2 these gradually spread out two beautiful fan-like rows of tentacles1 surrounded by cilia of a rich purple or red colour4 ,these serve the double purpose of breathing and feeding organs4 ,when withdrawn from its calcareous case1 the soft body is seen to be constructed of a series of rings1 with a terminal prehensile foot by which it attaches itself4 ,many ,annelids are without tubes or cells of any kind1 simply burying their bodies in the sand near tidal mark4 ,the ,arenicola1 lob-worm1 is a well-known specimen of the class2 its body is so transparent that the circulating fluids can be distinctly seen under a moderate magnifying power4 ,two kinds of fluids flow through the vessels1 one nearly colourless1 the other red2 the vessels through which the latter circulate are described as blood-vessels4 ,not very much interest attaches to the developmental stage of the ,annelida4 ,they issue forth from ova1 and the embryo so closely resemble ciliated polypes1 that competent observers have mistaken them for animals belonging to a lower class2 a few hours' careful watching is sufficient to dispel a belief of the kind1 when the embryonic1 globular1 or shapeless mass is seen to assume a form of segmentation1 and soon the various internal organs become more and more developed1 eye spots appear1 and the young animal arrives at the adult stage of its existence4 ,crustacea4 ,the crustaceans comprise a large assemblage of ,arthropods1 presenting great diversity of structure4 ,some of the parasitic species have become so simplified in organisation that they appear to present no relationship with the higher members of the class1 yet it is certain that all the species1 whether terrestrial or aquatic1 belong to the same stock1 and may have had origin in the same fundamental plan of structure4 ,essentially1 the body consists of a large number of segments1 to each of which is attached a pair of two-branched appendages2 the external branch is termed the exopodite and the internal the endopodite4 ,five segments at the front end of the body unite to form a head1 the appendages of the first two being situated in front of the mouth1 and performing the office of feelers or antenn1 while those of the remaining three segments are transformed into jaws1 the first pair of jaws being the mandibles and the following two pairs the maxill4 ,the rest of the appendages are variously modified and to some are attached respiratory organs in the form of gills4 ,crustaceans are broadly divided from ,centipedes1 ,millipedes1 ,insects1 c41 by the presence of two pairs instead of one pair of antenn1 and by the possession of branchial and not tubular 7tracheal7 respiratory organs4 ,arachnida and some other species are again widely separated4 ,the majority of the young on leaving the egg are quite unlike the parent1 and only acquires their definite form after undergoing a series of changes4 ,the earliest stage1 which has been called the ,nauplius1 already referred to in connection with the barnacle1 is a minute body showing no trace of segmentation1 and provided with a single eye1 and three pairs of swimming appendages1 which become the two pairs of antenn and the mandibles of the adult4 ,this stage is by no means of invariable occurrence1 but is chiefly characteristic of the lowest members1 the ,entomostraca1 and is rare in the higher1 ,malacostraca4 ,the typical crustaceans are shrimps1 crayfish1 c41 so familiarly described by ,huxley4 ,the zoa stage of the crab1 a minute transparent creature1 which undergoes several changes1 swims about flapping its long jointed abdomen1 like some of the ,entomostraca1 and the shrimp in particular4 ,the larva of crayfish1 the so-called glass-crab1 is very peculiar and interesting4 ,the sessile-eyed series1 in which the compound eyes are never mounted on a movable stalk1 and to which the ,isopoda belong1 exhibits great diversity of structure as well as of habits and habitat4 ,some live in fresh water1 most are marine1 while others live on land and take to a parasitic life4 ,illustration3 ,fig4 #chb4--,male ,gnathia1 enlarged4 ,this genus contains ,gnathia1 in which the male and female are so dissimilar1 that they are frequently referred to as members of two families4 ,in the adult male the mandibles are powerful and prominent1 and the head is large1 squared1 and as wide as the thorax4 ,in the female1 on the contrary1 the head is curiously small and triangular1 without visible mandibles1 and the thorax is much dilated4 ,the creatures are about one-sixth of an inch long1 and of a greyish colour1 and the destruction they bring about is due to their habit of boring into timber below water mark4 ,fig4 #chb represents an enlarged view of the male ,gnathia4 ,these crustaceans are vegetarians1 and feed on wood4 ,other members of the group1 known as fish lice1 are much larger in size1 and chiefly infest the cetacea1 and bear in addition two large eyes4 ,by means of their powerful fore feet the ,cymothord attach themselves to both marine and fresh-water fish1 showing a preference for the inside of the mouth of their host4 ,illustration3 ,fig4 #chc4--a4 ,cypris2 #b4 ,cyclops2 #c4 ,branchipus grubei4 ,the bar-footed group ,copepoda are free living1 and the thorax bears four or five swimming feet2 the abdomen is without appendages4 ,the best known fresh-water form is ,cyclops1 the structure of which serves as a type of the order4 ,the body is1 as is well known to microscopists1 broad in front and tapering behind1 being thus1 when viewed swimming1 pear-shaped in outline4 ,the dorsal elements of the head are fused to form a carapace1 which bears a single eye1 from which circumstance it derives its name4 ,the eggs are carried by the female in a couple of ova-sacs attached to the last segment of the thorax1 and so prolific are these creatures that a female will produce over four thousand million young4 ,the young when hatched is an oval ,nauplius1 which after two or three moults acquires the adult state4 ,in the family of the ,apodid we have an equally well-known crustacean1 the ,branchipus4 ,in the ,branchipodid the body is also elongated1 but there are no appendages to the abdomen1 which consists of nine segments1 while there are eleven pairs of thoracic appendages4 ,the head shield is not developed backwards1 and the large separated eyes are supported on distinct stalks4 ,in the male the second antenn are converted into claspers4 ,these crustaceans swim upside down 7,fig4 #chc74 ,cladocera 7,daphniad of ,dr4 ,baird74--,the water-flea 7,daphnia pulex7 may be taken as the best known example of the order4 ,the body of this little active animal is narrowed in front1 and at the posterior end1 where the carapace is deeply notched1 is the tip of the abdomen bearing the pair of rigid barbed set from which the genus takes its name4 ,at the front of the head is a large compound eye and two pairs of branched plumed appendages1 antenn4 ,the first pair of these are small and simple4 ,the jaws consist of the mandibles and the first pair of maxill1 the second pair of maxill being obsolete in the adult4 ,the thorax comprises five segments1 each bearing a pair of leaf-like swimming limbs4 ,the abdomen consists of three segments1 and is destitute of limbs4 ,the males are usually smaller than the females1 and much rarer1 being rarely met with before the end of summer4 ,eggs are laid both in summer and winter1 and are passed into a brood-pouch1 separating the upper surface of the thorax from the backward extension of the carapace4 ,here the summer eggs hatch1 but the winter set are enclosed in a kind of capsule developed from the carapace4 ,this capsule1 termed the ephippium1 is cast off with the next moult of the mother's integument 7a process necessary for the gradual growth of the crustacean71 and falling to the bottom of the water1 gives exit to the embryos1 which hatch in its interior1 and the young born from these 8ephippial0 eggs produce young1 which in their turn become mothers4 ,it appears1 then1 the winter eggs are enclosed in capsules of more than usual hardness to enable them to withstand any degree of cold that might otherwise prove fatal to the parent4 ,dr4 ,baird found1 on examining ponds that had been again filled up by rain after remaining two months dry1 numerous specimens of ,daphnia and ,cyclops quadricornis in all stages of growth4#hj ,we learn also from his investigations that the ,daphnia have many enemies4 8,the larva of the ,corethra plumicornis1 known to microscopical observers as the skeleton larva1 is exceedingly rapacious of ,daphnia4 ,pritchard says they are the choice food of a species of ,nais2 and ,dr4 ,parnell states that the ,lochleven trout owes its superior sweetness and richness of flavour to its food1 which consists of small shell-fish and ,entomostraca40 ,these crustaceans abound in fresh and salt water4 ,artemi are formed exclusively in salt water1 in salt marshes1 and in water highly charged with salt4 ,myriads of these ,entomostraca are found in the salterns at ,lymington1 in the open tanks or reservoirs where the brine is deposited previous to boiling4 ,a pint of the fluid contains about a quarter of a pound of salt1 and this concentrated solution destroys most other marine animals4 ,during the fine days in summer ,artemi may be observed in immense numbers near the surface of the water1 and1 as they are frequently of a lively red colour1 the water appears tinged with the same hue4 ,the movements of this little animal are peculiar4 ,it swims about on its back1 and by means of its tail1 its feet being at the same time in constant motion4 ,they are both oviparous and ovoviviparous1 according to the season of the year4 ,at certain periods they only lay eggs1 while during the hot summer months they produce their young alive4 ,in about fifteen days the eggs are expelled in numbers varying from #ej to #aej4 ,as is the case with many of the ,entomostraca1 the young present a very different appearance from the adult animals2 and they are so exactly like the young of ,chirocephalus1 that with difficulty are they distinguishable one from the other4 ,the ova of other species are furnished with thick capsules1 and imbedded in a dark opaque substance1 presenting a minutely cellular appearance1 and occupying the interspace between the body of the animal and the back of the shell2 this is called the ephippium4 ,the shell is often beautifully transparent1 sometimes spotted with pigment2 it consists of a substance known as chitine1 impregnated with a variable amount of calcium carbonate1 which produces a copious effervescence on the addition of a small quantity of a strong acid to the water in which the shell is immersed4 ,when boiled1 ,artemi turn red as their congeners1 lobsters4 ,their shells may be said to consist of two valves united at the back1 resembling the bivalve shell of a mussel1 or simply folded at the back to appear like a bivalve1 but are really not so2 or they may consist of a number of rings or segments4 ,the body of ,cypris presents a reticulated appearance1 somewhat resembling cell structure4 ,entomostraca should be narcotised and prepared for examination under the microscope as directed by ,mr4 ,rousselet at pages #cde1 #cdf4 ,,insects' ,,eggs1 ,,etc4 ,illustration3 ,tuffen ,west1 del4 ,edmund ,evans4 ,,plate ,,vi4 ,,chapter ,,iv4 ,arthropoda--,insecta4 ,distinctive ,characters of ,insects4--,the term ,insect1 although originally and according to the meaning of the word correctly employed in a wide sense to embrace all those articulate creatures in which the body is externally divided into a number of segments1 including1 of course1 flies1 butterflies1 beetles1 bugs1 spiders1 scorpions1 crabs1 shrimps1 c41 is now by common consent used in a much more restricted sense to apply only to such of these animals as have six walking legs4 ,insects belong to a class of ,arthropoda1 and are distinguished by having the head1 chest1 and abdomen distinctly marked out and separable2 by having not more than three pairs of legs in the adult state2 by having the legs borne by the thoracic segments only2 by having usually two pairs of wings2 by the possession of trache1 or air-tubes1 as respiratory organs2 and by being provided with a single pair of antenn1 or feelers4 ,the insect class is one exhibiting uniformity of type and structure4 ,extreme variations are no doubt seen within certain limits1 but these variations are sharply marked off from the groups we have been previously considering4 ,the examination of insects may be pursued according to a defined order1 and it will be found that no class of animals will afford the microscopist a more wonderful field of observation and a greater variety of interesting objects than that of the insect tribes4 ,in the insect1 as in the crustacean1 the hard parts of the body form an outer and protecting covering1 and also serve for the attachment of muscles4 ,the casing1 however1 in insects is purely of a chitinous1 or horny nature1 and has in its composition only a trace of calcium carbonate4 ,each somite1 or joint of the body1 is usually composed of six pieces2 the upper1 or dorsal half of each segment is named the tergum1 the lower half the sternum1 the side pieces pleura1 the sternum being further sub-divided into epimeral and espisternal pieces4 ,the body as a whole consists of some twenty segments1 of which five or six form the head1 the thorax of three joints1 while the abdomen may number from nine to eleven4 ,the head segments are united to form apparently a single mass1 and the appendages of this region are modified for sensory purposes1 and also serve as cutting and masticatory organs4 ,the appendages of the head1 examined in order1 will be found to consist of eyes1 antenn1 or feelers1 and organs of the mouth4 ,the antenn of insects rarely exceed two in number1 but these present great variations in form and size4 ,in their simplest form they exist as straight jointed filaments1 but in many insects they are forked1 in others club-shaped1 while in others they mimic forms of vegetation1 and for the most part are extremely interesting objects for the microscope4 ,illustration3 ,fig4 #chd4--,vertical section of cornea of ,eye of ,fly4 ,the principal use of these antenn is that of organs of touch1 but it is quite probable that they may subserve other functions1 as of taste or even hearing4 ,the eyes of insects consist of either a pair of ocelli1 or of a great number1 when they are termed compound eyes1 formed of an aggregation of external hexagonal facets and lenses1 and nerve filaments1 all of which have a distinct connection with the mass of ganglia recognised as the brain1 as will be seen in ,fig4 #chd1 a section of the eye of a fly4 ,the number of facets varies very greatly in these compound eyes2 ants1 for example1 have fifty facets1 flies two thousand or more1 and butterflies as many4 ,dr4 ,hooke counted seven thousand1 and ,leuwenhoeck as many as twelve thousand in the eye of a dragon fly4 ,the eyes of some insects are supported on short stalks or pedicles1 but these are never movable1 as1 for example1 in ,stalk-eyed crustaceans4 ,the organs of the mouth in insects present a striking homology or similarity in their fundamental structure4 ,two chief types of mouth are found4 ,the biting or masticatory1 as in beetles1 includes a labium or upper lip1 a pair of mandibles or lower jaws1 a pair of lesser jaws or maxill1 which bear one or two pairs of palpi1 and a lower lip or labium1 also with palpi4 ,this latter and primitive condition of the labium is seen in ,orthropterous insects and some ,neuroptera4 ,other structures occurring in those of the mouth are the ligula1 this being sometimes divided1 as in bees1 into three lobes1 of which the two outer are the paragloss and the middle process the lingua or tongue4 ,there is a second form of mouth1 termed the suctorial4 ,this is seen in ,lepidoptera 7butterflies71 and is adapted for extracting the pollen and juices of flowers1 and in which the palpi are greatly developed1 and form two hairy pads or cushions1 between which the proboscis is coiled up when at rest4 ,thus we find in the ,lepidoptera the same fundamental condition of mouth as in some ,coleoptera4 ,in ,hymenoptera 7wasps and bees71 a variety of mouth is found which presents a combination of the masticatory with the suctorial types4 ,the labium and mandibles exist as in the beetle1 the maxill being developed to form long sheaths protecting the labium1 which now takes the form of a tongue4 ,in ,hemiptera 7bugs and their allies71 the mandibles and maxill exist as sharp lancets1 while the labium forms a protective sheath4 ,in the ,diptera 7flies1 gnats1 c471 the labium undergoes a great development1 and forms a very prominent tongue1 the other parts of the mouth being developed simply as sheaths to the labium4 ,see ,figs4 #chi and #cij4 ,the thorax or chest of insects consists of three segments1 named from before backwards3 the prothorax1 mesothorax1 and metathorax4 ,the first bears the anterior pair of legs2 the mesothorax1 the second pair of legs and the first pair of wings2 and the metathorax1 the third pair of legs and second pair of wings4 ,the last joints of the leg constitute the tarsus or foot-claws4 ,the nervures of the wings are in reality hollow tubes1 and are extensions of the spiracles1 or respiratory apertures4 ,the muscles of insects lie concealed beneath the integument2 they are not gathered into distinct bundles as in the higher animals1 although they exhibit in many cases a striated or striped structure4 ,this is well seen in some of the beetle tribe1 the water-beetle in particular4 ,in certain larv the muscles are exceedingly complicated4 ,lyonnet found in the larva of the goat-moth1 two hundred and twenty-eight muscles in the head alone1 and in the whole body no less than three thousand nine hundred and ninety-three4 ,the muscular power of insects is1 relatively to the size of the body1 very great4 ,the flea1 for instance1 leaps two hundred times its own height4 ,there are beetles weighing a few grammes that will escape from a pressure of from twenty to thirty ounces4 ,professor ,schfer infers that the structure of the wing-muscles of insects furnishes the key to the comprehension of the more intricate muscular structure of vertebrates4 ,the sarcode element1 however1 is not made up of a bundle of rods1 but of a continuous sarcous element1 readily made out by staining with hmatoxylin4 ,this substance is then seen to be pierced by minute tubular canals1 and the longitudinal striation of muscle is due to this canalisation4 ,the whole is connected and enclosed by a membrane of extreme delicacy4 ,the digestive system of insects varies with their habits and food4 ,in ,stylops1 bee-parasites1 and in young bees living on fluids1 the intestine ends in a blind sac4 ,there are three coats of structure throughout the digestive system4 ,the sophagus or gullet is provided with a crop in flies1 bees1 and butterflies2 a true analogue of the gizzard in birds4 ,there is in some respects a curious likeness between the conformation of the digestive organs of birds and that of insects4 ,no true liver1 but salivary glands in the mouth have been made out2 the heart lies dorsally1 and consists of a pulsating sac divided into compartments1 and the fluid flows through it towards the head1 whence it circulates freely to other parts of the body4 ,each trachea is an elastic tube formed of two delicate membranes1 between which the spiral filament is coiled up1 and is of sufficient density to prevent the collapse of the tube by the movements of the body4 ,these trache are distributed throughout the muscular tissue and the whole of the body4 ,thus the insect1 like the bird1 may be said to breathe in every part of the body1 and is in this way rendered light and buoyant for flight4 ,the air is admitted to the trache by apertures termed spiracles1 which the insect can close at will1 and these are distributed to the number of eleven on each side of the body4 ,the nervous system consists of a chain of ganglia or nerve-knots1 which unite towards the head to form a single cord1 as seen in the section made through the spider 7,fig4 #dji74 ,the reproduction of all insects takes place by ova1 and they are diceous--that is1 have two distinct sexes4 ,in some few instances1 as that of ,aphides1 or plant-lice1 we have the peculiar phenomenon of parthenogenesis1 the process of reproduction being performed by imperfect wingless females4 ,these bring forth living young ones1 which begin to feed the moment they are born1 and constitute a viviparous brood2 in other cases females lay eggs1 and the process proceeds in the ordinary way1 and nearly all the year round4 ,the former is provided with a lancet-like beak for piercing and sucking the juices of the leaf1 and a pair of curious honey-tubes4 ,insects generally undergo a transformation or metamorphosis in passing from the egg to the adult stage4 ,while within the egg the body may be seen to become segmented1 and in the course of time--in such insects as flies1 bees1 beetles1 and butterflies--issue forth from the egg as larv1 or caterpillars4 ,this worm-like creature makes for itself an investing case or cocoon1 in which it passes into the pupa stage of its existence4 ,within the pupa case a wonderful transformation takes place2 the larval body being literally broken down by the process of histolysis1 while its elements are rebuilt and transformed into that of the imago1 or perfect insect4 ,in grasshoppers1 crickets1 dragon-flies1 bugs1 c41 the metamorphosis is incomplete 7hemimetabolic74 ,some few lower insect forms 7lice1 spring-tails1 c47 undergo no change of the kind1 and in no way differ from the adult except in size4 ,these are termed ametabolic insects4 ,others again1 as the cockchafer and gold beetle1 pass three years in the larval stage4 ,development in all cases is arrested or retarded by cold4 ,reaumur kept a butterfly pupa for two years in an ice-house1 and it exhibited no tendency towards a change until removed to a warm temperature4 ,from the short natural history of insect life ,i have endeavoured to sketch out1 it will have been surmised that insects offer a wide field of research1 and an almost endless number of objects of interest for the microscope4 ,the variety of material is great1 and the structure and adaptation of means to an end is of the most fascinating kind4 ,most cabinets abound in preparations gathered together with some care and mounted with all the skill at the command of the collector1 affording1 as a rule1 as endless an amount of pleasure to the tyro as to the more practised entomologist4 ,it may be surmised1 then1 that to enter fully into a description of the several parts of insect structure would require a volume#ha of very large bulk1 and occupy months and years4 ,i will1 therefore1 take some points of interest in the structural characteristics of insects1 and take them in the order in which they have already been brought to notice4 ,the head1 eyes1 and other appendages of these insects we are more or less acquainted with4 ,illustration3 ,fig4 #che4--;,a tangential or side section of ,eye of ,fly1 with palp or pads protruded4 ,we will take for examination a typical member of ,muscid1 a family embracing a large and varied assortment of species1 among which the house-fly and the blow-fly are the best known forms4 ,musca domestica needs no description4 ,an interesting part of the house-fly to the microscopist is the wonderful component parts of the head4 ,on examination we find a couple of protuberances1 more or less prominent1 and situated symmetrically one on each side4 ,their outline at the base is for the most part oval1 elliptical1 circular1 or truncated2 while their curved surfaces are spherical1 spheroidal1 or pyriform4 ,these horny1 round1 and naked parts are the corne of the compound eye of the fly1 and they are appropriately so termed1 from the analogy they bear to the larger transparent tunics in the higher classes of animals4 ,they differ1 however1 from the latter1 as when viewed by the microscope they display a large number of hexagonal facets1 which constitute the medium for the admission of light to several hundred simple eyes4 ,under an ordinary lens1 and by reflected light1 the entire surface of one cornea presents a beautiful reticulation1 like very fine wire gauze1 with minute papilla1 or at least a slight elevation1 in the centre of each mesh4 ,these are resolved1 however1 by the aid of a compound microscope1 and with a power of from #hj to #ajj diameters1 into an almost incredible number 7when compared with the space they occupy7 of minute1 regular1 geometrical hexagons1 well defined1 and capable of being computed with tolerable ease1 their exceeding minuteness being taken into consideration4 ,fig4 #chf represents a vertical section of the eye1 showing the hexagonal faceted arrangement of cylindrical tubes4 ,illustration3 ,fig4 #chf4--,section of ,eye of ,fly4 l4 ,lenses2 co4 ,cones2 pl4 ,pigment layer1 consisting of rings round the rods2 r4r4 ,rods2 a4v#a4 ,air vessels between the rods2 m#a4 ,membrane on which the rods and air vessels rest2 a4v#b4 ,shorter lengths of air vessels which form a layer above the first nerve junction2 n4j#a4 ,first nerve junction2 m#b4 ,membrane on which it stands2 ,a4 ,v41 ,a4 ,v4 ,large air vessel surrounding the eye2 n4j#b4 ,second nerve junction2 a4v#c4 ,air vessels2 op4 n4 ,optic nerve2 b4n4 ,brain substance4 7,magnified #afj47 ,in this section it appears to be questionable whether the normal shape of the lenses is not round1 assuming the hexagonal shape during the process of growth in consequence of their agglomeration4 ,the corneal surface can be peeled off1 and if carefully flattened out and mounted it will be seen that each lens is not a simple lens1 but a double-convex compound one1 composed of two plano-convex lenses of different densities or refracting power joined together4 ,experiments made on the eyes of insects1 and also of crustace1 show that in the insect a real and reversed image of external bodies is formed in each ommatidium2 it coincides with the internal face of the crystalline cone in immediate contact with the retina4 ,although small1 the retinal image is distinct and subtends an angle of nearly forty-five4 ,in the same way in the crustacean1 the crystalline lens forms on the retinula a reversed image1 but the refractive media have a longer focus1 and the retinal membrane is not connected with the lens1 the interval being filled up by a substance analogous to the vitreous of vertebrates4 ,in both cases it would appear that light does not act directly on the rods2 these latter can only receive impressions through the intermediary retinal cells4 ,the retinal images of arthropods1 as might have been surmised1 are much less perfect than those of the higher orders2 on the other hand1 their eyes seem to be better adapted for seeing objects in relief and the movements of bodies4 ,the shyness of butterflies and moths is certainly an inherited instinct as a protection against danger from their many enemies4 ,illustration3 ,fig4 #chg4 ,a4 ,vertical section of ,eye of ,melolontha vulgans1 ,cockchafer2 ,b4 ,a few facets more highly magnified1 showing facets and pigment layer4 ,in the accompanying ,fig4 #chg1 ,a is a vertical section of the eye of ,melolontha vulgans1 the fan-like arrangement of the facets1 together with the transparent pyramidal gathering of the retinal rods proceeding towards the brain2 ,b is a few of the corneal tubes more highly magnified1 the darker portion representing the pigment layer of the corneal tubes4 ,in ,plate ,,vi41 ,no4 #acc1 the under surface of the head and mouth of the 8,tsetse0 fly1 ,glossina morsitans1 is shown4 ,the proboscis of this fly is long and prominent1 and the antenn are peculiar1 inasmuch as the third segment is long1 and produced almost as far as the flagellum1 which is furnished with barbed hairs along its outer surface only4 ,although this fly barely equals the blow-fly in size1 it is one of the greatest pests to the domestic cattle of ,equatorial ,africa4 ,the palpi1 although arising from two roots1 are seen joined together when the fly is at rest1 but when in the act of piercing or sucking they divide and the sheath is thrown directly upwards4 ,the palpi are furnished on their convex sides with long and sharply-pointed dark-brown set or hairs1 while the inner concave sides1 which are brought into contact with the proboscis1 are perfectly smooth and fleshy4 ,three circular openings seem to indicate the tubular nature of what in the house-fly is a fleshy1 expanded1 and highly-developed muscular proboscis 7seen in ,fig4 #chh1 ,musca domestica74 ,the proboscis 7labium7 forms the chief part of the organ1 dilates into wonderful muscular lips1 and enables the insect to employ the tongue as a prehensile organ4 ,the lips are covered with rows of minute set1 directed a little backwards and arranged rather closely together4 ,illustration3 ,fig4 #chh4--,proboscis of ,house-fly1 ,musca domestica4 7,the small circle indicates the object about the natural size47 ,there are very many rows of these minute hairs on each of the lips1 and from being arranged in a similar direction are employed by the insect in scraping or tearing delicate surfaces4 ,these hairs are tests for the best of high powers4 ,it is by means of these that it teases human beings in the heat of summer1 when it alights on the hand or face1 to sip the perspiration as it exudes from the skin4 ,the fluid ascends the proboscis1 partly by a sucking action1 assisted by the muscles of the lips themselves1 which are of a spiral form1 arranged around a highly elastic1 tendinous1 and ligamentous structure1 with other retractile additions for rapidity and facility of motion4 ,illustration3 ,fig4 #chi4--,spiral structure of ,tongue of ,house-fly1 from a micro-photograph made with a ,zeiss #af mm4 and apochromatic projection eye-piece #aej4 ,the beautiful form of the spiral structure of the tongue should be viewed under a high magnifying power1 when it will be seen that no continuing spiral structure really exists2 each ring1 apparently detached1 does not extend quite round2 their action is that of sucking tubes4 ,fluids are evidently drawn up through the entire fissure caused by the opening between the ends of the whole series of rings4 ,it may well be pronounced a marvellous structure4 ,the mounting of the tongue must be done with a considerable amount of care to show this structure1 imperfectly represented in my woodcut4 ,these insects are of some service in the economy of nature1 by their consumption of decaying animal matter1 found about in quantities ordinarily imperceptible to most people1 and that would not be removed by ordinary means during hot weather4 ,it was asserted by ,linnus that three flies would consume a dead horse as quickly as a lion4 ,this was1 of course1 said with reference to the offspring of such three flies2 and it is quite possible the assertion may be correct1 since the young begin to eat as soon as hatched1 and a female blow-fly will produce twenty thousand living larv 7one of which is represented in ,plate ,,vi41 ,no4 #ada74 ,in twenty-four hours1 each will have increased in weight two hundred times1 in five days it attains to its full size1 and changes into the pupa1 and then to the perfect insect4 ,illustration3 ,,tongue ,,of ,,drone-,,fly4 ,fig4 #cij4--,tongue1 ,proboscis1 and piercing apparatus of ,drone-fly 7,eristalis tenax74 ,illustration3 ,fig4 #cia4--,under-surface of a ,wasp's ,tongue1 ,feelers1 c4 7,seen within the circle is the tongue about life-size47 ,in the drone-fly 7,eristalis tenax71 the mouth organs are larger than in the house-fly1 and differ in many respects4 ,the tongue is split up for a certain distance1 and then again united1 as represented in ,fig4 #cij4 ,the labium1 mandibles1 and maxill are converted into well-developed lancet-shaped organs2 these both pierce the skin of animals1 and form tubes by which their blood may be sucked up4 ,next to the maxillary palpi a couple of lancets are seen to project out2 these again are associated with two other instruments1 one resembling in appearance a two-edged sword1 and a peculiar one with pincers or cutting teeth at the extremity4 ,it is very peculiar1 and resembles an instrument used in surgery for enlarging the wound1 and in this case to increase the flow of blood4 ,this remarkable compound piercing apparatus of the drone-fly is of exquisite finish1 and must strike the observer with amazement1 while it greatly transcends the work of human mechanism4 ,the fleshy tongue itself projects some distance from the apparatus described1 and is furnished with set or hairs1 shorter and fewer in number than those of the house-fly1 and while its spiral structure is not so fully developed1 its retractor1 muscles1 and ligaments are even more so4 ,the further development of the mouth organs must be looked for in other members of the insect tribe1 when it will be seen many assume a more or less modified form of structure1 that1 for example1 in ,hymenoptera 7the bee and wasp71 in which insects the mouth and tongue are divided into lobes which are used to extract the nectary 7as ,linnus termed it7 from the plants on which they feed4 ,the tongue in most species is capable of extension and contraction4 ,illustration3 ,fig4 #cib4 #a4 ,sting of ,wasp 7,vespa vulgaris71 with its muscular attachments and palpi for cleansing the apparatus2 #b4 ,sting of ,bee4 ,in ,fig4 #cia the under-surface of the wasp's tongue is shown1 together with its two pairs of antenn1 and pair of brushes on either side1 for brushing off the gathered pollen and honey from the broad tongue4 ,it is amply provided with muscular structure4 ,the antenn1 or feelers1 are as curious in form as they are delicate in structure4 ,those of the male differ from those of the female4 ,both the bee and the wasp are armed with an exceedingly venomous sting1 as is well known4 ,this structure takes the form of a well-adapted mechanical contrivance1 and is a weapon of offence as well as of defence4 ,the sting consists of two barbed needle-points1 of a sufficient length to pierce the flesh to some depth4 ,from the peculiar arrangement of their serrated edges their immediate withdrawal cannot take place1 and it is this circumstance1 with the drop of poison injected into the open wound1 that renders their sting of the most painful and irritating kind4 ,the gland containing the poison is contained in a minute sac situated at the root of the piercing apparatus4 ,in ,fig4 #cib is shown the sting of the wasp and the bee4 ,very many insects are provided with instruments for boring into the bark or solid wood itself4 ,the female ,cynip bores into the oak-apple for the purpose of depositing her egg4 ,the larva1 when full grown1 eats its way out of the nut1 and drops to the ground1 where it attains the form of the perfect fly 7,fig4 #cic74 ,illustration3 ,fig4 #cic4--;,female ,gall-fly and ,larva4 ,there are numbers of species living exclusively upon the leaves of plants1 to which they do much damage by the excrescences or galls they form4 ,each tree seems to be infested by its own species of gall-mite1 the so-called nail-gall of the lime being caused by a species named ,phytoptus tibi4 ,these galls take the form of a pointed column1 standing erect on the upper side of the leaf4 ,galls of much the same structure occur in the sycamore1 maple1 elm1 and various fruit trees4 ,the gnat 7,culex pipiens7 is furnished with a sting curiously constructed 7,fig4 #cid71 and enclosed in a perfectly clothed sheath covered throughout by scales or feathers4 ,this is folded up when not in use4 ,the mouth is provided with a complete set of lancets for piercing the flesh2 after having inflicted a severe wound1 it injects an acid poison through the proboscis4 ,the scales of the gnat vary in structure accordingly as these are found on the wing1 the body1 or the proboscis4 ,a magnified wing is shown at ,no4 #b1 ,fig4 #cid1 and a magnified scale from the proboscis at ,no4 #c4 ,in ,fig4 #dje1 ,nos4 #c and #e1 more highly magnified wing and body scales are given4 ,the proboscis is protected on either side by antenn and feelers4 ,illustration3 ,fig4 #cid4 #a4 ,head of ,culex pipiens1 female ,gnat1 detached from body2 #b4 ,wing1 showing nervature and fringed edges2 #c4 ,scale from ,proboscis2 #d4 ,proboscis and ,lancets4 ,the reticulated markings on each side of the head show the proportionate space occupied by the eyes4 ,the giant-tailed wasp1 ,sirax gigas1 is furnished with an even more curious mechanical boring apparatus 7,fig4 #cie7 than its congeners4 ,this is a boring ovipositor1 skilfully contrived for piercing the bark of trees1 in which the insect deposits her eggs1 and where the larva1 when hatched1 will find an ample supply of food to carry it through this stage of existence4 ,the boring tube1 it will be seen1 is a perfect muscular structure 7c1 c1 a1 and x72 in short1 it is an endless form of drill1 well known to the mechanic1 such as is employed in fine work for drilling holes4 ,the females are of some size1 and may be surprised and taken in the act of boring through the bark of the pine tree1 for which they have a preference4 ,illustration3 ,fig4 #cie4--;,boring apparatus of ,giant-tailed ,wasp 7,sirex gigas71 #cej4 ,there is also a species of the broad-bodied saw-fly1 ,lyda campestris4 ,these bore the ,scotch fir1 and deposit their eggs4 ,the larv from these eggs1 when hatched out1 feed upon the pine-needles1 first spinning a fine web to conceal their work of depredation4 ,a better known saw-fly1 ,abraxas grossulariata1 plays havoc among our gooseberry trees4 ,the female is provided with a curious mechanical apparatus as an ovipositor1 with which she cuts into the thicker under-leaf of the plant4 ,this penetrating and cutting tool consists of a double-saw 7,fig4 #cif7 of elaborate construction1 which when not in use is kept concealed in a long narrow case situated beneath the abdomen4 ,it is further protected by two horny plates4 ,the saws pass out through a deep groove so arranged that the saws work side by side backwards and forwards1 without a possibility of running out of the groove4 ,when the cut is made1 the four are drawn together and form a central canal1 through which an egg is forced into the leaf4 ,the cutting edges of the saws are provided with about eighteen or twenty teeth2 these have sharp points of extreme delicacy1 and together make a serrated edge of the exact form given to the finest and best-made surgical saws of the present day4 ,in the summer-time the proceedings of the female insect may be witnessed1 and the method of using this curious instrument seen1 by the aid of a hand magnifier4 ,these insects are not easily alarmed when busy at work4 ,illustration3 ,fig4 #cif4--,saws of the ,gooseberry-fly 7,abraxas grossulariata74 ,before bringing my remarks on proboscides of insects to a conclusion1 attention must be given to that of the honey bee 7,apis mellifica71 and its curious accessories4 ,the mouth of bees exhibits a combination of the suctorial and the masticatory form of oral apparatus4 ,thus the labial1 or upper lip1 and the mandibles1 or large pair of jaws1 are well developed1 while the maxill1 or lesser pair1 are elongated to form a tubular organ1 through which1 together with the tongue1 the flower juices1 8honey-dew10 may be sucked up4 ,the labium1 lower lip1 is also rather prolonged1 and the palpi1 or organs of touch1 with which it is endowed form a useful protective apparatus4 ,the mandibles are employed by bees in the construction of their abodes1 while the suctorial portion of the mouth is devoted to the reception of nourishment and to prehension4 ,the sting of the bee1 already noticed1 is in fact an ovipositor1 the female alone being provided with this weapon as an egg-depositing organ1 although better known as an aculeus or sting2 but it forms no part of the oral apparatus 7as shown in ,fig4 #cig74 ,the proboscis itself will be seen to be curiously divided2 the divisions are elegant and regular1 beset with numerous set or hairs4 ,the two horny outside lancets are spear-shaped and partially set with short hairs2 at the base of each is a hinge articulation2 this permits of considerable motion in several directions1 and is much used by the busy insect for forcing open the more internal parts of flowers1 thus facilitating the introduction of the proboscis4 ,the two shorter feelers are closely connected with the proboscis1 and terminate in three-jointed articulations4 ,the structure of the proboscis is so arranged that it can be enlarged at the base1 and thus made to contain a greater quantity of the collected honey-dew2 at the same time it is in this cavity the nectar appears to be converted into pure honey4 ,the proboscis tapers off to a little nipple-like extremity1 and at its base is seen two shorter and stronger mandibles1 from between which is protruded a long and narrow lance-like tongue1 the whole being most curiously connected by a series of strong muscles and ligaments4 ,the basal or first joint of the hind leg in the neuter or working bee is developed into an enlarged form of pocket1 used by the insect for conveying the pollen of flowers and the propolis to the hive4 ,indeed1 both the tibia and the first joint of the tarsus are broadened out into plates1 but the two sides of the plates are differently furnished4 ,on one side is a thick coating of hairs1 those on the tarsus taking the form of a brush1 evidently used for brushing out the pollen1 as these special developments are not found on the hind legs of the drones or of the queen4 ,illustration3 ,fig4 #cig4 #a4 ,honey bee's tongue2 #b4 ,leg of worker bee4 7,the small circles show the objects about the natural size47 ,illustration3 ,fig4 #cih4 #a4 ,foot and leg of ,ophion2 #b4 ,foot and leg of ,flesh-fly2 #c4 ,foot and leg of ,drone-fly1 with pad or sucker appendage4 ,the wax used in the formation of cells is a secretion that exudes through certain portions of the body of the bee1 since it is found in little pouches situated on the under part of the body1 but it is not brought home ready for use4 ,the walls of the cells are strengthened when completed by a kind of varnish1 already referred to as the propolis1 collected from the buds of poplar and lime trees1 and this is spread over the walls of the cell by that wonderful pair of broad spatul1 represented in the drawing4 ,many interesting variations will be found in the legs and feet of flies1 as well as in those of other orders of insects 7,lepidoptera74 ,one or two typical forms are represented in ,plate ,,vi41 and in ,fig4 #cih4 ,illustration3 ,fig4 #cii4--,sucker on the leg of ,water-beetle4 7,the dot in the circle represents the object natural size47 ,the tarsus1 or foot of the fly 7,fig4 #cih71 consists of a deeply bifid1 membranous structure1 pulvillus2 anterior to its attachment to the fifth tarsal joint1 or the upper surface1 are seated two claws1 or 8tarsal ungues02 these are freely movable in every direction4 ,these ungues differ greatly in their outline1 size1 and relative development to the tarsi1 and to the bodies of the insects possessing them1 and in their covering2 most are naked over their entire surface1 having however a hexagonal network at their bases1 which indicates a rudimentary condition of minute scale-like hairs1 such as are common on some part of the integument of all insects4 ,flexor and extensor muscles are attached to both ungues and flaps2 the flaps are either corrugated or arranged on the ridge and furrow plan1 in other cases they are perfectly smooth on their free surface1 while others are covered with minute scale-like hairs4 ,the thickness of the divided membrane on the blow-fly does not exceed the #a_/bjjjth of an inch at the margin2 they somewhat increase in thickness towards the point of attachment4 ,projecting from the flap are organs which have been termed 8hairs10 8hair-like appendages10 8trumpet-shaped hairs40 ,these are doubtless the immediate agents in holding on to a smooth surface1 as that of glass1 and are termed 8tenent-hairs10 in allusion to their office4 ,the under surface of left forefoot of ,musca vomitoria is shown with tenent-hairs 7,plate ,,vi41 ,no4 #adj72 a and b are more magnified hairs1 a from below1 b from the side4 ,no4 #adb is the left forefoot of ,amara communis1 showing the under surface and form of tenent appendages1 one of which is seen more magnified at a2 ,no4 #adc1 under surface of left forefoot1 ,ephydra riparia4 ,this fly is met with in immense numbers on the surface water in salt marshes4 ,it does not possess the power of climbing glass2 this is explained by the structure of the tenent-hairs2 the central tactile organ is also very peculiar1 the whole acting as a float1 one to each foot1 to enable the fly to rest on the surface of the water2 a is one of the external hairs1 ,no4 #ace1 under surface of left forefoot of ,cassida viridis 7tortoise-beetle71 showing the bifurcate tenent appendages1 one of which is given at a more magnified4 ,these1 in ground beetles1 are met with only in males1 and are used for sexual purposes4 ,the delicacy of the structure of these hairs in the fly and the elastic membranous expansion of the foot are marvellous4 ,when the fly is climbing1 a minute quantity of some glutinous fluid is exuded1 so that the tubular nature of the tenent-hairs hardly admits of a doubt4 8,at the root of the pulvillus1 or its under surface1 is a process1 which in some instances is short and thick1 in others long and curved1 and tapering to its extremity 7,scatophaga71 setose 7,empis71 plumose 7,hippoboscid71 or1 in one remarkable example 7,ephydra71 closely resembling in its appearance the very rudimentary pulvillus with which it is associated4 ,just at the base of the fifth tarsal joint1 on its under surface1 there is present1 in ,eristalis1 a pair of short1 very slightly curved hairs1 which point almost directly downwards40#hb ,tenent-hairs are usually present in some modification or other4 ,it is really difficult to name a beetle which has not some form of them2 the only one ,i yet know that seems to me really to possess nothing of the kind is a species of ,helops1 living on sandy heaths4 ,i suppose the dense cushion of hairs on the tarsi to be for the protection1 simply1 of the joints to which they are attached4 ,i have detected them on the tarsal joints of species of ,ephydra1 and on the first basal tarsal joint of the drone of the hive-bee4 ,a very rudimentary form of tenent-hairs is present on the under surface of some of the tree-bugs 7,pentatomid71 which have in addition a large1 deeply-cleft organ at the extremity of the tarsus2 this appears to be a true sucker4 ,when walking on a rough surface1 the foot represents that of a ,coleopterous insect without any tenent appendages4 ,the ungues are always attached to the last joint of an insect's tarsus4 ,they are not attached to the fifth tarsal joint of a ,dipterous insect1 neither are they attached to the fifth tarsal joint of a ,hymenopterous insect1 but to the terminal sucker1 which again1 in this great order1 is a sixth tarsal joint1 membranous1 flexible1 elastic in the highest degree1 retractile to almost its fullest extent within the fifth tarsal joint--a joint modified to an extraordinary degree for special purposes4 ,in plantula of ,lucanus1 with its pair of minute claws1 the ungues are hairs modified for special purposes2 and they have the structure of true hairs4 ,the sustentacula of ,epeira1 the analogous structures on the entire under surface of the last tarsal joints in ,pholcus1 the condition of the parts in the hind limbs of ,notonecta1 in both its mature and earlier conditions1 as well as in ,sarcoptes1 ,psoroptes1 and some other ,acari1 all may be cited in proof of this fact4 ,the various orders of insects have1 for the most part1 each their own type of foot4 ,thus there is the ,coleopterous type1 the ,hymenopterous type1 the ,dipterous type1 the ,homopterous type1 c42 each so very distinctive1 that in critical instances they will sometimes serve at once to show to which order an insect should be referred4 ,thus1 amongst all the ,diptera1 ,i have as yet met with but one subdivision which presents an exception to the structure described4 ,this exception is furnished by the ,tipulid1 which have the ,hymenopterous foot4 ,with hardly an exception1 then1 ,i believe the form of foot described will be found universal among the ,diptera4 ,it may be desirable to add a few words on the best plan of conducting observations on the feet of insects4 ,their action should be studied by placing the insect under the influence of chloroform4 ,it is of advantage to carefully preserve the parts examined1 and for this purpose ,deane's medium or glycerine jelly suits very well2 some of the more delicate preparations1 however1 can only be kept unchanged in a solution of chloride of zinc4 ,the plan of soaking in caustic potash1 crushing1 washing1 putting into spirits of wine and then into turpentine1 and lastly into ,canada balsam1 is perfectly useless1 excepting in rare instances where points connected with the structure of the integument have to be made out4 ,of course1 the parts should be viewed from above1 from below1 and in profile1 in order to gain exact ideas of their relations4 ,the binocular microscope diminishes the difficulties which formerly had to be encountered1 as by its aid many parts may be clearly viewed without preparation of any kind4 ,illustration3 ,fig4 #djj4 #a4 ,antenna of the ,silkworm-moth2 #b4 ,tongue of ,butterfly2 #c4 ,a portion of tongue highly magnified1 showing its muscular fibre2 #d4 ,trache of silkworm2 #e4 ,foot of silkworm4 7,the small circles enclose each object somewhat near the natural size47 ,moths and butterflies supply the microscopist with some of the most beautiful objects for examination4 ,what can be more wonderful in its adaptation than the antenna of the moth 7represented in ,fig4 #djj1 ,no4 #a71 with a thin1 finger-like extremity almost supplying the insect with a perfect and useful hand1 moved throughout its extent by a muscular apparatus of the most exquisite construction4 ,the tongue of butterfly 7,no4 #b7 is evidently made for the purpose of dipping into the interior of flowers and extracting the juices2 this act is assisted by a series of fine muscles4 ,an enlarged view of a portion is given at ,no4 #c2 see ,plate ,,vi41 ,nos4 #acb and #acc1 antenn of ,vapour ,moth4 ,illustration3 ,fig4 #dja4--;,breathing aperture or spiracle of silkworm4 7,in the circle it is shown about the natural size47 ,illustration3 ,fig4 #djb4--,magnified portions of the trachea of the ,hydrophilus1 showing spiral tubes4 ,the inconceivably delicate structure of the maxill or tongues 7for there are two7 of the butterfly1 rolled up like the trunk of an elephant1 and capable1 like it1 of every variety of movement1 has been carefully examined and described by ,mr4 ,newport4 8,each maxilla is convex on its outer surface1 but concave on its inner2 so that when the two are united they form a tube1 haustellium1 by their union1 through which fluids may be drawn into the mouth4 ,the inner or concave surface1 which forms the tube1 is lined with a very smooth membrane1 and extends throughout the whole length of the organ2 while that of each maxilla is hollow in its interior1 apparently forming a tube #8in itself1' but this is not so2 the mistake has arisen from the existence of large trache1 or breathing tubes1 in the interior of the proboscis4 ,in some species the extremity of the haustellium is studded externally with a number of minute papill1 or fringes--as in ,vanessa atalanta--in which they become small elongated barrel-shaped bodies1 terminated by smaller papill at their extremities4 ,on alighting on a flower1 the insect makes a powerful expiratory effort1 by which the air is expelled from the interior air-tubes1 and from those with which they are connected in the head and body2 and at the moment of applying its proboscis to the food1 it makes an inspiratory effort1 by which the central canal in the proboscis is dilated1 and the food ascends it at the same instant to supply the vacuum produced2 and thus it passes into the mouth and stomach1 the constant ascent of the fluid being assisted by the action of the muscles of the proboscis1 which continues during the whole time that the insect is feeding4 ,by this combined agency of the acts of respiration and the muscles of the proboscis we are also enabled to understand the manner in which the humming-bird sphynx extracts in an instant the honey from a flower while hovering over it1 without alighting2 and which it certainly would be unable to do were the ascent of the fluid entirely dependent upon the action of the muscles of the organ40 ,the trachal or respiratory system of insects varies1 or rather is found to exist in modified forms to suit their varied conditions of life4 ,while in the larval stage the breathing apertures are seen to recur at intervals on each side of the abdomen 7as that of the silkworm1 ,fig4 #dja71 thus ensuring a continuous supply of air to the circulating fluids throughout the whole body4 ,these spiracles are usually nine or ten in number1 and consist of a membranous ring of an oval form4 ,the air-tubes are exquisitely composed of two thin membranes1 between which a delicate elastic thread or spiral fibre is interposed1 forming a cylindrical opening and keeping the tube in a distended condition1 thus mechanically preserving the sides from collapse or pressure in their passage through the air1 which otherwise might occasion suffocation4 ,fig4 #djb represents the double spiral arrangement of a portion of a trachea of ,hydrophilus1 which ensures both elasticity and strength4 ,there are other points of interest confined to the water-beetle tribe1 among the more striking of which is the foreleg of the ,dytiscus marginalis4 ,here the first three joints of the tarsus are expanded into a broad surface1 and fringed throughout with curved hairs4 ,from the surface of these spring a number of short hairs1 with cup-like discs at their extremities1 one of which is seen highly magnified in ,plate ,,vi41 ,no4 #adb4 ,these are so cup-like in form that they have been hitherto described as 8suckers10 but it is believed they are simply a special apparatus for the development of the hairs seen on the leg and foot of the beetle4 ,another curious example occurs in the ,gyrinus1 or whirligig-beetle4 ,the front pair of legs are of the ordinary kind1 but the under pair are furnished with expanding paddles4 ,the trochanter1 femur1 and tibia1 are flat plates of a triangular shape1 pointed at their outer angles1 from which the apex springs4 ,but the tarsus is jointed on the inner angle of the furthermost end of the tibia1 and each of its four joints expands into a flat paddle blade4 ,in the accompanying ,fig4 #djc one paddle is seen expanded1 the other closed4 ,illustration3 ,fig4 #djc4 #a4 ,leg of ,gyrinus1 ,whirligig1 paddle shown expanded4 #b4 ,paddle closed up4 ,these paddles are adapted with much precision to ensure the most effectual application of the propelling power2 as the beetle strikes out in the act of swimming1 the membranous expansion described enables it to move about with great rapidity2 upon the legs being drawn back towards the body1 the membrane closes up1 and thus offers no resistance to the water4 ,the eyes are not the least curious part of the merry little beetle3 the upper section is fitted for seeing in the air1 and is adapted to the upper or superior part of the head2 the lower portion1 for seeing under the water1 being placed at a lower angle1 a thin division only separating the two4 ,illustration3 ,fig4 #djd4--,scales from ,butterflies' and ,moths' wings1 magnified #bjj diameters4 #a4 ,scale of ,morpho menelaus2 #b4 ,large scale of ,polyommatus argiolus1 azure blue2 #c4 ,hipparchia janira argiolus2 #d4 ,pontia brassica2 #e4 ,podura plumbea2 #f4 ,small scale of azure blue4 ,wings of ,insects4--,these exhibit variety of form and structure1 as well as of beauty of colouring4 ,at an early period the orders of insects were mainly founded upon these interesting appendages4 ,the ,orthoptera were the straight wings2 the ,neuroptera the nerved2 the ,trichoptera the hairy wings2 the ,coleoptera the cased or sheathed wings2 the ,diptera the two wings2 the ,hymenoptera the married wings2 and the ,lepidoptera the scaled wings4 ,a number of wings are small and membranous1 and may be mounted dry for examination under the microscope4 ,others are better seen mounted in benzol-balsam4 ,the elytra1 iridescent wing cases of the diamond1 and other beetles1 as well as the wings of the more highly coloured butterflies1 make pretty objects mounted dry for opaque illumination by the ,lieberkhn or reflector4 ,the thicker horny cases of other members of the beetle tribe require long soaking1 as described in a former chapter4 ,the wings of moths and butterflies are covered with scales or feathers1 carefully overlapping each other1 as tiles are made to cover the tops of houses4 ,the iridescent variety of colouring on insects' wings arises from the peculiar wavy arrangement of the scales4 ,figs4 #djd and #dje are magnified representations of a few of them4 ,no4 #a1 a scale of the ,morpho menelaus1 taken from the side of the wing1 is of a pale-blue colour2 it measures about #a_/abjth of an inch in length1 and exhibits a series of longitudinal stri or lines1 between which are disposed cross-lines or other stri1 giving it very much an appearance of brick-work 7better seen in ,fig4 #dje1 ,no4 #a74 ,illustration3 ,fig4 #dje4--,portions of ,scales1 magnified #ejj diameters4 #a4 ,portion of scale of ,morpho menelaus2 #b4 ,portion of large scale of ,podura plumbea2 #c4 ,scale from the wing of ,gnat1 its two layers being represented2 #d4 ,portion of a large scale of ,lepisma ,saccharina2 #e4 ,body scale of ,gnat1 magnified #fej diameters4 ,polyommatus argiolus1 azure-blue 7,fig4 #djd1 ,nos4 #b and #f71 are large and small scales taken from the under-side of the wing of this beautiful blue butterfly2 the small scale is covered with a series of spots1 and exhibits both longitudinal and transverse stri1 these should be clearly defined1 and the spots separated by a quarter-inch object-glass4 ,no4 #c1 ,hipparchia janira1 is a scale from the meadow-brown butterfly3 on this brown spots1 having an irregular shape with longitudinal stri1 are seen4 ,no4 #d1 ,pontia brassica1 cabbage butterfly1 was at one time taken to be an excellent criterion of the penetration and definition of an object glass4 ,it is seen to have a free extremity or brush-like appendage4 ,with a fairly good power1 the longitudinal markings appear like rows of small beads4 ,chevalier selected for his test object the scale of the ,pontia brassica4 ,mohl and ,schacht extolled ,hipparchia janira as a good test of penetration in an objective of moderate angular aperture4 ,amici's test object is ,navicula rhomboides1 the display of the lines forming the test4 ,illustration3 ,fig4 #djf4--,podura villosa1 male and female1 highly magnified4 ,the ,tinea vestianella1 clothes-moth1 is furnished with unique scales4 ,small and destructive as this moth is1 it suffers much from a parasitic mite1 and from which it is unable to free itself4 ,the ,podura scale 7,fig4 #dje71 with its delicate transparent membrane and curiously inserted 8notes of admiration10 as they were called1 was long believed to be an excellent test object for the highest powers of the microscope1 but ,i believe it is no longer regarded in that light3 indeed1 most insect scales have declined in the value and estimation of the skilled microscopist4 ,this is in part due to the improvements made in the objective4 ,the high-angled glasses have cleared up obscure points in the structural characters of the minuter forms of life1 and the scales of insects are no longer found to be difficult test objects for the modern objective of a ,zeiss or a ,powell to resolve4 ,nevertheless1 the scale of the ,podura belonging to the order ,thysanura1 a curious little insect commonly known by the name of springtail1 usually found living in most obscure places1 and too small to attract attention1 is not likely to be entirely thrust aside4 ,the springtails 7,collembola7 are furnished on the under-side of the first abdominal segment with a curious tube or sucker1 from the orifice of which glandular process a secreted viscid matter is protruded2 they are remarkable also from the fact that in most of them no trace of a tracheal system has yet been discovered4 ,the eyes when present are in the form of simple or grouped ocelli1 the antenn number six joints1 and the abdomen has but six segments1 often only three4 ,the forked tail is a curious process turned forward and attached to one of the tender segments and held in position under the body2 when released it springs back and bounds up to a very considerable height4 ,fig4 #djf represents ,podura villosa4 ,there are several species1 one of which 7,p4 aquatica7 is found floating in patches on pools of water on bright summer days4 ,lepisma saccharina belongs to the same genus as ,podura4 ,this minute springtail derives its name from having been discovered in old sugar-casks4 ,it has a spindle-shaped body covered with silvery scales1 long used as test objects4 ,the sides of the abdomen are furnished with a series of appendages with long bristle-like set1 or hairs1 at their extremities4 ,the head is concealed under a prothorax1 the antenn are long1 and the maxillary palpi are either five or seven-jointed1 and very conspicuous1 to enable them to cut the dry wood on which they principally feed4 ,the scales must be mounted under thin cover-glasses2 oblique illumination shows up some portions to advantage1 while central light from an achromatic condenser and a wide-angled objective renders their markings more distinct4 ,portion of a scale more highly magnified is shown in ,fig4 #dje4 ,eggs of ,insects 7,plate ,,vi41 ,nos4 #abd-aci74--;,in form1 colour1 and variety of design1 the eggs of insects are more surprisingly varied than those of the feathered tribes2 but as from extreme smallness they escape observation1 an acquaintance with their structure is not so familiar as it might be4 ,although the eggs of the bird tribe differ much in their external characteristics1 they closely resemble each other while yet a part of the ovarian ova1 and prior to their detachment from the ovary4 ,at one period of their formation all eggs consist of three similar parts3--#ast4 ,the internal nucleated cell1 or germinal vesicle1 with its macula2 #bnd4 ,the vitellus1 or yolk-substance2 and #crd4 ,the vesicular envelope1 or vitelline membrane4 ,the germinal vesicle is the first produced1 then the yolk substance1 which gradually envelops it1 and the vitelline membrane1 the latest formed1 incloses the whole4 ,the chemical constituents of the egg are the same in all cases1 albumen1 fatty matters1 and a proportion of a substance precipitable by water4 ,the production of the chorion1 or shell membrane1 does not take place till the ovum has attained nearly its full size1 and it then appears to proceed1 in part at least1 from the consolidation over the whole surface of one or more layers of an albuminous fluid secreted from the wall of the oviduct4 ,the embryo cell is so directly connected with the germinal vesicle that at a certain period it disappears altogether1 and is absorbed into the germinal yolk1 or rather becomes the nucleus of the embryo1 when a greater degree of compactness is observed in the yolk1 and all that remains of the germinal vesicle is one or more highly refracting fat globules and albuminoid bodies4 ,towards the end of the period of incubation1 the head of the young caterpillar is said to lie towards the dot or opening in the lid1 termed the micropyle1#hc from its resemblance to a small gate1 or opening through which the larva emerges forth as a butterfly4 ,the germinal vesicle is comparatively large and well-marked while the egg is yet in the ova-sac4 ,by preparing sections after ,dr4 ,halifax's method1#hd we find that the germinal vesicle in the bee's egg is not situated immediately near or even below the so-called micropyle1 but rather more to the side of the egg2 just in the position which the head of the embryo is subsequently found to occupy at maturity4 ,the egg membrane1 or envelope1 of all the ,lepidoptera is composed of three separate and distinct layers3 an external slightly raised coat1 tough and hard in its character1 a middle one of united cells1 and a fine transparent vitelline lining membrane1 perfectly smooth and homogeneous in structure1 imparting solidity1 and giving a fine iridescent hue to the surface4 ,the germinal vesicle is of a proportionately large size for the egg1 and its macula is at first single1 then multiple4 ,in the egg of the silkworm the outer membrane is comprised of an inner reticulated membrane of non-nucleated cells1 in the outer layer the cells are arranged in an irregular circular form1 also non-nucleated1 with minute interstitial set or hairs projecting outward4 ,the outer surface of the egg-shell of ,coccus ,persic is covered by minute rings1 of which the ends somewhat overlap4 ,these rings are thought to be identical in their character with the whitish substance which exudes through pores on the under-side of the body2 it is more than probable that a succession of layers of rings fully accounts for the beautiful prismatic hues they present viewed as opaque objects under the microscope1 and illuminated by ,lieberkhn or side-condenser4 ,this white substance1 it should be observed1 forms a part of the intimate structure of the egg-shell1 and is in nowise affected by methylated spirit or dilute acids4 ,sir ,john ,lubbock#he states that in the greenish eggs of ,phryganea1 8the colour is due to the yolk-globules themselves4 ,in ,coccus1 however1 this is not so2 the yolk-globules are slightly yellow1 and the green hue of the egg is owing to the green granules1 which are minute oil globules4 ,when1 however1 the egg arrives at maturity1 and the upper chamber has been removed by absorption1 these green granules will be found to be replaced by dark-green globules1 regular in size1 and about #a_/hjjjth of an inch in diameter1 and which appear to be in no way the same in the yolk of ,phryganea eggs40 ,another curious fact has been noticed1 which partially bears on the question of colour3 the production of parasite bodies within the eggs of some insects4 ,in the ,coccus1 for instance1 parasitic cells of a green colour occur1 8shaped like a string of sausages1 in length about the #a_/bjjjth of an inch by about the #a_/gjjjth in breadth40 ,the eggs of moths and butterflies present many varying tints of colour2 in speaking of this quality ,i do not restrict the term solely to those prismatic changes to which allusion has been made1 and which are liable to constant mutations according to the accident of the rays of light thrown upon them2 but ,i more particularly refer to the several natural transitions of colour1 the prevailing tints of which are yellow1 white1 grey1 and a light-brown4 ,in some eggs the yellow1 white1 and grey are delicately blended1 and1 when viewed with a magnifying power of about fifty diameters1 and by the aid of the side-reflector 7parabolic-reflector71 exhibit many beautiful combinations4 ,the more delicate opalescent1 or rather iridescent1 tints appear on the eggs of insects1 while those of the feathered tribes furnish no like example4 ,the egg of the mottled umber moth1 ,erannis defoliaria 7,plate ,,vi41 ,no4 #acg71 is in every way very beautiful4 ,it is in shape ovoid1 with regular hexagonal reticulations1 each corner being studded with a knob or button2 the space within the hexagon is finely punctated1 and the play of colours is exquisitely delicate4 ,in this egg no micropyle can be seen4 ,the egg of the thorn moth1 ,ennomos erosaria 7,plate ,,vi41 ,no4 #ach71 is of an elongated brick-looking form1 one end of which is slightly tapered off1 while the other1 in which the lid is placed1 is flattened and surrounded by a beautifully white-beaded border1 having for its centre a slightly raised reticulated micropyle4 ,the empty egg-shell gives a fine opalescent play of colours1 while that containing the young worm is of a brownish-yellow4 ,the egg of the straw-belle moth1 ,aspillates gilvaria 7,plate ,,vi41 ,no4 #aci71 is delicately tinted1 somewhat long and narrow1 with sides slightly flattened or rounded off1 and irregularly serrated4 ,the top is convex1 and the base a little indented1 in which are seen the lid and micropyle4 ,the young worm1 however1 usually makes its way through the upper convex side3 the indentation represented in the drawing shows the place of exit4 ,an example of those eggs possessing a good deal of natural colour is presented in that of the common puss-moth1 ,cerura vinula1 a large spheroidal-shaped egg1 having1 under the microscope1 the appearance of a fine ripe orange2 the micropyle exactly corresponds to the depression left in this fruit on the removal of the stalk4 ,the surface is finely reticulated1 and the natural colour a deep orange4 ,the egg of the mottled rustic moth1 ,caradina morpheus 7,no4 #abd71 is subconical1 and equally divided throughout by a series of ribs1 which terminate in a well-marked geometrically-formed lid4 ,the egg of the tortoise-shell butterfly1 ,vanessa urtic 7,no4 #abe71 is ovoid and divided into segments1 the ribs turning in towards the micropyle4 ,the common footman1 ,lithosia campanula 7,no4 #abf71 produces a perfectly globular egg covered with fine reticulations of a delicate buff colour4 ,the egg of the shark moth1 ,cucullia umbratica 7,no4 #abg71 is subconical in form1 with ribs and cross-bars passing up from a flattened base to the summit1 and turning over to form the lid4 ,no4 #acf is the egg of blue argus butterfly1 ,polyommatus argus4 ,that of the small emerald moth1 ,jodis ,vernaria 7,no4 #acd71 is an egg of singular form and beauty--an oval1 flattened on both sides1 of silvery iridescence1 and covered throughout with minute reticulations and dots4 ,it is particularly translucent1 so much so that the yellow-brown worm is readily seen curled up within4 ,the lid or micropyle is not detected until the larva eats its way out of the shell4 ,it should be noted that the series of eggs in ,plate ,,vii4 are somewhat over-coloured1 and consequently lose much of their natural transparency4 ,the eggs of flies and parasites also present much variety in form1 colour1 and construction4 ,many of their eggs are provided with a veritable lid1 which opens up with a hinge-like articulation4 ,this lid is seen in the egg of bot-fly1 ,plate ,,vi41 ,no4 #add1 from which the larva is just escaping2 ,no4 #adf1 egg of ,scatophaga2 ,no4 #adg1 egg of parasite of magpie4#hf ,still more remarkable in the delicate and beautiful forms are some of the parasities which infest birds in particular3 ,plate ,,vi41 ,no4 #ade1 the egg of parasite of pheasant2 ,no4 #adg1 that of the magpie1 while that of the peacock is curiously interesting4 ,in ,fig4 #djg the larv of the horn-bill are seen just about to emerge from their eggs4 ,illustration3 ,fig4 #djg4--,larv of the ,hornbill emerging from eggs4 ,the larv of most ,hymenoptera are footless grubs1 furnished with a soft head1 and exhibiting but little1 if any1 advance upon those of ,diptera 7,plate ,,vi41 ,no4 #ada74 ,in the saw-fly1 however1 the larva1 instead of being as above described1 a mere footless maggot1 presents the closest resemblance to the caterpillar of the ,lepidoptera2 it is provided with a distinct head1 with six thoracic legs1 and in most cases from twelve to sixteen pro-legs are appended to the abdominal segments4 ,one other conspicuous object represented in ,plate ,,vi41 ,no4 #abh1 is the maple ,aphis1 also known as the leaf-insect1 averaging in size about the one-fiftieth of an inch in length4 ,although recognised and described under the name of the leaf-insect1 nothing was known of its origin and history1 with the exception of what the ,rev4 ,j4 ,thornton published in #aheb1 and to whom we owe its re-discovery on the leaves of the maple4 ,subsequently it attracted the attention of the ,dutch naturalist1 ,van der ,hoeven1 who regarded it as the larval form of a species of ,aphis1 and named it ,periphyllus4 ,it has more recently engaged the attention of ,dr4 ,balbiani and ,m4 ,siguoret1 whose united investigations will be found in 8,comptes ,rendus10 #ahfg4 ,these observers assigned it definitely to ,aphis4 ,a brown species is also met with during a great part of the year feeding upon the young shoots of the maple4 ,the female produces two kinds of young1 as do all the genus ,aphis1 one normal the other abnormal2 the first are alone capable of reproducing their species1 while the latter retain their original form1 which is not changed throughout their existence4 ,they increase so slowly in size that it may appear doubtful whether they eat1 the mouth being rudimentary2 they undergo no change2 do not acquire wings1 and their antenn always retain the five joints peculiar to all young ,aphides before the first moult4 ,neither are they all of the same colour1 some being of a bright green1 as represented in ,plate ,,vi41 while others are of a darker1 or brownish-green colour4 ,the brown-green embryos differ from the adult female only in those characters analogous to all other species1 and this chiefly with regard to the minute hairs1 which are long and simple4 ,in the green embryos1 in the place of set1 the body is surrounded by transparent lamell1 oblong in shape4 ,these scales not only cover the body1 but also the anterior portion of the head1 the first joint of the antenn1 and the outer edge of the tibi of the first pair of legs4 ,the dorsal surface in these insects is covered with a mosaic of hexagonal plates1 very closely resembling the plates of the carapace of the tortoise4 ,in this particular my artist has fallen into a slight error4 ,another peculiarity is that the body is much flattened out1 and looks so much like a scale on the surface of the leaf that it requires considerable practice1 as well as quickness of sight1 to detect the young maple ,aphis4 ,one of the lamell is seen highly magnified at c1 and a tenent-hair at b4 ,the antenn1 tapering off towards the apex1 are serrate on both edges1 and terminate in a fine lancet 7shown at a71 with which it penetrates the leaf of the plant4 ,beneath the insertions of the antenn is a complex form of sucking mouth1 and on either side of the head are two brilliant scarlet-coloured eyes4 ,aphides1 as is well known1 live upon the juices of plants1 which they suck1 and when they occur in great numbers cause considerable damage to the gardener and farmer4 ,many plants are liable to be attacked by swarms of these insects1 when their leaves curl up1 they grow sickly1 and their produce is either greatly reduced or utterly ruined4 ,one striking instance is presented in the devastation caused by the hop-fly 7,aphis humuli74 ,illustration3 ,fig4 #djh4--;,aphrophora spumaria1 ,cuckoo-spit4 a4 ,the frothy substance2 b4 ,the pupa4 ,the ,aphrophora bifasciata1 common frog-hopper1 is a well-known garden pest4 ,the antenn of this insect are placed between the eyes1 and the scutellum is not covered2 the eyes1 never more than two in number1 are occasionally wanting4 ,these pests are furnished with long hind legs1 that enable them to perform most extraordinary leaping feats4 ,the best-known ,british species is the cuckoo-spit1 froth-fly 7,fig4 #djh74 ,the names cuckoo-spit and froth-fly both allude to the peculiar habit of the insect1 while in the larva state1 of enveloping itself in a kind of frothy secretion1 somewhat resembling saliva4 ,arachnid4--,in this class of insects1 spiders1 scorpions1 and mites are included1 all of which belong to a sub-class of ,arthropoda1 and are appropriately placed between the ,crustacea on the one hand and the ,insecta on the other4 ,the highest ,crustaceans have ten feet1 the ,arachnid eight1 and insects six4 ,the ,arachnid are wingless1 have no antenn1 and breathe by means of tracheal tubes1 or pulmonary sacs1 these performing the function of lungs4 ,as a rule they have several simple eyes1 have no proper metamorphosis1 and they are essentially predaceous1 the females being larger than the males4 ,most of the ,arachnid live on insects1 and may therefore be regarded in the light of a friend to the florist and gardener4 ,the ,epeira diadema is the best known member of the species2 in summer spiders abound on every shrub1 and spin out their wonderful webs from branch to branch4 ,illustration3 ,fig4 #dji4--;,a lengthways section through the body of female ,epeira diadema4 ,explanation of reference4--ey4 ,eyes2 p4g4 ,poison gland2 ht4 ,heart2 in4 ,intestine1 alimentary canal2 l4 ,liver2 r4 ,rectum or cloaca2 dt4 and sp4 ,discharge tubes of spinnerets2 o4 ,slit1 or air opening2 ov4 ,ovipositor2 ph4 ,pharynx2 br4 ,brain2 thr4 ,throat1 or gullet1 filled with eggs2 un4 l4 ,under lip2 m4 ,mouth2 f4 ,fang1 or claw2 j4 ,jaw4 ,the gills1 or breathing apparatus are situated at the air opening1 o2 and the silk glands are above this4 7,magnified #bj diameters47 ,the body1 seen in my illustration1 ,fig4 #dji1 in section1 consists of two parts2 the foremost is the cephalothorax1 or head1 upon which is mounted four pairs of eyes 7two of which are seen in section71 while to the thorax is attached eight jointed well-developed legs terminating in feet1 with claws adapted for climbing and holding on4 ,the other half consists1 of the abdomen1 together with spinnerets and glands1 which secrete the fluid out of which the web is spun1 and this1 although it hardens to some extent on exposure to the air1 retains its viscid nature for the purpose of entangling its prey4 ,the spinnerets are the most interesting feature in the anatomy of the ,epeira 7,figs4 #daj and #daa74 ,illustration3 ,fig4 #daj4 #a4 ,spinnerets of ,spider2 #b4 ,extreme end of one of the upper pair of spinnerets2 #c4 ,end of under pair of spinnerets2 #d4 ,foot of ,spider2 #e4 ,side view of eye2 #f4 ,the arrangement of the four pairs of eyes4 ,five kinds of spinning glands are found in spiders4 ,the glandul aciniformes are those which consist of a proper tunica and an epithelium2 these exhibit in all parts the same reaction to staining agents4 ,the glandul pyriformes consist of a tunica proper and an epithelium1 which in their lower parts 7or those near the efferent ducts7 stain more deeply than the upper4 ,the glandul ampullace and glandul tubuliformes have similar coverings1 the latter terminating in a large spool4 ,the glandul aggregat have a wide and branched lumen1 the efferent duct of which is provided with cells and an accessory piece1 which draws out to a tip4 ,all the glands have secreting portions1 which serve as collecting cavities for the spinning material4 ,the spools are two-jointed basal and one-jointed accessory pieces4 ,in addition to the five glands enumerated1 there are also lobate and cribelleum glands2 these are variously distributed1 and exercise different functions1 one set preparing the so-called moist filaments from the moist droplets1 another spins the egg-cocoon1 as nearly all spiders envelop their eggs in a covering of silken threads and store them up in some sheltered place awaiting the warm weather of spring to hatch them out4 ,the bag that holds the eggs is not one of the least curious efforts of skill and care4 ,the mother uses her body as a gauge to measure her work1 precisely as a bird uses her body to gauge the size and form of its nest4 ,the spider first spreads a thin coating of silk as a foundation1 taking care to have this circular by turning its body round during the process4 ,in the same manner it spins a raised border round this till it takes the form of a cup2 it is at this stage of the work the female begins to lay her eggs in the cup1 and not content to fill it up to the brim1 she also piles up a heap as high as the cup is deep4 ,here1 then1 is a cup full of eggs1 the under half covered and protected by the silken sides of the cup1 but the upper still exposed to the air and the cold4 ,she now sets to work to cover this2 the process is similar to the preceding--that is1 she weaves a thick web of silk all round the top1 and instead of a cup-shaped nest1 like those of the bird tribe1 the whole partakes of the form of a ball much larger than the body of the spider4 ,illustration3 ,fig4 #daa4--,spinnerets of ,spider greatly enlarged4 ,the eight legs and feet of the spider 7one only is represented ,fig4 #daj1 ,no4 #d7 are curiously constructed4 ,each foot1 when magnified1 is seen to be armed with strong horny claws1 with serrations on their under-surface4 ,by this arrangement the spider is enabled to regulate the issue of its web from the spinnerets4 ,in addition1 a remarkable comb-like claw is provided for the purpose of separating certain threads which enter into the composition of the delicate web1 so that everything is arranged and planned in the most geometrical order1 while the mouth or jaws with their two movable poison-fangs convert the ,arachnid into formidable and dangerous foes4 ,the maternal industry and instincts of spiders1 the ballooning habits of others1 the cave dwellers1 with their limited vision1 combined with an increased delicacy of touch and hearing1 their disguise of feigned death when a strong enemy approaches1 are all of the most interesting character4 ,one of the more remarkable1 the ,argyroneta aquatica 7diving spider71 weaves itself a curious little bell-shaped globule1 which it takes with it to the bottom of the water1 whither it retires to devour its prey4 ,notwithstanding its aquatic habits1 this1 like the rest of its species1 is fitted only for aerial respiration2 it therefore carries down1 entangled amongst the hairs of its body1 a small bubble of air4 ,this contrivance presents us with the earliest form of diving-bell4 ,mites and ,ticks constitute a group which for diversity of structure1 number of species and individuals1 and minuteness of size1 has no equal4 ,the typical genus of the family--,ixodid--being wholly parasitic in their habits1 are so modified in organisation1 so marked by degeneration1 that some authors have proposed to remove them into a class by themselves4 ,one leading character distinguishes the whole3 the abdomen rarely presents a trace of segmentation1 but is confluent with the cephalothorax1 the fusion between the two being so complete that1 as in the harvest spiders belonging to ,palpatores1 the anterior sternal plates of the abdomen are thrust far forward between the cox of the cephalothoracic limbs4 ,as in ,arachnid1 however1 the mouth is adapted for sucking1 but the jaws are often partially united1 and form1 with a plate termed the epistome and the labium1 a beak4 ,the mandibles are either pincer-like1 or simply pointed at the tip1 forming piercing organs2 the palpi have their basal segments1 or maxill1 united1 which form a conspicuous plate1 or hypostomes1 constituting the floor of the mouth4 ,these organs are often seen to be separated from the rest of the cephalothorax by a membranous joint1 and constitute a kind of head1 the capitulum4 ,in most cases no trace of special respiratory organs can be found4 ,another characteristic of value in separating ticks from harvest-spiders is that in the former the young undergo a metamorphosis in the course of growth1 being hatched as six-footed larv1 and acquiring later in life a fourth pair of legs4 ,illustration3 ,fig4 #dab4 ,a4 ,atax spinipes1 water mite seen from below2 ,b4 ,water ,scorpion infested by ,atax4 ,the ,acari include a number of families1 all distinguished by the position of the respiratory stigmata and the form of the mandibles and palpi4 ,in the velvety mites 7,trombidiid71 the integument is soft and covered with variously-coloured fine hairs1 and the legs are adapted for walking1 running or swimming4 ,the latter live in fresh-water ponds1 creeping over the leaves of aquatic plants4 ,the fresh-water mites 7,atax spinipes1 ,fig4 #dab7 swim about freely by means of vigorous strokes of their legs1 which act as oars4 ,in the adult the body is more or less spherical1 and usually of a bright red or greenish colour4 ,the males of one species have a curious blunt tail-like prolongation from the hinder end of the abdomen4 ,the eggs are laid in the spring on the stems of water plants1 and the six-footed larv when hatched attach themselves to water-bugs 7,nepa7 or water-beetles 7,dytiscus7 by means of a large sucker developed on the front of the head4 ,illustration3 ,fig4 #dac4--;,ixodes ricinus or ,sheep-tick 7under surface74 ,the small circle encloses one life-size4 ,of all the ,acari1 the best known and most troublesome are those belonging to the family ,ixodid2 these infest the whole animal creation4 ,they are furnished with a long cylindrical beak1 armed with recurved hooks1 formed of the two mandibles above and the long slender labium below4 ,they have no eyes1 nor apparently any dermaploptic sense1 but there are various seemingly sensitive set distributed over the body and on the appendages4 ,the whole of the mites will be found suitable objects for the study of development1 as the process is slow and their eggs do not require much care4 ,the segmentation of the eggs differs2 some of the cells are distinguished by their large nuclei1 which stain feebly by carmine4 ,during the cleavage of the egg no division of the so-called yolk has been observed1 but later on this breaks up into several minute pieces4 ,illustration3 ,fig #dad4--,mouth organs of ,sheep-tick4 c4 ,capitulum2 d1 e1 f1 g4 ,segments of palpi2 h4 ,labial process2 i4 ,spiny beak formed of fused mandibles4--7,warne47 ,the accompanying ,fig4 #dac shows the under surface of the body and the mouth parts of the common ,english dog and sheep tick1 ,ixodes ricinus1 with its six formidable legs4 ,the upper surface is shown in ,fig4 #dae2 the head 7capitulum7 and mouth organs in ,fig4 #dad1 c1 d1 e1 f1 g1 together with the four segments of the palpi2 h the labial process armed with hooks forming the lower side of the beak1 and i indicating the tips of the two mandibles forming the upper side1 and projecting beyond the apex of the labium4 ,by means of this beak1 which is thrust to its base into the integument1 the tick adheres firmly to its host1 and in detaching them care must be taken that the head is not left behind buried in the skin4 ,this tick is found in all stages of growth2 the females1 gorging themselves with blood1 swell up to the size of a pea1 as seen in ,fig4 #dac1 but the male1 formerly regarded as a distinct species1 is of a much smaller size4 ,in distribution these pests are almost cosmopolitan1 and in tropical countries they grow to much greater dimensions1 the females sometimes attaining the size of a large gooseberry4 ,the family of true mites is that of the ,sarcoptid2 these are either free or parasitic4 ,they have no breathing organs2 the palpi are basally fused to the rostrum1 the mandibles are pincer-like1 and the tarsi are often furnished at their tips with a sucker4 ,the most familiar is the cheese mite1 ,tyroglyphus1 which feeds upon decaying matter4 ,illustration3 ,fig4 #dae4 #a4 ,female ,sheep-tick2 #b4 ,rat-tick2 #c4 ,head of ,cat-flea2 #d4 ,larva of ,flea4 7,the life size is given in circles47 ,the well-known cheese mite attains to a size plainly visible to the naked eye1 but when first hatched out from the egg 7shown in its several stages of development in ,fig4 #dag71 requires a moderate amount of magnification4 ,its growth1 however1 is rapid and the young begin to feed as soon as they leave the egg4 ,the body is partially covered over by set1 or hairs1 and the feet terminate in hooklets1 as seen in the full-grown acarus4 ,the mandibles are cutting1 but as a rule they prefer soft and partially-decayed kinds of food4 ,it also feeds upon damaged flour1 sugar1 and other domestic articles4 ,the ,dermestes lardarius1 one of the minute beetle tribe 7,fig4 #dah71 commits even greater depredations among insect and other collections during the larval stage of its existence4 ,illustration3 ,fig4 #daf4 ,tyroglyphus4 #a4 ,pediculus vulgaris #ej diameters2 #b4 ,acarus destructor under surface2 #c4 ,sarcoptes scabici1 ,itch-insect1 magnified #cej diameters2 #d4 ,demodex folliculorum from the human skin in various stages of growth1 from the egg upwards1 magnified #djj diameters4 7,the small circles enclose the objects of the natural size47 ,illustration3 ,fig4 #dag4--,the ,cheese ,mite1 ,acarus domesticus1 seen in its several stages of development4 ,illustration3 ,fig4 #dah4--;,dermestes lardarius3 larva1 pupa1 and imago4 7,natural size47 ,birds suffer much from mites living parasitically upon them belonging to ,sarcoptid2 these likewise infest mankind1 and give rise to a disease known as the itch 7,fig4 #daf1 ,no4 #c74 ,this malady and the irritation accompanying it are caused by the mite excavating tunnels under the skin4 ,in these the eggs are laid and hatched1 and the young then start burrowing on their own account2 their burrows are traced as whitish lines on the surface of the skin4 ,fig4 #daf1 ,no4 #d1 ,demodex folliculorum1 is another remarkable parasite found beneath the skin2 this is usually obtained from a spot where the sebaceous follicles or fat glands are abundant1 such as the forehead1 the side of the nose1 and the angles between the nose and lip4 ,if the part where a little black spot or a pustule is seen be squeezed rather hard1 the oily matter there accumulated will be forced out in a globular form4 ,this minute mite is less than one-fiftieth of an inch in length2 if it be laid on a glass slide1 and a small quantity of glycerine added to cause the separation of the harder portions1 the parasite in all probability will float out1 and1 by means of a fine-pointed pencil or brush1 can be transferred to a clean slide and mounted in ,canada balsam4 ,an allied species is found in the skin of dogs suffering from mange4 ,illustration3 ,fig4 #dai4 #a4 ,parasite of ,turkey2 #b4 ,acarus of common ,fowl1 under surface2 #c4 ,parasite of ,pheasant4 7,the small circles enclose each about life size47 ,the ,stylopid are remarkable parasites1 living upon the bodies of wasps1 bees1 and bugs1 and present a type of structure quite distinct from beetles or the ticks described4 ,the male 7,xenos peckii1 ,fig4 #dbj7 is a winged insect with coarsely faceted eyes1 large fan-shaped wings1 extremely small inconspicuous elytra1 the two first thoracic rings short1 while the metathorax is elongated and covers the base of the abdomen1 and the hind legs are placed a long way behind the middle pair4 ,the female1 on the other hand1 is a grub-like creature1 without legs1 wings1 or eyes2 she never leaves the body of her host1 and from her eggs active little larv develop and get carried into the nests of bees and wasps4 ,illustration3 ,fig4 #dbj4--,xenos peckii4 #a4 ,male2 #b4 ,female4 ,mites are very numerous1 differ in form1 and are interesting objects under the microscope4 ,the body of the common flea 7,fig4 #dba7 is divided into distinct segments1 those about the thorax being separated4 ,although apterous1 the flea has the rudiments of four wings in the form of horny plates on both sides of the thoracic segments4 ,its mouth consists of a pair of sword-shaped mandibles1 finely serrated2 these1 with a sharp1 penetrating1 needle-like organ1 constitute the formidable weapons with which it pierces through the skin4 ,the neck is distinctly separated1 and the body covered with scales1 the edges of which are beset with short set2 from the head project a short pair of antenn1 below which are a proboscis and a lance-shaped cutting apparatus4 ,on each side of the head a large compound eye is placed2 it has six many-jointed powerful legs1 terminating in two-hooked claws2 a pair of long hind legs are kept folded up when the insect is at rest1 which1 in the act of jumping1 it suddenly straightens out with great muscular force4 ,the female flea 7,fig4 #dba7 lays a great number of eggs1 sticking them together with a glutinous secretion2 the flea infesting the dog or cat glues its eggs to the roots of the hairs4 ,in about four days the eggs are hatched out1 and a small white larva or grub is seen crawling about1 and feeding most actively4 ,plate ,,vi41 ,no4 #ada1 is a magnified view of one covered with short hairs4 ,after nine or ten days the larva assumes the pupa form2 this it retains four days1 and in nine days more it becomes a perfect flea4 ,the head of the flea found in the cat 7,fig4 #dae1 ,no4 #c7 somewhat differs in form from that of the species infesting the human being2 its jaws are furnished with more formidable-looking mandibles1 and from between the first and second joints behind the head short strong spines project4 ,illustration3 ,fig4 #dba4 #a4 ,female ,flea2 #b4 ,male ,flea4 7,the small circles enclose fleas of about life size47 ,illustration3 ,fig4 #dbb4 #a4 ,parasite of ,eagle2 #b4 ,parasite of ,vulture2 #c4 ,parasite of ,pigeon1 ,sarcoptes palumbinus4 7,the circles enclose each about life size47 ,two small and obscure groups of the mites and ticks have been associated with the latter1 but for no better reason than that their affinities are unknown4 ,the first of these are the ,tardigrada1 or bear animalcules1 which comprise microscopical animals living in damp1 sandy1 and mossy places2 the body is long and oval in shape1 and possesses four pairs of bud-like unjointed appendages1 each tipped with claws3 the last pair of legs project from the hinder part of the body4 ,the mouth is much subdued1 and only a trace of jaws is found as a pair of stylets2 there appear to be no organs of respiration or circulation1 and1 unlike what obtains in all true ,arachnida1 the sexes are united in each individual4 ,these curious infusorial creatures have been found by myself in an infusion of cow manure4 ,injurious ,insects4--,in describing some of the more interesting points in connection with insect life1 ,i have only quite incidentally referred to the destructive habits of the larger number of insects and the ravages annually inflicted1 chiefly by the smaller parasitical tribes1 upon our cultivated crops of all kinds4 ,here we have a wide field of research open to the microscopist1 whose investigations must be carried out systematically1 day by day1 and for which a moderate power will effectually serve his purpose4 ,there are some ten or twelve species of injurious insects that attack the hop plant4 ,by way of example1 ,i will select one of the least known among them1 the hop-flea1 or beetle 7,haltica concinna74 ,this is sufficiently minute to require the aid of the microscope1 and very closely resembles the turnip-flea proper1 ,h4 nemorum4 ,under the microscope the former will be seen to differ considerably4 ,its colour is brassy1 whereas the colour of its congener is dusky or black1 and its wing-cases are striped4 ,they both have wonderful powers of jumping4 ,h4 concinna has a curious toothed formation of the tibia1 with a set of spines1 while the tibia of the turnip-flea is without any curve4 ,it presents other points of difference4 ,the hop-flea is1 in fact1 a winged beetle1 and passes the winter in the perfect state under clods1 tufts of grass1 or weeds outside the hop-plantation1 and here it lays its eggs4 ,in the early spring the larv are hatched out as a little white maggot1 which immediately makes its way to the hop-plant and burrows into the young leaves and feeds upon its tissues4 ,here we have an insect taken at random from among thousands of others of the most destructive kinds which annually destroy crops of enormous value to the nation4 ,illustration3 ,tuffen ,west1 del4 ,edmund ,evans4 ,,plate ,,vii4 ,,chapter ,v4 ,vertebrata4 ,the most complicated condition in which matter exists is where1 under the influence of life1 it forms bodies with a structure of tubes and cavities in which fluids are incessantly in motion1 and producing continuous changes4 ,these have been rightly designated 8organised bodies10 because of the various organs they contain4 ,the two principal classes into which organised bodies have been divided are recognised as vegetable and animal4 ,it was ,bichat who taught that our animal life is double1 while our organic life is single4 ,in organic life1 to stop is to die2 and the life we have in common with vegetables never sleeps1 and if the circulation of the fluids within the animal body ceases for a few seconds1 it ceases for ever4 ,in the vertebrate body1 however1 the combination of organs attains to the highest development1 in striking contrast with that of the class we have previously considered1 the ,invertebrata1 the animal kingdom being divided into ,vertebrates and ,invertebrates4 ,the ,vertebrata are distinguished from all other animals by the circumstance that a transverse and a vertical section of the body exhibits two cavities completely separated from one another by a partition4 ,a still more characteristic feature separates the one from the other2 it is the specialisation of the chief nervous centres1 and their peculiar relation to the other systems of the body4 ,the dorsal cavity of the body contains the cerebro-spinal nervous system1 the ventral1 the alimentary canal1 the heart1 and usually a double chain of ganglia2 these pass under the name of the sympathetic system4 ,it is very probable that this sympathetic nervous system represents1 wholly or partially1 the principal nervous system of the ,annulosa and ,mollusca4 ,in any case1 the central parts of the cerebro-spinal nervous system--i4e41 the brain and the spinal cord--would appear to be unrepresented among invertebrate animals4 ,likewise1 in the partition between the cerebro-spinal and visceral tubes1 certain structures which are not represented in ,invertebrates are contained4 ,during the embryonic condition of all ,vertebrates1 the centre of the partition is occupied by an elongated cellular cylindrical mass1 the notochord1 or chorda dorsalis4 ,this structure persists throughout the life in some ,vertebrata1 but in most it is more or less completely replaced by a jointed1 partly fibrous1 cartilaginous1 and bony vertical column4 ,all vertebrate animals have a complete vascular system4 ,in the thorax and abdomen1 in place of a single perivisceral cavity1 in communication with the vascular system1 and serving as a blood-sinus1 there are one or more serous sacs4 ,these invest the principal viscera1 and may or may not communicate with the exterior1 recalling in the latter case the atrial cavities of the ,mollusca4 ,in all ,vertebrata1 except ,amphioxus1 there is a single valvular heart1 and all possess a hepatic portal system1 the blood of the alimentary canal never being wholly returned directly to the heart by the ordinary veins1 but being more or less completely collected into a trunk 7the portal vein71 which ramifies through and supplies the liver4 ,with reference to one other point of importance1 the development of the ova of ,vertebrates1 these have the same primary composition as those of other animals1 consisting of a germinal vesicle containing one or more germinal nuclei1 and included within a vitellus4 ,but as this forms a part of general anatomy1 and as my object is simply the investigation of the fundamental and microscopical structure of animal organisms1 ,i shall not further pursue the morphological part of the subject1 especially as so many excellent text-books are within reach of the student who desires to fully acquaint himself with precise information4 ,notwithstanding1 then1 the apparent diversity in the structure of the vertebrate and the invertebrate and the various tissues of which animals and vegetables are constituted1 microscopical research has satisfactorily demonstrated that all textures have their origin in cells2 in fact1 when the formative process is complete1 the animal cell is seen to consist of the same parts and almost the same chemical constituents as the typical cell of the plant--namely1 a definite cell-wall enclosing cell contents1 of which the nature may be diverse1 but the cell nucleus is precisely the same and is the actual seat and origin of all formative activity4 ,the cell and nucleus grow by assimilation or intersusception1 that is1 by inflowing of nutrition among all parts1 the new replacing the old1 yet maintaining its original structure and composition4 ,that which was once thought special to animals is now found to be common to both plants and animals3 they are found to be alike fundamentally in internal structure1 and in the discharge of the mysterious processes of reproduction and of nutrition1 although the latter forms a convenient line of separation4 ,life in plants goes on indefinitely2 cuttings may be taken without injury to their vigour and duration of life4 ,the same may be said of some of the lower forms of invertebrate life2 for example1 the hydra1 the anemone1 and some other well-known animals1 may be cut up1 divided into several parts1 each one of which will form a new animal1 provided a nucleus be included in the section4 ,nevertheless1 the organisation of the amba and the hydra is as complete for its purpose as that of man for his1 and the evidence of continuity forbids the drawing of hard and fast lines1 as was formerly done between the two kingdoms1 the animal and vegetable4 ,the amount of similarity or agreement in the organisation of animals is various4 ,animals indeed differ from each other in slight points only1 for the discovery of which the microscope must be brought into requisition4 ,living matter in its earliest stage and simplest form appears to the naked eye as a homogeneous structure1 but when placed under the highest powers of the microscope1 it is seen not to be so4 ,but perhaps the most marked feature of the age has been the increasing attention given to the study of the lower forms of life1 using their simpler structures and more diffuse phenomena to elucidate the more general properties of living matter4 ,to understand life we must understand protoplasm4 ,of this there can be no doubt1 as we have seen in a previous chapter that a whole family1 the ,monera1 consists of this simple living1 microscopic1 jelly-like substance1 which has not even begun to be differentiated1 as in the amba1 which has as yet no special organs1 and every speck becomes a mouth or a stomach1 and which can be turned inside out and shoot out tongues of jelly to move and feel with4 8,reproduction is the faculty most characteristic of life1 and sharply distinguishes the organic from the inorganic40 ,it is1 then1 the corpuscles of protoplasm1 called cells 7cellul71 which have so much interest for the physiologist1 and these1 like the cytods1 may form independent organisms1 which are then termed unicellular4 ,again1 cells form other cells1 and a multicellular organism results1 and goes on increasing in geometrical progression4 ,in the ,vertebrata the cell retains its characteristic spheroidal shape1 as seen in ,fig4 #dbc1 and undergoes division by virtue of its living protoplasmic mass4 ,illustration3 ,fig4 #dbc4 #a4 ,newly formed cell structure2 #b4 ,division of the nucleus2 #c4 ,it changes its situation in the cell2 #d4 ,subdivides and breaks up2 #e4 ,cell-walls increase in thickness2 #f4 ,branch out into stellate cells2 #g4 ,two cells coalesce2 #h and #i4 ,become multicellular4 ,epithelial ,cells4--,all free surfaces of the human body1 both internal and external1 are to a very considerable extent covered by epithelium cells4 ,these cells are everywhere the same1 but with modifications in shape and arrangement4 ,epithelial cells are nucleated and always joined by their surfaces or edges1 without1 on the external surfaces1 the intervention of connective tissue4 ,there are four essential varieties3--#a4 ,tesselated2 #b4 ,columnar2 #c4 ,spheroidal2 #d4 ,ciliated2 in all of which the nucleus remains remarkably uniform in its characters1 is either round or oval1 and flattened out1 measuring #a_/fjjjth to #a_/djjjth of an inch in diameter4 ,they are insoluble in acetic acid1 colourless1 or slightly tinted by the structure with which they are in contact1 and usually contain one or more nucleoli with a few minute irregular granules1 as represented in ,fig4 #dbd4 ,the simplest and most commonly distributed variety is the tesselated1 known also as the scaly1 squamous1 pavement1 and flattened epithelium1 always arranged in single layers1 lining serous cavities1 many parts of the mucous membrane1 and the interior of ducts and blood vessels4 ,upon the external surface of the body it occurs in superimposed layers1 forming the 8stratified epidermis40 ,to obtain specimens of lamellar epithelium it is only necessary to collect a little saliva1 or pass a glass slide over the lining membrane of the cheek1 cover it with a thin cover glass1 and examine it with a #a_/d-;inch objective4 ,pavement epithelium is the elementary structure of hair1 nails1 and horn4 ,illustration3 ,,plate ,,xix4 ,,animal ,,tissues4 ,columnar epithelium exists upon the mucous membrane of the stomach1 on the villi of the intestines1 and in the several canals4 ,it occupies either a vertical or horizontal position1 and may be detached in rows1 as shown in ,plate ,,xix41 ,no4 #b1 a section taken from the intestine of a rabbit4 ,this variety1 when more highly magnified1 as in ,fig4 #dbd1 is seen to consist of club-shaped nucleated cells1 the thicker end being turned towards the surface4 ,the protoplasm of the cell is granular1 and the presence of minute vacuoles and fatty globules occupy a great part of the space4 ,the nucleus is now seen to contain a fine network4 ,at times the outer end of the cell is distended1 as in ,fig4 #c4 ,this form of columnar epithelium 7known as the 8goblet0 cell7 presents a close and remarkable resemblance to the cilio-flagellate 8collared0 infusorial monad in its extended 8wine-glass0 form4 ,illustration3 ,fig4 #dbd4 ,no4 #a4 ,pavement epithelium1 taken from an internal membrane2 #b4 ,columnar epithelium1 from the intestine of a rabbit1 showing central fat globules1 and at str a fine ciliated border2 #c4 ,a so-called 8goblet0-cell4 ,spheroidal epithelium is confined to the closed cavities of the body1 and in the internal structure of the ducts of secreting glands4 ,the cells are1 for the most part1 circular1 although some are flattened out at the sides in which they are in contact with each other 7,plate ,,xix41 ,no4 #a;a74 ,specimens of this form may be taken from the internal surface of one of the lower animals with a scalpel4 ,the collected matter must be placed in a drop of distilled water and examined with a high power4 ,ciliated epithelium is characterised by the presence of those fine hair-like filaments 7cilia7 attached to the free surface of the cell4 ,during life1 and for some time after death1 the cilia are seen to retain their constant waving motion4 ,the cilia all move in one direction and rhythmically1 thus giving rise to the appearance of a succession of undulations4 ,ciliated epithelium is found lining the mucous membrane of the air passages and nasal ducts1 and wherever it is necessary to urge on a secretion by mechanical means1 ciliated epithelium exists4 ,specimens for examination are easily obtained from the oyster1 and with care will show the characteristic motion4 ,a portion of a gill separated from the mollusc will live on for a considerable time if kept in a little of its natural secretion4 ,the parameci1 rotifera1 and all the ciliata1 are furnished with cilia as a means of locomotion and obtaining sustenance4 ,by snipping off a small piece from the gills of the mussel1 always accessible to the microscopist1 and covering it over with thin glass to prevent evaporation of the animal juices1 its cilia will continue to work for hours4 ,lymph and ,blood1 ,fig4 #dbe ,b1 a a4--,there are other cells in the animal body which possess a certain amount of resemblance to those confined to the more superficial structures--i4e41 the lymph1 chyle1 and blood4 ,these fluids present in one respect a physical uniformity of composition1 and a resemblance in the size of their characteristic corpuscles4 ,chyle contains besides the corpuscles of lymph1 a quantity of minute granules which imparts a white colour to the fluid4 ,intermixed are oil globules1 free nuclei1 and sometimes a few red blood discs4 ,chyle may be had for microscopic examination by squeezing a little juice from the lymphatic gland of a sheep just slaughtered4 ,illustration3 ,fig4 #dbe4--;,human ,blood ,corpuscles and ,crystals4 ,a4 a a4 ,red blood corpuscles lying flat on the warm stage2 b b4 in profile2 c c4 arranged in rouleaux2 d4 crenated2 e4 rendered spherical by water2 ,i4 leucocytes and white amboid corpuscles2 ,b4 ,blood discs of fowl1 red and white1 others seen in convexity and with a nucleus4 ,blood ,crystals4--,c4 ,hmatin from human blood2 ,d4 ,hmatoidin2 ,e4 ,hmin2 ,f4 ,tetrahedral2 ,g4 ,pentagonal2 ,h4 ,octahedral crystals from blood of mouse4 ,blood ,corpuscles or cells vary considerably in mammals1 birds1 reptiles1 and fishes4 ,fig4 #ajb 7page #adc7 is a microphotograph of a drop of blood magnified #c1ejj times2 and ,fig4 #dbe1 ,a1 shows both red and white discs drawn to scale1 magnified #a1bjj diameters4 ,the red corpuscles of human blood are distinguished by their clearly defined outlines and dark centres4 ,each disc is biconcave in form1 and hence the whole surface cannot be focussed at the same time4 ,when the circumference is well illuminated the centre is dark1 but by bringing the objective nearer to the object1 the concavity of the disc is brought into focus4 ,it generally happens that blood corpuscles1 on being first drawn1 run together1 and present the appearance of rolls of coins2 or they may be scattered about over the field4 ,there is a considerable difference in the form of the discs2 they are circular in all mammals1 except the camel1 dromedary1 and llama1 these being oval4 ,in profile blood corpuscles are biconcave1 their investing membrane is homogeneous and elastic1 and will readily move along the smallest capillary vessels4 ,there is no trace of a nucleus in the blood-discs of the adult ,mammalia1 while in size they bear no proportion to the bulk of the animal in whose blood-vessels they circulate4 ,the corpuscles of ,mammalia in general are like those of man in form and size1 being either a little larger or smaller4 ,the most marked exception is the blood of the musk-deer1 in which the corpuscles are of extreme smallness1 about the #a_/abjjjth of an inch in diameter4 ,in the elephant they are large1 about #a_/bgjjth of an inch in diameter4 ,the goat1 among common animals1 has very small corpuscles1 but they are1 withal1 twice as large as those of the musk-deer4 ,in the ,menobranchus lateralis they are of a much larger size than in any animal1 being the #a_/cejth of an inch2 in the proteus1 the #a_/djjth of an inch in the longest diameter2 in the salamander1 or water-newt1 #a_/fjjth2 in the frog1 #a_/ijjth2 lizards1 #a_/adjjth2 in birds1 #a_/agjjth2 and in man1 #a_/cbjjth of an inch4 ,of fishes1 the cartilaginous have the largest corpuscles2 in gold-fish1 they are about the #a_/agjjth of an inch in their longest diameter4 ,the large size of the blood discs in reptiles1 especially in the ,batrachia1 has been of great service to physiologists by enabling them to ascertain many particulars regarding structure which could not have been otherwise determined with certainty4 ,the value of the spectroscope in the chemical examination of the blood has been already referred to4 ,see page #beb4 ,white corpuscles or leucocytes 7,fig4 #dbe1 ,i7 differ materially from the red4 ,they are large1 spheroidal1 finely granular masses of about #a_/bhjjth of an inch in diameter4 ,in a cubic millimtre of human blood there are about #aj1jjj white corpuscles4 ,they have a lower specific gravity than the red1 have no cell-wall1 and their substance mainly consists of protoplasm4 ,the internal granular appearance is now believed to be due to a fine intercellular network having small dots at the intersections of the web4 ,in the meshes of the net a hyaline substance is interspersed4 ,they possess one or more nuclei2 these are seen on the application of a few drops of acetic acid4 ,when examined in a perfectly fresh state1 especially if the glass slide be placed on the warm stage of the microscope1 they exhibit a spontaneous change of shape1 amba-like1 such movements being accordingly termed amboid4 ,the movements referred to consist in the protrusion of processes of protoplasm which are retracted and other processes protruded as represented 7,fig4 #dbe1 ,i74 ,both in human blood and in newts there are colourless corpuscles which contain coarser granules than others2 these are called granular corpuscles4 ,some are shown near the amboid bodies4 ,the white corpuscles are readily found in various tissues of the body1 as in the lymphatic glands4 ,in inflammatory diseases these leucocytes pass through the walls of the capillaries into the tissues1 and form morbid products1 pus-cells4 ,sections of blood discs are made by dipping a fine needle in a drop of blood as it exudes from a prick of the finger and drawing thin lines across the glass slip1 allowing time to dry1 and then cutting the lines across in all directions with a razor4 ,the loosened portions should be removed with a camel's-hair brush4 ,in birds1 the blood discs are oval in shape and possess a nucleus1 shown in ,fig4 #dbe ,b1 in the blood of the fowl2 this is rendered more apparent on adding a drop of acetic acid4 ,the blood of fishes is also oval and nucleated1 rather more pointed than that of birds4 ,in reptiles generally the red blood discs are large1 oval1 nucleated bodies1 the white corpuscles still preserving their invariable circular form and granular appearance4 ,in the salamander and proteus the discs attain to their greatest size4 ,in the former they measure #a_/gjjth of an inch1 and in the latter #a_/djjth4 ,blood ,crystals4--,in addition to the elements described1 the blood contains various crystalline forms1 represented in ,fig4 #dbe1 ,c to ,h4 ,in connection with the micro-spectroscope 7p4 #bec71 the spectra of certain blood crystals are given2 although varying in different animals1 sufficient uniformity prevails as to render them characteristic4 ,the crystals are formed when a little blood is mixed with water on the slide1 allowing a short time for crystallisation4 ,near the edge of the cover-glass1 where crystals begin to form1 they are more distinct1 but a high power is required for their examination4 ,in human blood the crystals are prismatic2 in that of the guinea-pig1 tetrahedral2 in the blood of the mouse1 octahedral4 ,other forms may be obtained by the aid of chemical reagents4 ,in human blood there are at least three distinct forms of crystals3 ,hmatin is formed in normal blood1 is made visible on the addition of a little water to blood1 or by agitation with ether1 so as to dissolve the cell-wall of the blood corpuscles1 and allow the contents to escape4 ,a drop of blood will furnish crystals large enough to be seen with a moderate power4 ,hmatoidin crystals are abnormal products1 found in connection with certain diseased conditions4 ,these crystals are seen as represented at ,d4 ,hmin crystals must be regarded as artificial chemical products1 the result of treating blood with glacial acetic acid2 the acicular crystals at ,e1 reddish-brown in colour1 are artificially produced4 ,illustration3 ,fig4 #dbf4 #a4 ,white fibrous or non-elastic tissue2 #b4 ,yellow fibrous elastic tissue4 ,basement ,membrane--,connective ,tissue ,system4--,connective or areolar tissue is present almost throughout the whole of the human body1 and serves to connect the various organs with one another1 as well as to bind together the several parts4 ,the muscles are surrounded by a connective tissue sheath2 this penetrates into their substance1 and binds together fasciculi and fibres4 ,the same tissue is present in the skin and the mucous membranes2 it also forms a sheath for the arteries1 veins1 and nerves4 ,it is plentifully supplied by blood-vessels1 and nerves pass through its substance4 ,microscopically1 four different elements can be clearly made out3--#a4 ,connective tissue cells or corpuscles2 #b4 ,white fibrous tissue2 #c4 ,yellow fibrous tissue2 #d4 ,ground substance4 ,on examining the connective tissue cells of young animals1 various cells will be seen with fine granular contents1 together with nuclei1 lying in spaces in the ground substance1 some branched1 others flattened or rounded4 ,even tissues supposed to be homogeneous in structure1 are on staining seen to have connective tissue cells1 such as those represented in a section of the cornea of the eye 7see p4 #ca74 ,in this case the connective tissue cells are termed corneal corpuscles2 the branched cells1 it will be noticed1 are united by branches4 ,the cells in the fibrous tissue of tendons are square or oblong1 and form continuous rows4 ,white fibrous tissue is distributed throughout the animal body1 but in a variety of forms2 it is found in the skin and other membranes1 and in all parts where strength and flexibility are necessary4 ,the structure of white and yellow fibrous tissues is shown in ,figs4 #dbf and #dbg4 ,illustration3 ,fig4 #dbg4 #a4 ,white fibrous tissue lining the interior of the egg shell1 with the calcium carbonate removed by immersion in hydrochloric acid2 #b4 ,white fibrous tissue1 from the sclerotic coat of the eye4 ,white fibrous tissue presents silver-lustre bundles1 running for the most part in parallel directions through and over the muscles and tendons4 ,for examination under the microscope1 obtain a fragment of fresh meat cut in the longitudinal direction2 place it in water1 and tease it out with needles as directed in a former chapter4 ,the smallest fragment will suffice for examination under a quarter or one-sixth inch objective4 ,these filaments are exceedingly minute1 measuring #a_/cjjjth to #a_/bejjth of an inch in diameter1 and do not interlace through the bundles1 although they intersect each other occasionally4 ,transverse sections may be made by drying a piece of tendon until it becomes sufficiently firm to cut with a razor or microtome1 and mounted as a permanent specimen4 ,from the cut ends of the fibres small dark points will be seen1 especially in the denser structure of the tendons2 these are termed 8connective tissue corpuscles40 ,yellow elastic fibrous tissue is remarkable in contradistinction to the white for its elasticity and capability of extension4 ,it is found on the coats of blood-vessels1 between the vertebral arches1 and in quadrupeds it forms a strong elastic band1 extending from the occiput1 throughout the spines of the vertebra1 and enabling the animal to support the head in the pendent position1 without muscular exertion4 ,these fibres can only be separated from each other with difficulty1 and their elasticity is shown by a tendency to curl up4 ,these yellow fibres are somewhat coarser than the white1 and they remain unaffected by acetic acid of the ordinary strength4 ,elastic tissue is a constituent of the skin1 mucous1 and serous membranes1 and of the areolar or cellular tissue4 ,in order to microscopically examine this structure1 take a small portion of the strong ligament of the neck of the ox1 place it as before in water1 and tease it out with needles2 place a fragment on a glass slip1 cover with a thin cover-glass1 and submit it to a high magnifying power4 ,transverse sections made as directed in the case of white tissue will be seen to be hexagonal in form4 ,adipose ,tissue4--,fat is found in many situations in the animal body1 and on examination is seen to consist entirely of vesicles1 distributed through a delicate membrane of connective tissue1 shown in ,plate ,,xix41 ,nos4 #d and #e4 ,on pressure1 the circular or oval form of the cells becomes polyhedral2 occasionally the fatty acids in the interior of the vesicles crystallise1 and give rise to a star-like appearance4 ,for the examination of adipose tissue1 take a portion of the mesentery of any small animal--a mouse1 or rat4 ,retiform ,tissue4--,adenoid1 or retiform tissue1 consists of a delicate network of connective tissue corpuscles1 joining their branches together4 ,this forms the stroma or framework of lymphoid tissue4 ,it is found in connection with all the lymphatic glands1 spleen1 c4 ,plate ,,xix41 ,no4 #c1 a b1 shows small sections of a lymphatic1 together with capillary vessels4 ,muscular ,fibre4--,there are two varieties of muscular fibre in the body--i4e41 striated1 and non-striated4 ,the striated is formed in muscles attached to bony structures1 as those of the arm and leg1 and in some of the soft structures1 as the tongue1 palate1 sophagus1 in short1 all muscles under the control of the will4 ,striped muscle is of a dull red colour and marked with peculiar longitudinal furrows on its surface4 ,voluntary muscle consists of3--#a1 a connective tissue sheath2 #b1 fasciculi2 #c1 fibres and sarcolemma2 #d1 discs1 fibrilla and sarcous elements4 ,these are shown in connection with other tissues in ,plate ,,xix41 ,nos4 #aa and #ab1 and also in ,fig4 #dbh 7#a1 #b1 #c74 ,illustration3 ,fig4 #dbh4 #a4 ,muscular fibre broken across1 the fragments connected by the connective tissue membrane #ajj2 #b4 ,fibre broken up into irregular distinct bands3 a few blood corpuscles distributed about #bjj2 #c4 ,a fasciculus of muscular fibre from leg of pig #fjj4 ,in ,plate ,,xix41 ,fig4 #aa1 the muscular fibre taken from the tongue of a lamb shows the continuity of the upper portion with the connective tissue membrane4 ,in ,fig4 #ab1 a branching-out bundle of muscular fibre1 taken from the upper lip of the rat1 is seen to end in stellate connective cells4 ,the delicate homogeneous sheath that binds the fibres together is termed sarcolemma4 ,this is readily seen in prepared muscle of the frog and water-beetle1 less plainly in man4 ,each muscle is provided with a sheath of connective tissue2 this surrounds it1 binds the fasciculi together1 and supports the blood-vessels2 it is called the perimysium1 and sends fine prolongations in between the fibres1 termed endomysium4 ,the intervals seen on high amplification between the dark stri are called ,kruse's membrane4 ,on breaking up the striated structure it is resolvable into fibrill and furthermore into discs4 ,illustration3 ,fig4 #dbi4 #a4 ,vertical section of epidermis2 #b4 ,pigment cells from a lower layer of cutis4 ,among mammalia the pig furnishes the best examples of muscle fibrill2 among insects the water-beetle and the thorax of the housefly4 ,a power of #fjj or #hjj diameters is required to separate the fibrill4 ,blood-vessels are well supplied with striated muscle1 but none of their minuter branches penetrate the sarcolemma4 ,the involuntary or non-striated variety of muscular fibre exists in all parts of the body where movements occur independently of the will1 also in the ciliary muscle and the iris of the eye1 as well as in the middle coats of the arteries4 ,non-striated fibres are pale in colour1 prismatic in shape1 and easily flattened by pressure4 ,in size1 they vary from #a_/gjjjth to #a_/cejjth of an inch in diameter1 and are marked at short intervals by oblong corpuscles4 ,the ,integument or ,skin consists of epidermis or cuticle1 dermis1 corium or cutis vera1 sweat-glands1 nails1 hairs1 sebaceous glands1 and numerous nerves and vessels4 ,the epidermis forms a protective covering over the whole surface of the body1 and is moulded on to the surface of the corium beneath1 covering the ridges1 depressions and papill4 ,it is made up of three principal layers3 the horny layer or stratium corneum1 the most superficial1 this consists of layers of flattened cells1 which are without a nucleus2 the stratum lucidum1 composed of layers of nucleated cells1 more or less indistinct in section2 the rete mucosum or malpighian layer2 is composed in its upper part of layers of 8prickle cells0 and its inferior of a single stratum of columnar cells4 ,pigment is principally found in the lowest layer1 ,fig4 #dbi4 ,the gradations of colour in the skin are due to the granular contents of the pigment cells4 ,this is seen on steeping sections cut from the skin of a negro in chlorine2 the colour is discharged4 ,in ,plate ,,xix41 ,no4 #ac1 the pigment cells of the choroid coat of eye are shown4 ,here the pigment is darker in colour1 and its function is the absorption of light and the prevention of disturbing effects occasioned by circles of dispersion4 ,illustration3 ,fig4 #dcj4--,vertical section of skin and subcutaneous tissues1 showing the sweat-glands and fat-globules1 ducts passing upwards to the epidermis or external cuticle4 ,magnified #bej diameters4 ,the ,dermis1 or true skin1 consists of an interlacing network of connective tissue1 yellow elastic tissue corpuscles1 vessels1 and nerves4 ,there are also small muscular fibres in connection with the hair follicles1 and beneath the subcutaneous tissues contain an abundant supply of fat adipose tissue4 ,numerous ridges are seen on the surface1 especially on the palm of the hand and sole of the foot1 caused by rows of little elevations of the cutis vera1 termed papill4 ,these are more or less conical1 and contain a capillary loop1 nerve1 and touch corpuscle1 which serve to increase the sensitiveness of the part1 lodging a touch corpuscle in a favourable position for receiving sensations of touch1 ,fig4 #dcj4 ,sweat glands are situated in the subcutaneous tissue1 and consist of fine tubes1 which form the duct 7seen in the section1 ,fig4 #dcj72 these are continuous with a blind extremity1 coiled up into a ball one-sixtieth of an inch in diameter1 and surrounded by a plexus of capillaries to form the gland 7,fig4 #dca1 ,no4 #b74 ,between the layer of columnar cells and the limiting membrane is a layer of non-striated muscle1 and beneath the rite mucosum there are several layers of polyhedral cells1 and an external and internal limiting membrane2 the epithelium of the duct is at its mouth continuous with the epithelium of the epidermis4 ,illustration3 ,fig4 #dca4 #a4 ,blood vessels of papill supplied to cutis2 #b4 ,perpendicular section through the scalp1 with two hair-sacs2 a4 epidermis2 b4 cutis2 c4 muscles of the hair follicles4 ,nails consist of a root and body1 the lunular of which is the whitish portion of the body near the root1 where the skin beneath is less vascular than any other portion of the finger4 ,the nail closely resembles the epidermis1 and consists of hard and thin layers of cells on the surface1 and round1 moist cells beneath4 ,posteriorly the nail fits into a groove which lodges its root4 ,the part to which the nail is attached is known as the nail-bed4 ,the stratified appearance produced by the coalescence of the cells1 and their lying over each other1 is shown in ,plate ,,vii41 ,no4 #adi1 the toe of the mouse2 while the special arrangement of tissue is better seen under polarised light 7,plate ,,viii41 ,no4 #agd74 ,hairs consist of a shaft and root4 ,the shaft is cylindrical1 and covered with a layer of imbricated scales1 arranged with their edges upwards4 ,the substance of the hair consists of fibres1 or elongated fusiform cells1 in which nuclei are seen4 ,there are present in some hairs 7,fig4 #dcb7 small air spaces or lacun4 ,in the coarser hair of the body there is a pith 7medulla71 occupied by small angular cells and fat granules4 ,illustration3 ,fig4 #dcb4 #a4 ,single ,hair-root and ,shaft2 #b4 ,vertical section1 showing fibrous character of the hair together with colouring matter1 external edges serrated2 #c4 ,transverse section of human hair1 medullary substance1 and central pith4 ,the root of the hair is seen to dilate that it may fit more firmly into the skin hair-follicle4 ,the latter consists of two coats1 an outer and an inner1 continuous with the epidermis1 and this is called the root sheath4 ,the outer portion consists of three layers1 formed of connective tissue1 blood-vessels1 and nerves4 ,the inner1 or epidermic1 coat comes away when the hair is pulled out1 and hence is called the root sheath4 ,this again is made up of two layers1 the outer of which corresponds with the horny layer1 and is composed of flattened cells4 ,the bulbous root of the hair is connected with the papilla4 ,in the cat the tactile nasal hairs are very large4 ,small bundles of involuntary muscular fibres connect the corium with the root1 so that in contracting they elevate or expand the hair4 ,illustration3 ,fig4 #dcc4 #a4 ,jointed hairs of ,indian bat2 #b4 ,hair of flying-fox1 showing imbricated scales2 #c4 ,hair of mouse1 showing pigment layers2 #d4 ,hair of a small beetle 7,dermestes74 #bej4 ,the hair of the lower animals presents a diversity of structure1 especially on the outer surface1 and with reference to the arrangement of the scales4 ,the hair of the ,indian bat1 for instance1 consists of a shaft invested with erectile scales1 placed at regular intervals2 these stand out from the shaft1 as in ,fig4 #dcc1 ,no4 #a4 ,this form of scale varies considerably in the different species of these animals1 and a portion of hair near the root is nearly divested of scales4 ,many of the scales are not unlike those of certain of the insect tribe1 seen in that of ,dermestes1 ,no4 #c1 while the hair of the mouse has a series of transverse imbricated scales arranged as tiles on a house1 due to accumulated pigment4 ,hairs taken from various animals form interesting objects of study for the microscope1 as already noticed4 ,other hairs are shown in ,fig4 #dcd4 ,no4 #a is a transverse section of a hair from the ant-eater2 the central part consists of air-cells1 the outer of a granular pith4 ,no4 #b is a transverse section of hair of peccary1 with a diversified arrangement of the cortical envelope1 sending outward a set of radial prolongations and air-cells2 this kind of structure is also found in the quills of the porcupine4 ,no4 #c is a transverse section of a hair of the elephant1 which shows a combination of a number of tubes united together1 somewhat resembling the arrangement of the hoof-horn of some of the ruminants1 and the denser horny growth on the snout of the rhinoceros1 ,no4 #d4 ,the curious modification of these horny structures is seen in the horns of other animals1 and which may be likened to a bundle of hairs4 ,on making a transverse section1 as in ,fig4 #dcd1 and submitting it to polarised light1 on rotating the analyser1 the dark central spot shown is replaced by a bright one with a play of colours due to the interference of light 7,plate ,,viii41 ,no4 #agh74 ,the scales of fish are also of interest 7,fig4 #dce74 ,these have been shown to afford an unerring guide in the classification of fishes and in the examination of their fossil remains4 ,as a class of objects for the microscope1 they are found to be both curious and beautiful4 ,plate ,,viii41 ,no4 #agf1 is a scale of the grayling1 seen under polarised light4 ,illustration3 ,fig4 #dcd4 #a4 ,hair of ant-eater2 #b4 ,hair of peccary2 #c4 ,hair of elephant2 #d4 ,horn of ,rhinoceros4 ,illustration3 ,fig4 #dce4--;,fish ,scale 7,sole74 ,of the harder outgrowths of the dermal structures1 the teeth afford the chief example among animals4 ,the rough anatomy of the tooth in mankind consists of a crown1 that projects from the gum2 a root1 or fangs1 fixed in a socket of the jawbone1 and a short intermediary neck4 ,each tooth is supplied with an artery and nerve1 and has a central cavity filled with a soft1 vascular1 sensitive substance1 the pulp4 ,on making a vertical section of a tooth1 we recognise the several structures in the order of1 pulp1 crusta1 petrosa1 dentine1 and enamel4 ,a section through a human molar tooth 7shown in ,fig4 #dcf7 will convey some idea of the arrangement of the denser structures referred to above4 ,illustration3 ,fig4 #dcf4--,sections of ,human ,molar ,tooth 7magnified #ej diameters74 #a4 ,vertical section2 #b4 ,horizontal section4 ,blandin was the first to demonstrate that teeth are developed in the mucous membrane1 similar to that of hair and nails4 ,teeth are formed in grooves of the mucous membrane1 and subsequently converted into closed sacs by a process of involution1 and their final adhesion to the jaw is a later process4 ,it is very generally conceded that teeth belong to the muco-dermoid1 and not to the periosteal1 series of tissues2 that1 instead of standing in close relation to the endo-skeleton1 they are part of the dermal or exo-skeleton2 their true analogues being the hair1 and some other epidermic appendages4 ,huxley proved that1 although teeth are developed in two ways1 they are mere varieties of the usual mode in the animal kingdom4 ,in the first1 which is typified by the mackerel and the frog1 the pulp is never free1 but from the first is inclosed within the capsule1 seeming to sink down as fast as it grows4 ,in the other1 the pulp projects freely at one period above the surface of the mucous membrane1 becoming subsequently included within a capsule formed by the involution of the latter2 this occurs in the human subject4 ,the skate offers a sort of intermediate structure4 ,illustration3 ,fig4 #dcg4 #a4 ,section of a cusp of the posterior molar of a child4 ,the inner outline represents it before the addition of acetic acid--the outer afterwards1 when ,nasmyth's membrane g is seen raised up in folds2 f4 the enamel organ2 c4 the dentine2 the central portion being filled with pulp4 #b4 ,edge of the pulp of a molar cusp1 showing the first rudiment of the dentine1 commencing in a perfectly transparent layer between the nuclei of the pulp and the membrana preformativa4 #c4 ,nasmyth's membrane detached from the subjacent enamel by acetic acid4 #d4 ,stellate-cells of the enamel organ4 #e4 ,tooth of frog1 acted on by dilute hydrochloric acid1 so as to dissolve out the enamel and free ,nasmyth's membrane4 ,the structure of the dentine e is rendered indistinct4 ,at the base1 ,nasmyth's membrane is continued over the bony substance at z1 in which the nuclei of the lacun are visible4 7,after ,huxley47 #f4 ,decalcified tooth-structure2 a4 the dentine2 b4 enamel organ2 c4 enamel2 d4 ,nasmyth's membrane4 ,the enamel forms a continuous layer1 and invests the crown of the tooth2 it is thickest upon the masticating surface1 and decreases towards the neck1 where it usually terminates4 ,the external surface of the enamel appears smooth1 but is always marked by delicate elevations and transverse ridges1 and covered by a fine membrane 7,nasmyth's membrane71 containing calcareous matter4 ,this membrane is separable after being subjected to hydrochloric acid2 it then appears like a network of areolar tissue1 shown in ,fig4 #dch1 ,no4 #f2 ,huxley's 8calcified membrana10 which commence at the pulp cavity1 and pass up to the enamel4 ,illustration3 ,fig4 #dch4--,tooth ,structure4 #a4 ,longitudinal section of superior canine tooth1 exhibiting general arrangement1 and contour markings1 slightly magnified2 #b and #c4 ,portions from same1 highly magnified1 showing the relative position of bone-cells1 cementum at #b1 dentine fibres1 and commencement of enamel at #c2 #d4 ,dentine fibres decalcified2 #e4 ,nasmyth's membrane separated and the calcareous matter dissolved out with dilute acid2 #f4 ,cells of the pulp lying between it and the ivory2 #g4 ,a transverse section of enamel1 showing the sheaths of fibres1 contents removed1 and magnified #cjj diameters4 ,czermak discovered that the curious appearances of globular conglomerate formations in the substance of dentine depend on its mode of calcification and the presence of earthy material2 and he attributed the contour lines to the same cause4 ,contour markings vary in intensity and number2 they are most abundant in the root1 and most marked in the crown4 ,vertical sections exhibit them the best2 as ,fig4 #ddj1 ,no4 #a4 ,in preparing a specimen1 first make the section accurately1 then decalcify it by submersion in dilute hydrochloric acid2 dry it and mount in ,canada balsam2 place the specimen in the hot chamber for some time to soak in the fluid resin before it cools4 ,the white opacity at the extremity of the contour markings gives the appearance of rings to the tooth-fang4 8,the tooth-substance appears10 says ,czermak1 8on its inner surface1 not as a symmetrical whole1 but consisting of balls of various diameter1 which are fused together into a mass with one another in different degrees1 and in which the dentine tubes in contact with the germ cavity terminate4 ,by reflected light1 dark-ground illumination1 one perceives this stalactite-like condition of the inner surface of the tooth-substance very distinctly1 by means of the varied illumination of the globular elevations1 and by the shadows which they cast40 ,to see this structure to advantage the preparation should be made from a tooth root1 the growth of which is not complete4 ,with such preparations1 the ground-substance of the last formed layer of the tooth-substance is seen to be1 at least partly1 in the form of globular masses1 fused together with those of the penultimate layers4 ,the cementum is the cortical layer of osseous tissue1 forming an outer coating to the fangs1 which it sometimes cements together4 ,its internal surface is intimately united with the dentine1 and in many teeth it would appear as if the earliest determined arrangement of the fibres of the dentine started from the canaliculi1 as they radiate from the lacun in the cement4 ,the inter-lacunar layer is often striated1 and exhibits a laminated structure3 sometimes it appears as if ,haversian canals were running in a perpendicular direction to the pulp cavity4 ,the canaliculi frequently run out into numerous branches1 connecting one with another1 and anastomising with the ends of the dentine fibres4 ,the thick layers of cement which occur in old teeth show immense quantities of aggregated lacun of an irregular and elongated form4 ,illustration3 ,fig4 #dci4--,transverse section of ,tooth of ,pristis1 showing orifices of medullary canals1 with systems of radiating fibres 7tubuli7 analogous to the ,haversian canals in true bone4 ,compact ,tissues1 ,cartilage and ,bone4--,cartilage is a bluish or yellowish-white1 semi-transparent1 elastic substance1 without vessels or nerves1 and surrounded by a membrane1 termed pericondrium1 of a dense fibrous nature4 ,that kind1 however1 known as articular cartilage1 receives a layer of epithelium from the synovial membrane1 but this is confined to marginal portions1 in consequence of the central wear which occurs as soon as the parts are subjected to friction1 during the movement of the limbs4 ,cartilage covers the ends of all bones in apposition to form joints1 and thus lessens the effects of concussion4 ,besides the ordinary kind of cartilage1 temporary and permanent1 there are two modifications of the tissue1 confined to certain portions of the body3 cellular cartilage1 composed of cells lying close together1 in a mesh formed of fine fibres2 and fibro-cartilage1 cells distributed in a matrix of fibrous tissue4 ,examined with a low power1 cartilage appears to be homogeneous in structure1 studded over with numerous round1 oval1 oblong1 semilunar1 and irregular-shaped corpuscles1 as seen in ,plate ,,xix41 ,no4 #h1 a vertical section of animal cartilage1 arranged in columns1 and condensed at the lower surface previous to its conversion into bone4 ,the greater opacity of this portion is owing to the increase of osseous fibres1 and the multiplication of oil globules1 and the intercellular spaces becoming filled with vessels4 ,no4 #i shows a small transverse section of the same1 with a further change of the cartilage cells at a into bone cells1 and at b with the characteristic canaliculi and lacun4 ,no4 #g further shows a section of the large tendon fixed to the back of the heel of the foot1 near the juncture of the tendo-,archillis with the cartilage4 ,for the examination of these several changes a high power is necessary1 and for the purpose pieces taken from the ox may be easily obtained from the butcher1 and fine sections cut with a razor parallel to the surface4 ,illustration3 ,fig4 #ddj4 #a4 ,cartilage from a mouse's ear closely resembling vegetable tissue #bjj2 #b4 ,cartilage from rabbit's ear1 with nucleated cells embedded in matrix2 #c4 ,cartilage from the end of a human rib #cjj4 ,the better specimens for microscopical examination are those taken from very young animals1 in whom the ossific process is still incomplete4 ,in order to examine cellular cartilage1 the ear of the mouse should be taken and just dried sufficiently to enable fine sections to be cut by the microtome transversely 7,fig4 #ddj74 ,cartilage forms the entire skeleton of a certain number of fishes1 as the skate1 lamprey1 ray1 shark1 c41 the cells of which are embedded in a matrix of granular matter1 which has been properly termed intercellular4 ,the nearest approach to ossification of cartilage in fishes is that of the cuttle-fish2 in this stellate cells are freely distributed1 as shown in ,fig4 #dda1 ,no4 #c4 ,illustration3 ,fig4 #dda4 #a4 ,cartilage from the head of the skate1 cells filled with nuclei2 #b4 ,cartilage from frog1 oblong cells with nuclei2 #c4 ,cartilage from cuttle-fish1 with stellate cells1 #bjj4 ,white fibro-cartilage occurs between the bodies of the vertebr as a connecting medium4 ,in this kind the cells are more widely distributed1 specimens of which may be taken from the central portion of an interarticular disc of any animal4 ,the oval or circular corpuscles will be seen surrounded by an abundance of fibrous tissue4 ,an acquaintance with the degeneration of the textures with which we have been dealing may be of service to the student1 as he may1 in the course of his examination1 meet with an abnormal condition altogether different to those described4 ,the process of degeneration is usually a slow one1 except in the case of fatty infiltration1 an example of which is furnished by the fatty degeneration of the liver in ,strasburg geese4 ,muscular tissue is very prone to fatty degeneration1 and fatty heart is often met with4 ,calcareous degeneration of the muscles1 ligaments1 and cartilages1 as well as morbid deposits1 are not at all uncommon in these structures4 ,in ,plate ,,xix41 ,no4 #i1 a small section is given of an enchondroma1 and in which the round or ovoid cells of the cartilage are seen degenerated and converted into granular masses of a calcareous nature4 ,fig4 #ddb is a somewhat more highly magnified section of a calcareous or morbid growth1 taken from a human subject in which a morbid growth was seen to be gradually destroying the bone and cartilage cells4 ,illustration3 ,fig4 #ddb4--;,cartilage taken from a diseased finger1 in which both cartilage and bone were in a state of degeneration4 ,bone4--,bone is a hard unyielding structure1 and which in the vertebrata forms the skeleton of the adult4 ,it is the framework for the support of the soft tissues of the body1 and forms various cavities for the reception of important organs1 as the brain1 spinal cord1 eyes1 heart and lungs1 and acts as levers for the action of the muscles and joints4 ,the partial elasticity of bone is seen in the ribs1 and the rebound when the skull is dropped on the ground4 ,bone consists of earthy and animal matters intimately combined2 the removal of either1 however1 does not destroy the form of the bone1 if the process of separation be carefully conducted4 ,the earthy constituents may all be dissolved out by hydrochloric acid1 but the form of the bone is preserved in its minute particular1 and in this state sections may be cut for microscopical examination4 ,if allowed to become dry it shrivels1 and assumes the density of horn4 ,the interior of a bone is of a spongy or cancellated structure1 particularly at the ends4 ,the outer portion of the bone is more dense than the internal part4 ,the study of bone should commence with sections of the softened structure4 ,directions for making sections of bone are given in the chapter on ,practical ,microscopy4 ,illustration3 ,,plate ,,xx ,,vertebrata1 ,,bone ,,structure4 ,the intimate structure of bone will be studied in connection with ,plate ,,xx4 ,two series of lamell may be demonstrated in bone after maceration in acid1 a larger system surrounding the medullary canal1 and a smaller surrounding the ,haversian canals1 both of which are seen in ,nos4 #a and #b4 ,in macerating bones1 the lamell of the layer concentric system may be peeled off in layers2 these are seen to be pierced with fine apertures1 caused by the canaliculi4 ,in some parts larger apertures are seen through which bundles of fibres pass1 pinning1 as it were1 the several layers together2 these are the perforating fibres4 ,the outermost of the layers1 being near the periosteum1 the membrane covering the bone1 are termed periosteal layers2 the innermost1 being close to the canal1 are called medullary layers4 ,no4 #a is a transverse section of a flat bone1 the clavicle1 and it shows the ,haversian canals1 varying in size from #a_/bjjjth to #a_/bjjth of an inch in diameter1 the largest being near the medullary canal4 ,in shape they are round1 oval1 or oblong1 according to the line of section4 ,each canal is surrounded by rings1 none of which are complete1 and running one into the other at various parts4 ,under a higher power1 those irregular shaped bodies termed lacun1 with fine radiating fibres1 are seen to be smaller canals1 canaliculi4 ,by means of this complete and intricate distribution of the canals of the ,haversian system1 the nutritive fluids pass into the most compact parts of the osseous tissue4 ,longitudinal sections of the long bones show these canals as continuous branching-out cells4 ,in many of the lower animals the bony structure differs from those of man1 as will be seen in ,plate ,,xx4 ,no4 #c shows a transverse section of the femur1 or leg-bone of an ostrich1 magnified ninety-five times1 in which the ,haversian canals are much smaller and more numerous1 and many of them run in the transverse direction4 ,no4 #d1 again1 is a transverse section of the humerus1 or fore-arm bone of a turtle 7,chelonia mydas74 ,this exhibits traces of ,haversian canals1 with a slight tendency to a concentric arrangement of bone-cells around them1 the bone-cells being large and numerous1 and occur1 for the most part1 in parallel rows4 ,in ,no4 #e1 a horizontal section of the lower jaw-bone of a conger-eel exhibits a single plane of bone-cells arranged in parallel lines4 ,there are no ,haversian canals present1 and when this specimen is contrasted with that of ,no4 #d1 it will be noticed that the canaliculi given off from each of the bone-cells of this fish are very few in number in comparison with that of the reptile4 ,no4 #f is a section of a portion of the cranium of a siren 7,siren lacertina71 remarkable for the large size of the bone-cells1 and of the canaliculi1 which are larger in this animal than in any other yet examined2 and as in the preceding specimen1 no ,haversian canals are present4 ,no4 #g is a section of bone taken from the exterior of the shaft of the humerus of a ,pterodactyle2 this exhibits the elongated bone-cells characteristic of the order ,reptilia4 ,no4 #h is a horizontal section of a scale1 or flattened spine1 from the skin of a ,trygon1 or sting ray2 this exhibits large ,haversian canals1 with numerous wavy parallel tubes1 like those of dentine1 communicating with them4 ,this specimen shows1 besides wavy tubes1 numerous bone-cells1 whose canaliculi communicate with the tubes1 as in dentine4 ,the following points may be noted with regard to the several sections of bone described4 ,that of the bird1 for instance1 contrasted with that of the mammal1 exhibits the following peculiarities3 the ,haversian canals are more abundant1 much smaller1 and often run in a direction at right angles to that of the shaft1 by which means the concentric laminated arrangement is in some cases lost2 the direction of the canals follows the curve of the bone2 the bone-cells are much smaller and more numerous2 while the number of canaliculi sent off from the cells is less than in those of mammals4 ,no4 #c is the average length of a bone-cell of the ostrich1 #a_/bjjjth of an inch1 in breadth #a_/fjjjth4 ,in the ,reptilia1 the bones may be either hollow1 cancellated1 or solid2 and their specific gravity is less than that of birds or mammals4 ,the short bones of most of the chelonian reptiles are solid1 and the long bones are either hollow or cancellated2 the ribs of the serpent-tribe are hollow1 the medullary cavity performing the office of a ,haversian canal2 the bone-cells are accordingly arranged in concentric circles around their canals4 ,the vertebr of these animals are solid2 and the bone1 like that of certain birds1 is remarkable for density and whiteness4 ,when a transverse section is taken from one of the long bones1 and contrasted with that of a mammal or bird1 the difference will be noticed2 there are very few1 if any1 ,haversian canals1 and these are large2 and at one view1 in the section1 ,no4 #g1 the canals and bone-cells are arranged both vertically and longitudinally4 ,the bone-cells are remarkable for the great size to which they attain2 in the turtle they are #a_/cgeth of an inch in length1 the canaliculi are extremely numerous1 and are of a size proportionate to that of the bone-cell4 ,in fishes a greater variation occurs in the minute structure of the skeleton than in either of the three preceding classes4 ,a rare structure is that of the sword of the sword-fish 7,istiophorus74 ,in this1 ,haversian canals and a concentric laminated arrangement of the bone are found1 but no bone-cells4 ,the ,haversian canals1 when they are present1 are of large size1 and very numerous1 and then the bone-cells are1 generally speaking1 either absent or but few in number1 their place being occupied by tubes or canaliculi1 which are often of a very large size4 ,the bone-cells are remarkable for their graduate figure1 and the canaliculi derived from them are comparatively few in number4 ,in a thin section of the scale of an osseous fish1 the cells lie nearly all in one plane1 and the anastomoses of the canaliculi are more distinctly seen2 in the hard scales of many1 as the ,lepidosteus and ,calicthys1 and in spines of the ,silurid1 the bone-cells are well differentiated4 ,in the true bony scales comprising the exo-skeleton of cartilaginous fishes the bone-cells are seen in great numbers4 ,now1 if we proceed at once to the application of the facts which have been laid down1 and make a fragment of bone of an extinct animal the subject of investigation1 it will be found that the bone-cells in ,mammalia are tolerably uniform in size2 and if we take #a_/bjjjth of an inch as a standard1 the bone-cells of birds fall below that standard2 but the bone-cells of reptiles are much above either of the two preceding1 while those of fishes are essentially different1 both in size and shape1 and are not likely to be mistaken for one or the other2 so that the determination of a minute yet characteristic fragment of fishes' bone is a task easily performed4 ,if the portion of bone does not exhibit bone-cells1 but presents either one or other of the characters indicated1 the task of discrimination is equally easy4 ,we have now the mammal1 the bird1 and the reptile to deal with4 ,in consequence of the very great size of the cells and their canaliculi in the reptile1 a portion of bone of one of these animals can readily be distinguished from that of a bird1 or a mammal4 ,the only difficulty lies between these two last2 but1 notwithstanding that on a cursory glance the bone of a bird appears very like that of a mammal1 there are certain points in their minute structure in which they differ2 and one is the difference in size of the bone-cells4 ,to determine accurately1 therefore1 between the two1 we must1 if the section be a transverse one1 also note the comparative sizes of the ,haversian canals1 and the tortuosity of their course2 for the diameter of the canal bears a certain proportion to the size of the bone-cells1 and after close examination the eye will readily detect differences4 ,illustration3 ,fig4 #ddc4 #a4 ,a portion of the web of frog's foot1 spread out and slightly magnified to show distribution of blood-vessels2 #b4 ,is a portion magnified #bej diameters to show the ovoid form of the blood discs in a vessel1 beneath which hexagonal nucleated epithelium cells appear4 ,arteries and ,veins4--,the circulation of the animal frame is maintained by arteries1 veins1 and capillaries4 ,the arteries are elastic and contractile tubes2 these convey the blood from the heart to the capillaries4 ,the larger arteries are exceedingly elastic1 but feebly contractile on account of the muscular tissue in their walls4 ,the veins ramify throughout the body1 are more numerous than the arteries1 and of greater capacity4 ,they usually accompany the arteries and correspond to them in structure1 the larger veins possessing semi-lunar valves2 these project into their interiors1 and thus prevent the regurgitation of the blood4 ,they have four coats1 consisting of areolar tissue1 yellow fibres combined with muscular fibres1 and white fibrous tissue1 two layers of yellow fibres arranged longitudinally1 and a single layer of epithelial cells4 ,intermediate between the arteries and veins there are exceedingly fine tubes1 termed capillaries1 in which the arteries terminate1 and from which the veins arise4 ,these are composed of a fine homogeneous membrane1 with here and there a nucleus4 ,the capillary circulation of the blood is readily seen in the tail of the newt and the foot of the frog1 ,fig4 #ddc4 ,illustration3 ,fig4 #ddd4--;,a network of capillaries4 ,a network of capillaries conveying blood to the lungs1 and ramifying throughout the structure1 is shown in ,fig4 #ddd1 and in ,plate ,,xix41 ,no4 #f1 the termination of a capillary of a blood-vessel in the fat-cells of the human body4 ,plate ,,vii4 illustrates the distribution of the arteries and veins to various parts of the animal body4 ,this coloured plate1 however1 is designed to show the value of injected preparations in the delineation of animal structures4 ,by thus artificially restoring the blood and distending the tissues1 a much better idea is obtained of the relative condition of parts1 the appearance presented by the erectile papill1 c4 ,in the section of foot of mouse 7,no4 #adi71 the bone is seen surrounded by its vascular supply1 arterial and venous2 in ,no4 #aej1 the papill of the tongue are distended and seen erect2 in ,no4 #aeb1 a vertical section of the fungi-form papill on the tongue of cat1 with capillary loops passing into them1 is demonstrated2 in ,no4 #aea1 the vertical section of brain of a rat1 the vascular supply is shown2 ,no4 #aec1 the malpighian tufts 7circular bodies7 and arteries ramifying about the structure2 in ,no4 #aed1 the vertical section through the intestine of the rat1 shows villi 7arteries and veins7 surmounted by epithelium1 and supported on a layer of the mucous membrane2 in ,no4 #aee1 the vascular supply sent to the roots of the whisker of the nose of the mouse2 in ,no4 #aeg1 a tangential section cut through the several textures1 the sclerotic coat and retina of the eye of a cat is clearly made out although not highly magnified2 again1 in ,no4 #aef1 the beautiful vascular arrangement of the internal gill of the tadpole could scarcely be so strikingly illustrated in any other way2 while in the central1 ,no4 #aeh1 the vascular system throughout the whole of the body of a fully developed tadpole1 with the way in which the blood is carried from the remotest part of the tail to the heart1 and sent to the gills1 the brain1 c41 it is quite unnecessary to enlarge upon4 ,these are seen under a low power1 but for the purpose of studying the basement membrane1 together with the intimate association and termination of the nerves accompanying the arteries and veins1 it is absolutely necessary to resort to a staining process1 and cutting fine sections with the microtome4 ,small portions of a nerve may be cut off with fine scissors1 teased out with needles1 and a drop of acetic acid added to render the sheath more transparent2 in a few seconds the connective tissue corpuscles will be brought into view4 ,for the microscopical examination of nerve-fibrill take a small section from the leg of a frog1 and tease it out in blood serum or white of egg4 ,in size the fibrill vary1 even in the same nerve1 from the #a_/abjjjth to the #a_/aejjth of an inch in diameter4 ,illustration3 ,fig4 #dde4 ,to show the circulation of the blood in the frog's foot1 and without causing the animal pain or much inconvenience1 it is better to enclose it in a black silk bag1 and draw out the foot as shown at a a a1 ,fig4 #dde4 ,the bag provided should be from three to four inches in length1 and two and a half inches broad1 shown at b b1 having a piece of tape1 c c1 sewn to each side1 about midway between the mouth and the bottom1 and the mouth itself capable of being closed by a drawing-in string1 d d4 ,into this bag the frog is placed1 and only the leg which is about to be examined kept outside2 the string d d must then be drawn sufficiently tight around the small part of the leg to prevent the foot from being pulled into the bag1 but not to stop the circulation2 three short pieces of thread1 f f f1 are now passed around the three principal toes2 and the bag with the frog must be fastened to the plate a a by means of the tapes c c4 ,when this is accomplished1 the threads f f f are passed either through some of the holes in the edge of the plate1 three of which are shown at g g g1 in order to keep the web open2 or1 what answers better1 in a series of pegs of the shape represented by h1 each having a slit1 i1 extending more than halfway down it2 the threads are wound round these two or three times1 and then the end is secured by putting it into the slit i4 ,the plate is now ready to be adapted to the stage of the microscope3 the square opening over which the foot is secured must be brought over the aperture in the stage through which the light passes from the mirror4 ,the tadpole circulation is readily seen by placing the creature on its back1 when we immediately observe the beating heart1 a bulbous-looking cavity1 formed of delicate1 transparent tissue1 through which the blood alternately enters by one orifice and leaves by a more distant exit4 ,the heart1 it will be noticed1 is enclosed within its pericardium1 this being the more delicate part of the creature's organisation4 ,the binocular microscope should be used for viewing the circulation4 ,passing along the course of the great blood-vessels to the right and left of the heart1 the eye is arrested by a large oval body1 of a more complicated structure4 ,this is the inner gill1 formed of delicate1 transparent tissue1 traversed by arteries1 and a network of blood-vessels4 ,it is almost unnecessary to say the tadpole has a respiratory and circulatory system resembling those of fishes4 ,in nearly all fish the heart has but two cavities1 an auricle and ventricle2 the blood is returned by the veins to the auricle1 passes into the ventricle1 and is then transmitted to the gills1 where1 being exposed to the air contained in the water1 it becomes deprived of carbonic acid1 aerated1 and rendered fit to breathe4 ,in the reptile we find a modification of plan4 ,the heart has three cavities1 two auricles and one ventricle2 by this contrivance there is a perpetual mixture in the heart of the impure carbonized blood which has already circulated through the body1 and flows into the ventricle from the right auricle1 with the purer aerated blood returned from the lungs1 which flows at the same instant into the ventricle from the left auricle4 ,for the purpose of subsequent observations the tadpole should be selected at a period in which the skin is perfectly transparent1 otherwise the appearances already described of the form and situation of the heart1 and the three great arterial trunks 7proceeding right and left71 will not be clearly made out4 ,the anatomical arrangement of the vessels will be seen to be closely connected with the corresponding gill1 the upper one 7the cephalic7 running along the upper edge of the gill1 giving off1 in its course1 a branch which ascends to the mouth1 with its accompanying vein2 this is termed the labial artery and vein4 ,the cephalic artery continues its course around the gill1 until it suddenly curves upwards and backwards1 and reaches the upper surface of the head1 when it dips down between the eye and the brain4 ,it must not be supposed that this can be made out in the average tadpole1 the obstacle to which is the large coil of intestines1 usually distended with dark-coloured food4 ,this must first be reduced by making your tadpole live on plain water for some days4 ,plate ,,vii41 ,no4 #aeh1 affords a view of the vessels obtained under the influence of low diet1 and whereby we are enabled to trace the course of the three large arteries4 ,the third trunk1 traversing the lung1 is seen to emerge from the lower edge and descend into the abdomen to form the great abdominal aorta4 ,a small half-starved tadpole shows the heart beating and the blood circulating1 but the latter is quite colourless1 not a single red globule visible anywhere4 ,the heart is a colourless globe1 the gills two transparent ovals1 and the intestines a colourless1 transparent coil4 ,through the empty coil the artery is seen on either side leaving the gills1 and converging towards the spine1 and uniting to form the abdominal aorta1 the large central vessel coloured red in the figure4 ,after the aorta has supplied the abdominal viscera1 a prolongation1 or caudal artery is seen descending to the tail1 the all-important organ of locomotion in the tadpole4 ,this artery1 entering the root of the tail1 is imbedded deeply in the flesh1 whence it emerges1 and then continues its course1 closely accompanied by the vein1 to within a short distance of the extremity1 where1 being reduced to a state of extreme fineness1 it terminates in a capillary loop1 composed of the end of the artery and the beginning of the vein4 ,the artery1 in its course1 gives off branches continually to supply the neighbouring tissue4 ,the blood-current in the tail is often seen1 even in the main artery or vein1 to be sluggish4 ,this occurs independently of the heart1 which will continue to beat as usual2 it happens1 because the circulation in the tail depends very much on the motion of the organ4 ,when this is suspended 7as in the confined tadpole under the microscope71 the blood moves sluggishly1 or stops1 till the tail regains its freedom and motion1 when the activity of the current is restored4 ,having traced the arterial system which conveys the blood from the heart to the extremities1 we will now note its return by the veins back again to the heart4 ,the caudal vein runs near the artery during the greater part of its course1 with its stream of blood towards the heart4 ,this stream is swollen by perpetual tributaries from numerous vessels4 ,as the vein approaches the root of the tail it is inclined towards the artery1 and diverges from it at the point of entering the abdomen4 ,here it approaches the kidneys and sends off branches1 while the main trunk continues its course onward2 and1 passing upwards behind a coil of intestine1 it approaches the liver1 and runs in a curved course along the margin of that organ4 ,the blood is now seen to enter the vena cava by several channels1 that converge towards the great vein as it passes in close proximity to the organ4 ,beyond the liver the vena cava continues its course upwards and inwards to its termination in the sinus venosus or rudimentary auricle of the heart4 ,this termination is the junction of not less than six distinct venous trunks1 incessantly pouring their blood into the heart4 ,the circulation in the fringed lips forms a most complicated network of vessels1 out of which proceeds a vein corresponding to the artery already traced4 ,this descends in a direct course till it joins the principal vein of the head1 which corresponds to the jugular in the mammalia4 ,thus it will be seen the blood is driven by the heart into each inner gill through three large blood-vessels1 which arise directly from the truncus arteriosus1 and may be called the afferent vessels of the gill4 ,in ,plate ,,vii41 ,no4 #aef1 an enlarged view of a gill is shown4 ,on closer examination 8each internal gill or entire branchial organ is seen to consist of cartilaginous arches1 with a piece of additional framework of a triangular form1 stretching beyond the arches1 composed of semi-transparent1 gelatinous-looking material4 ,these form the framework of the organ and support upon their upper surface the three rows of crests with their vascular network1 and the main arterial and venous trunks lying parallel to and between them4 ,the three systemic arteries arising1 right and left1 from the truncus arteriosus1 enter each gill on its cardiac side1 and then follow the course of the crests1 lying in close proximity to them4 ,the upper of these branchial arteries runs alone on the outside of the upper crest1 and another branch leaving the trunk and passing into the network of the crest1 whence a returning vessel may be traced carrying back the blood across the branchial artery1 and to a vessel lying close to and taking the same course as the artery itself4 ,carrying the eye along the latter vessel we find1 at a short distance from the first of these crest branches1 a second1 leaving the main trunk and entering the crest1 when a corresponding returning vessel conveys the blood across the arterial trunk into the vessel lying beside it1 as in the former instance4 ,a number of these branches may be traced from one crest to the other4 ,but it is now seen that the trunk from which these arterial branches spring diminishes in size as it proceeds in its course 7like the gill artery in fishes71 while the vessel running parallel to it and receiving the stream as it returns from the crest enlarges to some extent4 ,thus1 the artery or afferent vessel which brings the blood to the gill is large at its entrance1 but gradually diminishes and dwindles to a point at the opposite end of the crest2 while the venous or efferent vessel1 beginning as a mere radical1 gradually enlarges1 and thus becomes the trunk that conveys the blood out of the gill to its ultimate destination4 ,this vessel is the upper branchial vein so long as it remains in contact with the gill2 subsequently it changes its name on leaving the gill and as it passes upwards for distribution to the head1 when it is designated the cephalic artery4 ,the middle branchial artery and vein proceed in like manner in connection with the middle crest1 and the lower artery and vein in connection with the lower crest4 ,the middle and lower venous trunks1 having reached the extremity of the crests1 curve downwards and inwards1 and leave the gill4 ,the former trunk1 converging towards the spine1 meets its fellow1 and with it forms the ventral aorta4 ,the latter gives origin to the pulmonary artery1 and supplies also the integuments of the neck4 ,curious and interesting is the final stage of the metamorphosis1 when the waning tadpole and incipient frog coexist1 and are actually seen together in the same subject4 ,the dwindling gills and the shrinking tail--the last remnants of the tadpole form--are yet seen1 in company with the coloured1 spotted skin1 the newly formed and slender legs1 the flat head1 the wide and toothless mouth1 and the crouching attitude of the all but perfect reptile40#hg ,to observe the circulation and how it is carried on during life in the gills1 the outer covering must be carefully raised1 or even stripped off4 ,this will be better accomplished by putting the tadpole under the influence of cocaine or chloroform--a drop of the fluid is sufficient for the purpose4 ,the metamorphosis in the embryo of the frog is by no means exceptional4 ,the ascidian begins life in the form of a tadpole1 with a muscular tail2 subsequently it fixes itself by its head to a rock1 and its tail disappears4 ,the changes the tadpole of the frog passes through are in every respect1 except in one or two minor details1 similar to those of adult amphibia which pass their whole lives in water4 ,the newly-hatched flat-fish is symmetrical1 an eye being placed on each side of its head1 with the adults of other fishes4 ,the ftal whale has well-developed hind limbs1 and which1 after passing into a condition almost perfect in proportion to the rest of the body1 gradually dwindle away again to the merest rudimentary structures4 ,in all these1 and a number of similar cases1 it is seen that the earlier condition of existing animals represents1 and is in agreement with that of its adult ancestor of a remote period in the past4 ,collected facts bearing upon this question have been made the groundwork of a theory of hereditary properties in the germ1 and a disposition to go through the same phases of life as the parent4 ,,chapter ,,vi4 ,the ,mineral and ,geological ,kingdoms4 ,the structure of rocks and the formation of crystals will be found to furnish an endless supply of instructive material for the microscope4 ,in sciences of pure observation1 as those of mineralogy and geology1 the facts to be observed are of several different kinds1 and where so many observers are at work all over the world1 constant progress will necessarily be made1 as well as continued correction required from change and improvement in the methods of observation4 ,it would be impossible to give even a slight sketch of what has been done in the two departments of nature referred to during the past few years4 ,mineralogical and geological research have derived very great advantage from having been assigned to professional teaching4 ,but1 as ,professor ,bonney reminds us1 the progress made in geological work in particular1 has been directly due to the revelations of the microscope4 ,it called forth an instrument of special construction for the purpose1 the petrological microscope 7,fig4 #gi71 well equipped with ,nicol's prisms1 and numerous other appliances demanded for the important investigations4 8,upon the history of the two main groups of rocks the microscope has thrown much light4 ,for the igneous rocks it has simplified their classification and determined their mutual relations2 while for the rudimentary group1 it has shown the true nature of their constituents1 and pointed out the sources from which they were derived4 ,but it is in helping to elucidate the problem of the metamorphic rocks1 of which much less was known1 that the microscope has been of the most service4 ,it has likewise greatly assisted in the attempt to determine the history and mutual relation of these rocks4 ,one of the most important results within the last few years has been the demonstration that without exception these crystallin schists are very old1 all probably older than the first rocks in which traces of life have been found4 ,the conclusion arrived at1 is that 8the environment necessary for changing an ordinary sediment into a crystalline schist existed generally only in the earliest ages1 and but very rarely and locally1 if ever1 since palozoic time began40 ,the crystalline schists then are the relics still preserved to us of the early days of the earth's history1 when the temperature near the surface was still high4 ,since that time the zone for marked mineralogical changes has been continually sinking1 until at the present day it has reached a depth practically unattainable4 8,the subterranean laboratory still exists1 but the way to it was virtually closed at a comparatively early period in the earth's history40 ,greater progress has been made since the microscope was pressed into the service of geology1 and inspires the hope that we shall yet learn something more of the earliest ages1 when the mystery of life began4 8,it may be regarded as one of the most remarkable results of geological science1 that an acquaintance with organic forms is at least as necessary for a geologist as a knowledge of minerals1 and that a correct knowledge of organic remains 7portions of fossil plants and animals7 should prove a more certain and unerring guide in unravelling the structure of complicated districts of countries1 than the most wide and general acquaintance with inorganic substances4 ,the cause of this1 however1 is obvious1 as the mineral substances produced at any one period of a vast succession of ages1 do not appear to have had any essential difference from those formed under like circumstances at another4 ,the animals and plants1 however1 living at one period of the earth's history were widely different from those living at other periods4 ,there has been a continuous succession of different races of living beings on the earth following each other in a certain regular and ascertainable order1 and when that order has been determined1 it is equally certain that we can at once assign to its proper period of production1 and therefore to its proper place in the series of rocks1 any portion of earthy matter we may meet with containing any one1 or even any recognisable fragment of one1 of these once living beings40 ,the method of preparing sections of minerals and rocks for microscopic examination will be found at pp4 #bda1 #cjg-cji4 ,the sections1 it is almost needless to say1 must be prepared thin enough to permit the use of transmitted light1 as well as for that of polarised light3 that is to say1 they should range from about #a_/ajjth to #a_/ajjjth of an inch4 ,almost any lapidary will cut sections of any choice specimen4#hh ,the formation of crystals1 and the method of preparing them for examination1 has also been fully explained in the chapter on polarised light1 pp4 #bai et seq41 and illustrated on ,plate ,,viii4 ,it is well known in micro-chemistry that 8almost every substance1 simple or compound1 capable of existing in the solid state1 assumes1 under favourable conditions1 a distinct geometrical figure1 usually bounded by plane surfaces and having angles of constant value4 ,much useful information may be gained upon micro-crystallography1 as well as on almost everything having any relation to the technique of the microscope1 in the 8,journal of the ,royal ,microscopical ,society40 ,to the ,june number 7#ahih7 ,mr4 ,t4 ,charters ,white contributes an article on crystals1 and reminds us that the presence of much or little moisture will modify and alter forms1 as much and as often as varying degrees of temperature4 ,at the same time he offers a few useful suggestions for the purpose of securing better results1 for which purpose he employs hippuric acid1 hydroquinine1 and picric acid alone or in combination with hippuric acid1 and an aqueous solution of bichromate of potassium1 crystallised in a tolerably thick emulsion of gum arabic4 ,this is the only aqueous solution2 the other solvents have been methylated spirit1 acetone1 and absolute alcohol1 taking these three solvents as types of the greatest volatility1 because in making certain crystals it is necessary that the solvent should evaporate quickly1 otherwise the crystals will assume their original forms4 ,it is further desirable to make saturated1 or even super-saturated solutions of the three chemicals named1 as the colours produced under polarised light are of a deeper and richer character than they are if made from weaker solutions4 ,of the three chemicals named he prefers hippuric acid1 for reasons stated1 that it is the most manageable1 and allows of more time being taken in modifying the formation of the crystals4 ,it is also advisable to slightly warm the glass slide before the drop of fluid is applied4 ,on the whole1 picric acid appears to furnish a greater variety of crystals when used in combination with bichromate of potassium and a solution of gum arabic4 ,,appendices ,,and ,,tables ,,useful ,,to ,,the ,,microscopist4 ,,appendix ,a4 ,,illumination ,,arrangements ,,of ,,the ,,microscope4 ,a doubt has of late been expressed among practical microscopists as to the value of the illumination arrangements of the lamp and the microscope1 so as to secure the more perfect definition of the flagellate organ of the monas and other minute forms of infusorial life4 ,we have been told that better results will be obtained by turning the mirror aside1 and so disposing the microscope and lamp in the horizontal position1 that the central rays of light from the mirror-edge of the lamp-flame shall pass through the optical axis of the achromatic condenser1 the focus of which must be accurately brought upon the field of view by means of the substage centring screws and rack-work1 and in such a manner1 that by employing a #a-;inch objective1 a sharply-defined image of the lamp-flame1 edge-on1 is projected on to the centre of the field in association with the specimen under examination4 ,if the #a-;inch objective be now replaced by a #a-abth or #a-afth inch immersion and once again focussed into place1 and a slight re-adjustment of the centring made1 it will be found that the field is brilliantly illuminated1 and the most minute portions of infusorial life are well defined1 and with a sharpness otherwise unattainable4 ,at the same time the graduating or iris diaphragm must be brought into use4 ,dr4 ,clifford ,mercer1 the ,president of the ,american ,microscopical ,society1 who has quite recently reinvestigated the question of illumination1 utterly condemns the narrow cone1 as well as that of oblique light in all such investigations1 and considers the #c-dths axil cone as the most suitable method for microscopical illumination1 and he bases his resolving limit accordingly4 ,some important experiments are brought forward by ,dr4 ,mercer1 which at the same time demonstrate the correctness of ,lord ,rayleigh's limit of resolution 7referred to in a previous chapter1 p4 #dd71 for circular apertures as contrasted with that calculated by the late ,sir ,george ,airy4 ,with regard to the ,abb ,theory1 ,dr4 ,mercer says3 8,resolution in the ,abb ,theory may be said to increase by bounds4 ,so long as the central image of the source of light alone is to be seen at the back of the objective1 resolution is not present4 ,the aperture may be increased without change in the contraction of the diffraction pattern1 and in accompanying resolution1 so long as the central image alone is to be seen at the back of the objective2 but the moment the increase in aperture is sufficient to uncover or admit one flanking spectrum image1 resolution is present4 ,with greater increase in aperture1 no improvement in the picture as to the contraction of the diffraction pattern is to be seen until another spectrum image is uncovered or admitted4 ,dr4 ,mercer gives his reasons for considering that the advantageous reduction in a cone of light between an object and the objective should not exceed1 in the case of first-class objectives1 one-fourth to one-third 7never more than one-half7 of the diameter of the cone4 ,on the other hand1 with full cone illumination1 resolution increases continuously1 and not by jumps or by periodic accessions4 ,with regard to the use of oblique light1 he says his ,photos #b1 #c1 and #dhi are a pictorial warning for a second time against the use of oblique illumination in ordinary work us a means of increasing1 or of attempting to exhaust the resolving power of the microscope4 ,at the same time it becomes evident that every substage should be provided with a means by which its condenser may be accurately centred1 and that every student using the microscope should be familiar with a method of centring his substage condenser4 ,dr4 ,mercer summarises the results of his experiments thus3-- #a4 8,diffraction rays on leaving an object may be considered in the same category with other rays changed in direction by an object4 #b4 8,the diffraction phenomena seen in a projected image are essentially the effect of changes in light above the objective1 due to a function of aperture1 and not to changes below the objective1 due to diffraction of light in the plane of the object4 #c4 8,diffraction in the plane of the object does1 under some circumstances1 furnish light to certain parts of an aperture from which primary rays are absent1 and this enables aperture to more fully determine the character of the projected image1 resulting in a more nearly truthful image1 or1 on the other hand1 in false appearances4 ,this is the gist of the ,abb phenomena of microscopic vision4 #d4 8,but such phenomena are not peculiar to microscopic vision1 notwithstanding ,professor ,abb's claim to the contrary4 #e4 8,with any positive lens similar and more brilliant results may be got by utilising corresponding pencils of primary rays1 instead of isolated pencils of diffracted rays4 #f4 8,still more trustworthy results may be got by using primary rays in place of the isolated pencils of primary rays4 #g4 8,an advantage peculiar to using narrow cone illumination with an objective of wide aperture 7the only illumination admissible in the ,abb theory71 consists in giving1 under suitable conditions1 approximately the acme of resolving power simultaneously in each several diameters4 ,thus a circular aperture is approximately squared or made rectangular as to resolving power in several of its diameters simultaneously4 #h4 8,special attention is called to the fact that the ,abb theory deals with complex objects2 for only such objects are subject to resolution4 ,single particles and uniform areas are outside its domain4 ,these latter1 however1 are microscopic objects1 and all objects are essentially different shaped aggregations of points4 ,an isolated point-like particle1 no matter what its minuteness1 may be seen if it present sufficient contrast with the surrounding microscopic field4 ,the size of the disc image is no less than a limit determined finally by aperture4 ,that limit in size varying inversely with aperture1 determines the limit of resolving power4 ,this is the gist of the theory of microscopic vision which harmonises with our experimental study of aperture40 ,,appendix ,b4 ,,micro-,,photography4 ,owing in some measure to the more complete knowledge of the subject gained by the experience of years1 and the extreme value of micro-photography in the delineation of bacteria1 and perhaps in a measure to the advent of the perfected dry-plate process1 photography is being rapidly pressed forward in conjunction with the microscope4 ,in the course of the year #ahih no less than six1 more or less1 new forms of micro-photographic apparatus have appeared2 two are simple1 one for daylight1 one for lamp1 one for electric1 and one for lime-light illumination4 ,passing over the simpler forms1 for a notice of which ,i am unable to find room1 there is one piece of new apparatus1 that of ,mr4 ,e4 ,b4 ,stringer1 which is not only new1 but is in every way adapted to the work of micro-photography4 ,it is in fact a well-arranged camera1 fitted with a powerful condensing arrangement1 each portion of which is capable of being independently centred and controlled4 ,indeed1 the specially interesting feature of the apparatus is the control of the gas and the beautiful and uniformally illuminating disc of zircon1 about a quarter of an inch in diameter4 ,illustration3 ,fig4 #ddf4--,mr4 ,e4 ,b4 ,stringer's ,improved ,micro-photography ,apparatus4 ,b4 ,oxyhydrogen jet with zirconium cylinder1 covered by the cowl ,a when working4 ,c4 ,doublet parallelising condenser1 with centering screws4 ,d4 ,iris diaphragm4 ,e4 ,holder for trough and light-filtering media4 ,f4 ,plano-convex lens1 #d-a_/d;ins4 diameter1 with centering screws ,g ,h4 ,plano-concave lens1 with iris diaphragm ,t4 ,k4 ,connecting pulleys between focussing rod of camera and fine adjustment of ,microscope4 ,l4 ,triangular frame in which ,microscope feet are placed4 ,m4 ,flap shutter4 ,n4 ,door through which image is observed on card screen1 etc4 ,o4 ,solid block of mahogany on which camera body is fixed and supported4 ,p4 ,dark slide4 ,this efficient photo-micrographic apparatus 7,fig4 #ddf7 is made by ,messrs4 ,w4 ,watson ,sons1 under the instructions of ,mr4 ,e4 ,b4 ,stringer4 ,the illuminating condensing system is mounted on a square brass bar1 the illuminant being oxygen-hydrogen light burning on zirconium4 ,immediately in front of this is a condenser1 c1 four and a half inches diameter1 with an iris diaphragm1 ,d1 immediately in front of it4 ,the holder1 ,e1 carries the light filtering media through which the beam passes and enters the condenser1 ,f4 ,it then goes through a tank of water contained in the cone1 ,f to ,h1 and emerges a practically parallel beam of great intensity through a plano-concave lens1 h1 of such a diameter as to exactly fill the back lens of the substage condenser4 ,there is an iris diaphragm1 ,t1 for cutting off stray light4 ,the whole of the apparatus is fitted with centring screws and clamps1 and after having been once adjusted it is ready for use at any moment without preparation4 ,by means of this apparatus1 instantaneous pictures can be taken of living rotifers1 so brilliant is the illumination1 while photographs of such fine objects as the flagella of bacteria cannot be secured with the same amount of certainty by any other microphotographic apparatus with which ,i have made myself acquainted4 ,,appendix ,c4 ,,formul ,,and ,,methods3--,,cementing1 ,,clearing1 ,,hardening ,,and ,,mounting4#ij ,,clearing ,,agents4 ,the object of employing a clearing agent is to replace the alcohol in the dehydrated section by a liquid which has a refractive index about the same as the balsam into which it is to be placed1 and which will readily mix with it4 ,,oil ,,of ,,bergamot will clear quickly from #ij per cent4 of alcohol4 ,clove oil clears more rapidly1 but it dissolves out aniline colours to a considerable extent4 ,xylol is without action on aniline colours4 ,this strength of alcohol is chosen because of its being that of the methylated spirit sold in ,london1 and which is much used in washing and dehydrating on account of its cheapness4 ,,oil ,,of ,,cedar ,,wood1 although an essential oil1 resembles xylol1 but evaporates slowly4 ,it has very little solvent action on the aniline colours4 ,it clears rapidly from absolute alcohol1 but not well from #ij per cent4 ,sections can be left in it for several days4 ,it is a convenient medium in which to examine tissues before mounting them permanently4 ,it clears celloidin without dissolving it2 and as a connecting fluid between the object and objective nothing better has been discovered4 ,other clearing agents have been tried1 but as they dissolve out the aniline colours1 are no longer used4 ,,cements4 ,,grove',s ,,mastic ,,and ,,bismuth4--,dissolve gum mastic in chloroform1 and thicken with nitrate of bismuth4 ,the solution of mastic should be nearly saturated4 ,,grove',s ,,oxide ,,of ,,zinc1 ,,dammar1 ,,and ,,drying ,,oil4--,rub up well-ground oxide of zinc1 #b ozs41 with drying oil1 to the consistence of thick paint4 ,then add an equal quantity of gum dammar1 previously dissolved in benzoline1 and of the thickness of syrup4 ,strain through close-meshed muslin4 ,keep in well-corked bottle1 and1 if necessary1 thin with benzoline4 ,,isinglass ,,cement4--,heat the isinglass in a covered vessel on the water-bath with a little glacial acetic acid1 until it is thoroughly softened and forms a stiff mass1 then gradually add more acid until it produces a thick solution which is of uniform consistence1 and just fluid while hot4 ,then run into wide-mouth bottles and close with good corks4 ,,kitton',s ,,cement of white lead and red lead in powder1 and litharge powder in equal parts4 ,grind together with a little turpentine1 until thoroughly incorporated1 and mix with gold size4 ,the mixture should be thin enough to use with a brush2 in using1 one coat should be allowed to dry before applying another4 ,no more cement should be mixed with the gold size than is required for immediate use1 as it sets quickly1 and becomes unworkable4 ,,kr,,nig',s ,,cement4--,gradually add ordinary resin1 #g to #i parts1 to melted beeswax1 #b parts1 then steam and cool4 ,,shellac ,,cement4--,dissolve shellac in an equal weight of methylated spirit1 then pour off the clear portion and add a few drops of balsam and castor oil4 ,,marine ,,glue4--,dissolve indiarubber in mineral naphtha1 and add twice the quantity of powdered shellac2 or make chloroform the solvent1 and use mastic instead of shellac4 ,for casting battery trays1 use a composition of #d parts resin and #a of gutta percha1 with a little boiled oil4 ,,selier 7,cleaning ,glass ,slides74--,new slides or cover-glasses must be placed for a few hours in a mixture of #a part of potassium bichromate1 #a of sulphuric acid1 and #be of water4 ,subsequently wash with water and wipe dry with a linen rag1 after draining off the excess of moisture4 ,covers that have been used should be previously immersed for a few days in a mixture of equal parts of alcohol and hydrochloric acid4 ,scrape old slides free of mounting medium before immersing them in the bichromate solution4 ,,elsching',s ,,celloidin ,,solution4--,allow the celloidin shavings to swell up for #bd hours in the necessary quantity of absolute alcohol1 then add the proper amount of ether4 ,,koch',s ,,copal4--,stain small pieces of material in bulk1 and dehydrate with alcohol1 then immerse in a thin solution of copal in chloroform4 ,evaporate with a gentle heat until the solution is so far concentrated as to draw out into threads that are brittle on cooling4 ,then remove the objects and leave on a tile for a few days to dry4 ,sections may then be cut by means of a fine saw4 ,if objects are imbedded unstained1 remove copal from sections by soaking in chloroform1 decalcify if necessary1 and stain4 ,,eulenstein',s ,,cement4--,mix equal parts of ,brunswick black and gold size with a very little ,canada balsam4 ,,decalcifying ,,and ,,bleaching4 ,in the case of bony structures1 or tissues so impregnated with calcium salts1 the material should be decalcified by an acid capable of dissolving out the mineral matter4 ,hydrochloric acid with alcohol is in more general use4 ,the older the bone the stronger will be the acid required1 nitric with alcohol and chromic acid4 ,picric acid is preferred for ftal bone4 ,,andeer1 ,j4 ,j41 finds an aqueous solution of phloroglucin acts as a powerful decalcifying agent on the bones of animals1 but is without action on the most delicate organic tissue4 ,if treatment with hydrochloric acid be employed as well1 the residual 8ossein0 will be without a trace of either calcium phosphate or carbonate4 ,,ebner',s ,,fluids4--7#a7 ,mix #ajj ,c4c4 of cold saturated aqueous solution of sodium chloride1 #ajj ,c4c4 of water1 and #d ,c4c4 of hydrochloric acid4 ,preparations are placed in the fluid1 and #a to #b ,c4c4 of hydrochloric acid added daily until they are soft4 7#b7 ,mix #be parts of hydrochloric acid 7sp4 gr4 #aaf7 with #ejj of alcohol 7#ij per cent471 #ajj of water1 and #be of sodium chloride4 ,,fol',s ,,liquid4--,mix #gj volumes of #a per cent4 chromic acid1 #c of nitric acid1 and #bjj of water4 ,,mayer',s ,,desilification ,,process4--,place the objects in alcohol contained in a glass vessel coated internally with paraffin1 then add hydrofluoric acid drop by drop until desilification is complete1 avoiding the fumes meanwhile4 ,,marsh',s ,,chlorine ,,method4--,chlorine is generated in a small bottle by treating crystals of potassium chlorate with strong ,h,cl41 and the gas is led through a piece of glass tubing1 bent twice at right angles1 to the bottom of a bottle containing the sections immersed in water4 ,,ranvier',s ,,fluid4--,use #ej per cent4 hydrochloric acid with the addition of sodium chloride to counteract its swelling action4 ,,squire',s ,,fluid4--7#a7 ,mix #ie parts of glycerine with #e parts of hydrochloric acid2 used for softening teeth4 7#b7 ,use a #d per cent4 aqueous solution of arsenic acid at a temperature of #cj to #dj ,c4 ,after softening tissues in this solution1 keep them in alcohol4 ,,waldeyer4--,to a #ja per cent4 solution of palladium chloride1 add one-tenth its volume of hydrochloric acid4 ,,hardening1 ,,freezing1 ,,and ,,embedding4 ,,altmann 7,fixing ,solution74--,a mixture of equal parts of #e per cent4 potassium bichromate solution and #b per cent4 osmic acid4 ,,alcohol4--,strengths of alcoholic solutions1 as given by ,squire1 will be found of practical value4 ,absolute alcohol 7sp4 gr4 ,o#gig7 containing about #ih per cent4 of ethylic alcohol is taken as the basis in most instances4 ,alcohol of #ij per cent4 7sp4 gr4 #jhbc7 is prepared by mixing #ad volumes of absolute alcohol and #a volume of distilled water2 #hd per cent4 alcohol 7sp4 gr4 #jhch7 is rectified spirit ,b4,p42 #gj per cent4 alcohol 7sp4 gr4 #jhgb7 may be obtained by adding #a volume of distilled water to #c volumes of absolute alcohol1 #f volumes of rectified spirit1 or #d volumes of methylated spirit2 #ej per cent4 alcohol 7sp4 gr4 #jiah7 is prepared by adding #d volumes of distilled water to #e volumes of absolute alcohol1 #c volumes of water to #e volumes of rectified spirit1 or #ce volumes of water to #e volumes of methylated spirit4 ,absolute alcohol1 #ge ,c4c41 mixed with acetic acid1 #be ,c4c41 serves as an excellent fixing agent for nuclei4 ,immerse tissues in it for #f to #ab hours1 then transfer to #ij per cent4 alcohol until hardened1 afterwards preserving in #gj per cent4 alcohol till wanted4 ,,betz',s ,,hardening ,,fluid4--,a mixture of equal parts of sulphuric ether and alcohol4 ,this is used for hardening the brain of insects prior to cutting sections4 ,,cole',s ,,freezing ,,process4--,dissolve picked gum acacia1 #d ozs41 in distilled water1 #f ozs41 and to each #e parts of the resulting mucilage add #c parts of syrup made by dissolving loaf sugar1 #a lb41 in distilled water1 #a pint4 ,to each ounce of the medium add #e grains of pure carbolic acid1 and soak the tissues in it prior to freezing4 ,for tissues liable to come to pieces1 mix #d parts of syrup with #e of mucilage4 ,,flemming',s ,,fixing ,,solution4--,osmic acid 7#a per cent4 solution71 #hj ,c4c42 chromic acid 7#aj per cent4 solution71 #ae ,c4c42 glacial acetic acid1 #aj ,c4c42 distilled water1 #ie ,c4c4 ,,fol',s ,,fixing--,osmic acid 7#a per cent4 solution71 #d ,c4c42 chromic acid 7#aj per cent4 solution71 #e ,c4c42 glacial acetic acid1 #aj ,c4c42 distilled water1 #aha ,c4c4 ,,fischer',s ,,imbedding ,,mass4--,dissolve #ae parts of transparent soap in #age parts of #if per cent4 alcohol4 ,,klein',s ,,hardening4--,mix #a ,c4c4 of #aj per cent4 chromic acid solution with #fj ,c4c4 of water1 and add #cj ,c4c4 of #ij per cent4 alcohol4 ,m,,ller',s ,,fluid ,,formula1 see page #bhh4--,this solution is sometimes mixed with one-third its volume of #ij per cent4 alcohol1 its hardening action being then much more rapid4 ,,rabl',s ,,hardening ,,fluid4--,chromic acid solution 7#aj per cent471 #g ,c4c42 water1 #bjj ,c4c42 formic acid 7sp4 gr4 #ab71 #e drops4 ,,rollett',s ,,freezing ,,process4--,small portions of tissue placed on the stage of microtome1 after immersion in the white of an egg1 then frozen and cut with a very cold knife4 ,,ryder 7,double ,embedding74--,after the celloidin bath1 soak objects in chloroform1 then remove into a mixture of chloroform and paraffin1 heated to not more than #dj ,c41 and finally into a bath of pure paraffin4 ,,stricker 7,imbedding ,mass74--,prepare the objects in alcohol and imbed in a concentrated solution in gum arabic in a paper case1 then throw the whole into alcohol and cut after #b or #c days4 ,,webb 7,dextrin ,freezing74--,a thick solution of dextrin 7#a3dj7 in aqueous solution of carbolic acid is used for imbedding1 and subsequently frozen4 ,,mounting ,,media4 ,sections are usually mounted in balsam1 dammar1 glycerine1 c41 but it is not a necessity that the cover-glass should be fixed or cemented down4 ,some cements 7caoutchouc by preference7 should be employed when glycerine or aqueous 7,farrant's7 media are used4 ,,alleger',s ,,gelatine ,,process4--,add a few drops of formalin to each gramme of #je to #a per cent4 gelatine solution4 ,after mounting the section in this1 apply heat to the slide until the paraffin is softened1 and allow the superfluous gelatine to drain from the edge of the slide4 ,,ap,,thy',s ,,mounting ,,medium4--,picked gum arabic1 #ej ,gm42 cane-sugar1 #ej ,gm42 distilled water1 #ej ,gm42 dissolve over a warm bath and add #jje ,gm4 of thymol4 ,this medium sets very hard1 and combined with a paper cell it may be used for ringing glycerine mounts4 ,,cole',s ,,slow ,,or ,,exposure ,,method ,,of ,,mounting4--,dissolve dried ,canada balsam1 #c ozs41 in benzole1 #c fl4 ozs41 and filter4 ,apply a clean cover-glass to a slide that has been moistened by breathing on it1 and place a few drops of the balsam solution on the cover-glass4 ,then remove a section from turpentine1 and put it into the balsam4 ,put aside for #ab hours to allow the benzole to evaporate1 and having warmed a slide and added a drop of fresh balsam solution to that on the cover-glass1 bring the fluid balsam in contact with the warmed slide4 ,press the cover down carefully to avoid the inclusion of air bubbles1 and when the excess of balsam is squeezed out1 put the slide aside to cool1 after which it may be cleaned with a camel-hair brush or soft rag moistened with methylated spirit4 ,,farrant',s ,,solution4--,take of gum arabic #e parts2 water #e parts2 when the gum is fairly dissolved add #aj parts of a #e per cent4 solution of carbolic acid4 ,,flemming',s ,,glycerine ,,preservative4--,mix equal parts of alcohol1 glycerine1 and water4 ,lee recommends the addition of #je to #jge per cent4 of acetic acid4 ,,lee',s ,,turpentine ,,colophonium ,,mounting ,,medium4--,this is highly recommended for general work1 and is prepared by adding small pieces of colophonium to rectified oil of turpentine1 heating in a stove1 and when the solution is sufficiently thick filtering twice in the stove4 ,,seaman 7,glycerine ,jelly74--,dissolve isinglass in water so as to make a jelly that remains stiff at the ordinary temperature of the room1 and add one-tenth part of glycerine1 together with a little solution of borax1 carbolic acid1 or camphor water4 ,filter through muslin whilst warm and add a little alcohol4 ,,seiler 7,alcohol ,balsam74--,heat ,canada balsam until it becomes brittle when cold1 then dissolve in warm absolute alcohol and filter through absorbent cotton-wool4 ,this is chiefly useful as a mounting medium for objects stained with carmine4 ,,squire 7,farrant's ,medium74--,dissolve in #bjj ,c4c4 of distilled water #a ,gm4 of arsenious acid and #acj ,gm4 of gum arabic1 then add #ajj ,c4c4 of glycerine4 ,filter through fine ,swedish filter paper upon which has been deposited a thin layer of talc4 ,,squire 7,glycerine and ,gum74--,dissolve #acj ,gm4 of gum arabic in #bjj ,c4c4 of chloroform water 7#a in #bjj71 then add #ajj ,c4c4 of glycerine and filter4 ,,squire 7,glycerine ,jelly74--,soak #ajj ,gm4 of ,french gelatine in chloroform water1 drain when soft1 and dissolve with heat in #gej ,gm4 of glycerine4 ,add #djj ,gm4 of chloroform water1 with which has been incorporated about #ej ,gm4 of fresh egg albumen1 mix thoroughly1 and heat to boiling point for about #e minutes4 ,make up the total weight to #aeej ,gm4 with chloroform water and filter in a warm chamber4 ,,squire 7,canada ,balsam74--,dry the balsam over a water bath until brittle when cooled1 then to each #bjj ,gm4 add #ajj ,c4c4 of benzole or rather less xylol4 ,,squire 7,dammar ,solution74--7#a7 ,dissolve #ajj ,gm4 of dammar in #ajj ,c4c4 of benzole4 7#b7 ,dissolve #ajj ,gm4 of dammar in #bjj ,c4c4 of turpentine oil1 and add #ej ,gm4 of mastic dissolved in #bjj ,c4c4 of chloroform4 ,,squire 7,potassium ,acetate ,solution74--,dissolve #bej ,gm4 of potassium acetate in #ajj ,c4c4 of water1 by the aid of gentle heat1 and filter4 ,this is used as a mounting medium4 ,,squire 7,treatment of ,sections74--,imbed tissues to be cut in paraffin melting between #de and #ej ,c41 according to the temperature of the room and the nature of the material4 ,afterwards preserve the sections1 prior to staining and mounting1 in #ej per cent4 alcohol1 or in a mixture of equal volumes of glycerine and thymol water 7#a in #aejj74 ,sections may be conveniently washed in alcohol1 dehydrated1 and cleared1 in small wide-mouthed bottles4 ,,topping',s ,,solution4--,mix #a part of absolute alcohol with #e parts of water1 or #d parts of water and #a part of aluminium acetate4 ,add an equal volume of glycerine before use4 ,,stains ,,and ,,staining ,,methods4 ,,ap,,thy',s ,h,,matoxylin ,,stain4--,after staining in #a per cent4 solution of hmatoxylin in #gj or #hj per cent4 alcohol1 wash out in #a per cent4 solution of potassium bichromate in alcohol of the same strength4 ,the bichromate solution should be freshly made by mixing #a part of a #e per cent4 aqueous solution with about #d parts of #hj to #ij per cent4 alcohol4 ,,alferow 7,silver ,staining74--,an acid solution of silver picrate1 lactate1 acetate1 or citrate1 is prepared by adding to #hjj ,c4c4 of the solution #aj to #ae drops of a concentrated solution of the acid of the salt taken4 ,,bethe',s ,,stain ,,for ,,chitin4--,place series of mounted sections on slides in a freshly prepared #aj per cent4 solution of aniline hydrochloride1 containing #a drop of hydrochloric acid for each #aj ,c4c41 for #c or #d minutes1 then rinse in water1 and put the slide with sections downwards in a #aj per cent4 solution of potassium bichromate4 ,the process may be repeated if the stain is not sufficiently intense1 but the sections must be well rinsed with water after each immersion4 ,,beale',s ,,ammonia ,,carmine4--,carmine1 #aj grs42 strong solution of ammonia1 #cj mins42 distilled water1 #b ozs42 alcohol1 #je oz42 glycerine1 #b ozs4 ,dissolve the carmine in the ammonia by the aid of heat1 boil for a few seconds1 and let the solution cool4 ,then allow the excess of ammonia to evaporate1 add the other ingredients1 and filter4 ,if any carmine should deposit on keeping add one or two drops of ammonia solution to redissolve it4 ,,benda',s ,,copper ,h,,matoxylin4--,harden the material with chromic acid or ,flemming's solution and leave sections for #bd hours in a #e per cent4 solution of neutral copper acetate at a temperature of about #dj ,c41 wash out well with distilled water1 and stain to a dark grey or blackish tint in a saturated aqueous hmatoxylin solution4 ,decolourise the sections in #jb per cent4 hydrochloric acid until light yellow1 put back into the copper solution until they turn bluish-grey1 then wash1 dehydrate1 clear1 and mount in balsam4 ,,bismarck ,,brown4--,vesuvine #je ,gm41 rectified spirit #b1 and distilled water #hj ,c4c42 or a concentrated alcoholic solution may be kept ready for dilution4 ,,bochmer',s ,h,,matoxylin4--,dissolve 7a7 crystallised hmatoxylin1 #a ,gm41 in absolute alcohol1 #aj ,c4c41 and 7b7 alum ammonia1 #aj ,gm41 in distilled water1 #bjj ,c4c4 ,mix the two solutions1 and allow to ripen for some days before use4 ,filter after standing a week4 ,wash out with aqueous solution of alum 7#je per cent47 or with acids4 ,,calberla',s ,,indulin ,,stain4--,dilute a concentrated aqueous solution with #f volumes of water and stain sections for #e to #bj minutes4 ,afterwards wash in water or alcohol1 and examine in glycerine or clove oil4 ,,calberla',s ,,macerating ,,mixture 7for nerve and muscle of embryos74--,dissolve potassium chloride1 #jd ,gm41 sodium chloride1 #jc ,gm41 sodium phosphate1 #jb ,gm41 and calcium chloride1 #jb ,gm41 in water1 #ajj ,gm41 saturated with carbon dioxide just before using4 ,mix one volume of this solution with half a volume of ,mller's solution and one volume of water4 ,the ,mller's solution may be replaced by a #be per cent4 solution of ammonium chromate4 ,tissues macerated in this mixture are isolated by teasing and shaking1 and mount specimens in concentrated potassium acetate solution4 ,,canoy',s ,,salt ,,solution4--,add a trace of osmic acid to a #jge per cent4 solution of sodium chloride in water4 ,,chenzinsky',s ,,methylene ,,blue ,,and ,,eosine4--,mix saturated aqueous solution of methylene blue1 #dj parts1 with #je per cent4 solution of eosine in #gj per cent4 alcohol1 #bj parts1 and distilled water or glycerine1 #dj parts4 ,,cohnheim',s ,,gold ,,method4--,place pieces of tissue in #je per cent4 gold chloride solution until quite yellow1 then expose to light in water acidulated with acetic acid until the gold is thoroughly reduced4 ,mount specimens in acidulated glycerine4 ,,crookshank',s ,,method ,,of ,,staining ,,flagella4--,cover-glass preparations are stained with a drop of concentrated alcoholic solution of gentian violet1 then rinsed in water1 allowed to dry1 and mounted in balsam4 ,,czoker',s ,,alum ,,cochineal4--,dissolve alum #a ,gm4 in distilled water1 #ajj ,c4c41 add powdered cochineal1 #a ,gm41 and boil2 evaporate down to half of its original bulk1 filter1 and add #a_/b ,c4c4 of liquid carbolic acid4 ,,delafield',s ,h,,matoxylin4--,dissolve hmatoxylin1 #d ,gm41 in absolute alcohol1 #be ,c4c41 and add the solution to #djj ,c4c4 of a saturated aqueous solution of ammonia alum4 ,expose the mixture to light and air for #c or #d days1 then filter and add glycerine1 #ajj ,c4c41 and methylic alcohol1 #ajj ,c4c4 ,again expose the solution to light until it becomes dark-coloured1 then filter and preserve in a stoppered bottle4 ,,ehrlich',s ,,acid ,h,,matoxylin4--,dissolve hmatoxylin1 #b ,gm41 in absolute alcohol1 #ajj ,c4c41 and add glycerine1 #ajj ,c4c41 distilled water1 #ajj ,c4c41 ammonia alum1 #b ,gm41 glacial acetic acid1 #aj ,c4c4 ,expose to daylight for at least a month before use1 removing the stopper at intervals4 ,,ehrlich',s ,h,,matoxylin 7,,ammoniated74--,dissolve ammonium carbonate1 #jd ,gm41 and hmatoxylin1 #b ,gm41 in proof spirit1 #dj ,c4c41 and expose to the air in a shallow dish for #bd hours4 ,then make up the volume to #dj ,c4c4 with proof spirit 7warming if necessary to re-dissolve any separate crystals71 and add ammonia alum1 #b ,gm41 dissolved in distilled water1 #hj ,c4c41 together with glycerine1 #ajj ,c4c41 rectified spirit1 #hj ,c4c41 and glacial acetic acid1 #aj ,c4c4 ,,ehrlich-,,biondi ,,mixture 7or ,ehrlich-,biondi-,heidenheim mixture74--,dissolve 7a7 methyl green1 #je ,gm41 in distilled water1 #ajj ,c4c42 7b7 acid fuchsine1 #je ,gm41 in distilled water1 #dj ,c4c42 7c7 orange1 #b ,gm41 in distilled water1 #bjj ,c4c4 ,mix the three solutions and filter before use4 ,stain sections for #ab hours1 then wash1 dehydrate1 clear1 and mount4 ,,ehrlich-,,weigert-,,koch',s ,,gentian-,,violet-,,aniline-,,water4--, aniline water1 #ajj ,c4c41 concentrated alcoholic solution of gentian violet1 #aa ,c4c42 absolute alcohol1 #aj ,c4c4 ,,everard1 ,,demoor1 ,,and ,,massart',s ,h,,matoxylin-,,eosine4--,dissolve alum1 #bj ,gm41 in water1 #bjj ,gm41 by the aid of heat1 then filter1 and after #bd hours add a solution of hmatoxylin1 #a ,gm41 in alcohol1 #aj ,gm4 ,let the solution stand for #h days1 again filter1 and mix with an equal volume of the following solution3--,eosine1 #a ,gm41 alcohol1 #be ,gm41 water1 #ge ,gm41 glycerine1 #ej ,gm4 ,,flemming',s ,,gentian ,,violet ,,method4--,use a concentrated alcoholic solution of ,gentian ,violet diluted with about one half its bulk of water4 ,differentiate the stained objects in alcohol acidulated with about #je per cent4 of hydrochloric acid1 followed by pure alcohol and clove oil4 ,,flemming',s ,,orange ,,method4--,stain for days or weeks in strong alcoholic safranine solution diluted with half its bulk of aniline water 7saturated72 then rinse in distilled water1 differentiate in absolute alcohol containing #ja per cent4 of hydrochloric acid1 stain for #a to #c hours in strong aqueous gentian violet solution1 again wash in distilled water1 and finally treat with concentrated aqueous solution of ,orange4 ,after a few minutes transfer sections to absolute alcohol1 then clear in clove or bergamot oil1 and mount in dammar or balsam4 ,,fol',s ,,ferric ,,chloride ,,fixing ,,and ,,staining ,,process4--,preparations are treated with tincture of ferric chloride diluted with #e to #aj times its bulk of #gj per cent4 alcohol1 and then transfer for #bd hours to alcohol containing a trace of gallic acid4 ,,frey',s ,,fuchsine ,,solution4--,a solution of #jja ,gm4 of crystallised fuchsine1 #bj to #be drops absolute alcohol1 and #ae ,c4c4 of water4 ,,friedlaender',s ,,staining ,,methods4--,cover-glass preparations are treated for #c minutes with a #a per cent4 solution of acetic acid1 and allowed to dry after removal of excess of liquid by filter paper4 ,next place them in gentian violet aniline water 7aniline water1 #ajj ,c4c41 concentrated alcoholic solution of gentian violet1 #aa ,c4c42 absolute alcohol1 #aj ,c4c47 for half a minute1 wash in water1 mount and dry in balsam4 ,sections are kept for #bd hours in a warm place1 in the following solution3--,concentrated alcoholic solution of gentian violet1 #ej ,c4c42 distilled water1 #ajj ,c4c42 glacial acetic acid1 #aj ,c4c4 ,then treat for #a or #b minutes with #ja per cent4 acetic acid1 dehydrate1 clear1 and mount in balsam4 ,,gaffky',s ,,staining ,,methods4--,sections of material hardened in alcohol are left for #bj to #bd hours in a deep blue opaque solution1 freshly made by adding saturated alcoholic solution of methylene blue to distilled water4 ,then wash in distilled water1 dehydrate in absolute alcohol1 clear in turpentine oil1 and mount in balsam4 ,,giacomi',s ,,staining ,,method4--,stain cover-glass preparations for a few minutes in a hot solution of fuchsine1 then place in water containing a few drops of ferric chloride solution1 and afterwards decolourise in strong ferric chloride solution4 ,if any precipitate be formed with the iron solution1 complete the decolourisation in alcohol4 ,counterstain with vesuvine4 ,,gibbes' ,,double ,,staining ,,method4--,well mix magenta1 #b ,gm41 and methylene blue1 #a ,gm41 then add slowly aniline oil1 #c ,c4c41 dissolve in rectified spirit1 #ae ,c4c4 ,subsequently add #ae ,c4c4 of distilled water and keep the stain in a stoppered bottle4 ,cover-glass preparations are placed for #d minutes in the slightly heated stain and sections left for some hours in the stain at the ordinary temperature4 ,afterwards1 wash in methylated spirit until no more colour comes away1 then dehydrate1 clear in cedar oil1 and mount in balsam4 ,,gibbes' ,,magenta ,,stain4--,mix magenta1 #b ,gm42 aniline oil1 #c ,gm42 rectified spirit1 #bj ,c4c42 and distilled water1 #bj ,c4c4 ,,golgi',s ,,sublimated ,,method4--,small cubes of tissue are hardened for #ae to #cj days in ,mller's fluid1 which should be frequently changed4 ,then transfer for #h to #aj days to #jbe to #a per cent4 aqueous mercuric chloride solution1 which must be changed1 as it becomes coloured4 ,if desired1 treat subsequently with weak sodium sulphide solution to darken the stain and make it sharper4 ,after cutting sections from material thus prepared they must be well washed with water4 ,,gram',s ,,stain ,,for ,,bacteria4--,this is prepared by shaking #ae drops of aniline oil with #ae ,gm4 of water1 filtering the solution and adding to the filtrate #d to #e drops of saturated alcoholic solution of gentian violet4 ,or shake #cc ,c4c4 of aniline with #ajj ,c4c4 of distilled water and1 after filtering1 add #aa ,c4c4 of concentrated alcoholic solution of gentian violet and #aj ,c4c4 of absolute alcohol4 ,after preparations have been stained for #a to #c minutes in one of the above they are quickly rinsed in absolute alcohol and then placed in ,gram's solution of iodine in potassium iodine 7iodine1 #a ,gm42 potassium iodine1 #b ,gm42 water1 #cjj ,c4c471 until they have acquired a brown colour4 ,this takes about #a to #c minutes1 and they are next washed in #ij per cent4 alcohol until they become pale yellow1 then dehydrated1 cleared1 and mounted in balsam4 ,counterstain with eosine or vesuvine if desired4 ,,gram',s ,,solution4--,iodine1 #a ,gm42 potassium iodine1 #b ,gm42 distilled water1 #cjj ,gm4 ,,grenacher',s ,,alum ,,carmine4--,dissolve #e ,gm4 of ammonium alum in #ajj ,c4c4 of distilled water1 add #a ,gm4 of carmine1 and boil for #bj minutes1 filter when cool1 and add distilled water to make up to #ajj ,c4c4 ,,grenacher',s ,,alcoholic ,,borax ,,carmine4--,dissolve #d ,gm4 of borax in #ajj ,c4c4 of distilled water1 then add #c ,gm4 of carmine1 and heat gently4 ,finally1 add #ajj ,c4c4 of #gj per cent4 alcohol1 filter the solution1 if necessary1 before use4 ,pieces of tissues are stained in this for #a to #c days1 and then transferred to #gj per cent4 alcohol1 containing #je to #a per cent4 of hydrochloric acid4 ,,heidenhain',s ,h,,matoxylin ,,method4--,dissolve 7a7 hmatoxylin1 #a ,gm41 in distilled water1 #cjj ,c4c42 7b7 potassium chromate1 #a ,gm41 in distilled water1 #bjj ,c4c4 ,small pieces of tissue hardened in alcohol or picric acid are placed in 7a7 for #ab to #bd hours1 and then transferred for a similar length of time to 7b74 ,wash thoroughly in water1 dehydrate in alcohol1 and imbed in paraffin4 ,,henle',s ,,stain 7for nervous tissue74--,sections are left in palladium chloride solution 7#a3cjj to #a3fjj7 till they are of a straw colour1 then rinsed in water and stained with strong ammonia carmine4 ,,henneguy',s ,,alum ,,carmine4--,excess of carmine is boiled in saturated solution of potash alum1 and #aj per cent4 of glacial acetic acid added on cooling4 ,allow to settle for some days1 and then filter4 ,,henneguy',s ,,permanganate ,,method4--,treat sections for #e minutes with #a per cent4 potassium permanganate solution1 then wash in water and stain with safranine1 rubin1 gentian violet1 vesuvine1 preference being given to a safranine solution prepared with aniline water4 ,,hermann',s ,,platino-,,aceto-,,osmic ,,mixture4--,mix #ae parts of #a per cent4 platinic chloride solution1 #a part of glacial acetic acid1 and #b or #d parts of #b per cent4 osmic acid4 ,,hertwig',s ,,macerating ,,fluid4--,mix equal parts of #jje per cent4 osmic acid1 and #jb per cent4 acetic acid4 ,medus are treated with this mixture for #b or #c minutes1 then washed in #ja per cent4 acetic acid until free from osmic acid4 ,leave them for #bd hours in the dilute acetic acid1 then wash in water1 stain with ,beale's carmine1 and mount in glycerine4 ,for ,actini use #jjd per cent4 osmic acid and make both solutions with sea water4 ,wash out with #jb per cent4 acetic acid1 and stain with picro-carmine4 ,,hessert',s ,,method ,,for ,,staining ,,flagella4--,fix the film by treating cover-glass preparations with a saturated alcoholic solution of mercuric chloride1 wash1 and stain for #cj or #dj minutes in a hot #aj per cent4 aqueous solution of saturated alcoholic solution of fuchsine4 ,,hoffmann',s ,,blue ,,stain4--,dissolve #a ,gm4 of ,hoffmann's blue in #bj ,c4c4 of rectified spirit and #hj ,c4c4 of distilled water1 then add #je ,c4c4 of glacial acetic acid4 ,as a nuclear stain immerse sections for #aj minutes or more1 rinse in water1 wash in #ij per cent4 alcohol1 dehydrate1 clear1 and mount in balsam4 ,to stain sieve areas1 less time is required1 #e to #aj minutes1 rinse in distilled water1 and mount in glycerine2 or dehydrate1 clear1 and mount in balsam4 ,,hoyer',s ,,shellac ,,injection ,,mass4--,dissolve shellac in #hj per cent4 alcohol to the consistency of a thin syrup1 and strain through muslin of medium thickness4 ,colour with aniline colours in alcoholic solution1 or by means of vermilion or other pigment suspended in alcohol4 ,,hoyer',s ,,silver ,,nitrate ,,gelatine ,,mass4--,mix a concentrated solution of gelatine with an equal volume of a #d per cent4 silver nitrate solution and warm1 then add a very small quantity of aqueous pyrogallic acid solution to reduce the silver salt1 and add chloral and glycerine as in the carmine gelatine mass4 ,,hoyer',s ,,silver ,,stain4--,add ammonia to a solution of silver nitrate of known strength1 until the precipitate formed just re-dissolves1 then dilute the solution until it contains #jge to #jej per cent4 of the salt4 ,,kaiser',s ,,bismarck ,,brown ,,stain4 ,sections are stained for #dh hours1 at a temperature of #fj ,c41 in a saturated solution of ,bismarck brown in #fj per cent4 alcohol1 and washed out in #fj per cent4 alcohol containing #b per cent4 of ,h4,c4,l41 or #c per cent4 of acetic acid4 ,,kaiser',s ,,nerve ,,stain4--,this is a modification of ,weigert's process4 ,the material is hardened in ,mller's solution for #b or #c days1 then cut into slices #b to #d ,mm4 thick1 and treated with the solution for #e or #f days more4 ,subsequently immerse in ,marchi's solution for #h days1 then wash1 pass through alcohol1 and imbed in celloidin4 ,sections are mordanted for #e minutes in the following mixture3--,solutions of ferric chloride1 #a part2 distilled water1 #a part2 rectified spirit1 #h parts4 ,next wash in ,weigert's hmatoxylin1 and warm in a fresh quantity of the same for a few minutes1 wash with water1 differentiate in ,pal's solution1 and neutralise the oxalic acid by washing in water containing a little ammonia4 ,,kaiser',s ,,stain ,,for ,,the ,,spinal ,,cord4--,sections are stained for a few hours in solution of nphthylamine brown1 #a part1 in water1 #bjj parts1 and alcohol1 #ajj parts4 ,afterwards wash with alcohol and clear with origanum oil4 ,,kallin',s ,,neurological ,,method4--,dissolve hydroquinone1 #e ,gm41 sodium sulphite1 #dj ,gm41 and potassium carbonate1 #ge ,gm41 in #be ,gm4 of distilled water4 ,at the time of using1 dilute this solution with one-third to one-half its bulk of absolute alcohol2 immerse sections of silvered material for several minutes until reduction is complete4 ,then place them in #gj per cent4 alcohol for #aj to #ae minutes1 and subsequently leave in aqueous solution of sodium hyposulphite 7#a3e7 for #bd hours or more4 ,finally dehydrate and mount4 ,carmine may be used as an afterstain4 ,,kleinenberg',s ,,solution 7,improved ,formula74--,hmatoxylin1 #b-a_/b ,gm42 crystallised calcium chloride1 #bj ,gm4 in #aj ,c4c4 of distilled water2 alum1 #c ,gm4 in #af ,c4c4 of distilled water2 rectified spirit1 #bdj ,c4c4 ,dissolve the calcium chloride and alum in their respective quantities of water by the aid of heat2 mix the solutions and immediately dilute with rectified spirit2 after an hour filter and add the hmatoxylin4 ,this makes a good working solution which keeps well4 ,of course it contains the alumina in solution1 not as alum but aluminium chloride4 ,if in special cases the colour is considered too strong1 the dilution 7when staining in bulk7 must be made with some of the solution to which hmatoxylin has not been added4 ,,koch',s ,,method ,,for ,,staining ,,flagella4--,immerse cover-glass preparations in a #a per cent4 aqueous solution of hmatoxylin1 then transfer to a #e per cent4 solution of chromic acid or to ,mller's fluid2 dry and mount in balsam4 ,,koch-,,ehrlich1 ,,bacilli4--,place sections1 or cover-glass preparations1 for at least #ab hours in gentian violet1 or fuchsine aniline water 7aniline water1 #ajj ,c4c42 concentrated alcoholic solution of gentian violet1 or fuchsine1 #aa ,c4c42 absolute alcohol1 #aj ,c4c471 then immerse in a mixture of pure nitric acid 7sp4 gr4 #adb71 #aj ,c4c41 and distilled water1 #cj ,c4c41 for some seconds4 ,rinse in #fj per cent4 alcohol for a few minutes1 and then counterstain with vesuvine 7vesuvine1 #je ,gm42 rectified spirit1 #bj ,c4c42 distilled water1 #hj ,c4c47 after gentian violet2 or methylene blue 7methylene blue1 #jbe ,gm42 rectified spirit1 #bj ,c4c42 distilled water1 #hj ,c4c47 after fuchsine4 ,finally rinse in water1 dehydrate1 clear1 and mount in balsam4 ,according to ,squire1 who points out that nitric acid is apt to injure delicate sections1 ,watson ,cheyne recommends that sections should be transferred from fuchsine aniline water to distilled water1 then rinsed in alcohol1 and placed in the following contrast stain for #a or #b hours3--,saturated alcoholic solution of methylene blue1 #bj ,c4c42 distilled water1 #ajj ,c4c42 formic acid 7sp4 gr4 #ab71 #a ,c4c4 ,k,,hne',s ,,carbolic ,,methylene ,,blue4--,rub up #ae ,gm4 of methylene blue with #aj ,c4c4 of absolute alcohol1 and add #ajj ,c4c4 of a #e per cent4 aqueous solution of carbolic acid4 ,k,,hne',s ,,methyl ,,violet ,,solution4--,dissolve #a ,gm4 of methyl violet in #ij ,c4c4 of distilled water and #ajj ,c4c4 of alcohol4 ,k,,hne',s ,,aniline ,,oil ,,solutions4--,rub up as much methylene blue1 methyl green1 or safranine as will go upon the point of a knife1 with #aj ,c4c4 of aniline1 and allow to settle4 ,k,,hne',s ,,carbolic ,,fuchsine ,,or ,,black ,,brown4--,dissolve #a ,gm4 of fuchsine or black brown in #aj ,c4c4 of absolute alcohol1 and add #ajj ,c4c4 of a #e per cent4 aqueous solution of carbolic acid4 ,k,,hne',s ,,modification ,,of ,,gram',s ,,method4--,stain nuclei with carmine1 then treat sections for #e minutes in methyl violet solution1 diluted one-sixth with a #a per cent4 aqueous solution of ammonium carbonate1 or in a solution of ,victoria blue1 #jbe ,gm41 in rectified spirit1 #bj ,c4c41 and distilled water1 #hj ,c4c4 ,next rinse thoroughly in water and transfer to ,grain's solution for #b to #c minutes2 again rinse in water and extract excess of stain with solution of yellow fluorescine1 #a ,gm41 in absolute alcohol1 #ej ,c4c4 ,finally1 pass through pure alcohol1 aniline1 terebene1 and xylol1 and mount in balsam4 ,l,,ffler',s ,,solution4--,concentrated alcoholic solution of methylene blue1 #cj ,c4c42 solution of 7caustic potash7 potassium hydrate 7#a3aj1jjj71 #ajj ,c4c4 ,mix and filter shortly before use4 ,sections are stained for a few minutes 7tubercle sections for some hours71 and excess of stain can be removed by immersion for a few seconds in #je per cent4 acetic acid4 ,dehydrate in absolute alcohol1 clear in cedar oil1 and mount in balsam4 ,lffler found that most bacteria stained better in this solution than in the weaker solutions used by ,koch for turbercle bacillus4 ,,lavdowsky',s ,,bilberry ,,juice ,,stain4--,well wash the fresh berries of ,vaccinium myrtillus1 then express the juice and mix with twice its bulk of distilled water1 mixed with a little #ij per cent4 alcohol4 ,heat for a short time and filter whilst warm4 ,dilute the stain with #b or #c volumes of distilled water before use4 ,,lee',s ,,formaldehyde ,,solutions4--7#a7 ,mix #a part of #dj per cent4 formaldehyde solution with two parts of #a per cent4 chromic acid solution1 and add #d per cent4 of acetic acid4 7#b7 ,mix #a part of #dj per cent4 formaldehyde solution with #d parts of #a per cent4 platinic chloride solution1 and add #b per cent4 of acetic acid4 ,,lee',s ,,osmic ,,acid ,,and ,,pyrogallol ,,stain4--,fix the tissues in ,hermann's mixture or ,flemming's mixture for half an hour1 then place in a weak solution of pyrogallol1 which may be prepared with alcohol in some cases4 ,safranine may be used as a second stain4 ,,martinotti',s ,,picro-,,nigrosine ,,stain4--,pathological objects are stained for #b or #c hours or days1 in a saturated solution of nigrosine in saturated alcoholic picric acid solution4 ,then wash out in a mixture of #a part of formic acid with #b parts of alcohol until the grey matter appears clearly differentiated from the white to the naked eye4 ,,mayer',s ,,aluminium ,,chloride ,,carmine4--,dissolve #a ,gm4 of carminic acid and #c ,gm4 of aluminium chloride in #bjj ,c4c4 of water4 ,,mayer',s ,,berlin ,,blue ,,injection4--,add a solution of #aj ,c4c4 of tincture of ferric chloride in #ejj ,c4c4 of water1 to a solution of #bj ,gm4 of potassium ferrocyanide in #ejj ,c4c4 of water1 allow to stand for #ab hours1 decant1 wash the deposit for #a or #b days with distilled water until the washings come through dark blue1 then dissolve the blue in about a litre of water4 ,,mayer',s ,,carmalum4--,dissolve #a ,gm4 of carminic acid and #aj ,gm4 of alum in #bjj ,c4c4 of distilled water2 decant1 or filter1 and add a few crystals of thymol1 #ja per cent4 of salicylic acid1 or #je per cent4 of sodium salicylate4 ,a weaker solution contains #c to #e times as much alum and #e times as much water4 ,,merbel',s ,,carmine ,,and ,,indigo ,,fluids 7give a blue and red stain1 and are very selective74--,to prepare the red fluid1 take--,carmine1 #b dr42 borax1 #b dr42 distilled water1 #d ozs4 ,for the blue fluid1 take--,indigo carmine1 #b dr42 borax1 #b dr42 distilled water1 #d ozs4 ,mix each in a mortar1 and allow it to stand1 then pour off the supernatant fluid4 ,if the sections have been hardened in chromic acid1 picric acid1 or a bichromate1 they must be washed in water till no tinge appears4 ,place them in alcohol for fifteen or twenty minutes1 then in the two fluids mixed in equal proportions1 after which wash them in a saturated aqueous solution of oxalic acid1 where they should remain a rather shorter time than in the staining fluids4 ,when sufficiently bleached1 wash them in water1 to get rid of the acid1 then pass them through spirit and oil of cloves1 and mount in balsam or dammar4 ,,mitrophanow',s ,,gold ,,process ,,for ,,prickle-,,cells ,,and ,,intercellular ,,canals4--,wash the tail of an axolotl larva with distilled water1 place for an hour in a watch-glassful of #jbe per cent4 solution of gold chloride1 containing #a drop of hydrochloric acid2 wash1 and reduce in a mixture of #a part of formic acid with #f parts of water4 ,,mitrophanow',s ,,maceration ,,method ,,for ,,epithelium4--,fix the embryo for #ae minutes in #c per cent4 nitric acid2 then place for an hour in a mixture of alcohol1 #a volume1 and water #b volumes1 and finally treat with stronger alcohol for #bd hours to separate the epidermis4 ,m,,ller',s ,,berlin ,,blue ,,for ,,injections4--,precipitate a concentrated solution of ,berlin blue by means of #ij per cent4 alcohol4 ,the precipitate is very finely divided1 whilst the fluid is perfectly neutral and much easier to prepare than that of ,beale4 ,,neilsen',s ,,solution ,,of ,,methyl ,,violet4--,dissolve fuchsine1 #a part1 in alcohol1 #aj parts1 and add a #e per cent4 watery solution of carbolic acid1 #ajj parts4 ,,neisser',s ,,double-,,staining ,,for ,,spore-,,bearing ,,bacilli4--,cover-glass preparations are immersed for #bj minutes in fuchsine aniline water 7concentrated alcoholic solution of fuchsine1 #aa ,c4c42 absolute alcohol1 #aj ,c4c42 aniline water1 #ajj ,c4c42 then heat to #hj or #ij ,c42 next rinse in water1 alcohol1 or weak acid1 according to the nature of the bacilli1 counterstain with aqueous solution of methylene blue1 rinse in water1 dry and mount in balsam74 ,the spores are stained red and the rest of the bacilli blue4 ,,nissl',s ,,fuchsine ,,stain ,,for ,,nerve ,,cells4--7#a7 ,fresh material in pieces measuring #a ,c4c4 are hardened in a 8chromic solution in #gj per cent4 alcohol0 for #b days1 then transferred to absolute alcohol for #e days1 and afterwards cut4 ,stain the sections singly in a saturated solution of fuchsine1 warming in a deep watch-glass until vapours begin to be given off4 ,next plunge the section into absolute alcohol for #a or #b minutes1 then place it on a slide1 flood with clove oil1 and when no more colour is given off1 drain and mount in balsam4 ,,ohlmacher',s ,,formaldehyde ,,staining4--,formalin in a #b to #d per cent4 solution is used as a mordant for tar colours4 ,the tissues may be mordanted separately by treatment for #a minute or longer1 or the formalin may be added to the stain4 ,dissolve #a ,gm4 of fuchsine in #aj ,c4c4 of absolute alcohol1 and add to #ajj ,c4c4 of #d per cent4 formalin solution4 ,or1 add saturated alcoholic solution of gentian violet or methyl violet #e ,b4 to the formalin solution1 in the proportion of #a3aj4 ,in the case of methylene blue1 dissolve #a ,g4m4 in #ajj ,c4c4 of the formalin solution4 ,sections stain in half a minute1 and are said to resist alcohol much more than if formalin were not used4 ,,oppitz',s ,,silver ,,staining4--,reduction is very rapidly effected by placing the preparations for #b or #c minutes in a #jbe to #je per cent4 solution of chloride of tin4 ,,pal',s ,h,,matoxylin ,,stain4--,dissolve #jge ,gm4 of hmatoxylin in #ij ,c4c4 of distilled water and #aj ,c4c4 of absolute alcohol4 ,just before use add saturated solution of lithium carbonate in the proportion of #c drops to each #aj ,c4c4 of hmatoxylin solution4 7,see ,weigert47 ,,pal',s ,h,,matoxylin ,,method4--,proceed at first as in ,weigert's process for nerve fibre1 omitting the copper bath1 and stain in ,pal's hmatoxylin solution 7see above7 for #e or #f hours4 ,then wash the sections in distilled water 7containing a trace of lithium carbonate if the sections are not deep blue71 next treat for #ae to #cj seconds with a #jbe per cent4 potassium permanganate solution1 rinse in water1 and decolourise in ,pal's bleaching solution4 7,if black spots appear replace in the permanganate solution1 again bleach1 and wash for #ae minutes in water47 ,the grey substance of the sections is decolourised in a few sections2 the sections should then be well washed out1 and may be double-stained with picro-carmine or acetic acid carmine 7see ,schneider71 ,magdala red1 or eosine4 ,the nuclei may be stained with alum carmine4 ,finally dehydrate1 clear1 and mount4 ,,pal-,,exner',s ,,osmic ,,acid ,,method4--,spinal cord or brain in #jbe inch cubes is immersed in #je per cent4 osmic acid solution for #b days1 the solution being changed each day2 then wash in water1 transfer to absolute alcohol1 and imbed in celloidin or paraffin4 ,place sections as cut in glycerine1 then wash in water1 treat with potassium permanganate and ,pal's solution1 as in ,pal's hmatoxylin method1 counter-stain with carmine1 dehydrate1 clear1 and mount in balsam4 ,,plant',s ,,method ,,of ,,staining ,,actinomycosis4--,sections are placed for #aj minutes in ,gibbes' magenta solution or carbolic fuchsine1 at #de ,c42 next they are rinsed in water and placed in saturated aqueous solution of picric acid1 mixed with an equal volume of absolute alcohol1 for #e or #aj minutes2 they are then washed once more1 passed through #ej per cent4 alcohol into absolute alcohol1 cleared in cedar oil1 and mounted in balsam4 ,,ranvier',s ,,lemon ,,juice ,,method4--,soak pieces of fresh tissue in fresh lemon juice until transparent 7#e to #aj minutes71 then rapidly wash in distilled water1 treat for #aj to #fj minutes with #a per cent4 gold chloride solution1 again wash and expose to light in a bottle containing #ej ,c4c4 of distilled water and #b drops of acetic acid4 ,reduction is complete in #bd to #dh hours4 ,if it is not desired to retain the superficial epithelium1 reduction may be more completely effected in the dark1 by treatment with formic acid 7sp4 gr4 #ab71 diluted with #c times its volume of water4 ,the lemon juice in the above process may be replaced by an aqueous solution of citric acid 7#dj grains in each ounce74 ,,ranvier',s ,,picro-,,carmine4--,carmine1 #a part2 distilled water1 #aj parts2 solution of ammonia1 #c parts2 mix and add of a cold saturated solution of picric acid #bjj parts4 ,,renaut',s ,h,,matoxylic ,,eosine4--,mix #cj ,c4c4 of concentrated aqueous solution of eosine1 #dj ,c4c4 of saturated alcoholic solution of hmatoxylin 7which has been kept for some time and precipitated71 and #acj ,c4c4 of saturated solution of potash alum in glycerine 7sp4 gr4 #abf74 ,stand for #e or #f weeks in a partially covered vessel1 protected from dust1 until the alcohol is evaporated1 and then filter4 ,the filtrate can be diluted with glycerine if desired4 ,mount objects in this fluid diluted with #a or #b volumes of glycerine1 or1 stain separately for some days or weeks and mount in balsam1 after washing in alcohol charged with a sufficient quantity of eosine4 ,,ranvier ,,and ,,vignal',s ,,osmium ,,mixture4--,fix tissues in a freshly-prepared mixture of equal volumes of #a per cent4 osmic acid and #ij per cent4 alcohol1 then wash out in #hj per cent4 alcohol1 next with water1 and stain for #dh hours with picro-carmine or hmatoxylin4 ,this method has been applied to the histology of insects4 ,,renaut',s ,,glycerine ,h,,matoxylin4--,to a saturated solution of potash alum in glycerine1 add a saturated solution of homatoxylin in #ij per cent4 alcohol drop by drop1 so as to form a deeply coloured solution4 ,expose to daylight for a week1 and then filter4 ,this solution1 like ,renaut's hmatoxylic cosine1 may be used for mounting unstained sections1 which after some time absorb the colour from the liquid and become stained4 ,,safranine4--,safranine1 #je ,gm42 rectified spirit1 #bj ,c4c42 distilled water1 #hj ,c4c4 ,,sch,,fer',s ,,acid ,,logwood ,,solution is especially useful for certain structures1 as tendon1 cells1 c4 ,it is thus prepared3--,a #a per cent4 solution of acetic acid is coloured by the addition of #ac of its volume of logwood solution4 ,,sch,,fer',s ,,aniline ,,dyes1 whether in aqueous or alcoholic solutions1 give good results1 and are prepared as follows3--,roseanilin or magenta 7#a gr4 to #a oz4 of alcohol71 red2 acetate of mauvein 7#d gr41 alcohol #a oz41 acid nitric #b drops71 blue2 aniline black 7#b gr41 water #a oz471 grey-black2 ,nicholson's soluble blue 7#a-f gr41 alcohol #a oz41 and nitric #b m471 blue4 ,these stains should be used weak2 and after sections are stained they should be passed through alcohol and oil of cloves as rapidly as possible2 otherwise the colour will dissolve out before they can be mounted in balsam4 ,,schultze 7,staining ,bacilli74--,stain sections and cover-glass preparations for some hours in aqueous methylene blue solution1 differentiate in #je per cent4 acetic acid1 dehydrate in alcohol1 clear in cedar oil1 and mount in balsam4 ,,sclavo',s ,,stain ,,for ,,flagella4--,leave the preparations for #a minute in a solution of #a ,gm4 of tannin in #ajj ,c4c4 of #ej per cent4 alcohol2 wash in distilled water2 transfer for #a minute to #ej per cent4 phospho-molybdic acid2 again wash1 and stain for #c to #e minutes in a hot saturated solution of fuchsine in aniline water4 ,then wash in water1 dry on filter paper1 and mount in balsam4 ,,squire',s ,,picro-,,carmine4--7#a7 ,dissolve #a ,gm4 of carmine with a gentle heat in #c ,c4c4 of strong solution of ammonia1 and #e ,c4c4 of distilled water1 then add #bjj ,c4c4 of saturated aqueous solution of picric acid1 heat to boiling1 and filter4 7#b7 ,dissolve #aj ,gm4 of carmine in a solution of #a ,gm4 of caustic soda in #ajjj ,c4c4 of distilled water2 boil1 filter and make up to #ajjj ,c4c4 with water4 ,mix the solution with an equal quantity of water1 and add #a per cent4 aqueous solution of picric acid so long as the turbidity produced disappears on agitation4 ,,squire',s ,,blueing ,,of ,,sections4--,after staining with hmatoxylin1 treat for a few seconds with a solution of sodium bicarbonate 7#a3ajjj7 in distilled water4 ,,valentine 7,fuchsine74--,ether shaken with a solution containing fuchsine is coloured violet after adding ferrous iodide1 but not before4 ,,victoria ,,blue4--,victoria blue1 #jbe ,gm42 rectified spirit1 #bj ,c4c42 distilled water1 #hj ,c4c4 ,,wedl',s ,,orseille ,,or ,,orchella ,,stain4--,mix #e ,c4c4 of acetic acid1 #bj ,c4c4 of absolute alcohol1 and #dj ,c4c4 of distilled water2 then add sufficient archil1 from which excess of ammonia has been driven off1 to form a dark reddish fluid4 ,,weigert',s ,h,,matoxylin4--,dissolve #a part of hmatoxylin in #aj parts of absolute alcohol2 then add #ij parts of distilled water and #a part of aqueous solution 7#a3gj7 of lithium carbonate4 ,,weigert 7,gram's ,method74--,in this modification aniline is substituted for alcohol1 in order to avoid prolonged washing with the latter1 and the process is conducted on a slide4 ,the section is placed on a slide1 stained with a few drops of gentian violet aniline water1 prepared as in ,gram's method1 the excess of fluid removed1 and a few drops of ,gram's solution applied4 ,subsequently remove the liquid by gently blotting it off1 then wash the section by allowing aniline to flow' backwards and forwards over it1 and when colour ceases to come away1 repeat the operation with xylol for about #a minute1 then mount in balsam4 ,,weigert 7,staining in ,actinomycosis74--,immerse sections for #a hour in ,wedl's ,orseille stain1 then quickly rinse with alcohol and counterstain with gentian violet4 ,if it be desired to stain the mycelium also1 afterwards submit the sections to ,weigert's modification of ,gram's method4 ,see page #cce4 ,,weigert 7,staining ,brain ,tissue74--,pieces of brain and spinal cord are hardened in bichromate solution1 followed by alcohol1 then imbedded in celloidin or gum4 ,if imbedded in celloidin1 the pieces are subsequently taken from the spirit in which they are immersed1 and placed for one or two days in saturated aqueous solution of copper acetate1 diluted with an equal bulk of water1 the mixture being kept at about #dj ,c4 ,afterwards transfer the pieces to #hj per cent4 alcohol until required for cutting4 ,or1 the sections can be cut first1 and then treated with copper acetate4 ,to stain the sections1 after being well washed in #ij per cent4 alcohol1 they are transferred to ,weigert's hmatoxylin and left from a few hours to two days1 according to the differentiation required4 ,when opaque and of a deep blue-black colour1 they should be well washed for two or three days in distilled water4 ,next decolourise for #je to #b hours in a solution of #b ,gm4 of borax and #be ,gm4 of potassium ferrocyanide in #bjj ,c4c4 of water4 ,as soon as the grey and white substances are sharply defined1 again wash the sections in water for half an hour1 then dehydrate1 clear1 and mount in balsam4 ,,woodhead',s ,,method ,,of ,,staining ,,tubercle ,,bacilli4--,take a small quantity of sputum rich in bacilli1 and spread it out by pressure between two cover-glasses1 so that a fairly thin film remains on each4 ,then carefully slip one over the other until they come apart4 ,thoroughly dry the covers1 and pass them rapidly three times through the flame of a spirit lamp1 care being taken not to scorch the film1 then float them face downwards on the staining solution1 which has been previously prepared and filtered into a watch-glass4 ,the stain should consist of saturated alcoholic solution of basic fuchsine1 #a part2 absolute alcohol or rectified spirit1 #aj parts2 carbolic acid solution 7#e per cent471 #aj parts4 ,leave the preparations in the watch-glass for #ab to #bd hours1 unless time is an object4 ,in the latter case heat the fluid gently until vapour is given off1 then drop the films on the surface1 and leave them for #c to #e minutes only4 ,next transfer the covers to an aqueous solution of sulphuric acid 7#be per cent471 and when decolourisation is complete1 as evidenced by the pink colouration not returning when the specimens are plunged into a bowl of tap-water containing a single drop of ammonia solution1 thoroughly rinse in the slightly alkaline water and counter-stain in an aqueous solution of methylene blue4 ,finally1 wash in water1 carefully dry and mount in ,canada balsam4 ,the bacilli should stand out as bright red rods on a blue background of cells4 ,,ziehl-,,neelsen 7,staining ,bacilli74--,sections are removed from weak spirit into ,neelsen's carbolic fuchsine and left for #aj or #ae minutes2 next decolourise in sulphuric acid 7sp4 gr4 #ahd7 or nitric acid 7sp4 gr4 #adb7 diluted with #c volumes of water1 rinse in #fj per cent4 alcohol1 and wash in a large volume of water to remove the acid4 ,tubercle and leprosy bacilli are the only micro-organisms that can retain the stain after treatment with acid4 ,if the presence of traces of nitrous acid in the nitric acid be suspected1 ,squire recommends the use of saturated aqueous solution of sulphanilic acid mixed with one-third its bulk of nitric acid4 ,the sulphanilic acid destroys any free nitrous acid1 which would otherwise exercise a bleaching action on the fuchsine-stained bacilli4 ,the sections may be counterstained with a solution of #je ,gm4 of methyl green 7or #jbe ,gm4 of methylene blue7 in #bj ,c4c4 of rectified spirit and #hj ,c4c4 of distilled water4 ,finally dehydrate in absolute alcohol1 clear in cedar oil1 and mount in balsam4 ,,appendix ,d4 ,,the ,,metric ,,system ,,of ,,weights ,,and ,,measures4 ,the initial unit of the ,metric ,system is the ,metre or unit of length1 which represents one ten millionth part of the earth's quadrant1 or one forty-millionth part of the circumference of the earth around the poles4 ,the multiples and sub-divisions of this and all the other units are obtained by the use of decimals1 and for this reason the system is also known as the decimal system4 ,the multiples are designated by the ,greek prefixes1 deca #aj2 hecto #ajj2 kilo #ajjj2 myria #aj1jjj4 ,for the sub-divisions ,latin prefixes are employed1 as follows3 deci #a_/aj2 centi #a_/ajj2 milli #a_/ajjj4 ,thus for measures of length we have the following expressions1 showing the abbreviations commonly employed1 and the equivalents in the ordinary ,english standards of measurement-- #a ,myriametre1 ,mm4 #aj1jjj4j ,m4 #f4bacg miles4 #a ,kilometre1 ,km4 #a1jjj4j ,m4 #j4fbac mile4 #a ,hectometre1 ,hm4 #ajj4j ,m4 #aji4cfb yards4 #a ,decametre1 ,dm4 #aj4j ,m4 #cb4hjhf feet4 #a ,metre1 ,m4 #a4j ,m4 #ci4cgjd inches4 #a ,decimetre1 dm4 #j4a ,m4 #c4icgj #a ,centimetre1 cm4 #j4ja ,m4 #j4cicg #a ,millimetre1 mm4 #j4jja ,m4 #j4jcic ,from the unit of linear measure of metre is derived the unit of the measure of capacity or ,,litre4 ,this represents the cube of one-tenth part of a metre1 or a cubic decimetre1 and its multiples and sub-divisions with their corresponding equivalents in ,imperial fluid measure are as follows3-- #a ,myrialitre1 ,ml4 #aj1jjj4j ,l4 #bbjj4iffg imperial gallons4#ia #a ,kilolitre1 ,kl4 #a1jjj4j #bbj4jiff #a ,hectolitre ,hl4 #ajj4j #bb4jjif #a ,decalitre1 ,dl4 #aj4j #b4bjji #a ,litre1 ,l4 #a4j #ce4baed fluid ounces imperial4 #a ,decilitre1 dl4 #j4a #c4ebae #a ,centilitre1 cl4 #j4ja #j4ceba #a ,millilitre1 ml4 #j4jja #j4jceb or #a ,cubic ,centimetre1 ccm4 #j4jja ,l4 #j4jceb ,the unit of weight in the metric system is the ,,gramme4 ,this is also derived from the metre1 and represents the weight of one cubic centimetre1 of water1 or the quantity of distilled water1 at its maximum density1 #d ,c4 7#cib ,f471 which would fill the cube of one-hundredth part of a metre4 ,the relative value of the gramme1 together with its multiples and sub-divisions1 as compared with the ,english standards of weight1 may be seen from the following table3-- #a ,myriagramme1 ,mg4 #aj1jjj4j ,gm4 #bb4jdfa pounds4 #a ,kilogramme1 ,kg4 #a1jjj4j #b4bjdf #a ,hectogramme1 ,hg4 #ajj4j #c4ebgc ounces avoir4 #a ,decagramme1 ,dg4 #aj4j #aed4cbce grains4 #a ,gramme1 ,gm4 #a4j #ae4dcbc #a ,decigramme1 dg4 #j4a #a4edcb #a ,centigramme1 cg4 #j4ja #j4aedc #a ,milligramme1 mg4 #j4jja #j4jaed ,the expression micro-millimetre is used for microscopic measurements1 and denotes the thousandth part of a millimetre4 ,of the measures of capacity1 the terms most commonly employed are the litre and the cubic centimetre4 ,thus a decalitre may also be expressed as #aj litres1 a centilitre as #aj cubic centimetres1 etc4 ,of the metric weights the gramme and its fractional parts1 with their respective prefixes1 are much used in analytical work4 ,the kilogramme is largely employed in commercial transactions1 and is commonly abbreviated kilo4 ,as a comparison of the values of some of the more frequently employed expressions of the metric and ,english systems1 the following may be found convenient for reference3-- #a mm4 7millimetre7 #a_/be of an inch4 #a cm4 7centimetre7 #b_/e of an inch4 #a inch #be millimetres or #b-a_/b centimetres4 #a mg4 7milligramme7 #j4jaedc grain 7or approx4 #a_/fd grain74 #a gm4 7gramme7 #ae4dcbd grains4 #a ,kg4 78,kilo0 or kilogramme7 #b lbs4 #c-a_/d ozs4 av4 #a pound avoir4 #dec1eib grammes4 #a ounce avoir4 #bh1cej grammes4 #a grain #j4jfdgi gramme or #fd4gi milligrammes4 #a cc4 7cubic centimetre7 #af4i minims ,imperial measure4 #a ,l4 7litre7 #ce4ba fluid ounces ,imperial measure1 or #cc4hae fluid ounces ,wine measure4 #a fluid ounce ,imperial measure #bh4cej grammes4 #a pint ,imperial measure #efg4j grammes4 #a gallon ,imperial measure #d4ecf litres1 or #aj lbs4 avoir4 of pure water at #fb ,f4 and under an atmospheric pressure of #cj inches of mercury4 ,it may be well to bear in mind that on the ,continent liquids are always weighed1 not measured4 ,,appendix ,e4 ,,comparison ,,between ,,the ,,centigrade ,,and ,,fahrenheit ,,thermometers4 ,f4 ,c4 #bab #ajj #bjj #ic4c #aej #fe4f #aab #dd4d #aaj #dc4c #ajh #db4b #ajf #da4a #aje #dj4e #ajd #dj #ajc #ci4d #ajb #ch4i #aja #ch4c #ajj #cg4h #ii #cg4b #ih #cf4g #if #ce4f #id #cd4d #ib #cc4c #ij #cb4b #hh #ca4a #hf #cj #hd #bh4i #hb #bg4h #hj #bf4g #gh #be4f #gf #bd4d #gd #bc4c #gb #bb4b #gj #ba4a #fh #bj #ff #ah4i #fd #ag4h #fb #af4g #fj #ae4f #eh #ad4d #ef #ac4c #ed #ab4b #eb #aa4a #cb #j #be -#c4i ,illustration3 ,dr4 ,culpeper's ,microscope #agch4 ,,index4 ,abb on microscopical vision1 #cg ,abb's apertometer1 #ei ---- condenser1 #agf ---- stereoscopic eye-pieces1 #fd ---- test-plate1 #afd ,aberration1 chromatic1 #be ---- of the eye1 chromatic1 #cc ---- spherical1 #bc ,abraxas grossulariata1 #eih ,absolute alcohol as a hardening reagent1 #bhg ,acaras domesticus1 #fbe ,accessories of the microscope1 #aig ,achromatic condenser1 ,beck's1 #ahj ---- ---- ,gillett's1 #agc ---- ---- method of using1 #aij ---- ---- ,powell's1 #agh ---- ---- ,ross's1 #agf ---- ---- ,smith ,beck's1 #agc ---- ---- ,watson's1 #agg ,achromatic objective1 the1 #aeb ,acineta1 #die ,actini1 #ebg ,actinophrys-sol1 #dhi ,adams's book on the microscope1 #h ,adipose tissue1 #fdd dogoniace1 #dji ,aerobic spores1 #cii ,agar-agar1 to prepare nutrient1 #ccj ,air bubbles1 #cdh ,alcyonella1 #ecd ,alg1 #cii ---- media for preserving1 #cdc ---- red1 #dac ,alvarez's discovery of bacillus1 #cib ,amici prism1 the1 #aij ,amba1 #dhj ,amphibian changes1 #ffi ,amphistoma1 #egj ,amyot finder1 the1 #bje ,anacharis alsinastrum1 #dai ,anemones1 sea1 #ebf ,angle of vision1 #gb ,anguillula1 #efg ,animal structures1 staining1 #bib ,annulosa1 #efb ,antenn of insects1 #ehd ,antenna of silkworm moth1 #fje ,anthrax bacillus1 #cfi ,anthrozoa1 #ebc ,apertometer1 ,abb's1 #ei ,aperture1 definition of1 #de ---- measurement of1 #eg ---- numerical1 #eg ---- table1 #eh ,aphides1 #ehg ,aphrophora bifasciata1 #fah ,apis mellifica1 #eih ,aplysiid1 #edi ---- dipilans1 #edi ,apparatus for mounting1 #ceb ,appendices1 #fgc ,arachnid1 #fah ,aragonite1 #bcb ,arcella1 #dhc ,arenicola1 #egg ,argyroneta aquatica1 #fba ,artemi1 #eha ,arteries1 #fbb ,artery-needle1 #cjc ,arthropoda1 #ehc ,arthrospores1 #cff ,ascidian1 #ffi ,astroides calyculcaris1 #ebi ,bab's method of staining bacteria1 #ccd ,bacillus1 anthrax1 #cfi ---- of plague1 #cgb ---- ---- in rat's blood1 #cgb ---- splenic fever1 #cfi ---- typhoid1 #cgj ,bacteria1 #cag ---- aerobic1 #cii ---- classification of1 #cgc ---- ,cohn on multiplication of1 #cfg ---- cultivation of1 #cbg ---- ---- in tubes1 #cca ---- ---- on plates1 #cca ---- faculties of1 #cgc ---- in butter1 #cic ---- in cheese1 #cic ---- in milk1 #cic ---- in sections of tissue1 #ccg ---- invasion of potato-tubers by1 #cih ---- microscopical examination of1 #ccc ---- phosphorescent1 #cgc ---- reproduction of1 #cfe ---- size of1 #cfe ---- staining1 #ccd ---- ,winogradsky's investigations of1 #cih ,bacterial action in tanning skins1 #cic ---- fermentations1 #cia ,bacteriological investigations1 apparatus for1 #cah ---- ---- mounting media1 #cbj ---- ---- reagents used1 #cbj ---- microscope1 the1 #ace ,bacteriology of the dairy1 #cic ,baker's advanced student's microscope1 #abc ---- collecting stick1 #cej ---- histological microscope1 #abe ---- micro-photographic apparatus1 #bag ---- microscope lamp1 #aia ---- microscopes1 #abj ---- ,nelson condenser1 #ahd ---- ---- model microscope1 #abj ---- objectives1 #afh ---- student's condenser1 #ahd ,baird1 ,dr41 on daphnia1 #eha ,barnacle1 #eci ,bartley's warm-stage1 #bha ,batrachosperm1 #dji ,beck's binocular dissecting microscope1 #aja ---- ---- ,national microscope1 #ii ---- complete microscope lamp1 #bjb ---- compressor1 #bge ---- disc-holder1 #aih ---- large ,continental model microscope1 #ih ---- microscopes1 #ie ---- objectives1 #afg ---- pathological microscope1 #ie ---- ,star microscope1 #aja ,beggiatoa1 #djj ,benjamin ,martin's microscope1 #e ,beroid1 #eai ,biaxial crystals1 #bbh ,bilharzia hmatobra1 #egc ,binocular microscope1 advantage of1 #fi ---- ---- ,carpenter on1 #fi ---- ---- ,nachet's1 #fb ---- ---- ,pillischer's1 #abh ---- ---- ,riddell's1 #fb ---- ---- ,stephenson's erecting1 #ga ---- ---- ,wenham's1 #fe ---- vision1 #fj ,bismarck-brown for staining protoplasm1 #cjf ,bivalves1 #ech ,bleaching process1 #cae ,blood as a test1 #bfc ---- circulation of1 in frog's foot1 #ffe ---- ---- ---- tadpole1 #ffe ---- corpuscles1 #fch ---- ---- double staining1 #bie ---- ---- size of1 #fdj ---- crystals1 #fda ---- spectrum1 #beb ,bombay plague1 #cga ,bone1 #feh ---- of fish1 #ffa ---- of reptilia1 #ffj ---- structure of1 #fei ,borax1 #bca ,boring sponges1 #eac ,botterill's live-trough1 #bgf ,brachiopoda1 #ech ,branchipodid1 #ehj ,brewster's microscope1 #aa ,brittleworts1 #dbg ,browning-,huggins micro-spectroscope1 #bde ,browning's pocket lens1 #gf ,bryophyta1 #ddd ,bryozoa1 #eca ,buchner's experiments on yeast1 #chi ,bull's-eye condensing-lens1 #aii ,butter1 bacteria in1 #cic ,butterfly's tongue1 #fje ---- wings1 #faj ,calc-spar1 #bca ,cambridge rocking microtome1 #bij ,camera lucida1 the1 #bjg ---- ---- the ,abb1 #bjh ---- ---- the ,wollaston1 #bjg ---- ,swift's horizontal1 #bac ,canada balsam1 #bic ,carbonate of lead1 #bcb ,carmine as a nuclear stain1 #cab ,cartilage1 #fee ,catheart's freezing microtome1 #bia ,cedar oil1 use of1 #aga ,cell1 definition of1 #ceh ,cell-making turn-table1 ,walmsley's #cdj ,cells1 epithelial1 #fcf ---- for living objects1 #bgf ---- for mounting1 #cdj ---- live1 #bgg ,cellulose1 #ceg ---- staining1 #cad ,cements1 #cdg ---- list of1 #fgf ,centipedes1 #egh ,cercari1 #ega ,cereal parasites1 #cha ,chtophorace1 #dji ,chara1 fructification of1 #dag ---- mounting1 #cdg ---- vulgaris1 #dae ,charace1 #dae ,cheese1 bacteria in1 #cic ---- mite1 #fbe ,chilinid1 #eea ,chitonid1 #ede ,chloride of gold as stain1 #big ---- of palladium as stain1 #bih ,chromatic aberration1 #be ---- ---- of the eye1 #cc ,chromic acid as hardening reagent1 #bhh ,ciliata1 #dih ,circulation of the blood1 #ffe ,cistula catenata1 #eeh ,cladocera1 #ehj ,clavatella prolifera1 #eba ,clearing agents1 list of1 #fgf ,clepsinid1 #egf ,clion1 #eac ,closterium1 #dbd ---- lunula1 #dbe ,cnidaria1 #eai ,cockchafer's eye1 #eij ,coddington lens1 the1 #gf ,codosiga1 #dig ,clenterata1 #eae ,cohn on multiplication of bacteria1 #cfg ,cole's direction for section cutting1 #bhe ---- section-cutting microtome1 #bhi ,collecting stick1 ,baker's1 #cej ,collection of objects1 #cdi ,compound microscope1 #gh ,compressor1 ,beck's1 #bge ,compressorium1 #bgd ---- ,ross's1 #bge ---- ,rousselet's1 #bge ,concave lenses1 #bc ---- surfaces1 #ag ,condenser1 ,abb's1 #agf ---- ,baker's ,nelson1 #ahd ---- ---- student's1 #ahd ---- ,beck's achromatic1 #ahj ---- ,gillett's achromatic1 #agc ---- method of using1 #aij ---- ,powell's achromatic1 #agh ---- ,ross's achromatic1 #agf ---- ,smith ,beck's achromatic1 #agc ---- ---- substage1 #aic ,condenser1 ,swift's1 #ahc ---- ,watson's achromatic1 #agg ---- ---- parachromatic1 #ahb ---- ,webster-,collins1 #ahf ---- ,wenham's immersion1 #ahi ---- ---- parabolic1 #ahf ,confervace1 #djh ,conjugate foci1 #ag ---- real and virtual1 #ba ,continental microscopes1 #acj ,contrast stains1 #cac ,convex lens1 #ah ,copepoda1 #ehj ,corals1 #eae1 #ebe ---- true1 #ebh ---- typical forms of1 #ecc ,correction collar1 ,lister's1 #aee ,coryne stauridia1 #ecd ,cotton fibres1 #dgd ,cover glass gauge1 ,zeiss's1 #afe ,crinoids1 #edb ,critical angle1 #ad ,crookshank's incubator1 #cbd ---- method of staining bacteria1 #cce ,crustace1 #egh ,crystals1 formation and polarisation of1 #bci ,ctenophora1 #eah ,cuckoo-spit1 #fah ,culex pipiens1 #eif ,cultivation of bacteria1 #cbg ---- of micro-organisms1 #cbg ,cutleria dichotoma1 #dac ,cutting sections of hard woods1 #caf ,cuttle-fish1 #eef ,cyclops1 #ehj ,cyclosis1 phenomenon of1 #cei ,cyclostomata1 #ecg ,cyclotus translucidus1 #eeh ,cydippid1 #eah ,cymba olla1 #eeg ,cymothord1 #ehj ,dairy1 bacteriology of1 #cic ,daphnia1 enemies of1 #eha ---- ephippial eggs of1 #ehj ,daphnia pulex1 #ehj ,de ,bary's investigations in parasitism1 #cie ,decalcifying and bleaching agents1 list of1 #fgg ,decalcifying solution as hardening reagent1 #bhh ,demodex folliculorum1 #fbg ,dental structure1 #feb ,dermestes lardarius1 #fbg ,dermis1 the human1 #fdg ,desmidiace1 #dbj ---- reproduction of1 #dbc ,diamond microscope1 ,pritchard's1 #i ,diaphragm1 the1 #aid ---- the iris1 #agf ,diatomace1 #dbj1 #dbg ---- fossilised1 #dcg ---- ,max ,schultze's researches1 #dcj ---- where found1 #dbh ,diatoms1 mounting medium1 #cdc ---- movements of1 #dca ,didymoprium grevelli1 #dbj ,difflugia1 #dhb ,digestive system of insects1 #ehg ,dipping-tubes1 #bgi ,disc-holder1 ,beck's1 #aih ,dissecting-knives1 #bhd ,dog-tick1 #fbd ,double convex lens1 #ai ,draparnaldia glomerata1 #dji ,draw-tube1 ,swift's1 #aaf ---- ,watson's1 #ajd ,drone fly1 #eid ,dytiscus marginalis1 #fjg ,echinococcus1 #efe ,echinodermata1 #eci ,eggs of insects1 #fab ,elementary optics1 #ab ,embedding fluids1 list of1 #fgh ---- in paraffin wax1 #bhe ,entomological specimens1 mounting1 #cda ,entozoa1 #efb ,eosin stain1 #cae ,eozoon1 #dib ,epeira diadema1 #fai ,epidermis of plants1 #dee ,epithelial cells1 #fcf ,epithelium1 mounting1 #bie ,equisetace1 #ddi ,ergot of rye1 #chb ,eristalis tenax1 #eid ,erysiphe ,tuckeri1 #chj ,eudorina1 #djf ,euglypta1 #dhb ,eurotium repens1 #chc ,exposure table for photo-micrography1 #bac ,eye1 chromatic aberration of the1 #cc ---- of cockchafer1 #eij ---- of fly1 #ehh ---- of whirligig beetle1 #fjh ---- the human1 #cj ,eye-piece1 ,abb's stereoscopic1 #fd ---- compensating1 #adg ---- ---- ,zeiss's1 #adg ---- ,huyghenian1 #aci ---- ,jackson's micrometer1 #adc ---- ,ramsden1 #adb ---- ---- micrometer1 #ade ---- ,ross's1 #fh ---- ,wenham's double1 #fc ---- ,zeiss's1 #adg ,eye-pieces1 #aci ---- achromatic1 #adi ---- magnifying powers of1 #afi ---- projections1 #aej ---- to clean1 #bei ,eyes of insects1 #ehd ,favellidium1 #dae ,feet of insects1 observation of1 #fjd ,felices1 #ddf ,fermentation experiments1 #cfa ,fermentations1 bacterial1 #cia ,ferns1 #ddf ---- development of1 #ddf ,fibro-cartilage1 #feg ,fibrous tissue1 #fdb ---- ---- mounting1 #bif ,filaria sanguinis hominis1 #efh ,finder1 the1 #bjd ---- the ,amyot1 #bje ---- the ,maltwood1 #bjd ---- the ,okeden1 #bje ---- ,pantacsek's1 #bje ,fission formation1 #cfe ,fixing solutions1 list of1 #fgh ,flabellum1 #ebh ,flagella1 staining of1 #ccf ,flagellate infusoria1 #die ,flatness of field1 #bfb ,flax1 fibres of1 #dgd ,flea1 #fbi ,floride1 #dac ,flowering plants1 #dea ,fluke1 the1 #efi ,flustra1 #ecb ,fly1 eye of1 #ehh ---- foot of1 #fjb ,focal length of lenses1 #bb ,focus1 method of finding1 #bga ,foot of fly1 #fjb ,foraminifera1 #dhc ,forceps1 #bhc ---- for mounting1 #bid ---- stage1 #aih ,formation and polarisation of crystals1 #bci ,fossil plants1 #dge ,fossilised diatomace1 #dch ,freezing agents1 list of1 #fgh ---- microtome1 ,cathcart's1 #bia ---- ---- directions for using1 #bia ,frog-bit1 #dah ---- plate1 #bgg ,froth-fly1 #fah ,fungi1 industrial uses of1 #cia ,fungoid diseases1 #cgd ,fungus on plants1 #cgf ---- root1 benefit to trees from1 #cif ---- sewage1 #djj ---- where found1 #cgi ,gall-fly1 #eif ,gapeworm1 #egb ,gelatine1 to prepare nutrient1 #cbh ,german yeast1 #chh ,gillett's achromatic condenser1 #agc ,globigerina1 #dhf ,glycerine agar-agar1 #ccj ---- jelly1 to make1 #big ,gnat1 #eif ,gnathia1 #egi ,goniometer1 ,dr4 ,leeson's1 #aej ,gorgoniid1 #ecj ,gosse on noctiluca1 #dif ,gram's method of staining bacteria1 #cce1 #cch ,grant's researches on sponges1 #ejg ,gregarin1 #dhb1 #efc ,gromia1 #dhd ,grove's recommendations for mounting1 #bii ,gyrinus1 eye of1 #fjh ---- leg of1 #fjh ,hmatoxylin stain1 #cab ,hairs1 structure of1 #fdh ,haliotis splendens1 #eei ---- tuberculatus1 #eeg ,hansen's investigations of yeast1 #chg ,hard structures1 mounting1 #cjg ---- woods1 cutting sections of1 #caf ,hardening agents1 list of1 #fgg ---- ---- absolute alcohol1 #bhg ---- ---- chromic acid as1 #bhh ---- ---- decalcifying solution as1 #bhh ---- ---- methylated spirit as1 #bhh ---- ---- ,muller's fluid as1 #bhh ---- ---- potassium bichromate1 #bhh ,hardening reagents1 #bhg ---- tissue1 #bhc ,hartea elegans1 #ece ,heliozoa1 #dhi ,helix absoluta1 #eeh ---- pomatia1 #eeh ,hepatic1 #ddb ,hexactinia1 #ebf ,hirudina medicinalis1 #egf ,hirudinid1 #ege ,his's method of staining bacteria1 #ccd ,holland's simple microscope1 #ge ,holman's life slide1 #bgg ---- moist chamber1 #bgg ---- syphon slide1 #bgh ,holothurioidea1 #edc ,honey bee1 #eih ,horse-tails1 #ddi ,house fly1 eye of1 #ehh ---- proboscis of1 #eia ---- tongue of1 #eib ,human eye1 the1 #cj ---- hair as a test1 #bfi ,huyghenian eye-piece1 #aci ,hydra1 #eaf ---- fasca1 #eaf ---- stinging1 #eai ---- viridis1 #eaf ,hydractinia echinata1 #ebc ,hydroid polyps1 colony of1 #ecg ,hydrozoa1 #eae ,ianthinid1 #eej ,iceland spar1 #bba ,illumination arrangements of the microscope1 #fgc ---- ,mercer on1 #fgc ,incubation1 apparatus for1 #cbb ---- test for1 #bfc ,incubator1 ,crookshank's1 #cbd ,incubators1 #cbd ,indigo plant1 #cib ,infusoria1 #dic ,infusorial life1 #cdi ,injecting1 directions for1 #cjd ---- insects1 #cjf ---- lower animals1 #cje ---- mollusca1 #cje ---- small animal bodies1 #cjb ---- ---- ---- ---- syringe for1 #cjb ---- with different colours1 #cjd ,injections1 to prepare1 #cjc ---- ---- subjects for1 #cjc ,injurious insects1 #fcb ,insects1 #egh1 #ehc ---- antenn of1 #ehd ---- digestive systems1 #ehf ---- distinctive character of1 #ehc ---- eggs of1 #fab ---- eyes of1 #ehd ---- injecting1 #cjf ---- injurious1 #fcb ---- mouths of1 #ehd ---- muscles of1 #ehe ---- reproduction of1 #ehg ---- respiratory system of1 #fjg ---- thorax of1 #ehe ---- wings of1 #fji ,interpretation1 errors of1 #bfc ,iris diaphragm1 #agf ,isthmia enervis1 #dcf ,ixodid1 #fbb ,ixodes ricinus1 #fbd ,jackson's micrometer eye-piece1 #adc ,jelly-fish1 #eai1 #ebc ,jungermannia1 #ddb ,koch's method of staining flagella1 #ccf ,lamp1 ,baker's microscope1 #aia ---- ,beck's complete microscope1 #bjb ---- shells1 #eci ---- the microscope1 #bja ---- ,watson's microscope1 #bjc ,lard1 embedding in1 #bhe ,larv of sea-anemones1 #ebi ,lathe for cutting sections of teeth1 #cjh ,laticiferous tissues1 #dff ,leaf tissue1 #dff ,leeson's goniometer1 #aej ,leeuwenhoek's microscope1 #d ,leitz's dissecting microscope1 #acb ---- microscopes1 #acb ,lens1 bull's-eye condensing1 #aii ---- ,steinheil's aplanatic1 #gg ---- the ,coddington1 #gf ,lenses1 concave1 #bc ---- convex1 #ah ---- double convex1 #ai ---- focal length of1 #bb ---- forms of1 #ah ---- meniscus form of1 #bd ---- optical centre of1 #bj ---- plano-convex1 #ai ,lepas1 #eci ,lepisma saccharina1 #fab ---- scales of1 as test1 #bfd ,leptothrix buccalis1 #djj ,lichenace1 #dci ,lichens1 #dci ---- erratic1 #dda ,lieberkhn's microscope1 #d ,lieberkhn1 the1 #aih ,light1 polarisation of1 #bai ,limax maximus1 #eeh ---- rufus1 #eeh ,limnan1 teeth of1 #eed ,limnid1 #eea ,limnus stagnalis1 #eea ,lingula pyramidata1 #ech ,lingulid1 #ech ,list of salts1 #bdj ,lister's correction collar1 #aee ---- flasks1 #cbb ---- microscope1 #ha ---- object glass1 #aed ,live-cages1 #bgd ,live-cells1 #bgg ,live-trough1 ,botterill's1 #bgf ,liverworts1 #ddb ,lobosa1 #dhb ,lffler's method of staining flagella1 #ccf ,logwood1 staining by1 #bic ,lophopus crystallinus1 #ece ,lyda campestris1 #eih ,lymph corpuscles1 #fch ,maddox growing stage1 the1 #bhj ,magnifying powers of eye-pieces and objectives1 #afi ,maltwood finder1 the1 #bjd ,maple aphis1 #fag ,mapping spectra1 #bec ,marchantia polymorphia1 #ddb ,martin's microscope1 #e ,marzoni's objective1 #aeb ,mayall's illuminator1 #ahd ---- mechanical stage1 #abd ,medus1 #eae1 #eba ---- a colony of budding1 #ecg ,melicerta ringens1 #eje ,melolontha vulgans1 eye of1 #eij ,meniscus form of lens1 #bd ,mercer on illumination1 #fgc ,mesogla1 #ebe ,mesoglia vermicularis1 #daj ,methylated spirit as hardening reagent1 #bhh ,metric system of weights and measures1 #fhg ,micrometer1 ,ramsden's1 #ade1 #bjf ---- the stage1 #bjf ,micrometers1 #bje ,micro-organisms1 #cgc ---- cultivation of1 #cbg ,micro-photography1 #baj1 #fgd ---- ,baker's apparatus for1 #bag ---- exposure table1 #bac ---- ,pringle's apparatus1 #bag ---- rules for1 #bad ---- ,stringer-,watson's apparatus for1 #fgd ---- ,swift's apparatus for1 #bac ,microscope1 accessories of the1 #aig ---- ,baker's advanced student's1 #abc ---- ---- histological1 #abe ---- ---- ,nelson model1 #abj ---- ,beck's binocular dissecting1 #aja ---- ---- ---- ,national1 #ii ---- ---- large ,continental model1 #ih ---- ---- pathological1 #ie ---- ---- ,star1 #aja ---- binocular1 ,pillischer's1 #abh ---- ---- ,wenham's1 #fe ---- ,carpenter on binocular1 #fi ---- compound1 #gh ---- early history of1 #a ---- ,holland's simple1 #ge ---- ,hooke's water1 #b ---- illumination arrangements of the1 #fgc ---- invention of1 #b ---- lamp1 the1 #bja ---- ---- ,baker's1 #aia ---- ---- ,beck's1 #bjb ---- ---- ,watson's1 #bjc ---- ,leitz's dissecting1 #acb ---- ,leeuwenhoek's1 #d ---- ,lieberkhn's1 #d ---- ,lister's1 #ha ---- manipulation and mode of using the1 #beh ---- ,martin's1 #e ---- ,nachet's1 #acc ---- ---- binocular1 #fb ---- ,pillischer's binocular1 #abh ---- ---- ,international1 #abf ---- ,pillischer's 8,kosmos10 #abh ---- ,powell ,lealand's1 #he ---- ---- student's1 #hh ---- ,pritchard's diamond1 #i ---- ,riddell's binocular1 #fb ---- ,ross's 8,eclipse10 #hi ---- ---- ,new ,industrial1 #ij ---- ,ross-,jackson1 #hb ---- ,ross-,jackson-,zentmayer1 #hc ---- ,ross-,zentmayer1 #ia ---- ,rousselet's tank1 #abf ---- simple1 #cj1 #gb1 #gg ---- simple pocket1 #gc ---- ,sir ,david ,brewster's1 #aa ---- ,stephenson's erecting binocular1 #ga ---- ,swift's advanced student's1 #aah ---- ---- bacteriological1 #aaf ---- ---- four-legged1 #aad ---- ---- histological student's1 #aaf ---- the bacteriological1 #ace ---- ,watson's bacteriological1 #ajh ---- ---- ,edinburgh student's1 #ajb ---- ---- histological1 #ajg ---- ---- petrological1 #aaa ---- ---- portable1 #aaj ---- ---- ,van ,heurck's1 #ajh ---- ,wenham's binocular1 #fe ---- ---- radial1 #ij ---- ,wollaston's simple1 #gd ---- ,zeiss's1 #acj ,microscopes1 ,baker's1 #abj ---- ,beck's1 #ie ---- ,continental1 #acj ---- ,leitz's1 #acb ---- ,pillischer's1 #abf ---- ,ross's1 #hh ---- ,swift's1 #aac ---- ,watson's1 #ajb ,microscopic forms of life1 #cec ---- vision1 principles of1 #de ---- ---- theory of1 #cg ,micro-spectroscope1 the1 #bdc ,micro-spectroscopic eye-piece1 the ,sorby-,browning1 #bdg ---- method of using1 #bej ---- the ,browning-,huggins1 #bde ,microtome1 ,cambridge rocking1 #bij ---- ,cathcart's freezing1 #bia ---- ,cole's section-cutting1 #bhi ---- method of using1 #bhi ,milk1 bacteria in1 #cic ,millipedes1 #egh ,mineral and geological kingdoms1 #fgj ,mirror1 manipulation of1 #bfj ---- the1 #aie ,mite1 cheese1 #fbe ,mites and ticks1 #fbb ,moist stage1 #bhj ,molecular rotation1 #bch ,mollusca1 #ede ---- injecting1 #cje ---- shell of1 #eeh ,monads in rat's blood1 #cgb ,monoxenia1 #ebc ,moss-animals1 #eca ,mosses1 #ddc ,moulds1 #chj1 #cha ,mounting apparatus1 #ceb ---- cells for1 #cdj ---- chara1 #cdg ---- entomological specimens1 #cda ---- epithelium1 #bie ---- fibrous tissue1 #bif ---- forceps1 #bid ---- hard structures1 #cjg ---- media1 list of1 #fgh ---- nerve tissue1 #bif ---- non-striated muscle1 #bif ---- objects1 materials required1 #cci ---- rock sections1 #cji ---- spring clip for1 #bif1 #cdb ---- teeth sections1 #cjh ---- vegetable tissues1 #caj ,mouse1 hair of1 #fej ,mouth1 leptothrix1 #djj ,mouths of insects1 #ehd ,mller's fluid1 a hardening reagent1 #bhh ,musca domestica1 #ehh ,musci1 #ddc ,muscid1 #ehh ,muscles of insects1 #ehe ,muscular fibre1 #fdd ---- ---- mounting1 #bif ,mycetoma1 #cgh ,mycetozoa1 #dhb ,mycorhiza1 #cif ,nachet's binocular microscope1 #fb ,nails1 structure of1 #fdh ,navicula1 #dbg ,neckera antiphyretica1 #dde ,needles for teasing out sections1 #bhf ,nematoid worms1 #eef ,nerve tissue1 mounting1 #bif ,nicol prism1 #bbj ,nitella1 #dah ,nitrate of silver as stain1 #big1 #bih ,noctiluca1 #dif ,non-striated muscle1 mounting1 #bif ,nose-pieces1 #bjc ,nuclear stains1 #caa ---- ---- carmine1 #cab ---- ---- hmatoxylin1 #cab ,nudibranchiata1 #edg ,nutrient agar-agar1 to prepare1 #ccj ---- gelatine1 to prepare1 #cbh ---- jelly1 to inoculate with bacteria1 #cca ,object glass1 ,lister's1 #aed ---- to clean1 #bfj ,objective1 achromatic1 #aeb ---- changers1 #bjc ---- ,powell ,lealand's oil immersion1 #aff ,objectives1 ,baker's1 #afh ---- ,beck's1 #afg ---- ,english and ,german1 #aei ---- high power1 #aga ---- magnifying powers of1 #afi ---- ,pillischer's1 #afi ---- ,ross's1 #aff ---- ,swift's1 #afh ---- ,watson's1 #afg ,objects1 collection of1 #cdi ,oblique illumination1 #ahf ,oidium albicans1 #chd ,okeden finder1 the1 #bje ,onion1 raphides of1 #dgb ,opisthobranchiata1 #edh ,optical centre of lenses1 #bj ,optics1 elementary1 #ab ,oscillariace1 #djg ,osmic acid as stain1 #bih ,palates of gastrapods1 #eef ,palmellace1 #djg ,palmogla macrococca1 #dja ,pandorina morum1 #djf ,parabolic reflector1 #ahh ,paraffin wax1 embedding in1 #bhe ,parasites1 cereal1 #cha ---- sponge1 #eab ---- vine1 #chj ,parasitic diseases of plants1 #cgb ---- fungi of men and animals1 #chc ,parasitism1 ,de ,bary's investigations in1 #cie ,patella radiata1 #eef ,pearls1 structure of1 #eei ,pectinibranchs1 #eej ,pediastre1 #dbb ,pedicellan1 #edc ,peltogaster curvatus1 #eci ,penetration in objective1 #bfa ,pennatulid1 #ecj ,pentacrinoids1 #edj ,pepperworts1 #dea ,peronospora viticola1 #cha ,petiole1 #dff ,phanerogami1 #dea ,phanerogams1 structure of1 #dec ,phloem of plants1 #ded ,pholadid1 #ede ,phomauvicola1 #cha ,photo-micrography1 #baj ---- apparatus for1 #bac ---- ,baker's apparatus for1 #bag ---- exposure table1 #bac ---- rules for1 #bad ---- ,swift's apparatus for1 #bac ,phylactolmata1 #ecc ,phylloxera vastatrix1 #cha ,physalia1 #eba ,physid1 #eea ,picro-carmine as stain1 #bii ,pigment cells1 #ddf ,pillischer's binocular microscope1 #abh ---- ,international microscope1 #abf ---- 8,kosmos0 microscope1 #abh ---- objectives1 #afi ,pinna ingens1 #eei ,pinnulari1 #dcd ,pipette1 #cai ---- ,pasteur's bulb1 #cbb ,plague1 bacillus of1 #cgj ---- the ,bombay1 #cga ,planari1 #ege ,plano-convex lens1 #ai ,plants1 epidermis of1 #dee ---- fibro-vascular system of1 #dfj ---- flowering1 #dea ---- fossil1 #dge ---- ground tissue1 system of1 #deh ---- hairs1 #deg1 #dgc ---- parasitic diseases of1 #cgd ---- raphides in1 #dgb ---- reproductive organs of1 #dfg ---- spores of parasitic fungus on1 #cgf ---- structure of1 #dec ---- tissue systems of1 #ded ---- vascular system of1 #dfd ,plasmodia1 #dhb ,pleurobranchus aurantiacus1 #edh ---- plumula1 #eeg ,pleurosigma angulatum1 #dbi ---- as a test1 #bfg ---- attenuatum1 #dbi ,plumularia1 #eba ,pocket lens1 ,browning's1 #gf ---- ,coddington's1 #gf ,podura-scale test1 #bfh ---- villosa1 #faa ,polarisation apparatus1 #bbc ---- of light1 #bai ---- prism1 #bbj ---- ---- method of employing1 #bbd ---- rotation of plane of1 #bca ,polarised crystal of quinidine1 #bce ,polarising apparatus1 ,watson's1 #bbd ,pollen grains1 #dfg ---- ---- method of mounting1 #dfg ,polycystina1 #dhi ,polymorphina1 #dhf ,polypomedus1 #eai ,polytrichum undulatum1 #dde ,polyzoa collecting1 #cej ,pond-snails1 #eea ,porifera1 #ejf ,portable microscope1 ,watson's1 #aaj ,potassium bichromate as hardening reagent1 #bhh ---- nitrate1 crystal of1 #bcb ,powell ,lealand's microscope1 #he ---- oil immersion objective1 #aff ---- student's microscope1 #hh ---- formula for objective1 #aff ,preparing tissue1 #bhc ,primordial cell1 #ceg ,principal focus1 #ah ,pringle's micro-photography apparatus1 #bag ,prism1 #ae ---- ,nicol's1 #bbj ,pritchard's diamond microscope1 #i ,proboscis of house fly1 #eia ,proteolepas1 #eci ,protococcus invalis1 #chj ---- pluvialis1 #dja ,protoplasm1 #cef ---- staining living1 #cjf ,protozoa1 #dgh ,puccinia graminis1 #cge ,pyrocystis1 #dif ,quartz1 #bca ,quekett on ,martin's microscope1 #f ,quinidine1 crystals of1 #bce ,radiolaria1 #dij ,ramsden eye-piece1 #adb ---- micrometer eye-piece1 #ade ,raphides in plants1 #dgb ,rayleigh's theory of formation of optical images1 #dd ,reflection1 #af ,reflector1 ,sorby's1 #aii ,refraction1 #ac ---- through prism1 #ae ,reproductive organs of plants1 #dfg ,resolving power1 #bfb ,retiform tissue1 #fdd ,rezner's mechanical finger1 #cdc ,rhizocarpe1 #dea ,rhizopoda1 #dhb ,riddell's binocular microscope1 #fb ,rochelle salt1 #bcb ,rock limpet1 #eef ---- sections1 mounting1 #cji ,ross's achromatic condenser1 #agf ---- compressorium1 #bge ---- ,eclipse microscope1 #hi ---- eye-pieces1 #fh ---- microscopes1 #hh ---- object glass1 #aed ---- objectives1 #aff ,ross-,hepworth arc lamp1 #bah ,ross-,jackson microscope1 #hb ,ross-,jackson-,zentmayer microscope1 #hc ,ross-,zentmayer microscope1 #ia ,rotatoria1 mounting1 #cde ,rotifera1 #ejb ,rousselet's compressorium1 #bge ---- method of mounting rotatoria1 #cde ---- tank microscope1 #abf ,rye1 ergot of1 #chb ,saccharomyces cerevisi1 #chd ---- ellipsoideus1 #che ---- mycoderma1 #chd ,saccharomycetes1 industrial uses of1 #cia ,salts1 list of1 #bdj ,saprolegnia ferox1 #daa ,sarcode1 #ceg ,saw-fly1 #eih ,scalariid1 #eej ,scales of butterfly's wings1 #faj ,scapander ligniarius1 #eeg ,schfer's warm-stage1 #bhb ,scyphomedus1 #ebc ,sea-anemone1 larv of1 #ebi ,sea-anemones1 #ebf ,sea-cucumber1 #edj1 #edc ,sea-hares1 #edi ,sea-mats1 #ecb ,sea-urchin1 #edj ,sea-weeds1 #dji ,section cutting1 #bhc ---- ---- ,cole's directions for1 #bhe ,section-cutting microtome1 ,cole's1 #bhi ---- lifters1 #cai ---- scissors1 #bhc ,sections of hard wood1 cutting1 #caf ,selenite1 #bbe ,sepia officinalis1 #eef ,sertularia1 #eba ,shadbolt's turn-table1 #bie ,sheep-tick1 #fbd ,shell1 structure of1 #eeh ---- formation in limna1 #eeb ,sieve-tubes1 #dfe ,silk filaments1 #dgd ,silk-worm1 #fje ,silk-worms1 disease of1 #cfc ,silver-side reflector1 #aih ,simple microscopes1 #cj1 #gb1 #gg ,siphonophora1 #eba ,sirax gigas1 #eig ,skin1 #fdf ,smith ,beck's achromatic condenser1 #agc ,snow crystals1 #bcg ,sorby-,browning micro-spectroscopic eye-piece1 #bdg ,sorby's reflector1 #aii ,spectroscope1 cells for use with1 #bea ---- the1 #bdd ,spectrum of chromule1 #bee ,sphroplea annulina1 #dji ,sphrosira volvex1 #djf ,sphagnace1 #ddf ,spherical aberration1 #bc ,spiders1 #fai ,spirilla1 #cfh ,spiro-bacteria1 #cfh ,splenic fever bacillus1 #cfi ,sponges1 #ejf ---- boring1 #eac ---- ,geodia ,barretti1 #eaj ---- ,grant's researches on1 #ejg ---- hyalonema1 #eab ---- parasite on1 #eab ---- reproduction of1 #eaj ,spongia coalita1 #ejg ,spongiad1 #ejf ,spore of parasitic fungus on plants1 #egf ,spores1 #cff ,spores1 aerobic1 #cii ---- endogenous1 #cff ---- staining of1 #ccf ,spring clip for mounting1 #bif1 #cdb ,stage1 ,bartley's warm1 #bha ---- forceps1 #aih ---- ,maddox growing1 #bhj ---- ,mayall's mechanical1 #abd ---- moist and warm1 #bhj ---- ,schfer's1 #bhb ---- ,stricker's1 #bhb ---- ,watson's semi-mechanical1 #ajg ,stain1 eosin1 #cae ,staining animal structures1 #bib ---- bacteria1 #ccd1 #cch ---- by logwood1 #bic ---- cellulose1 #cad ---- double1 #bic ---- double and treble1 #cjj ---- living protoplasm1 #cjf ---- of flagella1 #ccf ---- of spores1 #ccf ---- tissue1 #bhc ,stains and staining methods1 list of1 #fgi ,stains1 chloride of gold1 #big ---- chloride of palladium1 #bih ---- contrast1 #cac ---- double and treble1 #cjj ---- nitrate of silver1 #big1 #bih ---- osmic acid1 #bih ---- picro-carmine1 #bii ---- single1 #bih ,starch1 #bch ---- granules1 #dfi ---- ---- of arrowroot1 #dgj ---- ---- of potato1 #dgj ---- ---- of wheat1 #dgj ,star-fish1 #edj ,steinheil's aplanatic lens1 #gg ,stentors1 #eja ,stephanoceros1 #ejd ,stephanosphra pluvialis1 #djc ,stephenson's erecting binocular microscope1 #ga ,stereoscope1 the1 #fj ,stereoscopic binocular vision1 #fj ,sterilised instruments1 #cba ,sterilisers1 #cbd ---- ,hearson's1 #cbe ---- steam1 #cbe ---- ---- ,dr4 ,koch's1 #cbe ,sting of bee1 #eif ---- of wasp1 #eif ,stock-bottle1 #bgi ,stomata of iris1 #def ---- water pores1 #deg ,stone-lilies1 #edb ,stonewort1 #dae ,stricker's warm stage1 #bhb ,stringer's apparatus for micro-photography1 #fgd ,stylonychia mytilus1 #ejj ,stylopid1 #fbh ,substage condenser1 #aic ,subterranean fungi1 #cig ,sun-animalcules1 #dhi ,swift's advanced student's microscope1 #aah ---- bacteriological microscope1 #aaf ---- draw-tube1 #aaf ---- four-legged microscope1 #aad ---- histological student's microscope1 #aaf ---- horizontal camera1 #bac ---- illuminating apparatus1 #ahc ---- microscopes1 #aac -- objectives1 #afh ,tables1 aperture1 #eh ,tnia1 #efd ,tanning skins1 #cic ,tardigrada1 #fca ,teasing out sections1 needles for1 #bhf ---- ---- ---- under condensed light1 #bhg ,teeth1 #feb ---- lathe for cutting sections of1 #cjh ---- method of cutting sections of1 #cjh ---- mounting1 #cjh ,tenent-hairs1 #fjc ,terebella littoralis1 #egg ,terebratulata rubicuna1 #eei ,testacella maugei1 #eef ,test for illumination1 #bfc ,test object1 blood as a1 #bfc ,test object1 human hair as1 #bfi ---- ---- lepisma as1 #bfd ---- ---- pleurosigma1 #bfg ---- ---- podura-scale1 #bfh ,test-plate1 ,abb's1 #afd ,threadworm1 #eff ,thorax of insects1 #ehe ,thuricola valvata1 #ejj ,tick1 dog1 #fbd ---- sheep1 #fbd ,ticks1 #fbb ,tissue1 adipose1 #fdd ---- bacteria in sections of1 #ccg ---- fibrous1 #fdb ---- hardening1 #bhc ---- preparing1 #bhc ---- retiform1 #fdd ---- staining1 #bhc ---- systems of plants1 #ded ,tongue of butterfly1 #fje ---- of house fly1 #eib ---- of wasp1 #eie ,tooth substance1 #fed ,topaz1 #bca ,tourmaline1 #bbe ,trematode worms1 #efi ,trichina spiralis1 #efg ,trichomes of plants1 #deg ,troughs1 #bgd ,truffle1 #cig ,tuber cibarium1 #cig ,tubicola1 #egf ,tubipora1 #ecj ,tubularia dumortierii1 #ecg ,tunicata1 #edi ,turbo marmoratus1 #eeg ,turn-table1 ,shadbolt's1 #bie ,typhoid bacillus1 #cgj ,ulvace1 the1 #daa ,ulva lactuca1 #daa ---- thermalis1 #daa ,urinary salts1 #bcf ,vallisneria1 #dah ,varley's live-box1 #bgd ,varnishes1 #cci ,vascular system of plants1 #dfd ,vaucheria1 #daj ,vegetable tissues1 staining and mounting1 #caj ,veins1 #ffb ,velutina lvigata1 #eeg ,vertebrata1 #fcc ,vine parasites1 #chj ,violet sea-snail1 #eej ,visual angle1 #gb ---- judgment1 #cg ,volvocine1 #djd ,vorticellid1 #dii ,walmsley's turn-table1 #cdj ,warm chamber1 ,pfeiffer's1 #cbc ---- stage1 #bhj ---- ---- ,bartley's1 #bha ---- ---- ,schfer's1 #bhb ---- ---- ,stricker's1 #bhb ,wasp1 sting of1 #eif ---- tongue of1 #eie ,water thyme1 #dai ,watson's achromatic condenser1 #agg ---- bacteriological ,van ,heurck's microscope1 #ajh ---- ,edinburgh student's microscope1 #ajb ---- histological microscope1 #ajg ---- mechanical draw-tube1 #ajd ---- microscope lamp1 #bjc ---- microscopes1 #ajb ---- parachromatic condenser1 #ahb ---- petrological microscope1 #aaa ---- portable microscope1 #aaj ---- semi-mechanical stage1 #ajg ,webster-,collins condenser1 #ahf ,weights and measures1 metric system of1 #fhg ,wenham's binocular microscope1 #fe ---- double eye-piece1 #ahi ---- immersion condenser1 #ahi ---- parabolic condenser1 #ahf ---- ---- reflector1 #ahg ---- radial microscope1 #ij ,wheat rust1 #cgd ---- starch1 #dgj ,wheel animalcules1 #ejb ,whirligig-beetle1 eyes of1 #fjh ---- ---- leg of1 #fjh ,wings of butterfly1 #faj ---- of insects1 #fji ---- of moth1 #faj ,winogradsky's investigations of bacteria1 #cih ,wollaston's simple microscope1 #gd ,wood1 formation of1 #dfb ,wool1 #dgd ,worms1 #efb ,wort-gelatine1 #ccj ,xylem of plants1 #dfb ,yeast cells1 #chd ---- ,german1 #chh ---- ,hansen's investigations of1 #chg ,zeiss's compensating eye-piece1 #adg ---- cover-glass gauge1 #afe ---- microscope1 #acj ,zentmayer's ,holman syphon slide1 #bgh ,zoophytes1 #eae ,,bradbury1 ,,agnew1 ,,co4 ,,ld41 ,,printers1 ,,london ,,and ,,tonbridge4 ,transcriber's ,note3 ,page xxiii1 8l4 ,corystes cossivelaunus0 changed to read 8l4 ,corystes cassivelaunus04 ,page xxv ,,errata incorporated into project4 ,page xix1 8,acmea virginea1 part of palate--#aah40 changed to read 8,acma virginea1 part of palate--#aah40 ,page #ba1 8in ,fig4 #ac1 if ,s1 ,s are a pair of conjugate foci10 changed to read 8in ,fig4 #ab1 if ,s1 ,s are a pair of conjugate foci104 ,s and ,s are in ,fig4 #ab4 ,page #hi 8,bacteriological and ,histol gical0 changed to read 8,bacteriological and ,histological04 ,page #eih1 8,apis nillifica0 changed to read 8,apis mellifica01 also entry in index4 ,page #ffc1 8the papill of the tongue is distended and seen erect0 changed to read 8the papill of the tongue are distended and seen erect04 ,obvious printer errors corrected silently4 ,inconsistent spelling and hyphenation are as in the original4 ,,footnotes3 #a ,my earliest acquaintance with the ,microscope occurred in the thirties1 when ,i fortunately became possessed of a ,culpeper-,scarlet instrument1 figured in the title-page4 #b ,at the time this was written1 scarcely a book of the kind had been published at a price within the reach of the student4 #c ,for fuller information1 see the ,cantor ,lectures on the ,microscope1 by the late ,john ,mayall1 ,f4,r4,m4,s41 8,society of ,arts ,journal10 #ahhe4 #d 8,a ,practical ,treatise on the ,use of the ,microscope40 ,london1 #ahee4 #e ,for further information1 ,i must refer my readers to ,parkinson's 8,treatise on ,optics20 ,herschel's 8,familiar ,lectures on ,light20 8,cyclopdia ,britannica20 ,everett's translation of ,deschanel's 8,physics20 and ,ngeli and ,schwendener's 8,theory and ,practice of the ,microscope10 translated by ,frank ,crisp1 ,,ll4,d4 #f ,the cornea of the eye is not so entirely the simple transparent structure as it at first sight may appear to be4 ,it is composed of several layers1 the most important of which is the nerve layer1 consisting of innumerable ganglionic stellate plexus of cells held together by a network1 as seen in ,fig4 #ba1 a small section stained by chloride of gold1 and magnified #cjj diameters4 ,beneath the nucleated nerve cells is a second layer of stellate cells1 varying a little in their form4 ,these nerve and stellate cells serve the purpose of maintaining the cornea in health1 and must play a significant part in the dioptric system4 #g ,the standard condition of perfect vision is termed emmetropia4 #h ,landolt2 8,the ,accommodation and ,refraction of the ,eye10 #ahhf4 #i #jja of a millimetre4 ,this measurement is now universally employed in microscopy4 #aj ,diffraction effects may be observed without a microscope1 indeed1 the more striking are seen in connection with telescopic vision4 ,a beautiful series of phenomena in illustration of the diffraction of light may be produced as follows3 ,draw on a large sheet of paper a series of geometrical figures1 arranged at equal distances in a circle4 ,a collodion photographic picture of these being taken1 a series of small transparent apertures in the elsewhere opaque film will result4 ,this film is then mounted1 so that it may be in turn brought before the centre of a small hand telescope1 previously adjusted to view an image of the sun4 ,in this way we have an apparatus of the most compact form1 and by means of which a series of fifty or more phenomena may be brought into view in a few minutes4 ,these pictures being very small 7occupying on an average area one-tenth of an inch in diameter71 inaccuracies of surface and substance of the glass may be neglected4 ,a film of ,canada balsam with which the glass is cemented over the picture produces no disturbance4 ,there is a manifest advantage in the figures being small1 as the size of the image is in inverse proportion to the size of the aperture4 #aa ,carpenter1 8,the ,microscope10 p4 #fe1 #ahia4 #ab 8,phil4 ,mag410 viii41 p4 #afg 7#ahif74 #ac ,professor ,stokes wrote me in the following flattering terms3--8,what you have submitted to me on the subject of apertures is so sound1 clear1 and succinct1 that ,i have nothing to add to it4 ,the method adapted as you have explained respecting the immersion system1 ,i consider to be perfectly satisfactory40 ,subsequently1 and at my request1 ,sir ,george ,stokes contributed a valuable paper on the subject to the 8,transactions of the ,royal ,microscopical ,society10 #ahgf1 on 8,the ,theoretical ,limit of ,aperture40 #ad 8,on the ,estimation of ,aperture in the ,microscope10 8,journal of the ,royal ,microscopical ,society10 series ii4 vol4 i42 8,notes on ,aperture1 ,microscopic ,vision1 and the ,value of ,wide-angled ,immersion ,objectives10 #ahha4 #ae ,numerical aperture is generally used in the sense in which it was introduced in #ahgc by ,professor ,abbe1 on the basis of his theoretical investigations4 ,numerical aperture represents the ratio between the radius of the effective aperture 7p7 of the system on the side where the image is formed--more accurately the radius of the emerging pencils measured in the upper focal plane of the objective--and the equivalent focal length 7f7 of the latter1 i4e41 ,numerical aperture p_/f4 ,this ratio is equal to the product of the sine of half the angle of aperture u of the incident pencils and the refractive index n of the medium1 situated in front of the objective4 ,with dry lenses n has therefore the value #a2 with immersion lenses it is equal to the refractive index of the particular immersion fluid3 ,numerical aperture n ,sin u4 ,the numerical aperture of a lens determines all its essential qualities2 the brightness of the image increases with a given magnification and1 other things being equal1 as the square of the aperture2 the resolving and defining powers are directly related to it1 the focal depth of differentiation of depths varies inversely as the aperture1 and so forth4 7,abbe1 8,the ,estimation of ,aperture10 8,journal of the ,royal ,microscopical ,society10 #ahha1 p4 #chi47 #af 8,journal of the ,royal ,microscopical ,society40 #ag 8,journal ,roy4 ,micros4 ,soc410 p4 #ai1 #ahgh1 and p4 #bj1 #ahhj4 #ah 8,the ,magnifying ,power of ,short ,spaces0 has been ably elucidated by ,john ,gorham1 ,esq41 ,m4,r4,c4,s4 8,journal of ,microscopical ,society10 ,october1 #ahed4 #ai ,the late ,mr4 ,coddington1 of ,cambridge1 who had a high opinion of the value of this lens1 had one of these grooved spheres executed by ,mr4 ,carey1 who gave it the name of the ,coddington ,lens1 supposing that it was invented by the person who employed him1 whereas ,mr4 ,coddington never laid claim to it1 and the circumstance of his having one made was not known until nine years after it was described by ,sir ,david ,brewster in the 8,edinburgh ,journal40 #bj 8,journal of the ,royal ,microscopical ,society1 #ahij10 p4 #dbj4 #ba 8,journal of the ,royal ,microscopical ,society1 #ahhj10 p4 #ajej4 #bb ,apo-chromatic1 from the ,greek1 signifying freedom from colour4 #bc ,prof4 ,abbe 8,on ,stephenson's ,system of ,homogeneous ,immersion for ,microscope ,objectives10 8,journal of the ,royal ,microscopical ,society10 ,,ii4 7#ahgi71 p4 #bef1 and on 8,the ,essence of ,homogeneous ,immersion10 ,ibid41 ,i4 7#ahha71 p4 #aca4 #bd ,reichert1 in his catalogue1 does not clearly indicate what the initial powers of his eye-pieces are4 #be ,messrs4 ,ross have two series of eye-pieces1 both ,huyghenian4 ,one series is for use with the ,english #aj-;inch tube-body1 and is distinguished by ,roman letters1 and the other by numerals1 and made as is usual on the ,continent1 and for use with the shorter tube-body #f-a_/b-;inch4 ,the initial powers given in the table are for the #aj-;inch tube1 and for the shorter must be read as follows3-- #a #b #c #d with #f-a_/b-;inch tube4 #d #f #h #ab #bf ,this centring-glass consists of a tubular cap with a minute aperture1 containing two plano-convex lenses1 so adjusted that the image of the aperture in the object-glass and the images of the aperture of the lenses and the diaphragms contained in the tube which holds the illuminating combination1 may be all in focus at the same time1 so that by the same adjustment they may be brought sufficiently near to recognise their centricity4 #bg ,summary of the value of parabolic illumination and immersion illuminators1 by the late ,mr4 ,j4 ,mayall1 will be found on p4 #bg1 8,journal of the ,royal ,microscopical ,society0 7#ahgi74 #bh ,messrs4 ,baker and ,swift have constructed lamps with removal and fixed achromatic bull's-eye lenses in gymbal1 and changeable tinted glass screens4 ,either of these will add to the usefulness of the lamp in bacteriological research work4 ,baker's is constructed on the ,herschel doublet formula1 and should therefore be free from aberration4 ,it is mounted on a heavy brass tripod foot1 has vertical and horizontal movements by rack and pinion1 brass reservoir1 with screw opening for filling1 metal chimney to take #c #a-a_/b-;inch glass slip1 removable frame for carrying tinted glass screens1 c4 #bi 8,journal of the ,royal ,microscopical ,society10 p4 #cfe1 #ahif4 #cj ,dr4 ,g4 ,a4 ,piersoll1 8,american ,annual of ,photography10 #ahij4 #ca 8,journal of the ,royal ,microscopical ,society10 #ahib1 p4 #fhd4 #cb 8,journal of the ,royal ,microscopical ,society10 p4 #egh1 #ahig4 #cc ,herapath's test-fluid is a mixture of three drachms of pure acetic acid1 one drachm of alcohol1 and three drops of sulphuric acid4 #cd 8,journal of the ,royal ,microscopic ,society10 #ahfg4 #ce ,born in #aghg1 at ,straubing1 a small town in ,bavaria4 #cf ,dr4 ,thudicum's 8,tenth ,report of the ,medical ,officer of the ,privy ,council1 #ahfg40 ,mr4 ,sorby 8,on ,some ,improvements in the ,spectrum ,method of ,detecting ,blood40 8,journal of the ,royal ,microscopical ,society10 #ahga4 #cg 8,on the ,reduction and ,oxidation of the ,colouring-matter of the ,blood0 78,proc4 of the ,royal ,soc40 vol4 xiii4 p4 #cee74 ,the oxidising solution is made as follows3--,to a solution of proto-sulphate of iron1 enough tartaric acid is added to prevent precipitation by alkalies4 ,a small quantity of this solution1 made slightly alkaline by ammonia or carbonate of soda1 is to be added to the weak solution of blood in water4 #ch 8,journal of the ,royal ,microscopical ,society10 #ahfi4 #ci ,professor ,sylvanus ,thompson1 8,on the ,measurement of ,lenses10 8,journal of the ,royal ,microscopical ,society10 #ahib1 p4 #aji4 #dj 8,journal of the ,royal ,microscopical ,society10 #bnd ,series1 ,vol4 iv41 p4 #edb4 #da ,mr4 ,j4 ,f4 ,smith1 8,on the ,structure of the ,valve of ,pleurosigma ,pellucida10 8,quekett ,club ,trans40 #db 8,quarterly ,journal of ,microscopical ,science10 ,new ,series1 ,vol4 viii41 #ahgh4 #dc ,it is quite possible also for the student to make his own microscope stand4 ,mr4 ,field in the 8,english ,mechanic10 pp4 #aga et seq41 #ahig1 furnishes numerous working drawings for the construction of a high-class stand1 together with patterns for the metal work4 #dd 8,modern ,microscopy10 by ,martin ,j4 ,cole4 #de ,with regard to the use of absolute alcohol1 this re-agent requires to be used with caution2 all minute details are lost1 and it causes irregular shrinking of the finer tissues1 while fibrous tissue is brought into undue prominence at the expense of the cellular elements4 ,consequently in certain biological laboratories the method of hardening in alcohol has been abandoned in favour of other re-agents4 #df 8,journal of ,anatomy and ,physiology10 ,,xx4 #ahha1 p4 #cdi4 #dg 8,journal of the ,quekett ,club10 ,july1 #ahic1 and ,march1 #ahie4 #dh ,mr4 ,john ,hood1 #ej1 ,dallfield ,walk1 ,dundee1 offers a weekly supply of infusorial life for a small annual subscription1 or a single tube by post at the trifling cost of one shilling4 #di ,professor ,marshall ,ward1 ,f4,r4,s41 8,address to the ,botanical ,section of the ,british ,association1 #ahig40 #ej 8,british ,medical ,journal10 ,march #bf1 #ahei2 8,medical ,times and ,gazette0 and 8,popular ,science ,review10 #ahfb4 #ea 8,parasitic ,diseases10 8,journ4 of the ,royal ,micros4 ,soc4 of ,lond410 #ahei-fj4 #eb ,there are several other kinds of bacteria infesting milk1 some of which are motile1 others non-motile1 producing acidity and colouring matter1 as ,b4 prodigiosus1 red-milk2 ,b4 synxanthus1 yellow milk2 ,b4 lactis aerogens1 which are pathogenic2 ,b4 lactis albus1 which coagulate milk2 and another form1 which is productive of slimy or ropy-milk4 #ec 8,parasitic ,diseases of the ,skin10 #ahei-gc1 p4 #cj4 ,bailliere1 ,tindal1 and ,cox4 #ed 8,organic ,germ ,theory of ,disease10 8,medical ,times and ,gazette10 p4 #fhe1 #ahgj4 #ee ,f4 ,cohn on the 8,natural ,history of ,protococcus pluvialis40 #ef ,pritchard's 8,infusoria10 p4 #bd1 ,plate ,i41 #dth edition4 #eg ,in order to detect the presence of starch-grains in plants1 the tissue must be kept in alcohol exposed to light1 until the whole of the chlorophyll is dissolved out2 it must then be treated for several hours in a strong solution of potash4 ,after neutralisation with acetic acid1 the tissue may be treated with iodine1 which colours it blue1 or with coralline solution1 which colours it pink4 #eh ,verhandl4 d4 ,natur4 ,hist4 ,jahr4 xx4 p4 #a4 8,micros4 ,jour4 ,science10 vol4 iii41 p4 #abj4 #ei ,for instance1 where the yellow ,palmella is found the ,chlorococcus will assume a yellow tinge in its soridial stage4 ,viewed by transmitted light the sori are seen as opaque balls1 with an irregular outline4 #fj 8,contributions to the ,knowledge of the ,development of the ,gonidia of ,lichens40 ,by ,j4 ,braxton ,hicks1 ,m4,d41 8,quarterly ,journal of ,microscopical ,science10 vol4 viii41 #hfj1 p4 #bci4 #fa ,berkeley's 8,introduction to ,cryptogamic ,botany10 #aheg4 #fb ,for more detailed information on the structure and classification of unicellular plants1 and cryptogams1 the reader is referred to ,ralfs' 8,british ,desmidace02 ,smith's 8,british ,diatomace02 ,goebel's 8,outlines of ,classification and ,special ,morphology02 ,berkeley's 8,cryptogamic ,botany02 ,de ,bary's 8,comparative ,anatomy of the ,phaneragams and ,ferns02 ,professor ,marshall ,ward's 8,sach's ,physiology of ,plants10 and numerous memoirs on ,fungi2 and ,bower and ,sidney ,vine's 8,course of ,practical ,instruction in ,botany10 a most instructive book on the histology of plants4 #fc 8,a ,manual of the ,infusoria10 by ,w4 ,saville ,kent1 ,f4,l4,s41 c41 #ahhj4 #fd 8,journal of the ,linn4 ,society10 vol4 viii41 p4 #bjb2 vol4 ix41 p4 #adg1 #ahfe and #ahff4 #fe ,among the more important works on ,foraminifera for consultation will be found ,d',orbigny's 8,foraminiferes ,fossiles du ,bassin ,tertiaire de ,vienne0 7,autriche72 ,schultze1 8,ueber den ,organismus der ,polythalamien10 #ahed2 ,carpenter and ,williamson's 8,researches on the ,foraminifera10 8,phil4 ,trans4 #ahef20 ,parker and ,rupert-,jones in the 8,annals of ,natural ,history40 ,specimens of ,foraminifera may be obtained by shaking dried sponges2 but if required alive they must be dredged for1 or picked off the fronds of living seaweeds1 over the surface of which they are1 by the aid of a lens1 seen to move4 #ff ,w4 ,saville ,kent1 ,f4,l4,s41 ,op4 ,cit41 p4 #cce4 #fg ,difficulties formerly associated with the microscopic examination of flagellate forms of infusorial life have been overcome by improvements in the objectives1 by the knowledge gained of the monad groups1 and by the exhaustive researches of ,drs4 ,drysdale and ,dallinger1 whose joint investigations were published in the ,journal of the ,royal ,microscopical ,society1 #ahgc-ge4 ,by employing the highest and most perfectly constructed powers of the microscope1 and devoting an enormous amount of time and attention to unravelling mysteries so long associated with the production of the lowly organised flagellate organisms1 monads1 and patiently watching hour by hour1 the life-history of numerous species of these minute infusorial animalcules were obtained4 ,not only was it discovered that these organisms increased indefinitely by fission1 but that under certain conditions two or more individuals were united into encystments1 and whose contents broke up into a greater or less number of spore-like bodies1 were speedily developed into the parent type4 ,in the examination of these minute bodies1 it has been found that talc-films1 that is1 talc split into extremely fine lamin1 offer the best kind of cover1 in fact1 supersede ordinary glass covers1 and possess an advantage1 that of bending readily1 thus permitting the objective to be brought close down upon the object4 #fh ,r4 ,kirkpatrick1 ,warne1 ,op4 ,cit41 pp4 #ecb-c4 #fi ,saville ,kent1 op4 cit41 p4 #aia4 #gj ,fritz ,mller first demonstrated a nervous system in the ,polyzoa3--8,the nervous system of each branch consisting of--#ast1 a considerable sized ganglion situated at its origin2 #bnd1 of a nervous trunk running the entire length of the branch1 at the upper part of which it subdivides into branches1 going to the ganglia of the internodes arising at this part2 and #crd1 of a rich nervous plexus resting on the trunk1 and connecting the ganglia just mentioned1 as well as the basal ganglia of the individual polypides40 ,for further account1 see paper in the 8,micros4 ,journ410 vol4 i41 ,new ,series1 p4 #ccj4 #ga ,i have ventured to devote some considerable space to the development of the pond-snail1 and for an obvious reason1 that of making it perfectly clear to my readers that my microscopical investigations of ,limna1 made in #ahec1 were published in the 8,journal of the ,microscopical ,society10 ,june1 #ahed1 and republished in extenso in the several editions of this book1 dating from the last mentioned period4 ,nevertheless1 the fringe of cilia was1 it appears1 rediscovered in #ahgd1 just twenty years after my paper was published4 ,it is almost unnecessary to add that ,carpenter gravely errs in his statement 8that the existence of the fringe of cilia in the embryo snail had been overlooked until #ahgd40 #gb ,mr4 ,george ,rainey many years ago made us acquainted with the fact that certain of the appearances presented by the shell or other hard structures of animals1 and which had hitherto been referred to as cell-development1 are really governed by the physical laws which govern the aggregation of certain crystalline salts when exposed to the action of vegetable and animal substances in a state of solution4 ,mr4 ,rainey furnished a process for obtaining artificially a crystalline substance which shall so closely resemble shell structure that it can barely be distinguished from it4 ,the chemical substances to be used in the preparation of the artificial shell1 or calculi1 are a soluble compound of lime and carbonate of potash or soda1 dissolved in separate portions of water1 and mixed with some viscid vegetable or animal substance1 as gum or albumen1 and mixing the several solutions together4 ,the mechanical conditions required are that such a quantity of each of the viscid materials in each solution shall be of about the same density as that of the nascent carbonate of lime1 and at perfect rest4 ,this state of rest will require from two to three weeks or longer4 ,mr4 ,rainey shows the analogy or identity of his artificially formed crystals with those found in natural products both in animals and vegetables1 chiefly confining himself to the structure and formation of shells and bone1 pigmental and other cells1 and the structure and development of the crystalline lenses1 which he contends are all formed upon precisely the same physical principles as the artificial crystals4 #gc ,e4 ,ray ,lankester1 8,on the ,gregarin found in the common ,earthworm40--8,micros4 ,trans40 vol4 iii4 p4 #hc4 #gd ,for the fullest information of marine1 land1 and fresh-water species1 consult ,dr4 ,bastian's 8,monograph on the ,anguillulid02 8,lin4 ,soc4 ,trans40 vol4 xxv4 p4 #ge2 the 8,anguillula ,aceti10 by the author1 in the 8,popular ,science ,review10 ,january1 #ahfc4 #ge 8,cercaria parasitic on ,limna10 8,jour4 ,royal ,micros4 ,soc40 #ahgj4 #gf ,see my paper 8,the ,natural ,history of a ,nematode ,worm10 8,journ4 of ,microscopy and ,natural ,history10 ,october1 #ahhh4 #gg 8,the ,parasites of ,man and the ,diseases which proceed from them10 by ,professor ,rudolf ,leuckart1 #ahhf4 #gh ,r4 ,j4 ,pocock1 8,on ,worms0 7,warne1 ,op4 cit471 p4 #dfe4 #gi ,an interesting account of the formation of the tubes of ,serpula is given by ,mr4 ,watson1 8,jour4 ,micros4 ,soc410 vol4 #ahij1 p4 #fhe4 #hj ,dr4 ,baird1 8,natural ,history of ,british ,entomostraca10 printed for the ,ray ,society1 #ahej4 #ha ,see ,mr4 ,b4 ,t4 ,lowne's exhaustive treatise on 8,the ,anatomy and ,physiology of the ,blow-fly10 a volume of #gej pages and #eb plates1 #ahia4 #hb ,tuffen ,west1 8,trans4 ,linn4 ,soc410 vol4 xxiii41 p4 #cic4 #hc ,the term micropyle 7a little gate7 has heretofore only been used in its relation with the vegetable kingdom3 it is used to denote the opening or foramen towards which the radicle is always pointed4 #hd ,dr4 ,halifax adopts the method of killing the insect with chloroform2 he then immerses it in a bath of hot wax1 in which it is allowed to remain until the wax becomes cold and hard2 with a sharp knife sections are easily made in the required direction without in the least disturbing any of the more fragile parts1 or internal organs of the specimen4 #he 8,phil4 ,trans410 #ahei1 p4 #cda4 #hf ,see my paper on 8,the ,eggs of ,insects10 in 8,the ,intellectual ,observer10 ,oct4 #ahfg1 in which other varieties of eggs are given4 #hg ,w4 ,u4 ,whitney1 8,transactions of the ,microscopical ,society0 for #ahfa and #ahfg4 #hh ,mr4 ,f4 ,g4 ,cuttell1 #eb1 ,new ,compton ,street1 ,soho1 cuts and prepares excellent sections4 #hi ,published with his paper in detail1 8,aperture as a ,factor in ,microscopic ,vision10 8,journal of ,royal ,micros4 ,soc410 ,june1 #ahjh1 pp4 #ccd et seq4 #ij 8,squire's ,methods and ,formul20 8,modern ,microscopy10 ,cross and ,m4 ,f4 ,cole2 8,the ,microscopists' ,vade ,mecum10 ,a4 ,b4 ,lee2 8,bacteriology40 ,professor ,dr4 ,e4 ,crookshank1 ,messrs4 ,baird and ,tattock1 ,cross ,street1 ,hatton ,garden1 supply all ,scientific ,apparatus for ,bacteriological ,work4 #ia ,the imperial gallon contains #bgg4bgchd cubic inches1 and the imperial pint #bj fluid ounces1 whereas the wine gallon has #bca cubic inches and the pint #af fluid ounces4 ,in wine measure #a litre #cc4hae fluid ounces4 ,transcriber's ,note3 ,page xxiii1 8l4 ,corystes cossivelaunus0 changed to read 8l4 ,corystes cassivelaunus04 ,page xxv ,,errata incorporated into project4 ,page xix1 8,acmea virginea1 part of palate--#aah40 changed to read 8,acma virginea1 part of palate--#aah40 ,page #ba1 8in ,fig4 #ac1 if ,s1 ,s are a pair of conjugate foci10 changed to read 8in ,fig4 #ab1 if ,s1 ,s are a pair of conjugate foci104 ,s and ,s are in ,fig4 #ab4 ,page #hi 8,bacteriological and ,histol gical0 changed to read 8,bacteriological and ,histological04 ,page #eih1 8,apis nillifica0 changed to read 8,apis mellifica01 also entry in index4 ,page #ffc1 8the papill of the tongue is distended and seen erect0 changed to read 8the papill of the tongue are distended and seen erect04 ,obvious printer errors corrected silently4 ,inconsistent spelling and hyphenation are as in the original4