,,the ,,commonwealth ,,of ,,cells ,some ,popular ,essays on ,human ,physiology ,,by ,h4 ,g4 ,f4 ,,spurrell1 ,b4,a4 ,,oxon4 ,illustration ,,london ,,bailli,,re1 ,,tindall ,,and ,,cox #h1 ,,henrietta ,,street1 ,,strand #aija ,all rights reserved ,to ,,my ,,esteemed ,,friend ,,and ,,tutor1 ,,gustav ,,mann1 ,m4,d41 ,,etc4 ,,preface ,ever since the very beginning of my student days1 when my contemporaries took to plying me with embarrassing demands for information upon all matters medical1 ,i have been constantly impressed by the interest which the unscientific public take in the workings of their bodies and the material basis of their minds4 ,it is this general display of interest among my friends that has emboldened me to add yet another book to the many already dealing with the subject4 ,in using the word #8unscientific' ,i imply1 of course1 no reproach4 ,i mean simply to denote those people who have specialized in some branch of knowledge other than those collectively known as ,natural ,science4 ,i usually find1 when discussing physiology with such people1 that they take more interest in general principles than in details1 which they frequently find repellent1 and that they frame their questions in an appallingly comprehensive manner4 ,my object throughout this little work has therefore been to present the fundamental principles of physiology in a brief1 consecutive and readable form1 for those who do not care to study the text-books4 ,there is no lack of excellent books already1 books illustrated by careful drawings quite gruesome in their accuracy1 but they are almost all intended for 8students10 and the casual reader1 finding the organs divided up for exhaustive treatment1 fails to form a conception of the body as an organic whole1 and misses the very principles he is in search of1 in the heap of details under which they are buried4 ,it may cause some surprise that1 though in my efforts to be up-to-date ,i have in places outstripped the text-books1 ,i quote no authorities4 ,but a moment's consideration will show that it would defeat the very object of a sketch like this to burden the text with an account of how my views were formed1 while1 on the other hand1 the pioneers of science will forgive me4 ,their papers will be quoted in more durable works1 and their names honoured long after this little book has been forgotten4 ,h4 ,g4 ,f4 ,s4 ,,oxford1 ,march1 #aija4 ,,contents ,,page ,,introduction ix ,,essay ,i4 ,,living ,,matter #a ,,essay ,,ii4 ,,the ,,chemistry ,,of ,,the ,,body #h ,,essay ,,iii4 ,,the ,,mechanics ,,and ,,physics ,,of ,,the ,,body #ca ,,essay ,,iv4 ,,the ,,nervous ,,system #eh ,,essay ,v4 ,,the ,,body #id ,,conclusion #ajg ,,index #aac ,,introduction ,the unscientific public is extremely prone1 and not altogether without reason1 to take medicine as a starting-point1 and arrange all biological science around it4 ,as it is1 moreover1 apt to gauge the interest and utility of every branch of this science from a practical point of view1 and bestows most attention upon that which it imagines is of the greatest service to the doctor1 ,i think a series of popular essays on physiology could not commence with more advantage1 at any rate to physiology1 than by briefly discussing1 not with what it deals1 for that is pretty generally known1 but what is its relation to medicine4 ,further1 as the doctor is more easily discussed than medicine1 the physiologist will be more manageable for our immediate purpose than physiology in the abstract1 so we will devote the first few pages to the question of how his labours benefit the patient4 ,everyone knows the doctor1 and everyone knows that physiology deals with the #8functions of different organs of the body'2 but the public rarely meet the physiologist1 except in the fanciful caricatures of his enemies1 which though frequently personal are rarely accurate4 ,these rancorous libels1 if anyone heeded them1 would tend to raise doubts as to whether the physiologist was a good companion for the doctor1 and if it were not as well for them to see as little of each other as possible4 ,the doctor1 however1 cannot move a step without the physiologist4 ,his business is to correct the revolt of any organ from its allotted task1 and repair the damage done by its deviation from the normal path4 ,this he cannot possibly do if he does not know what that organ's normal conditions are1 and what they are it is the physiologist's duty to tell him4 ,a doctor1 therefore1 should be an enlightened physiologist1 knowing how the body ought to work1 and referring diseases to their real cause1 such as the poisons formed by an invasion of bacteria or otherwise1 or wrong feeding--that is to say1 deficiency or excess of fuel for one of the body's many engines4 ,medicine is still to a large extent rule of thumb4 ,we don't know to what many diseases are due1 or why certain things relieve them1 if any remedy is known2 and until these questions are satisfactorily settled1 it is vain to hope that disease as a whole can be successfully combated4 ,it is no use knowing what will stop certain unpleasant symptoms if we do not know how to remove their real cause1 and for this end the whole body and every individual component organ is being studied1 that the process of life may be accurately understood2 and the man who is doing this for his friend the doctor is the physiologist4 ,the physiologist has many enemies1 a motley array of cranks held together by such noble bonds as general hatred of science and prejudiced ignorance masquerading as scepticism2 but he can afford to ignore them1 for the very good reason that people cannot get on without him4 ,it is only on account of this that they are mentioned4 ,people say1 #8,the doctor is the person who requires a knowledge of physiology2 he is the man who is most likely to study it successfully'--presumably by his mistakes--#8and not waste more time on it than is necessary1' a point about which they are most solicitous4 ,the doctor1 however1 prefers to trust the physiologist4 ,if he did not1 he would have very little time to do anything else4 ,you might as well expect a tailor to make his own cloth before he makes a coat4 ,he will doubtless be able to make better coats if the quality of the cloth supplied him is improved2 but if in order to improve the finished article he lays down his scissors and applies his fingers to weaving1 his business will be sure to suffer4 ,that physiology is a thing which can take up a man's whole energies will1 ,i think1 be admitted by anyone who realizes how wide is its scope4 ,the physiologist himself must specialize1 for the subject is too vast for one man to undertake the whole4 ,the body is composed of the same elements as the rest of the world1 and their arrangement is very important1 so he must be a proficient chemist4 ,it is composed of solids1 liquids and gases1 and diffusion1 filtration1 leverage1 are frequent processes1 and every motion is accompanied by an electric manifestation1 so that mechanics and physics must have been part of his training4 ,he can scarcely study organs if he does not know their shape1 so he should know some anatomy4 ,and1 lastly1 as his business is to study life and all its attendant phenomena--and the basis of life is the cell--he must be a histologist4 ,to be all these things is a great deal to require of one man2 but though he may specialize for the advancement of a particular branch of his science1 he must be au fait with the rest1 as no vital function is dependent upon one alone of the factors enumerated4 ,hard work is required of him1 though some people say he has done but little4 ,what he has discovered is briefly1 very briefly1 set forth in the ensuing essays1 with a hint or two at the knots he would like and is trying now to unravel4 ,,the ,,commonwealth ,,of ,,cells4 ,some ,popular ,essays on ,human ,physiology4 ,,essay ,i4 ,,living ,,matter4 ,physiology is the study of life1 and the thing of all others which the physiologist would like to discover is what life really is4 ,if this were fully known1 all physiological processes could probably be deduced from it1 and disease1 which is an interference with one or other of them1 could be scientifically treated4 ,so far he has not got beyond describing the consequences of life1 and his deductions carry him no further than this3 life is a property of a substance1 protoplasm1 and protoplasm can only continue to exist in the form of a cell4 ,this definition may seem a little cryptic to some people1 and very shocking to others4 #8,life1' many people are accustomed to say1 #8means the presence of a soul1 and is supernatural2 and as to its being a question of chemical composition1 that is absurd4 ,my being made of cells1 too1 will not account for my thinking4' ,but when people dogmatize thus about what they have not considered1 they usually find themselves landed in difficulties4 ,they go so fast3 the most spiritual of men is so dependent upon matter and its properties that his soul will speedily quit his body if he is prevented from breathing4 ,and the reason of this is1 that if he cannot get air1 the chemistry of the cells of which his body is made becomes altered2 he no longer consists of protoplasm1 therefore he no longer lives4 ,life1 that it may exist in a material world1 must have a material basis1 and if that is interfered with it becomes extinct or quits the material plane2 in any case1 ceases to interest the physiologist as a physiologist4 ,i do not think anyone need be shocked at this being recognised4 ,it is1 of course1 the ambition of the physiologist to make protoplasm1 but so far he has got no further than making some of the complicated bodies into which protoplasm breaks up when it dies4 ,a little while ago this bare possibility was loudly derided1 but the advance in organic chemistry has been so great of late years1 and so many complicated substances which once seemed as unobtainable as protoplasm itself have been made in the laboratory1 that we now have hope of a precise knowledge of the chemistry of life some day1 though that day may be yet very distant4 ,to give an account of life is to describe as far as we are able the nature of the living substance1 protoplasm2 and as protoplasm is a #8structure of compounds1' a word or two about chemical compounds may clear the ground for discussing it4 ,if you were to take a compound1 say a lump of sugar1 and start breaking it up1 you could hammer for a very long time and it would be still sugar2 but if a tiny fairy with a minute hammer and chisel were to go on breaking up the grains1 he would ultimately have molecules of sugar before him4 ,each molecule would consist of exactly the same number of atoms of carbon1 hydrogen and oxygen1 and if he divided it further by the removal of a single atom1 it would no longer be sugar4 ,he could hammer away at the atoms as hard as he liked1 for they are incapable of further division4 ,there are seventy odd different kinds of atoms4 ,when the molecules of a substance are composed of only one kind1 it is said to be simple2 when of several kinds1 compound4 ,now1 the difference between the various substances we see around us consists not only in what different kinds of atoms their molecules are composed of and their number1 but in their arrangement4 ,this arrangement may be in chains or rings1 and the relative position which the different atoms occupy in the structure of a molecule makes all the difference in the world4 ,this difference of composition gives the difference of properties to compounds2 so a compound must consist only of molecules which are all alike4 ,if a substance is made up of molecules of different kinds1 ununited by chemical bonds1 and therefore capable of being mixed in any proportions1 it is called1 not a compound1 but a mixture of compounds4 ,but just as atoms combine to form molecules1 so the smaller molecules sometimes enter into combinations with one another to form new compounds having larger and more complex molecules4 ,such a compound is said to be composed of radicles1 or groups of atoms1 and on being decomposed can be broken up1 first into simpler compounds1 which can afterwards be further divided into their constituent elements4 ,now1 of all substances1 protoplasm seems to consist of the largest number of components1 and to have them arranged in the most complicated way known2 though #8known' is really not the right word to use in this connection4 ,the reason why we do not know what life is1 is that we cannot find out in what way the constituent compounds in the protoplasmic structure are combined4 ,directly we try to analyze protoplasm1 it dies2 that is1 it splits up into a number of simpler bodies and is altered beyond reconstruction4 ,these compounds into which protoplasm breaks up when it dies are themselves extremely complex2 but though much careful study has been bestowed upon them1 we cannot as yet say how they are put together to form the living substance4 ,protoplasm is too variable a body to be considered a single compound1 while1 on the other hand1 the chemical relationships of its components must be too close to admit of its being called a mixture4 ,its chemical position is therefore unique1 and we can only speak of it as a substance of unknown composition4 ,what1 then1 is it that makes protoplasm unmistakable and different to all other substances8 ,the complexity of its structure is1 after all1 merely a matter of degree4 ,the difference is not easily defined1 but it roughly amounts to this3 ,protoplasm is always changing1 yet always remains the same4 ,life is the change in the molecules4 ,if our definition of life seemed obscure1 this sounds like a paradox2 but perhaps the following fact may help to explain it3 ,under certain conditions some of the simpler compounds behave in a somewhat similar way4 ,for instance1 there is one which is so greedy of oxygen that it grabs it from whatever will readily give it up1 and in order to do so is obliged to relinquish that which it has already got in its molecule to make room for that freshly acquired4 ,protoplasm is always behaving in this sort of way as long as it is protected from extremes of heat and cold1 and from active chemicals which split up its molecules to form fresh compounds4 ,then it dies1 or ceases to be protoplasm4 ,but the importance of this constant change lies in the fact that by continually breaking down its own molecules protoplasm obtains the energy to rebuild them out of non-living compounds of high potential energy1 to modify its environment1 and1 in fact1 to do the work of life4 ,it was said above that protoplasm only continued to exist in the form of a cell2 therefore1 what is a cell1 and why its necessity8 ,we have seen that protoplasm has a very complicated structure1 and that its normal condition is one of change4 ,this being so1 it obviously cannot exist in large masses1 for if it did the change would be sure to be uneven in different parts from its very complexity2 and the centre of the lump would either be starved or poisoned by the products of its own life4 ,to avoid this1 the mass is divided up into a vast number of small units each complete in itself1 in communication more or less direct with its neighbours1 and all equally accessible to fluids which both feed and cleanse them4 ,but there is another and still more important reason for such a division4 ,the protoplasm is constantly discharging decomposition products1 and needs to be repairing its waste by building in fresh compounds4 ,the raw material around it requires dressing before it can be of use1 and the building in is a difficult business4 ,in each cell there is1 therefore1 a place set apart1 where the protoplasm has peculiar capabilities1 and it is here that this elaboration is carried out4 ,this spot is called the nucleus4 ,thus it will be seen that the formation of an animal's body by the aggregation of cells is a necessary and ingenious way of avoiding a difficulty4 ,to say1 however1 that an animal's body consists of cells is to take an entirely wrong starting-point4 ,a cell is complete in itself1 and can live if properly fed1 even though separated from its neighbours4 ,many whole animals consist of only one cell4 ,a cell is1 moreover1 capable of growing and dividing1 thus giving rise to two cells with two nuclei1 and it is only because cells find that it pays better not to separate1 but to form masses and specialize at different kinds of work1 that we have large animals composed of millions of cells like ourselves4 ,given a cell1 it is necessary to keep that cell under favourable conditions4 ,otherwise the unstable protoplasm breaks up4 ,it must have the elements necessary to keep up its cycle of changes in the proper form1 which we may now call food1 and many cells have to go and find this requisite4 ,it must keep away from injurious influences1 and it must race other cells for localities favourable to its growth and multiplication2 in fact1 the cell must work4 ,that a cell can1 in virtue of its chemical affinities alone1 move about1 seeking favourable conditions1 showing discrimination and doing work1 seems incomprehensible4 ,in the first place1 how can it move8 ,there is only one way3 it must effect a redistribution of its substance1 and contrive that those parts of the cell whose activity is applied to this end shall be so situated as to produce definite changes in its shape according to the cause which evokes them4 ,of the way in which different cells move we shall have a good deal more to say later4 ,why protoplasm should be influenced to move still requires explanation4 ,yet the gap between protoplasm and other substances is really not so great1 after all4 ,heat and magnetism cause movement in inanimate matter1 and the response of protoplasm as exemplified by some of the minute unicellular animals is almost as mechanical4 ,some kinds which swim in water move to the positive pole of a galvanic battery1 others to the negative1 if the wires are dipped into the vessel containing them4 ,some move towards light1 others away from it1 with unvarying regularity4 ,temperature and chemical substances also cause a definite effect upon these micro-organisms4 ,and all these movements are wholly involuntary1 absolutely invariable1 and1 in fact1 reactions evoked by fixed causes4 ,nevertheless1 it will be seen that protoplasm can only continue to exist in the form of a cell1 since1 unless thus organized1 it can neither keep itself among favourable surroundings nor prepare fresh ingredients to make good its waste4 ,if a cell be cut up into several pieces1 these detached bits of protoplasm will live for a time2 but death overtakes them as soon as they have used up their reserve material4 ,when this is gone1 they have to consume their own substance1 a process which quickly proves fatal4 ,should a fragment contain a small part of the nucleus cut away with it1 it will live a little longer2 but it is only the piece which contains the nucleus more or less intact--in other words1 the cell1 damaged though it be--which can survive and recover from such mutilation4 ,the specialization of protoplasm to form a cell is perhaps its most remarkable peculiarity4 ,not only is protoplasm differentiated to form different structures1 but it devotes the energy evolved in its ceaseless change to different purposes4 ,the protoplasm of the motor organs of the cell expends itself wholly in producing the physical movements necessary to approach and capture food4 ,when this has been passed into the cell1 protoplasm of another variety works to refine and dissolve it1 and then passes it on to the nucleus4 ,the protoplasm of the nucleus1 again1 has different work to do4 ,it devotes its energy to producing chemical changes in the raw material1 and converting it into new compounds which the various parts of the cell can assimilate4 ,some of these it retains for its own needs2 the rest it dispenses to the motor and other organs to repair their waste1 and supply them with energy to obtain more food4 ,thus do the different varieties of protoplasm which compose a cell supply one another's needs1 and enable one another to live2 and thus does a cycle of chemical changes form the foundation upon which the whole fabric of life rests4 ,but into details we cannot yet go1 for our investigations of the material basis of life have not yet carried us beyond these general conclusions4 ,at present we know nothing definite about the first causes of life1 and1 though we have hopes1 perhaps we never shall4 ,meanwhile we are observing1 analyzing1 and classifying the phenomena in which life is manifested1 in the hope that at last light may break through upon our researches1 and we may be able1 if not to synthesise protoplasm in a test-tube1 at least to demonstrate its workings in equations4 ,in the meantime1 our actual knowledge of living matter can still be compressed into the words in which ,professor ,huxley summed it up years ago3 #8,carbon1 hydrogen1 oxygen1 and nitrogen are all lifeless bodies4 ,of these1 carbon and oxygen unite1 in certain proportions and under certain conditions1 to give rise to carbonic acid2 hydrogen and oxygen produce water2 nitrogen and hydrogen give rise to ammonia4 ,these new compounds1 like the elementary bodies of which they are composed1 are lifeless4 ,but when they are brought together under certain conditions they give rise to the still more complex body1 protoplasm1 and this protoplasm exhibits the phenomena of life4' ,until we have further knowledge of the changes which constitute these phenomena1 physiology must remain descriptive rather than explanatory4 ,,essay ,,ii4 ,,the ,,chemistry ,,of ,,the ,,body4 ,i4 ,the cell is usually very minute--indeed1 absolutely invisible without a microscope1 though in some cases it is a fair size4 ,the whole yolk of an egg is a single cell until its minute nucleus1 a speck on one side1 starts dividing and it becomes several4 ,by the time the chick is ready to be hatched there are millions4 ,usually1 however1 a cell is small--just as much protoplasm as its still more minute nucleus can keep going2 though here1 again1 one must be guarded1 for there may be several nuclei instead of only one4 ,the protoplasm on the external surface and around the nucleus is specialized into a more or less definite membrane4 ,to this outer envelope are attached fine fibrils1 which join up to a small body within the cell1 called the centrosome1 and by the lengthening and shortening of these its shape can be altered4 ,the contents are fluids2 so if the containing membrane is loosened in any direction1 they tend to bulge out and form an excrescence1 and in this way the cell is enabled to throw out limbs and surround particles of food1 and1 by relaxing the fibrils in one direction and contracting them in others1 to crawl whither its chemical1 thermal1 or physical affinities direct4 7,see ,diagram #a47 ,not particularly inspiring is the sight of life in its simplest form1 but when a few millions of these cells group together and form one body1 dividing the labour between them1 the result is something stupendous4 ,there are animals composed in this way1 some of whose cells have developed their digestive capabilities to such an extent that they have almost lost all their others4 ,these are carefully guarded in the interior of the body4 ,other cells in this same beast1 receiving their food in a fluid form from these digestive specialists1 secrete lime around them till a skeleton is built up4 ,to the levers of this skeleton are attached bundles and strands of cells1 which1 if they can do nothing else1 can lengthen and shorten and make it move4 ,yet1 again1 there are cells which have especial facilities for receiving1 weighing1 and transmitting chemical and physical promptings4 ,these cells1 again1 lie in a protected corner of the interior1 but they send out fine threads to one another and every part of the body1 and control the whole4 ,the animal in which this beautiful system of division of labour has been carried to its greatest perfection has many and varied powers4 ,he can in some cases even apply to the individuals of the species the principles of his own cellular economy1 and thereby achieve not only the making of poetry and jokes1 but the building of a ,westminster ,abbey1 the construction of ,maxim guns1 and the enforcing of his economic refinements upon his less highly specialized neighbours4 ,we have now traced out a general idea of life4 ,we have seen that its basis rests upon a chemical structure which1 to maintain its identity1 must be always changing4 ,we have seen that to do this it must keep breaking down its substance1 and giving off the products1 and taking hold of extraneous materials1 and building them in1 not only to repair the loss1 but in order to grow2 and that to do that it has to be more or less modified in parts1 in order that the main bulk may be brought within reach of its food1 and be then able to convert it into the most useful form4 ,and1 lastly1 we have seen that just as several specialized forms of plasm together make up a cell1 so several kinds of cells1 each with some peculiarity exaggerated1 aggregate1 and1 supplying one another's needs1 compose a body4 ,having now roughly sketched out the scheme upon which such a body works1 we can go on to a more detailed examination of the division of the labour1 and the way in which each department supplies1 and is dependent upon1 the others4 ,if we were to do this thoroughly1 it would take a great deal of time and space1 for the physiology of a potato plant1 though essentially the same1 presents many differences from that of a horse2 but the physiology of the great human interest is also that of the most complicated animal1 namely1 man1 so it is on him that we shall focus our attention4 ,protoplasm is more easily studied the more specialized is the animal it composes4 ,when all the events of life are taking place in a speck of matter1 invisible without a microscope1 it is impossible to analyze the changes which it is working in its surroundings1 or to infer those which are going on in itself4 ,but when large numbers of cells are examined collectively1 we can deal with what they take in and what they give out in sufficient bulk to arrive at a fairly accurate determination4 ,the study is rendered still easier in an animal with extremely specialized organs1 like man1 in which food is nearly all taken in by the mouth1 and thus kept quite distinct from what is eliminated2 the latter1 again1 being mostly given off by the kidneys is kept equally distinct4 ,moreover1 the intermediate changes being performed in different organs still further simplifies investigation of the vital process2 for the physical effects are also more easily studied when exaggerated in a particular part of the animal4 ,the electrical changes in a single cell might long have remained unsuspected had we not been able to observe those in a muscle with the galvanometer4 ,now1 while the cells which make up the body of man differ very greatly owing to the different tasks which they have to perform in obtaining food and getting rid of refuse1 they all require very much the same fuel to enable them to live1 and having got it1 they all treat it in very much the same way2 therefore our first business is to consider what the body wants1 and what it does with it4 ,afterwards we can try to find out how it gets it1 and where4 ,the first and most indispensable requirement of protoplasm is water4 ,the next is probably nitrogen1 compounds of which seem to form the framework of the protoplasmic structure4 ,the next is probably carbon1 and the next free oxygen4 ,the two last-mentioned combine with a release of energy4 ,this happens in the grate when coal burns1 and the result is heat4 ,in the tissues of a body the result may be heat1 growth1 or movement1 all three being present in the phenomenon of muscular activity4 ,finally there are mineral salts1 the most important being sodium chloride1 which is placed on the table at every civilized meal4 ,but though these elements are given here in order1 their importance is really equal1 for all are necessary4 ,that is about as much as it is wise to say here4 ,the chemistry of the living cells--their anabolism1 or how fresh material is built into their structure2 their katabolism1 or how the same structure is broken down that work may be done2 in fact1 the general metabolism--is so complicated1 and so little understood as yet1 and requires so extensive a knowledge of chemistry to follow1 that it is best left alone by people who do not want to go into it deeply4 ,at best1 such a discussion resolves itself into an exposition of different observers' theories1 with the reasons why they hold them--reasons based on laborious and technical studies4 ,pages might be written on the various theories1 backed by pages more of chemical formul1 to show why this view deserves deep consideration1 while that1 in spite of the obstinacy with which it is upheld1 is absurd2 but though such discussions take one nearest the secret of life1 the general public is not unnaturally apt to stigmatize this side of physiology as dry4 ,it is a matter which interests experts1 not the casual reader4 ,quite a different affair is the question of diet4 ,that is everybody's business1 as the number of faddist societies and blatantly advertised #8foods' attest4 ,and though the preparation of the food in the body up to the point where it merges into living matter and is lost sight of--in a word1 #8digestion'--is again a question of chemistry1 it is one which may be approached without such an exhaustive knowledge of that science as the previous considerations would have required4 ,it is1 moreover1 to judge from the way it is discussed1 a topic of universal interest4 ,a casual glance at the animal kingdom will show that diet is a wide subject4 ,a pigeon will eat peas2 a tiger would not know what to do with the peas if he got them2 while a monkey will eat almost anything he can lay hands on4 ,a plant takes us still further afield1 for it can use the atoms of substances with an extremely simple molecule--carbonic acid gas1 for instance4 ,our task1 however1 is simplified by our having only man to consider2 and although most of the higher animals are so much alike that they might be considered in general and contrasted in detail1 it is a great thing to get rid of the whole vegetable kingdom with bacteria and parasitic animals4 ,one of the first requisites for the maintenance of life1 as was mentioned above1 is nitrogen4 ,now1 nitrogen is one of the commonest elements in the world1 but it is the hardest to supply to the body4 ,four-fifths of the air is pure nitrogen1 but pure nitrogen is useless as a food4 ,we draw it into our lungs at every breath1 and are none the better for it1 for we breathe it out again unchanged2 and if it were completely absent from the air we should not be so very much the worse4 ,the ,ancient ,mariner exclaimed1 #8,water1 water everywhere1 and not a drop to drink'2 a starving man might exclaim1 #8,nitrogen1 nitrogen everywhere1 and not an atom to assimilate4' ,animals have to get their nitrogen in the form of proteid1 a substance whose molecule is composed of nitrogen1 oxygen1 hydrogen1 carbon1 etc41 and might roughly be described as dead protoplasm4 ,plants on which animals feed1 when they do not get their proteid by the simpler1 though less moral1 method of eating one another1 are able to get their nitrogen in a simpler form2 but with that we are not concerned4 ,the proteids are a group of substances which resemble protoplasm in the elements of which they are composed and in the complexity with which they are combined4 ,the various proteids seem1 however1 to have a definite chemical composition1 and therefore differ from protoplasm in being true compounds2 moreover1 if kept from bacteria they undergo no changes4 ,one of the best forms of proteid for examination is white of egg2 this1 as is known1 sets or coagulates when boiled1 dissolves in water1 from which it may be precipitated by boiling1 and displays various other chemical properties common to all proteids4 ,there is1 however1 a good deal of difference between the several varieties of proteids1 and the more complex ones have to be converted into the simpler before they can be absorbed4 ,hence the necessity for digestion4 ,now1 as proteid resembles dead protoplasm1 it might be supposed that a diet of proteid alone would be the most economical2 but this is not so4 ,if it were possible to live without work1 i4e41 without movement of any kind1 it might be2 but to do work1 more carbon must be oxidized than the proteid molecule contains4 ,carbon1 the next item on our list1 is familiar to everyone in the comparatively pure form of coal1 charcoal1 and the #8lead' of pencils4 ,it is commonly used to burn--i4e41 oxidize--that heat may be obtained to boil water and to work machinery4 ,this is precisely what it is required to do in the body1 where it is burnt by oxygen taken in by the lungs1 that heat and energy may result4 ,it is a commonplace that severe exercise causes laboured breathing1 and the reason of this is that the carbon in the body is being oxidized1 and the product1 carbonic acid gas1 has to be got rid of4 ,the more work is being done1 the more oxygen is required to burn carbon in the muscles4 ,the more carbon is burnt1 the more heat is evolved1 and the more necessary it is that the blood should be cooled by drawing cool air into the lungs4 ,hence the more rapid breathing4 ,the air normally breathed out is always warmer than that taken in1 and always contains extra carbonic acid gas4 ,after exercise the quantity is increased1 and its increase on the normal amount given off can readily be demonstrated by analyzing samples of the air taken in and given out4 ,but carbon1 like nitrogen1 cannot be taken in in the crude form4 ,no one would try to make a meal of charcoal4 ,a certain amount is contained in the proteid molecule1 enough1 no doubt1 to secure the basis of the protoplasmic structure2 but unless one is prepared to eat an excessive quantity of proteid1 a proceeding entailing waste and exhaustion of the digestive apparatus1 the balance must be made up by eating carbohydrate4 ,the forms in which people are most familiar with carbohydrate are starch and sugar4 ,sugar is the better food1 as it is so much more soluble than starch2 and1 in fact1 starch is always turned into a kind of sugar before it is used by the body4 ,the common cane-sugar1 which everyone knows so well1 is about the most useful food we have1 owing to its purity1 and therefore concentration1 and its simplicity4 ,a very small amount of digestion is necessary to convert it into the simplest of all carbohydrates1 a substance easily stored1 as glycogen1 till wanted1 which is present in muscle after a meal1 and is used up when the muscle is active1 being oxidized to carbonic acid gas1 sarcolactic acid1 and alcohol4 ,the importance of carbon in the diet is therefore obvious2 and people who intend doing extra muscular work should take extra sugary food rather than extra proteid4 ,a locomotive which is about to make a record run takes in more coal1 not more engine-drivers1 and our athletes now follow the same principle4 ,we shall1 however1 have a good deal more to say about athletes presently4 ,there is yet another point to be considered in respect to carbon4 ,carbon need not be taken in the form of carbohydrate1 the alternative being fats and oils4 ,fats and carbohydrates are both composed of the elements carbon1 hydrogen1 and oxygen1 but the proportions in which they are joined are different4 ,fats are not such useful foods as carbohydrates1 nor to most people so pleasant--compare a spoonful of olive-oil and a lump of sugar4 ,but there is one important point to be urged in their favour3 they yield twice as much heat as either proteids or carbohydrates2 so their position among foods is assured4 ,the other chemical necessities of the body we need only mention here4 ,hydrogen is one of the components of proteid1 carbohydrate1 fat1 and water2 and if it does not enter in the last form1 it--at any rate1 most of it--leaves as such1 being oxidized in the tissues4 ,sulphur and iron deserve honourable mention2 common salt is required by the blood2 lime and phosphates go to make bone2 but important as they all are1 they need not detain us further at present4 ,with regard to the amount of these elements which is required per day1 and which is ascertained by collecting and weighing all that is given off1 it is found that about ounce of nitrogen and #aj ounces of carbon are necessary to an average man--i4e41 weighing about #aj stone4 ,the ounce of nitrogen and about #b ounces of the carbon are contained in #d ounces of dry proteid1 which leaves a balance of #h ounces of carbon to be made up2 and this is usually obtained by eating #d ounces of fat and #ah ounces of carbohydrate4 ,roughly speaking1 these principles are contained in pound of ordinary butcher's meat and #b pounds of bread2 but it would be well to defer considering diet for the present1 until we have examined the apparatus by which the body extracts what it wants from the raw materials1 and which of these offer it the least resistance4 ,,ii4 ,the way in which protoplasm gets its chemical requisites for growth is doubtless simply by absorbing them4 ,some of the lower structureless forms carry this to an absurd extreme1 for when two individuals meet they fuse1 and each no doubt claims to have eaten the other4 ,as1 moreover1 the first thing which a cell does when it grows is to divide1 the whole proceeding looks rather futile4 ,but ready-made protoplasm of an assimilable shape is rare1 and it is not often that a cell1 unless it be a plant or a parasite1 finds itself in a substance which can be handed straight to the nucleus without further elaboration4 ,usually the cell has to discharge from itself a reagent1 which will develop the right chemical qualities in the matter it wants to absorb4 ,this substance is known as an enzyme1 or ferment4 ,ferments1 however1 are an expense to the cell1 requiring a certain effort for their production2 so1 in order that they may be economized1 they are1 in the higher forms1 poured over the food while it is in an enclosed cavity1 or stomach4 ,in the simplest animals1 consisting of a single cell1 the protoplasm simply flows round the particle of food1 and it is #8ingested' with a drop of water4 ,into this #8food vacuole' the ferments are secreted1 and when all that is useful has been dissolved out and absorbed1 the bubble moves to the surface and bursts2 or1 to put it differently1 the cell flows on its way1 and the vacuole1 with any shell or refuse it may contain1 gets left behind4 7,see ,diagram #a47 ,in other cells which are constant in shape there is an opening leading to the interior of the cell4 ,round this there are little projecting threads1 which beat the water regularly4 ,in some positions these threads enable the cell to swim1 but here their duty is to cause a current and wash particles of food down the primitive throat into the interior1 where1 as in the preceding case1 they become enclosed in a vacuole4 7,see ,diagram #b47 ,illustration3 ,,diagram #a4--,,the ,,am,,ba4 ,illustration3 ,,diagram #b4--,,param,,cium4 ,moving a stage higher1 we find animals consisting of several cells4 ,of these it is only natural to suppose that some have greater enzyme-forming powers than others4 ,illustration3 ,,diagram #c4--;,,development ,,of ,,an ,,embryo3 ,,first ,,stage4 ,illustration3 ,,diagram #d4--;,,formation ,,of ,a ,,digestive ,,cavity4 ,illustration3 ,,diagram #e4--;,,cross ,,section ,,of ,a ,,developing ,,embryo4 ,a step higher in the animal scale1 or a further advance in the development of the schematic embryo 7depicted in ,diagrams #c to #f71 and we find that these special digestive cells are losing their sturdier qualities and being placed in a position protected by cells which have specialized in another direction4 ,this is shown in ,diagram #d1 where the hollow ball of cells which resulted from the repeated division of one cell is represented in section4 ,one side of the ball is pushed in1 and now the beast consists of two layers of cells1 an outer protecting and an inner digesting 7,hydra and sea-anemone74 ,soon1 however1 it is found more convenient to have a tube for digesting food1 for then different substances can be digested and absorbed in different parts2 and the refuse1 of which the animal can make no use1 need not be brought back to the mouth to be got rid of4 ,this1 however1 requires a number of other changes in the structure of the animal1 which are roughly shown in ,diagrams #e and #f4 ,it is not to our purpose here to discuss the development of animals or an animal2 but the figures are worth glancing at1 as they show not only how certain of the cells are set apart for digesting food1 but also that a large body consists really only of a mass of protoplasm1 composing kindred cells of common origin4 ,illustration3 ,,diagram #f4--,,showing ,,development ,,of ,,an ,,embryo4 ,now1 for obvious reasons1 the longer1 within certain limits1 this tube is the better4 ,all sorts of different food-stuffs have to be acted upon in it1 and some offer considerable resistance to digestion2 and the further they have to travel in the tube1 the more chance there is of their being successfully treated4 ,besides1 different parts have different functions1 and the longer the tube--again within necessary limits--the greater scope is there for division of labour1 and consequent economy4 ,the comparative length of the alimentary canal is not the same in all animals by any means4 ,carnivorous animals1 like the cat1 whose food is soft and easily digested1 have a fairly short one4 ,herbivora1 like the sheep1 whose food is difficult to digest and mixed with much husk1 which is wholly indigestible1 have a comparatively very long one4 ,man1 who is omnivorous1 but eats less and more judiciously chosen food than either of the above classes1 has one of medium length4 ,but in all cases among the higher animals there is an attempt made to obviate the necessity of increasing the length of the animal by coiling the tube within the body4 ,the annexed diagram 7#g7 illustrates this principle4 ,it shows a schematic animal whose digestive canal is much longer than itself4 ,illustration3 ,,diagram #g4--,,showing ,,how ,,the ,,digestive ,,canal ,,is ,,lengthened4 ,illustration3 ,,diagram #h4--;,,cross-,,section ,,of ,,the ,,digestive ,,tube4 ,the digestive canal has1 however1 another function4 ,the cells which compose it have not only to secrete juices1 to convert the food into a usable form2 they have then to absorb it4 ,the nearer a particle of food is to the wall of cells1 the sooner it is reached by these juices1 and the less chance there is of useful material being swept away and lost4 ,in view of this fact1 along certain tracts the digestive canal is folded inwards1 and there are projections1 which increase the number of cells to secrete and their opportunities of absorption4 7,see ,diagram #h47 ,illustration3 ,,diagram #i4--,,showing ,,how ,,glands ,,arise4 ,here again we have an illustration of a constantly recurring need1 with a device for meeting it--increase of surface without increase of bulk4 ,we met with it before in the cellular system2 we shall meet with it again in glands1 lungs1 and brain1 at least4 ,the importance of a device for gaining this end is apparent when one remembers what the comparative value of surface and bulk is to an animal1 and that1 while surface increases by the square1 bulk increases by the cube4 ,the principle is pressed to an extreme1 together with the allied principle of division of labour1 in glands4 ,the object of these is to increase the number of secreting cells1 and1 as they are delicate1 to keep them protected from contact with coarse particles of food4 ,and1 in order that nothing may interfere with their efficiency1 they are absolved from the duty of absorbing4 ,hence tubes grow out from the cavity of the alimentary canal lined with the same cells1 but1 as no food ever enters1 the cells which line them devote themselves entirely to pouring out digestive juices4 ,glands differ considerably in structure and in the liquids which they secrete4 ,some are very small2 some1 like the liver1 very large4 ,in some the tube is very short1 in some long1 coiled and branched1 and sometimes the gland is connected with the surface by more or less of a duct4 ,some glands only secrete one enzyme1 some several4 ,in each1 however1 the principle is that shown in ,diagram #i1 no matter how its structure is masked by the bloodvessels and supporting cells or connective tissue which envelop it4 ,after a meal1 or1 rather1 when the process of digestion is over and the animal is beginning to think about its next1 the gland cells start preparing their enzyme4 ,there is great activity in the nucleus1 and granules stream out from it towards the lumen of the gland in much the same way1 to take a homely illustration1 as bubbles in some effervescing drink form at the bottom of the tumbler and rise till the surface is covered with foam4 ,at the right moment these granules are discharged1 just as the bubbles on the surface of a liquid break at a slight jog4 ,they are usually not the ferment or enzyme1 but its precursor1 a substance which only turns into the ferment when it gets outside the cells4 ,the ferments1 when formed1 are very peculiar substances about which we should like the chemist to tell us more1 though great advances have been made in our knowledge of them lately4 ,among other peculiarities1 one may mention that1 though they will keep indefinitely if bottled1 they are easily destroyed by too extreme a temperature or too acid or alkaline surroundings1 that their composition is entirely unknown1 and1 strangest of all1 that they do not become used up4 ,a given amount of rennet will clot any amount of milk within reasonable limits1 and yet remain rennet4 ,the clergyman has been quoted as an illustration of the action of a ferment1 and he makes a good one4 ,he can make any number of suitable men and women into married couples1 and yet his own state is unchanged4 ,,iii4 ,in man1 the digestive process may be divided into three stages4 ,they are arranged progressively1 so that each clears the way for the next1 and take place in the mouth1 the stomach1 and the upper part of the small intestine1 the rest of the canal being mainly occupied in absorption4 ,illustration3 ,,diagram #aj4--;,,general ,,scheme ,,of ,,the ,,alimentary ,,canal1 ,,with ,,its ,,offshoots--,,lungs ,,and ,,glands4 ,by far the largest proportion of the food is carbohydrate1 in some form1 so one naturally expects the first stage of digestion will deal with the constituents which represent this class4 ,this is the case4 ,the food is taken into the mouth in small quantities and ground up with the teeth1 during which process it is subjected to the action of the saliva4 ,this fluid1 which is the secretion of three pairs of glands1 converts a large proportion of the carbohydrates1 starch1 cane-sugar1 etc41 into a very simple sugar which is absorbed directly it reaches the stomach4 ,one of the most sensational discoveries of the physiologist has been that the saliva leaving the gland does not contain the ferment necessary to effect this change until it has been subjected to the action of putrefactive bacteria4 ,these1 fortunately for us1 it is pleasant to know1 simply swarm in the mouth4 ,when the food is swallowed1 it passes very rapidly down the first part of the alimentary canal1 which is straight1 and is then kept for some time in the stomach4 ,the stomach differs from the rest of the canal in several particulars1 among them the following3 it is a large cavity1 and is closed at each end by a valve to keep the food in until it has been thoroughly treated1 and it deals with the whole mass of food taken at a meal at one time1 and yet has no contrivances for increasing its surface4 ,here the food is subjected to a most important and searching examination4 ,enclosed in this bag1 it is thoroughly mixed with weak hydrochloric acid1 secreted by numerous glands1 and kept churning round and round by the muscular action of its walls1 that the contents may be kept well mixed4 ,the acid is just strong enough to kill protoplasm1 and hence the putrefactive bacteria which were necessary in the mouth1 but would be a very doubtful blessing in the interior of the body1 are disposed of4 ,other things are also killed4 ,not only does the stomach execute intruding bacteria1 but it also kills a good deal of our food4 ,fruit and salad consist largely of still living cells1 and occasionally there is bigger game1 e4g41 oysters4 ,one thing1 however1 the acid does not kill1 and that is the cells lining the stomach1 and it may as well be said here that the parts of the body exposed to ferments have the very necessary power of resisting them1 so that a normal animal does not digest itself4 ,the stomach1 however1 is a kitchen as well as a slaughter-house4 ,the gastric juice1 or secretion of all the glands opening into it1 contains1 besides the acid1 two important ferments1 both of which act on proteids4 ,carbohydrates are absorbed1 but not digested1 in the stomach1 as acid destroys saliva4 ,one of the ferments is rennet1 an article familiar to the culinary profession1 which solidifies milk4 ,the other acts on proteids generally1 converting them ultimately into a very simple form1 peptone1 which is absorbed at once4 ,how much of the proteid in the stomach is converted into peptone is not known1 for the action of acid alone is sufficient to enable it to be absorbed4 ,a solution of proteid1 e4g41 white of egg1 is quite altered if made slightly acid2 it no longer coagulates when boiled1 but the change of the most practical interest is that1 if injected into the veins1 it seems to become part of the blood1 while ordinary proteids act as poisons4 ,the peptonizing ferment1 however1 has one very important function3 it digests the collagen of the connective tissue1 the substance which becomes gelatin when boiled4 ,the reason why this is so important is not only that nothing else in the body affects it1 but that fat is enclosed in it1 and if it were not thus set free would pass through the body unabsorbed4 ,the final stage is the digestion by the pancreatic juice4 ,after the food has been exposed for some time to the gastric juice1 it is allowed to escape a little at a time from the stomach1 and continues its way along the alimentary tube4 ,before it has gone many inches it comes to the openings of two ducts1 those of the liver and the pancreas1 and immediately the acid stimulates them1 and the glands pour out their secretion4 ,that of the liver is largely excretion or refuse from the blood without direct action on the food1 but it enables the pancreatic juice to do its work by making the food again alkaline1 and stimulates the muscular coats of the intestine to force its contents along4 ,that of the pancreas is the most important digestive fluid in the body1 containing many ferments2 it acts alike on proteids1 carbohydrates1 and fats--in fact1 digests everything--so that the rest of the long tube is freed from any more laborious duty than absorbing them as they pass4 ,,note4--,the digestive ferments are now prepared for examination by chopping up the gland and placing it in glycerine2 this extracts the ferment and preserves it from the action of bacteria4 ,the first experiments on digestion1 however1 constitute one of the romances of physiology4 ,a ,canadian named ,st4 ,martin got into trouble with ,red ,indians whilst in the ,united ,states1 ,america1 and was shot through the body4 ,the surgeon who attended him was unable to make the wound close1 and when it healed there remained an opening in the man's body communicating directly with his stomach4 ,the surgeon1 ,beaumont1 saw possibilities in this1 and1 obtaining gastric juice from his patient1 made those classical experiments which entitled him to a place among the fathers of physiology4 ,americans do well to be proud of ,beaumont1 for it cost him many sacrifices1 and his patience and courage are above praise4 ,not only was he devoid of all but the crudest appliances out in the backwoods1 but his subject proved intractable and mercenary4 ,no sooner did he discover his value than he crossed the border1 and refused to return except upon exorbitant payment4 ,even after this had been arranged1 he repeated the performance whenever he thought fresh extortion possible4 ,in spite of these difficulties1 the investigations proved wonderfully accurate and complete4 ,,iv4 ,of the absorption of the materials thus prepared it is not necessary to say much in a work of this compass1 but the absorption of oxygen is too important to be passed over4 ,oxygen is required by the body pure1 and1 as it is uncombined with anything in the air1 it needs no digestion to free it4 ,a special organ1 however1 is necessary to absorb it4 ,this is the lung4 ,the lungs originate1 just like a gland1 by a pouching of the alimentary canal near its origin1 but differ from a gland in their cells being very much flattened1 to offer a large surface to the air on one side and to the bloodvessels on the other4 ,incessantly during life air is being drawn into the lungs2 that the cells to which it is there exposed may transfer its oxygen to the blood2 and then1 after the cells have also transferred the carbonic acid gas from the blood to the air1 driven out again to be replaced by fresh4 7,the mechanical means by which the lungs are filled and emptied come under another heading47 ,v4 ,food having been absorbed by cells set apart for the purpose1 the next problem is1 ,how is it distributed to those specialized for other work8 ,the medium for this distribution is a liquid called lymph4 ,all the spaces in the body are filled with lymph1 all the organs bathed with it1 every cell moistened with it2 yet it is comparatively stagnant1 and the food has to be conveyed from the walls of the alimentary canal to the lymph in the neighbourhood of the cell requiring nourishment by a more expeditious agent4 ,this is done by the blood4 ,illustration3 ,,diagram #aa4--,,principle ,,of ,,the ,,system ,,of ,,bloodvessels4 ,illustration3 ,,diagram #ab4--,,principle ,,of ,,double ,,circulatory ,,system4 ,the blood is a fluid akin to the lymph1 but confined in a system of tubes4 ,through these tubes it is driven at a considerable velocity1 and in the course it takes passes within a reasonable distance of every cell in the body4 ,as it passes the cells of the alimentary canal1 they discharge the nutriment they have absorbed into it2 as it passes through the other organs of the body1 it discharges the requisite materials into the lymph bathing the actual cells3 these are then able to help themselves4 ,the lymphatic system is very simple4 ,lymph is practically fluid which has exuded through the walls of the bloodvessels1 and is like the plasma of the blood1 a thin solution of proteids in water containing just enough salt to hold them in solution4 ,from different parts of the body a series of tubes run towards the heart1 going up with increase in size and decrease in number as they near it4 ,into these tubes the lymph is forced with every movement of the body4 ,at a slow rate1 but varying with the activity of the animal1 it is forced to flow along these tubes1 regurgitation being prevented by valves at intervals1 until it reaches the place where the lymphatic vessels join a large vein1 and it is poured back into the blood-stream1 thus completing its cycle4 ,the blood is entirely confined in a closed system of tubes1 along which it moves always in the same direction4 ,the main principle of the system is that of a ring4 ,one side of the ring is split into a vast number of fine tubes to give a large surface for absorption and discharge of food among the cells2 the other side is a single tube1 with an enlargement in which the blood from different parts is mixed 7see ,diagram #aa74 ,this enlargement1 which is contractile and fitted with valves1 rhythmically draws the blood in from one direction and pumps it out in another4 7,the mechanics of the process we shall study later47 ,as a matter of fact1 this system is twofold1 as in ,diagram #ab4 ,in passing through one-half of its course the blood absorbs oxygen in the lungs2 in the other it yields oxygen to the tissues1 and absorbs1 whilst passing over the alimentary canal1 proteid1 carbohydrate1 water1 and salts1 which are duly distributed to the other organs4 ,fat is absorbed by the lymph direct1 but poured into the blood for distribution4 ,the blood which passes over the alimentary canal on its way back to the heart goes through the liver4 ,in this gland it leaves the carbohydrate which it has taken up1 and a large store is laid down there after a meal1 to be doled out as it is wanted4 ,blood also passes through the liver from the spleen1 where it has been1 so to speak1 overhauled for repairs4 ,illustration3 ,,diagram #ac4--,,scheme ,,of ,,the ,,circulatory ,,system4 ,blood system on the right1 lymph system on the left4 ,as the medium for chemical communication throughout the community of cells1 the blood has another all-important and obvious function1 viz41 that of clearing away the waste products of life4 ,of these there is1 of course1 the same quantity as of new material introduced4 ,carbonic acid gas is discharged into the lungs1 but all the nitrogen and most of the other elements in the new combinations which protoplasm has made them assume leave by the kidneys1 plus a little water by the skin as sweat and a few items discharged into the last part of the alimentary canal amongst the unabsorbed portions of the food4 ,in their constituents1 blood and lymph resemble one another1 being both weak solutions of salts and proteid material2 but the blood is distinguished from the lymph by the presence of innumerable extremely minute bodies1 which give it its red colour4 ,these corpuscles1 to give them their proper name1 are the vehicle by which oxygen is transported from the lungs to the tissues4 ,they consist of an envelope of protoplasm filled with a red fluid 7hmoglobin71 which combines loosely and easily with oxygen4 ,in shape they are discoid1 with a thickened rim and biconcave sides1 another device for increasing surface and reducing bulk4 7,see ,diagram #ad47 ,illustration3 ,,diagram #ad4--;,a ,,red ,,blood ,,corpuscle4 ,with one more fact we may now conclude the chemical survey of the body4 ,the blood has to pass through certain glands1 or it becomes poisoned1 and this quite apart from whether the gland secretes healthily or not4 ,disease of the thyroid 7a ductless gland in the ,adam's apple7 causes goitre2 of the suprarenal1 ,addison's disease2 of the pancreas1 diabetes4 ,whether these organs secrete some substance into the blood which counteracts poisons formed in it1 or whether they remove injurious elements from it1 is not certain1 but they are necessary to keep the great means of chemical communication in order4 ,,note4--,the thyroid gland no longer secretes anything into the alimentary canal1 and its duct disappears at an early age4 ,if1 however1 it become diseased or is surgically removed1 the distressing symptoms of goitre supervene4 ,such a patient may be completely cured by grafting a thyroid1 excised from another animal1 anywhere in his body4 ,doctors usually1 however1 give the patient extract of sheep's thyroid either in pills or injections4 ,,essay ,,iii4 ,,the ,,mechanics ,,and ,,physics ,,of ,,the ,,body4 ,i4 ,in the preceding essay we regarded protoplasm as a chemical factor in the universe4 ,we have seen how it is always changing1 always taking in food1 always giving off waste materials4 ,we have seen1 too1 that it grows and that it does work1 and that in a large mass the cells which compose it share the labour instead of each component cell performing all the vital functions4 ,we have now to consider the work which protoplasm does--in a word1 the mechanical effect of the chemical actions just described4 ,the simplest movement of protoplasm is to be seen by the aid of the microscope in certain vegetable cells1 where granules seem always streaming about in different directions4 ,a step higher1 and we find this streaming movement converted into movements of the whole cell4 ,in the simplest unicellular animals the fluid protoplasm is contained in a membrane1 or denser bounding layer1 to which are attached fine filaments springing from a minute body known as the centrosome4 ,these centrosomes--for there are sometimes several in a cell--seem to control the mechanical department1 just as the nucleus does the chemical4 ,along the fibrils at intervals are minute globules1 and by watching the distance between them it is seen that the fibrils undergo changes in length1 pulling in the membrane when they shorten1 and letting the cell flow out in any direction when they relax4 ,by adjusting these two movements to balance one another1 the cell can move in any direction1 surround and engulf particles of food1 and assume a strange variety of shapes4 7,see ,diagram #a47 ,illustration3 ,,diagram #ae4--;,,cell ,,division4 ,in some cells1 probably in all1 the centrosome presides over division4 ,cells1 however1 do not always divide in the same way4 ,some simply lengthen1 the nucleus also lengthening inside1 become constricted in the middle like a dumb-bell1 and separate4 7,see ,diagram #ae47 ,illustration3 ,,diagram #af4--;,,cell ,,division4 ,others manage differently4 ,in them the nucleus simply bursts1 and turns its essential elements1 a number--always a constant number--of coarse threads1 adrift4 ,meanwhile1 two centrosomes have moved to opposite ends of the cell1 and there anchored themselves by fibrils2 other fibrils springing from them become attached to the nuclear threads1 and when all is ready pull them apart1 equally divided1 to their respective ends1 where they re-form into two fresh nuclei4 7,see ,diagram #af47 ,unicellular animals1 which are constant in shape and swim instead of flowing when they want to get anywhere1 have at first sight nothing in common with those which do the latter4 ,from their surfaces spring fringes of free protoplasmic threads1 called cilia1 from their fancied resemblance to eyelashes1 which serve as motor organs1 and beat the water like oars4 7,see ,diagram #b47 ,waves of movement1 as they lash one after another1 all in the same direction1 seem to pass over the cell1 and it is propelled through the water2 while others1 which are situated in the neighbourhood of the cell's mouth1 stir the water into eddies1 and drive food particles into it4 ,illustration3 ,,diagram #ag4--;,,cilia ,,of ,,an ,,epithelial ,,cell4 ,these cilia are important1 as they are adapted for many purposes in large animals4 ,the cells which line the cavity at the back of the nose1 the tubes of the lungs1 and other parts of the body1 have a few cilia on their free surface1 and it is in them that the structure of these organs can best be made out4 ,at the foot of each cilium is a minute globule1 from which a fine fibril passes into the cell1 and the fibrils1 collectively forming a leash1 are attached to its opposite end4 7,see ,diagram #ag47 ,it seems highly probable that the globule is a centrosome giving rise to two fibrils1 one attached as described1 the other passing up one side of the cilium1 and fast to its apex4 ,the result of this arrangement is that when the fibrils contract the cilium is bent over with a jerk to the side up which the fibril runs1 and when they relax it slowly straightens itself4 ,there is1 therefore1 no fundamental difference between this and the other mode of progression2 both are dependent upon the centrosome4 ,finally we have muscle cells4 ,these are only found in a fairly complicated animal1 since they are a product of the division of labour principle1 and their sole business is movement4 ,there are two varieties of muscle1 but the principle is the same in both--a long thin cell1 with fibrils traversing its length whose contraction causes the cell to shorten and thicken1 thus reducing the distance between its two ends4 ,at present the development of muscle and the way in which it #8contracts1' to use the word accepted in this case for describing a redistribution of bulk1 are little understood1 and there are accordingly many opinions2 but ,i think careful study will eventually show that some modification of the centrosome1 with its contractile fibrils1 is responsible for the movement4 ,illustration3 ,,diagram #ah4--,,muscle4 ,the two varieties are3 the smooth1 or involuntary1 and the striped1 or voluntary1 muscle4 ,smooth muscle consists of spindle-shaped cells with one elongated nucleus4 7,see ,diagram #ah1 ,fig4 #a47 ,it only contracts very slowly1 and is not under control of the will2 but it is very abundant in the body1 since it effects practically all the movements of the alimentary canal and bloodvessels4 ,voluntary or striped muscle1 so called from its appearance under the low power of a microscope1 consists of long fibres1 each containing many nuclei4 7,see ,diagram #ah1 ,fig4 #b47 ,its protoplasm is rich in hmoglobin1 and in it1 under powerful microscopes1 can be made out two kinds of fibrils3 ,rutherford's fibrils1 the complicated structure of which gives muscle its striped appearance2 and ,marshall's fibrils1 which are much finer and more difficult to see4 ,the muscle of the heart1 though not under control of the will1 is striped2 but it differs from ordinary striped muscle in being made up of small branched cells with only one nucleus4 ,the way in which the three elements of striped muscle contribute to a contraction is practically unknown1 and the subject of much dispute4 ,in fact1 one could hardly wish for a better soil for theories1 and some which grow in it are very wonderful indeed4 ,we have reason for supposing that there are two contractile substances--one which gives a sharp twitch1 the other a slow1 hard pull2 and on the whole there seems good reason to believe that ,rutherford's fibrils give the sudden movements1 while ,marshall's give the more forcible ones2 and that the ordinary protoplasm of the cell is restricted to the duty of nourishing the fibrils4 ,illustration3 ,,diagram #ai4--,,striped ,,muscle ,,fibre1 ,,more ,,highly ,,magnified ,,than ,,in ,,diagram #ah4 ,the muscle cells are modified from among those of the bud forming the middle layers of the embryo4 7,see ,diagram #e47 ,other cells of this bud form connective tissue1 by1 so to speak1 spinning long fibres of the substance called collagen1 which turns to gelatin when boiled4 7,see ,diagram #bj47 ,this connective tissue permeates the whole body1 affording a firm foundation for the many layers of cells which form the skin and the single layer of digestive cells2 supporting the other organs throughout1 and keeping the different parts of the body in their places1 in doing which1 however1 it is assisted by other fibres which are not collagenous1 but elastic4 ,it also forms tracts which become lymph and blood vessels4 ,in parts of the animal which require special support it forms solid rods1 the collagen combining with calcium salts to form a clear1 hard substance--cartilage4 ,at one period in the development of an animal or animals we find the only solid support is cartilage1 but cartilage is not sufficiently rigid for a very large beast1 especially on land1 so is only used for outlying parts1 the main framework being bone4 ,illustration3 ,,diagram #bj4--;,a ,,connective-,,tissue ,,cell ,,giving ,,rise ,,to ,,long ,,collagenous ,,fibres4 ,bone is formed very much as if ,nature were rectifying a mistake4 ,when a rod of cartilage is unequal to its work it is eaten hollow1 and fresh connective-tissue cells immigrate and fill up the cavity1 eventually laying down a fine network of cells in its place1 the meshes of which are filled with inorganic calcium salts1 chiefly phosphate of lime4 ,nature then benefits by experience1 and the last bones to be formed are not preceded by any makeshift cartilage1 but built up straight away in ordinary connective tissue4 ,this brings us back again to muscle1 for the object of nearly all the voluntary muscle is to cause movement among the bones4 ,for this purpose the muscle cells or fibres are arranged parallel to one another1 and bound up together by connective tissue1 the whole bundle being known as #8a muscle4' ,the two ends of a muscle are attached to two bones by connective tissue1 which sometimes forms a short cord1 or tendon4 ,then1 when the muscle contracts1 the two places of its attachment are pulled towards one another1 and something has to move4 ,but before saying more about the way in which the bones are jointed and muscles attached--in fact1 what movements are possible in the human body--it would be as well here to describe the chief properties of muscle and the way in which they are studied4 ,,ii4 ,illustration3 ,,diagram #ba4--;,,apparatus ,,for ,,recording ,a ,,muscular ,,contraction4 ,the way in which voluntary muscle is studied is very simple4 ,a frog is killed by thrusting a probe into the brain and down the spinal cord1 and a muscle is then dissected out and attached to a piece of apparatus 7see ,diagram #ba7 in such a way that on its contracting it raises a lever1 and draws a line on a moving surface4 ,the rate at which the surface is moving is ascertained1 so that the nature of the curve1 which is a graphic record of the contraction1 can be analyzed4 7,see ,diagram #bb47 ,for instance1 when an electric shock is used to make the muscle contract1 we find that a slight shock causes a small contraction1 as shown by a low curve1 while a stronger one1 up to a certain point1 causes an increase4 ,illustration3 ,,diagram #bb4--;,,graphic ,,record ,,of ,a ,,response ,,to ,a ,,single ,,stimulus ,,applied ,,at ,a4 ,lower line tuning-fork records of 4 ,but having described how muscle is studied1 it is only necessary to state a few facts concerning it2 to discuss muscle1 fully describing the experiments by which its more obscure properties have been elucidated1 and the devices by which causes of error have been eliminated1 would fill volumes4 ,illustration3 ,,diagram #bc4--;,,contractions ,,with ,,two ,,stimuli ,,at ,,different ,,intervals ,,of ,,time4 ,muscle is thrown into a state of contraction by an impulse reaching it from a nerve1 but it contracts quite as readily if excited directly by a mechanical or electrical shock4 ,a second shock causes a second contraction1 or1 if the muscle is still in a state of contraction owing to the first1 causes it to contract still more4 7,see ,diagram #bc47 ,if a number of stimuli are applied to a muscle in such rapid succession that the effect of the preceding one has not passed off by the time the next arrives1 it will contract as far as possible1 and remain contracted--a state known as tetanus4 7,see ,diagram #bd47 ,a muscle is therefore kept in a state of contraction by a continuous nervous effort1 not arranged and then left contracted4 ,illustration3 ,,diagram #bd4--,,tetanus4 ,illustration3 ,,diagram #be4--;,,fatigue ,,curves4 ,fast drum3 a1 point of stimulation4 ,every tenth contraction recorded4 ,illustration3 ,,diagram #bf4--;,,effect ,,of ,,fatigue ,,on ,,muscular ,,contraction4 ,slow drum4 ,every contraction recorded4 ,various conditions alter the character of a muscular response4 ,with repeated stimuli at short intervals a muscle fatigues1 and each contraction becomes smaller in extent and longer in duration4 7,see ,diagrams #be and #bf47 ,if the muscle has to lift a load it has a certain check on its contraction1 and its relaxation time is shortened4 ,temperature also affects muscular contraction1 moderate increase causing a sharper1 and moderate cooling a slower1 rise and fall of the lever on stimulation4 7,see ,diagram #bg47 ,lastly1 we have drugs which exert an influence1 but the only one of these which it is necessary to mention here is veratria1 which makes the slowly contracting fibrils continue their activity after the quick ones have subsided4 7,see ,diagram #bh47 ,illustration3 ,,diagram #bg4--;,,effect ,,of ,,temperature4 ,illustration3 ,,diagram #bh4--,,veratria ,,curve4 ,finally1 there are the electrical changes in muscle4 ,these1 again1 may be passed over briefly1 since they are not easily understood or described4 ,to put the facts in a nutshell1 the part of a muscle which is in activity is negative to all other parts4 ,thus1 if a muscle be dissected out and cut across1 the activity at the seat of the injury1 while it lasts1 causes a current to pass through a galvanometer from uninjured parts to the wounded4 7,see ,diagram #bi47 ,again1 if a muscle be dissected out without injury1 connected at two points with a galvanometer1 and then stimulated at one end1 as the wave of contraction passes along it1 first one1 then the other1 contact becomes negative4 7,see ,diagram #cj47 ,s1 ,stimulating electrodes2 ,n1 contraction which marks the wave of excitation passing along the muscle2 ,g1 galvanometer which shows that the seat of activity 7,n7 is negative to the rest of the muscle4 ,illustration3 ,,diagram #bi4--;,,injury ,,current3 ,,cross-,,section ,,of ,,muscle ,,negative ,,to ,,rest4 ,illustration3 ,,diagram #cj4--;,,action ,,current4 ,in passing1 it may be mentioned that1 as the heart is a muscle slung obliquely across the body1 and waves of contraction are continually passing down its long axis1 the whole body is affected by continual electrical changes4 ,by very delicate instruments it can be demonstrated that with each beat the two hands alternately become electrically positive and negative to each other4 ,whilst dealing with the electrical phenomena of muscle1 it may be as well to state that nerve fibres1 which are studied with very much the same apparatus1 show the same electrical changes1 the point of injury or of the greatest activity being negative to all the rest4 ,single cells are less easily investigated1 but in glands it is possible to show that the same rule holds4 ,undoubtedly the most curious fact about the generation of electricity by protoplasm is that1 by a modification of muscle and nerve1 which causes them to lose their ordinary properties1 they are converted into a special organ for giving electric shocks4 ,armed with powerful batteries of this description1 an otherwise rather helpless class of fish are enabled to defend themselves from their enemies1 and deal unexpected death to their more agile prey4 99 99 99 99 99 ,having now run over a few of the physical properties of protoplasm1 we may pass on to a brief investigation of the movements we find in the body of man4 ,,iii4 ,in describing the movements of the body1 we shall have to treat them as several and distinct1 as indeed they are2 but the fact should not be lost sight of that they cannot really be isolated3 one idea embraces the whole4 ,two kinds of movement may1 however1 be distinguished in the vital functions3 movement of the actual cells1 such as muscles2 and movement of non-protoplasmic elements acted upon by the cells--e4g41 lymph4 ,there is a parallel to this in the chemical side of life1 where we find some phenomena peculiar to the living elements1 and others1 like digestion1 going on in the living body1 but outside the cells4 ,taking the movements in the natural order--that is1 proceeding from the simpler to the more complex--the first to be considered is undoubtedly that of the leucocytes1 or general scavengers of the tissues4 ,the body consists1 so far as we have defined its anatomy1 of three layers of cells1 and its shape is that of a tube with hollow walls4 7,see ,diagram #f47 ,within the cavity of the body are various organs1 such as the muscles1 which are formed from the middle layer2 and its space is largely reduced by glands1 lungs1 and other ramifications of the inner layer which forms the alimentary canal4 ,these organs hang more or less freely in the body cavity1 slung to its walls by enveloping sheets of connective tissue1 the whole being bathed in lymph4 ,now1 in such an arrangement the products of wear and tear must accumulate4 ,cells here and there die for various reasons1 and pieces of cells become detached even in adult animals4 ,the interior of a bone is always being eaten away to decrease its weight1 or in order that it may be replaced by fresh bone of a closer texture1 and in young animals and embryos there are many structures which1 useful for a time1 have eventually to be removed2 as an instance1 we may quote the tadpole's tail4 ,in fact1 if the tissues were left to themselves1 the body would soon be choked with dbris1 and to avoid this it is supplied with an army of scavengers1 the leucocytes4 ,the leucocytes are detached cells which owe their origin to the middle layer4 ,in size they are1 of course1 very small1 quite invisible to the naked eye4 ,in appearance they resemble unicellular organisms of the amba type1 which we have had occasion to mention several times already 7,essay ,,ii41 ,section ,,ii42 ,essay ,,iii41 ,section ,i41 ,diagram #a74 ,they are of several different varieties1 some being larger and more active than others2 but they all wander about in the lymph and blood like independent animals1 creeping in and out between the cells of the organs1 and devouring any foreign matter they come across4 ,they sometimes multiply1 like independent animals1 by division1 especially in the presence of inflammation1 or when they have much work to do1 and a rapid increase in their numbers is needed2 and they have been induced to live1 and feed1 and multiply1 outside the body 7in which case they must be considered to have become independent organisms71 thanks to the careful attentions of the experimenter4 ,apart from their duties of devouring the inside layers of bones and clearing away dead tissue1 they are supposed by some to assist in the absorption of food by creeping between the cells lining the alimentary canal1 and1 after throwing out arms to engulf particles of food1 returning with their spoils into the body4 ,perhaps1 however1 the most interesting1 or at any rate most romantic1 of their many and important functions are what may be called their emergency duties4 ,frequently people1 especially those who live in smoky towns1 draw into their lungs particles of dust and soot1 which if left adhering to the walls of the air cavities would cause dangerous irritation4 ,as if by magic a leucocyte will discover the presence of such a nuisance1 and1 crawling between the cells forming the wall of the lung1 in which1 by the way1 it is outside the body proper1 will engulf it and carry it away with him4 ,this exploit1 however1 pales beside the warfare which goes on in the body between leucocytes and invading bacteria4 ,a bacterium thrives in the blood or lymph1 since it finds itself in a warm alkaline fluid containing complex organic substances1 by breaking down which it can easily obtain energy4 ,unfortunately1 the products of such a process are frequently virulent poisons1 the effect of which upon neighbouring cells produces the distressing symptoms which we associate with disease4 ,no sooner1 however1 has the bacterium begun to generate poisons1 than leucocytes1 influenced by chemical attraction 7,essay ,i471 swarm upon it4 ,first come leucocytes of a small kind1 full of zymogen granules1 which crowd round the bacterium till they have covered it4 ,after a time they creep away1 leaving it dead4 ,they are now in an exhausted condition1 and no longer contain granules1 having doubtless discharged them as a destructive ferment upon their enemy4 ,then a leucocyte of another kind moves to the attack1 or1 rather1 to clear up the remains1 for he is a large1 non-granular1 active fellow1 and eats up the dead bacterium by the simple process of engulfing him whole4 7,see ,diagram #ca47 ,a natural question arising out of the study of leucocytes is1 ,what becomes of them8 ,particles of soot and similar refuse can hardly be considered nutritious1 or even digestible1 food1 and one is rather drawn to the conclusion that the leucocyte performs its functions for the good of the body at large1 not of itself1 and that when its work is done it must die4 ,many leucocytes1 probably1 loaded with unconsidered and undesirable trifles1 cast themselves into the alimentary canal1 and are got rid of with the useless portions of the food2 but they do not always have the luck or energy to get to a natural outlet4 ,an unpleasantly familiar phenomenon is the boil4 ,here we have some irritating substance under the skin setting up inflammation1 and leucocytes swarm up to remove the cause of the trouble4 ,before1 however1 this is done1 many have perished in the fray1 and they have collected in numbers to the formation of what is commonly known as pus1 or matter4 ,their dispersal into the body is now neither easy nor desirable1 and the surgeon usually lets them escape from the surface by a touch of the lancet4 ,illustration3 ,,diagram #ca4 ,a1 ,eosinophile leucocyte2 ,b1 bacterium2 ,c1 leucocytes killing bacterium with their enzyme2 ,d1 leucocytes leaving bacterium dead2 ,e1 hyaline leucocyte devouring dead bacterium4 ,such1 then1 is very briefly the story of the leucocyte1 neglecting such problems as the differences between those found in the blood1 called white corpuscles to distinguish them from the red corpuscles1 with which they have no sort of connection2 those found in the lymph1 called lymphocytes to distinguish them from those found in the blood2 those caught in the act of devouring bone1 called osteoclasts2 and those found with bacteria inside them1 therefore known as phagocytes2 and without speculating on how long an individual lives1 and whether the different varieties differ in origin or are merely at progressive stages of development4 ,the study of leucocytes is one of the most fascinating in physiology1 but we have many other things calling for our attention1 and we have said enough about the part they play in the life of the body to justify our passing on to consider another essential movement4 ,,iv4 ,next in natural order for consideration come the movements of the alimentary canal4 ,so far we have considered this structure as a chemical laboratory1 a tube consisting of a single layer of cells which secrete ferments into the lumen1 where digestion takes place1 and then absorb the products1 and we have not yet accounted for the food travelling along the tube1 without which its functions1 as described in the earlier part of the book1 could not be performed4 ,that the passage of the food is not due to gravitation is obvious from the many directions of the tube's coils--not to quote the old instance of a horse drinking1 in which case the liquid first travels upwards4 ,one must therefore conclude in favour of some muscular method of propulsion4 ,we have so far described the alimentary canal as a single layer of cells1 but it must be obvious that these soft secreting portions of the tube are not capable of vigorous movement4 ,the canal proper is surrounded by a tough sheath of connective tissue which prevents its being overdistended or ruptured1 and1 by means of a layer--or1 rather1 two layers--of non-striped muscle which it contains1 produces the movements which result in the passage of its contents along the tube4 ,these two layers lie well to the outside of the connective-tissue sheath4 ,the fibres of the inner layer are arranged circularly1 so as to form rings round the tube2 those of the outer have a longitudinal direction1 running1 therefore1 parallel with its long axis4 ,when the former contract1 the diameter of the tube is reduced1 while contraction of the latter has the effect of enlarging it4 7,see ,diagram #cb47 ,the movements of the intestine are what is known as peristaltic4 ,contraction of the muscle fibres is not simultaneous in all parts1 but passes in waves along it4 ,just in front of the food the longitudinal fibres contract1 and thus offer less resistance1 while just behind the circular fibres reduce the size of the tube1 and so get up a pressure4 ,the result of a number of successive waves of contraction passing down the alimentary canal is that the food is propelled along it4 ,illustration3 ,,diagram #cb4--,,to ,,illustrate ,,the ,,passage ,,of ,,food ,,along ,,the ,,intestine4 ,the arrangement of the muscle varies in places to suit special needs4 ,where the tube suddenly enlarges to form the stomach1 and where the stomach suddenly narrows to the intestine1 there are two strong rings of muscle1 whose constricting influence converts the enlargement into a closed chamber during gastric digestion2 while the coats which actually clothe it here run obliquely1 and their activity causes the contents to be slowly churned about inside4 ,thus it will be seen that it is not only the voluntary muscles which give the alimentary system its opportunities2 without these unobtrusive non-striped cells we should toil for our bread and swallow it in vain4 ,v4 ,our next step1 after having surveyed the principle of movement by which the chemical necessities of the body are exposed to its absorbing surface1 must be to see how the fluid which transports them is made to pass along the tubes containing it4 ,we have already had occasion to describe how these blood and lymph vessels ramify through all the organs1 when we were dealing with the chemical influence of the blood and lymph4 ,the tubes through which the lymph is brought back to the blood-stream have thin walls1 and no muscle of their own4 ,they are subjected1 however1 to a constantly varying pressure by the movements of the limbs and trunk1 and as1 owing to valves inside them1 the lymph can only escape in one direction1 there is a constant flow towards the junction with the bloodvessels4 ,the bloodvessels are quite different4 ,a far more certain and expeditious current is necessary--hence the steady circulation through a system of closed tubes4 ,in order to understand this passage of the blood1 it is necessary to keep in mind the great principle with which hydrostatics supplies us1 viz41 that a liquid always flows from a region of high to a region of lower pressure4 ,the problem of the vascular system is1 therefore3 ,how can the pressure within a ring of tube be so arranged as to maintain a regular flow always in the same direction8 ,let us begin with the structure of the system4 ,the tube through which the blood first passes on leaving the heart is composed of four distinct and essential elements3 ,a lining of endothelial cells1 which we need not discuss at length2 a main substance of tough white fibrous connective tissue2 elastic fibres and muscle fibres1 the two last arranged in the substance of the connective tissue4 ,all these parts are present in the main arteries which leave the heart1 but in the fine meshwork of capillaries to which the arteries give rise by repeated branchings there is nothing left of the outer coats1 only the lining of endothelial cells separating the blood from the organ traversed4 ,in the veins which these capillaries unite to form1 the connective-tissue sheath reappears1 and also some muscle2 but the elastic coat is quite absent4 ,the heart is really a double coil of the tube 7see ,diagram #ab71 in which the muscular coat is predominant1 and is divided into four chambers by the valves1 which insure the blood flowing in the right direction when it contracts4 7,see ,diagram #cc47 ,illustration3 ,,diagram #cc4--,,scheme ,,of ,,circulation ,the way in which these structures work is as follows3 ,two of the chambers of the heart 7the auricles7 receive blood from the veins1 and when full suddenly contract1 driving their contents into the other two chambers 7the ventricles74 ,the blood does not run back into the veins1 although the pressure in them is very low and there are no valves to prevent it1 because there is still less pressure in the ventricles1 and also because the veins enter the auricles obliquely1 and the tendency of the increasing pressure is to close their orifices4 ,having discharged the blood into the ventricles1 the auricles relax1 and the pressure within being a minus quantity1 they are speedily filled with blood from the veins1 blood not being able to return after entering the ventricles1 as valves close automatically to prevent it4 ,stimulated by the blood distending them1 the ventricles then contract simultaneously like the auricles1 only with much greater force3 for the right ventricle has to drive the blood all through the vessels pervading the lungs back to the left auricle2 whilst the left ventricle1 which is proportionately stronger than the right1 has to send its contents to the furthest extremities of the body4 ,they then relax1 in order that conditions of their internal pressure may favour another inflow from the auricles1 return of blood from the arteries being1 as in the preceding case1 prevented by valves4 ,the pressure in the arteries during life is always fairly high2 indeed1 the ventricles have to get up a considerable force before the valves leading from them will open4 ,the result of this is not only that the blood is driven along them with a rush1 but also that they are slightly distended at each beat2 and so1 owing to the elasticity of their walls1 the blood continues to flow forwards even between the beats of the heart4 ,the rest of the journey is quite simple2 the pressure in the capillaries is lower than in the arteries1 and the pressure in the veins lower than in the capillaries1 and lower in the veins1 too1 as they approach the heart1 till1 where they join the auricle1 it is actually minus1 and the blood has no other course open to it but to return to the auricle4 ,it looks as though accidents might happen in the veins owing to there being so low a pressure there to direct the current1 but this is prevented by the presence of valves at intervals1 to stop any return4 ,the rate at which the blood travels is another point which has an important bearing on the nutrition4 ,it does its work--i4e41 gives out nutriment and picks up refuse--whilst flowing through the capillaries2 so here one finds that it moves slowly4 ,on the other hand1 the sooner it reaches them the better1 so it races fast through the arteries4 ,finally1 its return to the heart need not be delayed1 so it is quickened up again through the veins4 ,the principle by which this variation in the rate of flow is obtained is simple and inevitable4 ,if a tube through which liquid is flowing is not the same size all the way along1 the liquid will be found to flow faster in the narrow parts than in the wider ones4 ,now1 in branching1 the arteries do not keep becoming smaller in regular proportion1 and the result is that the capillaries have collectively a diameter five hundred times larger than the aorta2 hence the blood flows through them only one-five-hundredth of the pace at which it leaves the heart4 ,but in uniting again to form the veins their cross-section is reduced once more1 so that that of the large veins near the heart is only two and a half times larger than that of the aorta1 and hence a flow only two and a half times slower results4 ,the pace of the blood-stream must depend1 obviously1 on the pressure of the blood in the arteries4 ,this pressure is altered either by changing the rapidity of the heart-beat or the diameter of the arteries1 which are capable of considerable variation owing to their muscular coat4 ,the regulation of the blood-pressure is managed by the nervous system1 so does not belong here1 and we may leave it after mentioning one or two facts4 ,high pressure is due to a large quantity of blood being in the arteries1 and this may be due either to the rapidity with which it is injected by the heart or to the reduced capacity of the bloodvessels themselves4 ,high pressure1 due to the latter cause1 throws a great strain upon the heart1 owing to the hard work it has in pumping blood into the arteries2 with a low pressure the heart beats feebly1 having less resistance to overcome4 ,blood-pressure can be raised by stimulating the muscular coat and reducing the capacity of the bloodvessels1 and lowered by causing the heart to beat more slowly or by removing blood from the body4 ,this latter operation was a favourite way with doctors of the old school2 but as our knowledge of physiology1 and with it our control over the vital functions1 increases1 such crude and heroic remedies are able to be replaced by others which are less dangerous4 ,,vi4 ,comparisons are rightly regarded as objectionable1 so it would hardly be safe to say that the group of movements whose primary object is filling the lungs1 and which we must study next1 is the most important in the body1 especially when we have just been speaking of the circulation1 which1 however1 would be of but little use if the blood could not be oxidized2 but we can at least say that its importance cannot be overrated1 so far-reaching are its effects4 ,the lungs are1 as we have described them above1 a pair of delicate membranous sacs connected by a tube1 the trachea1 with the alimentary canal1 from which they originally budded out4 ,they are subdivided1 though how we need not describe in detail1 into a vast number of small compartments1 so as to give the maximum surface in the space accorded them1 and the whole somewhat resembles a cluster of grapes1 the stalks being the branches of the trachea4 ,the membranous parts are pervaded by an elastic network1 enveloping the compartments in such a way that it would reduce them permanently to the resemblance of a bunch of raisins rather than grapes1 were it not that they are enclosed in an airtight box--the thorax--from the walls of which they cannot shrink without causing a vacuum4 ,owing1 however1 to the latter arrangement and the trachea being open to the external world1 they are always more or less distended with air4 ,the thorax1 which they thus must always exactly fill1 is a conical-shaped box1 its walls being the ribs1 and its floor a sheet of muscle known as the diaphragm4 ,it contains1 besides the lungs1 only the heart and large bloodvessels4 ,the problem1 therefore1 of drawing air into the lungs and 7after the gaseous interchange described in ,essay ,,ii41 ,section ,,iv41 has taken place7 of expelling it again1 becomes solely a matter of increasing and decreasing the capacity of the thorax4 7,see ,diagram #cd47 ,this can be done in two ways3 the diameter through the ribs can be increased1 or the diaphragm can be pulled down1 increasing its depth4 ,actually1 both these methods come into play together4 ,diagram #ce will probably give a better idea of how this is done than could easily be conveyed by a verbal description4 ,an attempt is here made to show the action of the ribs and the diaphragm--first1 of each separately1 then of the two combined4 ,the elasticity of the lungs themselves is sufficient to drive out the tidal air if the diaphragm and the muscles of the ribs are relaxed1 though in hard breathing a muscular movement may depress the ribs and a contraction of the abdominal muscles force up the diaphragm4 ,illustration3 ,,diagram #cd4--,,model 7,,adapted ,,from ,,rutherford7 ,,for ,,showing ,,how ,,the ,,lungs ,,are ,,filled ,,with ,,air ,,by ,,altering ,,the ,,size ,,of ,,the ,,thorax4 ,but though the primary object of raising the ribs and depressing the diaphragm may be to fill the lungs1 its secondary influence upon the trunk as a whole is hardly less important4 ,the effect upon the circulation is profound4 ,the compartments of the lungs are enveloped in innumerable capillary bloodvessels1 and1 as these lie around and between them in the cavity of the thorax1 they must1 when breath is drawn in1 be subjected to a negative pressure before the lung itself1 and be the first to experience a positive pressure when the air is expelled4 ,here1 again1 a diagram is the best explanation4 7,see ,diagram #cf47 ,the pulmonary vessels1 moreover1 are not the only ones influenced4 ,the reader who attentively examined ,diagram #ac must have been struck by the peculiarities of the circulation through the spleen1 intestine and liver1 and the obstacles which this repeated breaking up into fine vessels must offer to the flow of blood1 as described in ,section ,v4 of this essay4 ,illustration3 ,,diagram #ce4--,,showing ,,how ,,the ,,capacity ,,of ,,the ,,thorax ,,is ,,increased ,,by ,,raising ,,the ,,ribs ,,and ,,depressing ,,the ,,diaphragm4 ,illustration3 ,,diagram #cf4--,,model ,,for ,,showing ,,effect ,,of ,,movements ,,of ,,the ,,thorax ,,on ,,the ,,pulmonary ,,circulation4 ,the liver forms the crux of the situation4 7,see ,diagram #cg47 ,a vein carrying blood from the intestine and spleen is broken up into fine capillaries to pass through that organ1 and the pressure in this vein is extremely low4 ,how is a sufficiently rapid flow of blood to be maintained8 ,the answer to this riddle is best given by ,diagram #ch1 which shows how1 by the contraction of the diaphragm at each breath1 the large veins entering the heart are subjected to a negative pressure which draws blood out of the liver1 while1 simultaneously1 that organ is squeezed and the blood it contains forced out4 ,obviously this natural pump influences not only the flow of blood1 but also that of the lymph1 and what was said about the hepatic vessels also holds good for the thoracic duct1 up which the lymph1 rich with fat absorbed from the intestine1 passes to be emptied into the large veins near the heart4 ,so1 though vigour in the action of the diaphragm is more favourable to health than necessary to life1 deep breathing is an essential factor in the well-being of the body4 ,illustration3 ,,diagram #cg4--;,a ,,diagrammatic ,,view ,,of ,,the ,,circulation ,,through ,,the ,,organs ,,upon ,,which ,,the ,,diaphragm ,,presses ,,when ,,it ,,descends4 ,illustration3 ,,diagram #ch4--;,,illustrating ,,the ,,influence ,,of ,,the ,,diaphragm ,,upon ,,the ,,circulation ,,through ,,the ,,viscera4 ,,vii4 ,all the movements as yet described are absolutely necessary to the continuation of life2 they are1 moreover1 independent of the efforts of the will4 ,but there remains yet another kind of movement without which the body1 left to itself1 would die4 ,this is the movement of the limbs--organs by which the body is able to move from one place to another1 to capture its food and convey it1 vi the mouth1 to its stomach--in a word1 to satisfy its chemical and physical needs4 ,to understand how the limbs work requires a knowledge of their anatomy1 for which we have not time or space here2 but the principle throughout is that of a system of levers1 the bones1 worked by the voluntary muscles4 ,here1 as before1 a diagram will probably be found to convey more than could ever be expressed in words4 7,see ,diagram #ci47 ,the diagram represents very roughly1 but it is hoped very plainly1 the main principle of the elbow-joint2 but for an exact knowledge of the mechanism of the joint1 and the comparative strain upon1 and therefore strength of1 each muscle1 the reader must consult some work on anatomy4 ,he will there find1 if he goes on to read the description of the hand1 what a wonderful precision1 complexity1 and amount of movement can be obtained by variations of this simple device4 ,illustration3 ,,diagram #ci4--;,,diagram ,,of ,,the ,,arm4 #a1 ,lifting2 #b1 pressing4 ,here1 however1 we must leave the study of the manner and object of the bodily movements1 and proceed to investigate the far more intricate question of how they originate and are controlled4 ,,essay ,,iv4 ,,the ,,nervous ,,system4 ,i4 ,now comes the final problem4 ,protoplasm forms a structure always changing1 always making good its waste by chemical action upon raw material1 always capturing raw material or in search of it1 always1 when it exists in large quantities1 and the labour is therefore divided between many cells1 economically apportioning the work and the spoils4 ,how is it that all the actions1 chemical as well as physical1 of a vast number of cells composing a large body are1 no matter how complicated1 always harmonious1 and always with purpose directed to the advantage of the whole animal8 ,in the first essay in this book we discussed the phenomenon of life1 and described briefly the chemical and physical peculiarities of protoplasm4 ,these in the two succeeding essays we have gone into more fully2 but there is one characteristic of that interesting substance which yet remains for us to examine in specialized cells1 viz41 its extreme readiness to respond to changes in its environment4 ,in ,essay ,i4 we saw that chemical agents1 light1 heat1 electricity1 etc4--had a definite effect upon protoplasm1 and that1 though they might influence different kinds in different ways1 the effect was nevertheless invariable2 in a word1 the response of protoplasm to circumstances is automatic4 ,but the most remarkable thing about this is that the response is not confined to the protoplasm actually affected1 but is transmitted to that nearest to the part stimulated1 and again passed on to that beyond1 so that a wave of excitation passes through the whole mass1 not stopping till it has reached the extreme confines of the cell4 ,it may even pass beyond these and set up activity in neighbouring cells4 ,the power of conductivity once grasped1 it may easily be seen that certain cells1 by specializing in this direction and adapting their shape to the needs of the body1 might by throwing out long threads to reach distant parts set up an organic system of telegraphy4 ,the organs developed for the control of the body owe their origin to the outer layer4 7,see ,diagram #e47 ,this was only to be expected4 ,in the second essay1 in which we treated of the chemistry of the body1 we1 of course1 touched upon all three layers from which the body is built up2 but the one which chiefly occupied our attention was the innermost layer1 which is so admirably arranged as a chemical laboratory4 ,in the third essay we dealt chiefly with the middle layer1 which both by its position and its bulk might have been guessed to be the foundation of most of the motor organs4 ,now that we have come to the organs of perception and transmission of impressions1 it is only natural to expect that they should be specialized from the cells already in contact with the external world1 and which1 since they form the envelope of the animal1 must allow all such stimuli as reach the subjacent motor layer to pass through them4 ,hitherto we have not dealt at great length with the development of the organs whose functions we have been describing1 either from the point of view of the embryologist or the evolutionist4 ,nor have we spent much time upon their gross anatomy4 ,with the nervous system we must proceed rather differently2 for to understand how its higher functions can be performed they must be traced from their origin step by step1 while their complexity is largely vested in the structure of special organs4 ,the way in which the nervous system was evolved is shown in ,diagram #e4 ,originally1 no doubt1 the cells of the outer layer1 when the latter was in its simplest form--that is to say1 only one cell thick1 not several1 as it is in our skin--would1 when influenced in any way directly call forth the activity of the motor cells lying beneath them4 7,see ,diagram #dj1 ,fig4 #a47 ,in ,fig4 #b1 however1 we see one cell of the outer layer becoming specialized4 ,it has thrown out a process above the surface of the skin the more readily to catch impressions1 and has sent another down into the body the better to distribute them4 ,diagram #da1 ,fig4 #a shows the nerve cell at a further stage4 ,the principle is the same1 but the cell is removed to a safer place4 ,in ,fig4 #b it is not exposed to the outside world at all1 but by receiving its impulses second-hand from several cells the same work is done with greater economy and uniformity4 ,some of the special sense organs are still developed in this way4 ,illustration3 ,,diagram #dj4--,,showing ,,origin ,,of ,a ,,nerve ,,cell4 ,illustration3 ,,diagram #da4--,,showing ,,the ,,development ,,of ,a ,,nerve ,,cell4 ,once the nerve cell is developed and safely shifted into the interior of the body1 it is clothed with a protecting feltwork of connective tissue1 and the nerve fibres are also surrounded by connective-tissue cells which secrete around them the fatty substance which makes nerves look white4 ,such is the nerve cell or intermediary between the world and the muscles2 but thence to harmonious movement in a body with complex organs capable of varied actions is a long step4 ,to obtain precision and uniformity throughout the body1 all the impressions received must be collected and balanced1 and stimuli1 the correct outcome of this balancing1 must be transmitted to the muscles1 glands1 etc41 whose activity circumstances require4 ,the way in which cells of the outer layer become enclosed to form a central nervous system is shown in ,diagram #e2 but its development will be better seen in the figures of ,diagram #db4 ,illustration3 ,,diagram #db4--,,to ,,illustrate ,,the ,,development ,,of ,,the ,,nervous ,,system4 ,illustration3 ,,diagram #dc4--;,,cross-,,section ,,of ,,the ,,spinal ,,cord1 ,,showing ,,how ,,it ,,gives ,,off ,,nerves4 ,illustration3 ,,diagram #dd4 ,this diagram shows how certain cells of the outer layer are budded off and transferred to a safe place within the body4 ,in this position the cells are further developed1 throwing out one long fibre1 which goes to some distant organ of the body1 and short fibres1 which1 though they do not join those of other cells and become continuous1 closely interlace and put them into communication4 ,they are also separated from one another by connective tissue1 which supports them1 holding them suspended with only their fibres approaching one another 7,diagram #dc74 ,diagram #dd shows how the bone which replaces the supporting rod 7see ,diagram #f7 throws an arch round the feltwork of connective tissue in which the nerve cells are suspended1 giving them still further protection4 ,it will be noticed in the figures of ,diagram #db1 which is fuller than ,diagram #e1 that there are three of these buds--one central and two lateral4 ,the central one becomes a tube running the whole length of the animal1 while the lateral buds form solid clusters or ganglia1 arranged in pairs at intervals beside it 7see ,diagram #de74 ,fibres from these ganglia go to the skin1 and bring to the nerve cells information from the outside world1 which they duly pass on to the cells of the central column4 ,the cells of the central column1 when set in motion by the ganglion cells1 send out impulses to the muscles1 whose contraction is necessary to perform the movement which circumstances indicate4 ,a movement brought about in this way is called reflex4 ,illustration3 ,,diagram #de4--;,,central ,,nerve ,,tube ,,and ,,ganglia4 ,the reflex movements are1 however1 not quite the simplest4 ,for instance1 the food is moved along the alimentary canal by the contraction of two sets of muscle fibres--an outer longitudinal coat and an inner circular one4 ,between these two coats are some nerve cells1 which are thrown into activity by the presence of food and the iron compounds of the bile secreted by the liver in the tube4 ,these sympathetic cells do not send their impulses to any centre for examination1 but at once stimulate the muscle fibres between which they lie1 thereby producing the peristaltic movements we have already described4 ,yet it should be remembered that1 though these cells act independently of the central nervous system1 they are under its control1 and can1 if need be1 have their action modified for the benefit of the body as a whole4 ,for convenience' sake1 we had better here specify the chief kinds of nervous action4 ,first there is what we may call the immediate nerve action1 such as that we have just been describing2 secondly there is reflex action1 the centres for which are in the spinal cord and the base of the brain2 and thirdly there is voluntary movement1 which arises out of the interaction of centres in the hemisphere of the brain1 where the most complex machinery of all is kept4 ,,ii4 ,of the first kind we need say no more4 ,the instance of peristaltic movement illustrates it sufficiently2 so we can at once begin a more careful examination of reflex action4 ,the simplest instance of reflex action may be taken from the schoolroom4 ,if a boy suddenly sticks a pin into an unsuspecting schoolfellow1 the latter invariably starts1 and frequently lets fall an exclamation also4 ,in this case the presence of an injurious agency is reported to the nearest motor centre1 which is in the spinal cord1 and this automatically convulses the body1 jerking the limb out of danger4 ,this is reflex movement2 the nerve fibre1 which conveys an intimation of the injurious influence1 is a prolongation1 or really two prolongations1 of a spinal ganglion cell4 7,see ,diagram #df47 ,the near end of this fibre1 which enters the cord1 has several branches4 ,some run a little way up the cord1 and some a little way down1 so as to communicate with several motor cells2 but one branch runs right up the cord1 and sends the message on to the brain4 ,our outraged schoolboy starts a fraction of a second before he is conscious of the pain of being pricked1 and this first response is involuntary and unvarying2 the sensation1 however1 is reported to his brain1 and the workings of that wonderful organ are less easy to predict4 ,it leads to his taking stock of the aggressor1 on the strength of which he decides whether it is safe to attempt a reprisal1 and1 if so1 in what form it will be most effective and least likely to attract the master's attention4 ,this knotty point settled1 the motor cells of the brain send down messages to the motor cells of different parts of the spinal cord1 and these in turn set the necessary muscles in motion for delivering a surreptitious kick or aiming a splash of ink1 as the case may be4 ,this is voluntary movement4 ,illustration3 ,,diagram #df4--;,,evolution ,,of ,a ,,spinal ,,ganglion ,,cell4 ,illustration3 ,,diagram #dg4--,,scheme ,,of ,,the ,,central ,,nervous ,,system4 shows the path taken by an impulse in reflex action4 shows the path for a voluntary action4 ,the difference between reflex and voluntary movement is1 as may be seen from the above instances1 very much a matter of degree2 but we had better leave a comparison between them1 and any discussion as to the extent to which the manifestations of consciousness are automatic1 until we have finished describing reflex movement1 and set forth the little we know about voluntary movement4 ,time and space forbid a complete list of reflex movements4 ,the following are1 however1 a few typical examples of how the body is automatically made to perform such acts as are necessary1 and of how such as do not require deliberation are brought about without taxing the intellect4 ,a reflex action which is unpleasantly familiar is the cough1 also the somewhat similar phenomenon of the sneeze4 ,in this case1 a foreign body which obstructs the windpipe1 or causes irritation to the membrane lining the nose1 is1 on being reported at the spinal cord1 incontinently blown out by an explosive blast of air from the lungs4 ,an organ which is very important1 and at the same time very sensitive--viz41 the eye--has many protective reflexes4 ,the external surface of the eye is covered by a very delicate membrane1 which must be kept moist and scrupulously clean4 ,whenever this membrane gets in the least dry1 or any dust falls on it1 the eyelids are closed for a moment1 thereby bathing it with the secretion of the tear glands4 ,few people are aware1 ,i think1 that they blink their eyes on an average twice every minute4 ,the eyes are also closed quite involuntarily by a reflex when any danger threatens them--for instance1 a sudden dazzling light1 a strong wind1 or a blow aimed at the face2 and if any foreign substance--say a fly--does get into one of them1 the secretion of the tear glands is enormously increased to wash it out4 ,the size of the pupil1 again1 is quite involuntarily1 i4e41 reflexly1 altered in proportion to the strength of the light4 ,reflex actions are1 however1 by no means only protective4 ,the act of swallowing is reflex4 ,so is the secretion of the digestive glands when the lining membranes of the stomach are stimulated by the presence of food4 ,the very act of standing depends on the reflex principle1 the tendency of the body to collapse and fall being unconsciously perceived and corrected by the spinal cord4 ,walking is also a reflex action4 ,it may be objected that we think about walking1 and do so with intention2 but it is of common experience that we can walk along #8thinking of something else1' and the way in which an intellectual though absent-minded man will run into people1 charge lamp-posts1 trip over steps1 and tread upon dogs1 is sufficient to absolve the organ of thought and intention from any share in the performance4 ,the blood-pressure is also automatically regulated1 both the diameter of the bloodvessels and the frequency of the heart-beat being under reflex control2 and we may1 as a final instance of reflex action1 describe one of ,nature's most perfect and merciful contrivances--fainting4 ,suppose a man receives a severe wound--say1 has his hand struck off by a sword--the shock to his system causes an immediate dilatation of the large bloodvessels of the abdomen2 this results in a great fall of blood-pressure1 and the heart1 finding that it has much less resistance to overcome1 slackens its beats so that soon the flow of blood is very slow indeed4 ,hence1 it has time to clot over the wound1 and the man does not bleed to death4 ,incidentally1 the feeble current of blood is insufficient to keep the most delicate organ of the body1 the brain1 in its normal state of activity1 and the man is relieved from his pain by unconsciousness1 which passes off when the heart again quickens its beat4 ,it is perhaps needless to remark that fainting fits are not always and only caused by flesh wounds2 they may be due to weakness or other causes4 ,now1 if we consider the instances quoted above1 we are able to deduce a few general principles from them4 ,in the first place1 it may be noticed that reflex action compels us to perform the movements necessary to our existence whether we like it or no4 ,it is not for us to decide whether we will breathe or not4 ,we must4 ,the strongest-willed man who ever lived1 no matter how much a philosopher1 could not commit suicide by holding his breath1 as ,cato boasted he could4 ,directly he lost consciousness1 supposing he managed to hold out till then1 the tainted blood bathing the respiratory centre would awake it to activity1 and he would start breathing afresh4 ,again1 it is noticeable that many of these actions could not possibly be performed by a voluntary effort4 ,we can1 to a certain extent1 regulate the depth and frequency of our breathing1 and we can blink our eyes voluntarily2 but an average man would be quite at a loss what to do if asked to make the pupil of his eye dilate and contract1 the glands of his stomach secrete1 or his heart alter its rhythm4 ,it is a familiar fact that some reflex actions can be altered by an effort of the will2 in other words1 an impulse from a brain cell will prevent a nerve cell in the spinal cord from discharging4 ,but it is an equally familiar fact that with continuous stimulation the impulses accumulate and ultimately overcome this resistance4 ,most people have at some time or other striven to resist the inclination to cough1 consequent upon a tickling sensation in the throat1 and know that there comes a time when they can restrain themselves no longer4 ,this is because the accumulated stimuli from the throat1 having reached a greater strength than the prohibitive impulse from the brain1 succeed in compelling the cells in the cord to discharge4 ,lastly1 reflexes can be learnt4 ,when a young child first endeavours to stand upright1 the sensation of falling is doubtless conveyed to the brain1 and thought taken of how the erect position can be maintained4 ,but it is not until after many experiments and failures that the brain-cells can send messages to the right cells in the cord1 and these set the necessary muscles in motion4 ,experience teaches what must be done1 and constant practice eventually enables the spinal cord to act for itself without referring for orders to the brain4 ,it is on the same principle that we learn to ride the bicycle4 ,at first we have to devote our whole attention to keeping our balance1 but in a short time we find we are doing it with our mind free to contemplate the scenery4 ,what can be done by reflex action can only be appreciated by observing an animal from which the brain has been removed4 ,a frog which has been treated in this way--the operation1 it should be said1 if performed under an ansthetic can cause no pain1 either at the moment or afterwards--will live for weeks--in fact1 almost indefinitely--if proper precautions be taken4 ,but it is an automaton pure and simple4 ,unless touched it sits absolutely still4 ,if touched it hops once or twice straight ahead regardless of obstacles4 ,if placed in water it swims1 equally regardless of obstacles4 ,if turned on its back it immediately resumes its normal position4 ,if small chips of wood are placed on its back it kicks them off4 ,if the table on which it is sitting be tilted it will crawl up the incline until it reaches a level4 ,but it will starve in the midst of plenty1 having lost all power of thought1 memory and perception4 ,if diligently fed by hand a frog1 a fish1 or a bird will live for a long time without any brain1 since their repertoire of movements is small and mostly reflex1 and their occasions for deliberated action comparatively few4 ,but the higher we get in the scale of life the more the brain takes over the duties of the cord1 the less automatic become the greater number of the actions1 and hence the more open does the animal's conduct lie to moral criticism4 ,,iii4 ,we have now seen how protoplasm exists in a large body1 sharing the work of living amongst specialized cells1 and how it responds as a whole to the influences exerted upon it by its surroundings4 ,the next thing to consider is how it is situated with regard to matter which does not form part of its own body2 how protected from1 and how put into communication with1 the rest of the universe4 ,with regard to the former1 we have seen that in the single cells1 constituting unicellular organisms1 there is always a bounding membrane of denser texture than the rest of the protoplasm4 ,as the cell develops its capabilities1 we have a shell or case of non-living matter secreted around it1 with apertures for communication with the outside world1 and increasingly effective protection is provided as protoplasm1 whether in the single cell or the body1 leaves the water1 and has to face the inclemencies of terrestrial life4 ,illustration3 ,,diagram #dh4--,,showing ,,the ,,formation ,,of ,,the ,,skin4 ,illustration3 ,,diagram #di4--,,structure ,,of ,,skin4 ,in the schematic embryo 7,diagram #f7 and other diagrams contained in this volume1 the skin has so far been represented as consisting of a single layer of living cells2 but we must now admit that the skin of man is quite different4 ,such a covering would be no protection from heat1 cold1 or irritating chemicals1 while1 in order to prevent its drying up1 it would have to be kept moist with slime1 and we should look very like frogs4 ,in order that an adequate defence may be provided for the body1 this layer of cells divides tangentially1 forming two layers4 ,the inner of these two then divides tangentially again1 and a second layer is interposed between the innermost and that first formed4 ,the skin now consists of three layers1 and so the process is repeated until it is several layers thick4 7,see ,diagram #dh47 ,it is the innermost and best-nourished layer which keeps dividing2 the other layers1 as they get pushed outwards1 are only reached by a little lymph which filters between the cells1 and are eventually starved even of that4 ,as they get pushed away from the dividing layer1 however1 they set to work to surround themselves with a horny wall1 which thickens and thickens1 until eventually there is hardly any cell left4 7,see ,diagram #di47 ,finally the cells die and the horny envelopes form a dead cuticle1 protecting the living layers beneath1 and are ultimately sloughed off when their successors are ready to replace them4 ,illustration3 ,,diagram #ej4--,,showing ,,the ,,development ,,of ,,hair4 ,not even a horny layer of dead cells is1 however1 always sufficient protection1 and the growing layer has sometimes to supplement it by hair or feathers4 ,how hair is developed is shown in the accompanying diagram 7#ej74 ,the growing layer sends a strand straight downwards into the connective tissue1 which forms the basement of the skin4 ,the cells in the middle of this strand1 which behaves like ordinary skin1 are the least well nourished1 and accordingly die and leave a tube4 ,this tube1 if no further development took place1 might become a sweat gland2 but if it is to give rise to a hair it becomes cup-shaped at the base1 enclosing a small loop of bloodvessel4 ,the cells just above the capillary1 being better nourished than the rest1 grow more rapidly than their neighbours1 and the result is that a column of cells which we know as a hair pushes its way up through the tube4 7,see ,diagram #ej47 ,this outer layer comes everywhere between the main bulk of the body and the outer world4 ,hair and sweat glands do not by any means represent its only modifications4 ,teeth are formed from it in somewhat the same manner as hair1 while we have already seen that it gives rise to the whole nervous system4 ,the next thing which we have to consider is how knowledge of the external world reaches the central nervous system4 ,sensations of touch1 temperature1 and pain are fairly easy to understand1 since the nerves which convey such impressions have numerous endings in the skin4 ,end organs of nerves in the joints and muscles doubtless enable the animal to perceive and estimate strain and resistance in moving or lifting things4 ,but the power of perceiving the chemical peculiarities of things2 light1 involving the formation of visual images1 which we call seeing2 sound2 and position and equilibrium1 it is not possible for the whole surface of the body to possess4 ,the principle of division of labour is extended to the task of perception as well as to that of motion2 and cells1 with their property of responding to light1 vibration1 chemical stimulation1 etc41 are grouped together to form special organs1 connected with the central nervous system by special nerves4 ,perhaps the most important factor which can influence protoplasm is the chemical nature of its surroundings2 and in the first essay1 on the general nature of protoplasm1 we touched upon the way in which it is drawn towards some substances1 and repelled by others4 ,in the body there are two sets of cells deputed to act for the rest in this particular4 ,one set is situated in the membrane lining the nose1 over which the air we breathe passes2 and these cells examine our gaseous surroundings1 and warn us1 by what we term #8smell1' whether the atmosphere is fit for us or we had better seek a purer4 ,the other set is for the examination of liquids4 ,against these we are protected by our skin1 and1 as we do not absorb anything through it1 it is devoid of the power of examining the things it touches4 ,but with our food it is different2 we must have the power of testing that4 ,accordingly1 there are ,customs officers in our mouth in the form of little groups of cells1 which report upon the liquids and solids moistened by saliva1 and enable the animal to reject pernicious imports4 ,thus1 the stimulation of a small portion of the protoplasm composing a body is transmitted over the whole1 and is able to awake in it the necessary response4 ,illustration3 ,,diagram #ea4 ,illustration3 ,,diagram #eb4 ,illustration3 ,,diagram #ec4 ,illustration3 ,,diagram #ed4 ,illustration3 ,,diagram #ee4 ,illustration3 ,,diagram #ef4 ,so much for the chemical sense organs2 they are comparatively simple4 ,but between a single cell1 which always makes towards or always hurries out of a ray of light passing through the water in which it swims1 and an animal with eyes capable of recognising the colour1 shape1 size1 and distance of objects in space1 there really does seem to be a wide gulf4 ,it is not1 however1 too wide to be bridged4 ,after the single-cell stage has been passed1 and we have beasts consisting of an inner layer of cells which is digestive in function1 and an outer layer which is protective1 motor1 and sensory1 the power of perceiving light is doubtless vested in the outer layer4 ,when we get beasts consisting of three layers progressing along the straight path of development which leads to man1 we find the outer layer becoming too opaque for this purpose1 and the torch is handed on to the sensory tube derived from it4 7,see ,diagram #e47 ,as more and more protection is required1 the skin thickens1 and the neural tube comes to lie deeper1 as in ,diagram #ea4 ,in order not to lose the light altogether1 it has to throw out buds1 which concentrate in themselves the peculiar faculty of perceiving it1 and at the same time little pits are formed in the skin just over them to help the light to reach them4 7,see ,diagram #eb47 ,in ,diagram #ec both the nervous elements and the integumentary are developing their possibilities2 and in ,diagram #ed a large surface has been prepared for the reception of light1 and a lens formed to focus the rays upon it4 ,diagrams #ee and #ef give the concluding stages in the development of the eye3 the formation of the cornea and its protecting eyelids4 ,the two cavities are filled with clear liquids1 and the whole eyeball supported by connective tissue4 ,so fascinating is everything connected with the eye that the temptation to describe it in detail is great2 but in a book of rough outlines1 and in consideration of the many important matters yet awaiting their turn1 we must confine ourselves to briefly mentioning a few of the more important points concerning it4 ,the light is focussed by the lens upon the nervous curtain at the back1 and produces there a picture1 as in the photographic camera4 ,thus we perceive the shape of objects4 ,the different rays of the spectrum affect different elements in this curtain or retina1 whereby we get sensations of colour4 ,finally1 the clearness of the picture1 its size1 the degree of convergence of the two eyes1 and the effort of focussing--for the curvature of the surface of the lens can be altered--enable us to estimate the size and distance of an object4 ,and now1 though it would take volumes to do justice to the physiology of vision1 we must pass on to deal equally briefly with the functions of that no less important organ1 the ear4 ,the essential part of the ear is a membranous bag1 formed by the pouching in of the outer layer of cells--as shown in ,figs4 #a1 #b1 and #c of ,diagram #eg--which comes to lie in a bony chamber beneath the skull1 and assumes the somewhat complicated shape depicted in ,fig4 #d4 ,we have not time1 nor is it for our purpose necessary1 to trace all the steps in the development of the ear1 either external or internal1 nor need we spend much time upon its structure1 beyond indicating its position4 ,but its position1 which is shown in ,diagram #eh1 must be grasped in order to understand how it is influenced by sound4 ,illustration3 ,,diagram #eg4--,,showing ,,development ,,of ,,the ,,membranous ,,labyrinth ,,of ,,the ,,ear4 ,u1 ,utricle2 ,c1 cochlea2 ,s1 saccule2 ,s4,c41 semicircular canals4 ,it will be seen that the membranous bag1 which is fitly termed the labyrinth1 is situated in a bony cavity which fits so closely as to be termed the bony labyrinth 7,c74 ,the membranous labyrinth is filled with a liquid1 called endolymph1 and the bony labyrinth 7,c7 is also filled with a liquid1 called perilymph1 in which the membranous bag swims4 ,all this is called the inner ear4 ,the inner ear communicates with a second cavity--the middle ear 7,b7--by two apertures in the bony wall1 which are closed by membranes4 ,the middle ear is full1 not of liquid1 but of air1 and is separated from the external ear1 the cavity marked ,a1 which is open to the external world1 by another membrane called the tympanum1 or drum1 of the ear4 ,the middle ear is connected by a tube with the throat1 so that the pressure of the air on both sides of the drum may be the same4 ,illustration3 ,,diagram #eh4--,,showing ,,the ,,position ,,of ,,the ,,ear4 ,a41 ,outer ear2 ,b41 middle ear2 ,c41 inner ear4 ,now1 the object of this arrangement is that the ear may be able to fulfil one of its principal duties1 namely1 the perception of sound4 ,sound1 as the reader is doubtless aware1 is transmitted through the air as waves of condensation and rarefaction1 due to the swinging backwards and forwards of its particles2 it resembles the passing on of a bump along a line of trucks on the railway when the engine runs up against the end one preparatory to coupling4 ,the magnitude of this oscillation we perceive as the loudness1 the frequency as the pitch of a note4 ,now1 when the waves of sound strike against the drum of the ear1 they cause it to vibrate backwards and forwards also4 ,supposing there was no middle ear1 and the sound waves beat directly upon the membranous windows of the inner ear1 these could not be made to vibrate1 as there is liquid behind them1 and liquids are incompressible2 so1 in order that the movements of the drum may be transmitted to the liquids of the inner ear1 they are carried across the middle ear by a chain of small bones1 by which their extent is curtailed1 but their force increased1 and brought to bear upon one only of the two openings4 ,the consequence of this is that the membrane closing it is able to vibrate and pass on the vibrations to the liquid within1 since when it is pushed in1 the membrane covering the other hole is pushed out4 ,illustration3 ,,diagram #ei4--,,the ,,semicircular ,,canals4 ,exactly how the different parts of the membranous labyrinth contribute to our perception of sound we do not quite know4 ,it appears as though the difference of pressure in saccule and utricle originally conveyed to the brain a sensation of noise without any idea of quality1 while the cochlea was developed later to analyze sounds and give information as to pitch and tone4 ,whether the rest of the labyrinth has any longer a part to play in the perception of sound1 we cannot say with certainty2 but it seems pretty certain that the cochlea is the organ for receiving musical impressions4 ,here1 again1 though1 we are at a loss1 for we do not know with certainty how the cochlea acts4 ,in shape it is a long tube1 and in the head is coiled spirally--like a snail's shell to look at4 ,along its whole length is a ridge of cells with short hairs projecting from their inner surface into the liquid it contains2 and to the cells along this ridge a branch of the auditory nerve is distributed4 ,but as to whether one of the cells along this keyboard responds to each of the notes we can distinguish1 or whether they are affected as a whole1 physiologists are not yet agreed4 ,at least one other important duty the ear performs2 it tells us in what position we are1 and how our whole head moves or is moved4 ,on the top of the saccule1 in ,diagram #eg1 ,fig4 #d1 there are shown three little loops which are called the semicircular canals4 ,they are shown again more clearly by themselves in ,diagram #ei4 ,fig4 #a shows their position with regard to each other4 ,it will be seen that two of them are vertical1 with their loops forming a right angle with one another1 and that the other is horizontal--in fact1 that they lie in the three planes of space4 ,fig4 #b shows the structure of one of them2 it has a swelling at one end 7a71 and a knob projecting into it where the nerve joins it 7b74 ,in ,fig4 #c is shown a section through this knob1 which gives the key to the use of these structures4 ,a little head of cells projects from the wall of the canal into its lumen1 and from these cells hairs bristle out into a dome-like covering of jelly1 weighted1 to prevent its moving too easily1 with small particles of lime4 ,now1 if you take up a round vessel full of liquid--say a bowl of gold-fish--and give it a twist round1 you will notice that1 though the bowl turns1 the water inside does not2 the fish remain in their old position4 ,if there were a rod projecting from the side of the bowl1 it would1 of course1 move with it1 and if a fish came in its way would strike against it4 ,this is the principle of the semicircular canal4 ,for if we turn our head1 the tube of the canal turns1 passing over the liquid in it1 which of course does not move1 though it appears to flow in the opposite direction4 ,the consequence is that the hairs on the side of the knob in the direction in which the head is being moved are pressed upon by the dome of jelly1 which1 as it floats in the liquid1 tends to remain where it is4 ,the nerves1 stimulated in this way1 inform the animal generally of the movement4 ,these little organs are very important to us1 though we have our eyes to correct our ideas of position1 and they are still more so to the fish1 which dart and turn in the wide expanse of the ocean1 and the birds and bats1 which wheel about in the air4 ,there are1 however1 some occasions when we do not feel inclined to bless them2 for1 inasmuch as they faithfully report every roll and plunge of a ship to a person on board1 it is they which are mainly responsible for sea-sickness4 99 99 99 99 99 ,and now that we have seen how the body lies with regard to the external world2 how it is efficiently protected from its surroundings2 how it is placed in communication with them2 and have briefly examined the organs by which it makes its chemical and physical investigations1 looks out into space1 and is kept aware of what is going on therein1 we may return to the means whereby it responds as a whole to the stimuli thus reported--the central nervous system--and try to learn how the right response is brought about4 ,,iv4 ,there is but one thing more to describe in the mechanism of the body--the connecting link between the last two sections4 ,in the last we saw how the body receives stimuli from the external world2 in the one before1 that when these stimuli reach the central nervous canal it in turn stimulates the organs to perform such movements as circumstances require4 ,what1 therefore1 remains to be described is the working of that canal by which these necessary movements are ordered and controlled4 ,now1 in speaking of reflex action a few pages back1 we said that the nerves which bring in stimuli from the periphery distribute them about the neural canal to those cells whose activity1 by sending out fresh stimuli to the muscles1 produces the requisite movements4 ,these motor cells1 however1 are not scattered about the spinal cord anyhow4 ,they are collected into clusters1 or nuclei1 as they are sometimes called1 and each cluster has special duties--i4e41 a special organ to control4 ,thus1 we say that there are in the central nervous system centres--a nervous centre to control the leg2 another to work the diaphragm2 another for the muscles of the ribs2 more for the arm1 hand1 etc4 ,and these centres are in communication with one another1 so that they may not pull different ways4 ,in the first example of reflex action given in ,section ,,ii4 of this essay1 the sensation of a pin-prick was first conveyed to the centres controlling the limb injured1 by whose activity it was drawn away from the danger4 ,but the nerve which gave the warning which produced this elementary movement distributed the impression that something was wrong to the higher centres1 so that the whole body was involved in protecting1 doctoring1 and avenging the outraged member2 from which it would appear that the lower centres are under control of higher ones4 ,and this is the case4 ,if we may be allowed the metaphor1 there are captains of tens1 who are under the direction of captains of fifties1 and the captains of fifties receive their orders from captains of hundreds4 ,the nerve canal1 the manner of whose formation as a simple tube is shown in ,diagrams #e and #db1 has therefore different functions in different parts1 and this to such an extent that considerable differentiation in bulk and structure is produced4 ,the neural canal may be roughly divided into two parts--a comparatively simple tube1 running the greater part of the animal's length1 containing many centres from which nerves run to the organs they control2 and a complicated bulbous enlargement at one end1 with thickened walls1 in which are the centres controlling those in the cord1 and thereby managing not so much organs as the whole animal4 ,the former is called the spinal cord1 the latter the brain4 ,this division1 accustomed as we all are to take it for granted1 offers plenty of food for reflection4 ,why should an animal have such a brain placed in its head8 ,why1 indeed1 should it have a head1 regarding that member as a group composed of eyes1 nose1 mouth1 ears and brain8 ,the mouth gives us the key to the riddle2 the mouth is the essential organ1 and all the rest are its accessories4 ,in the first essay we saw that the basis of life was chemical1 and in the second that the materials necessary for the chemical action1 or food1 must1 in the higher animals1 be taken into the digestive tube through the opening which we call the mouth4 ,therefore1 as it is highly important that only the most beneficial substances shall be received into it1 and that all which are actively injurious shall be excluded1 it is plain that the organs of chemical perception must be placed in its neighbourhood--the organs of smell to enable the mouth to find its food1 and the organs of taste to aid in selecting it4 ,as1 moreover1 our humble ancestors1 the fishes1 move literally mouth foremost1 it is not surprising to find the organs of space perception1 the eyes1 also situated in its neighbourhood1 especially when one considers that their food is often of a lively character1 and requires precision of movement to secure it4 ,the inevitable consequence of thus grouping the more important organs of perception under the fore-end of the neural canal is that it grows and develops more highly here than elsewhere along its length1 and soon is in a position to dictate to the rest of the body4 ,another reason why it must develop is that it must contain centres for turning its impressions to practical account1 not only by producing complicated movements in the jaws1 eyes and gills1 but also by ruling the centres in the cord1 and instructing the body to carry the mouth whither it needs to go4 ,illustration3 ,,diagram #fj4--,,showing ,,primary ,,division ,,of ,,nervous ,,tube4 ,in the preceding diagram 7#fj7 the origin of the brain is shown as a dilatation of the end of the neural canal into a bulb with thickened walls1 which has already become constricted in places1 so that it is subdivided into three4 ,the next diagram 7#fa7 is intended to give1 in no matter how crude and schematic a way1 some idea of the lines on which the development continues4 ,we do not show all1 or even half1 the structures which go to make up the brain4 ,to do so would be out of place in a book like this4 ,further1 we shall endeavour as far as possible to speak of the brain in general terms1 avoiding the five-syllable bastard ,grco-,latin names with which the early anatomists have endowed almost every square inch of its substance1 and confine ourselves to summing up its functions as briefly as can be done with justice4 ,illustration3 ,,diagram #fa4--;,,giving ,a ,,rough ,,idea ,,of ,,how ,,the ,,brain ,,is ,,developed4 ,in pursuance of this method1 attention must be drawn to the fact that only the foremost of the three original bulbs 7marked ,a in the diagram7 and the hindermost 7,c7 continue to grow4 ,the middle one 7,b7 remains comparatively simple4 ,from the foremost lobe buds grow out to form the eyes in the manner which we have already described1 and other buds push forwards to meet the nerves from the nose4 ,the latter have1 even in the early stages shown in ,diagram #fa1 reached an extraordinary size2 and when we come to trace them further1 we shall find that they become very complex1 and acquire remarkable and unexpected powers1 considering their humble origin4 ,strange changes also take place in the hindermost bulb4 ,it splits along the top1 so that the cavity it contains is open like a saucer1 though bridged over by a three-lobed body called the cerebellum4 ,following the spinal cord up into the brain1 we are conscious of no sudden line of demarcation separating the one from the other1 only of an increasing size and complexity4 ,the lower parts of the brain send out and receive nerves much as the cord does2 three pairs go to the muscles which turn the eyes2 other pairs bring in sensations from the face and throat2 others control the muscles of the face1 tongue and throat4 ,but the brain differs from the cord in being directly connected by nerves1 not only with adjacent parts1 but also with the distant and more important organs in the interior of the body--heart1 lungs1 etc42 in containing groups of cells which have stimuli sent on to them from all over the body vi the cord2 and in possessing centres which control those lower down in the nervous system4 ,it therefore not only receives and balances stimuli from all over the body1 but1 by governing the centres which preside over the bodily movements1 is able to wield and direct the body as a whole4 ,the hinder divisions of the brain1 which we shall consider first1 have no connection with consciousness or volition4 ,they only produce reflex movements1 which1 however1 owing to the wealth of material they have to work upon1 are wonderfully complex and far-reaching4 ,let us take a few examples4 ,in the hindermost division of the brain 7,c in the diagrams7 there is the centre which presides over the oxygen supply1 the importance of which we saw in the essay on vital chemistry4 ,this centre perceives when the lungs have been filled with a gas1 and causes them to be emptied2 it perceives when they are empty1 and again does not allow them to remain too long in that state1 before ordering an inspiration2 it notes the quality of the air which is passing through the nose1 and it notes the quality of the blood which bathes its own cells4 ,the condition of the blood1 indeed1 is closely watched4 ,an excessive quantity of carbonic acid gas1 poverty of oxygen1 even temperature1 all produce through it an effect upon the rhythm of the breathing4 ,close by the respiratory centre is the centre which controls the circulation4 ,but enough has been said in the section on reflex action1 wherein the process of fainting was described1 to give an idea of the part it plays in the body2 so it need not detain us here4 ,we cannot1 however1 pass over its neighbour1 the centre of temperature1 so briefly4 ,its methods not only afford one of the most striking and interesting examples of harmonious regulations by reflex action1 but the subject of temperature itself is so important that we must describe in some detail how that of the body is kept level4 ,as we said when discussing protoplasm generally1 life--that is1 the change always going on in the protoplasmic substance--is influenced by temperature3 the single cell becomes less active at a low temperature1 and dies at a high one2 so obviously there is a temperature at which its functions are most easily carried on4 ,inside the body the cells are all kept at the temperature best for them by the circulation of the blood2 but the absolute temperature of the whole body depends upon the heat which is generated within it by chemical action1 and the heat which it loses to1 or receives from1 its surroundings4 ,under normal conditions this temperature in man is #ihd ,f41 when the production of heat from its own metabolism is balanced by the loss of heat by radiation4 ,if1 however1 the atmosphere be very hot1 less heat is developed in the body1 the general metabolism being slower2 and more heat is lost1 since by reflex action the skin is bathed in sweat and cooled by its evaporation1 and the small bloodvessels under the skin are dilated1 so that more blood being brought to the surface1 its chance of being cooled by radiation is thereby increased4 ,if1 on the other hand1 the atmosphere is cool1 the loss at the surface is minimized by constriction of the cutaneous bloodvessels1 and a checking of the perspiration and consequent evaporation2 while internally more heat is generated by increased metabolism4 ,the cells which are mainly responsible for the production of heat are those of the muscles2 and when much heat is required they increase in activity1 not only in their general tone1 but even by a visible movement1 which we describe as shivering4 ,so1 within reasonable limits1 whatever the temperature of its surroundings may be1 that of the body remains the same1 and though we may raise or lower our temperature by lying in a hot or cold bath1 reflex adjustment of the sweat glands1 bloodvessels and muscles brings it quickly back to normal when we emerge4 ,with a passing mention of the cerebellum1 the three-lobed organ shown in ,diagram #fa1 and seen again in a more advanced stage in ,diagram #fc1 we may dismiss the two hinder divisions of the brain4 ,the cerebellum lies on the upward path of fibres from the cord to the higher centres in the fore-brain4 ,it is a somewhat complicated organ1 and its functions are not yet fully known4 ,the older physiologists took a very extreme view of its importance1 assigning to it1 among other romantic duties1 that of providing a habitation for the soul4 ,this opinion on the strength of later research we can hardly endorse4 ,the cerebellum really seems mainly concerned in co-ordinating the action of the muscles1 especially in maintaining equilibrium in standing and walking4 ,our knowledge of the whole brain is very far from complete4 ,we should like to know the peculiar function of each little group of cells that can be made out under the microscope1 and the paths of all the fibres connecting the different parts of the nervous system4 ,as it is1 we have to wait with the best patience we can while they are being investigated1 and hope4 ,in few departments1 however1 have the labours of the physiologist proved more fruitful and interesting than in the study of the fore-brain 7,a in the diagrams74 ,in the simpler form1 as shown in ,diagram #fa1 ,a1 and ,diagram #fb1 ,fig4 #a1 ,a1 the fore-brain is remarkable in that it throws out buds for the two most important sense organs--those of sight and smell4 ,so important are these senses1 especially in our humble ancestors1 as we have already pointed out1 that it is not surprising to find the impressions of the other senses brought on up from the hinder parts of the brain to be compared with them4 ,the fore-brain is1 in fact1 a sort of terminus whither the whole of the afferent or incoming stimuli are brought1 and whence1 since information is only received in order to be acted upon1 the supreme orders to the body issue4 ,in the fore-brain there are centres for specially governing all the motor organs2 but by a strange arrangement the main root of the brain is overwhelmed by its own offshoot1 the hemisphere1 or lobe which gives rise to the olfactory bud4 ,in fact1 so great is the importance of the sense of smell to an animal whose one object in life is to find food1 that1 instead of the hemisphere being subordinate to its parent1 it seems to take over most of the latter's business1 receiving a report of the sensations collected by it1 and sending out orders upon its own initiative4 ,yet1 unimposing though the history of this division of the brain may be1 it ultimately becomes the seat of consciousness1 whereby the mental processes are carried on1 and whence all voluntary movements spring4 ,illustration3 ,,diagram #fb4--,,showing ,,how ,,the ,,cerebral ,,hemispheres ,,are ,,developed ,,from ,a1 ,,the ,,foremost ,,bulb ,,of ,,the ,,brain4 ,of course1 in order to do this1 the hemispheres have to grow considerably1 and thus we find them enveloping the rest of the fore-brain and swamping it in structure as well as in function4 ,diagram #fb indicates how this is done1 while ,diagram #fc shows roughly the proportion and position the different parts of the brain ultimately attain4 ,finally1 ,diagram #fd1 which is rather more realistic1 but still much simplified1 presents a view of the organ in the head4 ,the size of the cerebral hemispheres1 compared with the rest of the brain1 is especially remarkable4 ,so1 too1 is their endeavour to increase their surface still more by throwing it into deep folds4 7,see ,diagram #fd47 ,these two features vary with the position of the animal in the scale of development2 in man1 who stands highest in intelligence and dexterity1 the hemispheres are very large indeed compared with the other organs1 and seamed all over with a maze of winding furrows4 ,another remarkable feature is the extreme degree to which specialization is carried out4 ,different parts of the body are represented1 each by a small area of the cortex1 or surface layer1 and we know at what spot on the cortex such sensations as sight and hearing are perceived1 and from exactly what little patch the impulse to move each limb emanates4 ,in the accompanying diagrams 7#fe and #ff7 these areas are mapped out1 their locality being fixed by the principal folds which act as landmarks on the surface of the hemisphere4 ,illustration3 ,,diagram #fc4--,,relation ,,of ,,different ,,parts ,,of ,,the ,,brain4 ,there is another important fact which we must not omit to mention in speaking of this localization3 each hemisphere presides over the opposite side of the body4 ,early in development the nerve fibres from the eye cross over to the opposite side of the brain1 and the afferent fibres from the lower parts of the body have accordingly to follow suit4 ,then1 as the efferent fibres--i4e41 those which set the muscles in motion--have to bring about the movements in response to information received1 they must also cross to get back to the side from which it came4 ,so1 if a tumour grows inside the head on the right side1 it is the left eye which becomes sightless1 or the left hand which grows numb and powerless1 according to the part of the cortex which is pressed upon4 ,perhaps the most interesting part of the whole body is that little band of the cortex running upwards from behind the temple to the crown of the head1 in which 7cf4 ,diagrams #fd1 #fe and #ff7 the motor areas of the limbs1 and the perception of those sensations which we have grouped together and called #8touch1' are situated4 ,the minute structure of this region is roughly shown in section in ,diagram #fg1 as it has been made out with the microscope2 but only a few of the nerve cells are shown1 the connective tissue of feltwork in which they are suspended1 and the bloodvessels by which they are nourished1 being left out4 ,all the structures represented are of course very1 very small2 the large black patches which represent cells would really be invisible1 and the whole field of the diagram only a mere speck1 to the naked eye4 ,illustration3 ,,diagram #fd4--,,position ,,of ,,the ,,brain ,,in ,,the ,,head4 ,a represents the nerve by which impulses are brought in4 ,it runs straight up to the surface of the cortex1 and there its branches end1 interlaced with those of a many-branched distributing cell 7,b74 ,the two cells 7,c and ,d7 shaped like pyramids1 which send up branched processes from their apexes1 receive an impulse from the distributing cell1 and transmit it along the fibre which runs downwards from the middle of their base4 ,where the fibre from the smaller one goes to we are not sure--probably to another part of the brain to insure harmonious working--but the large pyramidal cell sends its fibre right away through the lower parts of the brain1 passing the cell-stations they contain1 on into the spinal cord1 till it reaches the centre there1 which immediately works some particular limb4 ,illustration3 ,,diagram #fe4--,,map ,,of ,,the ,,cerebral ,,hemisphere1 ,,showing ,,the ,,areas ,,in ,,which ,,various ,,functions ,,are ,,localized4 ,supposing we ansthetized somebody1 throwing him into deep unconsciousness1 and then opened his skull1 laying bare the brain as is done in ,diagram #fd1 only not quite in such a wholesale manner4 ,if we then stimulated the part of the brain we are now considering at different places with electric needles1 using a weak induction current1 we should see him moving different members according to the different regions touched--now an arm1 now a leg1 now the whole head4 ,if we were to place the electrodes in the centre for the hand1 and then gradually increase the strength of the current1 the activity of the hand centre would throw other centres into activity4 ,the arm would move next1 raising the hand towards the face4 ,then the eyes would turn1 and the whole head to meet the hand4 ,lastly the mouth would open4 ,the movements are those of putting something into the mouth--the ruling passion strong in unconsciousness4 ,illustration3 ,,diagram #ff4--,,map ,,of ,,the ,,cerebral ,,hemisphere1 ,,showing ,,the ,,areas ,,in ,,which ,,various ,,functions ,,are ,,localized4 ,such experiments were1 of course1 first made upon animals1 but they have been fully verified on the human subject4 ,the story of how this was done is not1 however1 a romance with a martyr or a criminal for the central figure4 ,the corpus vile was not provided by a volunteer1 or kidnapped and bound in a dark cellar1 but treated as a patient in the airy wards of a hospital4 ,with increasing knowledge of the brain1 it was found that epilepsy was cortical in origin4 ,a little piece of the cortex becomes diseased and hyperexcitable4 ,the sufferer suddenly becomes acutely conscious of one of his members--a hand or a foot1 say--not because there is anything the matter with it1 but because the corresponding area in the brain is morbidly active1 and he refers the sensation to the part from which it receives its nerves4 ,the next moment the limb begins to twitch1 and the excitement spreading1 as in the experiment we described above1 to other centres which are not diseased1 they1 too1 become morbidly active1 and the whole body is thrown into convulsions4 ,this is a disease which must be checked as soon as possible4 ,the surgeon accordingly lays bare the part of the brain affected1 knowing now where to look2 finds the exact spot which is diseased by reproducing the first twitchings of a fit by electric stimulation1 and removes the source of the trouble4 ,illustration3 ,,diagram #fg4--,,showing ,,the ,,system ,,of ,,nerve ,,cells ,,in ,,the ,,cortex4 ,a1 ,afferent fibre2 ,b1 distributing cell2 ,c1 small pyramidal cell2 ,d1 large pyramidal cell4 ,returning to general considerations1 an important point is the way in which the different centres are connected by fibres1 which put them into relation4 ,the brain may consist of many centres1 just as the body consists of many organs1 but both body and brain must live as a whole4 ,if the heart and lungs get out of harmony there is trouble1 and if the bridge which connects hearing with motion in the brain breaks down1 as occasionally happens for a time in an overworked man1 he is mentally at a discount4 ,he can hear and understand1 but he cannot write or talk sense3 he is sane1 but quite helpless1 and generally very frightened4 ,still more important are the intermediate stations and sidings on these lines of communication1 for it is here that the most exhaustive weighing and comparing of incoming stimuli is carried on--the final balancing before a voluntary action2 in a word1 thought4 ,these courts of inquiry are called association centres4 ,it used to be believed that they were all in the fore-part of the brain1 under the forehead2 but this is evidently not the case4 ,several men in war or by accident have had the frontal lobes of their brain damaged beyond repair2 and when they have been discharged from hospital1 where1 thanks to the advance made by surgery since ansthetics and antiseptics were discovered1 they have been successfully treated1 they have gone back to their work seemingly in no way different from men whose brains were whole4 ,in some cases they have even been reported as having become quicker and sharper than before1 probably owing to there being fewer association centres1 and thought being accelerated by simpler machinery3 facts are thenceforward shaken through a larger-meshed sieve4 ,a few general considerations1 and we have done4 ,there is no centre for memory in the brain4 ,the facts which we remember are not stored as in a box1 nor can one imagine how they could be1 considering that the physical basis of an idea is molecular change4 ,the whole nervous system is probably concerned in memory1 a particular change1 which has momentarily occurred in its tissues1 being more likely to occur again under certain circumstances than a fresh one1 and certain tracks becoming well beaten and more permeable than others4 ,pleasure and pain are other general phenomena3 they are not to be localized in the brain like vision or hearing4 ,pleasure is the consciousness that the whole body is under favourable conditions2 and pain1 the knowledge that the protoplasm of certain cells of the body is being acted upon by injurious agents1 chemical or physical4 ,there seems to be good evidence that separate nerves convey impressions of injury1 distinct from those of touch and temperature2 but it is the revolt of the whole body against conditions affecting a part which constitutes pain4 ,amidst the maze of perplexities which lies between physiology and psychology1 there is1 however1 one fact which stands out clear and bold3 the brain can create nothing4 ,we have seen how matter is taken into the body and matter is cast off from the body4 ,we have seen how energy is released in the body from chemical compounds1 and made use of by the body4 ,so now1 after a moment's thought1 it must be plain that every stimulus which goes to the brain must have its effect there1 and that a man's thoughts and conduct are entirely dependent on what has1 at some time or other1 come in from the external world4 ,the association centres can evolve wonderful thoughts1 but they are structurally derived from the grosser sense organs1 and must get all the material they work upon from them4 ,the nervous system puts the body into relation with the external world as a whole1 but for convenience it is subdivided into the afferent system1 by which impressions come in1 and the efferent system1 by which the muscles are set in motion4 ,of the two halves1 the afferent system has a just right to priority1 for the efferent system is merely its consequence4 ,sights1 sounds1 smells1 etc41 reach the brain by afferent paths from the external world1 and are there moulded into thoughts4 ,their effects we see in poetry1 architecture1 sculpture1 or laundry work1 according to the method of the brain in treating the raw material it receives1 and of a quality corresponding to the fineness with which the brain examines them1 and can control the motor organs of the body4 ,whatever goes in at the afferent door1 and some people's sensory apparatus is much more easily affected than others1 produces its effect within4 ,sometimes the energy is expended in thought1 sometimes in action2 sometimes it trickles away as laughter4 ,but all these phenomena have a material basis3 matter producing changes in matter4 #8,those delicate tissues wherein the soul transacts its earthly business1' as ,stevenson so picturesquely describes the brain1 stick to their earthly business4 ,there is no astral department opened yet4 ,a man may evolve a great idea from the data he receives1 but he must give it a material coefficient if he does not wish it to be lost to his earth-bound brothers4 ,he may write it in a book1 or he may sculpture it in marble2 but the most convenient means of communicating with his fellows is by sound1 which he can command by expelling the air in his lungs over vibrating cords in his throat4 ,these cords are adjusted at the position and tension to give a desired note2 and the cavities of the chest1 throat and mouth acting as resonators1 a noise is produced1 which is shaped by the tongue1 lips and teeth into words4 ,by means of language the human body is enabled to co-operate with others of its kind for the development of the resources of the earth1 the shaping of society1 and the forming of individual character4 ,but here physiology ends and other sciences begin4 ,,essay ,v4 ,,the ,,body4 ,i4 ,such1 as far as it can be compressed into four short essays1 is the nature of protoplasm4 ,we have sketched out its powers2 described how it exists only in the form of a cell2 and shown how cells1 by forming a community and sharing the work1 simplify the business of living1 and secure great advantages for themselves individually4 ,but now we have something fresh--the body4 ,the body is an organic whole1 like the cell4 ,it is composed of cells1 but these cells only develop one of their many powers to its utmost that they may justify their existence in the community2 they do not acquire fresh properties4 ,so really the body is merely a mass of protoplasm in which--though in a greater quantity--the same changes are going on that we find in a single cell4 ,yet how utterly different is the body from the cell6 what a wide gulf yawns between a man and an amba6 ,the body has powers of its own1 distinct from those of protoplasm2 and the protoplasm may still be alive when the body it helped to compose is dead4 ,a few thousand pounds of protoplasm could not have built ,westminster ,abbey1 but a few hundred men did2 for just as out of protoplasm arises the body1 so the body gives rise to the mind1 a thing as much above it as it is above the cell4 ,so far we have taken the cellular units as our starting-point in discussing life2 but a bird's-eye view of physiology would be incomplete which contained no mention of the major tactics of protoplasm--the life of the body4 ,we must consider the needs of a man as such4 ,a man requires1 as we have described before1 air and food4 ,the air must contain the proper amount of oxygen1 and the food must consist of liquids and solids4 ,the important liquid is water4 ,more than half by weight of the whole body is water1 and we are always losing it3 through the skin1 through the lungs1 and through the kidneys4 ,people may drink alcohol with water1 but not instead of it4 ,indeed1 the more alcohol they take1 the more water they require1 for if they take their spirits in an undiluted form1 they take water out of the body4 ,if you dip a piece of wet cloth into alcohol for a minute1 it dries with remarkable rapidity1 because the water has been absorbed out of it4 ,in the same way1 if you drink neat spirits1 they pass into the blood and stimulate the nervous system1 ultimately being excreted by the kidneys2 but on their way through the tissues they absorb a great deal of water1 which must be replaced4 ,milk is often spoken of as the ideal food1 and so it may be for very young animals2 but it lacks one important constituent--iron4 ,a young animal is born with enough iron in its body to do without any in its food until it can take something better than milk4 ,if it is weaned late it becomes anmic4 ,an adult animal requires iron and also a certain amount of solid food4 ,its alimentary canal is provided with a good deal of muscle2 and this muscle1 to be kept healthy1 must have something to work upon--in fact1 be exercised4 ,a man's food should contain a certain amount of coarse material--cellulose1 for instance1 which forms the envelope of vegetable cells4 ,and here we see a distinctive feature of the body4 ,protoplasm can make no use of cellulose1 there is no digestive juice which will act upon it2 but its presence in the alimentary canal in the form of husk and small seeds stimulates the walls by contact1 and produces peristaltic movements4 ,in ,essay ,,ii41 which dealt with the chemistry of the body1 we said that if we were only to live upon meat we should tax our digestive apparatus severely by having to eat more proteid than we required in order to get enough carbon4 ,the converse1 however1 is equally true3 if we fed only upon vegetables1 we should again have to over-eat4 ,plants most of them contain large stores of carbohydrate2 potatoes and rice are rich in starch1 onions in sugar2 but an exclusively vegetarian diet would necessitate our consuming huge quantities1 as its proteid-supply is bad4 ,it is defective not only in amount--for sometimes1 as in beans1 the proportion is fairly large--but in being so indigestible that a good deal of it passes through the body unabsorbed4 ,both science and experience teach that we live most economically upon the carbohydrates of vegetables and the proteid of animals1 and that our food is the better for being cooked4 ,in cooking1 parasitic animals which are strong enough to survive the ordeal by acid in the stomach are killed1 and the food itself is made more accessible1 the indigestible cellulose envelopes of the vegetable cells being burst open1 and the collagen of the connective tissues converted into gelatin4 ,no less important than the quality of our food is the quantity2 and here1 again1 we get a good illustration of the necessity for regarding the body as a whole4 ,a healthy man's appetite is his best guide1 and if he follows it he cannot go far wrong4 ,people who arrogate to themselves a wisdom superior to that of ,nature little know the harm they do when they force food down an unwilling throat4 ,the cells of the alimentary canal digest and absorb what is sent to them1 minding their own business1 which is not to criticise the appetite4 #8,theirs not to question why2 ,theirs but to do and die4' ,so the digestive and excretory systems embark on hard and profitless labour1 and the whole body suffers4 ,passing on to another subject1 we find that the body eats that it may work1 and works that it may eat4 ,this cycle comes naturally enough to animals which have to go and find their food1 but men with a sedentary occupation have1 in view of the artificial conditions under which they live1 to take constitutional exercise4 ,there are many reasons why the numerous and bulky muscles with which the body is endowed must be constantly used4 ,in the third essay in this volume we saw that the flow of the lymph and the blood in the veins is largely dependent upon the movements of the limbs4 ,muscular exercise1 therefore1 must be taken to prevent the circulating streams from growing sluggish4 ,obviously1 many evils must arise if they do so4 ,not only would the muscles be starved by the slowness with which they received their food1 but they would also be poisoned by the slowness with which the products of their own metabolism were removed4 ,the blood-stream would become tainted1 and the brain1 which requires pure blood1 would suffer4 ,in other ways1 however1 than by their action on the vessels themselves do the muscles help the circulation4 ,exercise has secondary effects upon the circulatory and respiratory centres in the base of the brain1 and makes the heart beat more strongly and the diaphragm contract more forcibly4 ,the influence of the latter upon the circulation we have already described2 but its vigorous action is required not only to aid the circulation through the liver and viscera1 but to inflate the lungs to their fullest extent4 ,in the breathing of a man who takes no exercise only a small part of the air which the lungs hold is pumped out at each breath1 the greater part remaining stagnant in chambers which are practically unused4 ,thus1 not only is the revenue of oxygen diminished1 but there are numerous little crannies in the body filled with still1 warm air which are ideal nurseries for bacteria4 ,the devil of consumption does not allow such dwellings to long remain swept and garnished4 ,without exercise the sweat glands of the skin will not act1 and its pores get closed up4 ,the muscular coats of the alimentary canal1 too1 reflect in their state of health the condition of the voluntary muscles2 laziness is followed by constipation1 for if the voluntary muscles rust1 so do the involuntary4 ,the muscles1 moreover1 must be well developed and kept in a healthy condition for their own sake4 ,they form a large part of the whole bulk1 and no healthy man can have unhealthy muscles4 ,ignorant people sneeringly say that they have no ambition to lift weights or bend pokers2 but they should remember that they are dependent upon their muscles for their bodily warmth1 and also to save their internal organs from being oppressed by their own weight4 ,the bones of the skeleton do not rest one upon another2 they are jointed1 and kept slung in position by springing bands of muscle attached to their levers4 ,if these muscles are not properly developed1 they tire under the strain of holding the frame up1 and a disastrous rearrangement of the organs is made to save labour4 ,the chest is drawn in1 the hips and knees thrust forward1 and the man stands with cramped chest1 compressed viscera1 and his diaphragm under dire constraint4 ,the result of the redistribution of weight is that his bones tend to rest upon one another like a column of bricks1 and his whole weight is upon his heels4 ,such an individual cannot walk2 he stumps along1 jarring his whole body at every step4 ,a pleasant contrast is the athlete4 ,the athlete is a man who endeavours to develop the latent powers of his body to the utmost2 and in the achievement of this desirable object the physiologist takes great interest4 ,physiology has revolutionized our ideas of training1 as well as many other things1 during the last half-century4 ,we now recognise two kinds of training--the preparation which a healthy man makes for an occasion on which unusual exertions will be expected of him1 and the slower and permanent strengthening of the whole body1 now usually called physical culture4 ,the former is a comparatively short process now that athletes no longer think it de rigueur to live in bestial intemperance when they have no contest in immediate prospect4 ,a little extra exercise1 to stimulate excretion and clear away any waste products that may have accumulated in the tissues2 a little extra proteid in the diet1 since there is at first a slight inclination to growth2 a good deal of extra carbohydrate1 since the muscles want extra fuel2 rest--and the man is ready4 ,many athletes live continually in training1 and are ready at any moment to #8fight for their lives4' ,the second kind of training is for those who are weakly or those who wish to excel4 ,its object is not only to improve the health1 but to increase the absolute strength and size of the body1 and its effects are permanent4 ,it necessitates careful diet and constant exercise for a long period1 and proves equally beneficial to both sexes4 ,this book has been written in vain if the reader has not grasped by now that the activity of the muscles implies the activity of all the organs in the body4 ,accordingly1 the whole muscular system is by appropriate methods given frequent exercise3 gentle at first2 never exhausting2 but constantly increasing as the strength grows4 ,the result is a general development of the organs throughout the body1 which will in time work a complete metamorphosis in the individual's physique4 ,yet by strength alone no athlete can excel2 success depends upon skill4 ,he must have the strength to work with1 but he must have the knowledge to apply it without wasting energy1 and the ability to do this with precision4 ,he must practise well the sport he intends to adopt--in other words1 train his central nervous system4 ,here1 again1 we must hark back to the main idea--the unity of the body4 ,we have already dealt in this essay with the bodily needs in the way of food and exercise1 and we must now consider the needs of its nervous components4 ,the chief of these is education2 but education of the nervous system means1 of course1 education of the whole body4 ,there are still people who cling to the old fallacy that the mind can be developed at the expense of the body1 but a visit to a hospital or a lunatic asylum will afford many opportunities of seeing how ,nature avenges ill-treatment of #8those delicate tissues wherein the soul transacts its earthly business4' ,physical culture must come before mental3 ,mens sana in corpore sano--hackneyed1 but true4 ,i do not1 of course1 say that a man must develop equally both his body and mind2 only1 that the former must be functionally competent4 ,the absurdity of supposing that the brain can benefit by forming part of an unhealthy body is1 surely1 obvious to all4 ,determined invalids may produce splendid work1 as ,darwin did1 in spite of ill-health1 but not because of it1 and men of great mental energy will sometimes wear themselves out prematurely by their restlessness2 but starvation and maltreatment of the body will not create intellect1 however morbidly it may stimulate the imagination4 ,granting the tenement of a healthy body1 the education of the central nervous system must proceed along four distinct lines4 ,a child must learn useful reflex actions1 such as walking2 have its association centres trained1 that it may reason quickly and correctly2 be endued1 if it is not to live upon a desert island1 with a sense of moral responsibility and ethical principles2 and have its head stored with useful facts1 from the meaning of words and the ,a ,b ,c to the value of the coinage4 ,few people seem to realize how much a child has to learn before it gets to the ,a ,b ,c4 ,it begins life with very little beyond a capacity for learning1 and even its sense organs tell it little until it has had practice in using them4 ,if baby is so unfortunate as to get a scratch from a pin1 he wriggles1 and makes the whole house aware of it2 but he does not seem to have a clear idea at all as to where he is hurt4 ,he has to learn the way about his own body4 ,he passes his hand over his face1 and learns that he has features with a definite position and magnitude2 he then waves his arms in the air1 and learns that there is such a thing as empty space2 finally1 he knocks his knuckles against the edge of his cradle1 and learns that there are other things in existence besides himself4 ,of course1 his eyes help him considerably to form his ideas of things1 but his eyes tell him nothing until he has learnt how far to believe them by correcting their impressions by touch4 ,he learns the properties of matter by experiment1 not intuition4 ,very interesting experiments have been made upon people who have been born blind1 and to whom sight has been given late in life by an operation4 ,they generally take some time to appreciate their good fortune4 ,things1 they say1 are all pressed up against their eyes1 and they are afraid to move4 ,objects with which they have carefully been made familiar before the operation--wooden spheres1 cubes1 cones and prisms--they have been absolutely unable to recognise by sight until they have handled them4 ,they have mistaken sparrows for tea-cups1 and it is sometimes only after weeks that they have suddenly discovered that pictures are something more than a mixture of irregular splashes of colour on a flat surface4 ,babies have to learn to interpret what they see in much the same way1 and take longer about it4 ,the child who cries for the moon is probably not so unreasonable as people think4 ,he focuses his eyes upon the little1 bright1 sharply-defined disc1 and it appears to him1 if not actually within arm's length1 at any rate near enough to be caught with a butterfly-net4 ,it is only after he has seen it sink behind a large tree on the distant horizon that he gathers a vague idea of its real size and remoteness4 ,the term #8physical culture1' as usually applied1 is supposed only to mean the development of the muscles and viscera2 really it only begins there4 ,after the organs of nutrition have been got into a healthy state the motor organs are developed4 ,finally the nervous system should be trained4 ,mere muscle will not make even a good runner4 ,he must practise carefully till he can take his full stride1 and do so without wasting energy by any needless movements4 ,then he must make the action which his brain has decided is the most effective for his build the property of his spinal cord1 that in a race he may use his strength economically1 with his thoughts free to deal with the tactics of his opponents and the peculiarities of the course1 or he will not make his supreme effort at the most advantageous moment4 ,this is only one instance4 ,many men having a normal body develop organs of perception1 not motion3 the musician and the wine-taster1 as well as the juggler and the athlete1 are products of physical culture4 ,even the philosopher must foster the physical basis of intellect4 ,the education of the nervous system goes on all through life2 and just as oft-repeated actions become automatic1 so are habits of thought formed which are almost as regular2 in fact1 we might almost call them cerebral reflexes4 ,without constant exercise1 men lose their flexibility of mind as well as of body4 ,but we have already passed the boundaries of our subject1 and it is time for us to pull up1 lest we trench further upon another science2 for the study of the mind is the province1 not of the physiologist1 but of the psychologist4 ,,ii4 ,notwithstanding the strange powers of protoplasm1 and notwithstanding that these are accumulated and intensified in the body1 as we saw in the last chapter1 there are immovable limitations to vital activity4 ,this is a fact familiar to all4 ,we can trace diminishing vitality through a series of stages1 from slight fatigue right up to death itself4 ,sleep is perhaps one of the most interesting1 though it is little understood4 ,during sleep and the hypnotic trance1 we know that the cells of the hemispheres pause in their work and chemically recruit themselves2 that there is an interruption of consciousness2 and that changes occur in the respiratory and circulatory1 and1 in fact1 in most of the functions4 ,but exactly how these states are induced we do not know4 ,it has been suggested that during sleep less blood passes through the brain2 but this is unlikely1 and still less probable is it that the nerve cells draw in their processes and shut up like sea-anemones1 as another daring theorist supposed4 ,we can only draw parallels between the cells of the central nervous system and any others2 all need rest4 ,the simplest unicellular animals1 which we have mentioned so often already1 spend their lives in alternate spells of activity and rest4 ,in the third essay we mentioned briefly the weakening of each successive response when a muscle1 in which tissue fatigue has chiefly been studied1 is stimulated4 ,before the muscle contracted it contained a form of sugar2 when it is tired the sugar is gone1 and has been replaced by the products of the chemical action by which the energy was evolved4 ,a period of rest must then follow1 for the muscle to be cleansed and replenished4 ,the case of glands1 described in ,essay ,,ii41 is somewhat similar4 ,after the gland cell has discharged its ferment1 it must spend some time secreting a fresh stock before it is ready to discharge again4 ,in fact1 a cell seems to load itself up with supplies1 like a locomotive with coal1 and1 after working till the fuel is nearly exhausted1 it has to stop to take in more4 ,all the cells in the body rest at times2 even the cells of the heart1 carefully as they are nourished and incessant as their work seems1 rest between each beat1 and the cells of the nervous system form no exception4 ,the brain no less than the body requires periodic rests to renew its chemical stores1 and these rests have to be all the longer1 as during the waking hours the brain works harder and less intermittently than any other organ4 ,it is only because the brain is the seat of consciousness and the source of voluntary movements that these phenomena are suspended during sleep4 ,death may seem at first sight a very simple affair1 the breaking up of protoplasm into simpler non-living compounds2 but the death of the body is anything but simple--in fact1 it is not always easy to say when the body is dead4 ,usually1 however1 it is considered dead when the central nervous system has succumbed1 though the muscles may continue to live for several hours4 ,death may begin in many ways4 ,the loss of some organs will bring death only after a considerable time1 while the failure of others disturbs its economy fatally1 and causes an almost immediate cessation of the vital functions4 ,any interference with the normal conditions of the brain1 heart1 or lungs is very dangerous1 and it is injury or disease of one of the three which puts an end to most men's troubles4 ,if the brain weakens so that it no longer keeps the heart beating or the muscles1 which fill and empty the lungs1 to their duties1 the body1 for obvious reasons1 can no longer keep up the cycle of changes we call life4 ,on the other hand1 if the lungs cannot oxidize the blood1 or the heart drive fresh pabulum to the brain1 that organ collapses immediately1 and1 if a stream of pure blood is not quickly restored to it1 dies4 ,no return of the circulation can then restore it2 the death of the rest of the animal must follow4 ,being the most delicate1 the cells of the central nervous system usually die first1 and we then say that the man is dead4 ,so the body may be1 but much of the protoplasm of which it is composed--whole organs1 in fact--remains alive2 the muscles will respond to electrical stimulation1 and in case some people may dispute that this is a sign of life1 if pieces of his skin be removed and grafted into another person1 they will grow there1 produce hair1 and become1 in fact1 a part of the new body4 ,this they could not possibly do if they were dead2 we cannot endow inanimate matter with life4 ,as death creeps on over the tissues1 the leucocytes die1 and in doing so form a ferment which solidifies one of the proteids dissolved in the blood1 so that the familiar clotting takes place4 ,by a similar process certain constituents of the muscles are also clotted1 the muscles stiffening and passing into what is technically1 but also pretty generally1 known as rigor mortis4 ,rigor is said to set in soon after death if the body is kept in a warm place1 or if death has been preceded by violent exercise2 but death in this instance means only the death of the body4 ,it is at the precise moment that a muscle fibre dies that it passes into rigor4 ,by keeping it cool1 so that the processes of life may go on slowly1 especially if it be in a healthy condition1 its death may be deferred for hours2 while1 on the other hand1 at the end of a severe and protracted battle1 exhausted soldiers sometimes die instantaneously on being shot1 and are found fixed in the position in which the fatal bullet found them--on their knees1 with gun to shoulder1 in the act of firing4 ,but if the manner of death is not to be lightly dealt with1 its causes are still more obscure4 ,it seems natural enough that people should be killed by violence or by diseases with an external or septic origin1 or even by one particular organ wearing out and involving the whole body in the fate of its part4 ,but why should people die of old age8 ,why should their vitality ebb till they quietly go out8 ,life is a mechanical cycle of changes4 ,for a time even after it has stopped growing1 the body replaces what it wastes1 and keeps itself in a condition of equilibrium4 ,why1 then1 without any apparent external cause1 does it1 after a more or less circumscribed period1 enter into a decline8 ,and1 finally1 could we1 by taking the proper precautions1 delay or prevent old age and death8 ,in the first place1 regarding protoplasm as a chemical structure1 why1 if kept under favourable conditions1 should it ever break down8 ,we have no reason to suppose that it need4 ,it is hard to see how the minute animals1 consisting of only one cell1 can die of old age1 provided that no injurious influence be brought to bear upon them4 ,when an individual has grown to a certain size1 it divides in two1 and each enters upon life afresh4 ,why1 therefore1 should not all the cells of the body continue to renew their youth8 ,the reason why the body can only last a certain time1 in spite of the many quacks with recipes for immortality--recipes including such items as the avoidance of all trouble1 worry1 or work--must remain a secret until we know the chemical basis of life4 ,it seems to lie in the cell4 ,if a unicellular organism1 as described above1 be placed in a vessel of sterilized water and left to live alone under otherwise ideal conditions1 it will start dividing and multiplying1 as though it meant to reproduce itself indefinitely4 ,after a time1 however1 the shoal begins to deteriorate2 each successive generation is feebler than the last1 and eventually all die4 ,if1 however1 before this happens one of the effete cells be placed in another vessel with a similar individual derived from a different ancestor1 the two will fuse and form a single fresh animal with entirely restored vigour1 ready to multiply to the same extent as either of its original ancestors4 ,a few individuals of a different stock will in this way revivify the whole brood4 ,there is1 therefore1 evidently something in the cell which wears out after it has divided a certain number of times--something which must be restored by blending with cells of another strain4 ,what this is we do not know1 and perhaps never shall4 ,the most we know is that it seems to be something inherent in the nucleus1 not the main body of protoplasm of the cell1 for some unicellular animals do not fuse1 under the circumstances related above1 but exchange only pieces of their nuclei1 and yet derive the advantages of mutually increased vitality4 ,but if we apply the fact to our conception of the body as a vast colony of cells with a common origin1 we find that it has an important bearing upon the duration of its life4 ,the single eggcell which gave rise to our schematic embryo in ,diagram #c1 ,fig4 #a1 was formed by the fusion of two cells shed by two distinct animals4 ,how this one cell grows and multiplies by division is roughly shown in the diagram and those immediately following it2 but though the cells do not separate1 but hang together and form a body1 it is obvious that the colony only amounts to a shoal of unicellular organisms1 like that described above as growing weaker with each successive division unless blended with individuals of a different stock4 ,this cannot be done in the body2 what would become of our individuality even if such a thing were possible8 ,the body can help to give rise to new bodies1 but its own tissues must wear out1 and when the colony of cells is exhausted it must die4 ,careful diet and regular habits1 the minimum of wear and tear1 may enable the body to run its full term2 but they cannot lengthen the lease of life4 ,so far only can the physiologist take us4 ,physiology may teach us how to develop our powers and economize our strength2 it is already beginning to convert medicine from an art into a science2 it will1 it is to be hoped1 shortly work a revolution in our at present barbarous ideas of how to rear and educate children2 it may1 in short1 teach us how to make the very most of life and die easily2 but not until1 if ever1 it understands the physical basis of life1 and perhaps not even then1 will it be likely to succeed in prolonging a man's days much beyond the traditional fourscore years4 ,,conclusion4 ,while the physiologist is quietly working1 making slow but sure progress1 his critics1 friendly and otherwise1 buzz about him like bees4 ,there are some who are in a chronic state of excitement1 expecting a revolutionizing discovery from hour to hour2 there are others who assure him that he has reached the limit of human powers of comprehension1 and can never know much more than he does to-day2 and1 lastly1 there are those who declare that he has done next to nothing1 and that his utmost endeavours have failed to effect any real result1 and leave all the important secrets of life untouched4 ,no one knows better than the physiologist how mistaken is the oversanguine class first mentioned4 ,in no department of science1 certainly not in physiology1 is it possible to reach the top of the ladder by a bound2 each rung must be mastered in order4 ,in invading the unknown land the scientist must thoroughly explore and effectively occupy as he advances4 ,he must annex as he goes along2 the flying columns which try to reach the enemy's capital by a dash are never heard of again4 ,in physiology the publication of the various steps is sometimes withheld until the objective has been reached1 but our knowledge of life is like ,solomon's temple3 a ,david collects the material1 and his successor raises the edifice4 ,the world watches it grow4 ,it is not like those bewildering and unstable palaces of the #8,arabian ,nights1' built by genii in a single night1 and often vanishing as mysteriously4 ,in every age there have existed people who declare that men can never know more than they do at the moment4 ,there were plenty of them when the science of physiology was unborn1 and there will be plenty more of them a hundred years hence2 only then they will refer with tolerant amusement to the crude and elementary ideas of their predecessors at the beginning of the twentieth century4 ,the third class1 who take such delight in minimizing the achievements of the physiologist1 usually are found1 if anyone takes them seriously1 to know very little either about the science of physiology itself or the history of its growth4 ,i leave the reader to form his own verdict upon the value of the results obtained from their exceedingly brief and sketchy description in this little volume1 with the remark that the science is barely more than three-quarters of a century old1 and the most important additions to our knowledge have been made within the last twenty years4 ,there were1 paradoxical as it may sound1 great physiologists before then2 the work of ,harvey1 who three centuries ago discovered the circulation of the blood1 is above all praise2 but how nebulous must have been their ideas may be seen from the following facts3 ,it was only at the beginning of the nineteenth century that the atomic theory of matter was formulated2 it was not until twenty years later that the world was startled by a daring chemist who showed that organic compounds obeyed the same natural laws as inorganic2 and not until ten years later was the cellular structure of animals1 the groundwork in all study of life1 recognised4 ,even when the science was set upon firm foundations1 progress was at first necessarily slow3 the organic chemist took some time in examining and classifying the compounds met with in the body--he has not finished yet2 and even when the cell theory was grasped1 it required much ingenuity and long patience to devise ways of examining organs under the microscope1 so that their structure could be made out4 ,the microscope itself was a poor toy fifty years ago1 magnifying a diameter ten times where now it magnifies a hundred1 and giving only a dim and distorted image4 ,the perfecting of the microscope1 and the introduction of ansthetics and antiseptics1 have led to enormous strides being made within the last two decades4 ,the result of the advance in chemical knowledge1 and the introduction of fresh aids to investigation1 led to the discarding of vital force as a working hypothesis4 ,vital force was the bane of the earlier biologists4 ,they made it accountable for all they could not understand1 and with this restatement of their difficulties--a restatement which they called an explanation--refrained from further research4 ,but when it was found that many of these inexplicable phenomena1 though refractory1 yielded to careful study1 and could be explained by chemical and physical laws1 the physiologist ceased to say of them1 #8,they are problems connected with ,life1 and therefore explained by ,vital ,force1 which is past man's understanding1' and frankly admitted that there were many things which he did not as yet fathom4 ,recently a vitalistic school has cropped up again1 declaring that all that it cannot understand must infallibly be due to some occult agency4 ,it shows remarkable vitality in surviving the shocks of successive discoveries4 ,turning once more to the present day1 we will conclude with a brief glance round a physiological laboratory1 and see by what methods the physiologist is preparing future surprises4 ,the chemical department first claims our attention4 ,the imports and exports of animals are carefully balanced1 and the changes produced in the food examined4 ,the animal is enclosed in an airtight chamber1 air of known composition being pumped into it1 and the air which escapes analyzed4 ,the animal most used for this experiment is man himself1 since he will take rest and exercise to order1 the latter usually on the treadmill1 by which it can be also measured1 and can be relied upon not to while away the tedium of his imprisonment by gnawing holes in the walls or upsetting his food4 ,all the substances used as food1 found in or excreted by the body1 are being thoroughly studied2 but it should be remembered that this is chemistry1 not physiology4 ,physiology is only concerned with protoplasm1 and the physiologist who goes deeply into the chemistry of non-living matter has to discipline his mind against forgetting its ceaseless change1 and trying to regard it as though it were constant4 ,the actual chemistry of protoplasm will be a very hard nut to crack1 and may defy us until we can depict molecules as well actually as we now can symbolically4 ,some idea of the difficulty may be formed if we consider that it is impossible to imagine a pure sample4 ,from the restless activity which is the condition of its existence1 it is always working changes in its surrounding1 always mixed with raw material1 and always masked by the products of its own metabolism4 ,even if we withhold the former1 it consumes its own substance until the moment of death4 ,it does not even look homogeneous under the microscope4 ,before1 however1 we can pursue the chemical methods further1 it will be necessary to describe the histological4 ,the reader may have already wondered how we managed to find out so much about the cellular structure of the body4 ,it is no easy matter to cut up soft tissue1 of the consistency of an unboiled egg1 into thin slices which can be examined under the microscope4 ,it is done in the following manner3 ,the bloodvessels of the freshly killed body are injected with a fluid which instantaneously kills and fixes the cells in much the same way as an egg is fixed by being hard-boiled4 ,the natural shape of the cells is thus preserved1 and the loss of any of their chemical constituents by putrefaction prevented4 ,the piece of organ is then impregnated with and cast in the middle of a solid block of paraffin wax1 which is put into a machine and shaved up into thin slices1 about #dj1jjj to the inch sometimes4 ,one of these shavings is then stuck upon a glass slide1 and on the wax being dissolved away with some such substance as benzine1 a section of the tissue1 about one cell thick1 is left on the glass ready for microscopic survey4 ,to do anything like justice to the histological methods would require a volume in itself4 ,when the sections are fixed upon slides1 they are treated with a number of reagents to show their chemical and structural peculiarities4 ,one section is stained specially to show the nucleus2 another to show the centrosome2 another zymogen granules1 etc4 ,and1 as all these cannot be shown at their best in one cell1 the differently treated sections have to be separately drawn or photographed1 and the typical structure compiled from several4 ,by careful staining1 the chemical composition of the different parts of the cell is being worked out1 and the effects of rest1 activity1 feeding1 and other influences1 studied4 ,take as an example the effects of a meal4 ,a number of animals of the same litter are fed together out of the same trough4 ,one has been killed before the meal1 and the rest are killed at intervals dividing the time which must intervene before their next feeding-time comes round4 ,series of sections from their organs are prepared1 one from each animal being mounted in order upon the same piece of glass1 dipped in the same reagents1 and examined under the same microscope4 ,from a number of these sections the progressive effects of a meal upon each of the several constituents of the cell are traced out1 and some of the chemical processes deduced4 ,turning to the physical side of physiology1 it is unnecessary here to say more about the means employed for studying the properties of muscle and nerve than that many of the phenomena occur with such extreme rapidity that they can only be perceived by the photographic plate4 ,in the study of the large organs1 the physiologist finds a fascinating employment in devising models in which1 so far as possible1 all the physical conditions are reproduced1 and this not only for the benefit of his pupils1 but to help himself in perceiving their meaning4 ,too much reliance must not be placed on these models1 of course1 but they have added considerably to our knowledge of the eye and throat4 ,it requires no great imagination to perceive the difficulties which lie in the way of studying the nervous system4 ,tracing nerve fibres under the microscope through interminable series of sections is a labour which can neither be hurried nor scamped4 ,it is greatly aided by pathological specimens4 ,an animal which has been through life with only one eye will obviously have central organs of vision showing wide contrasts4 ,those connected with the blind eye will be undeveloped1 because never used1 while the corresponding lobes of the brain connected with the other eye will show the effects of doing extra work4 ,many of the problems which meet the physiologist can only be solved by experimenting upon a live animal1 and these experiments form by no means the easiest part of his work4 ,the animal must be kept1 so far as possible1 under physiological conditions--that is to say1 free from pain and fright and unpoisoned by drugs4 ,thanks1 however1 to an extensive knowledge and skilful use of ansthetics1 the obstacles to this method of investigation have been overcome1 and its results have proved very profitable4 ,the absence of pain is a very important factor in an experiment1 and even if the physiologist took the wanton delight in inflicting suffering which the imagination of his enemies attributes to him1 he would have to restrain its indulgence in his laboratory1 or forego the hope of even moderate success4 ,in this country1 moreover1 the ,government will not allow such experiments without its express permission1 and the license is very rightly only granted to men whose researches promise an adequate return1 and who are likely to conduct them humanely and successfully4 ,physiological research is not a hobby to be lightly taken up4 ,it is not one merry round of exciting tussles with tortured and infuriated cats and dogs2 on the contrary1 it entails arduous labour and needs infinite patience4 ,the experiments1 often tedious in themselves1 have to be repeated again and again in as many different ways as possible1 until every slight difference in result can be accounted for2 and the certainty that both the methods used and the interpretation given will1 when published1 receive the closest1 and not in every case the friendliest1 scrutiny by other members of the profession serves as an admirable corrective to jumping at conclusions4 ,it is1 however1 an occupation of absorbing interest1 and the physiologist feels amply repaid if he can think that his labours have added1 no matter how little1 to that control over ,nature which the severe conditions of modern life make every day more pressingly necessary4 ,,index ,a4 ,abdominal circulation1 #ed ,absorption1 #be ,acid1 hydrochloric1 #bc ,afferent system of nerves1 #ib ,alcohol1 #ie ,alimentary canal1 length of1 #ai movements of1 #df origin of1 #ag structure of1 #df ,amba1 #af ,amboid movement1 #ca ,amount of food1 #ae1 #if ,animalcula 7unicellular micro-organisms71 #e1 #h1 #af1 #ca1 #ajb1 #aje ,aorta1 #ea ,arm1 #eg ,artery1 #dh ,association centres1 #ia ,athletes1 #ih ,atom1 #b ,auditory mechanism1 #gd ,auricles1 #di ,b4 ,bacteria1 #bc1 #dd ,beaumont1 #be ,bile1 #bd1 #fb ,blind1 experiments with the1 #ajj ,blood1 #bf circulation of the1 #dh clotting after death1 #ajd corpuscles1 #bi1 #de course of the1 #bg1 #ee pressure1 #ea1 #ff ,body1 the1 #i1 #id ,boils1 #de ,bone1 #cf1 #ef1 #ih ,brain1 #fc1 #gi1 #ajb ,breathing1 #be1 #eb1 #hb1 #ig ,c4 ,canals1 semicircular1 #gg ,capillaries1 #dh ,carbohydrate1 #ad1 #if digestion of1 #bb ,carbon1 #aa1 #ac ,carbonic acid gas1 #ac1 #be ,cartilage1 #cf ,cavity of the body1 #dc ,cell1 #d a chemical laboratory1 #f division of1 #cb1 #aje exhaustion of1 #ajb movements of1 #e1 #ca nerve1 #fj1 #hg spinal ganglion1 #fc ,centres1 nervous1 #fc1 #gh1 #hh1 #ia ,centrosome1 #ca ,cerebellum1 #hd ,cerebral cortex1 #hf hemispheres1 #he ,chemical compounds1 #b needs of body1 #aa ,chemistry of the body1 #h ,chords1 vocal1 #ic ,cilia1 #cc ,circulation1 #bg1 #ig course of1 #bh1 #ee mechanism of1 #dh ,circulating fluids1 #bf ,clotting of blood1 #ajd ,cochlea1 #gf ,cold1 #hc ,collagen1 #bd1 #ce1 #if ,compounds1 chemical1 #b ,conductivity of protoplasm1 #ei ,connective tissue1 #bd1 #ce1 #if ,conservation of energy1 #ib ,contraction of heart1 #di of muscle1 #cd ,cooking1 #if ,cord1 spinal1 #fc1 #gh ,corpuscles1 red blood1 #bi white blood 7leucocytes71 #de ,cortex1 #hf ,cough1 #fe1 #fg ,d4 ,death1 #ajc ,diaphragm1 #eb1 #ig ,diet1 #aa1 #ie ,digestion1 #aa by body1 #bb by cell1 #af ,doctor1 ix ,drum of ear1 #ge ,e4 ,ear1 #gd ,education1 #ii ,efferent system of nerves1 #ib ,egg1 white of1 #ac ,electric manifestations in tissues1 #dj organs of fish1 #db stimulation of tissues1 #cg1 #hh ,embryo1 development of1 #ag ,endolymph1 #gd ,enzyme1 #ae ,epilepsy1 #hi ,equilibrium1 #ff1 #hd ,exercise1 #ig ,eye1 #gc education of1 #ajj protection of1 #fe ,f4 ,fainting1 #ff ,fat1 #ad1 #bd1 #bg ,fatigue1 #dj1 #ajb ,ferments1 #ae ,fibres1 connective tissue1 #ce muscle1 #cd nerve1 #db1 #fj ,fibrils1 muscle1 #ce ,fish1 electric1 #db ,food1 #aj1 #ie amount of1 #ae1 #if vacuole1 #af ,forehead1 #ia ,frog experiments on muscle1 #cg reflexes1 #fh ,g4 ,ganglion1 spinal1 #fb ,gastric juice1 #bc ,gelatin1 #bd1 #ce1 #if ,gland cells1 #ba ,glands1 origin of1 #bj salivary1 #bb sweat1 #ga tear1 #fe ,h4 ,hmoglobin1 #bi ,hair1 #gj ,harvey1 #ajh ,head1 #gi ,hearing1 #gd ,heart1 #dh1 #ff ,heat1 production of1 #ac regulation of1 #hc ,histological methods1 #aaj ,huxley1 #g ,hydrochloric acid1 #bc ,i4 ,internal secretion1 #bi ,intestine1 movements of1 #dg ,involuntary movements1 #fe muscle1 #cd ,iron1 #ie ,k4 ,kidneys1 #bi1 #ie ,l4 ,labyrinths of ear1 #gd ,leucocytes1 #db ,limbs1 #ef ,liver1 #bd circulation through1 #bg1 #ed ,living matter1 #a ,localization of function in the brain1 #hf1 #hh ,lungs1 #eb1 #ic absorption by1 #be ,lymph1 #bf circulation of1 #bg1 #dh ,m4 ,marshall's fibrils1 #ce ,meat in diet1 #ae1 #ie ,medicine1 ix ,medulla 7hind-brain71 #hb ,memory1 #ia ,micro-organisms1 #e1 #h1 #af1 #ca1 #ajb1 #aje ,microscope 7histological methods71 #aaj ,milk1 #ie ,mixture1 #c ,molecule1 #b ,mouth1 #gi ,muscle1 #cd how studied1 #cg of alimentary canal1 #df1 #ie ,muscles1 #ig of limbs1 #ef stiffening at death of1 #ajd ,n4 ,nerve cells1 #fj centres1 #fc1 #gh fibres1 #db1 #fj ,nervous system1 #eh ,nitrogen1 #ab ,nucleus1 #d1 #ba1 #cb1 #ajf ,o4 ,olfactory lobe of brain1 #he sense organs1 #gb ,oxygen1 #aa1 #ac1 #be1 #hb1 #ie ,p4 ,pain1 #ia ,pancreas1 #bd ,paramcium1 #af ,peptone1 #bd ,perilymph1 #gd ,peristaltic movements1 #bd1 #fc1 #ie ,physical culture1 #ih1 #aja ,physiological methods1 #cg1 #hh1 #aji ,physiology1 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