,,response ,,in ,,the ,,living ,,and ,,non-,,living ,,by ,,jagadis ,,chunder ,,bose1 ,m4,a47,,cantab471 ,d4,sc47,,lond47 ,,professor1 ,,presidency ,,college1 ,,calcutta ,,with ,,illustrations ,,longmans1 ,,green1 ,,and ,,co4 #ci ,,paternoster ,,row1 ,,london ,,new ,,york ,,and ,,bombay #aijb ,all rights reserved ',the real is one3 wise men call it variously' ,,rig ,,veda ,to my ,countrymen ,this ,work is ,dedicated ,,preface ,i have in the present work put in a connected and a more complete form results1 some of which have been published in the following ,papers3 ',de la ,gnralit des ,phnomnes ,molculaires produits par l',electricit sur la matire ,inorganique et sur la matire ,vivante4' 7,travaux du ,congrs ,international de ,physique4 ,paris1 #aijj47 ',on the ,similarity of ,effect of ,electrical ,stimulus on ,inorganic and ,living ,substances4' 7,report1 ,bradford ,meeting ,british ,association1 #aijj4--;,electrician47 ',response of ,inorganic ,matter to ,stimulus4' 7,friday ,evening ,discourse1 ,royal ,institution1 ,may#aija47 ',on ,electric ,response of ,inorganic ,substances4 ,preliminary ,notice4' 7,royal ,society1 ,june#aija47 ',on ,electric ,response of ,ordinary ,plants under ,mechanical ,stimulus4' 7,journal ,linnean ,society1 #aijb47 ',sur la ,rponse ,electrique dans les ,mtaux1 les ,tissus ,animaux et ,vgtaux4' 7,socit de ,physique1 ,paris1 #aijb47 ',on the ,electro-,motive ,wave accompanying ,mechanical ,disturbance in ,metals in contact with ,electrolyte4' 7,proceedings ,royal ,society1 vol4#gj47 ',on the ,strain ,theory of ,vision and of ,photographic ,action4' 7,journal ,royal ,photographic ,society1 vol4xxvi47 ,these investigations were commenced in ,india1 and ,i take this opportunity to express my grateful acknowledgments to the ,managers of the ,royal ,institution1 for the facilities offered me to complete them at the ,davy-,faraday ,laboratory4 ,j4,c4 ,,bose4 ,,davy-,,faraday ,,laboratory1 ,,royal ,,institution1 ,,london3 ,may#aijb4 ,,contents ,,chapter ,i ,,the ,,mechanical ,,response ,,of ,,living ,,substances ,,page ,mechanical response--,different kinds of stimuli--,myograph --,characteristics of response-curve3 period1 amplitude1 form--,modification of response-curves #a ,,chapter ,,ii ,,electric ,,response ,conditions for obtaining electric response--,method of injury--,current of injury--,injured end1 cuproid3 uninjured1 zincoid--,current of response in nerve from more excited to less excited--,difficulties of present nomenclature--,electric recorder--,two types of response1 positive and negative--,universal applicability of electric mode of response--,electric response a measure of physiological activity--,electric response in plants #e ,,chapter ,,iii ,,electric ,,response ,,in ,,plants--,,method ,,of ,,negative ,,variation ,negative variation--,response recorder--,photographic recorder--,compensator--,means of graduating intensity of stimulus--,spring-tapper and torsional vibrator--,intensity of stimulus dependent on amplitude of vibration--,effectiveness of stimulus dependent on rapidity also #ag ,,chapter ,,iv ,,electric ,,response ,,in ,,plants--,,block ,,method ,method of block--,advantages of block method--,plant response a physiological phenomenon--,abolition of response by ansthetics and poisons--,abolition of response when plant is killed by hot water #bg ,,chapter ,v ,,plant ,,response--,,on ,,the ,,effects ,,of ,,single ,,stimulus ,,and ,,of ,,superposed ,,stimuli ,effect of single stimulus--,superposition of stimuli--,additive effect--,staircase effect--,fatigue--,no fatigue when sufficient interval between stimuli--,apparent fatigue when stimulation frequency is increased--,fatigue under continuous stimulation #ce ,,chapter ,,vi ,,plant ,,response--,,on ,,diphasic ,,variation ,diphasic variation--,positive after-effect and positive response--,radial ,e4,m4 variation #dd ,,chapter ,,vii ,,plant ,,response--,,on ,,the ,,relation ,,between ,,stimulus ,,and ,,response ,increased response with increasing stimulus--,apparent diminution of response with excessively strong stimulus #ea ,,chapter ,,viii ,,plant ,,response--,,on ,,the ,,influence ,,of ,,temperature ,effect of very low temperature--,influence of high temperature--,determination of death-point--,increased response as after-effect of temperature variation--,death of plant and abolition of response by the action of steam #ei ,,chapter ,,ix ,,plant ,,response--,,effect ,,of ,,an,,sthetics ,,and ,,poisons ,effect of ansthetics1 a test of vital character of response--,effect of chloroform--,effect of chloral--,effect of formalin--,method in which response is unaffected by variation of resistance--,advantage of block method--,effect of dose #ga ,,chapter ,x ,,response ,,in ,,metals ,is response found in inorganic substances8--,experiment on tin1 block method--,anomalies of existing terminology--,response by method of depression--,response by method of exaltation #ha ,,chapter ,,xi ,,inorganic ,,response--,,modified ,,apparatus ,,to ,,exhibit ,,response ,,in ,,metals ,conditions of obtaining quantitative measurements--,modification of the block method--,vibration cell--,application of stimulus--,graduation of the intensity of stimulus--,considerations showing that electric response is due to molecular disturbance--,test experiment--,molecular voltaic cell #ia ,,chapter ,,xii ,,inorganic ,,response--,,method ,,of ,,ensuring ,,consistent ,,results ,preparation of wire--,effect of single stimulus #ajj ,,chapter ,,xiii ,,inorganic ,,response--,,molecular ,,mobility3 ,,its ,,influence ,,on ,,response ,effects of molecular inertia--,prolongation of period of recovery by overstrain--,molecular model--,reduction of molecular sluggishness attended by quickened recovery and heightened response--,effect of temperature--,modification of latent period and period of recovery by the action of chemical reagents--,diphasic variation #ajd ,,chapter ,,xiv ,,inorganic ,,response--,,fatigue1 ,,staircase1 ,,and ,,modified ,,response ,fatigue in metals--,fatigue under continuous stimulation--,staircase effect--,reversed responses due to molecular modification in nerve and in metal1 and their transformation into normal after continuous stimulation--,increased response after continuous stimulation #aah ,,chapter ,,xv ,,inorganic ,,response--,,relation ,,between ,,stimulus ,,and ,,response--,,superposition ,,of ,,stimuli ,relation between stimulus and response--,magnetic analogue--,increase of response with increasing stimulus--,threshold of response--,superposition of stimuli--,hysteresis #aca ,,chapter ,,xvi ,,inorganic ,,response--,,effect ,,of ,,chemical ,,reagents ,action of chemical reagents--,action of stimulants on metals--,action of depressants on metals--,effect of 'poisons' on metals--,opposite effect of large and small doses #aci ,,chapter ,,xvii ,,on ,,the ,,stimulus ,,of ,,light ,,and ,,retinal ,,currents ,visual impulse3 7#a7 chemical theory2 7#b7 electrical theory--,retinal currents--,normal response positive--,inorganic response under stimulus of light--,typical experiment on the electrical effect induced by light #adh ,,chapter ,,xviii ,,inorganic ,,response--,,influence ,,of ,,various ,,conditions ,,on ,,the ,,response ,,to ,,stimulus ,,of ,,light ,effect of temperature--,effect of increasing length of exposure--,relation between intensity of light and magnitude of response--,after-oscillation--,abnormal effects3 7#a7 preliminary negative twitch2 7#b7 reversal of response2 7#c7 transient positive twitch on cessation of light2 7#d7 decline and reversal--,rsum #aeh ,,chapter ,,xix ,,visual ,,analogues ,effect of light of short duration--,after-oscillation--,positive and negative after-images--,binocular alternation of vision--,period of alternation modified by physical condition--,after-images and their revival--,unconscious visual impression4 #agj ,,chapter ,,xx ,,general ,,survey ,,and ,,conclusion #aha ,,index #aic ,,illustrations ,,fig4 ,,page #a4 ,,mechanical ,,lever ,,recorder #c #b4 ,,electric ,,method ,,of ,,detecting ,,nerve ,,response #f #c4 ,,diagram ,,showing ,,injured ,,end ,,of ,,nerve ,,corresponds ,,to #h ,,copper ,,in ,a ,,voltaic ,,element #d4 ,,electric ,,recorder #aa #e4 ,,simultaneous ,,record ,,of ,,mechanical ,,and ,,electrical #ac ,,responses #f4 ,,negative ,,variation ,,in ,,plants #ai #g4 ,,photographic ,,record ,,of ,,negative ,,variation ,,in ,,plants #bj #h4 ,,response ,,recorder #ba #i4 ,,the ,,compensator #bb #aj4 ,,the ,,spring-,,tapper #bc #aa4 ,,the ,,torsional ,,vibrator #bd #ab4 ,,response ,,in ,,plant ,,to ,,mechanical ,,tap ,,or ,,vibration #be #ac4 ,,influence ,,of ,,suddenness ,,on ,,the ,,efficiency ,,of #bf ,,stimulus #ad4 ,,the ,,method ,,of ,,block #bh #ae4 ,,response ,,in ,,plant ,,completely ,,immersed ,,under ,,water #bi #af4 ,,uniform ,,responses ,,in ,,plant #cf #ag4 ,,fusion ,,of ,,effect ,,under ,,rapidly ,,succeeding ,,stimuli ,,in #cf ,,muscle ,,and ,,in ,,plant #ah4 ,,additive ,,effect ,,of ,,singly ,,ineffective ,,stimuli ,,on #cg ,,plant #ai4 ',,staircase ,,effect' ,,in ,,plant #cg #bj4 ,,appearance ,,of ,,fatigue ,,in ,,plant ,,under ,,shortened #ci ,,period ,,of ,,rest #ba4 ,,fatigue ,,in ,,celery #dj #bb4 ,,fatigue ,,in ,,cauliflower-,,stalk #da #bc4 ,,fatigue ,,from ,,previous ,,overstrain #da #bd4 ,,fatigue ,,under ,,continuous ,,stimulation ,,in ,,celery #db #be4 ,,effect ,,of ,,rest ,,in ,,removal ,,of ,,fatigue ,,in ,,plant #dc #bf4 ,,diphasic ,,variation ,,in ,,plant #df #bg1 #bh4 ,,abnormal ,,positive ,,responses ,,in ,,stale ,,plant #dh1 #di ,,transformed ,,into ,,normal ,,negative ,,under ,,strong ,,stimulation #bi4 ,,radial ,e4,m4 ,,variation #ej #cj4 ,,curves ,,showing ,,the ,,relation ,,between ,,intensity ,,of #eb ,,stimulus ,,and ,,response ,,in ,,muscle ,,and ,,nerve #ca4 ,,increasing ,,responses ,,to ,,increasing ,,stimuli 7,,taps7 ,,in #eb ,,plants #cb4 ,,increasing ,,responses ,,to ,,increasing ,,vibrational #ec ,,stimuli ,,in ,,plants #cc4 ,,responses ,,to ,,increasing ,,stimuli ,,in ,,fresh ,,and ,,stale #ed ,,specimens ,,of ,,plants #cd4 ,,apparent ,,diminution ,,of ,,response ,,caused ,,by ,,fatigue #eg ,,under ,,strong ,,stimulation #ce4 ,,diminution ,,of ,,response ,,in ,,eucharis ,,lily ,,at ,,low #fa ,,temperature #cf4 ,,records ,,showing ,,the ,,difference ,,in ,,the ,,effects ,,of ,,low #fb ,,temperature ,,on ,,ivy1 ,,holly1 ,,and ,,eucharis ,,lily #cg4 ,,plant ,,chamber ,,for ,,studying ,,the ,,effect ,,of ,,temperature #fd ,,and ,,an,,sthetics #ch4 ,,effect ,,of ,,high ,,temperature ,,on ,,plant ,,response #fd #ci4 ,,after-,,effect ,,on ,,the ,,response ,,due ,,to ,,temperature #ff ,,variation #dj4 ,,records ,,of ,,responses ,,in ,,eucharis ,,lily ,,during ,,rise #fg ,,and ,,fall ,,of ,,temperature #da4 ,,curve ,,showing ,,variation ,,of ,,sensitiveness ,,during ,a #fh ,,cycle ,,of ,,temperature ,,variation #db4 ,,record ,,of ,,effect ,,of ,,steam ,,in ,,abolition ,,of ,,response #fi ,,at ,,death ,,of ,,plant #dc4 ,,effect ,,of ,,chloroform ,,on ,,nerve ,,response #gb #dd4 ,,effect ,,of ,,chloroform ,,on ,,the ,,responses ,,of ,,carrot #gd #de4 ,,action ,,of ,,chloral ,,hydrate ,,on ,,plant ,,responses #ge #df4 ,,action ,,of ,,formalin ,,on ,,radish #ge #dg4 ,,action ,,of ,,sodium ,,hydrate ,,in ,,abolishing ,,the ,,response #gh ,,in ,,plant #dh4 ,,stimulating ,,action ,,of ,,poison ,,in ,,small ,,doses ,,in #gi ,,plants #di4 ,,the ,,poisonous ,,effect ,,of ,,stronger ,,dose ,,of ,,koh #gi #ej4 ,,block ,,method ,,for ,,obtaining ,,response ,,in ,,tin #hc #ea4 ,,response ,,to ,,mechanical ,,stimulation ,,in ,a ,zn-,cu ,,couple #he #eb4 ,,electric ,,response ,,in ,,metal ,,by ,,the ,,method ,,of ,,relative #hh ,,depression 7,,negative ,,variation7 #ec4 ,,method ,,of ,,relative ,,exaltation #hi #ed4 ,,various ,,cases ,,of ,,positive ,,and ,,negative ,,variation #ij #ee4 ,,modifications ,,of ,,the ,,block ,,method ,,for ,,exhibiting #ic ,,electric ,,response ,,in ,,metals #ef4 ,,equal ,,and ,,opposite ,,responses ,,given ,,by ,,two ,,ends ,,of #ie ,,the ,,wire #eg4 ,,top ,,view ,,of ,,the ,,vibration ,,cell #if #eh4 ,,influence ,,of ,,annealing ,,in ,,the ,,enhancement ,,of #aja ,,response ,,in ,,metals #ei4 ,,uniform ,,electric ,,responses ,,in ,,metals #ajb #fj4 ,,persistence ,,of ,,after-,,effect #aje #fa4 ,,prolongation ,,of ,,period ,,of ,,recovery ,,after ,,overstrain #ajf #fb4 ,,molecular ,,model #ajg #fc1 #fd4 ,,effects ,,of ,,removal ,,of ,,molecular ,,sluggishness ,,in #aji1 #aaj ,,quickened ,,recovery ,,and ,,heightened ,,response ,,in ,,metals #fe4 ,,effect ,,of ,,temperature ,,on ,,response ,,in ,,metals #aaa #ff4 ,,diphasic ,,variation ,,in ,,metals #aac #fg4 ,,negative1 ,,diphasic1 ,,and ,,positive ,,resultant ,,response #aae ,,in ,,metals #fh4 ,,continuous ,,transformation ,,from ,,negative ,,to ,,positive #aaf ,,through ,,intermediate ,,diphasic ,,response #fi4 ,,fatigue ,,in ,,muscle #aah #gj4 ,,fatigue ,,in ,,platinum #aah #ga4 ,,fatigue ,,in ,,tin #aai #gb4 ,,appearance ,,of ,,fatigue ,,due ,,to ,,shortening ,,the ,,period #abj ,,of ,,recovery #gc4 ,,fatigue ,,in ,,metal ,,under ,,continuous ,,stimulation #aba #gd4 ',,staircase' ,,response ,,in ,,muscle ,,and ,,in ,,metal #abb #ge4 ,,abnormal ,,response ,,in ,,nerve ,,converted ,,into ,,normal #abd ,,under ,,continued ,,stimulation #gf1 #gg4 ,,abnormal ,,response ,,in ,,tin ,,and ,,platinum ,,converted ,,into #abe ,,normal ,,under ,,continued ,,stimulation #gh4 ,,gradual ,,transition ,,from ,,abnormal ,,to ,,normal ,,response #abf ,,in ,,platinum #gi4 ,,increase ,,of ,,response ,,in ,,nerve ,,after ,,continuous #abg ,,stimulation #hj1 #ha4 ,,response ,,in ,,tin ,,and ,,platinum ,,enhanced ,,after #abg1 #abh ,,continuous ,,stimulation #hb4 ,,magnetic ,,analogue #acb #hc1 #hd4 ,,records ,,of ,,responses ,,to ,,increasing ,,stimuli ,,in ,,tin #acd1 #ace #he4 ,,ineffective ,,stimulus ,,becoming ,,effective ,,by #ace ,,superposition #hf4 ,,incomplete ,,and ,,complete ,,fusion ,,of ,,effects #acf #hg4 ,,cyclic ,,curve ,,for ,,maximum ,,effects ,,showing ,,hysteresis #acg #hh4 ,,action ,,of ,,poison ,,in ,,abolishing ,,response ,,in ,,nerve #aci #hi4 ,,action ,,of ,,stimulant ,,on ,,tin #ada #ij4 ,,action ,,of ,,stimulant ,,on ,,platinum #adb #ia4 ,,depressing ,,effect ,,of ,k,br ,,on ,,tin #adc #ib4 ,,abolition ,,of ,,response ,,in ,,metals ,,by ',,poison' #adc #ic4 ',,molecular ,,arrest' ,,by ,,the ,,action ,,of ',,poison' #ade #id4 ,,opposite ,,effects ,,of ,,small ,,and ,,large ,,doses ,,on ,,the #adf ,,response ,,in ,,metals #ie4 ,,retinal ,,response ,,to ,,light #aej #if4 ,,response ,,of ,,sensitive ,,cell ,,to ,,light #aeb #ig4 ,,typical ,,experiment ,,on ,,the ,e4,m4 ,,variation ,,produced ,,by #aed ,,light #ih4 ,,modification ,,of ,,the ,,photo-,,sensitive ,,cell #aee #ii4 ,,responses ,,in ,,frog',s ,,retina #aef #ajj4 ,,responses ,,in ,,sensitive ,,photo-,,cell #aeg #aja4 ,,effect ,,of ,,temperature ,,on ,,the ,,response ,,to ,,light #aei ,,stimulus #ajb4 ,,effect ,,of ,,duration ,,of ,,exposure ,,on ,,the ,,response #aei #ajc4 ,,responses ,,of ,,sensitive ,,cell ,,to ,,increasing #afa ,,intensities ,,of ,,light #ajd4 ,,relation ,,between ,,the ,,intensity ,,of ,,light ,,and #afb ,,magnitude ,,of ,,response #aje4 ,,after-,,oscillation #afc #ajf4 ,,transient ,,positive ,,increase ,,of ,,response ,,in ,,the #afd ,,frog',s ,,retina ,,on ,,the ,,cessation ,,of ,,light #ajg4 ,,transient ,,positive ,,increase ,,of ,,response ,,in ,,the #afe ,,sensitive ,,cell #ajh4 ,,decline ,,under ,,the ,,continuous ,,action ,,of ,,light #aff #aji4 ,,certain ,,after-,,effects ,,of ,,light #afh #aaj4 ,,after-,,effect ,,of ,,light ,,of ,,short ,,duration #agb #aaa4 ,,stereoscopic ,,design ,,for ,,the ,,exhibition ,,of ,,binocular #agf ,,alternation ,,of ,,vision #aab4 ,,uniform ,,responses ,,in ,,nerve1 ,,plant1 ,,and ,,metal #ahd #aac4 ,,fatigue ,,in ,,muscle1 ,,plant1 ,,and ,,metal #ahe #aad4 ',,staircase' ,,effect ,,in ,,muscle1 ,,plant1 ,,and ,,metal #ahf #aae4 ,,increase ,,of ,,response ,,after ,,continuous ,,stimulation ,,in #ahf ,,nerve ,,and ,,metal #aaf4 ,,modified ,,abnormal ,,response ,,in ,,nerve ,,and ,,metal #ahg ,,transformed ,,into ,,normal ,,response ,,after ,,continuous ,,stimulation #aag4 ,,action ,,of ,,the ,,same ',,poison' ,,in ,,the ,,abolition ,,of #ahi ,,response ,,in ,,nerve1 ,,plant1 ,,and ,,metal ,,response ,,in ,,the ,,living ,,and ,,non-,,living ,,chapter ,i ,,the ,,mechanical ,,response ,,of ,,living ,,substances ,mechanical response--,different kinds of stimuli--,myograph--,characteristics of response-curve3 period1 amplitude1 form--,modification of response-curves4 ,one of the most striking effects of external disturbance on certain types of living substance is a visible change of form4 ,thus1 a piece of muscle when pinched contracts4 ,the external disturbance which produced this change is called the stimulus4 ,the body which is thus capable of responding is said to be irritable or excitable4 ,a stimulus thus produces a state of excitability which may sometimes be expressed by change of form4 ,mechanical response to different kinds of stimuli4--,this reaction under stimulus is seen even in the lowest organisms2 in some of the amoeboid rhizopods1 for instance4 ,these lumpy protoplasmic bodies1 usually elongated while creeping1 if mechanically jarred1 contract into a spherical form4 ,if1 instead of mechanical disturbance1 we apply salt solution1 they again contract1 in the same way as before4 ,similar effects are produced by sudden illumination1 or by rise of temperature1 or by electric shock4 ,a living substance may thus be put into an excitatory state by either mechanical1 chemical1 thermal1 electrical1 or light stimulus4 ,not only does the point stimulated show the effect of stimulus1 but that effect may sometimes be conducted even to a considerable distance4 ,this power of conducting stimulus1 though common to all living substances1 is present in very different degrees4 ,while in some forms of animal tissue irritation spreads1 at a very slow rate1 only to points in close neighbourhood1 in other forms1 as for example in nerves1 conduction is very rapid and reaches far4 ,the visible mode of response by change of form may perhaps be best studied in a piece of muscle4 ,when this is pinched1 or an electrical shock is sent through it1 it becomes shorter and broader4 ,a responsive twitch is thus produced4 ,the excitatory state then disappears1 and the muscle is seen to relax into its normal form4 ,mechanical lever recorder4--,in the case of contraction of muscle1 the effect is very quick1 the twitch takes place in too short a time for detailed observation by ordinary means4 ,a myographic apparatus is therefore used1 by means of which the changes in the muscle are self-recorded4 ,thus we obtain a history of its change and recovery from the change4 ,the muscle is connected to one end of a writing lever4 ,when the muscle contracts1 the tracing point is pulled up in one direction1 say to the right4 ,the extent of this pull depends on the amount of contraction4 ,a band of paper or a revolving drum-surface moves at a uniform speed at right angles to the direction of motion of the writing lever4 ,when the muscle recovers from the stimulus1 it relaxes into its original form1 and the writing point traces the recovery as it moves now to the left1 regaining its first position4 ,a curve is thus described1 the rising portion of which is due to contraction1 and the falling portion to relaxation or recovery4 ,the ordinate of the curve represents the intensity of response1 and the abscissa the time 7fig4#a74 ,illustration3 ,,fig4#a4--,,mechanical ,,lever ,,recorder ,the muscle ,m with the attached bone is securely held at one end1 the other end being connected with the writing lever4 ,under the action of stimulus the contracting muscle pulls the lever and moves the tracing point to the right over the travelling recording surface ,p4 ,when the muscle recovers from contraction1 the tracing point returns to its original position4 ,see on ,p the record of muscle curve4 ,characteristics of the response-curve3 7#a7 ,period1 7#b7 ,amplitude1 7#c7 ,form4--,just as a wave of sound is characterised by its 7#a7 period1 7#b7 amplitude1 and 7#c7 form1 so may these response-curves be distinguished from each other4 ,as regards the period1 there is an enormous variation1 corresponding to the functional activity of the muscle4 ,for instance1 in tortoise it may be as high as a second1 whereas in the wing-muscles of many insects it is as small as #a_/cjj part of a second4 ',it is probable that a continuous graduated scale might1 as suggested by ,hermann1 be drawn up in the animal kingdom1 from the excessively rapid contraction of insects to those of tortoises and hibernating dormice4'#a ,differences in form and amplitude of curve are well illustrated by various muscles of the tortoise4 ,the curve for the muscle of the neck1 used for rapid withdrawal of the head on approach of danger1 is quite different from that of the pectoral muscle of the same animal1 used for its sluggish movements4 ,again1 progressive changes in the same muscle are well seen in the modifications of form which consecutive muscle-curves gradually undergo4 ,in a dying muscle1 for example1 the amplitude of succeeding curves is continuously diminished1 and the curves themselves are elongated4 ,numerous illustrations will be seen later1 of the effect1 in changing the form of the curve1 of the increased excitation or depression produced by various agencies4 ,thus these response records give us a means of studying the effect of stimulus1 and the modification of response1 under varying external conditions1 advantage being taken of the mechanical contraction produced in the tissue by the stimulus4 ,but there are other kinds of tissue where the excitation produced by stimulus is not exhibited in a visible form4 ,in order to study these we have to use an altogether independent method1 the method of electric response4 ,,footnotes3 #a ,biedermann1 ,electro-physiology1 p4#ei4 ,,chapter ,,ii ,,electric ,,response ,conditions for obtaining electric response--,method of injury--,current of injury--,injured end1 cuproid3 uninjured1 zincoid--,current of response in nerve from more excited to less excited--,difficulties of present nomenclature--,electric recorder--,two types of response1 positive and negative--,universal applicability of electric mode of response--,electric response a measure of physiological activity--,electric response in plants4 ,unlike muscle1 a length of nerve1 when mechanically or electrically excited1 does not undergo any visible change4 ,that it is thrown into an excitatory state1 and that it conducts the excitatory disturbance1 is shown however by the contraction produced in an attached piece of muscle1 which serves as an indicator4 ,but the excitatory effect produced in the nerve by stimulus can also be detected by an electrical method4 ,if an isolated piece of nerve be taken and two contacts be made on its surface by means of non-polarisable electrodes at ,a and ,b1 connection being made with a galvanometer1 no current will be observed1 as both ,a and ,b are in the same physico-chemical condition4 ,the two points1 that is to say1 are iso-electric4 ,if now the nerve be excited by stimulus1 similar disturbances will be evoked at both ,a and ,b4 ,if1 further1 these disturbances1 reaching ,a and ,b almost simultaneously1 cause any electrical change1 then1 similar changes taking place at both points1 and there being thus no relative difference between the two1 the galvanometer will still indicate no current4 ,this null-effect is due to the balancing action of ,b as against ,a4 7,see fig4#b1 a47 ,conditions for obtaining electric response4--,if then we wish to detect the response by means of the galvanometer1 one means of doing so will lie in the abolition of this balance1 which may be accomplished by making one of the two points1 say ,b1 more or less permanently irresponsive4 ,in that case1 stimulus will cause greater electrical disturbance at the more responsive point1 say ,a1 and this will be shown by the galvanometer as a current of response4 ,to make ,b less responsive we may injure it by means of a cross-sectional cut1 a burn1 or the action of strong chemical reagents4 ,illustration3 ,,fig4#b4--;,,electric ,,method ,,of ,,detecting ,,nerve ,,response 7a7 ,iso-electric contacts2 no current in the galvanometer4 7b7 ,the end ,b injured2 current of injury from ,b to ,a3 stimulation gives rise to an action current from ,a to ,b4 7c7 ,non-polarisable electrode4 ,current of injury4--,we shall revert to the subject of electric response2 meanwhile it is necessary to say a few words regarding the electric disturbance caused by the injury itself4 ,since the physico-chemical conditions of the uninjured ,a and the injured ,b are now no longer the same1 it follows that their electric conditions have also become different4 ,they are no longer iso-electric4 ,there is thus a more or less permanent or resting difference of electric potential between them4 ,a current--the current of injury--is found to flow in the nerve1 from the injured to the uninjured1 and in the galvanometer1 through the electrolytic contacts from the uninjured to the injured4 ,as long as there is no further disturbance this current of injury remains approximately constant1 and is therefore sometimes known as 'the current of rest' 7fig4#b1 b74 ,a piece of living tissue1 unequally injured at the two ends1 is thus seen to act like a voltaic element1 comparable to a copper and zinc couple4 ,as some confusion has arisen1 on the question of whether the injured end is like the zinc or copper in such a combination1 it will perhaps be well to enter upon this subject in detail4 ,if we take two rods1 of zinc and copper respectively1 in metallic contact1 and further1 if the points ,a and ,b are connected by a strip of cloth s moistened with salt solution1 it will be seen that we have a complete voltaic element4 ,a current will now flow from ,b to ,a in the metal 7fig4#c1 a7 and from ,a to ,b through the electrolyte s4 ,or instead of connecting ,a and ,b by a single strip of cloth s1 we may connect them by two strips ss'1 leading to non-polarisable electrodes ,e,e'4 ,the current will then be found just the same as before1 i4e4 from ,b to ,a in the metallic part1 and from ,a through ss' to ,b1 the wire ,w being interposed1 as it were1 in the electrolytic part of the circuit4 ,if now a galvanometer be interposed at ,o1 the current will flow from ,b to ,a through the galvanometer1 i4e4 from right to left4 ,but if we interpose the galvanometer in the electrolytic part of the circuit1 that is to say1 at ,w1 the same current will appear to flow in the opposite direction4 ,in fig4#c1 c1 the galvanometer is so interposed1 and in this case it is to be noticed that when the current in the galvanometer flows from left to right1 the metal connected to the left is zinc4 ,compare fig4#c1 d1 where ,a,b is a piece of nerve of which the ,b end is injured4 ,the current in the galvanometer through the non-polarisable electrode is from left to right4 ,the uninjured end is therefore comparable to the zinc in a voltaic cell 7is zincoid71 the injured being copper-like or cuproid4#b ,illustration3 ,,fig4#c4--;,,diagram ,,showing ,,the ,,correspondence ,,between ,,injured 7,b7 ,,and ,,uninjured 7,a7 ,,contacts ,,in ,,nerve1 ,,and ,cu ,,and ,zn ,,in ,a ,,voltaic ,,element ,comparison of 7c7 and 7d7 will show that the injured end of ,b in 7d7 corresponds with the ,cu in 7c74 ,if the electrical condition of1 say1 zinc in the voltaic couple 7fig4#c1 c7 undergo any change 7and ,i shall show later that this can be caused by molecular disturbance71 then the existing difference of potential between ,a and ,b will also undergo variation4 ,if for example the electrical condition of ,a approach that of ,b1 the potential difference will undergo a diminution1 and the current hitherto flowing in the circuit will1 as a consequence1 display a diminution1 or negative variation4 ,action current4--,we have seen that a current of injury--sometimes known as 'current of rest'--flows in a nerve from the injured to the uninjured1 and that the injured ,b is then less excitable than the uninjured ,a4 ,if now the nerve be excited1 there being a greater effect produced at ,a1 the existing difference of potential may thus be reduced1 with a consequent diminution of the current of injury4 ,during stimulation1 therefore1 a nerve exhibits a negative variation4 ,we may express this in a different way by saying that a 'current of action' was produced in response to stimulus1 and acted in an opposite direction to the current of injury 7fig4#b1 b74 ,the action current in the nerve is from the relatively more excited to the relatively less excited4 ,difficulties of present nomenclature4--,we shall deal later with a method by which a responsive current of action is obtained without any antecedent current of injury4 ',negative variation' has then no meaning4 ,or1 again1 a current of injury may sometimes undergo a change of direction 7see note1 p4#ab74 ,in view of these considerations it is necessary to have at our disposal other forms of expression by which the direction of the current of response can still be designated4 ,keeping in touch with the old phraseology1 we might then call a current 'negative' that flowed from the more excited to the less excited4 ,or1 bearing in mind the fact that an uninjured contact acts as the zinc in a voltaic couple1 we might call it 'zincoid1' and the injured contact 'cuproid4' ,stimulation of the uninjured end1 approximating it to the condition of the injured1 might then be said to induce a cuproid change4 ,the electric change produced in a normal nerve by stimulation may therefore be expressed by saying that there has been a negative variation1 or that there was a current of action from the more excited to the less excited1 or that stimulation has produced a cuproid change4 ,the excitation1 or molecular disturbance1 produced by a stimulus has thus a concomitant electrical expression4 ,as the excitatory state disappears with the return of the excitable tissue to its original condition1 the current of action will gradually disappear4#c ,the movement of the galvanometer needle during excitation of the tissue thus indicates a molecular upset by the stimulus2 and the gradual creeping back of the galvanometer deflection exhibits a molecular recovery4 ,this transitory electrical variation constitutes the 'response1' and its intensity varies according to that of the stimulus4 ,electric recorder4--,we have thus a method of obtaining curves of response electrically4 ,after all1 it is not essentially very different from the mechanical method4 ,in this case we use a magnetic lever 7fig4#d1 a71 the needle of the galvanometer1 which is deflected by the electromagnetic pull of the current1 generated under the action of stimulus1 just as the mechanical lever was deflected by the mechanical pull of the muscle contracting under stimulus4 ,the accompanying diagram 7fig4#d1 b7 shows how1 under the action of stimulus1 the current of rest undergoes a transitory diminution1 and how on the cessation of stimulus there is gradual recovery of the tissue1 as exhibited in the return of the galvanometer needle to its original position4 ,illustration3 ,,fig4#d4--;,,electric ,,recorder 7a7 ,m muscle2 ,a uninjured1 ,b injured ends4 ,e,e' non-polarising electrodes connecting ,a and ,b with galvanometer ,g4 ,stimulus produces 'negative variation' of current of rest4 ,index connected with galvanometer needle records curve on travelling paper 7in practice1 moving galvanometer spot of light traces curve on photographic plate74 ,rising part of curve shows effect of stimulus2 descending part1 recovery4 7b7 ,o is the zero position of the galvanometer2 injury produces a deflection ,a,b2 stimulus diminishes this deflection to ,c2 ,c,d is the recovery4 ,two types of response--positive and negative4--,it may here be added that though stimulus in general produces a diminution of current of rest1 or a negative variation 7e4g4 muscles and nerves71 yet1 in certain cases1 there is an increase1 or positive variation4 ,this is seen in the response of the retina to light4 ,again1 a tissue which normally gives a negative variation may undergo molecular changes1 after which it gives a positive variation4 ,thus ,dr4,waller finds that whereas fresh nerve always gives negative variation1 stale nerve sometimes gives positive2 and that retina1 which when fresh gives positive1 when stale1 exhibits negative variation4 ,the following is a tabular statement of the two types of response3 ,i4 ,negative variation4--,action current from more excited to less excited--cuproid change in the excited--e4g4 fresh muscle and nerve1 stale retina4 ,,ii4 ,positive variation4--,action current from less excited to more excited--zincoid change in the excited--e4g4 stale nerve1 fresh retina4#d ,from this it will be seen that it is the fact of the electrical response of living substances to stimulus that is of essential importance1 the sign plus or minus being a minor consideration4 ,universal applicability of the electrical mode of response4--,this mode of obtaining electrical response is applicable to all living tissues1 and in cases like that of muscle1 where mechanical response is also available1 it is found that the electrical and mechanical records are practically identical4 ,the two response-curves seen in the accompanying diagram 7fig4#e71 and taken from the same muscle by the two methods simultaneously1 clearly exhibit this4 ,thus we see that electrical response can not only take the place of the mechanical record1 but has the further advantage of being applicable in cases where the latter cannot be used4 ,electrical response3 ,a measure of physiological activity4--,these electrical changes are regarded as physiological1 or characteristic of living tissue1 for any conditions which enhance physiological activity also1 pari passu1 increase their intensity4 ,again1 when the tissue is killed by poison1 electrical response disappears1 the tissue passing into an irresponsive condition4 ,ansthetics1 like chloroform1 gradually diminish1 and finally altogether abolish1 electrical response4 ,illustration3 ,,fig4#e4--,,simultaneous ,,record ,,of ,,the ,,mechanical 7,m7 ,,and 7,e7 ,,electrical ,,responses ,,of ,,the ,,muscle ,,of ,,frog4 7,,waller47 ,from these observed facts--that living tissue gives response while a tissue that has been killed does not--it is concluded that the phenomenon of response is peculiar to living organisms4#e ,the response phenomena that we have been studying are therefore considered as due to some unknown1 super-physical 'vital' force and are thus relegated to a region beyond physical inquiry4 ,it may1 however1 be that this limitation is not justified1 and surely1 at least until we have explored the whole range of physical action1 it cannot be asserted definitely that a particular class of phenomena is by its very nature outside that category4 ,electric response in plants4--,but before we proceed to the inquiry as to whether these responses are or are not due to some physical property of matter1 and are to be met with even in inorganic substances1 it will perhaps be advisable to see whether they are not paralleled by phenomena in the transitional world of plants4 ,we shall thus pass from a study of response in highly complex animal tissues to those given under simpler vital conditions4 ,electric response has been found by ,munck1 ,burdon-,sanderson1 and others to occur in sensitive plants4 ,but it would be interesting to know whether these responses were confined to plants which exhibit such remarkable mechanical movements1 and whether they could not also be obtained from ordinary plants where visible movements are completely absent4 ,in this connection1 ,kunkel observed electrical changes in association with the injury or flexion of stems of ordinary plants4#f ,my own attempt1 however1 was directed1 not towards the obtaining of a mere qualitative response1 but rather to the determination of whether throughout the whole range of response phenomena a parallelism between animal and vegetable could be detected4 ,that is to say1 ,i desired to know1 with regard to plants1 what was the relation between intensity of stimulus and the corresponding response2 what were the effects of superposition of stimuli2 whether fatigue was present1 and in what manner it influenced response2 what were the effects of extremes of temperature on the response2 and1 lastly1 if chemical reagents could exercise any influence in the modification of plant response1 as stimulating1 ansthetic1 and poisonous drugs have been found to do with nerve and muscle4 ,if it could be proved that the electric response served as a faithful index of the physiological activity of plants1 it would then be possible successfully to attack many problems in plant physiology1 the solution of which at present offers many experimental difficulties4 ,with animal tissues1 experiments have to be carried on under many great and unavoidable difficulties4 ,the isolated tissue1 for example1 is subject to unknown changes inseparable from the rapid approach of death4 ,plants1 however1 offer a great advantage in this respect1 for they maintain their vitality unimpaired during a very great length of time4 ,in animal tissues1 again1 the vital conditions themselves are highly complex4 ,those essential factors which modify response can1 therefore1 be better determined under the simpler conditions which obtain in vegetable life4 ,in the succeeding chapters it will be shown that the response phenomena are exhibited not only by plants but by inorganic substances as well1 and that the responses are modified by various conditions in exactly the same manner as those of animal tissues4 ,in order to show how striking are these similarities1 ,i shall for comparison place side by side the responses of animal tissues and those ,i have obtained with plants and inorganic substances4 ,for the electric response in animal tissues1 ,i shall take the latest and most complete examples from the records made by ,dr4,waller4 ,but before we can obtain satisfactory and conclusive results regarding plant response1 many experimental difficulties will have to be surmounted4 ,i shall now describe how this has been accomplished4#g ,,footnotes3 #b ,in some physiological text-books much wrong inference has been made1 based on the supposition that the injured end is zinc-like4 #c ',the exciting cause is able to produce a particular molecular rearrangement in the nerve2 this constitutes the state of excitation and is accompanied by local electrical changes as an ascertained physical concomitant4' ',the excitatory state evoked by stimulus manifests itself in nerve fibres by ,e4,m4 changes1 and as far as our present knowledge goes by these only4 ,the conception of such an excitable living tissue as nerve implies that of a molecular state which is in stable equilibrium4 ,this equilibrium can be readily upset by an external agency1 the stimulus1 but the term stable expresses the fact that a change in any direction must be succeeded by one of opposite character1 this being the return of the living structure to its previous state4 ,thus the electrical manifestation of the excitatory state is one whose duration depends upon the time during which the external agent is able to upset and retain in a new poise the living equilibrium1 and if this is extremely brief1 then the recoil of the tissue causes such manifestation to be itself of very short duration4'--,text-book of ,physiology1 ed4 by ,schfer1 ii4#dec4 #d ,i shall here mention briefly one complication that might arise from regarding the current of injury as the current of reference1 and designating the response current either positive or negative in relation to it4 ,if this current of injury remained always invariable in direction--that is to say1 from the injured to the uninjured--there would be no source of uncertainty4 ,but it is often found1 for example in the retina1 that the current of injury undergoes a reversal1 or is reversed from the beginning4 ,that is to say1 the direction is now from the uninjured to the injured1 instead of the opposite4 ,confusion is thus very apt to arise4 ,no such misunderstanding can however occur if we call the current of response towards the more excited positive1 and towards the less excited negative4 #e ',the ,electrical ,sign of ,life4444 ,an isolated muscle gives sign of life by contracting when stimulated4444 ,an ordinary nerve1 normally connected with its terminal organs1 gives sign of life by means of muscle1 which by direct or reflex path is set in motion when the nerve trunk is stimulated4 ,but such nerve separated from its natural termini1 isolated from the rest of the organism1 gives no sign of life when excited1 either in the shape of chemical or of thermic changes1 and it is only by means of an electrical change that we can ascertain whether or no it is alive4444 ,the most general and most delicate sign of life is then the electrical response4'--,waller1 in ,brain1 pp4 #c and #d4 ,spring #aijj4 #f ,kunkel thought the electric disturbance to be due to movement of water through the tissue4 ,it will be shown that this explanation is inadequate4 #g ,my assistant ,mr4,j4 ,bull has rendered me very efficient help in these experiments4 ,,chapter ,,iii ,,electric ,,response ,,in ,,plants--,,method ,,of ,,negative ,,variation ,negative variation--,response recorder--,photographic recorder--,compensator--,means of graduating intensity of stimulus--,spring-tapper and torsional vibrator--,intensity of stimulus dependent on amplitude of vibration--,effectiveness of stimulus dependent on rapidity also4 ,i shall first proceed to show that an electric response is evoked in plants under stimulation4#h ,in experiments for the exhibition of electric response it is preferable to use a non-electrical form of stimulus1 for there is then a certainty that the observed response is entirely due to reaction from stimulus1 and not1 as might be the case with electric stimulus1 to mere escape of stimulating current through the tissue4 ,for this reason1 the mechanical form of stimulation is the most suitable4 ,i find that all parts of the living plant give electric response to a greater or less extent4 ,some1 however1 give stronger response than others4 ,in favourable cases1 we may have an ,e4,m4 variation as high as #avolt4 ,it must however be remembered that the response1 being a function of physiological activity of the plant1 is liable to undergo changes at different seasons of the year4 ,each plant has its particular season of maximum responsiveness4 ,the leaf-stalk of horse-chestnut1 for example1 exhibits fairly strong response in spring and summer1 but on the approach of autumn it undergoes diminution4 ,i give here a list of specimens which will be found to exhibit fairly good response3 ,root4--,carrot 7,daucus ,carota71 radish 7,raphanus sativus74 ,stem4--,geranium 7,pelargonium71 vine 7,vitis vinifera74 ,leaf-stalk4--,horse-chestnut 7sculus ,hippocastanum71 turnip 7,brassica ,napus71 cauliflower 7,brassica oleracea71 celery 7,apium graveolens71 ,eucharis lily 7,eucharis amazonica74 ,flower-stalk4--,arum lily 7,richardia africana74 ,fruit4--,egg-plant 7,solanum ,melongena74 ,negative variation4--,taking the leaf-stalk of turnip we kill an area on its surface1 say ,b1 by the application of a few drops of strong potash1 the area at ,a being left uninjured4 ,a current is now observed to flow1 in the stalk1 from the injured ,b to the uninjured ,a1 as was found to be the case in the animal tissue4 ,the potential difference depends on the condition of the plant1 and the season in which it may have been gathered4 ,in the experiment here described 7fig4#f1 a7 its value was #acvolt4 ,illustration3 ,,fig4#f4--7;a7 ,,experiment ,,for ,,exhibiting ,,electric ,,response ,,in ,,plants ,,by ,,method ,,of ,,negative ,,variation4 7b7 ,,responses ,,in ,,leaf-,,stalk ,,of ,,turnip ,,to ,,stimuli ,,of ,,two ,,successive ,,taps1 ,,the ,,second ,,being ,,stronger4 ,a and ,b contacts are about #b;cm4 apart1 ,b being injured4 ,plant is stimulated by a tap between ,a and ,b4 ,stimulus acts on both ,a and ,b1 but owing to injury of ,b1 effect at ,a is stronger and a negative variation due to differential action occurs4 ,a sharp tap was now given to the stalk1 and a sudden diminution1 or negative variation1 of current occurred1 the resting potential difference being decreased by #jbfvolt4 ,a second and stronger tap produced a second response1 causing a greater diminution of ,p4,d4 by #jdgvolt 7fig4#f1 b74 ,the accompanying figure is a photographic record of another set of response-curves 7fig4#g74 ,the first three responses are for a given intensity of stimulus1 and the next six in response to stimulus nearly twice as strong4 ,it will be noticed that fatigue is exhibited in these responses4 ,other experiments will be described in the next chapter which show conclusively that the response was not due to any accidental circumstance but was a direct result of stimulation4 ,but ,i shall first discuss the experimental arrangements and method of obtaining these graphic records4 ,illustration3 ,,fig4#g4--,,record ,,of ,,responses ,,in ,,plant 7,,leaf-,,stalk ,,of ,,cauliflower7 ,,by ,,method ,,of ,,negative ,,variation ,the first three records are for stimulus intensity #a2 the next six are for intensity twice as strong2 the successive responses exhibit fatigue4 ,the vertical line to the left represents #avolt4 ,the record is to be read from right to left4 ,response recorder4--,the galvanometer used is a sensitive dead-beat ,d',arsonval4 ,the period of complete swing of the coil under experimental conditions is about #aaseconds4 ,a current of #aj-i;ampere produces a deflection of #amm4 at a distance of #ametre4 ,for a quick and accurate method of obtaining the records1 ,i devised the following form of response recorder4 ,the curves are obtained directly1 by tracing the excursion of the galvanometer spot of light on a revolving drum 7fig4#h74 ,the drum1 on which is wrapped the paper for receiving the record1 is driven by clockwork4 ,different speeds of revolution can be given to it by adjustment of the clock-governor1 or by changing the size of the driving-wheel4 ,the galvanometer spot is thrown down on the drum by the inclined mirror ,m4 ,the galvanometer deflection takes place at right angles to the motion of the paper4 ,a stylographic pen attached to a carrier rests on the writing surface4 ,the carrier slides over a rod parallel to the drum4 ,as has been said before1 the galvanometer deflection takes place parallel to the drum1 and as long as the plant rests unstimulated1 the pen1 remaining coincident with the stationary galvanometer spot on the revolving paper1 describes a straight line4 ,if1 on stimulation1 we trace the resulting excursion of the spot of light1 by moving the carrier which holds the pen1 the rising portion of the response-curve will be obtained4 ,the galvanometer spot will then return more or less gradually to its original position1 and that part of the curve which is traced during the process constitutes the recovery4 ,the ordinate in these curves represents the ,e4,m4 variation1 and the abscissa the time4 ,illustration3 ,,fig4#h4--,,response ,,recorder ,we can calibrate the value of the deflection by applying a known ,e4,m4,f4 to the circuit from a compensator1 and noting the deflection which results4 ,the speed of the clock is previously adjusted so that the recording surface moves exactly through1 say1 one inch a minute4 ,of course this speed can be increased to suit the particular experiment1 and in some it is as high as six inches a minute4 ,in this simple manner very accurate records may be made4 ,it has the additional advantage that one is able at once to see whether the specimen is suitable for the purpose of investigation4 ,a large number of records might be taken by this means in a comparatively short time4 ,photographic recorder4--,or the records may be made photographically4 ,a clockwork arrangement moves a photographic plate at a known uniform rate1 and a curve is traced on the plate by the moving spot of light4 ,all the records that will be given are accurate reproductions of those obtained by one of these two methods4 ,photographic records are reproduced in white against a black background4 ,compensator4--,as the responses are on variation of current of injury1 and as the current of injury may be strong1 and throw the spot of light beyond the recording surface1 a potentiometer balancing arrangement may be used 7fig4#i71 by which the ,p4,d4 due to injury is exactly compensated2 ,e4,m4 variations produced by stimulus are then taken in the usual manner4 ,this compensating arrangement is also helpful1 as has been said before1 for calibrating the ,e4,m4 value of the deflection4 ,illustration3 ,,fig4#i4--,,the ,,compensator ,a,b is a stretched wire with added resistances ,r and ,r'4 ,s is a storage cell4 ,when the key ,k is turned to the right one scale division #jjavolt1 when turned to the left one scale division #javolt4 ,p is the plant4 ,means of graduating the intensity of stimulus4--,one of the necessities in connection with quantitative measurements is to be certain that the intensity of successive stimuli is 7#a7 constant1 or 7#b7 capable of gradual increase by known amounts4 ,no two taps given by the hand can be made exactly alike4 ,i have therefore devised the two following methods of stimulation1 which have been found to act satisfactorily4 ,illustration3 ,,fig4#aj4--,,the ,,spring-,,tapper ,the spring-tapper4--,this consists 7fig4#aj7 of the spring proper 7,s71 the attached rod 7,r7 carrying at its end the tapping-head 7,t74 ,a projecting rod--the lifter 7,l7--passes through ,s,r4 ,it is provided with a screw-thread1 by means of which its length1 projecting downwards1 is regulated4 ,this fact1 as we shall see1 is made to determine the height of the stroke4 7,c7 is a cogwheel4 ,as one of the spokes of the cogwheel is rotated past 7,l71 the spring is lifted and released1 and 7,t7 delivers a sharp tap4 ,the height of the lift1 and therefore the intensity of the stroke1 is measured by means of a graduated scale4 ,we can increase the intensity of the stroke through a wide range 7#a7 by increasing the projecting length of the lifter1 and 7#b7 by shortening the length of spring by a sliding catch4 ,we may give isolated single taps or superpose a series in rapid succession according as the wheel is rotated slow or fast4 ,the only disadvantage of the tapping method of stimulation is that in long-continued experiment the point struck is liable to be injured4 ,the vibrational mode of stimulation to be presently described labours under no such disadvantage4 ,the electric tapper4--,instead of the simple mechanical tapper1 an electromagnetic tapper may be used4 ,illustration3 ,,fig4#aa4--,,the ,,torsional ,,vibrator ,plant ,p is securely held by a vice ,v4 ,the two ends are clamped by holders ,c,c'4 ,by means of handles ,h,h'1 torsional vibration may be imparted to either the end ,a or end ,b of the plant4 ,the end view 7b7 shows how the amplitude of vibration is predetermined by means of movable stops ,s,s'4 ,vibrational stimulus4--,i find that torsional vibration affords another very effective method of stimulation 7fig4#aa74 ,the plant-stalk may be fixed in a vice 7,v71 the free ends being held in tubes 7,c,c'71 provided with three clamping jaws4 ,a rapid torsional vibration#i may now be imparted to the stalk by means of the handle 7,h74 ,the amplitude of vibration1 which determines the intensity of stimulus1 can be accurately measured by the graduated circle4 ,the amplitude of vibration may be predetermined by means of the sliding stops 7,s,s'74 ,intensity of stimulus dependent on amplitude of vibration4--,i shall now describe an experiment which shows that torsional vibration is as effective as stimulation by taps1 and that its stimulating intensity increases1 length of stalk being constant1 with amplitude of vibration4 ,it is of course obvious that if the length of the specimen be doubled1 the vibration1 in order to produce the same effect1 must be through twice the angle4 ,i took a leaf-stalk of turnip and fixed it in the torsional vibrator4 ,i then took record of responses to two successive taps1 the intensity of one being nearly double that of the other4 ,having done this1 ,i applied to the same stalk two successive torsional vibrations of #de and #fg respectively4 ,these successive responses to taps and torsional vibrations are given in fig4#ab1 and from them it will be seen that these two modes of stimulation may be used indifferently1 with equal effect4 ,the vibrational method has the advantage over tapping1 that1 while with the latter the stimulus is somewhat localised1 with vibration the tissue subjected to stimulus is uniformly stimulated throughout its length4 ,illustration3 ,,fig4#ab4--,,response ,,in ,,plant ,,to ,,mechanical ,,tap ,,or ,,vibration ,the end ,b is injured4 ,a tap was given between ,a and ,b and this gave the response-curve a4 ,a stronger tap gave the response b4 ,by means of the handle ,h1 a torsional vibration of #de was now imparted1 this gave the response c4 ,vibration through #fg gave d4 ,effectiveness of stimulus dependent on rapidity also4 ,in order that successive stimuli may be equally effective another point has to be borne in mind4 ,in all cases of stimulation of living tissue it is found that the effectiveness of a stimulus to arouse response depends on the rapidity of the onset of the disturbance4 ,it is thus found that the stimulus of the 'break' induction shock1 on a muscle for example1 is more effective1 by reason of its greater rapidity1 than the 'make' shock4 ,so also with the torsional vibrations of plants1 ,i find response depending on the quickness with which the vibration is effected4 ,i give below records of successive stimuli1 given by vibrations through the same amplitude1 but delivered with increasing rapidity 7fig4#ac74 ,illustration3 ,,fig4#ac4--;,,influence ,,of ,,suddenness ,,on ,,the ,,efficiency ,,of ,,stimulus ,the curves a1 b1 c1 d1 are responses to vibrations of the same amplitude1 #cj4 ,in a the vibration was very slow2 in b it was less slow2 it was rapid in c1 and very rapid in d4 ,thus if we wish to maintain the effective intensity of stimulus constant we must meet two conditions3 7#a7 ,the amplitude of vibration must be kept the same4 ,this is done by means of the graduated circle4 7#b7 ,the vibration period must be kept the same4 ,with a little practice1 this requirement is easily fulfilled4 ,the uniformity of stimulation which is thus attained solves the great difficulty of obtaining reliable quantitative values1 by whose means alone can rigorous demonstration of the phenomena we are studying become possible4 ,,footnotes3 #h ,a preliminary account of ,electric ,response in ,plants was given at the end of my paper on ',electric ,response of ,inorganic ,substances' read before the ,royal ,society on ,june#f1 #aija2 also at the ,friday ,evening ,discourse1 ,royal ,institution1 ,may#aj1 #aija4 ,a more complete account is given in my paper on ',electric ,response in ,ordinary ,plants under ,mechanical ,stimulus' read before the ,linnean ,society ,march#bj1 #aijb4 ,i thank the ,royal ,society and the ,linnean ,society for permission to reproduce some of my diagrams published in their ,proceedings4--,j4,c4,b4 #i ,by this is meant a rapid to-and-fro or complete vibration4 ,in order that successive responses should be uniform it is essential that there should be no resultant twist1 i4e4 the plant at the end of vibration should be in exactly the same condition as at the beginning4 ,,chapter ,,iv ,,electric ,,response ,,in ,,plants--,,block ,,method ,method of block--,advantages of block method--,plant response a physiological phenomenon--,abolition of response by ansthetics and poisons--,abolition of response when plant is killed by hot water4 ,i shall now proceed to describe another and independent method which ,i devised for obtaining plant response4 ,it has the advantage of offering us a complementary means of verifying the results found by the method of negative variation4 ,as it is also1 in itself1 for reasons which will be shown later1 a more perfect mode of inquiry1 it enables us to investigate problems which would otherwise have been difficult to attempt4 ,when electrolytic contacts are made on the uninjured surfaces of the stalk at ,a and ,b1 the two points1 being practically similar in every way1 are iso-electric1 and little or no current will flow in the galvanometer4 ,if now the whole stalk be uniformly stimulated1 and if both ends ,a and ,b be equally excited at the same moment1 it is clear that there will still be no responsive current1 owing to balancing action at the two ends4 ,this difficulty as regards the obtaining of response was overcome in the method of negative variation1 where the excitability of one end was depressed by chemical reagents or injury1 or abolished by excessive temperature4 ,on stimulating the stalk there was produced a greater excitation at ,a than at ,b1 and a current of action was then observed to flow in the stalk from the more excited ,a to the less excited ,b 7fig4#f74 ,but we can cause this differential action to become evident by another means4 ,for example1 if we produce a block1 by clamping at ,c between ,a and ,b 7fig4#ad1 a71 so that the disturbance made at ,a by tapping or vibration is prevented from reaching ,b1 we shall then have ,a thrown into a relatively greater excitatory condition than ,b4 ,it will now be found that a current of action flows in the stalk from ,a to ,b1 that is to say1 from the excited to the less excited4 ,when the ,b end is stimulated1 there will be a reverse current 7fig4#ad1 b74 ,illustration3 ,,fig4#ad4--,,the ,,method ,,of ,,block 7a7 ,the plant is clamped at ,c1 between ,a and ,b4 7b7 ,responses obtained by alternately stimulating the two ends4 ,stimulation of ,a produces upward response2 of ,b gives downward response4 ,we have in this method a great advantage over that of negative variation1 for we can always verify any set of results by making corroborative reversal experiments4 ,by the method of injury again1 one end is made initially abnormal1 i4e4 different from the condition which it maintains when intact4 ,further1 inevitable changes will proceed unequally at the injured and uninjured ends1 and the conditions of the experiment may thus undergo unknown variations4 ,but by the block method which has just been described1 there is no injury1 the plant is normal throughout1 and any physiological change 7which in plants will be exceedingly small during the time of the experiment7 will affect it as a whole4 ,illustration3 ,,fig4#ae4--,,response ,,in ,,plant 7,,from ,,the ,,stimulated ,a ,,to ,,unstimulated ,b7 ,,completely ,,immersed ,,under ,,water ,the leaf-stalk is clamped securely in the middle with the cork ,c1 inside the tube ,t1 which is filled with water1 the plant being completely immersed4 ,moistened threads in connection with the two non-polarisable electrodes are led to the side tubes tt'4 ,one end of the stalk is held in ebonite forceps and vibrated4 ,a current of response is found to flow in the stalk from the excited ,a to the unexcited ,b1 and outside1 through the liquid1 from ,b to ,a4 ,a portion of this current1 flowing through the side tubes tt'1 produces deflection in the galvanometer4 ,plant response a physiological or vital response4--,i now proceed to a demonstration of the fact that whatever be the mechanism by which they are brought about1 these plant responses are physiological in their character4 ,as the investigations described in the next few chapters will show1 they furnish an accurate index of physiological activity4 ,for it will be found that1 other things being equal1 whatever tends to exalt or depress the vitality of the plant tends also to increase or diminish its electric response4 ,these ,e4,m4 effects are well marked1 and attain considerable value1 rising sometimes1 as has been said before1 to as much as #avolt or more4 ,they are proportional to the intensity of stimulus4 ,it need hardly be added that special precautions are taken to avoid shifting of contacts4 ,variation of contact1 however1 could not in any case account for repeated transient responses to repeated stimuli1 when contact is made on iso-electric surfaces4 ,nor could it in any way explain the reversible nature of these responses1 when ,a and ,b are stimulated alternately4 ,these responses are obtained in the plants even when completely immersed in water1 as in the experimental arrangement 7fig4#ae74 ,it will be seen that in this case1 where there could be no possibility of shifting of contact1 or variation of surface1 there is still the usual current of response4 ,i shall describe here a few crucial experiments only1 in proof of the physiological character of electric response4 ,the test applied by physiologists1 in order to discriminate as to the physiological nature of response1 consists in finding out whether the response is diminished or abolished by the action of ansthetics1 poisons1 and excessively high temperature1 which are known to depress or destroy vitality4 ,i shall therefore apply these same tests to plant responses4 ,effect of ansthetics and poisons4--,ordinary ansthetics1 like chloroform1 and poisons1 like mercuric chloride1 are known to produce a profound depression or abolish all signs of response in the living tissue4 ,for the purpose of experiment1 ,i took two groups of stalks1 with leaves attached1 exactly similar to each other in every respect4 ,in order that the leaf-stalks might absorb chloroform ,i dipped their cut ends in chloroform-water1 a certain amount of which they absorbed1 the process being helped by the transpiration from the leaves4 ,the second group of stalks was placed simply in water1 in order to serve for control experiment4 ,the narcotic action of chloroform1 finally culminating in death1 soon became visually evident4 ,the leaves began to droop1 a peculiar death-discolouration began to spread from the mid rib along the venation of the leaves4 ,another peculiarity was also observed4 ,the aphides feeding on the leaves died even before the appearance of the discoloured patches1 whereas on the leaves of the stalks placed in water these little creatures maintained their accustomed activity1 nor did any discolouration occur4 ,in order to study the effect of poison1 another set was placed in water containing a small quantity of mercuric chloride4 ,the leaves here underwent the same change of appearance1 and the aphides met with the same untimely fate1 as in the case of those subjected to the action of chloroform4 ,there was hardly any visible change in the appearance of the stalks themselves1 which were to all outer seeming as living as ever1 indications of death being apparent only on the leaf surfaces4 ,i give below the results of several sets of experiments1 from which it would appear that whereas there was strong normal response in the group of stalks kept in water1 there was practically a total abolition of all response in those ansthetised or poisoned4 ,experiments on the effect of ansthetics and poisons4 ,a batch of ten leaf-stalks of plane-tree was placed with the cut ends in water1 and leaves in air2 an equal number was immersed in chloroform-water2 a third batch was placed in #epercent4 solution of mercuric chloride4 ,similarly a batch of three horse-chestnut leaf-stalks was put in water1 another batch in chloroform-water1 and a third batch in mercuric chloride solution4 ,i4 ,,leaf-,,stalk ,,of ,,plane-,,tree ,the stimulus applied was a single vibration of #ij4 ,a4 ,after #bd;hours in ,b4 ,after #bd;hours in ,c4 ,after #bd;hours in water chloroform water mercuric chloride ,all leaves standing up ,leaves began to ,leaves began to droop and fresh--aphides droop in #a;hour in #d;hours4 ,deep alive and bent over in discolouration along #c;hours--aphides the veins4 ,aphides dead dead ,electric ,electric ,electric ,response response response 7#a7 #ba dns4 7#a7 #a dn4 7#a7 #j dn4 7#b7 #ca 7#b7 #a 7#b7 #be 7#c7 #bf 7#c7 #b 7#c7 #be 7#d7 #ae 7#d7 #j 7#d7 #j 7#e7 #ag 7#e7 #a 7#e7 #be 7#f7 #bc 7#f7 #ae 7#f7 #be 7#g7 #cj 7#g7 #b 7#g7 #j 7#h7 #bg 7#h7 #a 7#h7 #be 7#i7 #bi 7#i7 #a 7#i7 #be 7#aj7 #ag 7#aj7 #e 7#aj7 #e ---------------------------------------- ----------------------------- ,mean response #bcf ,mean #a ,mean #ae ,,ii4 ,,leaf-,,stalk ,,of ,,horse-,,chestnut 7#a7 #ae dns4 7#a7 #e dn4 7#a7 #j dn4 7#b7 #ag 7#b7 #e 7#b7 #j 7#c7 #aj 7#c7 #j 7#c7 #j ---------------------------------------- ----------------------------- ,mean #ad ,mean #c ,mean #j ,these results conclusively prove the physiological nature of the response4 ,i shall in a succeeding chapter give a continuous series of response-curves showing how1 owing to progressive death from the action of poison1 the responses undergo steady diminution till they are completely abolished4 ,effect of high temperature4--,it is well known that plants are killed when subjected to high temperatures4 ,i took a stalk1 and1 using the block method1 with torsional vibration as the stimulus1 obtained strong responses at both ends ,a and ,b4 ,i then immersed the same stalk for a short time in hot water at about #fe;,c41 and again stimulated it as before4 ,but at neither ,a nor ,b could any response now be evoked4 ,as all the external conditions were the same in the first and second parts of this experiment1 the only difference being that in one the stalk was alive and in the other killed1 we have here further and conclusive proof of the physiological character of electric response in plants4 ,the same facts may be demonstrated in a still more striking manner by first obtaining two similar but opposite responses in a fresh stalk1 at ,a and ,b1 and then killing one half1 say ,b1 by immersing only that half of the stalk in hot water4 ,the stalk is replaced in the apparatus1 and it is now found that whereas the ,a half gives strong response1 the end ,b gives none4 ,in the experiments on negative variation1 it was tacitly assumed that the variation is due to a differential action1 stimulus producing a greater excitation at the uninjured than at the injured end4 ,the block method enables us to test the correctness of this assumption4 ,the ,b end of the stalk is injured or killed by a few drops of strong potash1 the other end being uninjured4 ,there is a clamp between ,a and ,b4 ,the end ,a is stimulated and a strong response is obtained4 ,the end ,b is now stimulated1 and there is little or no response4 ,the block is now removed and the plant stimulated throughout its length4 ,though the stimulus now acts on both ends1 yet1 owing to the irresponsive condition of ,b1 there is a resultant response1 which from its direction is found to be due to the responsive action of ,a4 ,this would not have been the case if the end ,b had been uninjured4 ,we have thus experimentally verified the assumption that in the same tissue an uninjured portion will be thrown into a greater excitatory state than an injured1 by the action of the same stimulus4 ,,chapter ,v ,,plant ,,response--,,on ,,the ,,effects ,,of ,,single ,,stimulus ,,and ,,of ,,superposed ,,stimuli ,effect of single stimulus--,superposition of stimuli--,additive effect--,staircase effect--,fatigue--,no fatigue when sufficient interval between stimuli--,apparent fatigue when stimulation frequency is increased--,fatigue under continuous stimulation4 ,effect of single stimulus4--,in a muscle a single stimulus gives rise to a single twitch which may be recorded either mechanically or electrically4 ,if there is no fatigue1 the successive responses to uniform stimuli are exactly similar4 ,muscle when strongly stimulated often exhibits fatigue1 and successive responses therefore become feebler and feebler4 ,in nerves1 however1 there is practically no fatigue and successive records are alike4 ,similarly1 in plants1 we shall find some exhibiting marked fatigue and others very little4 ,superposition of stimuli4--,if instead of a single stimulus a succession of stimuli be superposed1 it happens that a second shock is received before recovery from the first has taken place4 ,individual effects will then become more or less fused4 ,when the frequency is sufficiently increased1 the intermittent effects are fused1 and we find an almost unbroken curve4 ,when for example the muscle attains its maximum contraction 7corresponding to the frequency and strength of stimuli7 it is thrown into a state of complete tetanus1 in which it appears to be held rigid4 ,if the rapidity be not sufficient for this1 we have the jagged curve of incomplete tetanus4 ,if there is not much fatigue1 the upper part of the tetanic curve is approximately horizontal1 but in cases where fatigue sets in quickly1 the fact is shown by the rapid decline of the curve4 ,with regard to all these points we find strict parallels in plant response4 ,in cases where there is no fatigue1 the successive responses are identical 7fig4#af74 ,with superposition of stimuli we have fusion of effects1 analogous to the tetanus of muscle 7fig4#ag74 ,and lastly1 the influence of fatigue in plants is to produce a modification of response-curve exactly similar to that of muscle 7see below74 ,one effect of superposition of stimuli may be mentioned here4 ,illustration3 ,,fig4#af4--,,uniform ,,responses 7,,radish7 ,illustration3 ,,fig4#ag4--;,,fusion ,,of ,,effect ,,of ,,rapidly ,,succeeding ,,stimuli 7a7 in muscle2 7b7 in carrot4 ,additive effect4--,it is found in animal responses that there is a minimum intensity of stimulus1 below which no response can be evoked4 ,but even a sub-minimal stimulus will1 though singly ineffective1 become effective by the summation of several4 ,in plants1 too1 we obtain a similar effect1 i4e4 the summation of single ineffective stimuli produces effective response 7fig4#ah74 ,illustration3 ,,fig4#ah4--;,,additive ,,effect 7a7 ,a single stimulus of #c vibration produced little or no effect1 but the same stimulus when rapidly superposed thirty times1 produced the large effect 7b74 7,leaf-stalk of turnip47 ,staircase effect4--,animal tissues sometimes exhibit what is known as the 'staircase effect1' that is to say1 the heights of successive responses are gradually increased1 though the stimuli are maintained constant4 ,this is exhibited typically by cardiac muscle1 though it is not unknown even in nerve4 ,the cause is obscure1 but it seems to depend on the condition of the tissue4 ,it appears as if the molecular sluggishness of tissue were in these cases only gradually removed under stimulation1 and the increased effects were due to increased molecular mobility4 ,whatever be the explanation1 ,i have sometimes observed the same staircase effect in plants 7fig4#ai74 ,illustration3 ,,fig4#ai4--',,staircase ,,effect' ,,in ,,plant ,fatigue4--,it is assumed that in living substances like muscle1 fatigue is caused by the break down or dissimilation of tissue by stimulus4 ,and till this waste is repaired by the process of building-up or assimilation1 the functional activity of the tissue will remain below par4 ,there may also be an accumulation of the products of dissimilation--'the fatigue stuffs'--and these latter may act as poisons or chemical depressants4 ,in an animal it is supposed that the nutritive blood supply performs the two-fold task of bringing material for assimilation and removing the fatigue products1 thus causing the disappearance of fatigue4 ,this explanation1 however1 is shown to be insufficient by the fact that an excised bloodless muscle recovers from fatigue after a short period of rest4 ,it is obvious that here the fatigue has been removed by means other than that of renewed assimilation and removal of fatigue products by the circulating blood4 ,it may therefore be instructive to study certain phases of fatigue exhibited under simpler conditions in vegetable tissue1 where the constructive processes are in abeyance1 and there is no active circulation for the removal of fatigue products4 ,it has been said before that the ,e4,m4 variation caused by stimulus is the concomitant of a disturbance of the molecules of the responsive tissues from their normal equilibrium1 and that the curve of recovery exhibits the restoration of the tissue to equilibrium4 ,no fatigue when sufficient interval between successive stimuli4--,we may thus gather from a study of the response-curve some indication of the molecular distortion experienced by the excited tissue4 ,let us first take the case of an experiment whose record is given in fig4#bj1 a4 ,it will be seen from that curve that one minute after the application of stimulus there is a complete recovery of the tissue2 the molecular condition is exactly the same at the end of recovery as in the beginning of stimulation4 ,the second and succeeding response-curves therefore are exactly similar to the first1 provided a sufficient interval has been allowed in each case for complete recovery4 ,there is1 in such a case1 no diminution in intensity of response1 that is to say1 no fatigue4 ,we have an exactly parallel case in muscles4 ',in muscle with normal circulation and nutrition there is always an interval between each pair of stimuli1 in which the height of twitch does not diminish even after protracted excitation1 and no fatigue appears4'#aj ,illustration3 ,,fig4#bj4--,,record ,,showing ,,diminution ,,of ,,response ,,when ,,sufficient ,,time ,,is ,,not ,,allowed ,,for ,,full ,,recovery ,in 7a7 stimuli were applied at intervals of one minute2 in 7b7 the intervals were reduced to half a minute2 this caused a diminution of response4 ,in 7c7 the original rhythm is restored1 and the response is found to be enhanced4 7,radish47 ,apparent fatigue when stimulation frequency increased4--,if the rhythm of stimulation frequency be now changed1 and made quicker1 certain remarkable modifications will appear in the response-curves4 ,in fig4#bj1 the first part shows the responses at one minute interval1 by which time the individual recovery was complete4 ,the rhythm was now changed to intervals of half a minute1 instead of one1 while the stimuli were maintained at the same intensity as before4 ,it will be noticed 7fig4#bj1 b7 that these responses appear much feebler than the first set1 in spite of the equality of stimulus4 ,an inspection of the figure may perhaps throw some light on the subject4 ,it will be seen that when greater frequency of stimulation was introduced1 the tissue had not yet had time to effect complete recovery from previous strain4 ,the molecular swing towards equilibrium had not yet abated1 when the new stimulus1 with its opposing impulse1 was received4 ,there is thus a diminution of height in the resultant response4 ,the original rhythm of one minute was now restored1 and the succeeding curves 7fig4#bj1 c7 at once show increased response4 ,an analogous instance may be cited in the case of muscle response1 where 'the height of twitch diminishes more rapidly in proportion as the excitation interval is shorter4'#aa ,illustration3 ,,fig4#ba4--;,,fatigue ,,in ,,celery ,vibration of #cj at intervals of half a minute4 ,from what has just been said it would appear that one of the causes of diminution of response1 or fatigue1 is the residual strain4 ,this is clearly seen in fig4#ba1 in a record which ,i obtained with celery-stalk4 ,it will be noticed there that1 owing to the imperfect molecular recovery during the time allowed1 the succeeding heights of the responses have undergone a continuous diminution4 ,fig4#bb gives a photographic record of fatigue in the leaf-stalk of cauliflower4 ,illustration3 ,,fig4#bb4--;,,fatigue ,,in ,,leaf-,,stalk ,,of ,,cauliflower ,stimulus3 #cj vibration at intervals of one minute4 ,it is evident that residual strain1 other things being equal1 will be greater if the stimuli have been excessive4 ,this is well seen in fig4#bc1 where the set of first three curves ,a is for stimulus intensity of #de vibration1 and the second set ,b1 with an augmented response1 for stimulus intensity of #ij vibration4 ,on reverting in ,c to stimulus intensity of #de1 the responses are seen to have undergone a great diminution as compared with the first set ,a4 ,here is seen marked fatigue1 the result of overstrain from excessive stimulation4 ,illustration3 ,,fig4#bc4--;,,effect ,,of ,,overstrain ,,in ,,producing ,,fatigue ,successive stimuli applied at intervals of one minute4 ,the intensity of stimulus in ,c is the same as that of ,a1 but response is feebler owing to previous over-stimulation4 ,fatigue is to a great extent removed after fifteen minutes' rest1 and the responses in ,d are stronger than those in ,c4 ,the vertical line between arrows represents #jevolt4 7,turnip leaf-stalk47 ,if this fatigue be really due to residual strain effect1 then1 as strain disappears with time1 we may expect the responses to regain their former height after a period of rest4 ,in order to verify this1 therefore1 ,i renewed the stimulation 7at intensity #de7 after fifteen minutes4 ,it will at once be seen from record ,d how far the fatigue had been removed4 ,one peculiarity that will be noticed in these curves is that1 owing to the presence of comparatively little residual strain1 the first response of each set is relatively large4 ,the succeeding responses are approximately equal where the residual strains are similar4 ,the first response of ,a shows this because it had had long previous rest4 ,the first of ,b shows it because we are there passing for the first time to increased stimulation4 ,the first of ,c does not show it1 because there is now a strong residual strain4 ,d again shows it because the strain has been removed by fifteen minutes' rest4 ,fatigue under continuous stimulation4--,the effect of fatigue is exhibited in marked degree when a tissue is subjected to continuous stimulation4 ,in cases where there is marked fatigue1 as for instance in certain muscles1 the top of the tetanic curve undergoes rapid decline4 ,a similar effect is obtained also with plants 7fig4#bd74 ,illustration3 ,,fig4#bd4--,,rapid ,,fatigue ,,under ,,continuous ,,stimulation ,,in 7a7 ,,muscle2 7b7 ,,in ,,leaf-,,stalk ,,of ,,celery ,the effect of rest in producing molecular recovery1 and hence in the removal of fatigue1 is well illustrated in the following set of photographic records 7fig4#be74 ,the first shows the curve obtained with a fresh plant4 ,the effect is seen to be very large4 ,two minutes were allowed for recovery1 and then stimulation was repeated during another two minutes4 ,the response in this case is seen to be decidedly smaller4 ,a third case is somewhat similar to the second4 ,a period of rest of five minutes was now allowed1 and the curve obtained subsequently1 owing to partial removal of residual strain1 is found to exhibit greater response4 ,illustration3 ,,fig4#be4--;,,effect ,,of ,,continuous ,,vibration 7,,through #ej7 ,,in ,,carrot ,in the first three records1 two minutes' stimulation is followed by two minutes' recovery4 ,the last record was taken after the specimen had a rest of five minutes4 ,the response1 owing to removal of fatigue by rest1 is stronger4 ,the results thus arrived at1 under the simple conditions of vegetable life1 free as they are from all possible complications and uncertainties1 may perhaps throw some light on the obscure phenomena of fatigue in animal tissues4 ,,footnotes3 #aj ,biedermann1 ,electro-physiology1 p4#hf4 #aa ,biedermann1 loc4 cit4 ,,chapter ,,vi ,,plant ,,response--,,on ,,diphasic ,,variation ,diphasic variation--,positive after-effect and positive response--,radial ,e4,m4 variation4 ,when a plant is stimulated at any point1 a molecular disturbance--the excitatory wave--is propagated outwards from the point of its initiation4 ,diphasic variation4--,this wave of molecular disturbance is attended by a wave of electrical disturbance4 7,usually speaking1 the electrical relation between disturbed and less disturbed is that of copper to zinc47 ,it takes some time for a disturbance to travel from one point to another1 and its intensity may undergo a diminution as it recedes further from its point of origin4 ,suppose a disturbance originated at ,c2 if two points are taken near each other1 as ,a and ,b1 the disturbance will reach them almost at the same time1 and with the same intensity4 ,the electric disturbance will be the same in both4 ,the effect produced at ,a and ,b will balance each other and there will be no resultant current4 ,by killing or otherwise reducing the sensibility of ,b as is done in the method of injury1 there is no response at ,b1 and we obtain the unbalanced response1 due to disturbance at ,a2 the same effect is obtained by putting a clamp between ,a and ,b1 so that the disturbance may not reach ,b4 ,but we may get response even without injury or block4 ,if we have the contacts at ,a and ,b1 and if we give a tap nearer ,a than ,b 7fig4#bf1 a71 then we have 7#a7 the disturbance reaching ,a earlier than ,b4 7#b7 ,the disturbance reaching ,a is much stronger than at ,b4 ,the disturbance at ,b may be so comparatively feeble as to be negligible4 ,it will thus be seen that we might obtain responses even without injury or block1 in cases where the disturbance is enfeebled in reaching a distant point4 ,in such a case on giving a tap near ,a a responsive current would be produced in one direction1 and in the opposite direction when the tap is given near ,b 7fig4#bf1 b74 ,theoretically1 then1 we might find a neutral point between ,a and ,b1 so that1 on originating the disturbance there1 the waves of disturbance would reach ,a and ,b at the same instant and with the same intensity4 ,if1 further1 the rate of recovery be the same for both points1 then the electric disturbances produced at ,a and ,b will continue to balance each other1 and the galvanometer will show no current4 ,on taking a cylindrical root of radish ,i have sometimes succeeded in finding a neutral point1 which1 being disturbed1 did not give rise to any resultant current4 ,but disturbing a point to the right or to the left gave rise to opposite currents4 ,it is1 however1 difficult to obtain an absolutely cylindrical specimen1 as it always tapers in one direction4 ,the conductivity towards the tip of the root is not exactly the same as that in the ascending direction4 ,it is therefore difficult to fix an absolutely neutral point1 but a point may be found which approaches this very nearly1 and on stimulating the stalk near this1 a very interesting diphasic variation has been observed4 ,in a specimen of cauliflower-stalk1 7#a7 stimulus was applied very much nearer ,a than ,b 7the feeble disturbance reaching ,b was negligible74 ,the resulting response was upward and the recovery took place in about sixty seconds4 ,illustration3 ,,fig4#bf4--;,,diphasic ,,variation 7#b7 ,stimulus was next applied near ,b4 ,the resulting response was now downward 7fig4#bf1 b74 7#c7 ,the stimulus was now applied near the approximately neutral point ,n4 ,in this case1 owing to a slight difference in the rates of propagation in the two directions1 a very interesting diphasic variation was produced 7fig4#bf1 c74 ,from the record it will be seen that the disturbance arrived earlier at ,a than at ,b4 ,this produced an upward response4 ,but during the subsidence of the disturbance at ,a1 the wave reached ,b4 ,the effect of this was to produce a current in the opposite direction4 ,this apparently hastened the recovery of ,a 7from #fjseconds to #abseconds74 ,the excitation of ,a now disappeared1 and the second phase of response1 that due to excitation of ,b1 was fully displayed4 ,positive after-effect4--,if we regard the response due to excitation of ,a as negative1 the later effect on ,b would appear as a subsequent positive variation4 ,in the response of nerve1 for example1 where contacts are made at two surfaces1 injured and uninjured1 there is sometimes observed1 first a negative variation1 and then a positive after-effect4 ,this may sometimes at least be due to the proximal uninjured contact first giving the usual negative variation1 and the more distant contact of injury giving rise1 later1 to the opposite1 that is to say1 apparently positive1 response4 ,there is always a chance of an after-effect due to this cause1 unless 7#a7 the injured end be completely killed and rendered quite irresponsive1 or 7#b7 there be an effective block between ,a and ,b1 so that the disturbance due to stimulus can only act on one1 and not on the other4 ,i have found cases where1 even when there was a perfect block1 a positive after-effect occurred4 ,it would thus appear that if molecular distortion from stimulus give rise to a negative variation1 then during the process of molecular recovery there may be over-shooting of the equilibrium position1 which may be exhibited as a positive variation4 ,positive variation4--,the responses given by muscle or nerve are1 normally speaking1 negative4 ,but that of retina is positive4 ,the sign of response1 however1 is apt to be reversed if there be any molecular modification of the tissue from changes of external circumstances4 ,thus it is often found that nerve in a stale condition gives positive1 instead of the normal negative variation1 and stale retina often gives negative1 instead of the usual positive4 ,illustration3 ,,fig4#bg4--;,,abnormal ,,positive ,,responses ,,in ,,stale ,,leaf-,,stalk ,,of ,,turnip ,,converted ,,into ,,normal ,,negative ,,under ,,strong ,,stimulation#ab ,the relative intensities of stimuli in the two cases are in the ratio of #a3g4 ,curiously enough1 ,i have on many occasions found exactly parallel instances in the response of plants4 ,plants when fresh1 as stated1 give negative responses as a rule4 ,but when somewhat faded they sometimes give rise to positive response4 ,again1 just as in the modified nerve the abnormal positive response gives place to the normal negative under strong and long-continued stimulation1 so also in the modified plant the abnormal positive response passes into negative 7fig4#bg7 under strong stimulation4 ,i was able in some cases to trace this process of gradual reversal1 by continuously increasing the intensity of stimulus4 ,it was then found that as the stimulus was increased1 the positive at a certain point underwent a reversal into the normal negative response 7fig4#bh74 ,illustration3 ,,fig4#bh4 ,,abnormal ,,positive ,,passing ,,into ,,normal ,,negative ,,in ,a ,,stale ,,specimen ,,of ,,leaf-,,stalk ,,of ,,cauliflower ,stimulus was gradually increased from #a to #aj1 by means of spring-tapper4 ,when the stimulus intensity was #aj1 the response became reversed into normal negative4 7,parts of #h and #i are out of the plate47 ,the plant thus gives a reversed response under abnormal conditions of staleness4 ,i have sometimes found similar reversal of response when the plant is subjected to the abnormal conditions of excessively high or low temperature4 ,radial ,e4,m4 variation4--,we have seen that a current of response flows in the plant from the relatively more to the relatively less excited4 ,a theoretically important experiment is the following3 ,a thick stem of plant stalk was taken and a hole bored so as to make one contact with the interior of the tissue1 the other being on the surface4 ,after a while the current of injury was found to disappear4 ,on exciting the stem by taps or torsional vibration1 a responsive current was observed which flowed inwards from the more disturbed outer surface to the shielded core inside 7fig4#bi74 ,hence it is seen that when a wave of disturbance is propagated along the plant1 there is a concomitant wave of radial ,e4,m4 variation4 ,the swaying of a tree by the wind would thus appear to give rise to a radial ,e4,m4,f4 ,illustration3 ,,fig4#bi4--,,radial ,e4,m4 ,,variation ,,footnotes3 #ab ,for general purposes it is immaterial whether the responses are recorded up or down4 ,for convenience of inspection they are in general recorded up4 ,but in cases where it is necessary to discriminate the sign of response1 positive response will be recorded up1 and negative down4 ,,chapter ,,vii ,,plant ,,response--,,on ,,the ,,relation ,,between ,,stimulus ,,and ,,response ,increased response with increasing stimulus--,apparent diminution of response with excessively strong stimulus4 ,as already said1 in the living tissue1 molecular disturbance induced by stimulus is accompanied by an electric disturbance1 which gradually disappears with the return of the disturbed molecules to their position of equilibrium4 ,the greater the molecular distortion produced by the stimulus1 the greater is the electric variation produced4 ,the electric response is thus an outward expression of a molecular disturbance produced by an external agency1 the stimulus4 ,curve of relation between stimulus and response4--,in the curve showing the relation between stimulus and response in nerve and muscle1 it is found that the molecular effect as exhibited either by contraction or ,e4,m4 variation in muscle1 or simply by ,e4,m4 variation in nerve1 is at first slight4 ,in the second part1 there is a rapidly increasing effect with increased stimulus4 ,finally1 a tendency shows itself to approach a limit of response4 ,thus we find the curve at first slightly convex1 then straight and ascending1 and lastly1 concave to the abscissa 7fig4#cj74 ,in muscle the limit of response is reached much sooner than in nerve4 ,as will be seen1 the range of variation of stimulus in these curves is not very great4 ,when the stimulus is carried beyond moderate limits1 the response1 owing to fatigue or other causes1 may sometimes undergo an actual diminution4 ,illustration3 ,,fig4#cj4--;,,curves ,,showing ,,the ,,relation ,,between ,,the ,,intensity ,,of ,,stimulus ,,and ,,response ,absciss indicate increasing intensity of stimulus4 ,ordinates indicate magnitude of response4 7,waller47 ,i have obtained very interesting results1 with reference to the relation between stimulus and response1 when experimenting with plants4 ,these results are suggestive of various types of response met with in animal tissues4 #a4 ,in order to obtain the simplest type of effects1 not complicated by secondary phenomena1 one has to choose specimens which exhibit little fatigue4 ,having procured these1 ,i undertook two series of experiments4 ,in the first 7,a7 the stimulus was applied by means of the spring-tapper1 and in the second 7,b7 by torsional vibration4 ,illustration3 ,,fig4#ca ,taps of increasing strength #a3b3c3d producing increased response in leaf stalk of turnip4 7,a7 ,the first stimulus was given by a fall of the lever through h1 the second through #b;h1 and so on4 ,the response-curves clearly show increasing effect with increased stimulus 7fig4#ca74 ,illustration3 ,,fig4#cb4--;,,increased ,,response ,,with ,,increasing ,,vibrational ,,stimuli 7,,cauliflower-,,stalk7 ,stimuli applied at intervals of three minutes4 ,vertical line #avolt4 7,b7 #a4 ,the vibrational stimulus was increased from #be to #e to #ge to #aj to #abe in amplitude4 ,it will be observed how the intensity of response tends to approach a limit 7fig4#cb74 ,,table ,,showing ,,the ,,increased ,e4,m4 ,,variation ,,produced ,,by ,,increasing ,,stimulus ---------------------------------------- ,angle of ,vibration ,e4,m4,f ---------------------------------------- #be #jdd volt #e #jge volt #ge #jij volt #aj #ajj volt #abe #ajf volt --------------------------------------- #b4 ,the next figure shows how little variation is produced with low value of stimulus1 but with increasing stimulus the response undergoes a rapid increase1 after which it tends to approach a limit 7fig4#cc1 a74 ,illustration3 ,,fig4#cc4--,,responses ,,to ,,increasing ,,stimuli ,,produced ,,by ,,increasing ,,angle ,,of ,,vibration 7a7 ,record with a specimen of fresh radish4 ,stimuli applied at intervals of two minutes4 ,the record is taken for one minute4 7b7 ,record for stale radish4 ,there is a reversed response for the feeble stimulus of #e vibration4 #c4 ,as an extreme instance of the case just cited1 ,i have often come across a curious phenomenon4 ,during the gradual increase of the stimulus from a low value there would be apparently no response4 ,but when a critical value was reached a maximum response would suddenly occur1 and would not be exceeded when the stimulus was further increased4 ,here we have a parallel to what is known in animal physiology as the 'all or none' principle4 ,with the cardiac muscle1 for example1 there is a certain minimal intensity which is effective in producing response1 but further increase of stimulus produces no increase in response4 #d4 ,from an inspection of the records of responses which are given1 it will be seen that the slope of a curve which shows the relation of stimulus to response will at first be slight1 the curve will then ascend rapidly1 and at high values of stimulus tend to become horizontal4 ,the curve as a whole becomes1 first slightly convex to the abscissa1 then straight and ascending1 and lastly concave4 ,a far more pronounced convexity in the first part is shown in some cases1 especially when the specimen is stale4 ,this is due to the fact that under these circumstances response is apt to begin with an actual reversal of sign1 the plant under feebler than a certain critical intensity of stimulus giving positive1 instead of the normal negative1 response 7fig4#cc1 b74 ,diminution of response with excessively strong stimulus4--,it is found that in animal tissues there is sometimes an actual diminution of response with excessive increase of stimulus4 ,thus ,waller finds1 in working with retina1 that as the intensity of light stimulus is gradually increased1 the response at first increases1 and then sometimes undergoes a diminution4 ,this phenomenon is unfortunately complicated by fatigue1 itself regarded as obscure4 ,it is therefore difficult to say whether the diminution of response is due to fatigue or to some reversing action of an excessively strong stimulus4 ,from fig4#cc1 b1 above1 it is seen that there was an actual reversal of response in the lower portion of the curve4 ,it is therefore not improbable that there may be more than one point of reversal4 ,in physical phenomena we are1 however1 acquainted with numerous instances of reversals4 ,for example1 a common effect of magnetisation is to produce an elongation of an iron rod4 ,but ,bidwell finds that as the magnetising force is pushed to an extreme1 at a certain point elongation ceases and is succeeded1 with further increase of magnetising force1 by an actual contraction4 ,again a photographic plate1 when exposed continuously to light1 gives at first a negative image4 ,still longer exposure produces a positive4 ,then again we have a negative4 ,there is thus produced a series of recurrent reversals4 ,in photographic prints of flashes of lightning1 two kinds of images are observed1 one1 the positive--when the lightning discharge is moderately intense--and the other1 negative1 the so-called 'dark lightning'--due to the reversal action of an intensely strong discharge4 ,in studying the changes of conductivity produced in metallic particles by the stimulus of ,hertzian radiation1 ,i have often noticed that whereas feeble radiation produces one effect1 strong radiation produces the opposite4 ,again1 under the continuous action of electric radiation1 ,i have frequently found recurrent reversals4#ac ,diminution of response under strong stimulus traced to fatigue4--,but there are instances in plant response where the diminution effect can be definitely traced to fatigue4 ,the records of these cases are extremely suggestive as to the manner in which the diminution is brought about4 ,the accompanying figures 7fig4#cd7 give records of responses to increasing stimulus4 ,they were made with specimens of cauliflower-stalks1 one of which 7a7 showed little fatigue1 while in the other 7b7 fatigue was present4 ,it will be seen that the curves obtained by joining the apices of the successive single responses are very similar4 ,illustration3 ,,fig4#cd4--,,responses ,,to ,,increasing ,,stimulus ,,obtained ,,with ,,two ,,specimens ,,of ,,stalk ,,of ,,cauliflower ,in 7a7 fatigue is absent1 in 7b7 it is present4 ,in one case there is no fatigue1 the recovery from each stimulus being complete4 ,every response in the series therefore starts from a position of perfect equilibrium1 and the height of the single responses increases with increasing stimulation4 ,but in the second case1 the strain is not completely removed after any single stimulation of the series4 ,that recovery is partial is seen by the gradual shifting of the base line upwards4 ,in the former case the base line is horizontal and represents a condition of complete equilibrium4 ,now1 however1 the base line1 or line of modified equilibrium1 is tilted upwards4 ,thus even in this case if we measure the heights of successive responses from the line of absolute equilibrium1 they will be found to increase with increasing stimulus4 ,ordinarily1 however1 we make no allowance for the shifting of the base line1 measuring response rather from the place of its previous recovery1 or from the point of modified equilibrium4 ,judged in this way1 the responses undergo an apparent diminution4 ,,footnotes3 #ac ,see ',on ,electric ,touch1' ,proc4 ,roy4 ,soc4 ,aug4#aijj4 ,,chapter ,,viii ,,plant ,,response--,,on ,,the ,,influence ,,of ,,temperature ,effect of very low temperature--,influence of high temperature--,determination of death-point--,increased response as after-effect of temperature variation--,death of plant and abolition of response by the action of steam4 ,for every plant there is a range of temperature most favourable to its vital activity4 ,above this optimum1 the vital activity diminishes1 till a maximum is reached1 when it ceases altogether1 and if this point be maintained for a long time the plant is apt to be killed4 ,similarly1 the vital activity is diminished if the temperature be lowered below the optimum1 and again1 at a minimum point it ceases1 while below this minimum the plant may be killed4 ,we may regard these maximum and minimum temperatures as the death-points4 ,some plants can resist these extremes better than others4 ,length of exposure1 it should however be remembered1 is also a determining factor in the question as to whether or not the plant shall survive unfavourable conditions of temperature4 ,thus we have hardy plants1 and plants that are affected by excessive variations of temperature4 ,within the characteristic power of the species1 there may be1 again1 a certain amount of individual difference4 ,these facts being known1 ,i was anxious to determine whether the undoubted changes induced by temperature in the vital activity of plants would affect electrical response4 ,effect of very low temperature4--,as regards the influence of very low temperature1 ,i had opportunities of studying the question on the sudden appearance of frost4 ,in the previous week1 when the temperature was about #aj;,c41 ,i had obtained strong electric response in radishes whose value varied from #je to #avolt4 ,but two or three days later1 as the effect of the frost1 ,i found electric response to have practically disappeared4 ,a few radishes were1 however1 found somewhat resistant1 but the electric response had1 even in these cases1 fallen from the average value of #jge,v4 under normal temperature to #jjc,v4 after the frost4 ,that is to say1 the average sensitiveness had been reduced to about #a_/beth4 ,on warming the frost-bitten radish to #bj;,c4 there was an appreciable revival1 as shown by increase in response4 ,in specimens where the effect of frost had been very great1 i4e4 in those which showed little or no electric response1 warming did not restore responsiveness4 ,from this it would appear that frost killed some1 which could not be subsequently revived1 whereas others were only reduced to a condition of torpidity1 from which there was revival on warming4 ,i now tried the effect of artificial lowering of temperature on various plants4 ,a plant which is very easily affected by cold is a certain species of ,eucharis lily4 ,i first obtained responses with the leaf-stalk of this lily at the ordinary temperature of the room 7#ag;,c474 ,i then placed it for fifteen minutes in a cooling chamber1 temperature -#b;,c41 for only ten minutes1 after which1 on trying to obtain response1 it was found to have practically disappeared4 ,i now warmed the plant by immersing it for awhile in water at #bj;,c41 and this produced a revival of the response 7fig4#ce74 ,if the plant be subjected to low temperature for too long a time1 there is then no subsequent revival4 ,illustration3 ,,fig4#ce4--;,,diminution ,,of ,,response ,,in ,,eucharis ,,by ,,lowering ,,of ,,temperature 7a7 ,normal response at #ag;,c4 7b7 ,the response almost disappears when plant is subjected to -#b;,c4 for fifteen minutes4 7c7 ,revival of response on warming to #bj;,c4 ,i obtained a similar marked diminution of response with the flower-stalk of ,arum lily1 on lowering the temperature to zero4 ,my next attempt was to compare the sensibility of different plants to the effect of lowered temperatures4 ,for this purpose ,i chose three specimens3 7#a7 ,eucharis lily2 7#b7 ,ivy2 and 7#c7 ,holly4 ,i took their normal response at #ag;,c41 and found that1 generally speaking1 they attained a fairly constant value after the third or fourth response4 ,after taking these records of normal response1 ,i placed the specimens in an ice-chamber1 temperature #j;,c41 for twenty-four hours1 and afterwards took their records once more at the ordinary temperature of the room4 ,from these it will be seen that while the responsiveness of ,eucharis lily1 known to be susceptible to the effect of cold1 had entirely disappeared1 that of the hardier plants1 ,holly and ,ivy1 showed very little change 7fig4#cf74 ,another very curious effect that ,i have noticed is that when a plant approaches its death-point by reason of excessively high or low temperature1 not only is its general responsiveness diminished almost to zero1 but even the slight response occasionally becomes reversed4 ,illustration3 ,,fig4#cf4--;,,after-,,effect ,,of ,,cold ,,on ,,ivy1 ,,holly1 ,,and ,,eucharis ,,lily a4 ,the normal response2 b4 ,response after subjection to freezing temperature for twenty-four hours4 ,influence of high temperature1 and determination of death-point4--,i next tried to find out whether a rise of temperature produced a depression of response1 and whether the response disappeared at a maximum temperature--the temperature of death-point4 ,for this purpose ,i took a batch of six radishes and obtained from them responses at gradually increasing temperatures4 ,these specimens were obtained late in the season1 and their electric responsiveness was much lower than those obtained earlier4 ,the plant1 previously kept for five minutes in water at a definite temperature 7say #ag;,c471 was mounted in the vibration apparatus and responses observed4 ,the plant was then dismounted1 and replaced in the water-bath at a higher temperature 7say #cj;,c47 again1 for five minutes4 ,a second set of responses was now taken4 ,in this way observations were made with each specimen till the temperature at which response almost or altogether ceased was reached4 ,i give below a table of results obtained with six specimens of radish1 from which it would appear that response begins to be abolished in these cases at temperatures varying from #ec to #ee;,c4 ,,table ,,showing ,,effect ,,of ,,high ,,temperature ,,in ,,abolishing ,,response ,temperature ,galvanometric response 7#ajj;dns4 #jg,v47 7#a7 #ag;,c #gj dns4 #ec #d 7#b7 #ag #afj #ec #a 7#c7 #ag #ajj #ej #b 7#d7 #ag #hj #ee #j 7#e7 #ag #dj #fj #j 7#f7 #ag #fj #ee #j ,illustration3 ,,fig4#cg4--,,the ,,glass ,,chamber ,,containing ,,the ,,plant ,amplitude of vibration which determines the intensity of stimulus is measured by the graduated circle seen to the right4 ,temperature is regulated by the electric heating coil ,r4 ,for experiments on action of ansthetics1 vapour of chloroform is blown in through the side tube4 ,electric heating4--,the experiments just described were1 however1 rather troublesome1 inasmuch as1 in order to produce each variation of temperature1 the specimen had to be taken out of the apparatus1 warmed1 and remounted4 ,i therefore introduced a modification by which this difficulty was obviated4 ,the specimen was now enclosed in a glass chamber 7fig4#cg71 which also contained a spiral of ,german-silver wire1 through which electric currents could be sent1 for the purpose of heating the chamber4 ,by varying the intensity of the current1 the temperature could be regulated at will4 ,the specimen chosen for experiment was the leaf-stalk of celery4 ,it was kept at each given temperature for ten minutes1 and two records were taken during that time4 ,it was then raised by #aj;,c41 and the same process was repeated4 ,it will be noticed from the record 7fig4#ch7 that in this particular case1 as the temperature rose from #bj;,c4 to #cj;,c41 there was a marked diminution of response4 ,at the same time1 in this case at least1 recovery was quicker4 ,at #bj;,c41 for example1 the response was #ba;dns41 and the recovery was not complete in the course of a minute4 ,at #cj;,c41 however1 the response had been reduced to #ge;divisions1 but there was almost complete recovery in twelve seconds4 ,as the temperature was gradually increased1 a continuous decrease of response occurred4 ,this diminution of response with increased temperature appears to be universal1 but the quickening of recovery may be true of individual cases only4 ,illustration3 ,,fig4#ch4--;,,effect ,,of ,,temperature ,,on ,,response ,the response was abolished at the hot-water temperature of #ee;,c4 ,,table ,,showing ,,diminution ,,of ,,response ,,with ,,increasing ,,temperature 7#ja,volt #ce;divisions7 ,temperature ,response #bj #ba #cj #ge #dj #ee #ej #d #fe #c ,in radishes response disappeared completely at #ee;,c41 but with celery1 heated in the manner described1 ,i could not obtain its entire abolition at #fj;,c4 or even higher4 ,a noticeable circumstance1 however1 was the prolongation of the period of recovery at these high temperatures4 ,i soon understood the reason of this apparent anomaly4 ,the method adopted in the present case was that of dry heating1 whereas the previous experiments had been carried on by the use of hot water4 ,it is well known that one can stand a temperature of #ajj;,c4 without ill effects in the hot-air chamber of a ,turkish bath1 while immersion in water at #ajj;,c4 would be fatal4 ,in order to find out whether subjection to hot water would kill the celery-stalk1 ,i took it out and placed it for five minutes in water at #ee;,c4 ,this1 as will be seen from the record taken afterwards1 effectively killed the plant 7fig4#ch1 w74 ,illustration3 ,,fig4#ci4--;,,effect ,,of ,,rising ,,and ,,falling ,,temperature ,,on ,,the ,,response ,,of ,,scotch ,,kale ,increased sensitiveness as after-effect of temperature variation4--,a very curious effect of temperature variation is the marked increase of sensitiveness which often appears as its after-effect4 ,i noticed this first in a series of observations where records were taken during the rise of temperature and continued while the temperature was falling 7fig4#ci74 ,the temperature was adjusted by electric heating4 ,it was found that the responses were markedly enhanced during cooling1 as compared with responses given at the same temperatures while warming 7see table74 ,temperature variation thus seems to have a stimulating effect on response1 by increasing molecular mobility in some way4 ,the second record 7fig4#dj7 shows the variation of response in ,eucharis lily 7#a7 during the rise1 and 7#b7 during the fall of temperature4 ,fig4#da gives a curve of variation of response during the rise and fall of temperature4 ,,table ,,showing ,,the ,,variation ,,of ,,response ,,in ,,scotch ,,kale ,,during ,,the ,,rise ,,and ,,fall ,,of ,,temperature ,temperature ,response ,response ,temperature rising ,temperature falling #ai;,c4 #dg dns4 -- #be #bd -- #cj #aa #bc dns4 #ej #h #af #gj v #g -- ----- ,illustration3 ,,fig4#dj4--,,records ,,of ,,responses ,,in ,,eucharis ,,lily ,,during ,,rise ,,and ,,fall ,,of ,,temperature ,stimulus constant1 applied at intervals of one minute4 ,the temperature of plant-chamber gradually rose on starting current in the heating coil2 on breaking current1 the temperature fell gradually4 ,temperature corresponding to each record is given below4 ,temperature rising3 7#a7bj1 7#b7bj1 7#c7bb1 7#d7ch1 7#e7ec1 7#f7fh1 7#g7fe4 ,temperature falling3 7#h7fj1 7#i7ea1 7#aj7de1 7#aa7dj1 7#ab7ch4 ,point of temperature maximum4--,we have seen how1 in cases of lowered temperature1 response is abolished earlier in plants like ,eucharis1 which are affected by cold1 than in the hardier plants such as ,holly and ,ivy4 ,plants again are unequally affected as regards the upper range4 ,in the case of ,scotch kale1 for instance1 response disappears after ten minutes of water temperature of about #ee;,c41 but with ,eucharis fairly marked response can still be obtained after such immersion and does not disappear till it has been subjected for ten minutes to hot water1 at a temperature of #fe;,c4 or even higher4 ,the reason of this great power of resistance to heat is probably found in the fact that the ,eucharis is a tropical plant1 and is grown1 in this country1 in hot-houses where a comparatively high temperature is maintained4 ,illustration3 ,,fig4#da4--;,,curve ,,showing ,,variation ,,of ,,response ,,in ,,eucharis ,,with ,,the ,,rise ,,and ,,fall ,,of ,,temperature ,the effect of steam4--,i next wished to obtain a continuous record by which the effects of suddenly increased temperatures1 culminating in the death of the plant1 might be made evident4 ,for this purpose ,i mounted the plant in the glass chamber1 into which steam could be introduced4 ,i had chosen a specimen which gave regular response4 ,on the introduction of steam1 with the consequent sudden increase of temperature1 there was a transitory augmentation of excitability4 ,but this quickly disappeared1 and in five minutes the plant was effectively killed1 as will be seen graphically illustrated in the record 7fig4#db74 ,illustration3 ,,fig4#db4--;,,effect ,,of ,,steam ,,in ,,killing ,,response ,the two records to the left exhibit normal response at #ag;,c4 ,sudden warming by steam produced at first an increase of response1 but five minutes exposure to steam killed the plant 7carrot7 and abolished the response4 ,vibrational stimulus of #cj applied at intervals of one minute2 vertical line #avolt4 ,it will thus be seen that those modifications of vital activity which are produced in plants by temperature variation can be very accurately gauged by electric response4 ,indeed it may be said that there is no other method by which the moment of cessation of vitality can be so satisfactorily distinguished4 ,ordinarily1 we are able to judge that a plant has died1 only after various indirect effects of death1 such as withering1 have begun to appear4 ,but in the electric response we have an immediate indication of the arrest of vitality1 and we are thereby enabled to determine the death-point1 which it is impossible to do by any other means4 ,it may be mentioned here that the explanation suggested by ,kunkel1 of the response being due to movement of water in the plant1 is inadequate4 ,for in that case we should expect a definite stimulation to be under all conditions followed by a definite electric response1 whose intensity and sign should remain invariable4 ,but we find1 instead1 the response to be profoundly modified by any influence which affects the vitality of the plant4 ,for instance1 the response is at its maximum at an optimum temperature1 a rise of a few degrees producing a profound depression2 the response disappears at the maximum and minimum temperatures1 and is revived when brought back to the optimum4 ,ansthetics and poisons abolish the response4 ,again1 we have the response undergoing an actual reversal when the tissue is stale4 ,all these facts show that mere movement of water could not be the effective cause of plant response4 ,,chapter ,,ix ,,plant ,,response--,,effect ,,of ,,an,,sthetics ,,and ,,poisons ,effect of ansthetics1 a test of vital character of response--,effect of chloroform--,effect of chloral--,effect of formalin--,method in which response is unaffected by variation of resistance--,advantage of block method--,effect of dose4 ,the most important test by which vital phenomena are distinguished is the influence on response of narcotics and poisons4 ,for example1 a nerve when narcotised by chloroform exhibits a diminishing response as the action of the ansthetic proceeds4 7,see below1 fig4#dc47 ,similarly1 various poisons have the effect of permanently abolishing all response4 ,thus a nerve is killed by strong alkalis and strong acids4 ,i have already shown how plants which previously gave strong response did not1 after application of an ansthetic or poison1 give any response at all4 ,in these cases it was the last stage only that could be observed4 ,but it appeared important to be able to trace the growing effect of ansthetisation or poisoning throughout the process4 ,there were1 however1 two conditions which it at first appeared difficult to meet4 ,first it was necessary to find a specimen which would normally exhibit no fatigue1 and give rise for a long time to a uniform series of response4 ,the immediate changes made in the response1 in consequence of the application of chemical reagents1 could then be demonstrated in a striking manner4 ,and with a little trouble1 specimens can be secured in which perfect regularity of response is found4 ,the record given in fig4#af1 obtained with a specimen of radish1 shows how possible it is to secure plants in which response is absolutely regular4 ,i subjected this to uniform stimulation at intervals of one minute1 during half an hour1 without detecting the least variation in the responses4 ,but it is of course easier to find others in which the responses as a whole may be taken as regular1 though there may be slight rhythmic fluctuations4 ,and even in these cases the effect of reagents is too marked and sudden to escape notice4 ,illustration3 ,,fig4#dc4--;,,effect ,,of ,,chloroform ,,on ,,nerve ,,response 7,,waller7 ,for the obtaining of constant and strong response ,i found the best materials to be carrot and radish1 selected individuals from which gave most satisfactory results4 ,the carrots were at their best in ,august and ,september1 after which their sensitiveness rapidly declined4 ,later1 being obliged to seek for other specimens1 ,i came upon radish1 which gave good results in the early part of ,november2 but the setting-in of the frost had a prejudicial effect on its responsiveness4 ,less perfect than these1 but still serviceable1 are the leaf-stalks of turnip and cauliflower4 ,in these the successive responses as a whole may be regarded as regular1 though a curious alternation is sometimes noticed1 which1 however1 has a regularity of its own4 ,my second misgiving was as to whether the action of reagents would be sufficiently rapid to display itself within the time limit of a photographic record4 ,this would of course depend in turn upon the rapidity with which the tissues of the plant could absorb the reagent and be affected by it4 ,it was a surprise to me to find that1 with good specimens1 the effect was manifested in the course of so short a time as a minute or so4 ,effect of chloroform4--,in studying the effect of chemical reagents in plants1 the method is precisely similar to that employed with nerve2 that is to say1 where vapour of chloroform is used1 it is blown into the plant chamber4 ,in cases of liquid reagents1 they are applied on the points of contact ,a and ,b and their close neighbourhood4 ,the mode of experiment was 7#a7 to obtain a series of normal responses to uniform stimuli1 applied at regular intervals of time1 say one minute1 the record being taken the while on a photographic plate4 7#b7 ,without interrupting this procedure1 the ansthetic agent1 vapour of chloroform1 was blown into the closed chamber containing the plant4 ,it will be seen how rapidly chloroform produces depression of response 7fig4#dd71 and how the effect grows with time4 ,in these experiments with plants1 the same curious shifting of the zero line is sometimes noticed as in nerve when subjected similarly to the action of reagents4 ,this is a point of minor importance1 the essential point to be noticed being that the responses are rapidly reduced4 ,illustration3 ,,fig4#dd4--;,,effect ,,of ,,chloroform ,,on ,,responses ,,of ,,carrot ,stimuli of #be vibration at intervals of one minute4 ,effects of chloral and formalin4--,i give below 7figs4 #de1 #df7 two sets of records1 one for the reagent chloral and the other for formalin4 ,the reagents were applied in the form of a solution on the tissue at the two leading contacts1 and the contiguous surface4 ,the rhythmic fluctuation in the normal response shown in fig4#de is interesting4 ,the abrupt decline1 within a minute of the application of chloral1 is also extremely well marked4 ,illustration3 ,,fig4#de4--;,,action ,,of ,,chloral ,,hydrate ,,on ,,the ,,responses ,,of ,,leaf-,,stalk ,,of ,,cauliflower ,vibration of #be at intervals of one minute4 ,illustration3 ,,fig4#df4--;,,action ,,of ,,formalin 7,,radish7 ,response unaffected by variation of resistance4--,in order to bring out clearly the main phenomena1 ,i have postponed till now the consideration of a point of some difficulty4 ,to determine the influence of a reagent in modifying the excitability of the tissue1 we rely upon its effect in exalting or depressing the responsive ,e4,m4 variation4 ,we read this effect by means of galvanometric deflections4 ,and if the resistance of the circuit remained constant1 then an increase of galvanometer deflection would accurately indicate a heightened or depressed ,e4,m4 response1 due to greater or less excitability of tissue caused by the reagent4 ,but1 by the introduction of the chemical reagent1 the resistance of the tissue may undergo change1 and owing to this cause1 modification of response as read by the galvanometer may be produced without any ,e4,m4 variation4 ,the observed variation of response may thus be partly owing to some unknown change of resistance1 as well as to that of the ,e4,m4 variation in response to stimulus4 ,we may however discriminate as to how much of the observed change is due to variation of resistance by comparing the deflections produced in the galvanometer by the action of a definite small ,e4,m4,f4 before and after the introduction of the reagent4 ,if the deflections be the same in both cases1 we know that the resistance has not varied4 ,if there have been any change1 the variation of deflection will show the amount1 and we can make allowance accordingly4 ,i have however adopted another method1 by which all necessity of correction is obviated1 and the galvanometric deflections simply give ,e4,m4 variations1 unaffected by any change in the resistance of the tissue4 ,this is done by interposing a very large and constant resistance in the external circuit and thereby making other resistances negligible4 ,an example will make this point clear4 ,taking a carrot as the vegetable tissue1 ,i found its resistance plus the resistance of the non-polarisable electrode equal to #bj1jjjohms4 ,the introduction of a chemical reagent reduced it to #ai1jjjohms4 ,the resistance of the galvanometer is equal to #a1jjjohms4 ,the high external resistance was #a1jjj1jjjohms4 ,the variation of resistance produced in the circuit would therefore be #a1jjj in 7#a1jjj1jjjai1jjja1jjj7 or one part in #a1jbj4 ,therefore the variation of galvanometric deflection due to change of resistance would be less than one part in a thousand 7cf4 fig4#di74 ,the advantage of the block method4--,in these investigations ,i have used the block method1 instead of that of negative variation1 and ,i may here draw attention to the advantages which it offers4 ,in the method of negative variation1 one contact being injured1 the chemical reagents act on injured and uninjured unequally1 and it is conceivable that by this unequal action the resting difference of potential may be altered4 ,but the intensity of response in the method of injury depends on this resting difference4 ,it is thus hypothetically possible that on the method of negative variation there might be changes in the responses caused by variation of the resting difference1 and not necessarily due to the stimulating or depressing effect of the reagent on the tissue4 ,but by the block method the two contacts are made with uninjured surfaces1 and the effect of reagents on both is similar4 ,thus no advantage is given to one contact over the other4 ,the changes now detected in response are therefore due to no adventitious circumstance1 but to the reagent itself4 ,if further verification be desired as to the effect of the reagent1 we can obtain it by alternate stimulation of the ,a and ,b ends4 ,both ends will then show the given change4 ,i give below a record of responses given by two ends of leaf-stalk of turnip1 stimulated alternately in the manner described4 ,the stalk used was slightly conical1 and owing to this difference between the ,a and ,b ends the responses given by one end were slightly different from those given by the other1 though the stimuli were equal4 ,a few drops of #ajpercent4 solution of ,na,o,h was applied to both the ends4 ,it will be seen how quickly this reagent abolished the response of both ends 7fig4#dg74 ,illustration3 ,,fig4#dg4--;,,abolition ,,of ,,response ,,at ,,both ,a ,,and ,b ,,ends ,,by ,,the ,,action ,,of ,na,o,h ,stimuli of #cj vibration were applied at intervals of one minute to ,a and ,b alternately4 ,response was completely abolished twenty-four minutes after application of ,na,o,h4 ,effect of dose4--,it is sometimes found that while a reagent acts as a poison when given in large quantities1 it may act as a stimulant in small doses4 ,of the two following records fig4#dh shows the slight stimulating effect of very dilute ,,koh1 and fig4#di exhibits nearly complete abolition of response by the action of the same reagent when given in stronger doses4 ,illustration3 ,,fig4#dh4--,,stimulating ,,action ,,of ,,very ,,dilute ,,koh ,so we see that1 judged by the final criterion of the effect produced by ansthetics and poisons1 the plant response fulfils the test of vital phenomenon4 ,in previous chapters we have found that in the matter of response by negative variation1 of the presence or absence of fatigue1 of the relation between stimulus and response1 of modification of response by high and low temperatures1 and even in the matter of occasional abnormal variations such as positive response in a modified tissue1 they were strictly correspondent to similar phenomena in animal tissues4 ,the remaining test1 of the influence of chemical reagents1 having now been applied1 a complete parallelism may be held to have been established between plant response on the one hand1 and that of animal tissue on the other4 ,illustration3 ,,fig4#di4--,,nearly ,,complete ,,abolition ,,of ,,response ,,by ,,strong ,,koh ,the two vertical lines are galvanometer deflections due to #avolt1 before and after the application of reagent4 ,it will be noticed that the total resistance remains unchanged4 ,,chapter ,x ,,response ,,in ,,metals ,is response found in inorganic substances8--,experiment on tin1 block method--,anomalies of existing terminology--,response by method of depression--,response by method of exaltation4 ,we have now seen that the electrical sign of life is not confined to animals1 but is also found in plants4 ,and we have seen how electrical response serves as an index to the vital activity of the plant1 how with the arrest of this vital activity electrical response is also arrested temporarily1 as in the case amongst others of ansthetic action1 and permanently1 for instance under the action of poisons4 ,thus living tissues--both animal and vegetable--may pass from a responsive to an irresponsive condition1 from which latter there may or may not be subsequent revival4 ,hitherto1 as already said1 electrical response in animals has been regarded as a purely physiological phenomenon4 ,we have proved by various tests that response in plants is of the same character4 ,and we have seen that by physiological phenomena are generally understood those of which no physical explanation can be offered1 they being supposed to be due to the play of some unknown vital force existing in living substances and giving rise to electric response to stimulation as one of its manifestations4 ,is response found in inorganic substances8#ad--;,it is now for us1 however1 to examine into the alleged super-physical character of these phenomena by stimulating inorganic substances and discovering whether they do or do not give rise to the same electrical mode of response which was supposed to be the special characteristic of living substances4 ,we shall use the same apparatus and the same mode of stimulation as those employed in obtaining plant response1 merely substituting1 for the stalk of a plant1 a metallic wire1 say 'tin' 7fig4#ej74 ,any other metal could be used instead of tin4 ,experiment on tin1 block method4--,let us then take a piece of tin wire#ae from which all strains have been previously removed by annealing1 and hold it clamped in the middle at ,c4 ,if the strains have been successfully removed ,a and ,b will be found iso-electric1 and no current will pass through the galvanometer4 ,if ,a and ,b are not exactly similar1 there will be a slight current4 ,but this will not materially affect the results to be described presently1 the slight existing current merely adding itself algebraically to the current of response4 ,if we now stimulate the end ,a by taps1 or better still by torsional vibration1 a transitory 'current of action' will be found to flow in the wire from ,b to ,a1 from the unstimulated to the stimulated1 and in the galvanometer from the stimulated to the unstimulated4 ,stimulation of ,b will give rise to a current in an opposite direction4 ,illustration3 ,,fig4#ej4--;,,electric ,,response ,,in ,,metals 7a7 ,method of block2 7b7 ,equal and opposite responses when the ends ,a and ,b are stimulated2 the dotted portions of the curves show recovery2 7c7 ,balancing effect when both the ends are stimulated simultaneously4 ,experiment to exhibit the balancing effect4--,if the wire has been carefully annealed1 the molecular condition of its different portions is found to be approximately the same4 ,if such a wire be held at the 'balancing point' 7which is at or near the middle7 by the clamp1 and a quick vibration1 say1 of #ij be given to ,a1 an upward deflection will be produced2 if a vibration of #ij be given to ,b1 there will be an equal downward deflection4 ,if now both the ends ,a and ,b are vibrated simultaneously1 the responsive ,e4,m4 variation at the two ends will continuously balance each other and the galvanometer spot will remain quiescent 7fig4#cj1 ,a1 ,b1 ,r74 ,this balance will be still maintained when the block is removed and the wire is vibrated as a whole4 ,it is to be remembered that with the length of wire constant1 the intensity of stimulus increases with the amplitude of vibration4 ,again1 keeping the amplitude constant1 the intensity of stimulus is increased by shortening the wire4 ,hence it will be seen that if the clamp be shifted from the balancing point towards ,a1 simultaneous vibration of ,a and ,b through #ij will now give a resultant upward deflection1 showing that the ,a response is now relatively stronger4 ,thus keeping the rest of the circuit untouched1 merely moving the clamp from the left1 past the balancing point to the right1 we get either a positive1 or zero1 or negative1 resultant effect4 ,in tin the current of response is from the less to the more excited point4 ,in the retina also1 we found the current of action flowing from the less stimulated to the more stimulated1 and as that is known as a positive response1 we shall consider the normal response of tin to be in like manner positive4 ,just as the response of retina or nerve1 under certain molecular conditions1 undergoes reversal1 the positive being then converted into negative1 and negative into positive1 so it will be shown that the response in metallic wires under certain conditions is found to undergo reversal4 ,anomalies of present terminology4--,when there is no current of injury1 a particular current of response can hardly be called a negative1 or positive1 variation4 ,such nomenclature is purely arbitrary1 and leads1 as will be shown1 to much confusion4 ,a more definite terminology1 free from misunderstanding1 would be1 as already said1 to regard the current towards the more stimulated as positive1 and that towards the less stimulated1 in tissue or wire1 as negative4 ,the stimulated end of tin1 say the end ,a1 thus becomes zincoid1 i4e4 the current through the electrolyte 7non-polarisable electrodes with interposed galvanometer7 is from ,a to ,b1 and through the wire1 from the less stimulated ,b to the more stimulated ,a4 ,conversely1 when ,b is stimulated1 the action current flows round the circuit in an opposite direction4 ,this positive is the most usual form of response1 but there are cases where the response is negative4 ,in order to show that normally speaking a stimulated wire becomes zincoid1 and also to show once more the anomalies into which we may fall by adopting no more definite terminology than that of negative variation1 ,i have devised the following experiment 7fig4#ea74 ,let us take a bar1 one half of which is zinc and the other half copper1 clamped in the middle1 so that a disturbance produced at one end may not reach the other2 the two ends are connected to a galvanometer through non-polarisable electrodes4 ,the current through the electrolyte 7non-polarisable electrodes and interposed galvanometer7 will then flow from left to right4 ,we must remember that metals under stimulation generally become1 in an electrical sense1 more zinc-like4 ,on vibrating the copper end 7inasmuch as copper would then become more zinc-like7 the difference of potential between zinc and copper ought to be diminished1 and the current flowing in the circuit would therefore be lessened4 ,but vibration of the zinc end ought to increase the potential difference1 and there ought to be then an increase of current during stimulation of zinc4 ,illustration3 ,,fig4#ea4--;,,current ,,of ,,response ,,towards ,,the ,,stimulated ,,end ,hence when ,cu stimulated3 action current --1 normal ,e4,m4,f4 diminished 7#he-jji7 ,v4 ,when ,zn stimulated3 action current --1 normal ,e4,m4,f4 increased 7#hejac7 ,v4 ,in the particular experiment of fig4#ea1 the ,e4,m4,f4 between the zinc and copper ends was found to be #hevolt4 ,this was balanced by a potentiometer arrangement1 so that the galvanometer spot came to zero4 ,on vibrating the zinc wire1 a deflection of #cc;dns4 was obtained1 in a direction which showed an increase of ,e4,m4,f4 ,on stopping the vibration1 the spot of light came back to zero4 ,on now vibrating the copper wire1 a deflection of #bc;dns4 was obtained in an opposite direction1 showing a diminution of ,e4,m4,f4 ,this transitory responsive variation disappeared on the cessation of disturbance4 ,by disturbing the balance of the potentiometer1 the galvanometer deflection due to a known increase of ,e4,m4,f4 was found from which the absolute ,e4,m4 variation caused by disturbance of copper or zinc was determined4 ,it was thus found that stimulation of zinc had increased the ,p4,d4 by fifteen parts in #a1jjj1 whereas stimulation of copper had decreased it by eleven parts in #a1jjj4 ,according to the old terminology1 the response due to stimulation of zinc would have been regarded as positive variation1 that of copper negative4 ,the responses however are not essentially opposite in character1 the action current in the bar being in both cases towards the more excited4 ,for this reason it would be preferable1 as already said1 to employ the terms positive and negative in the sense ,i have suggested1 i4e4 positive1 when the current in the acted substance is towards the more excited1 and negative1 when towards the less excited4 ,the method of block is1 as ,i have already shown1 the most perfect for the study of these responses4 ,in the experiment fig4#ej1 if the block is abolished and the wire is struck in the middle1 a wave of molecular disturbance will reach ,a and ,b4 ,the mechanical and the attendant electrical disturbance will at these points reach a maximum and then gradually subside4 ,the resultant effect in the galvanometer will be due to ,e,a-,e,b when ,e,a and ,e,b are the electrical variations produced at ,a and ,b by the stimulus4 ,the electric changes at ,a and ,b will continuously balance each other1 and the resultant effect on the galvanometer will be zero3 7a7 if the exciting disturbance reaches ,a and ,b at the same time and with the same intensity2 7b7 if the molecular condition is similar at the two points2 and 7c7 if the rate of rise and subsidence of excitation is the same at the two points4 ,in order that a resultant effect may be exhibited in the galvanometer1 matters have to be so arranged that the disturbance may reach one point1 say ,a1 and not ,b1 and vice versa4 ,this was accomplished by means of a clamp1 in the method of block4 ,again a resultant differential action may be obtained even when the disturbance reaches both ,a and ,b1 if the electrical excitability of one point is exalted or depressed by physical or chemical means4 ,we shall in ,chap4 ,,xvi study in detail the effect of chemical reagents in producing the enhancement or depression of excitability4 ,there are thus two other means of obtaining a resultant effect--7#b7 by the method of relative depression1 7#c7 by the method of relative exaltation4 ,electric response by method of depression4--,we may thus by reducing or abolishing the excitability of one end by means of suitable chemical reagents 7so-called method of injury7 obtain response in metals without a block4 ,the entire length of the wire may then be stimulated and a resultant response will be produced1 owing to the difference between the excitability of the two ends4 ,a piece of tin wire is taken1 and one normal contact is made at ,a 7strip of cloth moistened with water1 or very dilute salt solution74 ,the excitability of ,b is depressed by a few drops of strong potash or oxalic acid4 ,by the application of the latter there will be a small ,p4,d4 between ,a and ,b2 this will simply produce a displacement of zero4 ,by means of a potentiometer the galvanometer spot may be brought back to the original position4 ,the shifting of the zero will not affect the general result4 ,the effect of mechanical stimulus is to produce a transient electro-motive response1 which will be superposed algebraically on the existing ,p4,d4 ,the deflection will take place from the modified zero to which the spot returns during recovery4 ,on now stimulating the wire as a whole by1 say1 torsional vibration1 the current of response will be found towards the more excitable1 i4e4 from ,b to ,a 7fig4#eb1 a74 ,illustration3 ,,fig4#eb4--,,response ,,by ,,method ,,of ,,depression 7,,without ,,block7 ,when the wire is stimulated as a whole the current of response is towards the more excitable4 ,in 7a7 ,a is a normal contact1 ,b has been depressed by oxalic acid2 current of response is towards the more excitable ,a4 ,in 7b7 the same wire is used1 only ,a is depressed by oxalic acid and a normal contact is made at a fresh point ,b'1 a little to the left of ,b in 7a74 ,current of response is now from ,a towards the more excitable ,b'4 ,a corroborative reversal experiment may next be made on the same piece of wire4 ,the normal contact1 through water or salt solution1 is now made at ,b'1 a little to the left of ,b4 ,the excitability of ,a is now depressed by oxalic acid4 ,on stimulation of the whole wire1 the current of response will now be found to flow in an opposite direction--i4e4 from ,a to ,b'--but still from the relatively less to the relatively more excitable 7fig4#eb1 b74 ,from these experiments it will be seen how in one identical piece of wire the responsive current flows now in one direction and then in the other1 in absolute conformity with theoretical considerations4 ,method of exaltation4--,a still more striking corroboration of these results may1 however1 be obtained by the converse process of relative exaltation of the responsiveness of one contact4 ,this may be accomplished by touching one contact1 say ,b1 with a reagent which like ,na#b;,,co#c exalts the electric excitability4 ,on stimulation of the wire1 the current of response is towards the more excitable ,b 7fig4#ec74 ,illustration3 ,,fig4#ec4--,,method ,,of ,,exaltation ,the contact ,b is made more excitable by chemical stimulant 7,na#b;,,co#c74 ,the current of response is towards the more excitable ,b4 ,i give four records 7fig4#ed7 which will clearly exhibit the responses as obtained by the methods of relative depression or exaltation4 ,in 7a7 ,b is touched with the excitant ,na#b;,,co#c1 a permanent current flows from ,a to ,b1 response to stimulus is in the same direction as the permanent current 7positive variation74 ,in 7b7 ,b is touched with a trace of the depressant oxalic acid1 the permanent current is in the same direction as before1 but the current of response is in the opposite direction 7negative variation74 ,in 7c7 ,b is touched with dilute ,,kho1 the response is exhibited by a positive variation4 ,in 7d7 ,b is touched with strong ,,kho1 the response is now exhibited by a negative variation4 ,the last two results1 apparently anomalous1 are due to the fact1 which will be demonstrated later1 that ,,kho in minute quantities is an excitant1 while in large quantities it is a depressant4 ,illustration3 ,,fig4#ed ---------------------------------------- ,current ,permanent of ,current ,response ---------------------------------------- ,b treated with sodium carbonate4 -- -- ---------------------------------------- ,b treated with oxalic acid -- -- ---------------------------------------- ,b treated with very dilute potash -- -- ---------------------------------------- ,b treated with strong potash -- -- ---------------------------------------- ,current of response is always towards the more excitable point4 7a7 ,response when ,b is treated with sodium carbonate4--,an apparent positive variation4 7b7 ,response when ,b is treated with oxalic acid4--,an apparent negative variation4 7c7 ,response when ,b is treated with very dilute potash4--,positive variation4 7d7 ,response when ,b is treated with strong potash4--,negative variation4 ,the response is up when ,b is more excitable1 and down when ,a is more excitable4 ,lines thus ------ indicate deflection due to permanent current4 ,we have thus seen that we may obtain response 7#a7 by block method1 7#b7 by the method of injury1 or relative depression of responsiveness of one contact1 and 7#c7 by the method of relative exaltation of responsiveness of one contact4 ,in all these cases alike we obtain a consistent action current1 which in tin is normally positive1 or towards the relatively more excited4 ,,footnotes3 #ad ,following another line of inquiry ,i obtained response to electric stimulus in inorganic substances using the method of conductivity variation 7see ',de la ,gnralit des ,phnomnes ,molculaires ,produits par l',electricit sur la ,matire ,inorganique et sur la ,matire ,vivante1' ,travaux du ,congrs ,international de ,physique1 ,paris1 #aijj2 and also ',on ,similarities of ,effect of ,electric ,stimulus on ,inorganic and ,living ,substances1' ,british ,association #aijj4 ,see ,electrician74 ,to bring out the parallelism in all details between the inorganic and living response1 ,i have in the following chapters used the method of electro-motive variation employed by physiologists4 #ae ,by 'tin' is meant an alloy of tin and lead used as electric fuse4 ,,chapter ,,xi ,,inorganic ,,response--,,modified ,,apparatus ,,to ,,exhibit ,,response ,,in ,,metals ,conditions of obtaining quantitative measurements--,modification of the block method--,vibration cell--,application of stimulus--,graduation of the intensity of stimulus--,considerations showing that electric response is due to molecular disturbance--,test experiment--,molecular voltaic cell4 ,we have already seen that metals respond to stimulus by ,e4,m4 variation1 just as do animal and vegetable tissues4 ,we have yet to see whether the similarity extends to this point only1 or goes still further1 whether the response-curves of living and in organic are alike1 and whether the inorganic response-curve is modified1 as living response was found to be1 by the influence of external agencies4 ,if so1 are the modifications similar8 ,what are the effects of superposition of stimuli8 ,is there fatigue8 ,if there be1 in what way does it affect the curves8 ,and lastly1 is the response of metals exalted or depressed by the action of chemical reagents8 ,conditions of obtaining quantitative measurements4--,in order to carry out these investigations1 it is necessary to remove all sources of uncertainty1 and obtain quantitative measurements4 ,many difficulties at first presented themselves in the course of this attempt1 but they were completely removed by the adoption of the following experimental modification4 ,in the simple arrangement for qualitative demonstration of response in metals previously described1 successive experiments will not give results which are strictly comparable 7#a7 unless the resistance of the circuit be maintained constant4 ,this would necessitate the adoption of some plan for keeping the electrolytic contacts at ,a and ,b absolutely invariable4 ,there should then be no chance of any shifting or variation of contact4 7#b7 ,there must also be some means of applying successive stimuli of equal intensity4 7#c7 ,and for certain further experiments it will be necessary to have some way of gradually increasing or decreasing the stimuli in a definite manner4 ,modification of the block method4--,by consideration of the following experimental modifications of the block method 7fig4#ee71 it will be found easy to construct a perfected form of apparatus1 in which all these conditions are fully met4 ,the essentials to be kept in mind were the introduction of a complete block midway in the wire1 so that the disturbance of one half should be prevented from reaching the other1 and the making of a perfect electrolytic contact for the electrodes leading to the galvanometer4 ,starting from the simple arrangement previously described where a straight wire is clamped in the middle 7fig4#ee1 a71 we next arrive at 7b74 ,here the wire ,a,b is placed in a ,u tube and clamped in the middle by a tightly fitting cork4 ,melted paraffin wax is poured to a certain depth in the bend of the tube4 ,the two limbs of the tube are now filled with water1 till the ends ,a and ,b are completely immersed4 ,connection is made with the non-polarisable electrodes by the side tubes4 ,vibration may be imparted to either ,a or ,b by means of ebonite clip holders seen at the upper ends ,a,b of the wire4 ,illustration3 ,,fig4#ee4--,,successive ,,modifications ,,of ,,the ,,block ,,method ,,from ,,the ',,straight ,,wire' 7a7 ,,to ',,cell ,,form' 7e7 ,when ,a is excited1 current of response in the wire is from less excited ,b to more excited ,a4 ,note that though the current of response is constant in direction1 the galvanometer deflection in 7d7 will be opposite to that in 7b74 ,it will be seen that the two limbs of the tube filled with water serve the purpose of the strip of moistened cloth used in the last experiment to make electric connections with the leading-out electrodes--with the advantage that we have here no chance of any shifting of contact or variation of surface1 the contact between the wire and the surrounding liquid being perfect and invariable4 ,on now vibrating the end ,a of the tin wire by means of the ebonite clip holder1 a current will be found to flow from ,b to ,a through the wire--that is to say1 towards the excited--and from ,a to ,b in the galvanometer4 ,the next modification 7c7 is to transfer the galvanometer from the electrolytic to the metallic part of the circuit1 that is to say1 it is interposed in a gap made by cutting the wire ,a,b1 the upper part of the circuit being directly connected by the electrolyte4 ,vibration of ,a will now give rise to a current of response which flows in the metallic part of the circuit with the interposed galvanometer from ,b to ,a4 ,we see that though the direction of the current in this is the same as in the last case1 yet the galvanometer deflection is now reversed1 for the evident reason that we have it interposed in the metallic and not in the electrolytic part of the circuit4 ,the next arrangement 7d7 consists simply of the preceding placed upside down4 ,here ,a and ,b are held parallel to each other in an electrolytic bath 7water74 ,mechanical vibration may now be applied to ,a without affecting ,b1 and vice versa4 ,the actual apparatus1 of which this is a diagrammatic representation1 is seen in 7e74 ,two pieces1 from the same specimen of wire1 are clamped separately at their lower ends by means of ebonite screws1 in an ,l-shaped piece of ebonite4 ,the wires are fixed at their upper ends to two electrodes--leading to the galvanometer--and kept moderately and uniformly stretched by spiral springs4 ,the handle1 by which a torsional vibration is imparted to the wire1 may be slipped over either electrode4 ,the amplitude of vibration is measured by means of a graduated circle4 ,it will be seen from these arrangements3 7#a7 ,that the cell depicted in 7e7 is essentially the same as that in 7a74 7#b7 ,that the wires in the cell being immersed to a definite depth in the electrolyte there is always a perfect and invariable contact between the wire and the electrolyte4 ,the difficulty as regards variation of contact is thus eliminated4 7#c7 ,that as the wires ,a and ,b are clamped separately below1 we may impart a sudden molecular disturbance to either ,a or ,b by giving a quick to-and-fro 7torsional7 vibration round the vertical wire1 as axis1 by means of the handle4 ,as the wire ,a is separate from ,b1 disturbance of one will not affect the other4 ,vibration of ,a produces a current in one direction1 vibration of ,b in the opposite direction4 ,thus we have means of verifying every experiment by obtaining corroborative and reversed effects4 ,when the two wires have been brought to exactly the same molecular condition by the processes of annealing or stretching1 the effects obtained on subjecting ,a or ,b to any given stimulus are always equal 7fig4#ef74 ,illustration3 ,,fig4#ef4--;,,equal ,,and ,,opposite ,,responses ,,exhibited ,,by ,a ,,and ,b ,usually ,i interpose an external resistance varying from one to five megohms according to the sensitiveness of the wire4 ,the resistance of the electrolyte in the cell is thus relatively small1 and the galvanometer deflections are proportional to the ,e4,m4 variations4 ,it is always advisable to have a high external resistance1 as by this means one is not only able to keep the deflections within the scale1 but one is not troubled by slight accidental disturbances4 ,graduation of intensity of stimulus4--,if now a rapid torsional vibration be given to ,a or ,b1 an ,e4,m4 variation will be induced4 ,if the amplitude of vibration be kept constant1 successive responses--in substances which1 like tin1 show no fatigue--will be found to be absolutely identical4 ,but as 'the amplitude of vibration' is increased1 response will also become enhanced 7see ,chap4 ,,xv74 ,illustration3 ,,fig4#eg4--,,top ,,view ,,of ,,the ,,vibration ,,cell ,the amplitude of vibration is determined by means of movable stops ,s,s'1 fixed to the edge of the graduated circle ,g4 ,the index arm ,i plays between the stops4 7,the second index arm1 connected with ,b1 and the second circle are not shown47 ,amplitude of vibration is measured by means of the graduated circle 7fig4#eg74 ,a projecting index1 in connection with the vibration-head1 plays between fixed and sliding stops 7,s and ,s'71 one at the zero point of the scale1 and the other movable4 ,the amplitude of a given vibration can thus be predetermined by the adjustment of the sliding stop4 ,in this way we can obtain either uniform or definitely graduated stimuli4 ,considerations showing that electric response is due to molecular disturbance4--,the electromotive variation varies with the substance4 ,with superposition of stimuli1 a relatively high value is obtained in tin1 amounting sometimes to nearly half a volt1 whereas in silver the electromotive variation is only about #ja of this value4 ,the intensity of the response1 however1 does not depend on the chemical activity of the substance1 for the electromotive variation in the relatively chemically inactive tin is greater than that of zinc4 ,again1 the sign of response1 positive or negative1 is sometimes modified by the molecular condition of the wire 7see ,chap4 ,,xii74 ,as regards the electrolyte1 dilute ,na,cl solution1 dilute solution of bichromate of potash c4 are normal in their action1 that is to say1 the electric response in such electrolytes is practically the same as with water4 ,ordinarily ,i use tap-water as the electrolyte4 ,zinc wires in ,zn,s,o#d solution give responses similar in character to those given by1 for example1 ,pt or ,sn in water4 ,test experiment4--,it may be urged that the ,e4,m4 effect is due in some way 7#a7 to the friction of the vibrating wire against the liquid2 or 7#b7 to some unknown surface action1 at the point in the wire of the contact of liquid and air surfaces4 ,this second objection has already been completely met in experimental modification1 fig4#ee1 b1 where the wire was shown to give response when kept completely immersed in water1 variation of surface being thus entirely eliminated4 ,both these questions may1 however1 be subjected to a definite and final test4 ,when the wire to be acted on is clamped below1 and vibration is imparted to it1 a strong molecular disturbance is produced4 ,if now it be carefully released from the clamp1 and the wire rotated backwards and forwards1 there could be little molecular disturbance1 but the liquid friction and surface variation1 if any1 would remain4 ,the effect of any slight disturbance outstanding owing to shaking of the wire would be relatively very small4 ,we can thus determine the effect of liquid friction and surface action by repeating an experiment with and without clamping4 ,in a tin wire cell1 with interposed external resistance equal to one million ohms1 the wire ,a was subjected to a series of vibrations through #ahj1 and a deflection of #baj;divisions was obtained4 ,a corresponding negative deflection resulted on vibrating the wire ,b4 ,now ,a was released from the clamp1 so that it could be rotated backwards and forwards in the water by means of the handle4 ,on vibrating the wire ,a no measurable deflection was produced1 thus showing that neither water friction nor surface variation had anything to do with the electric action4 ,the vibration of the still clamped ,b gave rise to the normal strong deflection4 ,as all the rest of the circuit was kept absolutely the same in the two different sets of experiments1 these results conclusively prove that the responsive electro-motive variation is solely due to the molecular disturbance produced by mechanical vibration in the acted wire4 ,a new and theoretically interesting molecular voltaic cell may thus be made1 in which the two elements consist of the same metal4 ,molecular disturbance is in this case the main source of energy4 ,a cell once made may be kept in working order for some time by pouring in a little vaseline to prevent evaporation of the liquid4 ,it will be shown further1 in succeeding chapters1 by numerous instances1 that any conditions which increase molecular mobility will also increase intensity of response1 and conversely that any conditions having the reverse effect will depress response4 ,,chapter ,,xii ,,inorganic ,,response--,,methods ,,of ,,ensuring ,,consistent ,,results ,preparation of wire--,effect of single stimulus4 ,i shall now proceed to describe in detail the response-curves obtained with metals4 ,the ,e4,m4 variations resulting from stimulus range1 as has been said1 from #dvolt to #ja of that value1 according to the metal employed4 ,and as these are molecular phenomena1 the effect will also depend on the molecular condition of the wire4 ,preparation of wire4--,in order to have our results thoroughly consistent1 it is necessary to bring the wire itself into a normal condition for experiment4 ,the very fact of mounting it in the cell strains it1 and the after-effect of this strain may cause irregularities in the response4 ,for the purpose of bringing the wire to this normal state1 one or all of the following devices may be used with advantage4 7#a7 ,the wires obtained are usually wound on spools4 ,it is1 therefore1 advisable to straighten any given length1 before mounting1 by holding it stretched1 and rubbing it up and down with a piece of cloth4 ,on washing with water1 they are now ready for mounting in the cell4 7#b7 ,the cell is usually filled with tap-water1 and a period of rest after making up1 generally speaking1 improves the sensitiveness4 ,these expedients are ordinarily sufficient1 but it occasionally happens that the wire has got into an abnormal condition4 ,illustration3 ,,fig4#eh4--;,,effect ,,of ,,annealing ,,on ,,increasing ,,the ,,response ,,of ,,both ,a ,,and ,b ,,wires 7,,tin7 ,stimuli 7vibration of #afj7 applied at intervals of one minute4 ,in this case it will be found helpful 7#c7 to have recourse to the process of annealing4 ,for if response be a molecular phenomenon1 then anything that increases molecular mobility will also increase its intensity4 ,hence we may expect annealing to enhance responsiveness4 ,this inference will be seen verified in the record given in fig4#eh4 ,in the case under consideration1 the convenient method employed was by pouring hot water into the cell1 and allowing it to stand and cool slowly4 ,the first three pairs of responses were taken by stimulating ,a and ,b alternately1 on mounting in the cell1 which was filled with water4 ,hot water was then substituted1 and the cell was allowed to cool down to its original temperature4 ,the six following pairs of responses were then taken4 ,that this beneficial effect of annealing was not due to any accidental circumstance will be seen from the fact that both wires have their sensitiveness equally enhanced4 7#d7 ,in addition to this mode of annealing1 both wires may be short-circuited and vibrated for a time4 ,lastly 7#e7 slight stretching in situ will also sometimes be found beneficial4 ,for this purpose ,i have a screw arrangement4 ,by one or all of these methods1 with a little practice1 it is always possible to bring the wires to a normal condition4 ,the responses subsequently obtained become extraordinarily consistent4 ,there is therefore no reason why perfect results should not be arrived at4 ,illustration3 ,,fig4#ei4--,,uniform ,,responses ,,in ,,tin ,effect of single stimulus4--,the accompanying figure 7fig4#ei7 gives a series1 each of which is the response curve for a single stimulus of uniform intensity1 the amplitude of vibration being kept constant4 ,the perfect regularity of responses will be noticed in this figure4 ,the wire after a long period of rest may be in an abnormal condition1 but after a short period of stimulation the responses become extremely regular1 as may be noticed in this figure4 ,tin is1 usually speaking1 almost indefatigable1 and ,i have often obtained several hundreds of successive responses showing practically no fatigue4 ,in the figure it will be noticed that the rising portion of the curve is somewhat steep1 and the recovery convex to the abscissa1 the fall being relatively rapid in its first1 and less rapid in its later1 parts4 ,as the electric variation is the concomitant effect of molecular disturbance--a temporary upset of the molecular equilibrium--on the cessation of the external stimulus1 the excitatory state1 and its expression in electric variation1 disappear with the return of the molecules to their condition of equilibrium4 ,this process is seen clearly in the curve of recovery4 ,different metals exhibit different periods of recovery1 and this again is modified by any influence which affects the molecular condition4 ,that the excitatory state persists for a time even on the cessation of stimulus can be independently shown by keeping the galvanometer circuit open during the application of stimulus1 and completing it at various short intervals after the cessation1 when a persisting electrical effect1 diminishing rapidly with time1 will be apparent4 ,the rate of recovery immediately on the cessation of stimulus is rather rapid1 but traces of strain persist for a short time4 ,,chapter ,,xiii ,,inorganic ,,response--,,molecular ,,mobility3 ,,its ,,influence ,,on ,,response ,effects of molecular inertia--,prolongation of period of recovery by overstrain--,molecular model--,reduction of molecular sluggishness attended by quickened recovery and heightened response--,effect of temperature--,modification of latent period and period of recovery by the action of chemical reagents--,diphasic variation4 ,we have seen that the stimulation of matter causes an electric variation1 and that the acted substance gradually recovers from the effect of stimulus4 ,we shall next study how the form of response-curves is modified by various agencies4 ,in order to study these effects we must use1 in practice1 a highly sensitive galvanometer as the recorder of ,e4,m4 variations4 ,this necessitates the use of an instrument with a comparatively long period of swing of needle1 or of suspended coil 7as in a ,d',arsonval74 ,owing to inertia of the recording galvanometer1 however1 there is a lag produced in the records of ,e4,m4 changes4 ,but this can be distinguished from the effect of the molecular inertia of the substance itself by comparing two successive records taken with the same instrument1 in one of which the latter effect is relatively absent1 and in the other present4 ,we wish1 for example1 to find out whether the ,e4,m4 effect of mechanical stimulus is instantaneous1 or1 again1 whether the effect disappears immediately4 ,we first take a galvanometer record of the sudden introduction and cessation of an ,e4,m4,f4 on the circuit containing the vibration-cell 7fig4#fj1 a74 ,we then take a record of the ,e4,m4 effect produced by a stimulus caused by a single torsional vibration4 ,in order to make the conditions of the two experiments as similar as possible1 the disturbing ,e4,m4,f41 from a potentiometer1 is previously adjusted to give a deflection nearly equal to that caused by stimulus4 ,the torsional vibration was accomplished in a quarter of a second1 and the contact with the potentiometer circuit was also made for the same length of time4 ,illustration3 ,,fig4#fj 7a7 ,arrangement for applying a short-lived ,e4,m4,f4 7b7 ,difference in the periods of recovery3 7#a7 from instantaneous ,e4,m4,f42 and 7#b7 that caused by mechanical stimulus4 ,the record was then taken as follows4 ,the recording drum had a fast speed of six inches in a minute1 one of the small subdivisions representing a second4 ,the battery contact in the main potentiometer circuit was made for a quarter of a second as just mentioned and a record taken of the effect of a short-lived ,e4,m4,f4 on the circuit containing the cell4 7#b7 ,a record was next taken of the ,e4,m4 variation produced in the cell by a single stimulus4 ,it will be seen on comparison of the two records that the maximum effect took place relatively later in the case of mechanical stimulus1 and that whereas the galvanometer recovery in the former case took place in #aaseconds1 the recovery in the latter was not complete till after #fjseconds 7fig4#fj1 b74 ,this shows that it takes some time for the effect of stimulus to attain its maximum1 and that the effect does not disappear till after the lapse of a certain interval4 ,the time of recovery from strain depends on the intensity of stimulus4 ,it takes a longer time to recover from a stronger stimulus4 ,but1 other things being equal1 successive recovery periods from successive stimulations of equal intensity are1 generally speaking1 the same4 ,we may now study the influence of any change in external conditions by observing the modifications it produces in the normal curve4 ,illustration3 ,,fig4#fa4--,,prolongation ,,of ,,period ,,of ,,recovery ,,after ,,overstrain ,recovery is complete in #fj when the stimulus is due to #bj vibration4 ,but with stronger stimulus of #dj vibration1 the period of recovery is prolonged to #ij4 ,prolongation of period of recovery by overstrain4--,the pair of records given in fig4#fa shows how recovery is delayed1 as the effect of overstrain4 ,curve 7a7 is for a single stimulus due to a vibration of amplitude #bj1 and curve 7b7 for a stimulus of #dj amplitude of vibration4 ,it will be noticed how relatively prolonged is the recovery in the latter case4 ,illustration3 ,,fig4#fb4--,,model ,,showing ,,the ,,effect ,,of ,,friction ,molecular ,model4--,we have seen that the electric response is an outward expression of the molecular disturbance produced by the action of the stimulus4 ,the rising part of the response-curve thus exhibits the effect of molecular upset1 and the falling part1 or recovery1 the restoration to equilibrium4 ,the mechanical model 7fig4#fb7 will help us to visualise many complex response phenomena4 ,the molecular model consists of a torsional pendulum--a wire with a dependent sphere4 ,by the stimulus of a blow there is produced a torsional vibration--a response followed by recovery4 ,the writing lever attached to the pendulum records the response-curves4 ,the form of these curves1 stimulus remaining constant1 will be modified by friction2 the less the friction1 the greater is the mobility4 ,the friction may be varied by more or less raising a vessel of sand touching the pendulum4 ,by varying the friction the following curves were obtained4 7a7 ,when there is little friction we get an after-oscillation1 to which we have the corresponding phenomenon in the retinal after-oscillation 7compare fig4#aje74 7b and c7 ,if the friction is increased1 there is a damping of oscillation4 ,in 7c7 we get recovery-curves similar to those found in nerve1 muscle1 plant1 and metal4 7d7 ,if the friction is still further increased the maximum is reached much later1 as will be seen in the increasing slant of the rising part of the curve2 the height of response is diminished and the period of recovery very much prolonged by partial molecular arrest4 ,the curve 7d7 is very similar to the 'molecular arrest' curve obtained by small dose of chemical reagents which act as 'poison' on living tissue or on metals 7compare fig4#ic1 a74 7e7 ,when the molecular mobility is further decreased there is no recovery 7compare fig4#ic1 b74 ,still further increase of friction completely arrests the molecular pendulum1 and there is no response4 ,from what has been said1 it will be seen that if in any way the friction is diminished or mobility increased the response will be enhanced4 ,this is well exemplified in the heightened response after annealing 7fig4#eh7 and after preliminary vibration 7figs4 #ha1 #hb74 ,possibly connected with this may be the increased responses exhibited by the action of stimulants 7figs4 #hi1 #ij74 ,reduction of molecular sluggishness attended 7#a7 by quickened recovery4--,sometimes1 after a cell has been resting for too long a period1 especially on cold days1 the wire gets into a sluggish condition1 and the period of recovery is thereby prolonged4 ,but successive vibrations gradually remove this inertness1 and recovery is then hastened4 ,this is shown in the accompanying curves1 fig4#fc1 where 7a7 exhibits only very partial recovery even after the expiration of #fjseconds1 whereas when a few vibrations had been given recovery was entirely completed in #dgseconds 7b74 ,there was here little change in the height of response4 ,illustration3 ,,fig4#fc 7a7 ,slow recovery of a wire in a sluggish condition4 7b7 ,quickened recovery in the same wire after a few vibrations4 ,or 7#b7 by heightened response4--,the removal of sluggishness by vibration1 resulting in increased molecular mobility1 is in other instances attended by increase in the height of response1 as will be seen from the two sets of records which follow 7fig4#fd74 ,cold1 due to prevailing frosty weather1 had made the wires in the cell somewhat lethargic4 ,the records in 7a7 were the first taken on the day of the experiment4 ,the amplitudes of vibration were #de1 #ij1 and #ace4 ,in 7b7 are given the records of the next series1 which are in every case greater than those of 7a74 ,this shows that previous vibration1 by conferring increased mobility1 had heightened the response4 ,in this case1 removal of molecular sluggishness is attended by greater intensity of response1 without much change in the period of recovery4 ,in connection with this it must be remembered that greater strain consequent on heightened response has a general tendency to a prolongation of the period of recovery4 ,illustration3 ,,fig4#fd 7a7 ,three sets of responses for #de1 #ij1 and #ace vibration in a sluggish wire4 7b7 ,the next three sets of responses in the same wire2 increased mobility conferred by previous vibration has heightened the response4 ,it is thus seen that when the wire is in a sluggish condition1 successive vibrations confer increased molecular mobility1 which finds expression in quickened recovery or heightened response4 ,effect of temperature4--,similar considerations lead us to expect that a moderate rise of temperature will be conducive to increase of response4 ,this is exhibited in the next series of records4 ,the wire at the low temperature of #e;,c4 happened to be in a sluggish condition1 and the responses to vibrations of #de to #ij in amplitude were feeble4 ,tepid water at #cj;,c4 was now substituted for the cold water in the cell1 and the responses underwent a remarkable enhancement4 ,but the excessive molecular disturbance caused by the high temperature of #ij;,c4 produced a great diminution of response 7fig4#fe74 ,illustration3 ,,fig4#fe4--,,responses ,,of ,a ,,wire ,,to ,,amplitudes ,,of ,,vibration #de ,,and #ij 7a7 ,responses when the wire was in a sluggish condition at temperature of #e;,c4 7b7 ,enhanced response at #cj;,c4 7c7 ,diminution of response at #ij;,c4 ,diphasic variation4--,it has already been said that if two points ,a and ,b are in the same physico-chemical condition1 then a given stimulus will give rise to similar excitatory electric effects at the two points4 ,if the galvanometer deflection is 'up' when ,a alone is excited1 the excitation of ,b will give rise to a downward deflection4 ,when the two points are simultaneously excited the electric variation at the two points will continuously balance each other4 ,under such conditions there will be no resultant deflection4 ,but if the intensity of stimulation of one point is relatively stronger1 then the balance will be disturbed1 and a resultant deflection produced whose sign and magnitude can be found independently by the algebraical summation of the individual effects of ,a and ,b4 ,it has also been shown that a balancing point for the block1 which is approximately near the middle of the wire1 may be found so that the vibrations of ,a and ,b through the same amplitude produce equal and opposite deflection4 ,simultaneous vibration of both will give no resultant current2 when the block is abolished and the wire is vibrated as a whole1 there will still be no resultant1 inasmuch as similar excitations are produced at ,a and ,b4 ,after obtaining the balance1 if we apply an exciting reagent like ,na#b;,,co#c at one point1 and a depressing reagent like ,k,br at the other1 the responses will now become unequal1 the more excitable point giving a stronger deflection4 ,we can1 however1 make the two deflections equal by increasing the amplitude of vibration of the less sensitive point4 ,the two deflections may thus be rendered equal and opposite1 but the time relations--the latent period1 the time rate for attaining the maximum excitation and recovery from that effect--will no longer be the same in the two cases4 ,there would therefore be no continuous balance1 and we obtain instead a very interesting diphasic record4 ,i give below an exact reproduction of the response-curves of ,a and ,b recorded on a fast-moving drum4 ,it will be remembered that one point was touched with ,na#b;,,co#c and the other with ,k,br4 ,by suitably increasing the amplitude of vibration of the less sensitive1 the two deflections were rendered approximately equal4 ,the records of ,a and ,b were at first taken separately 7fig4#ff1 a74 ,it will be noticed that the maximum deflection of ,a was attained relatively much earlier than that of ,b4 ,the resultant curve ,r' was obtained by summation4 ,illustration3 ,,fig4#ff4--;,,diphasic ,,variation 7a7 ,records of ,a and ,b obtained separately4 ,r' is the resultant by algebraical summation4 7b7 ,diphasic record obtained by simultaneous stimulation of ,a and ,b4 ,after taking the records of ,a and ,b separately1 a record of resultant effect ,r due to simultaneous vibration of ,a and ,b was next taken4 ,it gave the curious two-phased response--positive effect followed by negative after-vibration1 practically similar to the resultant curve ,r' 7fig4#ff1 b74 ,the positive portion of the curve is due to ,a effect and the negative to ,b4 ,if by any means1 say by either increasing the amplitude of vibration of ,a or increasing its sensitiveness1 the response of ,a is very greatly enhanced1 then the positive effect would be predominant and the negative effect would become inconspicuous4 ,when the two constituent responses are of the same order of magnitude1 we shall have a positive response followed by a negative after-vibration2 the first twitch will belong to the one which responds earlier4 ,if the response of ,a is very much reduced1 then the positive effect will be reduced to a mere twitch and the negative effect will become predominant4 ,i give a series of records1 fig4#fg1 in which these three principal types are well exhibited1 the two contacts having been rendered unequally excitable by solutions of the two reagents ,k,br and ,na#b;,,co#c4 ,a and ,b were vibrated simultaneously and records taken4 7a7 ,first1 the relative response of ,b 7downward7 is increased by increasing its amplitude of vibration4 ,the amplitude of vibration of ,a was throughout maintained constant4 ,the negative or downward response is now very conspicuous1 there being only a mere preliminary indication of the positive effect4 7b7 ,the amplitude of vibration of ,b is now slightly reduced1 and we obtain the diphasic effect4 7c7 ,the intensity of vibration of ,b is diminished still further1 and the negative effect is seen reduced to a slight downward after-vibration1 the positive up-curve being now very prominent 7fig4#fg74 ,illustration3 ,,fig4#fg4--,,negative1 ,,diphasic1 ,,and ,,positive ,,resultant ,,response ,continuous transformation from negative to positive4--,i have shown the three phases of transformation1 the intensity of one of the constituent responses being varied by altering the intensity of disturbance4 ,in the following record 7fig4#fh7 ,i succeeded in obtaining a continuous transformation from positive to negative phase by a continuous change in the relative sensitiveness of the two contacts4 ,i found that traces of after-effect due to the application of ,na#b;,,co#c remain for a time4 ,if the reagent is previously applied to an area and the traces of the carbonate then washed off1 the increased sensitiveness conferred disappears gradually4 ,again1 if we apply ,na#b;,,co#c solution to a fresh point1 the sensitiveness gradually increases4 ,there is another further interesting point to be noticed3 the beginning of response is earlier when the application of ,na#b;,,co#c is fresh4 ,illustration3 ,,fig4#fh4--;,,continuous ,,transformation ,,from ,,negative ,,to ,,positive ,,through ,,intermediate ,,diphasic ,,response ,thick dots represent the times of application of successive stimuli4 ,we have thus a wire held at one end1 and successive uniform vibrations at intervals of one minute imparted to the wire as a whole1 by means of a vibration head on the other end4 ,owing to the after-effect of previous application of ,na#b;,,co#c the sensitiveness of ,b is at the beginning great1 hence the three resultant responses at the beginning are negative or downward4 ,dilute solution of ,na#b;,,co#c is next applied to ,a4 ,the response of ,a 7up7 begins earlier and continues to grow stronger and stronger4 ,hence1 after this application1 the response shows a preliminary positive twitch of ,a followed by negative deflection of ,b4 ,the positive grows continuously4 ,at the fifth response the two phases1 positive and negative1 become equal1 after that the positive becomes very prominent1 the negative being reduced as a feeble after-vibration4 ,it need only be added here that the diphasic variations as exhibited by metals are in every way counterparts of similar phenomena observed in animal tissues4 ,,chapter ,,xiv ,,inorganic ,,response--,,fatigue1 ,,staircase1 ,,and ,,modified ,,response ,fatigue in metals--,fatigue under continuous stimulation--,staircase effect--,reversed responses due to molecular modification in nerve and metal1 and their transformation into normal after continuous stimulation--,increased response after continuous stimulation4 ,illustration3 ,,fig4#fi4--;,,fatigue ,,in ,,muscle 7,,waller7 ,illustration3 ,,fig4#gj4--;,,fatigue ,,in ,,platinum ,fatigue4--,in some metals1 as in muscle and in plant1 we find instances of that progressive diminution of response which is known as fatigue 7fig4#fi74 ,the accompanying record shows this in platinum 7fig4#gj74 ,it has been said that tin is practically indefatigable4 ,we must1 however1 remember that this is a question of degree only4 ,nothing is absolutely indefatigable4 ,the exhibition of fatigue depends on various conditions4 ,even in tin1 then1 ,i obtained the characteristic fatigue-curve with a specimen which had been in continuous use for many days 7fig4#ga74 ,while discussing the subject of fatigue in plants1 ,i have adduced considerations which showed that the residual effect of strain was one of the main causes for the production of fatigue4 ,this conclusion receives independent support from the records obtained with metals4 ,illustration3 ,,fig4#ga4--;,,fatigue ,,shown ,,by ,,tin ,,wire ,,which ,,had ,,been ,,continuously ,,stimulated ,,for ,,several ,,days ,in this connection the important fact is that the various typical fatigue effects exhibited in living substances are exactly reproduced in metals1 where there can be question neither of fatigue-product producing fatigue effects1 nor of those constructive processes by which they might be removed4 ,we have seen1 both in muscles and in plants1 that if sufficient time for complete recovery be allowed between each pair of stimuli1 the heights of successive responses are the same1 and there is no apparent fatigue 7see page#ci74 ,but the height of response diminishes as the excitation interval is shortened4 ,we find the same thing in metals4 ,below is given a record taken with tin 7fig4#gb74 ,throughout the experiment the amplitude of vibration was maintained constant1 but in 7a7 the interval between consecutive stimuli was #a'1 while in 7b7 this was reduced to #cj4 ,a diminution of height immediately occurs4 ,on restoring the original rhythm as in 7c71 the responses revert to their first large value4 ,thus we see that when the wire has not completely recovered1 its responses1 owing to residual strain1 undergo diminution4 ,height of response is thus decreased by incomplete recovery4 ,if then sufficient time be not allowed for perfect recovery1 we can understand how1 under certain circumstances1 the residual strain would progressively increase with repetition of stimulus1 and thus there would be a progressive diminution of height of response or fatigue4 ,again1 we saw in the last chapter that increase of strain necessitates a longer period of recovery4 ,thus the longer a wire is stimulated1 the more and more overstrained it becomes1 and it therefore requires a gradual prolongation of the interval between the successive stimuli1 if recovery is to be complete4 ,this interval1 however1 being maintained constant1 the recovery periods virtually undergo a gradual reduction1 and successive recoveries become more and more incomplete4 ,these considerations may be found to afford an insight into the progressive diminution of response in fatigued substances4 ,illustration3 ,,fig4#gb4--;,,diminution ,,of ,,response ,,due ,,to ,,shortening ,,the ,,period ,,of ,,recovery ,the stimulus is maintained constant4 ,in 7a7 the interval between two successive stimuli is one minute1 in 7b7 it is half a minute1 and in 7c7 it is again one minute4 ,the response in 7b7 is feebler than in either 7a7 or 7c74 ,fatigue under continuous stimulation4--,fatigue is perhaps best shown under continuous stimulation4 ,for example1 in muscles1 when fresh and not fatigued1 the top of the tetanic curve is horizontal1 or may even be ascending1 but with long-continued stimulation the curve declines4 ,the rapidity of this decline depends on the nature of the muscle and its previous condition4 ,in metals ,i have found exactly parallel instances4 ,in tin1 so little liable to fatigue1 the top of the curve is horizontal or ascending2 or it may exhibit a slight decline4 ,but the record with platinum shows the rapid decline due to fatigue 7fig4#gc74 ,illustration3 ,,fig4#gc 7a7 ,the top of response-curve under continuous stimulation in tin is horizontal or ascending as in figure4 7b7 ,in platinum there is rapid decline owing to fatigue4 ,taking any of these instances1 say that in which fatigue is most prominent1 it is found that short period of rest restores the original intensity of response4 ,this affords additional proof of the fact that fatigue is due to overstrain1 and that this strain1 with its sign of attendant fatigue1 disappears with time4 ,staircase effect4--,we shall now discuss an effect which appears to be the direct opposite of fatigue4 ,this is the curious phenomenon known to physiologists as 'the staircase' effect1 in which successive uniform stimuli produce a series of increasing responses4 ,this is seen under particular conditions in the response of certain muscles 7fig4#gd1 a74 ,it is also observed sometimes even in nerve1 which otherwise1 generally speaking1 gives uniform responses4 ,of this effect1 no satisfactory theory has as yet been offered4 ,it is in direct contradiction to that theory which supposes that each stimulus is followed by dissimilation or break-down of the tissue1 reducing its function below par4 ,for in these cases the supposed dissimilation is followed not by a decrease but by an increase of functional activity4 ,this 'staircase effect' ,i have shown to be occasionally exhibited by plants4 ,i have also found it in metals4 ,in the last chapter we have seen that a wire often falls1 especially after resting for a long time1 into a state of comparative sluggishness1 and that this molecular inertness then gradually gives place to increased mobility under stimulation4 ,as a consequence1 an increased response is thus obtained4 ,i give in fig4#gd1 b1 a series of responses to uniform stimuli1 exhibited by platinum which had been at rest for some time4 ,this effect is very clearly shown here4 ,so we see that in a substance which has previously been in a sluggish condition1 stimulation confers increased mobility4 ,response thus reaches a maximum1 but continued stimulation may afterwards produce overstrain1 and the subsequent responses may then show a decline4 ,this consideration will explain certain types of responses exhibited by muscles1 where the first part of the series exhibits a staircase increase followed by declining responses of fatigue4 ,illustration3 ,,fig4#gd4--',,staircase' ,,effect 7a7 in muscle 7after ,engelmann74 7b7 in metal4 ,reversed response due to molecular modification and its transformation into normal after continuous stimulation 7#a7 in nerve4--,reference has already been made to the fact that a nerve which1 when fresh1 exhibited the normal negative response1 will often1 if kept for some time in preservative saline1 undergo a molecular modification1 after which it gives a positive variation4 ,thus while the response given by fresh nerve is normal or negative1 a stale nerve gives modified1 i4e4 reversed or positive1 response4 ,this peculiar modification does not always occur1 yet is too frequent to be considered abnormal4 ,again1 when such a nerve is subjected to tetanisation or continuous stimulation1 this modified response tends once more to become normal4 ,it is found that not only tetanisation1 but also ,,co#b has the power of converting the modified response into normal4 ,hence it has been suggested that the conversion under tetanisation of modified response to normal1 in stale nerve1 is due to a hypothetical evolution of ,,co#b in the nerve during stimulation4#af 7#b7 ,in metals4--,i have1 however1 met with exactly parallel phenomena in metals1 where1 owing to some molecular modification1 the responses became reversed1 and where1 under continuous stimulation1 though here there could be no possibility of the evolution of ,,co#b1 they tended again to become normal4 ,if after mounting a wire in a cell filled with water1 it be set aside for too long a time1 ,i have sometimes noticed that it undergoes a certain modification1 owing to which its response ceases to be normal and becomes reversed in sign4 ,i have obtained this effect with various metals1 for instance lead and tin1 and even with the chemically inactive substance--platinum4 ,illustration3 ,,fig4#ge4--;,,abnormal ,,positive 7,,up7 ,,response ,,in ,,nerve ,,converted ,,into ,,normal 7,,down7 ,,response ,,after ,,continuous ,,stimulation ,t 7,,waller7 ,the galvanometer is not dead-beat1 and shows after-oscillation4 ,the subject will be made clearer if we first follow in detail the phenomenon exhibited by modified nerve1 giving this abnormal response4 ,the normal responses in nerve are usually represented by 'down' and the reversed abnormal responses by 'up' curves4 ,in the modified nerve1 then1 the abnormal responses are 'up' instead of the normal 'down4' ,the record of such abnormal response in the modified nerve is shown in fig4#ge4 ,it will be noticed that in this1 the successive responses are undergoing a diminution1 or tending towards the normal4 ,after continuous stimulation or tetanisation 7,t71 it will be seen that the abnormal or 'up' responses are converted into normal or 'down4' ,i shall now give a record which will exhibit an exactly similar transformation from the abnormal to normal response after continuous stimulation4 ,here the normal responses are represented by 'up' and the abnormal by 'down' curves4 ,this record was given by a tin wire1 which had been molecularly modified 7fig4#gf74 ,we have at first the abnormal responses2 successive responses are undergoing a diminution or tending towards the normal2 after continuous stimulation 7,t71 the subsequent responses are seen to have become normal4 ,another record1 obtained with platinum1 shows the same phenomenon 7fig4#gg74 ,illustration3 ,,fig4#gf ,,and ,,fig4#gg ,abnormal 'down' response in tin 7fig4#gf7 and in platinum 7fig4#gg7 transformed into normal 'up' response1 after continuous stimulation1 ,t4 ,on placing the three sets of records--nerve1 tin1 and platinum--side by side1 it will be seen how essentially similar they are in every respect4#ag ,this reversion to normal is seen to have appeared in a pronounced manner after rapidly continuous stimulation1 in process of which the modified molecular condition must in some way have reverted to the normal4 ,illustration3 ,,fig4#gh4--,,the ,,gradual ,,transition ,,from ,,abnormal ,,to ,,normal ,,response ,,in ,,platinum ,the transition will be seen to have commenced at the third and ended at the seventh1 counting from the left4 ,being desirous to trace this change gradually taking place1 ,i took a platinum wire cell giving modified responses1 and obtained a series of records of effects of individual stimuli continued for a long time4 ,in this series1 the points of transition from modified response to normal will be clearly seen 7fig4#gh74 ,illustration3 ,,fig4#gi4--,,the ,,normal ,,response a ,,in ,,nerve ,,enhanced ,,to b ,,after ,,continuous ,,stimulation ,t 7,,waller7 ,the normal response in nerve is recorded 'down4' ,illustration3 ,,fig4#hj4--;,,enhanced ,,response ,,in ,,platinum ,,after ,,continuous ,,stimulation ,t ,increased response after continuous stimulation4--,we have seen that responses to uniform stimuli sometimes show a staircase increase1 apparently owing to the gradual removal of molecular sluggishness4 ,possibly analogous to this is the increase of response in nerve after continuous stimulation or tetanisation1 observed by ,waller 7fig4#gi74 ,like the staircase effect1 this contravenes the commonly accepted theory of the dissimilation of tissue by stimulus1 and the consequent depression of response4 ,it is suggested by ,waller that this increase of response after tetanisation may be due to the hypothetical evolution of ,,co#b to which allusion has previously been made4 ,illustration3 ,,fig4#ha4--;,,enhanced ,,response ,,in ,,tin ,,after ,,continuous ,,stimulation ,t ,but there is an exact correspondence between this phenomenon and that exhibited by metals under similar conditions4 ,i give here two sets of records 7figs4 #hj1 #ha71 one obtained with platinum and the other with tin1 which demonstrate how the response is enhanced after continuous stimulation in a manner exactly similar to that noticed in the case of nerve4 ,the explanation which has been suggested with regard to the staircase effect--increased molecular mobility due to removal of sluggishness by repeated stimulation--would appear to be applicable in this case also4 ,it would appear1 then1 that in all the phenomena which we have studied under the heads of 'staircase' effect1 increase of response after continuous stimulation1 and fatigue1 there is a similarity between the observations made upon the response of muscle and nerve on the one hand1 and that of metals on the other4 ,even in their abnormalities we have seen an agreement4 ,but amongst these phenomena themselves1 though at first sight so diverse1 there is some kind of continuity4 ,calling all normal response positive1 for the sake of convenience1 we observe its gradual modification1 corresponding to changes in the molecular condition of the substance4 ,beginning with that case in which molecular modification is extreme1 we find a maximum variation of response from the normal1 that is to say1 to negative4 ,continued stimulation1 however1 brings back the molecular condition to normal1 as evidenced by the progressive lessening of the negative response1 culminating in reversion to the normal positive4 ,this is equally true of nerve and metal4 ,in the next class of phenomena1 the modification of molecular condition is not so great4 ,it now exhibits itself merely as a relative inertness1 and the responses1 though positive1 are feeble4 ,under continued stimulation1 they increase in the same direction as in the last case1 that is to say1 from less positive to more positive1 being the reverse of fatigue4 ,this is evidenced alike by the staircase effect and by the increase of response after tetanisation1 seen not only in nerve but also in platinum and tin4 ,the substance may next be in what we call the normal condition4 ,successive uniform stimuli now evoke uniform and equal positive responses1 that is to say1 there is no fatigue4 ,but after intense or long-continued stimulation1 the substance is overstrained4 ,the responses now undergo a change from positive to less positive2 fatigue1 that is to say1 appears4 ,again1 under very much prolonged stimulation the response may decline to zero1 or even undergo a reversal to negative1 a phenomenon which we shall find instanced in the reversed response of retina under the long-continued stimulus of light4 ,we must then recognise that a substance may exist in various molecular conditions1 whether due to internal changes or to the action of stimulus4 ,the responses give us indications of these conditions4 ,a complete cycle of molecular modifications can be traced1 from the abnormal negative to the normal positive1 and then again to negative seen in reversal under continuous stimulation4 ,,footnotes3 #af ',considering that we have no previous evidence of any chemical or physical change in tetanised nerve1 it seems to me not worth while pausing to deal with the criticism that it is not ,,co#b1 but something else that has given the result4'--,waller1 ,animal ,electricity1 p4#ei4 ,that this phenomenon is nevertheless capable of physical explanation will be shown presently4 #ag ,in order to explain the phenomena of electric response1 some physiologists assume that the negative response is due to a process of dissimilation1 or breakdown1 and the positive to a process of assimilation1 or building up1 of the tissue4 ,the modified or positive response in nerve is thus held to be due to assimilation2 after continuous stimulation1 this process is supposed to be transformed into one of dissimilation1 with the attendant negative response4 ,how arbitrary and unnecessary such assumptions are will become evident1 when the abnormal and normal responses1 and their transformation from one to the other1 are found repeated in all details in metals1 where there can be no question of the processes of assimilation or dissimilation4 ,,chapter ,,xv ,,inorganic ,,response--,,relation ,,between ,,stimulus ,,and ,,response--,,superposition ,,of ,,stimuli ,relation between stimulus and response--,magnetic analogue--,increase of response with increasing ,stimulus--,threshold of response--,superposition of ,stimuli--,hysteresis4 ,relation between stimulus and response4--,we have seen what extremely uniform responses are given by tin1 when the intensity of stimulus is maintained constant4 ,hence it is obvious that these phenomena are not accidental1 but governed by definite laws4 ,this fact becomes still more evident when we discover how invariably response is increased by increasing the intensity of stimulus4 ,electrical response is due1 as we have seen1 to a molecular disturbance1 the stimulus causing a distortion from a position of equilibrium4 ,in dealing with the subject of the relation between the disturbing force and the molecular effect it produces1 it may be instructive to consider certain analogous physical phenomena in which molecular deflections are also produced by a distorting force4 ,magnetic analogue4--,let us consider the effect that a magnetising force produces on a bar of soft iron4 ,it is known that each molecule in such a bar is an individual magnet4 ,the bar as a whole1 nevertheless1 exhibits no external magnetisation4 ,this is held to be due to the fact that the molecular magnets are turned either in haphazard directions or in closed chains1 and there is therefore no resultant polarity4 ,but when the bar is subjected to a magnetising force by means1 say1 of a solenoid carrying electrical current1 the individual molecules are elastically deflected1 so that all the molecular magnets tend to place themselves along the lines of magnetising force4 ,all the north poles thus point more or less one way1 and the south poles the other4 ,the stronger the magnetising force1 the nearer do the molecules approach to a perfect alignment1 and the greater is the induced magnetisation of the bar4 ,the intensity of this induced magnetisation may be measured by noting the deflection it produces on a freely suspended magnet in a magnetometer4 ,the force which produces that molecular deflection1 to which the magnetisation of the bar is immediately due1 is the magnetising current flowing round the solenoid4 ,the magnetisation1 or the molecular effect1 is measured by the deflection of the magnetometer4 ,we may express the relation between cause and effect by a curve in which the abscissa represents the magnetising current1 and the ordinate the magnetisation produced 7fig4#hb74 ,illustration3 ,,fig4#hb4--;,,curve ,,of ,,magnetisation ,in such a curve we may roughly distinguish three parts4 ,in the first1 where the force is feeble1 the molecular deflection is slight4 ,in the next1 the curve is rapidly ascending1 i4e4 a small variation of impressed force produces a relatively large molecular effect4 ,and lastly1 a limit is reached1 as seen in the third part1 where increasing force produces very little further effect4 ,in this cause-and-effect curve1 the first part is slightly convex to the abscissa1 the second straight and ascending1 and the third concave4 ,increase of response with increasing stimulus4--,we shall find in dealing with the relation between the stimulus and the molecular effect--i4e4 the response--something very similar4 ,on gradually increasing the intensity of stimulus1 which may be done1 as already stated1 by increasing the amplitude of vibration1 it will be found that1 beginning with feeble stimulation1 this increase is at first slight1 then more pronounced1 and lastly shows a tendency to approach a limit4 ,in all this we have a perfect parallel to corresponding phenomena in animal and vegetable response4 ,we saw that the proper investigation of this subject was much complicated1 in the case of animal and vegetable tissues1 by the appearance of fatigue4 ,the comparatively indefatigable nature of tin causes it to offer great advantages in the pursuit of this inquiry4 ,i give below two series of records made with tin4 ,the first record1 fig4#hc1 is for increasing amplitudes from #e to #dj by steps of #e4 ,the stimuli are imparted at intervals of one minute4 ,it will be noticed that whereas the recovery is complete in one minute when the stimulus is moderate1 it is not quite complete when the stimulus is stronger4 ,the recovery from the effect of stronger stimulus is more prolonged4 ,owing to want of complete recovery1 the base line is tilted slightly upward4 ,this slight displacement of the zero line does not materially affect the result1 provided the shifting is slight4 ,illustration3 ,,fig4#hc4--,,records ,,of ,,responses ,,in ,,tin ,,with ,,increasing ,,stimuli1 ,,amplitudes ,,of ,,vibration ,,from #e ,,to #dj ,the vertical line to the right represents #avolt4 ,,table ,,showing ,,the ,,increasing ,,electric ,,response ,,due ,,to ,,increasing ,,amplitude ,,of ,,vibration ------------------------------------- ,vibration amplitude ,e4,m4 variation ------------------------------------- #e #jbd volt #aj #jeg #bj #aaa #be #adc #cj #agj #ce #ahg #dj #bjd ------------------------------------- ,the next figure 7fig4#hd7 gives record of responses through a wider range4 ,for accurate quantitative measurements it is preferable to wait till the recovery is complete4 ,we may accomplish this within the limited space of the recording photographic plate by making the record for one minute2 during the rest of recovery1 the clockwork moving the plate is stopped and the galvanometer spot of light is cut off4 ,thus the next record starts from a point of completed recovery1 which will be noticed as a bright spot at the beginning of each curve4 ,with stimulation of high intensity1 a tendency will be noticed for the responses to approach a limit4 ,illustration3 ,,fig4#hd4--;,a ,,second ,,set ,,of ,,records ,,with ,a ,,different ,,specimen ,,of ,,tin ,the amplitudes of vibration are increased by steps of #aj1 from #bj to #afj4 7,the deflections are reduced by interposing a high external resistance47 ,illustration3 ,,fig4#he4--;,,effect ,,of ,,superposition ,,on ,,tin ,a single stimulus produces the feeble effect shown in the first response4 ,superposition of #e1 #i1 #ac such stimuli produce the succeeding stronger responses4 ,threshold of response4--,there is a minimum intensity of stimulus below which there is hardly any visible response4 ,we may regard this point as the threshold of response4 ,though apparently ineffective1 the subliminal stimuli produce some latent effect1 which may be demonstrated by their additive action4 ,the record in fig4#he shows how individually feeble stimuli become markedly effective by superposition4 ,illustration3 ,,fig4#hf4--;,,incomplete ,,and ,,complete ,,fusion ,,of ,,effect ,,in ,,tin ,as the frequency of stimulation is increased the fusion becomes more and more complete4 ,vertical line to the right represents #avolt4 ,superposition of stimuli4--,the additive effect of succeeding stimuli will be seen from the above4 ,the fusion of effect will be incomplete if the frequency of stimulation be not sufficiently great2 but it will tend to be more complete with higher frequency of stimulation 7fig4#hf74 ,we have here a parallel case to the complete and incomplete tetanus of muscles1 under similar conditions4 ,by the addition of these rapidly succeeding stimuli1 a maximum effect is produced1 and further stimulation adds nothing to this4 ,the effect is balanced by a force of restitution4 ,the response-curve thus rises to its maximum1 after which the deflection is held as it were rigid1 so long as the vibration is kept up4 ,illustration3 ,,fig4#hg4--;,,cyclic ,,curve ,,for ,,maximum ,,effects ,,showing ,,hysteresis ,it was found that increasing intensities of single stimuli produced correspondingly increased responses4 ,the same is true also of groups of stimuli4 ,the maximum effect produced by superposition of stimuli increases with the intensity of the constituent stimuli4 ,hysteresis4--,allusion has already been made to the increased responsiveness conferred by preliminary stimulation 7see p4#abg74 ,being desirous of finding out in what manner this is brought about1 ,i took a series of observations for an entire cycle1 that is to say1 a series of observations were taken for maximum effects1 starting from amplitude of vibration of #aj and ending in #ajj1 and backwards from #ajj to #aj4 ,effect of hysteresis is very clearly seen 7see ,a1 fig4#hg72 there is a considerable divergence between the forward and return curves1 the return curve being higher4 ,on repeating the cycle several times1 the divergence is found very much reduced1 the wire on the whole is found to assume a more constant sensitiveness4 ,in this steady condition1 generally speaking1 the sensitiveness for smaller amplitude of vibration is found to be greater than at the very beginning1 but the reverse is the case for stronger intensity of stimulation4 ,effect of annealing4--,i repeated the experiment with the same wire1 after pouring hot water into the cell and allowing it to cool to the old temperature4 ,from the cyclic curve 7,b1 fig4#hg7 it will be seen 7#a7 that the sensitiveness has become very much enhanced2 7#b7 that there is relatively less divergence between the forward and return curves4 ,even this divergence practically disappeared at the third cycle1 when the forward and backward curves coincided 7,c1 fig4#hg74 ,the above results show in what manner the excitability of the wire is enhanced by purely physical means4 ,it is very curious to notice that addition of ,na#b;,,co#c solution 7see ,chap4 ,,xv--,action of ,stimulants7 produces enhancement of responsive power similar to that produced by annealing2 that is to say1 not only is there a great increase of sensitiveness1 but there is also a reduction of hysteresis4 ,,chapter ,,xvi ,,inorganic ,,response--,,effect ,,of ,,chemical ,,reagent ,action of chemical reagents--,action of stimulants on metals--,action of depressants on metals--,effect of 'poisons' on metals--,opposite effect of large and small doses4 ,we have seen that the ultimate criterion of the physiological character of electric response is held to be its abolition when the substance is subjected to those chemical reagents which act as poisons4 ,illustration3 ,,fig4#hh4--;,,action ,,of ,,poison ,,in ,,abolishing ,,response ,,in ,,nerve 7,,waller7 ,action of chemical reagents4--,of these reagents1 some are universal in their action1 amongst which strong solutions of acids and alkalis1 and salts like mercuric chloride1 may be cited4 ,these act as powerful toxic agents1 killing the living tissue1 and causing electric response to disappear4 7,see fig4#hh47 ,it must1 however1 be remembered that there are again specific poisons which may affect one kind of tissue and not others4 ,poisons in general may be regarded as extreme cases of depressants4 ,as an example of those which produce moderate physiological depression1 potassium bromide may be mentioned1 and this also diminishes electric response4 ,there are other chemical reagents1 on the other hand1 which produce the opposite effect of increasing the excitability and causing a corresponding exaltation of electric response4 ,we shall now proceed to inquire whether the response of inorganic bodies is affected by chemical reagents1 so that their excitability is exalted by some1 and depressed or abolished by others4 ,should it prove to be so1 the last test will have been fulfilled1 and that parallelism which has been already demonstrated throughout a wide range of phenomena1 between the electric response of animal tissues on the one hand1 and that of plants and metals on the other1 will be completely established4 ,action of stimulants on metals4--,we shall first study the stimulating action of various chemical reagents4 ,the method of procedure is to take a series of normal responses to uniform stimuli1 the electrolyte being water4 ,the chemical reagent whose effect is to be observed is now added in small quantity to the water in the cell1 and a second series of responses taken1 using the same stimulus as before4 ,generally speaking1 the influence of the reagent is manifested in a short period1 but there may be occasional instances where the effect takes some time to develop fully4 ,we must remember that by the introduction of the chemical reagent some change may be produced in the internal resistance of the cell4 ,the effect of this on the deflection is eliminated by interposing a very high external resistance 7from one to five megohms7 in comparison with which the internal resistance of the cell is negligible4 ,the fact that the introduction of the reagent did not produce any variation in the total resistance of the circuit was demonstrated by taking two deflections1 due to a definite fraction of a volt1 before and after the introduction of the reagent4 ,these deflections were found equal4 ,illustration3 ,,fig4#hi4--,,stimulating ,,action ,,of ,na#b;,,co#c ,,on ,,tin ,i first give a record of the stimulating action of sodium carbonate on tin1 which will become evident by a comparison of the responses before and after the introduction of ,na#b;,,co#c 7fig4#hi74 ,the next record shows the effect of the same reagent on platinum 7fig4#ij74 ,illustration3 ,,fig4#ij4--,,stimulating ,,action ,,of ,na#b;,,co#c ,,on ,,platinum ,action of depressants4--,certain other reagents1 again1 produce an opposite effect4 ,that is to say1 they diminish the intensity of response4 ,the record given on the next page 7fig4#ia7 shows the depressing action of #ajpercent4 solution of ,k,br on tin4 ,illustration3 ,,fig4#ia4--;,,depressing ,,effect ,,of ,,kbr 7#aj,,per ,,cent47 ,,on ,,the ,,response ,,of ,,tin ,effect of 'poison4'--,living tissues are killed1 and their electric responses are at the same time abolished by the action of poisons4 ,it is very curious that various chemical reagents are similarly effective in killing the response of metals4 ,i give below a record 7fig4#ib7 to show how oxalic acid abolishes the response4 ,the depressive effect of this reagent is so great that a strength of one part in #aj1jjj is often sufficient to produce complete abolition4 ,another notable point with reference to the action of this reagent is the persistence of after-effect4 ,this will be clearly seen from an account of the following experiment4 ,the two wires ,a and ,b1 in the cell filled with water1 were found to give equal responses4 ,the wires were now lifted off1 and one wire ,b was touched with dilute oxalic acid4 ,all traces of acid were next removed by rubbing the wire with cloth under a stream of water4 ,on replacing the wire in the cell1 ,a gave the usual response1 whereas that of ,b was found to be abolished4 ,the depression produced is so great and passes in so deep that ,i have often failed to revive the response1 even after rubbing the wire with emery paper1 by which the molecular layer on the surface must have been removed4 ,illustration3 ,,fig4#ib4--;,,abolition ,,of ,,response ,,by ,,oxalic ,,acid ,we have seen in the molecular model 7fig4#fb1 d1 e7 how the attainment of maximum is delayed1 the response diminished1 and the recovery prolonged or arrested by increase of friction or reduction of molecular mobility4 ,it would appear as if the reagents which act as poisons produced some kind of molecular arrest4 ,the following records seen to lend support to this view4 ,if the oxalic acid is applied in large quantities1 the abolition of response is complete4 ,but on carefully adding just the proper amount ,i find that the first stimulus evokes a responsive electric twitch1 which is less than the normal1 and the period of recovery is very much prolonged from the normal one minute before1 to five minutes after1 the application of the reagent 7fig4#ic1 a74 ,in another record the arrest is more pronounced1 i4e4 there is now no recovery 7fig4#ic1 b74 ,note also that the maximum is attained much later4 ,stimuli applied after the arrest produce no effect1 as if the molecular mechanism became1 as it were1 clogged or locked up4 ,in connection with this it is interesting to note that the effect of veratrine poison on muscle is somewhat similar4 ,this reagent not only diminishes the excitability1 but causes a very great prolongation of the period of recovery4 ,in connection with the action of chemical reagents the following points are noteworthy4 ,illustration3 ,,fig4#ic4--',,molecular ,,arrest' ,,by ,,the ,,action ,,of ',,poison' ,in each1 curves to the left show the normal response1 curve to the right shows the effect of poison4 ,in 7a7 the arrest is evidenced by prolongation of period of recovery4 ,in 7b7 there is no recovery4 7#a7 ,the effect of these reagents is not only to increase or diminish the height of the response-curve1 but also to modify the time relations4 ,by the action of some the latent period is diminished1 others produce a prolongation of the period of recovery4 ,some curious effects produced by the change of time relations have been noticed in the account given of diphasic variation 7see p4#aac74 7#b7 ,the effect produced by a chemical reagent depends to some extent on the previous condition of the wire4 7#c7 ,a certain time is required for the full development of the effect4 ,with some reagents the full effect takes place almost instantaneously1 while with others the effect takes place slowly4 ,again the effect may with time reach a maximum1 after which there may be a slight decline4 7#d7 ,the after-effects of the reagents may be transitory or persistent2 that is to say1 in some cases the removal of the reagent causes the responses to revert to the normal1 while in others the effect persists even after the removal of all traces of the reagent4 ,opposite effects of large and small doses4--,there remains a very curious phenomenon1 known not only to students of physiological response but also known in medical practice1 namely that of the opposite effects produced by the same reagent when given in large or in small doses4 ,here1 too1 we have the same phenomena reproduced in an extraordinary manner in inorganic response4 ,the same reagent which becomes a 'poison' in large quantities may act as a stimulant when applied in small doses4 ,this is seen in record fig4#id1 in which 7a7 gives the normal responses in water2 ,,kho solution was now added so as to make the strength three parts in #a1jjj1 and 7b7 shows the consequent enhancement of response4 ,a further quantity of ,,kho was added so as to increase the strength to three parts in #ajj4 ,this caused a complete abolition 7c7 of response4 ,illustration3 ,,fig4#id4--,,opposite ,,effects ,,of ,,small ,,and ,,large ,,doses 7,,tin7 7a7 is the normal response2 7b7 is the stimulating action of small dose of potash 7#cparts in #a1jjj72 7c7 is the abolition of response with a stronger dose 7#cparts in #ajj74 ,it will thus be seen that as in the case of animal tissues and of plants1 so also in metals1 the electrical responses are exalted by the action of stimulants1 lowered by depressants1 and completely abolished by certain other reagents4 ,the parallelism will thus be found complete in every detail between the phenomena of response in the organic and the inorganic4 ,,chapter ,,xvii ,,on ,,the ,,stimulus ,,of ,,light ,,and ,,retinal ,,currents ,visual impulse3 7#a7 chemical theory2 7#b7 electrical theory--,retinal currents--,normal response positive--,inorganic response under stimulus of light--,typical experiment on the electrical effect induced by light4 ,the effect of the stimulus of light on the retina is perceived in the brain as a visual sensation4 ,the process by which the ether-wave disturbance causes this visual impulse is still very obscure4 ,two theories may be advanced in explanation4 7#a7 ,chemical theory4--,according to the first1 or chemical1 theory1 it is supposed that certain visual substances in the retina are affected by light1 and that vision originates from the metabolic changes produced in these visual substances4 ,it is also supposed that the metabolic changes consist of two phases1 the upward1 constructive1 or anabolic phase1 and the downward1 destructive1 or katabolic phase4 ,various visual substances by their anabolic or katabolic changes are supposed to produce the variations of sensation of light and colour4 ,this theory1 as will be seen1 is very complex1 and there are certain obstacles in the way of its acceptance4 ,it is1 for instance1 difficult to see how this very quick visual process could be due to a comparatively slow chemical action1 consisting of the destructive breaking-down of the tissue1 followed by its renovation4 ,some support was at first given to this chemical theory by the bleaching action of light on the visual purple present in the retina1 but it has been found that the presence or absence of visual purple could not be essential to vision1 and that its function1 when present1 is of only secondary importance4 ,for it is well known that in the most sensitive portion of the human retina1 the fovea centralis1 the visual purple is wanting2 it is also found to be completely absent from the retin of many animals possessing keen sight4 7#b7 ,electrical theory4--,the second1 or electrical1 theory supposes that the visual impulse is the concomitant of an electrical impulse2 that an electrical current is generated in the retina under the incidence of light1 and that this is transmitted to the brain by the optic nerve4 ,there is much to be said in favour of this view1 for it is an undoubted fact1 that light gives rise to retinal currents1 and that1 conversely1 an electrical current suitably applied causes the sensation of light4 ,retinal currents4--,holmgren1 ,dewar1 ,mc,kendrick1 ,kuhne1 ,steiner1 and others have shown that illumination produces electric variation in a freshly excised eye4 ,about this general fact of the electrical response there is a widespread agreement1 but there is some difference of opinion as regards the sign of this response immediately on the application1 cessation1 and during the continuance of light4 ,these slight discrepancies may be partly due to the unsatisfactory nomenclature--as regards use of terms positive and negative--hitherto in vogue and partly also to the differing states of the excised eyes observed4 ,waller1 in his excellent and detailed work on the retinal currents of the frog1 has shown how the sign of response is reversed in the moribund condition of the eye4 ,as to the confusion arising from our present terminology1 we must remember that the term positive or negative is used with regard to a current of reference--the so-called current of injury4 ,illustration3 ,,fig4#ie4 ,,retinal ,,response ,,to ,,light ,the current of response is from the nerve to the retina4 ,when the two galvanometric contacts are made1 one with the cut end of the nerve1 and the other on the uninjured cornea1 a current of injury is found which in the eye is from the nerve to the retina4 ,in the normal freshly excised eye1 the current of response due to the action of light on the retina is always from the nerve1 which is not directly stimulated by light1 to the retina1 that is1 from the less excited to the more excited 7fig4#ie74 ,this current of response flows1 then1 in the same direction as the existing current of reference--the current of injury--and may therefore be called positive4 ,unfortunately the current of injury is very often apt to change its sign2 it then flows through the eye from the cornea to the nerve4 ,and now1 though the current of response due to light may remain unchanged in direction1 still1 owing to the reversal of the current of reference1 it will appear as negative4 ,that is to say1 though its absolute direction is the same as before1 its relative direction is altered4 ,i have already advocated the use of the term positive for currents which flow towards the stimulated1 and negative for those whose flow is away from the stimulated4 ,if such a convention be adopted1 no confusion can arise1 even when1 as in the given cases1 the currents of injury undergo a change of direction4 ,normal response positive4--,the normal effect of light on the retina1 as noticed by all the observers already mentioned1 is a positive variation1 during exposure to light of not too long duration4 ,cessation of light is followed by recovery4 ,on these points there is general agreement amongst investigators4 ,deviations are regarded as due to abnormal conditions of the eye1 owing to rough usage1 or to the rapid approach of death4 ,for just as in the dying plant we found occasional reversals from negative to positive response1 so in the dying retina the response may undergo changes from the normal positive to negative4 ,the sign of response1 as we have already seen in numerous cases1 depends very much on the molecular condition of the sensitive substance1 and if this condition be in any way changed1 it is not surprising that the character of the response should also undergo alteration4 ,unlike muscle in this1 successive retinal responses exhibit little change1 for1 generally speaking1 fatigue is very slight1 the retina recovering quickly even under strong light if the exposure be not too long4 ,in exceptional cases1 however1 fatigue1 or its converse1 the staircase effect1 may be observed4 ,inorganic response under the stimulus of light4--,it may now be asked whether such a complex vital phenomenon as retinal response could have its counterpart in non-living response4 ,taking a rod of silver1 we may beat out one end into the form of a hollow cup1 sensitising the inside by exposing it for a short time to vapour of bromine4 ,the cup may now be filled with water1 and connection made with a galvanometer by non-polarisable electrodes4 ,there will now be a current due to difference between the inner surface and the rod4 ,this may be balanced1 however1 by a compensating ,e4,m4,f4 ,illustration3 ,,fig4#if4--,,record ,,of ,,responses ,,to ,,light ,,given ,,by ,,the ,,sensitive ,,cell ,thick lines represent the effect during illumination1 dotted lines the recovery in darkness4 ,note the preliminary negative twitch1 which is sometimes also observed in responses of frog's retina4 ,we have thus an arrangement somewhat resembling the eye1 with a sensitive layer corresponding to the retina1 and the less sensitive rod corresponding to the conducting nerve-stump 7fig4#if1 a74 ,the apparatus is next placed inside a black box1 with an aperture at the top4 ,by means of an inclined mirror1 light may be thrown down upon the sensitive surface through the opening4 ,on exposing the sensitive surface to light1 the balance is at once disturbed1 and a responsive current of positive character produced4 ,the current1 that is to say1 is from the less to the more stimulated sensitive layer4 ,on the cessation of light1 there is fairly quick recovery 7fig4#if1 b74 ,the character and the intensity of ,e4,m4 variation of the sensitive cell depend to some extent on the process of preparation4 ,the particular cell with which most of the following experiments were carried out usually gave rise to a positive variation of about #jjhvolt when acted on for one minute by the light of an incandescent gas-burner which was placed at a distance of #ej;cm4 ,typical experiment on the electrical effect induced by light4--,this subject of the production of an electrical current by the stimulus of light would appear at first sight very complex4 ,but we shall be able to advance naturally to a clear understanding of its most complicated phenomena if we go through a preliminary consideration of an ideally simple case4 ,we have seen1 in our experiments on the mechanical stimulation of1 for example1 tin1 that a difference of electric potential was induced between the more stimulated and less stimulated parts of the same rod1 and that an action current could thus be obtained1 on making suitable electrolytic connections4 ,whether the more excited was zincoid or cuproid depended on the substance and its molecular condition4 ,let us now imagine the metal rod flattened into a plate1 and one face stimulated by light1 while the other is protected4 ,would there be a difference of potential induced between the two faces of this same sheet of metal8 ,let two blocks of paraffin be taken and a large hole drilled through both4 ,next1 place a sheet of metal between the blocks1 and pour melted paraffin round the edge to seal up the junction1 the two open ends being also closed by panes of glass4 ,we shall have then two compartments separated by the sheet of metal1 and these compartments may be filled with water through the small apertures at the top 7fig4#ig1 a74 ,illustration3 ,,fig4#ig 7a7 ,a1 ,b are the two faces of a brominated sheet of silver4 ,one face1 say ,a1 is acted on by light4 ,the current of response is from ,b to ,a1 across the plate4 ,illustration3 ,,fig4#ig 7b74--,,record ,,of ,,responses ,,obtained ,,from ,,the ,,above ,,cell ,ten seconds' exposure to light followed by fifty seconds' recovery in the dark4 ,thick lines represent action in light1 dotted lines represent recovery4 ,the two liquid masses in the separated chambers thus make perfect electrolytic contacts with the two faces ,a and ,b of the sheet of metal4 ,these two faces may be put in connection with a galvanometer by means of two non-polarisable electrodes1 whose ends dip into the two chambers4 ,if the sheet of metal have been properly annealed1 there will now be no difference of potential between the two faces1 and no current in the galvanometer4 ,if the two faces are not molecularly similar1 however1 there will be a current1 and the electrical effects to be subsequently described will act additively1 in an algebraical sense4 ,let one face now be exposed to the stimulus of light4 ,a responsive current will be found to flow1 from the less to the more stimulated face1 in some cases1 and in others in an opposite direction4 ,it appears at first very curious that this difference of electric potential should be maintained between opposite faces of a very thin and highly conducting sheet of metal1 the intervening distance between the opposed surfaces being so extremely small1 and the electrical resistance quite infinitesimal4 ,a homogeneous sheet of metal has become by the unequal action of light1 molecularly speaking1 heterogeneous4 ,the two opposed surfaces are thrown into opposite kinds of electric condition1 the result of which is as if a certain thickness of the sheet1 electrically speaking1 were made zinc-like1 and the rest copper-like4 ,from such unfamiliar conceptions1 we shall now pass easily to others to which we are more accustomed4 ,instead of two opposed surfaces1 we may obtain a similar response by unequally lighting different portions of the same surface4 ,taking a sheet of metal1 we may expose one half1 say ,a1 to light1 the other half1 ,b1 being screened4 ,electrolytic contacts are made by plunging the two limbs in two vessels which are in connection with the two non-polarisable electrodes ,e and ,e' 7fig4#ih1 a74 ,on illumination of ,a and ,b alternately1 we shall now obtain currents flowing alternately in opposite directions4 ,illustration3 ,,fig4#ih4--,,modification ,,of ,,the ,,sensitive ,,cell ,just as in the strain cells the galvanometer contact was transferred from the electrolytic part to the metallic part of the circuit1 so we may next1 in an exactly similar manner1 cut this plate into two1 and connect these directly to the galvanometer1 electrolytic connection being made by partially plunging them into a cell containing water4 ,the posterior surfaces of the two half-plates may be covered with a non-conducting coating4 ,and we arrive at a typical photo-electric cell 7fig4#ih1 b74 ,these considerations will show that the eye is practically a photo-electric cell4 ,illustration3 ,,fig4#ii4--,,responses ,,to ,,light ,,in ,,frog',s ,,retina ,illumination ,l for one minute1 recovery in dark for two minutes during obscurity ,d4 7,waller47 ,we shall now give detailed experimental results obtained with the sensitive silver-bromide cell1 and compare its response-curve with those of the retina4 ,a series of uniform light stimuli gives rise to uniform responses1 which show very little sign of fatigue4 ,how similar these response-curves are to those of the retina will be seen from a pair of records given below1 where fig4#ii shows responses of frog's retina1 and fig4#ajj gives the responses obtained with the sensitive silver cell 7fig4#ajj74 ,it was said that the responses of the retina are uniform4 ,this is only approximately true4 ,in addition to numerous cases of uniform responses1 ,waller finds instances of 'staircase' increase1 and its opposite1 slight fatigue4 ,in the record here given of the silver cell1 the staircase effect is seen at the beginning1 and followed by slight fatigue4 ,i have other records where for a very long time the responses are perfectly uniform1 there being no sign of fatigue4 ,illustration3 ,,fig4#ajj4--,,responses ,,in ,,sensitive ,,silver ,,cell ,illumination for one minute and obscurity for one minute4 ,thick line represents record during illumination1 dotted line recovery during obscurity4 ,another curious phenomenon sometimes observed in the response of retina is an occasional slight increase of response immediately on the cessation of light1 after which there is the final recovery4 ,an indication of this is seen in the second and fourth curves in fig4#ii4 ,curiously enough1 this abnormality is also occasionally met with in the responses of the silver cell1 as seen in the first two curves of fig4#ajj4 ,other instances will be given later4 ,,chapter ,,xviii ,,inorganic ,,response--,,influence ,,of ,,various ,,conditions ,,on ,,the ,,response ,,to ,,stimulus ,,of ,,light ,effect of temperature--,effect of increasing length of exposure--,relation between intensity of light and magnitude of response--,after-oscillation--,abnormal effects3 7#a7 preliminary negative twitch2 7#b7 reversal of response2 7#c7 transient positive twitch on cessation of light2 7#d7 decline and reversal--,rsum4 ,we shall next proceed to study the effect1 on the response of the sensitive cell1 of all those conditions which influence the normal response of the retina4 ,we shall then briefly inquire whether even the abnormalities sometimes met with in retinal responses have not their parallel in the responses given by the inorganic4 ,illustration3 ,,fig4#aja4--;,,influence ,,of ,,temperature ,,on ,,response ,illumination#bj1 obscurity#dj4 ,in 7a7 is shown a series of responses at #bj;,c4--the record exhibits slight fatigue4 7b7 is the slight irregular response at #ej;,c4 7c7 is the record on re-cooling2 it exhibits 'staircase' increase4 ,effect of temperature4--,it has been found that when the temperature is raised above a certain point1 retinal response shows rapid diminution4 ,on cooling1 however1 response reappears1 with its original intensity4 ,in the response given by the sensitive cell1 the same peculiarity is noticed4 ,i give below 7fig4#aja1 a7 a set of response-curves for #bj;,c4 ,these responses1 after showing slight fatigue1 became fairly constant4 ,on raising the temperature to #ej;,c4 response practically disappeared 7#aja1 b74 ,but on cooling to the first temperature again1 it reappeared1 with its original if not slightly greater intensity 7fig4#aja1 c74 ,a curious point is that while in record 7a71 before warming1 slight fatigue is observed1 in 7c71 after cooling1 the reverse1 or staircase effect1 appears4 ,illustration3 ,,fig4#ajb4--,,response-,,curves ,,for ,,increasing ,,duration ,,of ,,illumination ,,from #a ,,to #aj ,in 7a7 the source of light was at a distance of #ej;cm42 in 7b7 it was at a distance of #be;cm4 ,note the after-oscillation4 ,effect of increasing length of exposure4--,if the intensity of light be kept constant1 the magnitude of response of the sensitive cell increases with length of exposure4 ,but this soon reaches a limit1 after which increase of duration does not increase magnitude of effect4 ,too long an exposure may however1 owing to fatigue1 produce an actual decline4 ,i give here two sets of curves 7fig4#ajb7 illustrating the effect of lengthening exposure4 ,the intensities of light in the two cases are as #a to #d4 ,the incandescent burner was in the two cases at distances #ej and #be;cm4 respectively4 ,it will be observed that beyond eight seconds' exposure the responses are approximately uniform4 ,another noticeable fact is that with long exposure there is an after-oscillation4 ,this growing effect with lengthening exposure and attainment of limit is exactly paralleled by responses of retina under similar conditions4 ,relation between intensity of light and magnitude of response4--,in the responses of retina1 it is found that increasing intensity of light produces an increasing effect4 ,but the rate of increase is not uniform3 increase of effect does not keep pace with increase of stimulus4 ,thus a curve giving the relation between stimulus and response is concave to the axis which represents the stimulus4 ,the same is true of the sensation of light4 ,that is to say1 within wide limits1 intensity of sensation does not increase so rapidly as stimulus4 ,this particular relation between stimulus and effect is also exhibited in a remarkable manner by the sensitive cell4 ,for a constant source of light ,i used an incandescent burner1 and graduated the intensity of the incident light by varying its distance from the sensitive cell4 ,the intensity of light incident on the cell1 when the incandescent burner is at a distance of #aej;cm41 has been taken as the arbitrary unit4 ,in order to make allowance for the possible effects of fatigue ,i took two successive series of responses 7fig4#ajc74 ,in the first1 records were taken with intensities diminishing from #g to #a1 and immediately afterwards increasing from #a to #g1 in the second4 ,illustration3 ,,fig4#ajc4--,,responses ,,of ,,sensitive ,,cell ,,to ,,various ,,intensities ,,of ,,light ,on the left the responses are for diminishing intensities in the ratios of #g1 #e1 #c1 and #a4 ,on the right they are for the increasing intensities #a1 #c1 #e1 and #g4 ,the thick lines are records during exposures of one minute2 the dotted lines represent recoveries for one minute4 ,,table ,,giving ,,response ,,to ,,varying ,,intensities ,,of ,,light 7,the intensity of an incandescent gas-burner at a distance of #aej;cm4 is taken as unit47 ---------------------------------------- -------------------------- ,response ,response ,intensity 7,light 7,light ,mean ,value in volt of ,light diminishing7 increasing7 ---------------------------------------- -------------------------- #g #dc #ci #da #fcj #aj- volt #e #ca #bi #cj #dfa #c #ahe #age #ah #bgg #a #aj #i #ie #adf ---------------------------------------- -------------------------- ,as the zero point was slightly shifted during the course of the experiment1 the deflection in each curve was measured from a line joining the beginning of the response to the end of its recovery4 ,a mean deflection1 corresponding to each intensity1 was obtained by taking the average of the descending and ascending readings4 ,the two sets of readings did not1 however1 vary to any marked extent4 ,the deflections corresponding to the intensities #a1 #c1 #e1 #g1 are1 then1 as #ie to #ah1 to #cj1 to #da4 ,if the deflections had been strictly proportionate to the intensities of light stimulus they would have been as #ie to #bhe1 to #dge1 to #ffe4 ,illustration3 ,,fig4#ajd4--;,,curves ,,giving ,,the ,,relation ,,between ,,intensity ,,of ,,light ,,and ,,magnitude ,,of ,,response ,in 7a7 sensitive cell1 7b7 in frog's retina4 ,in another set of records1 with a different cell1 ,i obtained the deflections of #f1 #aj1 #ac1 #ae1 corresponding to light intensities of #c1 #e1 #g1 and #i4 ,the two curves in fig4#ajd1 giving the relation between response and stimulus1 show that in the case of inorganic substances1 as in the retina 7,waller71 magnitude of response does not increase so rapidly as stimulus4 ,after-oscillation4--,when the sensitive surface is subjected to the continued action of light1 the ,e4,m4 effect attains a maximum at which it remains constant for some time4 ,if the exposure be maintained after this for a longer period1 there will be a decline1 as we found to be the case in other instances of continued stimulation4 ,the appearance of this decline1 and its rapidity1 depends on the particular condition of the substance4 ,when the sensitive element is considerably strained by the action of light1 and if that light be now cut off1 there is a rebound towards recovery and a subsequent after-oscillation4 ,that is to say1 the curve of recovery falls below the zero point1 and then slowly oscillates back to the position of equilibrium4 ,we have already seen an instance of this in fig4#ajb4 ,above is given a series of records showing the appearance of decline1 from too long-continued exposure and recovery1 followed by after-oscillation on the cessation of light 7fig4#aje74 ,certain visual analogues to this phenomenon will be noticed later4 ,illustration3 ,,fig4#aje4--;,,after-,,oscillation ,exposure of one minute followed by obscurity of one minute4 ,note the decline during illumination1 and after-oscillation in darkness4 ,abnormal effects4--,we have already treated of all the normal effects of the stimulus of light on the retina1 and their counterparts in the sensitive cell4 ,but the retina undergoes molecular changes when injured1 stale1 or in a dying condition1 and under these circumstances various complicated modifications are observed in the response4 ,illustration3 ,,fig4#ajf4--,,transient ,,positive ,,augmentation ,,given ,,by ,,the ,,frog',s ,,retina ,,on ,,the ,,cessation ,,of ,,light ,l 7,,waller7 #a4 ,preliminary negative twitch4--,when the light is incident on the frog's retina1 there is sometimes a transitory negative variation1 followed by the normal positive response4 ,this is frequently observed in the sensitive cell 7see fig4#if1 b74 #b4 ,reversal of response4--,again1 in a stale retina1 owing to molecular modification the response is apt to undergo reversal 7,waller74 ,that is to say1 it now becomes negative4 ,in working with the same sensitive cell on different days ,i have found it occasionally exhibiting this reversed response4 #c4 ,transient rise of current on cessation of light4--,another very curious fact observed in the retina by ,kuhne and ,steiner is that immediately on the stoppage of light there is sometimes a sudden increase in the retinal current1 before the usual recovery takes place4 ,this is very well shown in the series of records taken by ,waller 7fig4#ajf74 ,it will be noticed that on illumination the response-curve rises1 that continued illumination produces a decline1 and that on the cessation of light there is a transient rise of current4 ,i give here a series of records which will show the remarkable similarity between the responses of the cell and retina1 in respect even of abnormalities so marked as those described 7fig4#ajg74 ,i may mention here that some of these curious effects1 that is to say1 the preliminary negative twitch and sudden augmentation of the current on the cessation of light1 have also been noticed by ,minchin in photo-electric cells4 ,illustration3 ,,fig4#ajg4--,,responses ,,in ,,silver ,,cell ,the thick line represents response during light 7half a minute's exposure71 and dotted line the recovery during darkness4 ,note the terminal positive twitch4 #d4 ,decline and reversal4--,we have seen that under the continuous action of light1 response begins to decline4 ,sometimes this process is very rapid1 and in any case1 under continued light1 the deflection falls4 7#a7 ,the decline may nearly reach zero4 ,if now the light be cut off there is a rebound towards recovery downwards1 which carries it below zero1 followed by an after-oscillation 7fig4#ajh1 a74 ,illustration3 ,,fig4#ajh--;,,decline ,,under ,,the ,,continued ,,action ,,of ,,light 7a7 ,decline short of zero2 on stoppage of light1 rebound downwards to zero2 after-oscillation4 7b7 ,decline below zero2 on stoppage of light1 rebound towards zero1 with preliminary negative twitch4 7c7 ,the same1 decline further down2 negative twitch almost disappearing4 7#b7 ,if the light be continued for a longer time1 the decline goes on even below zero2 that is to say1 the response now becomes apparently negative4 ,if1 now1 the light be stopped1 there is a rebound upwards to recovery1 with1 generally speaking1 a slight preliminary twitch downwards 7fig4#ajh1 b1 c74 ,this rebound carries it back1 not only to the zero position1 but sometimes beyond that position4 ,we have here a parallel to the following observation of ,dewar and ,mc,kendrick3 ',when diffuse light is allowed to impinge on the eye of the frog1 after it has arrived at a tolerably stable condition1 the natural ,e4,m4,f4 is in the first place increased1 then diminished2 during the continuance of light it is still slowly diminished to a point where it remains tolerably constant1 and on the removal of light there is a sudden increase of the ,e4,m4 power nearly up to its original position4'#ah 7#c7 ,i have sometimes obtained the following curious result4 ,on the incidence of light there is a response1 say1 upward4 ,on the continuation of light the response declines to zero and remains at the zero position1 there being no further action during the continuation of stimulus4 ,but on the cessation or 'break' of light stimulus1 there is a response downwards1 followed by the usual recovery4 ,this reminds us of a somewhat similar responsive action produced by constant electric current on the muscle4 ,at the moment of 'make' there is a responsive twitch1 but afterwards the muscle remains quiescent during the passage of the current1 but on breaking the current there is seen a second responsive twitch4 ,rsum4--,so we see that the response of the sensitive inorganic cell1 to the stimulus of light1 is in every way similar to that of the retina4 ,in both we have1 under normal conditions1 a positive variation2 in both the intensity of response up to a certain limit increases with the duration of illumination2 it is affected1 in both alike1 by temperature2 in both there is comparatively little fatigue2 the increase of response with intensity of stimulus is similar in both2 and finally1 even in abnormalities--such as reversal of response1 preliminary negative twitch on commencement1 and terminal positive twitch on cessation of illumination1 and decline and reversal under continued action of light--parallel effects are noticed4 ,illustration3 ,,fig4#aji4--;,,certain ,,after-,,effects ,,of ,,light ,we may notice here certain curious relations even in these abnormal responses 7fig4#aji74 ,if the equilibrium position remain always constant1 then it is easy to understand how1 when the rising curve has attained its maximum1 on the cessation of light1 recovery should proceed downwards1 towards the equilibrium position 7fig4#aji1 a74 ,one can also understand how1 after reversal by the continued action of light1 there should be a recovery upwards towards the old equilibrium position 7fig4#aji1 b74 ,what is curious is that in certain cases we get1 on the stoppage of light1 a preliminary twitch away from the zero or equilibrium position1 upwards as in 7c7 7compare also fig4#ajg7 and downwards as in 7d7 7compare also fig4#ajh b74 ,in making a general retrospect1 finally1 of the effects produced by stimulus of light1 we find that there is not a single phenomenon in the responses1 normal or abnormal1 exhibited by the retina which has not its counterpart in the sensitive cell constructed of inorganic material4 ,,footnotes3 #ah ,proc4 ,roy4 ,soc4 ,edin41 #ahgc p4#aec4 ,,chapter ,,xix ,,visual ,,analogues ,effect of light of short duration--,after-oscillation--,positive and negative after-images--,binocular alternation of vision--,period of alternation modified by physical condition--,after-images and their revival--,unconscious visual impression4 ,we have already referred to the electrical theory of the visual impulse4 ,we have seen how a flash of light causes a transitory electric impulse not only in the retina1 but also in its inorganic substitute4 ,light thus produces not only a visual but also an electrical impulse1 and it is not improbable that the two may be identical4 ,again1 varying intensities of light give rise to corresponding intensities of current1 and the curves which represent the relation between the increasing stimulus and the increasing response have a general agreement with the corresponding curve of visual sensation4 ,in the present chapter we shall see how this electrical theory not only explains in a simple manner ordinary visual phenomena1 but is also deeply suggestive with regard to others which are very obscure4 ,we have seen in our silver cell that if the molecular conditions of the anterior and posterior surfaces were exactly similar1 there would be no current4 ,in practice1 however1 this is seldom the case4 ,there is1 generally speaking1 a slight difference1 and a feeble current in the circuit4 ,it is thus seen that there may be an existing feeble current1 to which the effect of light is added algebraically4 ,the stimulus of light may thus increase the existing current of darkness 7positive variation74 ,on the cessation of light again1 the current of response disappears and there remains only the feeble original current4 ,in the case of the retina1 also1 it is curious to note that on closing the eye the sensation is not one of absolute darkness1 but there is a general feeble sensation of light1 known as 'the intrinsic light of the retina4' ,the effect produced by external light is superposed on this intrinsic light1 and certain curious results of this algebraical summation will be noticed later4 ,illustration3 ,,fig4#aaj--,,response-,,curves ,,of ,,the ,,sensitive ,,silver ,,cell ,showing greater persistence of after-effect when the stimulus is strong4 7a7 ,short exposure of #b to light of intensity #a2 7b7 short exposure of #b to light nine times as strong4 ,effect of light of short duration4--,if we subject the sensitive cell to a flash of radiation1 the effect is not instantaneous but grows with time4 ,it attains a maximum some little time after the incidence of light1 and the effect then gradually passes away4 ,again1 as we have seen previously with regard to mechanical strain1 the after-effect persists for a slightly longer time when the stimulus is stronger4 ,the same is true of the after-effect of the stimulus of light4 ,two curves which exhibit this are given below 7fig4#aaj74 ,with regard to the first point--that the maximum effect is attained some time after the cessation of a short exposure--the corresponding experiment on the eye may be made as follows3 at the end of a tube is fixed a glass disc coated with lampblack1 on which1 by scratching with a pin1 some words are written in transparent characters4 ,the length of the tube is so adjusted that the disc is at the distance of most distinct vision from the end of the tube applied to the eye4 ,the blackened disc is turned towards a source of strong light1 and a short exposure is given by the release of a photographic shutter interposed between the disc and the eye4 ,on closing the eye1 immediately after a short exposure1 it will at first be found that there is hardly any well-defined visual sensation2 after a short time1 however1 the writing on the blackened disc begins to appear in luminous characters1 attains a maximum intensity1 and then fades away4 ,in this case the stimulus is of short duration1 the light being cut off before the maximum effect is attained4 ,the after-effect here is positive1 there being no reversal or interval of darkness between the direct image and the after-image1 the one being merely the continuation of the other4 ,but we shall see1 if light is cut off after a maximum effect is attained by long exposure1 that the immediate after-image would be negative 7see below74 ,the relative persistence of after-effect of lights of different intensities may be shown in the following manner3 ,if a bold design be traced with magnesium powder on a blackened board and fired in a dark room1 the observer not being acquainted with the design1 the instantaneous flash of light1 besides being too quick for detailed observation1 is obscured by the accompanying smoke4 ,but if the eyes be closed immediately after the flash1 the feebler obscuring sensation of smoke will first disappear1 and will leave clear the more persistent after-sensation of the design1 which can then be read distinctly4 ,in this manner ,i have often been able to see distinctly1 on closing the eyes1 extremely brief phenomena of light which could not otherwise have been observed1 owing either to their excessive rapidity or to their dazzling character4#ai ,after-oscillation4--,in the case of the sensitive silver cell1 we have seen 7fig4#aje71 when it has been subjected for some time to strong light1 that the current of response attains a maximum1 and that on the stoppage of the stimulus there is an immediate rebound towards recovery4 ,in this rebound there may be an over-shooting of the equilibrium position1 and an after-oscillation is thus produced4 ,if there has been a feeble initial current1 this oscillatory after-current1 by algebraical summation1 will cause the current in the circuit to be alternately weaker and stronger than the initial current4 ,visual recurrence4--,translated into the visual circuit1 this would mean an alternating series of after-images4 ,on the cessation of light of strong intensity and long duration1 the immediate effect would be a negative rebound1 unlike the positive after-effect which followed on a short exposure4 ,the next rebound is positive1 giving rise to a sensation of brightness4 ,this will go on in a recurrent series4 ,if we look for some time at a very bright object1 preferably with one eye1 on closing the eye there is an immediate dark sensation followed by a sensation of light4 ,these go on alternating and give rise to the phenomena of recurrent vision4 ,with the eyes closed1 the positive or luminous phases are the more prominent4 ,this phenomenon may be observed in a somewhat different manner4 ,after staring at a bright light we may look towards a well-lighted wall4 ,the dark phases will now become the more noticeable4 ,if1 however1 we look towards a dimly lighted wall1 both the dark and bright phases will be noticed alternately4 ,the negative effect is usually explained as due to fatigue4 ,that position of the retina affected by light is supposed to be 'tired1' and a negative image to be formed in consequence of exhaustion4 ,by this exhaustion is meant either the presence of fatigue-stuffs1 or the breaking-down of the sensitive element of the tissue1 or both of these4 ,in such a case we should expect that this fatigue1 with its consequent negative image1 would gradually and finally disappear on the restoration of the retina to its normal condition4 ,we find1 however1 that this is not the case1 for the negative image recurs with alternate positive4 ,the accepted theory of fatigue is incapable of explaining this phenomenon4 ,in the sensitive silver cell1 we found that the molecular strain produced by light gave rise to a current of response1 and that on the cessation of light an oscillatory after-effect was produced4 ,the alternating after-effect in the retina points to an exactly similar process4 ,binocular alternation of vision4--,it was while experimenting on the phenomena of recurrent vision that ,i discovered the curious fact that in normal eyes the two do not see equally well at a given instant1 but that the visual effect in each eye undergoes fluctuation from moment to moment1 in such a way that the sensation in the one is complementary to that in the other1 the sum of the two sensations remaining approximately constant4 ,thus they take up the work of seeing1 and then1 relatively speaking1 resting1 alternately4 ,this division of labour1 in binocular vision1 is of obvious advantage4 ,as regards maximum sensation in the two retin there is then a relative retardation of half a period4 ,this may be seen by means of a stereoscope1 carrying1 instead of stereo-photographs1 incised plates through which we look at light4 ,the design consists of two slanting cuts at a suitable distance from each other4 ,one cut1 ,r1 slants to the right1 and the other1 ,l1 to the left 7see fig4#aaa74 ,when the design is looked at through the stereoscope1 the right eye will see1 say ,r1 and the left ,l1 the two images will appear superimposed1 and we see an inclined cross4 ,when the stereoscope is turned towards the sky1 and the cross looked at steadily for some time1 it will be found1 owing to the alternation already referred to1 that while one arm of the cross begins to be dim1 the other becomes bright1 and vice versa4 ,the alternate fluctuations become far more conspicuous when the eyes are closed2 the pure oscillatory after-effects are then obtained in a most vivid manner4 ,after looking through the stereoscope for ten seconds or more1 the eyes are closed4 ,the first effect observed is one of darkness1 due to the rebound4 ,then one luminous arm of the cross first projects aslant the dark field1 and then slowly disappears1 after which the second 7perceived by the other eye7 shoots out suddenly in a direction athwart the first4 ,this alternation proceeds for a long time1 and produces the curious effect of two luminous blades crossing and recrossing each other4 ,illustration3 ,,fig4#aaa4--,,stereoscopic ,,design ,another method of bringing out the phenomenon of alternation in a still more striking manner is to look at two different sets of writing1 with the two eyes4 ,the resultant effect is a blur1 due to superposition1 and the inscription cannot be read with the eyes open4 ,but on closing them1 the composite image is analysed alternately into its component parts1 and thus we are enabled to read better with eyes shut than open4 ,this period of alternation is modified by age and by the condition of the eye4 ,it is1 generally speaking1 shorter in youth4 ,i have seen it vary in different individuals from #a to #aj or more4 ,about #d is the most usual4 ,with the same individual1 again1 the period is somewhat modified by previous conditions of rest or activity4 ,very early in the morning1 after sleep1 it is at its shortest4 ,i give below a set of readings given by an observer3 ,period #h ,a4,m4 #c #ab noon #d #c ,p4,m4 #e #f ,p4,m4 #ed #i #ef #aa #fe ,again1 if one eye be cooled and the other warmed1 the retinal oscillation in one eye is quicker than in the other4 ,the quicker oscillation overtakes the slower1 and we obtain the curious phenomenon of 'visual beats4' ,after-images and their revival4--,in the experiment with the stereoscope and the design of the cross1 the after-images of the cross seen with the eyes closed are at first very distinct--so distinct that any unevenness at the edges of the slanting cuts in the design can be distinctly made out4 ,there can thus be no doubt of the 'objective' nature of the strain impression on the retina1 which on the cessation of direct stimulus of light gives rise to after-oscillation with the concomitant visual recurrence4 ,this recurrence may therefore be taken as a proof of the physical strain produced on the retina4 ,the recurrent after-image is very distinct at the beginning and becomes fainter at each repetition2 a time comes when it is difficult to tell whether the image seen is the objective after-effect due to strain or merely an effect of 'memory4' ,in fact there is no line of demarcation between the two1 one simply merges into the other4 ,that this 'memory' image is due to objective strain is rendered evident by its recurrence4 ,in connection with this it is interesting to note that some of the undoubted phenomena of memory are also recurrent4 ',certain sensations for which there is no corresponding process outside the body are generally grouped for convenience under this term memory4 ,if the eyes be closed and a picture be called to memory1 it will be found that the picture cannot be held1 but will repeatedly disappear and appear4'#bj ,the visual impressions and their recurrence often persist for a very long time4 ,it usually happens that owing to weariness the recurrent images disappear2 but in some instances1 long after this disappearance1 they will spontaneously reappear at most unexpected moments4 ,in one instance the recurrence was observed in a dream1 about three weeks after the original impression was made4 ,in connection with this1 the revival of images1 on closing the eyes at night1 that have been seen during the day1 is extremely interesting4 ,unconscious visual impression4--,while repeating certain experiments on recurrent vision1 the above phenomenon became prominent in an unexpected manner4 ,i had been intently looking at a particular window1 and obtaining the subsequent after-images by closing the eye2 my attention was concentrated on the window1 and ,i saw nothing but the window either as a direct or as an after effect4 ,after this had been repeated a number of times1 ,i found on one occasion1 after closing the eye1 that1 owing to weariness of the particular portion of the retina1 ,i could no longer see the after-image of the window2 instead of this ,i however saw distinctly a circular opening closed with glass panes1 and ,i noticed even the jagged edges of a broken pane4 ,i was not aware of the existence of a circular opening higher up in the wall4 ,the image of this had impressed itself on the retina without my knowledge1 and had undoubtedly been producing the recurrent images which remained unnoticed because my principal field of after-vision was filled up and my attention directed towards the recurrent image of the window4 ,when this failed to appear1 my field of after-vision was relatively free from distraction1 and ,i could not help seeing what was unnoticed before4 ,it thus appears that1 in addition to the images impressed in the retina of which we are conscious1 there are many others which are imprinted without our knowledge4 ,we fail to notice them because our attention is directed to something else4 ,but at a subsequent period1 when the mind is in a passive state1 these impressions may suddenly revive owing to the phenomenon of recurrence4 ,this observation may afford an explanation of some of the phenomena connected with ocular phantoms and hallucinations not traceable to any disease4 ,in these cases the psychical effects produced appear to have no objective cause4 ,bearing in mind the numerous visual impressions which are being unconsciously made on the retina1 it is not at all unlikely that many of these visual phantoms may be due to objective causes4 ,,footnotes3 #ai ,as an instance of this ,i may mention the experiment which ,i saw on the quick fusion of metals exhibited at the ,royal ,institution by ,sir ,william ,roberts-,austen 7#aija71 where1 owing to the glare and the dense fumes1 it was impossible to see what happened in the crucible4 ,but ,i was able to see every detail on closing the eyes4 ,the effects of the smoke1 being of less luminescence1 cleared away first1 and left the after-image of the molten metal growing clearer on the retina4 #bj ,e4,w4 ,scripture1 ,the ,new ,psychology1 p4#aja4 ,,chapter ,,xx ,,general ,,survey ,,and ,,conclusion ,we have seen that stimulus produces a certain excitatory change in living substances1 and that the excitation produced sometimes expresses itself in a visible change of form1 as seen in muscle2 that in many other cases1 however--as in nerve or retina--there is no visible alteration1 but the disturbance produced by the stimulus exhibits itself in certain electrical changes1 and that whereas the mechanical mode of response is limited in its application1 this electrical form is universal4 ,this irritability of the tissue1 as shown in its capacity for response1 electrical or mechanical1 was found to depend on its physiological activity4 ,under certain conditions it could be converted from the responsive to an irresponsive state1 either temporarily as by ansthetics1 or permanently as by poisons4 ,when thus made permanently irresponsive by any means1 the tissue was said to have been killed4 ,we have seen further that from this observed fact--that a tissue when killed passes out of the state of responsiveness into that of irresponsiveness2 and from a confusion of 'dead' things with inanimate matter1 it has been tacitly assumed that inorganic substances1 like dead animal tissues1 must necessarily be irresponsive1 or incapable of being excited by stimulus--an assumption which has been shown to be gratuitous4 ,this 'unexplained conception of irritability became the starting-point1' to quote the words of ,verworn1#ba 'of vitalism1 which in its most complete form asserted a dualism of living and lifeless ,nature4444 ,the vitalists soon1' as he goes on to say1 'laid aside1 more or less completely1 mechanical and chemical explanations of vital phenomena1 and introduced1 as an explanatory principle1 an all-controlling unknown and inscrutable force hypermcanique4 ,while chemical and physical forces are responsible for all phenomena in lifeless bodies1 in living organisms this special force induces and rules all vital actions4 ',later vitalists1 however1 attempted no analysis of vital force2 they employed it in a wholly mystical form as a convenient explanation of all sorts of vital phenomena4444 ,in place of a real explanation a simple phrase such as vital force was satisfactory1 and signified a mystical force belonging to organisms only4 ,thus it was easy to explain the most complex vital phenomena4' ,from this position1 with its assumption of the super-physical character of response1 it is clear that on the discovery of similar effects amongst inorganic substances1 the necessity of theoretically maintaining such dualism in ,nature must immediately fall to the ground4 ,in the previous chapters ,i have shown that not the fact of response alone1 but all those modifications in response which occur under various conditions1 take place in plants and metals just as in animal tissues4 ,it may now be well to make a general survey of these phenomena1 as exhibited in the three classes of substances4 ,we have seen that the wave of molecular disturbance in a living animal tissue under stimulus is accompanied by a wave of electrical disturbance2 that in certain types of tissue the stimulated is relatively positive to the less disturbed1 while in others it is the reverse2 that it is essential to the obtaining of electric response to have the contacts leading to the galvanometer unequally affected by excitation2 and finally that this is accomplished either 7#a7 by 'injuring' one contact1 so that the excitation produced there would be relatively feeble1 or 7#b7 by introducing a perfect block between the two contacts1 so that the excitation reaches one and not the other4 ,further1 it has been shown that this characteristic of exhibiting electrical response under stimulus is not confined to animal1 but extends also to vegetable tissues4 ,in these the same electrical variations as in nerve and muscle were obtained1 by using the method of injury1 or that of the block4 ,passing to inorganic substances1 and using similar experimental arrangements1 we have found the same electrical responses evoked in metals under stimulus4 ,negative variation4--,in all cases1 animal1 vegetable1 and metal1 we may obtain response by the method of negative variation1 so called1 by reducing the excitability of one contact by physical or chemical means4 ,stimulus causes a transient diminution of the existing current1 the variation depending on the intensity of the stimulus 7figs4 #d1 #g1 #ed74 ,illustration3 ,,fig4#aab4--,,uniform ,,responses ,,in 7,a7 ,,nerve1 7,p7 ,,plant1 ,,and 7,m7 ,,metal ,the normal response in nerve is represented 'down4' ,in this and following figures1 7,a7 is the record of responses in animal1 7,p7 in plant1 and 7,m7 in metal4 ,relation between stimulus and response4--,in all three classes we have found that the intensity of response increases with increasing stimulus4 ,at very high intensities of stimulus1 however1 there is a tendency of the response to reach a limit 7figs4 #cj1 #cb1 #hd74 ,the law that is known as ,weber-,fechner's shows a similar characteristic in the relation between stimulus and sensation4 ,and if sensation be a measure of physiological effect we can understand this correspondence of the physiological and sensation curves4 ,we now see further that the physiological effects themselves are ultimately reducible to simple physical phenomena4 ,effects of superposition4--,in all three types1 ineffective stimuli become effective by superposition4 ,again1 rapidly succeeding stimuli produce a maximum effect1 kept balanced by a force of restitution1 and continuation of stimulus produces no further effect1 in the three cases alike 7figs4 #ag1 #ah1 #hf74 ,uniform responses4--,in the responses of animal1 vegetable1 and metal alike we meet with a type where the responses are uniform 7fig4#aab74 ,fatigue4--,there is1 again1 another type where fatigue is exhibited4 ,illustration3 ,,fig4#aac4--;,,fatigue 7,a7 ,,in ,,muscle1 7,p7 ,,in ,,plant1 7,m7 ,,in ,,metal ,the explanation hitherto given of fatigue in animal tissues--that it is due to dissimilation or breakdown of tissue1 complicated by the presence of fatigue-products1 while recovery is due to assimilation1 for which material is brought by the blood-supply--has long been seen to be inadequate1 since the restorative effect succeeds a short period of rest even in excised bloodless muscle4 ,but that the phenomena of fatigue and recovery were not primarily dependent on dissimilation or assimilation becomes self-evident when we find exactly similar effects produced not only in plants1 but also in metals 7fig4#aac74 ,it has been shown1 on the other hand1 that these effects are primarily due to cumulative residual strains1 and that a brief period of rest1 by removing the overstrain1 removes also the sign of fatigue4 ,staircase effect4--,the theory of dissimilation due to stimulus reducing the functional activity below par1 and thus causing fatigue1 is directly negatived by what is known as the 'staircase' effect1 where successive equal stimuli produce increasing response4 ,we saw an exactly similar phenomenon in plants and metals1 where successive responses to equal stimuli exhibited an increase1 apparently by a gradual removal of molecular sluggishness 7fig4#aad74 ,illustration3 ,,fig4#aad4--',,staircase' ,,in ,,muscle1 ,,plant1 ,,and ,,metal ,illustration3 ,,fig4#aae4--;,,increased ,,response ,,after ,,continuous ,,stimulation ,,in ,,nerve ,,and ,,metal ,the normal response in animal tissue is represented 'down1' in metal 'up4' ,increased response after continuous stimulation4--,an effect somewhat similar1 that is to say1 an increased response1 due to increased molecular mobility1 is also shown sometimes after continuous stimulation1 not only in animal tissues1 but also in metals 7fig4#aae74 ,modified response4--,in the case of nerve we saw that the normal response1 which is negative1 sometimes becomes reversed in sign1 i4e4 positive1 when the specimen is stale4 ,in retina again the normal positive response is converted into negative under the same conditions4 ,similarly1 we found that a plant when withering often shows a positive instead of the usual negative response 7fig4#bh74 ,on nearing the death-point1 also by subjection to extremes of temperature1 the same reversal of response is occasionally observed in plants4 ,this reversal of response due to peculiar molecular modification was also seen in metals4 ,illustration3 ,,fig4#aaf4--,,modified ,,abnormal ,,response ,,in 7,a7 ,,nerve ,,and 7,m7 ,,metal ,,converted ,,into ,,normal1 ,,after ,,continuous ,,stimulation 7,a7 is the record for nerve 7recording galvanometer not being dead-beat shows after-oscillation72 the abnormal 'up' is converted into normal 'down' after continuous stimulation4 7,m7 is the record for metal1 the abnormal 'down' being converted into normal 'up' after like stimulation4 ,but these modified responses usually become normal when the specimen is subjected to stimulation either strong or long continued 7fig4#aaf74 ,diphasic variation4--,a diphasic variation is observed in nerve1 if the wave of molecular disturbance does not reach the two contacts at the same moment1 or if the rate of excitation is not the same at the two points4 ,a similar diphasic variation is also observed in the responses of plants and metals 7figs4 #bf1 #fh74 ,effect of temperature4--,in animal tissues response becomes feeble at low temperatures4 ,at an optimum temperature it reaches its greatest amplitude1 and1 again1 beyond a maximum temperature it is very much reduced4 ,we have observed the same phenomena in plants4 ,in metals too1 at high temperatures1 the response is very much diminished 7figs4 #ch1 #fe74 ,effect of chemical reagents4--,finally1 just as the response of animal tissue is exalted by stimulants1 lowered by depressants1 and abolished by poisons1 so also we have found the response in plants and metals undergoing similar exaltation1 depression1 or abolition4 ,we have seen that the criterion by which vital response is differentiated is its abolition by the action of certain reagents--the so-called poisons4 ,we find1 however1 that 'poisons' also abolish the responses in plants and metals 7fig4#aag74 ,just as animal tissues pass from a state of responsiveness while living to a state of irresponsiveness when killed by poisons1 so also we find metals transformed from a responsive to an irresponsive condition by the action of similar 'poisonous' reagents4 ,the parallel is the more striking since it has long been known with regard to animal tissues that the same drug1 administered in large or small doses1 might have opposite effects1 and in preceding chapters we have seen that the same statement holds good of plants and metals also4 ,stimulus of light4--,even the responses of such a highly specialised organ as the retina are strictly paralleled by inorganic responses4 ,we have seen how the stimulus of light evokes in the artificial retina responses which coincide in all their detail with those produced in the real retina4 ,this was seen in ineffective stimuli becoming effective after repetition1 in the relation between stimulus and response1 and in the effects produced by temperature2 also in the phenomenon of after-oscillation4 ,these similarities went even further1 the very abnormalities of retinal response finding their reflection in the inorganic4 ,illustration3 ,,fig4#aag4--;,,abolition ,,of ,,response ,,in ,,nerve1 ,,plant1 ,,and ,,metal ,,by ,,the ,,action ,,of ,,the ,,same ',,poison' ,the first half in each set shows the normal response1 the second half the abolition of response after the application of the reagent4 ,thus living response in all its diverse manifestations is found to be only a repetition of responses seen in the inorganic4 ,there is in it no element of mystery or caprice1 such as we must admit to be applied in the assumption of a hypermechanical vital force1 acting in contradiction or defiance of those physical laws that govern the world of matter4 ,nowhere in the entire range of these response-phenomena--inclusive as that is of metals1 plants1 and animals--do we detect any breach of continuity4 ,in the study of processes apparently so complex as those of irritability1 we must1 of course1 expect to be confronted with many difficulties4 ,but if these are to be overcome1 they1 like others1 must be faced1 and their investigation patiently pursued1 without the postulation of special forces whose convenient property it is to meet all emergencies in virtue of their vagueness4 ,if1 at least1 we are ever to understand the intricate mechanism of the animal machine1 it will be granted that we must cease to evade the problems it presents by the use of mere phrases which really explain nothing4 ,we have seen that amongst the phenomena of response1 there is no necessity for the assumption of vital force4 ,they are1 on the contrary1 physico-chemical phenomena1 susceptible of a physical inquiry as definite as any other in inorganic regions4 ,physiologists have taught us to read in the response-curves a history of the influence of various external agencies and conditions on the phenomenon of life4 ,by these means we are able to trace the gradual diminution of responsiveness by fatigue1 by extremes of heat and cold1 its exaltation by stimulants1 the arrest of the life-process by poison4 ,the investigations which have just been described may possibly carry us one step further1 proving to us that these things are determined1 not by the play of an unknowable and arbitrary vital force1 but by the working of laws that know no change1 acting equally and uniformly throughout the organic and the inorganic worlds4 ,,footnotes3 #ba ,verworn1 ,general ,physiology1 p4#ah4 ,,index ,action current in metal1 #hh in nerve1 #h in plant1 #ai ,after-images and their revival1 #agg ,after-oscillation in photo-sensitive cell1 #aei1 #afc ,ansthetics1 effect on response in nerve1 #gb in plant1 #cj1 #gc1 #gd1 #ge ,annealing1 effect on response in metal1 #aja1 #ach ,binocular alternation of vision1 #age ,block method1 advantages of1 #bh1 #gg for obtaining response in metal1 #hb in plant1 #bh ,chloral1 effect on plant response1 #ge ,chloroform1 effect on nerve response1 #gb plant response1 #gd ,compensator1 #bb ,current of injury in nerve1 #g ,curves1 characteristics of response1 #c ,death-point1 determination of1 in plants1 #fa1 #fc ,depressants1 effect on inorganic response1 #adb ,depression1 response by relative1 #hg ,dewar on retinal current1 #adi ,diphasic variation in metal1 #aac1 #aad1 #aae1 #aaf1 #ahh in nerve1 #ahh in plant1 #df1 #ahh ,dose1 effect on inorganic response1 #hi1 #adf1 #ahi plant response1 #gi1 #ahi ,electrical recorder1 #aa ,electrical response4 ,see ,response1 electrical ,electric tapper1 #bd ,exaltation1 response by relative1 #hi ,fatigue1 absence of1 under certain conditions1 in metal1 #abj in muscle1 #ci in plant1 #ci apparent1 with increased frequency of stimulation1 in metal1 #abj in muscle1 #dj in plant1 #dj diminution of response under strong stimulus due to1 in plant1 #eg in metal1 #aah1 #aai1 #ahe in muscle1 #aah1 #ahe in plant1 #bj1 #ahe due to overstrain1 #da rapid1 under continuous stimulation in metal1 #aba1 #acj in muscle1 #db1 #acj in plant1 #db1 #acj removal of1 by rest in plant1 #dc theory of1 in muscle1 #ch1 #ahe ,holmgren on retinal current1 #adi ,hysteresis1 #acg ,injury1 current of1 in nerve1 #g ,inorganic response4 ,see ,metal1 electrical response in ,kuhne on retinal current1 #adi ,kunkel on electrical changes by injury or flexion in plant1 #ad1 #gj ,light1 after-effect of short exposure to1 on photo-sensitive cell1 #aga on retina1 #aga decline and reversal of response under continuous1 in photo-sensitive cell1 #aff in retina #aff effect of temperature on response of photo-sensitive cell produced by1 #aeh retinal response produced by1 #aeh relation between intensity and response to1 in photo-sensitive cell1 #afa1 #afb in retina1 #afb response to1 after-oscillation in photo-sensitive cell1 #aei1 #afc effect of increasing length of exposure in photo-sensitive cell1 #aei in retina1 #afj in frog's retina1 #aej1 #aea1 #aef1 #afd1 #aff in photo-sensitive cell1 #aeb1 #aec1 #aed1 #aee1 #aeg1 #afe1 #aff ,mc,kendrick on retinal response1 #adi ,mechanical recorder1 #c response1 #a stimulus by electric tapper1 #bd by spring-tapper1 #bc by vibrator1 #bd conditions of maintaining uniformity of1 #bf means of graduating intensity of1 #bb1 #bd1 #if ,metal1 electric response in1 abnormal1 #abe abolition of1 by 'poison1' #adc additive effect of superposition of stimulus on1 #ace annealing1 effect of1 on1 #aja by method of block1 #hb1 #ib negative variation1 #hg1 #ahc depressants1 effect of1 on1 #adb diphasic1 #aac1 #aad1 #aae1 #aaf1 #ahh enhancement of1 after continuous stimulation1 #abg1 #abh1 #ahf fatigue1 #aah1 #aai1 #abj1 #aba1 #ahe4 ,see also ,fatigue maximum effect due to superposition of stimuli1 #acf modified1 #abi 'molecular arrest1' effect of1 by 'poison' on1 #ade molecular friction1 effect of1 on1 #ajh1 #aji prolongation of recovery by overstrain1 #ajf by 'poison1' #ade relation between1 and stimulus1 #acd1 #ace staircase effect1 #abb1 #ahf stimulant1 effect of1 on1 #ada temperature1 effect of1 on1 #aaa uniform1 #ajb1 #ahd ,minchin on photo-electric cell1 #afe ,molecular 'arrest' in metals by 'poison1' #ade friction1 #ajh1 #aji model1 #ajg voltaic cell1 #ii ,munck on electric response in sensitive plants1 #ad ,muscle1 fatigue in1 #ch1 #ci1 #dj1 #db4 ,see also ,fatigue prolongation of recovery by 'poison' in1 #add relation between stimulus and response in1 #eb staircase effect in1 #abb stimulus1 effect of superposition of1 on1 #cf ,myograph1 #b ,negative variation1 response by method of1 in metal1 #hg1 #ahc in nerve1 #i1 #ahc in plant1 #ah1 #ahc ,nerve1 current of injury in1 #g injured and uninjured contacts corresponding to ,cu and ,zn in voltaic couple1 #h response in1 abnormal1 when stale1 #abd1 #ahg abolition of1 by 'poison1' #aci1 #ahi ansthetics1 effect of1 on1 #gb by method of negative variation1 #i current of action of1 #h enhancement of1 after continuous stimulation1 #abg modified1 #abh relation between1 and stimulus1 #eb reversed when stale1 #aa uniform1 #ahd ,nomenclature1 anomalies of present1 #i1 #he ,photographic recorder1 #aa1 #bb ,plant chamber1 #fd electrical response in1 abnormal1 when stale or dying1 #dh1 #ahg abolition of1 by high temperature1 #cb1 #fd additive effect of stimulus on1 #cg ansthetics1 effect of1 on1 #cj1 #gc1 #gd1 #ge by method of block1 #bh of negative variation1 #ah1 #ahc diphasic1 #df fatigue1 #bj1 #ci1 #dj1 #da1 #db1 #dc1 #eg1 #ahe4 ,see also ,fatigue physiological character1 #cj 'poison1' effect of1 on1 #cj1 #cb1 #gh1 #gi relation between1 and stimulus1 #eb1 #ec1 #ed staircase effect1 #cg1 #ahe stimulus1 effect of single1 on1 #ce effect of superposition of1 on1 #ce temperature1 effect of1 on1 #cb1 #ei-fi uniform1 #cf1 #ahd radial ,e4,m4 response in1 #di ,poison1 effect of1 on response in metal1 #adc1 #ahi in nerve1 #aci1 #ahi in plant1 #cj1 #cb1 #gh1 #gi1 #ahi 'molecular arrest' in metal by1 #ade prolongation of recovery by action of1 in metal1 #ade in muscle1 #add ,record1 simultaneous mechanical and electrical1 of response1 #ac ,recorder1 electrical1 #aa mechanical1 #c photographic1 #aa1 #bb response1 #ai ,response-curve1 characteristics of1 #c electrical1 abnormal1 in metal1 #abc1 #abe in stale nerve1 #aa1 #abc in stale or dying plant1 #dh1 #ahg in stale retina1 #aa1 #afd converted into normal after strong or continuous stimulation in metal1 #abe1 #ahg in nerve1 #abd1 #ahg in plant1 #dh abolition of1 by high temperature in plant1 #cb1 #fd by 'poison1' in metal1 #adc1 #ahi in nerve1 #aci1 #ahi in plant1 #cj1 #cb1 #gh1 #gi1 #ahi additive effect of stimulus on1 in metal1 #ace in plant1 #cg ansthetics1 effect of1 on1 in nerve1 #gb in plant1 #cj1 #gc1 #gd1 #ge annealing1 effect of1 on1 in metal1 #aja1 #ach by method of block1 #bh1 #hb1 #ib by negative variation1 #i1 #ah1 #hg1 #ahc by relative depression1 #hg by relative exaltation1 #hi conditions for obtaining1 #f1 #hf1 #hg continuous transformation from positive to negative in metal1 #aae decline and reversal of1 under continuous light in photo-sensitive cell1 #aff decline and reversal of1 under continuous light in retina1 #aff depressants1 effect of1 on inorganic1 #adb diminution of4 ,see ,fatigue diphasic in metal1 #aac1 #aad1 #aae1 #aaf1 #ahh in nerve1 #ahh in plant1 #df1 #ahh dose1 effect of1 on inorganic1 #hi1 #adf1 #ahi on1 in plant1 #gi1 #ahi enhancement of1 after continuous stimulation in metal1 #abg1 #abh1 #ahf enhancement of1 after continuous stimulation in nerve1 #abg1 #ahf maximum effect due to superposition of stimulus1 #ce1 #acf measure of physiological activity1 #ac molecular friction1 effect of1 on1 #ajh1 #aji modification1 effect of1 on1 #aa1 #dh1 #abc1 #abe1 #abi1 #afd1 #ahg physiological character of1 in plant1 #cj positive and negative1 #aa prolongation of recovery in1 by 'poison' in metal1 #ade prolongation of recovery in1 by 'poison' in muscle1 #add prolongation of recovery in1 from overstrain1 #ajf relation between1 and stimulus in metal1 #acd1 #ace in muscle1 #eb in nerve1 #eb in plant1 #eb1 #ec1 #ed in real and artificial retin1 #afb staircase effect1 in metal1 #abb1 #ahf in plant1 #cg1 #ahf stimulant1 effect of1 on1 in metal1 #ada temperature1 effect of1 on4 ,see ,temperature threshold of1 #ace to light4 ,see ,light uniform in metal1 #ajb1 #ahd in nerve1 #ahd in plant1 #cf1 #ahd universal applicability of1 #ab mechanical1 #a retinal4 ,see ,light simultaneous mechanical and electrical record of1 #ac ,retina4 ,see ,light ,sanderson1 ,burdon-1 on electrical response in sensitive plants1 #ad ,spring-tapper1 mechanical stimulus by1 #bc ,staircase effect in metal1 #abb1 #ahf in muscle1 #abb1 #ahf in plant1 #cg1 #ahf ,steiner on retinal response1 #adi ,stimuli1 maximum effect due to superposition of1 in metal1 #acf in muscle1 #cf in plant1 #cf ,stimulus1 advantages of vibrational1 #be and response1 relation between1 in metal1 #acd1 #ace in muscle1 #eb in nerve1 #eb in plant1 #eb1 #ec1 #ed in real and artificial retin1 #afb effect of different kinds of1 #b mechanical1 by spring-tapper1 #bd conditions for maintaining uniformity of1 #bf means of graduating intensity of1 #bb1 #if vibrational1 #bd1 #be1 #bf ,temperature1 death-points in plants1 #fa1 #fc effect of1 on response in metal1 #aaa in photo-sensitive cell1 #aeh in plants1 #cb1 #fj-fi in retina1 #aeh increased sensitiveness in plant due to variation of1 #ff1 #fg ,vibrational stimulus1 #bd1 #be1 #bf ,vision1 binocular alternation of1 #age effect of various conditions on the period of binocular alternation of1 #agg ,visual images1 revival of1 #agg impression1 unconscious1 #agh impulse1 chemical theory of1 #adh electrical theory of1 #adi phantoms1 #agi recurrence1 #agd ,vital force1 #ac ,vitalism1 #ahb ,waller on enhancement of nerve-response after continuous stimulation1 #abg on relation between stimulus and response in muscle1 nerve1 and retina1 #eb1 #afb on retinal response1 #aej1 #aef1 #afe on reversal of response in stale nerve and retina1 #aa1 #abd1 #afd on transformation from abnormal to normal response in nerve after continuous stimulation1 #abd ,,printed ,,by ,,spottiswoode ,,and ,,co4 ,,ltd41 ,,new-,,street ,,square ,,london ---------------------------------------- -------------------------- ,transcriber's note3 ,the following printer errors have been corrected3 ,diaphasic changed to ,diphasic 7fig4 #bf caption7 ,dash added 7section on ,continuous ,transformation7 ,blurr changed to blur 7after fig4 #aaa7 ,in creased changed to increased 7after fig4 #aad7 ,the inconsistent hyphenation of break-down1 electro-motive and vibration-head is as in the original4 ---------------------------------------- --------------------------