\ . 2 7 - “+ a : - <: en ‘ re = . + én E, - ; “4 ’ 4 - : - . be TA ‘ te - P Lo 5 - ‘= 4 ' f : ) 5 ~ . + aes : ; : is, oh aa i 7 } 5 . Digitized by the Internet Archive in 2007 with funding from Microsoft Corporation http://www.archive.org/details/comparativeelect0OOboseuoft COMPARATIVE ELEC LBR-O-P YSIOLOGY WORKS BY THE SAME AUTHOR RESPONSE IN THE LIVING AND NON- LIVING. With 117 Illustrations. 8vo. 10s. 6d. 1902. “PLANT RESPONSE; as a means of Physio- logical Investigations. With 278 Illustrations. 8vo. 21s. 1906. LONGMANS, GREEN & CO., 39 Paternoster Row, London, New York, Bombay, and Calcutta x ry ~? COMPARATIVE ELECTRO-PHYSIOLOGY A PHYSICO-PHYSIOLOGICAL STUDY BY JAGADIS CHUNDER BOSE, M.A., D.Sc. PROFESSOR, PRESIDENCY COLLEGE, CALCUTTA WITH ILLUSTRATIONS LONGMANS, GREEN, AND CO. 39 PATERNOSTER ROW, LONDON NEW YORK, BOMBAY, AND CALCUTTA 1907 All rights reserved is i = _ Ly - 2 i ro PREFACE THIs volume concludes the line of investigation on respon- sive phenomena in general, which I commenced with the publication of a Memoir’ at the International Congress of Science, Paris, 1900. In this first of my publications on the subject I undertook to show the similarities of response in inorganic and living substances. The method which I[ at that time employed for obtaining my response-records was that of Conductivity Variation. With the object of showing that the similarity of response here demonstrated to exist was due to some fundamental molecular reaction, common to matter in general, and therefore to be detected by any method of recording response, I next undertook to record the Electro-motive Variation under stimulus. Believing, as I did, in the continuity of these responsive phenomena, I used the same experimental devices by which I had already succeeded in obtaining the electric response of inorganic sub- stances, to test whether ordinary plants also, meaning those usually regarded as insensitive, would or would not exhibit excitatory electrical response to stimulus. The stimulation ' * De la Généralité des Phénoménes Moléculaires produits par 1|’Electricité sur la Matiére Inorganique et sur la Matiére Vivante’ (7ravaux du Congres International de Physique, Paris, 1900). See also ‘On the Similarity of Effects of Electrical Stimulus on Inorganic and Living Substances,’ Xefort Brit: Assoc., Bradford, September 1900 (Z/ectrician). > vi COMPARATIVE ELECTRO-PHYSIOLOGY employed was mechanical and quantitative, thus obviating many sources of complication. By this method I was able to show that every plant, and every organ of every plant, gave true excitatory electrical response. As observations similar to these were subsequently made by another investigator, I quote here the following summary of my results. from the preliminary account which I communicated to the Royal Society, May 7, and afterwards read, with accompanying ex- - perimental demonstration, before the Society, on June 6, 1goI. ‘An interesting link, between the response given by inor- ganic substances and the animal tissues, is that given by plant tissues. By methods. somewhat resembling that described above, I have obtained from plants a strong electric response to mechanical stimulus. The response is not confined to sensitive plants like Mimosa, but is universally present. I have, for example, obtained such response from the roots, stems, and leaves of, among others, horse-chestnut, vine, white lily, rhubarb, and horse-radish. . ‘The “current of injury” is, generally speaking, from the injured to the uninjured part. A “negative variation ” is also produced. | obtained both the single electric twitches and tetanus. Very interesting also are the effects of fatigue, of temperature, of stimulants, and of poison. Definite areas killed by poison exhibit no response, whereas neighbouring unaffected portions show.the normal response.’ ! | | , It may be well to point out here that at the time when this. communication was made, the view that ordinary plants were excitable, and responded to mechanical stimulus by 1A more complete: account: will be. found in the report of my ‘ Friday Evening Discourse’ before the Royal Institution, May 10, 1901, and in the Journal of the Linnean Society, vol. xxxv.. Pp. 275. PREFACE vii definite electro-motive changes, was regarded as highly controversial. Indeed, in the discussion which followed the reading of my Paper, on June 6, 1901, Sir John Burdon Sanderson went so far as to state that this excitatory response of ordinary plants to mechanical stimulation was an impossibility. My next investigation was directed towards the question whether the responsive effects which I had shown to occur in ordinary plants might not be further exhibited by means of visible mechanical response, thus finally removing the dis- tinction commonly assumed to exist between the ‘sensitive’ and supposed non-sensitive. These results were published in my work on Plant Response,’ where the effects of various environmental stimuli on the different plant organs were demonstrated by means of responsive movements. Many anomalous effects hitherto ascribed to specific sensibilities were here shown to be due to the differential excitability of anisotropic structures, and to the opposite effects of external and internal stimuli. Among other things, it was there shown that internal stimulus was in reality derived from external sources, and that the term ‘autonomous response’ was a misnomer, since all movements were due, either to the immediate effects of external stimulus, or to stimulus previously absorbed and held latent in the plant, to find subsequent ex- pression. It was further shown that not gross mechanical movements alone, but also other invisible movements, were initiated by the action of stimulus ; that external stimulus, so far from invariably causing a run-down of energy, more often brought about its accumulation by the plant ; and that the various activities, such as the ascent of sap and growth, ' Plant Response as a Means of Physiological Investigation, 1906, vill COMPARATIVE ELECTRO-PHYSIOLOGY were thus in reality different reactions to the stimulating action of energy supplied by the environment. With regard to these points, my results have been in direct opposition to current views, according to which the effect induced by stimulus is always disproportionately greater than the stimulus, From the plausible analogy of the firing-off of a gun by the pulling of a trigger, or the action of a combustion-engine, it has been customary to suppose that all response to stimulus must be of the nature of an explosive chemical change, accompanied by an inevitable run-down of energy. This supposition, however, overlooks the obvious fact that the plant is not consumed by the incessant and multifarious stimuli of its environment. Rather, as we all know, it is the energy of the environ- ment which is the agent that fashions the microscopic embryo into the gigantic banyan-tree. And it is clear that, for this to be possible, the energy contributed by the blow of external stimulus must have been largely conserved. In the course of the present work, I have not only been able to corroborate, by means of electrical response, the various results which I had already established, with regard to the plant, by mechanical response, but I have also ex- tended the electrical method in various directions, so as to include many more recondite problems in connection with the irritability of living tissues. It was my original inten- tion to confine this investigation to the Electro-physiology of Plants. But, finding that in the results so obtained I pos- sessed a key to that of the animal also, I proceeded to apply the same methods of inquiry, and to use the same experi- mental devices, in the one case as in the other. I have thus been able to trace out the gradual differentiation of various PREFACE ix responsive peculiarities, characteristic of given tissues, from © their simplest types in the plant to their most complex in the animal. The value of such a comparative method of study, for the elucidation of biological problems in general, is sufficiently obvious. Exception may be taken with regard to the unorthodox point of view from which various ques- tions in animal physiology have been approached. It must be remembered, however, that in this work the attempt has been to explain responsive phenomena in general on the consideration of that fundamental molecular reaction which occurs even in inorganic matter. My mode of investigation has thus been determined by the necessary progression from simple to complex, and by my conviction as to the continuity which existed between them. And from. this attempt it will be seen that various results, which, accord- ing to the so-called vitalistic assumption were anomalous, are, in fact, capable of an increasingly simple and _ satis- factory explanation. It must also be understood that my work deals mainly with the electrical response of plants, and that its extension into the field of Animal Electro- physiology was intended for the demonstration of the con- tinuity between the two. It was therefore impossible, in the short space at my disposal, to make more than the brief necessary references to the different theories already in vogue concerning the response of various animal tissues. These will be found, in all their detail, in the excellent account given in the standard work of Biedermann.' For the sake of clearness, however, I shall at this point enumerate a few only of the points of difference between current views and the results, obtained from actual experi- 1 Biedermann, Ziectro-physiology (English translation), 1896. x COMPARATIVE ELECTRO-PHYSIOLOGY ment, which I have set forth in the present volume. The reactions of different tissues have hitherto been re- garded as specifically different. As against this, a continuity has here been shown to exist between them. Thus, nerve was universally regarded as typically non-motile; its re- sponses were believed to be characteristically different from those of muscle. I have been able to show, however, that nerve is not only indisputably motile, but also that the investigation of its response by the mechanical method is capable of greater delicacy, and freedom from error, than that by the electrical. The characteristic variations in the response of nerve, moreover, are, generally speaking, similar to those of the muscle. It has been customary, again, to regard plants as devoid of the power to conduct true excita- tion. But I have shown that this view is incorrect. Experi- ments have been described, showing that the response of the isolated vegetal nerve is indistinguishable from that of animal nerve, throughout a long series of parallel variations of condition. So complete, indeed, has that similarity between the responses of plant and animal, of which this is an instance, been found, that the discovery of a given responsive characteristic in one case has proved a sure guide to its observation in the other, and the explanation of a phenomenon, under the simpler conditions of the plant, has been found fully sufficient for its elucidation under the more complex circumstances of the animal. , Many anomalous conclusions, with regard to the response of certain animal tissues, had arisen from the failure to take account of the differential excitability of anisotropic organs. Now this is a subject which, in the case of the simple plant organ, is capable of very exact investigation. I have been ety a eI ed i i ag KE a ) ee gr ee é PREFACE X1 able to show that this differential excitability is widely - present as a factor in determining the character of special responses, and that it finds its culminating expression in the electrical organs of certain well-known fishes, — Few conclusions in. Electro-physiology have been sup- _posed to rest on securer foundations than the generalisation known as Pfliiger’s Law of the polar effects of currents. I have found, however, that this law is not by any means of such universal application as had been supposed, since, above and below a certain range of electromotive intensity, the polar effects of currents are precisely opposite to those enunciated by Pfliiger. © Finally, that nervous impulse, which must necessarily form the basis of sensation, was supposed to lie beyond any conceivable power of visual scrutiny. But it has here been shown that this impulse is actually attended by change of form, and is therefore capable of direct observation. This wave of nerve-disturbance, moreover, instead of being single, has been shown to’ be of two different kinds, in which fact, as I have further explained, lies the significance of the two different qualities or tones of sensation. In the concluding portion. of the paper which I read before the Bradford meeting of the British Association in the year 1900, I said :— | ‘In the phenomena described above there is little breach of continuity. It is difficult to draw a line and say : “ Here the physical process ends, and the physiological process begins”; or “That is a phenomenon of inorganic matter, and this is a vital phenomenon, peculiar to living organisms”; or “These are the lines of demarcation that separate the physical, the physiological, and the beginning xil COMPARATIVE ELECTRO-PHYSIOLOGY of psychical processes.” Such arbitrary lines can hardly be drawn. , : ‘We may explain each of the above classes of phenomena by making numerous and independent assumptions ; or, finding some property of matter common and persistent in the living and non-living substances, attempt from this common underlying property to explain the many phe- nomena which at first appear so different. And for this it may be said that the tendency of science has always been to attempt to find, wherever facts justify it, an under- lying unity in apparent diversity.’ It was for the demonstration of this underlying unity that I set out on these investigations seven years ago. And now, in bringing to its close another stage of their publication, I may, perhaps, be permitted to express the hope that by them not only may a deeper perception of this unity have been made attainable, but also that many regions of inquiry may prove to have been opened out, which had at one time been regarded as beyond the scope of experi- mental exploration. I take this opportunity to thank my assistants for their efficient help in these researches. J. C. BOSE. PRESIDENCY COLLEGE, CALCUTTA : August 1906, CONTENTS CHAPTER I THE MOLECULAR RESPONSIVENESS OF MATTER PAGE Response to stimulus by change of form—Permeability variation— Variation of solubility— Method of resistivity variation : (a) positive variation ; (4) negative variation—Sign of response changed under different molecular modifications—Response of vegetable tissue by variation of electrical resistance—Response by electro-motive variation in inorganic substances —The method of block—Positive and negative responses—Similar responses in living tissues—Effects of fatigue, stimulants, and poisons on inorganic and organic responses-—-Method of relative depression, or negative variation, so called ; : F ; - j ; : I CHAPTER II THE ELECTRO-MOTIVE RESPONSE OF PLANTS TO DIFFERENT FORMS OF STIMULATION Historical—Difficulties of investigation—-Electrical response of pulvinus of Mimosa—Simultaneous mechanical and electrical records—Division of plants into ‘ordinary’ and ‘sensitive’ arbitrary —Mechanical and electrical response of ‘ ordinary’ plants—Direct and transmitted stimu- Jation—All forms of stimulus induce excitatory change of galvanometric negativily . ‘ ce , . : é : j i aE LR CHAPTER III THE APPLICATION OF QUANTITATIVE STIMULUS AND KELATION BETWEEN STIMULUS AND RESPONSE Conditions of obtaining uniform response—Torsional vibration as a form of stimulus— Method of block— Effective intensity of stimulus dependent on period of vibration—Additive action of feeble stimuli—Response Xiv COMPARATIVE ELECTRO-PHYSIOLOGY , PAGE recorder—Uniform electric responses—List of suitable specimens— Effect of season on excitability—Stimulation by thermal shocks —Thermal stimulator—Second method of confining excitation to one contact—In- creasing response to increasing stimulus—Effect of fatigue—Tetanus . 29 CHAPTER IV OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE IN PLANTS Response-curve showing general time-relations—Instantaneous mechanical stimulation by electro-magnetic release—Arrangement of the rheotome —Tabular statement of results of rheotomic observations—Rhythmic multiple responses. ; ; : ; ‘ : ; : - “5 CHAPTER V THE ELECTRICAL INDICATIONS OF POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS Motile responses of opposite signs, characteristic of positive and negative turgidity-variations—Indirect hydrostatic effect of stimulus causes expansion and erection of leaf-—Positive and negative work—Wave of increased hydrostatic tension transmitted with relatively greater velocity than wave of true excitation— Method of separating hydro-positive and excitatory effects— Indirect effect of stimulus, causing positive turgidity- variation induces galvanometric positivity—Antagonistic elements in the electrical response—Separation of hydro-positive from true excitatory effect by means of physiological block ; [ ; ‘ , - Sg CHAPTER VI EXTERNAL STIMULUS AND INTERNAL ENERGY Hydraulic transmission of energy in plants—True meaning of tonic condi- tion-—Opposite expressions of internal energy and external stimulus seen in growth-response—Parallelism between responses of growing and motile organs—Increased internal energy caused by augmentation o1 temperature finds expression in enhanced rate of growth; erection of motile leaf ; curling movement of spiral tendril ; and galvanometric positivity—External stimulus induces opposite eftect in all these cases— Sudden variation of temperature, acting as a stimulus, induces transient retardation of growth ; depression of motile leaf ; uncurling mevement of spiral tendril ; and galvanometric negativity— Laws of mechanical and electrical response ° : ‘ / : : 69 | : . " CONTENTS CHAPTER VII ABSORPTION AND EMISSION OF ENERGY IN RESPONSE Sign of response determined by latent energy of tissue, and by intensity of external stimulus—Sub-tonic, normal and hyper-tonic conditions—The. critical level—Outward manifestation of response possible only when critical level is exceeded—Three typical cases: response greater than stimulus ; response equal to stimulus; and response less than stimulus —lInvestigation by growth-response—The sum of work, internal and external, performed by stimulus constant—Positive response of tissues characterised by feeble protoplasmic activity or sub-tonicity—Enhance- ment of normal excitability of sub-tonic tissue by absorption of stimulus CHAPTER VIII VARIOUS TYPES OF RESPONSE Chemical theory of response—Insufficiency of the theory of assimilation and dissimilation --Similar responsive effects seen in inorganic matter— Modifying influence of molecular condition on response—Five molecular stages, A, B, C, D, E—Staircase effect, uniform response, fatigue—No sharp line of demarcation between physical and chemical phenomena— Volta-chemical effect and by-productions—Phasic alternation —Alter- nating fatigue—Rapid fatigue under continuous stimulation—In sub- tonic. tissue summated effect of latent components raises tonicity and excitability—Response not always disproportionately greater than stimulus—Instances of stimulus partially held latent: staircase and additive effects, multiple response, renewed growth . : ; ° CHAPTER IX DETECTION OF PHYSIOLCGICAL ANISOTROPY BY ELECTRIC RESPONSE Anomalies in mechanical and electrical response—Resultant response deter- mined by differential excitability—Responsive current from the more to the less excitable—Laws of response in anisotropic organ—Demonstra- tion by means of mechanical stimulation—Vibrational stimulus—Stimu- lation by pressure—Quantitative stimulation by thermal shocks CHAPTER X THE NATURAL CURRENT AND ITS VARIATIONS Natural current in anisotropic organ from the less to the more excitable— External stimulus induces responsive current in opposite direction— Increase of internal energy induces positive, and decrease negative, XV PAGE 76 86 107 xvi COMPARATIVE ELECTRO-PHYSIOLOGY . PAGE variation of natural current—Effect on natural current of variation of temperature—Effect of sudden variation—Variation of natural current by chemical agents, referred to physiological reaction—Agents which render tissue excitable, induce the positive, and those which cause excita- tion, the negative variation—Action of hydrochloric acid—Action of Na,CO,—Effect modified by strength of dose—Effect of CQ, and of alcohol vapour—Natural current and its variations—Extreme unrelia- bility of negative variation so-called as a test of excitatory reaction— Reversal of natural current by excessive cold or by stimulation—Re- versal of normal response under sub-tonicity or fatigue . ; ; + eto CHAPTER XI VARIATIONS OF EXCITABILITY UNDER CHEMICAL REAGENTS Induced variation of excitability studied by two methods: (1) direct (2) transmitted stimulation—Effect of chloroform—Effect of chloral— Effect of formalin—Advantage of the Method of Block over that of negative variation—Effect of KHO—Response unaffected by variation of resistance—Stimulating action of solution of sugar—Of sodium carbon- ate—Effect of doses— Effect of hydrochloric acid—Diphasic response on application of potash—Conversion of normal negative into abnormal positive response by abolition of true excitability . ‘ ; ‘ « o129 CHAPTER XII VARIATIONS OF EXCITABILITY DETERMINED BY METHOD OF INTERFERENCE Arrangement for interference of excitatory waves—Effect of increasing difference of phase—Interference effects causing change from positive to negative, through intermediate diphasic—Diametric balance—Effect of unilateral application of KHO—Effect of unilateral cooling . ; - Iq! CHAPTER XIII CURRENT OF INJURY AND NEGATIVE VARIATION Different theories of current of injury—Pre-existence theory of Du Bois- Reymond—Electrical distribution in a muscle-cylinder—Electro-mole- cular theory of Bernstein—Hermann’s Alteration Theory— Experiments demonstrating that so-called current of injury is a persistent after-effect of over-stimulation—Residual galvanometric negativity of strongly excited tissue—Distribution of electrical potential in vegetable tissue with one end sectioned—Electrical distribution in plant-cylinder similar to that in muscle-cylinder—True significance of response by negative variation—- Apparent abnormalities in so-called current of injury—‘ Positive ’ current of injury ; ‘ : ‘ eas ; ‘ . 149 CONTENTS Xvil CHAPTER XIV CURRENT OF DEATH—RESPONSE BY POSITIVE VARIATION PAGE Anomalous case of response by positive variation—Inquiry into the cause— Electric exploration of dying and dead tissue: death being natural— Determination of electric distribution in tissue with one end killed— Dying tissue shows maximum negativity, and dead tissue, positivity to living—Explanation of this peculiar distribution—Response by negative or positive variation, depending on degree of injury—Three typical cases —-Explanation by theory of assimilation and dissimilation misleading — All response finally traceable to simple fundamental reactions é - 164 CHAPTER XV EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE General observation of effect of temperature on plant—Effect of fall and rise of temperature on autonomous response of Desmodium—Effect of frost in abolition of electrical response—A fter-effects of application of cold, in Eucharis, Ivy and Holly—Effect of rise of temperature in diminishing height of response—This not probably due to diminution of excitability —Similar effect in autonomous motile response of Desmodium—En- hanced response as after-effect of cyclic variation of temperature—Aboli- tion of response at a critical high temperature. ‘ : ‘ . 180 CHAPTER XVI THE ELECTRICAL SPASM OF DEATH Different fost-mortem symptoms—Accurate methods for determination of death-point—Determination of death-point by abolition or reversal of normal electrical response —Determination of death-point by mechanical death-spasm—From thermo-mechanical inversion—By observation of electrical spasm : (a) in anisotropic organs: (4) in radial organs—Simul- taneous record of electrical inversion and reversal of normal electrical response—Remarkable consistency of results obtained by different methods— Tabulation of observations . ; , 2 . 2 - 582 CHAPTER XVII MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE Repeated responses under single strong stimulus—Multiple mechanical response in Biophytwm—Multiple electrical responses in various animal and vegetable tissues —Continuity of multiple and autonomous response —Transition from multiple response to autonomous, and dice versa— a XVili COMPARATIVE ELECTRO-PHYSIOLOGY PAGE Autonomous mechanical response of Desmodium gyrans and its time- relations—Simultaneous mechanical and electrical records of automatic pulsations in Desmodium—Double electrical pulsation, principal and subsidiary waves—Flectrical pulsation of Desmodium leaflet under physical restraint— Growth- pulsation — So-called current of rest in grow- ing plants . : ? MF Sette : ; ; ; ‘. . 207 CHAPTER XVIII RESPONSE OF LEAVES Observations of Burdon Sanderson on leaf-response in Déone@a—Leaf and stalk currents—Their opposite variations under stimulus—Similar leaf- and-stalk currents shown to exist in ordinary leaf of Ficus religiosa— Opposite-directioned currents in Cztrus decumana—True explanation of these resting-currents and their variations—Electrical effect of section of petiole on Dzonea and Ficus religiosa—Fundamental experiment of Burdon Sanderson on lamina of Dzone@a— Subsequent results—Expeti- mental arrangement with symmetrical contacts—Parallel experiments on > sheathing leaf of /usa—Explanation of various results : ‘ 1223 CHAPTER XIX THE LEAF CONSIDERED AS AN ELECTRIC ORGAN Electrical organs in fishes—Typical instances, Zorpedo and Malepterurus— Vegetal analogues, leaf of Pterospermum and carpel of D¢llenia indica or pitcher of Mefenthe—Electrical response to transmitted excitation —Response to direct excitation—Uni-directioned response to homo- - dromous and heterodromous shocks—Definite-directioned response shown to be due to differential excitability—Response to equi-alternating electrical shocks—Rheotomic observations—Multiple excitations— Multiplication of terminal electromotive effect, by pile-like arrangement, in bulb of Uric/zs lily : ‘ ‘ , ; ‘ , . . 241 CHAPTER XX THE THEORY OF ELECTRICAL ORGANS Existing theories—Their inadequacy—-The ‘ blaze-current’ so called—Re- sponse uni-directioned, to shocks homodromous or heterodromous, characteristic of electric organs—Similar results with inorganic specimens —Uni-directioned response due to differential excitability— Electrical response of pulvinus of A//mosa to equi-alternating electric shocks—Re- sponse of petiole of AZ#sa—Of plagiotropic stem of Cucurdita—-Of Eel— The organ-current of electric fishes—Multiple responses of electrical organ—Multiple responses of Bzofhyium . — . > : : . 250 CONTENTS XIX CHAPTER XXI DETERMINATION OF DIFFERENTIAL EXCITABILITY UNDER © ELECTRICAL STIMULATION | ) PAGE Advantage of electrical stimulation, in its flexibility—Drawbacks due to~ fluctuating factors of polar effects, and counter polarisation-current— Difficulties overcome by employment of equi-alternating © electric shocks—Methods of the After-effect and Direct-effect—Experiment of Von Fleischl on response of nerve—Complications arising from use of make and break shocks—Rotating reverser— Motor transformer—Re- sponse of Musa to equi-alternating shocks—Abolition of this response by chloroform—Response records of plagiotropic Cucurbita and Eel— Differential excitability of variegated leaves, demonstrated by electric response. é ita : > ; - ; : : eee CHAPTER XXII RESPONSE OF ANIMAL AND VEGETAL SKINS Currents of rest and action—Currents in animal skin—Theories regarding these—Response of vegetal skin—Stimulation by Rotary Mechanical _Stimulator—Response of intact human skin--Isolated responses of upper and. lower surfaces of specimens —Resultant response brought about by differential excitability of the two surfaces—Differences of excitability between two surfaces accounted for—Response of animal and vegetal skins not essentially different—General formula for all types of response of skin—Response of skin to different forms of stimulation gives similar results— Response to equi-alternating electric shocks : (1) Method of the After Effect ; (2) Method of Direct Effect—Response of grape skin—Similar response of frog’s skin—Phasic variation of current of rest induced as result of successive stimulation in (a) grape skin ; (4) frog’s skin; (¢c) pulvinus of Jimosa—Phasic variation in autonomous me- chanical response of Desmodium gyrans—Autonomous variation of current of rest—True current of rest in skin from outer to inner—This may be reversed as an excitatory after-effect of preparation—Electrical response of skin of neck of tortoise—Electrical response of skin of tomato—Normal response and positive after-effect—Response of skin of gecko—Explanation of abnormal response. . ; . . 287 CHAPTER XXIII RESPONSE OF EPITHELIUM AND GLANDS Epidermal, epithelial, and secreting membranes in plant tissues—Natural resting-current from epidermal to epithelial or secretory surfaces —Current of response from epithelial or secretory to epidermal surface:—Response a2 XX COMPARATIVE ELECTRO-PHYSIOLOGY ; PAGE of Dil/enza—Response of water-melon—Response of foot of snail—The so-called current of rest from glandular surface really due to injury— Misinterpretation arising from response by so-called ‘ positive variation ’ —Natural current in intact foot of snail, and its variation on section— Response of intact human armpit—Response of intact human lip— Lingual response in man—Reversal of normal response under sub- minimal or super-maximal stimulation—Differential excitations of two surfaces under different intensities of stimulus, with consequent changes in direction of responsive currents, diagrammatically represented in characteristic curves—Records exhibiting responsive reversals. rita. 3 Se CHAPTER XXIV RESPONSE OF DIGESTIVE ORGANS Consideration of the functional peculiarities of the digestive organ—Alter- nating phases of secretion and absorption—Relation between secretory and contractile responses. [Illustrated by (a) preparation of Mimosa; (4) glandular tentacle of Drvosera—General occurrence of contractile re- sponse—True current of rest in digestive organs—Experiments on the pitcher of Wepenthe—Three definite types of response under different con- ditions—Negative and positive electrical responses, concomitant with secretion and absorption— Multiple responses due to strong stimulation —Response in glandular leaf of Drosera—Normal negative response reversed to positive under continuous stimulation— Multiple response in Drosera—Response of frog’s stomach to mechanical stimulation—Re- sponse of stomach of tortoise—Response of stomach of gecko— Multiple _ response of frog’s stomach, showing three stages—-negative, diphasic, and positive —Phasic variations : : ; ‘ , 329 CHAPTER XXV ABSORPTION OF FOOD BY PLANT AND ASCENT OF SAP Parallelism between responsive reactions of root and digestive organ—Alter- nating phases of secretion and absorption—Association of absorptive process with ascent of sap—Electrical response of young and old roots— Different phasic reactions, as in pitcher of /Vepenthe—Response to chemical stimulation—Different theories of ascent of sap-——Physical versus excitatory theories—Objections to excitatory theory—Assumption that wood dead unjustified—Demonstration of excitatory electrical re- sponse of sap-wood—Strasburger’s experiments on effect of poisons on ascent of sap—Current inference unjustified . : : ‘ ; - 349 CONTENTS CHAPTER. XXVI THE EXCITATORY CHARACTER OF SUCTIONAL RESPONSE Propagation of excitatory wave in plant attended by progressive movement of water—Hydraulic response to stimulus—The Shoshungraph— Direct and photographic methods of record—Responsive variations of suction under physiological modifications induced by various agents—Effects of lower- ing and raising of temperature—Explanation of maintenance of suction, when root killed—Effect of poison influenced by tonic condition—Effect of anzesthetics on suctional response—Excitatory versws osmotic action —Stimulation by alternating induction-shocks—Terminal and sub-ter- minal modes of application—-Three modes of obtaining response-records, namely (1) the unbalanced, (2) the balanced, (3) the over-balanced— Renewal of suction previously at standstill, by action of stimulus--Re- ponsive enhancement of suction by stimulus—After-effect of stimulus— Diminution of latent period as after-effect of stimulus—Response under over-balance—Response under sub-terminal stimulation—Variation of response under seasonal changes . CHAPTER XXVII RESPONSE TO STIMULUS OF LIGHT Heliotropic plant movements reducible to fundamental reaction of contrac- tion or expansion—Various mechanical effects of light in pulvinated and growing organs—Electrical response induced by light not specific, but concomitant to excitatory effects—Electrical response of plant to light not determined by presence or absence of chloroplasts—Effect of unilateral application of stimulus on transversely distal point— Positive response due to indirect. effect and negative to transmission of true excitation—Mechanical response of leaf of AM/¢mosa to light applied on upper half of pulvinus—Mechanical response consists of erection or positive movement, followed by fall or negative movement—FElectrical response of leaf of A/zmosa to light applied on upper half of pulvinus ; induction in lower half of pulvinus of positivity followed by negativity— Longitudinal transmission of excitatory effect, with concomitant galvano- metric negativity --Direct effect of light and positive after effect— Circumstances which are effective in reversing normal response—Plants in slightly sub-tonic condition give positive followed by negative response —Exemplified by (a) electrical and (4) growth response—Examples of positive response to light—Periodic variation of excitability— Multiple mechanical response under light—Direct and after-effect— Multiple electrical response under light, with phasic alterations of (— + — +) or (+ — + —)--After-effects ; unmasking of antagonistic elements, either plus or minus—Three types of after-effects f S XXi PAGE 365 392 xxii COMPARATIVE ELECTRO-PHYSIOLOGY CHAPTER: XXVIII RESPONSE OF RETINA TO STIMULUS OF LIGHT PAGE Response of retina—Determination of true current of rest—Determination _ of differential excitabilities of optic’ nerve and cornea, and optic nerve and retina—The so-called positive variation of previous observers indicates the true excitatory negative—Retino-motor effects—Motile responses in nerve— Varying responsive effects under different conditions —Reversal of the normal response of light due to (1) depression of excitability below par ; (2) fatigue—The sequence of responsive phases during and after application of light—Demonstration of multiple responses in retina under light, as analogous fo those in vegetable tissues — Three types of after-effect—Multiple after-excitations in human retina—Binocular Alternation of Vision—Demonstration of pulsatory response in human retina during exposure to light —. , ‘ - 415 CHAPTER XXIX GEO-ELECTRIC RESPONSE ‘Theory of Hydrostatic Pressure and Theory of Statoliths—Question regarding active factor of curvature in geotropic response, whether contraction or expansion—Crucial experiment by local application of cold—Reasons for delay in initiation of true geotropic response—Geo-electric response of shoot —Due to active contraction of upper side, with concomitant gal-— vanometric negativity—Geo-electric response of an organ physically restrained . ; : ; : . , . : ; ; «5 @34 CHAPTER XXX DETERMINATION OF VELOCITY OF TRANSMISSION OF EXCITATION IN PLANT TISSUES ; Transmission of excitation in plants not due to hydromechanical disturbance, but instance of transmission of protoplasmic changes—Difficulties in accurate determination of velocity of transmission—A perfect method— Diminution of conductivity by fatigue—Increased velocity of transmission with increasing stimulus—Effect of cold in diminishing conductivity — Effect of rise of temperature in ‘enhancing conductivity— Excitatory concomitant of mechanical and electrical response—Electrical methods of determining velocity of transmission—Method of comparison of longi- tudinal and transverse conductivities—Tables of comparative velocities in animal and plant —Existence of two distinct nervous impulses, positive and negative ; ; Saas , ° . ; ; ; » 444 « CONTENTS atte xxiii CHAPTER XXXI ON x ‘NEW METHOD FOR THE QUANTITATIVE STIMULATION OF NERVE WA : PAGE Drawbacks to use of electrical stimulus in nehenpading electrical response — Response to equi-alternating electrical shocks—Modification of response by. decline of injury—Positive after-effect—Stimulation of nerve by thermal. shocks—Enhancement of normal response after tetanisation — Untenability of theory of evolution of carbonic acid—Abnormal positive response converted into normal negative after tetanisation—Gradual transition from positive to negative, through intermediate diphasic— Effect of depression of tonicity on excitability and conductivity—Con- version of abnormal into normal response by increase of stimulus-intensity —Cyclic variation of response under molecular modification . , - 456 CHAPTER XXXII ELECTRICAL RESPONSE OF ISOLATED VEGETAL NERVE Specialised conducting tissues—Isolated vegetal nerve—Method of ob- taining electrical response in vegetal nerve—Similarity of responses of plant and animal nerve: (a) action of ether—(4) action of carbonic acid—(c) action of vapour of alcohol—(d) action of ammonia—(e) ex- ‘ hibition of three types of response, negative, diphasic and positive— (/) effects of tetanisation of normal and modified specimens—Effect of increasing stimulus on response of modified tissue ‘ ; : . 468 CHAPTER XXXIII THE CONDUCTIVITY BALANCE Receptivity, conductivity, and responsivity—Necessity for distinguishing these—Advantages of the Method of Balance —Simultaneous comparison of variations of receptivity, conductivity and responsivity—The Conductivity Balance—Effect of Na,CO, on frog’s nerve—Effect of CuSO,—Effect of chemical reagents on plant nerve—Effect of CaCl, on responsivity— ‘Responsivity variation under KCl—Comparison of simultaneous effects of NaCl and NaBr on responsivity—Effects of Na,CO, in different dilutions on conductivity—Demonstration of two different elements in conductivity, velocity and intensity—Conductivity versus responsivily— (a) effect of KI—(é) Effect of NaI—Effect of alcohol on receptivity, conductivity, and responsivity Comparison of simultaneous effects of alcohol—(a) on receptivity verses conductivity-~ (4) on receptivity Versus responsivity... : : : , : ps reas , . -. 479 € i ‘ =: i oi f JF, * > 7 * > rel , ; ; : ; : , . 560 : CHAPTER XL INADEQUACY OF PFLUGER’S LAW Reversal of Pfliiger’s Law under high E.M.F.—Similar reversals under feeble E.M.F.—Investigation by responsive sensation—Experiments on living wounds— Under moderate E.M.F., intensity of sensation enhanced at kathode, and depressed at anode—Under feeble E.M.F., sensation intensified at anode and depressed at kathode Aas {apaeernre of electrical currents in medical practice s : : ¢ : ; ‘ »'s 578 XXVi COMPARATIVE ELECTRO-PHYSIOLOGY CHAPTER XLI THE MOLECULAR THEORY OF EXCITATION AND ITS TRANSMISSION : | ‘PAGE Two opposite responsive manifestations, negative and positive—Such opposite responses induced by polar effects of currents of different signs —Arbitrary nature of term ‘ excitatory ’"—Pro-excitatory and anti-excita- tory agents—Molecular distortion under magnetisation in magnetic sub- stances—Different forms of response under magnetic stimulation— Mechanical, magneto-metric, and electro-motive responses—Uniform magnetic responses—Response exhibiting periodic groupings—TIneffec- tive stimulus made effective by repetition—Response by resistivity- variation— Molecular model—Response of inorganic substance to electric radiation—Effect of rise of temperature in hastening period of recovery and diminishing amplitude of response—Sign of response reversed under feeble stimulation—Conduction of magnetic excitation—The Magnetic Conductivity Balance—Effect of A-tonus.and K-tonus, on excitability and conductivity—Conducting path fashioned by stimulus—Transmission of excitation temporarily blocked in iron wire, as in bporisar 7 nerve— Artificial nerve-and-muscle preparation ; ‘ : ‘ Mega 9 CHAPTER XLII MODIFICATION OF RESPONSE UNDER CYCLIC MOLECULAR VARIATION Anomalies of response—Explicable only from consideration of antecedent molecular changes—Continuous transformation from sub-tonic to hyper- tonic .conditions—Two methods of inquiry, first by means of character- istic curves, second by progressive change of response—Abnormal re- sponse characteristic generally of A or sub-tonic state—Abnormal trans- formed into normal, after transitional B state—B state characterised by staircase response—Responses at C stage normal and uniform—At stages D and E responses undergo diminution and reversal—Responsive pecu- liarities seen during ascent of curve, repeated in reverse order during descent—All these peculiarities seen not only in living but also in in- organic substances, under different methods of observation—Elucidation of effect of drugs—Response modified by tonic condition and past history . F : 3 ; , : , ; é ; . OFS CHAPTER XLIII CERTAIN PSYCHO-PHYSIOLOGICAL PHENOMENA—THE PHYSICAL BASIS OF SENSATION uf Indications of stimulatory changes in nerve : 1, Electrical ; 2, Mechanical— Transmission in both directions—Stimulatory changes in motor and 5 q ; CONTENTS XXVii : PAGE sensory nerves similar— Responsive molecular changes and the correlated tones of sensation—Two kinds of nervous impulse, and their character- istics— Different manifestations of the same nervous impulse determined by nature of indicator-—Electrical, motile, and sensory responses, and their mutual relations—The brain as a perceiving apparatus—Weber- Fechner’s Law—Elimination of psychic assumption from explanation of - particular relation between stimulus and resultant sensation—Explana- tion of the factor of quality in sensation—Explanation of conversion from positive to negative tone of sensation after tetanisation—Various effects of progressive molecular change in nerve—Effects of attention and inhibi- tion—Polar variations of tonus, inducing acceleration and retardation . 644 CHAPTER XLIV DISSOCIATION OF COMPLEX SENSATION Conversion of pleasurable into painful sensation, and vice versa, by electro- tonus—The Sensimeter—Mechanical stimulation—Stimulation by ther- mal shocks—Chemical stimulation—Opposite effects of anode and kathode—Normal effects reversed under feeble E.M.F. —Negative tone of sensation blocked by alcohol and anzesthetics—Separation of positive and negative sensations, by lag of one wave behind the other—Dissocia- tion of sensation by depression of conductivity—A bolition of the negative or painful element by block of conduction . ; : : ; . 666 CHAPTER XLV MEMORY jos oe be - 677 CHAPTER XLVI REVIEW OF RESPONSE OF ISOTROPIC ORGANS - . 687 CHAPTER XLVII REVIEW OF RESPONSE OF ANISOTROPIC ORGANS _ + 700 CHAPTER XLVIII REVIEW OF RESPONSE OF NERVE AND RELATED PSYCHOLOGICAL PHENOMENA . : é ' S55 CLASSIFIED LIST OF EXPERIMENTS ‘ ‘ ‘ : « » 925 OR ete See ee A go? gy a, ; a ; _ oe -s = i ; . 7 : F 2 Pes pS nb pease fio ation Pai? : ‘ , A , Sako ' 4° as. bet get s Te re fuices > rs Ri ” all . ? * j at . Lae = visa iE Le a oh stole ar eee 39 Bombe? + Sell dans ‘qu : Cage : Joes ans mae Ma nT : mes Oy ore. SS aiees - ay aon te ; o- sa, ig Fee ; . cre) ae < Fy Le vo Ae sie ; ” 7 Agta se i La “ibn. s PA na 2 Be 5 teh = itt >. ix aeeahe Giant ved ee Wiest sak “eh atte s nae cd Nees ata, ta pesen tye ‘ i “ pu Bt sehns Jatsoit Bhi iar hoe atthe pirat ye ‘Yrs j ¢ 4 ee ee Oa a Oa FIG. — BO APES Pet ILLUSTRATIONS Series of Contractile Responses in Muscle Response of Indiarubber Response of Selenium to the Siimulas of Light. Negative Response of Galena to Hertzian Radiation Positive Response of Ag’ to Electric Radiation... Electric Response in Metals é Uniform Electric Response in Tin ; Fatigue in the Electric Response of Metals . ; Stimulating Action of Na,CO, on Electric Response of Siatinum Abolition of Response in Metal by Oxalic Acid .. Response by Method of Relative Depression 12. Arrangement for observing Simultaneous Mechanical aa Flectrical Responses ; Simultaneous Merhantcal aa Hlectrical tone | in Biophytum Photographic Record of Electrical Response by Galvanometric Negativity of Pulvinus of J/mosa, when leaf is_ physically restrained from falling : . Se Method of Transmitted Stimulation . Excitation by Sudden Tension ’ Excitatory Response to Tension and Corspavarion The Mechanical Tapper The Torsional Vibrator The Vibratory Stimulator P Complete Apparatus for Method of Block a Nitcators Stinrulation . Influence of Suddenness on the Efficiency of Stimulus . iets Spring Attachment for obtaining Vibration of Uniform Rapidity Additive Effect . ‘ ‘ ; : : : Response Recorder . ; : Photographic Record of Uniform 7 te (Radish) Stimulation by Thermal Shocks Photographic Record of Uniform Response in Peiiole Fe em to transmitted excitation Taps of increasing strength I : 2: 3: “4 sadectan ep obey Sibente | in leafstalk of turnip ba] 2 OO ON ANUP WWD SY GF — ons XXX COMPARATIVE ELECTRO-PHYSIOLOGY Increased Response with Increasing Vibrational Stimuli (Caulifiower- stalk) ‘ Responses to Indicating Stimulus obtuined: with’ Two Rpeelneas of Stalk of Cauliflower Genesis of Tetanus in Muscle Photographic Record of Genesis of Tetanus in Methaeieal Response of Plants (Style of Datura alba) ‘ ee Fusion of Effect of Rapidly Succeeding SGmuli : ; - Response of (a) quickly reacting Amaranth ; (6) of iia Coletta Arrangement for Instantaneous Stimulation . Fos General Arrangement for Rheotomic Observation Enlarged View of Balanced Keys Curve showing Rise and Fall of Rc aesive E, M. Change: onder moderate stimulation Response Curve from Rheotomic ch eee in Sin sf tuarcith under strong stimulation . : Artificial Hydraulic Response of Minioss ° Experimental Arrangement for obtaining Records on Staoked Devas of Responses given to Direct and Indirect Stimulation, by Leaf of Mimosa . Mechanical Responiies: of Eoat of ‘Mihasa. Mechanical Response of Bzophytum to Thermal Stimuiation . Record of Response of A/imosa Leaf, taken on a fast-moving drum The Abnormal Positive preceding the Normal Negative in Mechanical and Electrical Responses in Biophytum Photographic Record of Electrical Response of Petiole 7 Ceutinwer Photographic Record of Electrical Responses of Potato-tuber Photographic Record of Electrical.Response of Petiole of Fern . Longitudinal Contraction and Retardation of Growth under Light in Hypocotyl of Szzapzs nigra Record of Growth in Crinum at Pen petacats of 34° C. and 3 5° C. Balanced Record of Variation of Growth in Flower-bud of Crinum Lily under Diffuse Stimulation of Light Diagrammatic Representation of the Tonic Level Photographic Record of Abnormal Positive passing into Recoial Negative Response in a Withered ica crie of Leaf-stalk of Cauliflower . ‘ Photographic Record af Sesieade Reeaenae | in Vascioias Net erve Staircase Increase in Electrical Response of Petiole of Pe rendered sluggish by cooling . : Photographic Record of Uniform Ronusaals: (Radic Photographic Record of Uniform Response in Petiole of Fern Record showing Diminution of Response, when sufficient Time is not allowed for Full Recovery Fatigue in Celery Fatigue in Leaf-stalk of Caulidowse” Photographic Record showing Fatigue in Tin Wire which had ids continuously stimulated for Several Days . : : + ti er”, = ee Sl ee i ea 78. QI. 92. ILLUSTRATIONS xXxxi Effect of Over-strain in producing Fatigue Rapid Fatigue under Continuous Stimulation in (a) Muscle’; (3) Beak. stalk of Celery (Electrical Response) ~ Photographic Records of Normal Mechanical Gee of Mitiova to Single Stimulus (upper figure), and to Continuous Stimulation . (lower figure) < ‘ i ; Effect of Continuous Vibration (dictieh 50°) i in Carrot . Oscillatory Response of Arsenic -acted on Continuously by iertion . Radiation : Mesusia Fatigue (a) in "Electrical Radpohies of Petiole of Cauli. flower; (4) in Multiple Electric Responses of Peduncle of . Biophytum ; (c) in Multiple Mechanical Responses of Leaflet of . Biophytum ; and (d@) in Autonomous Responses of Desmodium . Photographic Record of Periodic rio in the Automatic Pulsation . of Desmodium Eyraus . ‘ ‘ : ; ; Periodic . Fatigue in Pulsation of Frog’s s Heart (Pembrey and Phillips) . Photographic Record at Peisdie: F sae sete Continous: Sitiala: . tion in.Contractile Response (Filament of Uric/is Lily) . Fatigue in the.Contractile Response of Indiarubber Reversed Response of Fatigued Nerve PAGE 94 96 od 97 98 98 99 99 100 Iol 102 Preliminary Staircase, followed by iigiey in the Responses Br Muscle (Brodie) . . Preliminary Staircase, Riteeeics followed = ueasn: in we Rediolae of Galena to Hertzian Radiation ; Photographic Record of Responses of Style of Datura alba in oes Growth had come to a Temporary Stop ‘ : cae Differential Contractile Response of Artificial Strip Responses of AZzmosa to Sunlight. of not too long Duration Transverse Response of Pulvinus of Mimosa. ‘ Diametric Method of Stimulation of-an Anisotropic Crab The Thermal Variator Responsive Current in. Petiole of Musa frou Concave to Comvis Side Parallelism of Natural Current in Pulvinus of AZmosa and Sheathing Petiole of W/usa 2 got Effect of Variation of Tuapeecuse on Natural Cotrene: \; which in Petiole. of MZusa flows from Convex to Concave Side ‘ Photogiaphic Record showing effect of Sudden, followed by steady Rise of Temperature on Natural Current, |, in A/usa Action of 7 per cent. Solution of Na,CO, on Natural Current of Musa Effect of CO, on Natural Current of Musa . : Variation of the Transverse Natural and icapalaee Curfents: in . Pulvinus of JZ@mosa. Photographic Record of Effect of @hidroform on ecnbaak of Chae Photographic Record showing Action of Chloral Hydrate on the . Responses of Leaf-stalk. of Cauliflower . ; ‘ Photographic Record showing Action of Formalin (Radish) . Abolition of Response at both A and B Ends "7 yg Action of NaOH ‘ : : , ; 103 103 104 108 109 110 III 113 115 118 119 120 122 122 127 130 131 -132 134 XXXii COMPARATIVE ELECTRO-PHYSIOLOGY FIG, 116. 118. 119. Photographic Record showing the nearly complete Abolition of Response by strong KOH Photographic Record showing the Siieiilataky Aisin of Sdhition of Sugar : Ne Photographic Record Dowie Coctinens Actes wae 2 per seat: Na,CO, Solution . ‘ Photographic Record showing the Depressing Action af 5 per ceil HCl Acid . ‘ Photographic Record deeine Effect of I per oat KHO. Photographic Record of Effect of 5 per cent. KHO. : Striking-rods for stimulation of two ends of specimen and inducing phase-difference . Isolated and diphasic responses weit one aihesence of shins ; Photographic Record showing Negative, Diphasic, and Positive Resultant Responses in Tin ; Photographic Records of Response of Bryphyltin Photographic Record of ee of Petiole of Cauliflower by ‘the Diametric Method F : , ; Distribution of Electrical Tension in Maecte> oylinder . Photographic Record showing Persistent Electrical After- Effect i in Inorganic Substance under Strong Stimulation . Photographic Record exhibiting Persistent Galvanometric Negativity in Plant Tissue after Strong Stimulation Experimental Arrangement for ier Electrical Effect due to Section ‘ Records showing increasing Poe Galvansmeuie ‘Regativiey; according as injury is caused nearer to proximal contact . Curve showing the Electrical Distribution in Stem with one Sectioned © End. ‘ : ‘ ‘ . : ‘ : ‘ é Electrical Distribution in Plant-cylinder with Opposite Ends Sectioned Record of es wnces | in Plant (Leaf: stalk | Coulifiowes by Method of Negative Variation : - d Response by Positive Variation of Reasina Current Distribution of Electric Potential in Lamina of Colocasia along a enciial line from dead to living through intermediate stages Straight Form Potentiometer ° Distribution of Electric Potential in Penal of Nymphica ott one end of which has been killed Photographic Records of Responses of Vereinbie N erve, one end of which has been injured . ‘ Typical Cases of Variation of Current of Rest and ction: Corsent, Specimen originally isotropic , Typical Cases of Variation of Current of Rest and ‘Actiow: Cunrent:; intermediate point naturally less or more excitable than either of terminal Typical Cases of Vor aeon of Guceat of Het and Acton: Comeonit Anisotropic organ, B end originally more excitable than A PAGE 135 136 136 w= =—- 7 Ve ee ee ee eS SS Oe ' FIG, 120. 121. 122. 123. 124. 125. 126. 527. 128. 129. 130. 131. 132. 133. 134.. 135. 136. 137. 138. 139. 140. I4I. 142. 143. 144... 145. ILLUSTRATIONS | xXXxXi b —e me PAGE Photographic Record showing Effect of Rapid Cooling, by Ice-cold Water, on Pulsations of Desmodium gyrans 181 Photographic Record of Pulsations of Desmodium during Continuous Rise of Temperature from 30° C. to 39° C. f . 182 Diminution of Response in Zucharis by Lowering of Tesh peretavé «+883 _After-effect of Cold on Ivy, Holly, and Zucharis Lily . 184 Photographic Record of Responses in Zucharis Lily during the Rise and Fall of Temperature - 185 Diminished Amplitude of Response with Rising Temperature (Stem ‘of Amaranth) .. .- “ght 186 Photographic Records of AenblaGiindeas Dibleanie in Driiahisaes, showing Increase of Amplitude and Decrease of Frequency, with Lowering of Temperature 188 Photographic Record showing Effect of Sieant 3 in shicliabitinie ihiehoaes 190 Record of Electric Responses of Amaranth at various Temperatures. 195 Photographic Record of Thermo-mechanical Curve given by Coronal Filament of Passiflora 198 Thermo-mechanical Curve of Two Different nineciaiee of Style of Datura alba, obtained from Flowers of the same Plant 198 The Thermal Chamber 200 Photographic Record exhibiting Bicetsie Spades in the Petiole of Musa 202 Photographic Réecond showed Electric Taversion at Death siecle 59°5°, in the Petiole of Amaranth . 203 Record showing Inversion of Electric Curve and ‘Siti Nalepsises Reversal of Electric Response in Stem of Amaranth. 204 Multiple Mechanical Response of Aiophytum, due to a Single Strong Thermal Stimulus . 208 Multiple Electro-tactile Response in ‘Stem of Wenosa due # Bite Strong Thermal Stimulus . ; 209 Photographic Record of Multiple Electrical Ripon: in Lae a Biophytum . 209 Multiple Electrical ieasheses ade Different Bonus val Siiehlies | in Different Organs 210 Photographic Record of Multiple Electrical Response to Siteie Thermal Shock in Frog’s Stomach : 210 Induction of Autonomous Response in Siophytum ‘a Moderately High Temperature of 35°C. . 211 Initiation of Multiple Response in Ester Leaflet of ‘iceman originally at Standstill . : : ‘ 212 Photographic Record of Autonomous Mechanical Pislestion in Desmodium Leaflet . 213 Spark-record of Single Pulsation in . Leaflet of Detwotiiuats . 214 Photographic Records of Simultaneous Mechanical and Electrical Pulsation of Desmodium Leaflet é ; 218 Photographic Record of. Simultaneous Mathaniont tnd Electrical Pulsation in Leaflet of Desmodium, before and after Physical | Restraint of Leaflet . é : ; ; ‘ : « 220 “‘Xxxiv COMPARATIVE ELECTRO-PHYSIOLOGY FIG. 146. ~ 147... 148. . 149. 150. . I5I. 152. : 153. 154. . 155: 156. | 187. 7858... 159. 160. 161. 162. 163... 164. 165. 166. 167. 168. 169... $70. St. 172. 7% PAGE Crescographic Record of ee Growth- “responses in Peduncle of . Crocus. .« ‘ : ‘ 221 Natural and db co nonctet Guuveeste 3 in Teavek cp 2284 Burdon Sanderson’s Fundamental Experiment on Dioian Leaf 229° _ Parallel Experiment in Sheathing Petiole of A/usa » «2229 Positive Response of certain Leaves of Dionea — 230 Diphasic Response of Leaf of Dzonea ‘ in Hapa Positive followed . by negative. . . . ; 230 Positive Response of same bet when ‘ modified ? by" peeiiiies ae" stimulation. .. .. ” : 230 . Experimental Connections with Piosive asicviinn to the second ‘Experimental Method of Burdon Sanderson’... ioe RO Bam © Response. of Under-surface of, Leaf of Dionea, with Electrical Connections as in Fig. 153: Wee: iss - Photographic Records of Positive, Tiphasie, ee Megative Rape of. Petiole of J/Zusa depending on the Effective antensity OF <3 35 . Transmitted Stimulus .. . ° ° 238. Electrical Response of Lamina of Nymphaea alba due to Pamelor. ; Excitation from Petiole . / 246 Diagrammatic Representation by Du fois: Reymond for Explanation _ of Electrical Response in Organ’of Zorpedo . : i gaz Photographic Records of Responses given by Leaf of Coleus wromae ais: when both Surfaces are Excited Simultaneously by cigars VSRGGK To ye~ 4 Apa 248 Experimental Adan deiace ig Mhovicant Ghicteniices 252 Records of Two Successive Responses in Leaf of Soph lies calycinum under Equi-alternating Electrical Shocks. . ° - 253 . Response-curve from Rheotomic Observation on Leaf of Nymphaea alba . ; : : es | Series of Responses ees i hast a Fidrosferamum subtrifolium to Stimulus of Equi-alternating Electrical Shocks . : 0 255 Photographic Record of Responses of Carpel of Dzl/enia nikita 256 Photographic Record of Normal Responses given by Pitcher of Nepenthe, under Equi-alternating Electric Shocks . ‘ . 256 Responsive Currents in Lead Wire , 264 Flat Strip of Lead, of which lower Surface is omnittated:| . 265 Photographic Records of After-effect of Homodromous ¢ and Hetero- dromous | Induction-shocks:in prepared Strip of Lead .. ¥- 6 Lee Photographic Record of Responses to -Equi-alternating Electric °. Shocks in Prepared Lead Strip. -. ae » 267 Response of Pulvinus of AMtmosa- to Equi alternating Electric ey: Shocks .:+ . ; ; : 268 Experimental Arrangement. for Detantiination of Excitatory ‘Afver- effect of Equi-alternating Electrical Shocks. 276 Method of Direct Effect of Excitation by Equi- caltamvating Shocks 280 Excitation by Equi-alternating Shocks 281 Photographic Record of Response of Petiole of Bis: to “Equi: “alee nating Electric Shocks, before and after Application of Chloroform 284 A : ’ ~ ILLUSTRATIONS Tse XXXV Photographic Record of Responses of ee Stem of Cac ‘bila to Equi-alternating Electric Shocks. ¥: Electrical Responses of Eel to Equi-alternating Electrical Shocks Rotary Mechanical Stimulator. _.. - aes ea Diagram Representing Different Levels - Excitability, ne ‘Leto, and Minus .. . - Electrical Response of Grape: arte to Rotary Méchanical Stimulation Electrical Response of Frog’s Skin to Rotary Mechanical Stimulation Photographic Record of Electrical Kesponses of Upper Surface of Intact Human Forefinger to Rotary Mechanical Stimulation — Photographic Record of Electrical’: Responses ee ork skin to . Thermal Shocks .. } Photographic Record of Electrical Rexpceseh of Grape-skin to Stimid _ lation by. Equi-alternating Electrical.Shocks - Photographic Record of Series of Electrical Responses of Frog’s s Skin . to Equi-alternating Electrical Shocks .. -. Photographic Record of Transverse Response of. Palvinus af Mimosa . to Equi-alternating Electrical Shocks... ray Continuous. Photographic Record of Autonomous Pulsation of Des- _ modium gyrans from 6 P.M. to 6 A.M, an, Photographic Record of Electrical Responses in Skin ‘of Neck of . Tortoise.to Stimulus-of Equi-alternating Electrical Shocks .. - . Isolated Responses of Upper and Lower Surfaces of Skin of Tomato . to Rotary Mechanical Stimulus. ~ Photographic Record of Series of Wesncaaa: in Skin of Eatante er . Equi-alternatin Electrical Shocks. . A Single Response of Skin of Tomato to Equbslternating Shock . recorded on Faster Moving Drum . Photographic. Record of Series of Normal Responses in Skin ve - Geckow’ :, Photographic Riou of ‘AtiiGened Dipbasis aiienonecs in Skin of Gecko, converted to Normal, after Tetanisation : Transverse Section of Tissue of Hollow Peduncle of Diialis aly: Photographic Record of. Responses of Water-melon to- meek - nating Electric Shocks . Photographic Rece d of- Electrical Responses ved Tnteet: Hiutaah - Armpit’. . +. : ‘y Experimental Arrangement ioe Ritepoiine of Hein’ Lip ey Photographic Record of Electrical Response of Intact Human Lip Possible Variations of Responsive Current, as. between. Two Surfaces - A and R, shown by. Means- of "Diagrammatic. iss paca of . Characteristic Curves. --.. - a ae y SLE ety Photographic Record: showing Resariid of N ofmial 2 eee in . Pulvinus of A/émosa due to Fatigue - 2 a A Ee 2 - .. Photographic Record showing Reversal of Resconse in Carpe of . Dillenia indica, wnder Sub-minimal Stimulation - Pitcher of Vepenthe, with lid removed. - oo Glandular Surface of a Portion of the aug Menibtaine: ofthe Pitcher > Of Nepenthe-. -.0 2 were ie Se eee el 336- XXXVi COMPARATIVE ELECTRO-PHYSIOLOGY FIG, 202. 203. 204. 205. 206. 207. 208. 200. 210, 211. 212. 213. 214. 215. 216. 217. 218, 219, 220, 221. 222. 223. 224. 225. 226. 227. 228. 229. 230. Transverse Section of Tissue of Pitcher of Vepenthe. ‘ ; Photographic Record of Series of Normal Negative Responses of Glan- dular Surface of Wefenthe in Fresh Condition to Equi-alternating Electric Shocks Photographic Record of Réspdmses nf Pitcher i in Intermediate Stage, having Attracted a Few Insects . : Photographic Record of Responses of Pitcher in Third Stags) the whole Glandular Surface thickly Coated with Insects Multiple Response of Pitcher of Vepenthe, in First or Fresh Stage, to Single Strong Thermal Shock Multiple Response of Pitcher pf Wideathe: 3 in Third Siage, to Single Strong Thermal Shock . Photographic Record of Responses in Fresh Dest of D osera to Bau alternating Electrical Shocks Photographic Kecord of Multiple Remniaas é asd of \ Detniesh in Positive Phase Photographic Record of N etstad Negative Riepooies of Frog’: s Stomach to Mechanical Stimulation Photographic Record of Normal Negative Responses of Stomach of Tortoise to Stimulus of Equi-alternating Electric Shocks . Photographic Record of Normal Response in Stomach of Gecko to Equi-alternating Shocks, seen to be reversed after Tetanisation Photographic Record of Multiple Responses in Stomach of Frog to a _ Single Strong Thermal Shock Photographic Record of Normal Negative Relpdanie of Voume Root of Colocasia Photographic Record of Dasities Riaponie’ in Older Root of Caberastn Photographic Record of Electrical Response of Sap-wood Photographic Record showing Normal Responses of Living Wood te Vibrational Stimulus, and the Abolition of Response by a Toxic Dose of Copper Sulphate . a, ‘ The Shoshungraph Curve showing Normal Suction: at 23° Cy “Pricresisal Suction at 35° C., and the After-effect persisting on Return to Normal Tempera- ture . Action of Ansehibeticn 3 in ; Aiohiien of Suetion Effect of Strong KNO, Solution Effect of Strong NaCl Solution . Record of Blank Experiment showing Alwence of asiy Disturbenss of Record from Induction-shocks as such Terminal Mode of Application of Stimulus Sub-terminal Mode of Application of Stimulus Renewal of Suction, Previously at Standstill, by Action of Stineuies Photographic Record of Effect of Stimulus in Enhancing Rate of Suction -,. , ; ‘ Variation of Latent Peisad as Afar aie of Gitiaiie 5 Photographic Record showing Variation of Latent Period as After- effect of Stimulus ; Suctional Response under Over- Galaace 363 369 372 375 376 377 378 380 380 383 383 384 385 386 Se atl at ee ILLUSTRATIONS ’ XXXVii- Photographic Récord of Effect of Stimulus on Over-balance . : Photographic Record of Response to Continuous Sub- terminal Stimu- lation . Experimental Arauigeasent a Bictection of Electrical Change _ induced at the Point transversely Distal to Point stimulated . - Record of Response to Moderate Unilateral Stimulation under the Experimental Arrangement described . oles Record of Different Specimen under same Experimental boca: ment when Stimulus is first Moderate and then Increased Mechanical Response of Pulvinus of A/imosa to Continuous Action of Light from Above . : ° , Electrical Response in the Lower Half is the Pulvinus of Mimosa due to Stimulation of Distal Upper Half by Light . , Photographic Record of Series of Negative Responses of Petiole of . Bryophyllum to Stimuli of Sunlight . ‘ A : Record. of Responsive Growth-variation taken under céniliteie of balance in slightly Sub-tonic Flower-bud of Crz#zuwm Lily under Diffuse Stimulation of Light . , Photographic Record of Positive Response of the Petiole of Cauli- flower to Light . ‘ . Multiple Mechanical Response of Leaflet of Biohytun aa the Continuous Action of Light f : Photographic Record of Multiple Electrical eonceee in oe, 6 Bryophyllum under Continuous Action of Light . . Diagrammatic Representation of Phasic Alternations, and After- effect in Type I. , . : : Photographic Record of Pieaie Kisccnationk. showing Direct and After Effects of Lightin Type I., represented by Bryophyllum . Diagrammatic Representation of Phasic Alternations, and After Effect in Type III. . ; . Photographic Record of Phasic Aaveriatien, showing ‘Disect a _ After Effects in Type III., represented by Petiole of Cauli- flower . Photographic Recut of Pals of Diiciecee dabei witha a Sicknd Specimen of Cauliflower, representative of Type ITI. ‘ ‘ Experimental Arrangement for Determination of Differential Excita- bility of Optic Nerve and Cornea . Series of Photographic Records of Excitatory etieniore 3 in F vis ’s Eye to Equi-alternating Electric Shocks Experimental Arrangement for Demonstration of Differential Excita- bility as between Retina and Optic Nerve . Series of Photographic Records of Excitatory teauiies in F mt s Retina to Equi-alternating Electric Shocks Photographic Record of Multiple Response of Retina of Frog snide Continuous Action of Light. , Response of petiole of Bryophyllum. Fighé: was cut off on sities ment of maximum positivity in the second of the multiple KespOnses, «.. ‘ : , ; , orig Ge PAGE 386 388 397 398 399 400. 401 402 405 407 Xxxviii © COMPARATIVE ELECTRO-PHYSIOLOGY FIG. 254. 255. 256. 257: 258. 259. 260. 261. 262. 263. 264... 265. 266. 267. . 268. 260. 270.. \ 27 272. 273. 274. 275. 276. 277. 278, 279. Similar effect in response of tetina of Ophiocephalus-fish’. = . The same with another specimen. ‘Light was here‘cut ‘off after the first oscillation Response of retina of Ophistephalus whe slightly aid Response of frog’s eye (Kiihne and Steiner) -. ‘ After-effect of Light on Silver Bromide. . yal he : Response of petiole of cauliflower. Light was here cut off’ on attain. ment of maximum negativity... .° . reve ise Response of retina of Ophdocephalus fish hee ‘depneskeas te Response of isolated retina of fish as.observed by Kiihne and Steiner Inclined Slits for Stereoscope and Composite Image formed i in the Two Eyes : : Composite Indaaiphésable Word, “68 which Components iare . Seen Clearly on Shutting the Eyes - 2. -~. é Diagrammatic Representation: of a Multicellular. Organ laid ‘Hotei _ tally and Exposed to Geotropic Stimulus: . - Effect on Apogeotropic Movement of Temporary Application of Cold on Upper and Lower Surfaces respectively. Diagrammatic Representation of Experiment showing Curvature . Induced by Unilateral Pressure Exerted by Particles . : Record of Responsive Curvature Induced in Bud of Crinum ee by Unilateral Pressure of Particles .° -.. Record of Apogeotropic Response in Scape of Bricks! Lily” Photographic Record of Geo-electric Response in the Scape - of Uriclis Lily laid horizontally. . ere: Experimental Arrangement. for Sidijecting: Organ to Geetespie ‘Stimulus, Mechanical Response.being Restrained: Geo-electric Response of the’ Physically. Restrained Scape of Uriclis Labyet Ss: wae Lo . Diagrammatic Representation af Electrical Consheann for Deter- _mination of ‘Velocities of . Centrifugal and -Centripetal ‘Trans- missions .- . | s A ¢: ae i a Experimental Adregsinent fot coopster the Relative Conduc- tivities in Transverse and Longitudinal Directions eis Response of Frog’s Nerve under Simultaneous Excitation of both Contacts, by Equi- aereee Electrical Shek: one. Contact . being Injured e ; Bahbaticement of Amplitude of agus as After- effect * Thermal . Tetanisation, in Frog’s Nerve Conversion of Abnormal Positive into Normal Negative Response . after Thermal Tetanisation .. -. ia Gradual Transition from Abnormal Boultvh tieoaish Diphasic, i Normal Negative Responses. in Frog’s’ Nerve - Abnormal Positive Response converted through Dipheate to grat Negative under the increasingly Effective Intensity.of Stimulus, brought about by Lessening the ssa between the ee and Stimulated Points... ...: % é ; Frond of Fern with Conducting Nerves akgaed ptha as sith. PAGE . 427 427 428 428 . 429 430 430 430° 432 - 432- 435 - 436 437 437 438 440° 441 442° 447 454 457 462 463 464 466 469 ’ FIG. 280. 281. 282. 283. . 284. : 285. 286. 287. 288. ° - ILLUSTRATIONS: » ‘! XX XIX Photographic Record of Effect of Ether on he Electrical Response of Plant-nerve . Photographic Ratants et Effect of Co, on Electrical Rescane of Plant-nerve . Photographic Record of Ripken of Response by Strong Apeicatton _ of Alcohol ‘Photographic Record of Effect of Ammonia on 1 Ordinary ‘Tissue: sf Petiole of Walnut . Photographic Record of Effect. of. Similar Application of Socata . . on Plant-nerve. Photographic Resaca of Exhibition of Three Sues sf Response, . Normal Negative, Diphasic, and Abnormal Positive, in Nerve . of Fern under: Different Conditions : Photographic Record of Effect of Tetanisation in ES Enhative: ment of Normal Negative Response in Nerve of Fern . Photographic Record of Conversion of the Abnormal Di-phasic hitn . Normal Negative, after Tetanisation,.T, in. Nerve of Fern Photographic Record showing how the Abnormal Positive Response is converted through’ Diphasic into Normal Negative by the ' Increasing Effective Intensity of Stimulus, due to Lessening the . Distance between the Responding and Stimulated Points. . Diagrammatic Representation of the Conductivity Balance . : Photographic Record made during Preliminary Adjustment fay Balance of Nerve of Fern . ‘ ‘ é : ‘ ; . Complete Apparatus of Conductivity Bitarice Effect of Na,CO, Solution on Responsive Excitability a F Bee s Nerve Effect of CuSO, on Frog’s Nerve Photographic -Record showing iighsocemeat o Rimehivile by Application of CaCl, . . - Photographic Record showing Haviedslcn of Rendaastie Excitability by Application of KCl . Photographic Record exhibiting Comparative Effects of NaCl tad NaBr on Responsivity Photographic Record of Effect Fi Dilute (* 5 per cee. ) Sates of Na,CO, on Variation of Conductivity Giistageanis Record of Effect of Stronger Dobe: (2 per ents i) of . Na,CO, Solution on Conductivity . ~- . é . RESPONSIVITY versus CONDUCTIVITY under KI ~ RESPONSIVITY versus CONDUCTIVITY under Nal . Effect of Alcohol on the Responsivity of Frog’s Nerve Photographic Record of Effect of Alcohol Vapour on Receptivity: - Photographic Record of Effect of Alcohof on Conductivity . . . Photographic Record showing Effect. of Alcohol on Responsivity - Diagrammatic Representation of Experimental Arrangement’ for ’ Demonstration. of RECEPTIVITY versus CONDUCTIVITY, or of RECEPTIVITY versus RESPONSIVITY . ne haere RECEPTIVITY versus RESPONSIVITY under Alcohol Photographic Record aan Effect of spsiii on » Cohductivity of PjJant-nerve. : . . . PAGE 472 473 473 474 474 475 476 477 477 482 482 484 485 485 . 486 487 487 488 489 491 492 492 493 494 494 - 495 495 499 COMPARATIVE ELECTRO-PHYSIOLOGY The Cork Chamber for Gradual Raising of the Temperature of one Arm of the Balance .- : Photographic Record Skiing Effect of Riau Tenipedsaded on Conductivity i Experimental Arrangement for Riadyiing ‘After- effect of Seances on Conductivity and Excitability : Photographic Record Showing Effect of ‘ Mosiaeate Siteaniatiend in Enhancing Conductivity and Excitability - Photographic Record showing Effect of Excessive Stimulation i in De- pressing Excitability and Conductivity Record of Contractile Response in Frog’s Nerve indi Contiawdus Electric Tetanisation . . . Optical Kunchangraph for Machsiticel Résponss of Hise Diagrammatic Representation of meee for Obtaining Petes. mitted Effect of Stimulus . Photographic Record of Effect of aia on pivecbanines Resneiize -of Frog’s Nerve . : . Photographic Record showing Abobasis of Mechanics Response oa Frog’s Nerve by Action of Solution of Morphia Photographic Record showing Preliminary Exaltation in Mechsnical Response of Frog’s Nerve after Application of Alcohol ‘ Photographic Record showing Effect of Chloroform on Mechanical Response of Frog’s Nerve . . . Photographic Record showing Mocornal hace commento’ into ‘Negative Response after Tetanisation Photographic Records showing Gradual Dldatpéatanice oe Positive ‘Element in diphasic Mechanical Responses of Frog’s Nerve and Plant-nerve . . Photographic Record sional Sinairense Effect in Medalees Re- sponse of Frog’s Nerve . . . Photographic Reproduction of Recon of Méckanicat Rea ponus af Frog’s Nerve and Plant-nerve obtained on Smoked Glass Surface of Oscillating Recorder 324. Record of Mechanical Responses to Electrical Stamatis chaaiviell on. Smoked Glass, and given by the Optic Nerve of Fish Ophiocephalus 325. Record, obtained on Smoked Glass, of Transmitted Effect of Stimu- lation on Nerve of Gecko . , z ee 326. . Initiation of Multiple Response by Drying of Ne erve : . ‘327. . Diagrammatic Representation of Experimental Arrangement for Re- : cording Response by Resistivity Variation . 328. . Photographic Record of the Morographic Curve takin by Method of ; Resistivity Variation in Pistil of Hibiscus. Critical point of in- version at 60°8° C, . ‘ 329. Photographic Record of the Morographic aes ken os Method of Eléctromotive Variation in’ Petiole of JZusa. Critical point of inversion at 59:6° C. . 330. Photographic Record of the Morgeaphie Cave ‘sane by Method of Mechanical Response in Filament of Passifora. Critical point of inversion at 59°6 .C. . ; ; ‘ ° ‘ + Dhue . PAGE — 500 501 504 504 505 510 511 512 516 516 517 518 521 522 524 528 529 530 539 544 546 546 546 339- 341. 342. 343- 344. 345. 346. 347: 348. 349- 350. 351. 352. 353+ 354: ILLUSTRATIONS Response Records by Resistivity Variation, in the Nerve of Fern Effect of Chloroform seen in benim i of ee tg dk in Frog’s Nerve . Photographic Record of Effect of ali dienes in Enhancing Mechani- cal Response of Plant-nerve . Photographic Record showing Bekeucemeat of Excitability dndér Action of Light in Nerve of Fern Distribution of Fibro-vascular Elements in Siigle Sane of Stem df Papaya Extra-polar Kat- dccaponie Effect Extra-polar An-electrotonic Effect » Extra-polar Electrotonic Effects under an Maiae E. M. F, shins rises from *6 to 1°4 Volts . : Diagram illustrating Bernstein’s Dechanieat of Kat- cbiitioale Caiént Diagram illustrating Bernstein’s Decrement of An-electrotonic Current Diagram representing Hermann’s Polarisation-increment under Tetanising Shocks, with reversed polarising Current Diagram representing Hermann’s Polarisation-increment fades Tetanising Shocks, with reversed polarising Current : Experiment with Petiole of Fern demonstrating Variation of Cou ductivity by Polarising Current, Excitation travelling electrically Downhill : Experiment with Petiole of Fern desisghstraliais Masten of Bex: ductivity by Polarising Current, Excitation travelling electrically Uphill é ‘ Photographic Records of Rassonaes salons in last inegariseents when Excitation was transmitted with and against the Polarising Current. Photographic Record of Modification of Conduction during Passage of Excitation from Anodic to Kathodic Region, under Increasing Intensity of Polarising E.M.F. Photographic Record showing Eshanced Condectizin fie Kathodic to Anodic Region . Experimental Arrangement to Exhibit the eliccnmnent of xciat bility at Anode, when the Acting E.M.F. is feeble Experimental Arrangement to Exhibit Depression of Excitability a at Kathode, when the Acting E.M.F. is feeble . Photographic Records of Response, illustrating the Hevanchebiews: bf Excitability at Anode, and Depression at Kathode, under Feeble Acting E.M.F. in two Specimens of Nerve of Fern a and é. : Experimental Arrangement demonstrating the Joint Effects of Variation of Conductivity and Excitability by Polarising Current . Experimental Arrangement demonstrating the Joint Effects of Variation of Conductivity and Excitability by Polarising Current, when Current is Reversed . ‘ Photographic Record of Response under the Kerapasenenis given in Figs. 351, 352 in Nerve of Fern Experimental Arrangements for Showing so- called Polatisn tan: increment by the Joint Effect of Increased Excitability at Anode and Enhanced Conduction of Excitation electrically Uphill . Cc xli PAGE 548 55° 554 557 558 560 560 561 562 562 563 563 565 . 565 566 567 568 569 569 570 572 572 572 574 xlfi FIG, 355: 356. 357: 359. 360. 365. COMPARATIVE ELECTRO-PHYSIOLOGY Experimental Arrangements for Showing so-called Polarisation- increment by the Joint Effect of Increased Excitability at Anode and Enhanced Conduction of Excitation electrically Uphill. Direction of Current in this is Reversed : Photographic Record of Responses in Nerve of Fern, andes Anite and Kathodic Action as described in Figs. 354 and 355. Photographic Record of Similar Effects in Nerve of Frog . Make-kathode and Break-anode Effects in Biophytum : Effect of Anode and Kathode on Responsive Sensation in er Hand Polar Effects of Cureate ia to Eoclned Aprile on ones Half of Pulvinus of Erythrina indica 7 Experimental Arrangement for Magnetometric. Method of Recard Photographic Record of Uniform Magnetic Responses of Iron Photographic Record of Periodic Groupings in Magnetic Responses Photographic Record of Response and Recovery of Steel under Moderate and strong Magnetic Stimulus Photographic Record showing Ineffective Stimulus made Effective by Repetition Molecular Model Method of Resistivity Macaious Photographic Record of Response of prin esiaaine Powder in Sugpish Condition to Stimulus of Electric Radiation Photographic Record Showing Uniform Response of -Ahenvbetocn Powder to Uniform Stimulus of Electric Radiation . Photographic Record of Response of Tungsten Experimental Arrangement for obtaining Response in iro * i duction Current : ; Magnetic Conductivity Balance Process of Balancing illustrated by Pivotopra pate Record af Reiponnes. Effect of K- and a-Tonus on Magnetic Conduction : Opposite Effects of K-Tonus when moderate and strong Effects of k- and A-Tonus on Magnetic Excitability Gradual Enhancement of Conductivity by the Action of Stiendies Characteristic Curve of Iron under increasing Force of Magnetisation . Characteristic Conductivity Curve of Sensitive Metallic Particles be- longing to Negative Class, under increasing Electro-motive Force. Cyclic Curves of Magnetisation and of Conductivity Photographic Record of Magnetic Tetanisation of Steel, éthiblting Transient Enhancement of aba Speed on Cessation . Mechanical Response of Frog’s Nerve to successive equal Stimuli, applied at Intervals of One Minute Mechanical Response of Frog’s Nerve, showing Conversion of Ab- normal Positive into Normal Negative Response after Tetanisation . Photographic Record showing Conversion of Abnormal ‘ Down’ Re- sponse in Tin to Normal ‘ Up,’ after Tetanisation PAGE 574 575 575 579 582. 589 594 594 594 595 595 598 600 601 602 603 604 607 608 609 610 611 612 620 621 622 623 625 627 628 ee St is. ILLUSTRATIONS Gradual Transformation from tivity of B (fig. 19), the current of response being B Fic. 19.. The Torsional Vibrator (a) The plant is clamped at c, between now reversed. In the cases 7 A pee B. Pig tee" ; : . : esponses obtained by alternately just described, it will be stimulating the two ends. Stimula- noticed that stimulus is ap- tion of A produces upward response ; of B gives downward response. plied directly. This method is, therefore, specially applicable when we wish to study the excitability of such tissues as are not good conductors of excitation, the method of transmitted stimulation being here, therefore, inapplicable. In order to observe the effect of chemical sijinailabion, the given agent—sulphuric or hydrochloric acid—is applied at x at ashort distance from the proximal contact. The trans- mitted excitation is now again demonstrated by the induced galvanometric negativity of that contact. It will thus be seen that, whatever be the effective form of stimulus employed, it gives rise to a definite and invariable electrical response whose sign is always one of galvanometric negativity. It was shown, then, in the course of this chapter that the excitatory change in ‘sensitive’ plants is characterised by contraction, negative turgidity variation, mechanical depression of the leaf, and by the electricals response of 28 COMPARATIVE ELECTRO-PHYSIOLOGY galvanometric negativity, all these effects being concomitant. It was further shown that electrical response is independent of the mechanical, being unimpeded in its occurrence when the leaf is physically restrained. The same electrical response of galvanometric negativity is also obtained from the tissues of the so called ‘ ordinary’ plants. And these electrical responses of plant tissues, it was further noted, are identical in sign with the corresponding responses given by animal tissues. | All forms of stimulus, moreover—mechanical, thermal, photic, chemical, and electrical—induce the same excitatory response of galvanometric negativity. CHAPTER III THE APPLICATION OF QUANTITATIVE STIMULUS AND RELATION BETWEEN STIMULUS AND RESPONSE Conditions of obtaining uniform response—Torsional vibration as a form of stimulus—Method of block—Effective intensity of stimulus dependent on period of vibration—Additive action of feeble stimuli—Response recorder— Uniform electric responses—List of suitable specimens—Effect of season on excitability—Stimulation by thermal shocks—Thermal stimulator —Second method of confining excitation to one contact—-Increasing response to increas- ing stimulus— Effect of fatigue—Tetanus. A QUALITATIVE demonstration has been given in the last chapter of the induction of galvanometric negativity in plant tissues, in response to the excitation caused by various forms of stimulus. This galvanometric response is thus a sign or indication of the state of excitation ; and under normal con- ditions it will be of uniform extent, provided only that the stimuli are also uniform. Assuming this ideal condition to be secured, it is clear that the physiological modifications induced by various agents will be manifested by a corre- sponding modification of response. The conditions essential to such application of stimulus are, then, (1) that it should be capable of uniform repetition ; (2) that it should be capable of increase or decrease by definite amounts; and (3) that it should be of such a nature as to cause no injury, by which the excitability of the tissue might be changed in some unknown degree. These conditions, on which the success of the electro-physiological investigation depends, are very difficult to meet. Chemical stimulation, for example, cannot be uniformly repeated. Electrical stimulation, again, which has the advantage of being easy to render quantitative, is open to the objection that by escape of current it may induce 30 COMPARATIVE ELECTRO-PHYSIOLOGY galvanometric disturbance. Indeed, as the response is electrical, it is obvious that if we are to obtain unimpugnable results, a non-electrical form of stimulus is almost a necessity. But it is only after providing against various sources of error that the electrical form of stimulation can be used with con- fidence. The stimulation caused by mechanical blows can be repeated, it is true, with uniform intensity. But the point struck is subjected to increasing injury, and its excitability thus undergoes an unknown variation. | I have, however, been able to devise two different modes of stimulation, in which all these difficulties have been — Ss (a) (b) L : ) Fic. 20. The Vibratory Stimulator Plant P is securely held byavicev. The twoends are clamped by holders cc’. By means of handles H H’, torsional vibration may be imparted to either the end A or end B of the plant. The end view (4) shows how the amplitude of vibration is predetermined by means of movable stops, Ss’. successfully overcome. rendering the results as perfect as possible. These are (1) torsional vibration, and (2) the application of thermal shocks. For the obtaining of perfect responses, it must be said here that there is still another condition to be fulfilled. If we wish to obtain the pure effect of stimulus at one contact, say A, special care must be taken that excitation does not reach the second contact, B; for otherwise, unknown effects of interference will occur. This may, it is true, be obviated by means of the method of relative depression or method of negative variation, so called, to be described in a subsequent chapter. But the experi- mental mode which I am about to describe, in which a block THE APPLICATION OF QUANTITATIVE STIMULUS 31 is interposed between A and B, is much more perfect. According to this arrangement, the specimen is tightly clamped in the middle, by which device the excitation’ of either end is practically precluded from affecting the other. Stimulation is brought about by means of torsional vibration. The stem or petiole is fixed, at its middle, in a vice, V, the free ends being held in tubes, C C’, each provided :/ AZ Fic, 21. Complete Apparatus for Method of Block and Vibratory Stimulation Amplitude of vibration which determines the intensity of stimulus is measured by the graduated circle seen to the right. Temperature is regulated by the electric heating coil R. For experiments on action of anzesthetics, vapour of chloroform is blown in through the side tube. with three clamping jaws. A torsional vibration may now be imparted to the specimen at either end by means of the handles H and H’ (fig. 20). The amplitude of vibration which determines the intensity of stimulus can be accurately measured by the graduated circle, and may be predeter- mined by means of the sliding stops s Ss... The complete vibrational apparatus, by means of which various experi- mental investigations may be carried out, is given in fig. 21, 32 COMPARATIVE ELECTRO-PHYSIOLOGY Moistened cotton threads in connection with the non-polari- sable electrodes, E E, make secure electrical contacts with A and B. For experimenting on the effects of temperature, there is an electrical heating coil, R, inside the chamber. For the study of the effects of different gases, there are inlet and outlet tubes, which enable a stream of the required gas or vapour to be circulated through the chamber. If the A end of the specimen be now suddenly torsioned through a given number of degrees, a responsive electro- motive variation takes place, which after- wards subsides gradually. If next the torsioned end be suddenly brought back to the original position, a second electro- motive response is obtained, similar to the first. Hence, in the case of a to-and-fro ab e ad_ vibration, the responsive effects are addi- a tive, and we have the further advantage 7 aa 22. Influence of that the tissue at the end of the operation is uddenness on the F im ‘ a Efficiency of Stimu- returned to its original physical condition. his In order that successive stimuli may The curves a, 4, ¢, d, 2 : are responses to be equally effective, another factor besides vibrations of the the constancy of the amplitude of vibra- same amplitude, , : 2 30°. Ina the vi- tion has to be considered. It is to be bration was. Very borne in mind that the effectiveness of the slow; in 6 it was less slow; it was rapid in c, and very _ rapid in @. stimulus in evoking response depends also on the rapidity of the onset of the dis- turbance. In the application of vibratory stimulation to plants, I find the extent of response to depend to some degree on the quickness with which the vibration is effected. I give below records of responses to successive stimuli, induced by vibration through the same amplitude, which were delivered with increasing rapidity (fig. 22). It will be noticed that an increasing quickness of vibration increased the response, but that this reached a limit. If we wish, then, to maintain the effective intensity of stimulus constant, we must meet two conditions. First, the amplitude of vibration must be kept the same. This is done by means Se ee ee er So EL A TIA tatty, alas Batis sb: THE APPLICATION OF QUANTITATIVE STIMULUS 33 of the graduated circle and movable stops: and, second, the vibration period must be uniform. This last condition is effected by an arrangement shown in fig. 23. The torsion- head is kept tense by means of a stretched spiral spring, s, made of steel. From this torsion-head there projects an elastic brass piece, B. R is a striker which can be made to give a quick stroke to B, by the rotation of the handle. A quick to-and-fro vibration is thus produced, by the blow given to B, acting against the tension of the antagonistic spring S. The amplitude of the angular vibration is at the E oc Fic. 23. Spring Attachment for obtaining Vibration of Uniform Rapidity same time predetermined by means of the stops P and qQ. The arrangements described are as used in ordinary work. But for certain experiments on differential excitability, a second striker, R’, may be attached to the other end of the apparatus, and by this means the opposite contacts in con- nection with E and E’ may be excited simultaneously. In order to obtain responses of great amplitude, it is now necessary to increase the amplitude of vibration. But this may give rise to fatigue. By way of avoiding this, therefore, it is still possible to obtain enlarged response by the additive effect of repeated feeble stimuli. In the electrical response of plants a sub-minimal stimulus, singly ineffective, is found D 34 COMPARATIVE ELECTRO-PHYSIOLOGY to become effective by the summation of several. This is seen in fig. 24, where a single vibrational stimulus of 3°, b a —-. 1 1 ' + JOsec> Fic. 24. Additive Effect (z) A single stimulus of 3° vibration pro- duced little or no effect, but the same stimulus when rapidly superposed thirty times pro- duced the large effect (4). (Leaf stalk of turnip.) alone ineffective, was found to evoke a large response when repeated with rapidity thirty times in succession. For the delivering of such equal and rapidly succeeding stimuli, I substitute for the single striker R an eight-spoked wheel, a complete rotation of which, by means of the handle, gives rise to a definite sum- mated effect: and a series of responses to such summated stimulations is found to be uniform. The galvanometer used for these experiments is a dead-beat instru- ment of D’Arsonval type. The sensitive- ness of this is such that a current of 10° ampere causes a deflection of I mm. at a distance of I metre. For a quick and accurate method of obtaining. records, I devised the following form of response-recorder. The curves are obtained directly, by tracing the excursion of the Fic. 25. Response Recorder galvanometer spot of light on a revolving drum (fig. 25). This drum, on which is wrapped the paper for receiving the record, is driven by clockwork. Different speeds of THE APPLICATION OF QUANTITATIVE STIMULUS) 35 revolution can be given to it by adjustment of the clock- governor, or by changing the size of the driving-wheel. The galvanometer spot is thrown down on the drum by the inclined mirror M. The galvanometer deflection takes place at right angles to the motion of the paper; a stylographic pen attached to a carrier rests on the writing surface. The carrier slides over a rod parallel to the drum. As has been said before, the galvanometer deflection takes place parallel to the axis of the drum, and as long as the plant rests un- stimulated, the pen, remaining coincident with the stationary galvanometer spot on the revolving paper, describes a straight line. If, on stimulation, we trace the resulting excursion of the spot of light, by moving the carrier which holds the pen, the rising portion of the response curve will be obtained. The galvanometer spot will then return more or less gradually to its original position, and that part of the curve which is traced during this process constitutes the recovery. The ordinate in these curves represents the electro-motive variation, and the abscissa the time. _ We can calibrate the value of the deflection by applying a small known E.M.¥., say of ‘1 volt, to the circuit, and noting the deflection which results. This gives us the value of the ordinate. The value of the abscissa which represents time is determined by the distance through which the recording surface moves, in unit time. In this simple manner accurate records are obtained. It has the additional advantage of enabling the observer to see at once whether the specimen is suitable for the purpose of investigation. A large number of records might be taken by this means, in a comparatively short time. It is also easy to take the records photographically by wrapping a photographic film round the recording drum. I give in fig. 26 a series of responses taken from the root of radish (Raphanus sativus), in which the stimuli were applied at intervals of one minute. This shows how ex- tremely uniform the responses may be rendered, if proper precautions are taken, It may here be once more pointed D2 36 COMPARATIVE ELECTRO-PHYSIOLOGY out, that for convenience of inspection, the records in this book have been so taken that the normal electrical responses © of galvanometric negativity, unless specially stated to the contrary, are seen as up-curves, galvanometric positivity being represented by down-curves. These excitatory responses of Fic. 26. Photographic Record of Uniform Responses (Radish) galvanometric negativity are obtained with all plants, and with every organ of the plant. I give here a table containing a list of specimens which will be found on stimulation to give fairly large electro-motive effects, occasionally as high as ‘rt volt. Organ Specimen Carrot (Daucus carota) Radish (Raphanus sativus) Geranium (Pelargonium) Stem : : . | Vine (V7tds vinifera) Amaranth (Amaranthus) Horse Chestnut (4 sceulus hippocastanum) Turnip (Brassica napus) Petiole . , . | Cauliflower (4rasszca oleracea) Celery (Apium graveolens) | Eucharis lily (2ucharis amazonica) Peduncle. ; . | Arum lily (Azcardia africana) Fruit ° . | Egg-plant (Solanum melongena) THE APPLICATION OF QUANTITATIVE STIMULUS 37 These responses, being physiological, vary in intensity with the condition of the specimen. The same plant which gives strong electrical response in spring or summer, may exhibit but feeble responsiveness in autumn or winter. Again, we shall see in a subsequent chapter that any agent which depresses physiological activity will also depress the electri- cal response; and, lastly, when the specimen is killed, the normal response is abolished. I shall next describe a second and equally perfect method of stimulation, by means, namely, of thermal shocks. We have seen that a sudden thermal variation acts as an efficient stimulus. I have also shown in my ‘Plant Response’ that thermal radiation acts as a stimulating agent, in inducing excitatory contraction. Hence, if a tissue be surrounded by a platinum wire, through which an electrical heating-current can be sent, the enclosed tissue will be subjected to a sudden variation of temperature, and also to the thermal radiation proceeding from the heated wire. Now if in successive experiments the duration and intensity of the current flowing through the wire be maintained constant, the stimuli also will thereby be rendered constant. The thermal stimulator, as already said, surrounds the specimen, but is not in actual contact with it. This is to prevent any injury to the tissue, by scorching. The current is so adjusted as to make the platinum wire red-hot and this heating-current is closed for about half a second at a time. Should larger response be desired, it-can be obtained by the summated effect of a number of such shocks, or the thermal stimulator may be put in direct contact with the tissue, if care be taken that the rise of temperature is not so great as to injure it. : The difficulty of ensuring similarity of duration to each individual shock is overcome by the use of a balanced key actuated by a metronome (fig. 27). A second rod is attached at right angles to the vibrating rod of the metronome, and carries a bent piece of brass in the form of two prongs. During the course of each vibration these prongs dip into 38 COMPARATIVE ELECTRO-PHYSIOLOGY two cups of mercury, thus closing the electrical circuit for a brief and definite time. When a second press-key, not shown in the figure, is open, the circuit is incomplete, and there is no thermal stimulation. The observer then presses this key, and counts, say, five strokes of the metronome,. after is again opened. In this way, the sum- mated effect is ob- tained, of five equal thermal shocks. This Fic. 27. Stimulation by Thermal Shocks process is repeated as often as desired, at intervals of, say, one minute, by which time the tissue is generally found to have completely recovered from its ex- citatory electrical variation. : In the case of the experimental arrangements of which the diagram is given in fig. 27, stimulation is confined to one contact of the responding circuit. The method by which excitation was here prevented from reaching the distal contact is important. I shall, in the course of the present work, show that the parenchymatous tissue of the lamina of a leaf or leaflet is a bad conductor of excitation. Hence if the second contact of the circuit be made with this tissue, the stimulus does not reach the distal point. It is true that a certain small proportion might conceivably be conducted through the attenuated fibro-vascular channel of the midrib. But even so remote a contingency is provided against by a transverse cut across the midrib on the hither side of the contact. The arrangements, then, being made in the manner de- scribed, the tissue may be subjected to the action of successive uniform stimuli. How regular the resulting responses may be rendered will be seen from fig. 28, in which is given a series of responses obtained from the petiole of a fern (fig, 28) which the press-key © 8 eee THE APPLICATION OF QUANTITATIVE STIMULUS 39 under successive thermal shocks, imparted at intervals of one minute. We have hitherto studied the responses caused by uniform stimuli. We shall next observe the increase of responsive effects brought about by increase of stimulus. In Fic, 28. Photographic Record of Uniform Response in Petiole of Fern to transmitted excitation animal tissues it is found, speaking generally, that increasing stimuli induce increasing effects, but that this process has a limit ; and in plant tissues the same is found to be the case. In order to obtain effects of the simplest type, not compli- cated by any secondary phenomena, it is necessary to choose specimens which exhibit little fatigue. In the first of these the stimulus was ap- plied by means of the spring-tapper. The first stimulus was given by a fall of the striking-lever from the height h; the second from 2h; and ; Fic. the third from 3h. The response- ee F Taps of increasing strength curves (fig. 29) clearly show the in- 1:2:3:4 producing in- crease of effect due to this increasing acheter eaiinat ees stimulus. In the second series, the stimulus applied was vibrational, and increased from 2°5° to 12°5° by steps of 2°5° at a time. Fig. 30 shows how the intensity of response tends under these conditions to approach a limit. The following table gives the absolute values of the responsive electro-motive variations. ; 40 COMPARATIVE ELECTRO-PHYSIOLOGY TABLE SHOWING THE INCREASED ELECTRO-MOTIVE VARIATION INDUCED BY INCREASING STIMULUS. Angle of vibration Induced E.M.F. rg 044 volt. 5° "O75 7:5° "090 55 10° E0045 12°5° "106 ,, In such normal cases an inerease of response is always induced with increasing stimulation. A diminution of response may, however, sometimes appear, with increasing ° 23° 5° 74° 10 12° Fic. 30. Increased Response with Increasing Vibrational Stimuli (Cauliflower-stalk) Vertical line = +1 volt. Stimuli applied at intervals of three minutes. stimulus. But this is merely a secondary effect, due to fatigue. The following records (fig. 31) will show in what manner this may be brought about. They were taken with specimens of the petiole of cauliflower, in one of which (A) fatigue was absent, while in the other (B) it was present. In the first specimen the recovery from each stimulus was THE APPLICATION OF QUANTITATIVE STIMULUS 4qI complete. Every response in this series starts, therefore, from a position of equilibrium, and the height of each single response increases with increasing stimulation. In the second case, however, the molecular derangement consequent on stimulation is not completely removed after any single 40° so FIG. 31. Responses to Increasing Stimulus obtained with Two Specimens of Stalk of Cauliflower In (a) recovery is complete, in (4) it is incomplete. stimulus of the series. That the recovery is only partial is seen in the gradual shifting of the base-line upwards. In the former case the base-liné had been horizontal, represent- ing a condition of complete equilibrium. Now, however, the base-line, or line of modified equilibrium, is tilted upwards. Thus, even here, if we measure the heights of successive 42 COMPARATIVE ELECTRO-PHYSIOLOGY responses from the line of absolute equilibrium, they will be found to increase with increasing stimulus. Ordinarily, how- ever, no allowance is made for the shifting of the base-line, the responses being measured instead from the -place of its previous recovery, or point of modified equilibrium. In this way these responses undergo an apparent diminution. I have occasionally observed another curious phenomenon in connection with the subject of response under increasing stimulus. During the gradual increase of the stimulus from — a low value, there would at first be no response. But on reaching a certain critical value, a response would suddenly be evoked which was maximum—that is to say, would not be exceeded, even when the stimulus was further increased. We have here a parallel case to what is known in animal physiology as the ‘all or none’ principle. In the case of cardiac muscle, for example, there is a certain minimal intensity of stimulus which is effective in inducing response. ‘But further increase of stimulation causes no concomitant increase of effect. When a tissue is subjected to rapidly succeeding stimuli, the excitatory effects are superposed upon each other. In muscle, for example, the contractile effect of the second stimulus is added to that of the first, before that has time to disappear. The result is a summation of effects more or less complete ; and these attain a maximum. With moderate frequency of stimulation, such a tetanic effect is incomplete, tending to become more and more complete, with the progressive increase of frequency (fig. 52). I have obtained results in every way similar to these, with the mechanical response of ordinary plants. In fig. 33 is given a photo- graphic record of tetanus, taken from the longitudinal motile responses of the style of Datura alba. Similar tetanic effects are also obtained in the electric response of plants, of which the records seen in fig. 34 form an example. The difficulties in the quantitative observation of electrical response have thus been overcome by the employment of two different methods of stimulation—namely, torsional vibration, and stimulation by thermal shocks. In the case of the EE -_ _ THE APPLICATION OF QUANTITATIVE STIMULUS 43 former, the intensity of stimulation was seen to depend on the amplitude of vibration. In the latter, stimulus intensity was determined by that of the thermal variation, which again was regulated by the intensity and duration of the electrical heating-current. It was also seen to be important that the Fic. 32. Genesis of Tetanus in Muscle Record to left shows incomplete tetanus, with moderate frequency of stimulation. Record to right shows tetanus more complete, with greater frequency of stimulation (Brodie). excitation of one contact should be prevented from reaching the other, and this was provided against in two different ways. In the first of these, a physical block was interposed between the two contacts. In the second, the distal contact was made with the non-conducting tissue of a lateral leaf. & a es (b) Fic. 33. Photographic Record Fic. 34. Fusion of Effect ot of Genesis of Tetanus in Rapidly Succeeding Stimuli Mechanical KResponse of i scle ; (4) i t. Plants (Style of Datura alba) wi stg aati | let tin When these precautions were observed, it was found that uniform stimuli induced uniform response. Stimuli which were singly ineffective, were found on repetition to become effective. A tetanic effect was obtained by the rapid super- position of stimuli. CHAPTER IV OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE IN PLANTS Response - curve showing general time - relations — Instantaneous mechanical stimulation by electro-magnetic release—Arrangement of the rheotome— Tabular statement of results of rheotomic observations—Rhythmic multiple responses. IN taking records of the electric response of plants, a galvanometer of fairly high sensitiveness is required. One which gives a deflection of I mm. at a scale-distance of I-metre, under a current of 10°° ampere is found, as already said, to be suitable for practical purposes. I used for most of the experiments in this work a dead-beat galvanometer of the D’Arsonval type. The natural period of swing in these galvanometers is somewhat long, however, and the response- record thus lags behind the electro-motive changes induced by stimulus. In order, therefore, to investigate the time-relations of a growing electro-motive reaction in a plant, after the recep- tion of the stimulating shock, it is necessary to employ a rheotomic mode of investigation. An account of this, and of the results obtained, will be given in the course of the present chapter. The after-effect of stimulus is found to be somewhat persistent and to vary in duration in different specimens. In some cases, recovery is complete in a very short time; in others it takes very much longer. For the purpose of forming a general idea of this difference two response-records are given here, one of which was taken from a stem of the quickly-reacting Amaranth (fig. 35), and the other from the more sluggish Colocasza. It will be seen that oe a ee OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE 45 while in the first of these the recovery was completed in fifteen seconds, in the latter, even after the lapse of forty seconds, it was still far from complete. Indeed, in this case it was not altogether accomplished till after several minutes. The character of the tissue again is an important factor in determining the time required for recovery. Thus it will be shown that in a vegetable structure functioning as nerve, recovery is much more rapid than in ordinary tissue. The physiological modification induced by season, moreover, is seen in the fact that response and recovery are quicker in Fic. 35- Response of (a) quickly reacting Amaranth ; (4) of sluggish Colocasia summer than in winter. This difference is demonstrated by mechanical response also, for in that of the leaf of Mzmosa, as already stated, it is found that, whereas in summer the period is six minutes, in winter it is as long as eighteen, or three times as much. In the study of the time-relations of response, we may overcome the difficulty of the galvanometer-inertia by using, as already said, some modification of the rheotome, originally devised by Bernstein. The relative values of electrical variation induced at various periods after the impact of the excitatory shock may here be found by making brief 46 COMPARATIVE ELECTRO-PHYSIOLOGY galvanometric contacts of equal period at the required intervals. : 3 The difficulty in this investigation lies in the instan- taneous application of a stimulus at a definite moment, and in the successful adjustment of the subsequent interval at which the resulting responsive current is to be led to the gsalvanometer and recorded. Instantaneous stimulation can, it is true, be effected by electrical shock. But polarisation, and other disturbances caused by it, might give rise to unknown variations in the responsive effect. Hence, it is advisable when recording the electrical response to employ, if possible, a non-electrical form of stimulus. And it is only after the successful employment of such an unimpeachable method, that we can feel any confidence in the use, after due precautions have been taken, of the electrical stimulus itself, as will be described ina later chapter. Another obstacle to be overcome is the elimination of the unknown element of time required for transmission when stimulus is applied at a distance from the responding point. This uncertainty can only be removed by applying the stimulus directly on the responding point itself. All these difficulties I have successfully met by employing the mechanical form of stimulation, which I am now about to describe. We have seen that a stimulus of definite intensity may be imparted by a quick torsional vibration of either twist or un-twist, or of the one followed by the other. The intensity of this stimulus, as we saw, depends on the angle of torsion, and remains constant as long as that angle is maintained the same. For this-purpose I use the vibrational apparatus already described, successive excitations being produced on one side only, say the right. The torsion-head is set by pulling a vertical thread by which the index is made to rest against the stop P. This pull of the vertical thread is against the antagonistic action of the spiral spring S (fig. 36). During the process of the setting, which is carried out slowly, there is a slight excitatory disturbance. But this is allowed to subside, The vertical thread by which the torsion-head OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE 47 is ‘set,’ is kept pulled up by an electro-magnetic arrangement shown in fig. 37, where the electro-magnet is seen to hold a soft iron armature at the end of the thread. At the moment when stimulation is to be effected the current which energises the electro- magnet is interrupted by an automatic arrangement which will be described later. By the break of the current the armature is released and a semi-vibration of the torsion- Fic. 36. Arrangement for In- stantaneous Stimulation Torsion-head set by string against stop Q is suddenly let go by electro-magnetic release seen in fig. 37. head is suddenly produced, the amplitude of which has been predetermined by suitable adjustment of the stop P. Suc- Fic. 37. General arrangement for Rheotomic Observation A, B, striking rods attached to revolving rheotomic disc; K,, key for electro-magnetic release of torsional stimulator ; K,, for unshunting the galvanometer, G; E, electro-magnet with its armature by which the vibration-head, Vv, is set at a definite torsion-angle; N,, N,, non- polarisable electrodes making electric contacts with specimen ;?c, com- pensator. cessive stimuli of equal intensity may thus be applied on the experimental tissue at whatever time may be desired. 48 COMPARATIVE ELECTRO-PHYSIOLOGY The next point is to secure an automatic arrangement by which galvanometric connections can be made with the experimental tissue, for a short period of time, say, ‘o1 of a second. In order to study the growing electro-motive changes, these short-lived contacts are to be effected in successive experiments at gradually increasing intervals of ‘oI, ‘02, ‘03 seconds, and so on after stimulation. It should be remem- bered in connection with this subject that the reactions in plant tissues are much more sluggish than those in the. animal. The time-intervals here provided for, therefore, are even smaller than would have been strictly necessary, The general plan of the apparatus for carrying out this investigation is seen in fig. 37. The revolving rheotome-disc — carries two striking-bars, A and B, of which A is fixed, and B capable of an increasing angular adjustment behind A. The bar A, striking against the key K,, interrupts the electro- magnetic circuit E, thus causing stimulation. All this time, the galvanometer G is short-circuited by key K,, and it is -only when the striker B unshunts the galvanometer, by striking against K,, that the responsive current can act on the galvanometer. C is the compensating potentiometer, the object of which will be described presently. The rheotome- disc is rotated by means of a motor, provided with a perfect governor, the period of asingle rotation being adjusted to one second. The circumference of the disc is 100 cm. One centimetre of this circumference therefore represents an in- terval of time of ‘o1 second. The breadth of the striker B is also 1 cm. and it will therefore pass over a given point in the course of ‘or second. These striking-rods attached to the disc, impinge, as already said, against two electrical keys K,, and kK, which are adjusted along the same radius of the disc. K, is a balanced key, one end of which carries a two-pronged brass fork, both prongs of which are normally dipped in cups of mercury, thus completing the particular electric circuit. By the blow given by the striker A on a projecting rod attached to K,, this fork is tilted upwards, and the circuit is broken. The striker B then impinges on the second key, K,. OBSERVATIGN BY RHEOTOME ON ELECTRIC RESPONSE 49 Here, the prong is kept down by a spring S, the circuit being re-made, as soon as the breadth of the striker B has passed over the projecting rod—that is to say, in ‘oI second (fig. 38). The interval of time be- tween the actions on the two keys, by which the two different electrical cir- cuits are broken in suc- cession, can be gradually increased, by increasing the angle between A and B. The key K,, as already said, controls the electro- magnet, which, on _ its release, instantaneously effects. the mechanical 7 “stimulation of the tissue. *'* 38. en Sian £3 The rotation of the rheo- K,, actuated by rod A, K, by B. tome-disc does not at once become uniform, on the Starting of the motor, but attains this when one revolution has been completed. Therefore the experimental observations are not made till the speed has become steady. By pressing the key K, during the first revolution (fig. 37), the break-action of A on K, is postponed. K, is then opened, and during the next revolution, stimulation is effected. In order to obtain the galvanometric effect of excita- tion at definite short intervals of time after the stimulus has been applied, the galvanometer short circuit, as stated before, is removed at those definite intervals. The adjust- ment of the striking-rod: B, in relation to A, enables us to open the short circuit, for ‘ol of a second, at increasing intervals. When the rod B is at a distance of I cm. from 4, the short circuit is removed after ‘ol second, when at 2 cm. after ‘02 second, and so on. Thus, in the arrangement just described, the galvanometer is short-circuited, except at those definite intervals required for observation. In a second E 50 COMPARATIVE ELECTRO-PHYSIOLOGY arrangement, the galvanometer is kept open, and closed only during ‘or of a second at the required increasing intervals of time. Fe . There may be a pre-existing difference of potential in the plant, as between the two points of galvanometric contact, N, and N, In order that this may not be a source of disturbance, a compensating potentiometer arrangement, C, is employed. The slider of the compensator is so adjusted that it exactly balances the resting difference of potential in the specimen. Under these circumstances, neither make nor break of the galvanometer occasions any deflection. And this balance is readjusted for each experiment of the series. I give below two tables which. summarise rheotomic observations on specimens of the petiole of cauliflower. By successive intervals of a given length should always be under- stood the mean interval: that is to say, the period between-the application of stimulus and the mid-point in the removal of the short circuit. Thus, for the mean interval of ‘02 of a second, the middle of the .striking-rod 8B, whose breadth is I cm., placed at a distance of 2 cm. from A. The galvano- meter is therefore acted on for ‘oI of a second, throughout ‘the period from ‘o15 to ‘025 of a second, after stimulation. In the first two sets of results here given, the observations will -be seen to have been taken at the somewhat long intervals of ‘1 of asecond. The stimulus applied in these cases was moderate. In the case of a third specimen, the observations on which will be given subsequently, the results were recorded at intervals of ‘o1 of a second. SPECIMEN I SPECIMEN II Mean interval Galvanometric Mean interval Galvanometric .- after excitaton deflection after excitation deflection ‘I second 70 divisions — “I second 26 divisions ‘2 ” 100 29 | 2 ” ifele) 95 3 se 310 $9 ey 7° ” "4 iy 220 99 “4 ” 64 9 Hh sas 104 ee ae 56 2 I°O ” 7° re) i ie) ne) 42 $9 2°0 29 15 re) 2°O 55 24 <7 OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE 51 It will be seen from the observations made on the first of these two specimens that the maximum electro-motive effect was attained in three-tenths of a second after excitation. In the second case, the maximum was reached in two-tenths of a second. The curve given in fig. 39 shows how quickly the electro-motive variation attains a maximum, and how rapid is its decline after reaching this point. There apppears to be practically no latent period, the induction of the electro- motive effect being apparently immediate. This will be made evident by the results given in the next series. Fic. 39. Curve showing Rise and Fall of Responsive E.M. Change, under moderate stimulation Ordinate represents galvanometric deflection ; abscissa, time. Large division = 1 second. (Petiole of cauliflower. ) For the next experiment, I took the stem of Amaranth, which I find to be more excitable and more quickly reacting - than the petiole of cauliflower. The intensity of stimulus was here greater than in the last case. I may state now what will be demonstrated in full later, that a strong stimulus often gives rise, not to a single, but to multiple responses. I had previously detected these multiple responses by means of both mechanical and galvanometric indications, and found them to have periodicities varying from some I5 seconds to several minutes. . Indeed, had they been much*quicker than they were, they could not have been detected, owing to the E2 §2 COMPARATIVE ELECTRO-PHYSIOLOGY inertia of the motile leaflets or of the galvanometer needle. By the employment of the rheotomic method, however, I was able to detect multiple responses having periodicities of the order of one-tenth or so of a second. All the experiments carried out on Amaranth gave two or three waves of electro- motive variation, the character of which will be understood from the following table and curve (fig. 40). Mean interval after excitation | Galvanometric deflection | ‘OI second 63 divisions "05 29 77 29 ‘ | 7S eee | 82 55 | “20 Fs; | 68 - "30 | 765 | *40 rr 75 re) | 60s; | ce ea | 70 55 86 oe) | 80, | OF 555 | It will here be seen that even after so short an interval as ‘ol of a second, a considerable electromotive change had Fic. 40. Response Curve from Rheotomic Observation in Stem of Amaranth under strong stimulation Note occurrence of multiple response. Large division of abscissa = *1 second. already been induced. The first maximum occurred after y5, the second after *3, and the third after ‘6 of a second. Nea ce eae ee. ee ee eae ee ee OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE 53 We thus see that there is a rhythm in these multiple responses, the successive maxima being here found to occur at periods which constitute multiples of ‘15 second. The third of these rhythms may be presumed to be missing, owing to the fact that no observation was taken at ‘45 second, as, at the time when these experiments were carried out, I was unaware of the existence of such rhythmicities. It was by the curves plotted from these data that my attention was first drawn to their occurrence. It will thus be seen that the electro-motive variation is initiated practically simultaneously with the impact of stimulus on the organ. With moderate stimulus, the maxi- mum variation is reached within two-tenths of a second, or this period may be made still shorter by the employment either of a more quickly reacting tissue, or of a greater _intensity of stimulus. Strong stimulation is apt to give rise to rhythmic multiple responses. CHAPTER'..V THE ELECTRICAL INDICATIONS OF POSITIVE AND -NEGATIVE TURGIDITY VARIATIONS Motile responses of opposite signs, characteristic of positive and negative turgidity-variations—Indirect hydrostatic effect of stimulus causes expansion and erection of leaf—Dositive and negative work—Wave of increased hydro- static tension transmitted with relatively greater velocity than wave of true excitation — Method of separating hydro-positive and excitatory effects—In- . direct effect of stimulus, causing positive turgidity-variation’ induces galvano- ‘metric positivity—Antagonistic elements in the electrical response —Separation of hydro-positive from true excitatory effect by means of physiological block. ~HAVING now described that fundamental electrical response of galvanometric negativity which is characteristic of excita- tion, I shall next proceed to deal with an opposite type of response—namely, that of galvanometric positivity. The combination of these two factors, in varying degrees of each, in the electrical response of plants, has been a source in the past of the greatest perplexity, leading investigators to con- tradictory results. And it can only be by disentangling them, and by ascertaining the conditions under which each invari- ably occurs, that precision will be arrived at in the field of electrical response. We have seen that excitation of the pulvinus of Mimosa induces negative turgidity-variation, with fall of the leaf, and galvanometric negativity. What, then, would be the out- ward expression of an increase of turgidity—that is to say, of the positive turgidity-variation ? With regard, first, to the mechanical expression, we may subject the question to an experimental test. The cut end of a branch of Mimosa, bearing leaves, is fixed watertight in one end of a U-tube, filled with water, and the other POSITIYE AND NEGATIVE TURGIDITY-VARIATIONS 55 end is connected alternately with a vacuum and a force pump, by means of which a diminution or increase of hydro- static pressure may be induced at will. In this way it is possible to suck water away from, or force it into, the plant and its organs, thus producing negative and positive turgidity- variations at will. When turgidity is thus diminished the indicating leaf is seen to fall. This is what happens also under the ordinary negative turgidity-variation induced by excitation. When turgidity is increased, on the other hand, the leaf is erected (fig. 41). In the case of the negative variation of turgidity, the pulvinus as a whole loses water, 10° 20° 30° 40° 50’ 60’ 70’ 80° 90° Fic. 41. Artificial Hydraulic Response of AZimosa The plant was subjected to diminished pressure up to a, and to normal pressure to 4, after which the pressure was increased. The effect of diminished pressure, in the depression of the leaf, continues for a while. The ordinate represents movement of tip of leaf in cm., abscissa represents time. but more from the lower and more excitable half than from the upper. In the case of the positive turgidity- variation, also, it is again the more excitable lower half which absorbs the greater quantity of water. Thus, in Mzmosa, and in Bzophytum, the mechanical indication of increased turgidity is an erection of the leaf or leaflet. The characteristic electrical indication of this will be observed presently. It has already been mentioned that the direct application of stimulus at a point causes a negative turgidity-variation of that point. We shall now see whether, under any 56 COMPARATIVE ELECTRO-PHYSIOLOGY circumstances, stimulus will induce a positive turgidity- variation. If we now apply moderate stimulus on the stem of J/zmosa, at a certain distance below the pulvinus, an excitatory expulsion of water will occur at the point directly stimulated. Such an expulsion of water will then cause, it is clear, a hydrostatic disturbance of increased pressure. And this hydro-mechanical disturbance will be transmitted with relatively great velocity. Now such an increase of pressure, as we have seen, causes an increase of turgidity at the puivinus, in consequence of which the leaf ought to be erected. And although this hydrostatic disturbance is transmitted very quickly, yet a certain time is con- sumed in the process of forcing water into the pulvinus, by which to bring about the erection of the leaf. After the passage of the hydrostatic wave, there follows Fic. 42. Experimental Arrange- the wave of true excitation, passing sea arn ares from cell to cell, and inducing the given to Direct and In- Characteristic reaction, of negative eee eee by Leaf of tyroidity - variation. And when Thermal stimulator at s produces this excitatory wave reaches the trey smlstion my gene pulvinus, the previous erectile stimulation, at a distant point, Movement should give place ~ to Sys eterna to indirect effect excitatory depression, or fall of the leaf. In fig. 42 are seen the arrangements for an ptoknehiueiit on Mimosa by which these inductions may be verified. Moderate thermal stimulus is applied at S, at a certain distance below the indicating leaf. This latter is attached by a thread to a writing-lever, which traces the response-record on a smoked revolving drum. When the stimulus is applied at a point S very near the pulvinus, the response takes place by a negative turgidity- variation, with a concomitant fall of the leaf, seen in fig. 43 (a) as an up-curve. When a moderate stimulus is applied a lla le i POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 57 at a greater distance S,,, the hydrostatic wave causing the positive turgidity-variation brings about an erectile twitch. This is followed by a responsive fall, when the true excitation reaches the organ (fig. 43, 0). It has thus been shown that by separating the responding point from the point stimulated, or the receptive point, it is possible to discriminate two different effects which are both brought about by stimulus. It is most important, moreover, to distinguish between these two factors : namely, the direct effect of stimulus causing contraction, and its indirect effect, causing expansion. We have seen that direct excitation and transmitted excitation both induce contrac- tion, negative turgidity-variation and fall of the leaf. Unfor- tunately, in animal physiology, Fic. 43. Mechanical Responses it has been customary to apply Reet eaaesmesa eee (a) record of responsive fall when the term zuzdirect to that form stimulus applied near the re- of stimulation which is applied sponding organ; (4) response . : * when stimulus is applied on at a distance. And it has not same side, but at greater dis- . . tance, s,,. A preliminary erectile been noticed that such stimulus seuliocie ins bere: fallowed.” bey is capable of inducing diametri- the true excitatory depression. : ' This is due to the indirect effect cally opposite results, according first transmitted being succeeded as the true excitatory effect by the direct. Had the stimulus applied been feebler, or more reaches, or does not reach, the distant, there would have been responding organ. When the ons first, or indirect erectile intervening tissue is highly conducting, the transmitted effect induces exactly the same result as if stimulus were applied directly. But we shall see that when the intervening tissue is non-conducting or feebly conducting, true excitation is not transmitted, and the effect which makes its appearance at the responding point is then due to increase of hydrostatic tension, causing positive 58 COMPARATIVE ELECTRO-PHYSIOLOGY turgidity-variation, with the concomitant effect of expansion, and, in the case of J/zmosa, of erection of the leaf. This latter effect of positive turgidity-variation and expansion, I shall therefore distinguish as the INDIRECT EFFECT of stimulus, in contradistinction to the term INDIRECT STIMU- LATION, as it is generally used. The last-named, however, I shall myself always refer to under the title of TRANS- MITTED STIMULATION. If the intervening tissue be of Fic. 44. Mechanical Response of Biophy/um to Thermal Stimulation Stimulus was applied at some distance from the responding leaflet. And the preliminary erectile twitch is due to the prior arrival of the hydrostatic disturbance. Thick dot represents moment of application of stimulus. moderate conducting power, we shall, as in the case of the experiments on J/zmosa, obtain a preliminary erectile twitch, due to the indirect effect of stimulus, followed by a fall, in consequence of the transmission of the true excitatory effect. In fig. 44 is seen this twofold expression of the indirect and transmitted effects of stimulus, given by the leaflet of Biophytum. These two waves, then, of increased hydrostatic tension ah a hh ll al ee ee ’ “Me as tare, POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 59 and of true excitation, induce, as we have now seen, opposite responsive reactions. But of these, that due to true excita- tion is, generally. speaking, greatly predominant. Hence, when these two waves reach the responding organ in close succession, as is the case when the point of stimulation is very near, the excitatory effect masks the hydrostatic. In order, then; to ‘separate them, we may employ various methods. First, in the case of highly conducting tissues, the stimulus must be applied at a sufficient distance to make the slow excitatory wave lag adequately behind the quickly travelling hydrostatic wave. Or we may choose a direction of transmission of excitation which will be relatively slow. Thus I have found that transmission across a stem, for example, is very much slower than along its length. Hence, on applying moderate stimulus at S, (fig. 42) ata point on the stem diametrically opposite the pulvinus, of the given leaf, it is found that the excitation reaches the pulvinus only after a measurable interval, the hydrostatic effect inducing erectile response much earlier. Thus in a given experiment, whose record was taken on a fast-moving drum (fig. 45), the erectile response took place ‘6 second after the application of stimu- lus, whereas the true excitatory fall did not occur till 3:45 seconds had elapsed—that is to say, 2°85 seconds later. It is to be borne in mind that’ a certain interval of time passes, even after the arrival of the respective waves, before the tur- gidity-variation is able to give rise to the motile indication. Let us next examine the results at the responding tissue of the indirect effect of stimulus. The distant receptive point contracts on stimulation, and sends to the responding organ a wave of increased hydrostatic tension. This, as we have seen, forces water in, and expands the tissue.. Work is thus done ox the tissue which increases its store of energy. In this the indirect is unlike the typical direct effect of stimulus. For the latter causes the impulsive fall of the leaf, which represents work done dy the tissue, and an expenditure of energy. We must, therefore, recognise two distinct respon- sive effects, according as the work done is fosétive—done on 60 COMPARATIVE ELECTRO-PHYSIOLOGY the tissue—or negative: that is to say, done by the tissue. The outward manifestations of these two processes are respectively expansion and contraction. The positive, as we shall see, is not the result of hydrostatic disturbance as such, but is the effect of energy transmitted hydraulically. The indirect effect of stimulus, then, gives rise to positive turgidity-variation, and increases the internal or -potential Fic. 45. Record of Response of A/zmosa Leaf, taken on a fast- moving drum Stimulus applied at moment @, on point of stem diametrically opposite to responding leaf. Hydro-positive erectile response occurs at 4, *6 second after application of stimulus. True excitatory response of fall takes place at c, 3°45 seconds after application of stimulus. Time-marks represent fifths of a second. energy of the organ. A positive turgidity-variation is thus concomitant with an increase of internal energy and a negative turgidity-variation with the reverse. In observing the mechanical response, we saw that the expression of positive turgidity-variation, due to the indirect effect of stimulus, consisted of an erection, and was therefore of opposite sign to that of the negative turgidity-variation, caused by true excitation, and expressing itself in a fall, of POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 61 the leaf. We shall now see whether a similar difference exists between the electrical expressions of the positive and negative turgidity-variations. In carrying out this experiment, I took a specimen of Biophytum and applied stimulus at a distance from the par- ticular leaflet whose responses were to be observed, arranging, at the same time, for a simultaneous record of the mechanical and electrical responses. It will be seen from fig. 46 that the preliminary erectile twitch, due to the positive turgidity- variation, has, as its concomitant, galvanometric positivity. And this is followed in both records by its opposite: namely, the contractile fall and the galvanometric negativity of true excitation. It will thus be seen that the increase of internal energy, with its positive turgidity-variation, has, as its electrical expression, galvanometric positivity. Besides this, the mere physical movement of water in the tissue gives rise to a certain electrical varia- tion of positivity, and this can still be detected, even after the tissue is killed. The question of how to discriminate what proportion of the electro- positivity was due to this mere water - movement, and what to the increase of turgidity, associated with the. increase of in- Fic. 46. The Abnormal Positive preceding the Normal Negative in Mechanical and ternal energy, I at first Electrical Responses in Biophytuni found it very difficult to * represents the moment of application of ; , stimulus. The upper is the mechanical decide. But I ultimately and the lower the’ electrical record. The records downward indicate erection succeeded in doing this of the leaf or galvanometric positivity. by bringing a plant to a condition just short of death, and thus abolishing its true excitatory reaction. In this condition, the responsive 62 COMPARATIVE ELECTRO-PHYSIOLOGY indication was found to be one of considerable electro- positivity. On finally killing the-plant, however, the positive change due to water-movement was found to represent so insignificant a proportion of the whole as to be negligible, In order to exhibit the electrical expression of the excitatory and hydro-positive effects of stimulation, in ordinary plants, I took a petiole of cauliflower and made one connection, the proximal, with a point on it, and the other with an indifferent point on the surface of the lamina. In order to obtain the unmistakable hydro- static effect, the petiole was sud- denly squeezed, at a distance of 6.cm. from the proximal contact, and this gave rise, as will be seen (fig. 47, a), to a positive response, represented downwards. This was repeated once more, and the same effect observed. I next applied thermal stimulus at a dis- tance of 4 cm. from the respond- ing point. In this case hydro- static and excitatory disturbances reached the contact, the hydro- PIG, ty vical Reponse of Peticle Static shortly followed by the of Cauliflower excitatory, as in the case of the a, hydro-positive ; 2, di-phasic; experiment on Mimosa. This c, excitatory negative responses. : : is seen in the record, as a di- phasic response, the hydrostatic positive being followed by the excitatory negative (fig. 47, 0). Reference has already been made to the observation of Burdon Sanderson, that in the lamina of the Dzonea leaf the immediate response was one of galvanometric positivity. Mis- taking this for the true excitatory effect, he concluded that the response of the plant was of opposite sign to that of the POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 63 animal. From the experiment just described, however, it will be seen that the effect observed by him was in reality due, not to true excitation, but to the hydrostatic disturbance, or indirect effect of stimulus. In the next record (fig. 47, ¢) we see the effect of stimulus applied nearer: that is to say, at a distance of 2 cm. from the proximal contact. Owing to the propinquity of the point of stimulation, the two disturbances are not now sufficiently separated, and the excitatory negative reaction completely masks the hydrostatic positive effect. It is thus seen that, as has been said, one method of exhibiting these two effects separately is to apply stimulus at a point so distant from the proximal contact that there is an interval between the arrival of the two waves of hydro- static and excitatory disturbance respectively. It is obvious, then, that if the tissue under experiment be a good con- ductor of excitation, we must place the point of stimulation at a long distance from the first electrode, in order that the effect of excitation may lag sufficiently behind the hydrostatic wave. Similarly, in a bad conductor of excita-— tion, it will be the indirect effect alone which will reach the proximal contact, unless the stimulus applied be very near, and very strong. In order to distinguish these two opposite effects from each other, I shall in future refer to that hydrostatic effect which causes expansion and galvanometric positivity as ‘the hydro-positive effect, by way of differentiating it from ‘the true excitatory. effect, of negative turgidity- variation and galvanometric negativity. It has already been said that tissues which exhibit a high degree of. conduction are characterised by more or less of protoplasmic continuity. Hence, fibro-vascular elements are relatively good, and parenchymatous. tissues bad, conductors of excitation. The cells of the potato tuber for this reason exhibit very little power of transmitting excitation. When, therefore, in experimenting with this 64 COMPARATIVE ELECTRO-PHYSIOLOGY tissue, stimulation was caused by application of a hot wire so near as I cm. to the proximal contact, it was the hydro- positive effect alone which reached it, giving rise to posi- tive response. It was only, indeed, by applying the stimulus very near, at a distance of 3 mm., that the true excitatory response of galvanometric nega- tivity was in this case . obtained . (fig. 48). From what has been said, it will be seen that when a given point is excited by transmitted stimulation, two antagonistic elec- trical effects are induced—one of positivity, due to hydro-positive action, and the other of negativity, due to true excitation. When the stimulator is near to, or co- incides with, the responding point, the tissue is subjected to rapidly succeeding positive and negative turgidity-variations, and the elec- trical indication of the latter being the more intense, it masks the Fic. 48. Photographic Record former, and the resulting response of Electrical Responses of . : A Potato-tuber is determined by an _ algebraical a, Positive response to stimulus summation of the two. In a applied at distance ; 4, Negative yjgorous specimen, whose excit- response to stimulus applied tan : near. ability is great, the excitatory gal- vanometric negativity masks the positivity. The resultant electrical response in general is expressed by the formula N,z—P,, where N, is the galvano- metric negativity due to the true excitatory effect,and P,, the positivity due to the hydro-positive effect, which immediately precedes it. From this, it is clear that, as regards the resultant galvanometric response of vegetable tissues under stimulation, there may occur the two typical cases displayed in the following table : POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 65 TYPICAL CASES OF RESULTANT RESPONSE Conditions . Constituent Factors Resultant Response Excitability great Nez >Pu Galvanometric negativity Excitability diminished Ng wat “Se = ee ie oy - 414. 4t4 >. a A ee ae ee ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 81 the tonic condition, on the other hand, to the critical level, the greater will be the excitatory overflow, and the smaller the latent component. The internal and external factors will thus be complementary to each other. pia ‘On subjecting this inference to experimental demon- stration by means of growth-response, I fully succeeded in verifying it. According to this method of growth-response, it will be remembered, the true excitatory effect is measured by retardation of the normal rate of growth, the internal factor of increased latent energy being represented, on the other hand, by a corresponding enhancement of the rate of growth. This being understood, it was found that in a particular specimen of growing tissue, whose tonic condition was somewhat low, the external and internal effects caused by a given stimulus were in the proportion of 32 to 13'5. When the tonic condition of the specimen was raised, how- ever, and the same stimulus was applied, the external effect was found to be enhanced to 38 at the expense of the internal, which was now found to be lowered to 8°5. The sum of the work done, both internally and externally, is seen to be in both these cases approximately the same, being in the former experiment 455, and in the latter 46's. . ~ We have seen that, of the two antagonistic factors of response, the positive will predominate if the excitability of the tissue be in any way diminished. Such a loss of excitability may occur in either of two ways: (1) by the sub-tonicity of the tissue itself; (2) by the depression con- sequent on fatigue. Under either of these conditions then we may expect to obtain the exhibition of the positive effect. The exhibition of the positive effect. under fatigue will be described in the course of the next chapter. We shall here consider instances in addition to those already given, of the occurrence of the positive effect in a tissue which is sub-tonic. We have to bear in mind that the work which incident stimulus is called upon to perform is two-fold, both internal and external, and that there is a certain critical excitatory level, above which only is the normal responsive expression G : So COMPARATIVE ELECTRO-PHYSIOLOGY possible. The actual potential or excitatory level of a tissue depends on its tonic condition and the intensity of the incident stimulus. Now this existing potential of the tissue - may be anything within a wide range, S T, when sub-tonic, N when normal, or H T when hyper-tonic or above the ordinary normal degree (fig. 53). Since wb Roes Ph FeRAt ara it is necessary that the incident stimulus should cause the critical level C to be slightly exceeded, if there is to be an excitatory overflow, we can see that the intensity of the stimulus re- oh. ee. quisite to evoke response will be greater eg Poe in proportion as the tonicity of the tissue itself is low. Thus when the tissue is extremely sub-tonic, a stimulus of or- dinary intensity could never avail to raise the energy of the system above See rad fa se the critical point, and the response Tonic Level must then therefore be positive. Under N,normal;sT,sub-tonic; these circumstances it will only be by HT, hyper-tonic ; and » : ; z c, the critical level | the impact of excessively strong sti- mulus, or by the cumulative action of a series of moderate stimuli, that the critical point can be reached and passed, and the normal negative response evoked. Thus the intensity of the minimally-effective stimulus in evoking normal response will afford us a measure of the tonicity of the tissue. If the latter be high, then the feeblest stimulus will precipitate outward response, and indeed, if excessive, response will occur on little or no provocation, and such movements we call‘autonomous.’ It must be remem- bered, however, that it was by the previous absorption of stimuli that the tissue was brought to this point of unstable equilibrium at which the added impact of an infinitesimal stimulus causes it to bubble over, as it were, into apparently spontaneous activity. The predominant expression of the highly tonic tissue ee ee eT ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 83 being thus negative, we must go to the other extreme of great sub-tonicity if we are to be successful in demonstrating the occurrence of the unmixed positive response. This considera- tion leads us to expect that positive response will be evoked on moderate stimulation from tissues that are either not highly tonic or protoplasmically defective. I shall show in Chapter XXII. that in cells of epidermis, where the proto- plasmic contents have been reduced to a minimum, response to moderate stimulus tends in general to be positive, Even highly excitable tissues like nerve, as will be shown later, when cut off from their supply of energy, often become so sub-tonic as to give positive response. I shall here show how ordinary tissues exhibit this effect, when the tonic con- dition is allowed to fall to such an extent as to render the tissue extremely sub-tonic. For this purpose I took a cut specimen of petiole of cauliflower, and kept it without water for a couple of days. By this process the specimen, became somewhat withered. I next proceeded to take records of its electrical responses under increasing stimuli. The intensity of these stimuli rose from I to 10 units. It will be seen from the record (fig. 54) that each stimulus up to 9 evoked positive response, and that it was the strong stimulus of | 10 which gave rise to the normal response of negativity. This constitutes the first instance of a phenomenon which I shall show later to be of very extended occurrence—the induction, namely, of one effect under moderate, and its opposite under very feeble stimulation. It is not so easy to demonstrate this fact with a highly excitable, as with a some- what sub-tonic tissue, where the critical intensity of stimulus for the evoking of normal response need not be impracticably low. A point to be taken into account here is the after-effect of sub-minimal stimulus in enhancing subsequent normal excitability. Thus it is found in taking the record of responses to a succession of feeble stimuli, that though they are at first abnormal positive, they are afterwards converted into ‘normal negative. That it is the after-effect of the. previous stimulation which thus enhances previous excitability. G2 84 COMPARATIVE ELECTRO-PHYSIOLOGY may also be demonstrated by subjecting the tissue to con- tinuous stimulation or tetanisation, when the abnormal positive is found to pass into normal negative. From the experiments that have been described, it would appear that the several kinds of response characteristic of various tissues are relatively rather than absolutely different. The true excitatory reaction of an excitable tissue, is one of galvanometric negativity. Any diminution of the ex-— citability—whether by lowering of tonic condition or other Fic. 54. Photographic Record of Abnormal Positive passing into Normal Nega- tive Response in a Withered Specimen of Leaf-stalk of Cauliflower Stimulus was gradually increased from I to 10, by means of spring-tapper. When the stimulus intensity was 10, the response became reversed into normal negative. (Parts of 8 and 9 are out of the plate.) This record is to be read from right to left. _Down-records stand for positive, and up-curves for negative responses. causes—will bring about a decrease of this negativity, which may culminate in actual positivity. Thus negative is not separated from positive response by any break of continuity ; but we are able, on the contrary, to trace a gradual transition from one to the other. Moreover, in every response we have the two antagonistic elements, positive and negative, either actually or potentially present. The form taken by the resultant response is entirely determined by the question of what proportion of the stimulus impinging upon the tissue becomes latent ; and this in its turn depends upon the tonic See? poe, ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 85 condition of the tissue. When the absorbed stimulus is wholly retained, response is positive, but by this absorption the tonicity of the tissue and its excitability are both raised. When the tonic condition of the tissue, on the other hand, is already high, and its excitability great, a large proportion of the energy finds outward expression, and we obtain the normal negative response. Between these two extremes, we may observe many effects of interference, due to the play of the two antagonistic elements. If, then, the time-relations be not coincident, variations will be induced which will find expression in different types, diphasic response, positive followed by negative, and vzce versa. The question considered in the course of the present chapter has been that of the energy received and given out by the tissue, and the molecular work, positive and negative, performed during these processes. Such work, however, is itself the result of molecular distortions brought about by stimulus, and the question of the amplitude of response, as related to the degree of distortion, will be discussed in the following chapter. CHAPTER VIII VARIOUS TYPES OF RESPONSE Chemical theory of response—Insufficiency of the theory of assimilation and dis- | similation—Similar responsive effects seen in inorganic matter—Modifying in- fluence of molecular condition on response— Five molecular stages, A, B, C, D, E —Staircase effect, uniform response, fatigue—No sharp line of demarcation between physical and chemical phenomena—Volta-chemical effect and by- products—Phasic alternation—Alternating fatigue—Rapid fatigue under con- tinuous stimulation—In sub-tonic tissue summated effect of latent components raises tonicity and excitability—Response not always disproportionately greater than stimulus—Instances of stimulus partially held latent : staircase and ad- ditive effects, multiple response, renewed growth— Bifurcated responsive ex- pression. ACCORDING to current theories, living matter is maintained in a state of equilibrium by the two opposed chemical pro- cesses of assimilation and dissimilation. It is supposed that stimulus causes a down or dissimilatory change, which is again compensated during recovery by the building-up or assimilative change. In the case of uniform responses, again, these two processes are regarded as balancing each other. On this theory, when the down change is the greater of the two, the potential energy of the system falls below par ; for the building-up process cannot then sufficiently repair the chemical depreciation caused by it. Hence occurs dimi- nution of response, or fatigue, which is supposed to be further accentuated by the accumulation of deleterious fatigue-stuffs. The disappearance of fatigue after a period of rest is ex- plained by the renovating action of the blood-supply, which is also regarded as the means of carrying away the fatigue- stuffs. A serious objection to these explanations lies, however, in the fact, that even excised and bloodless muscles exhibit recovery from fatigue after a period of rest. In isolated Se ee a a a el te te ee ee ee ee VARIOUS TYPES OF RESPONSE 87 vegetable tissues, again, where there is no active circulation of renovating material, the same effect, and its removal after a period of rest, are observed. Thus the difficulties en- countered in explaining fatigue, on purely chemical ‘con- siderations, are great enough; but still greater are those difficulties which arise when we come to deal with the stair- case effect—typically shown in cardiac muscle—in which successive responses to uniform stimuli exhibit a gradual enhancement of amplitude. The results obtained here are in direct opposition to the theory described; for in this particular case we have to assume that the same stimulus which is usually supposed to cause a chemical breakdown, has become efficient to induce. an effect exactly the reverse. Of the two antagonistic elements in the electrical response, moreover, it is the positive which is supposed to be associated with the assimilative, and the negative with the dissimilative change. If this supposition were correct, however, it would be natural to expect that the positive response would be manifested predominantly in vigorously growing tissues, in which assimilation must be at its greatest. Fatigued tissues on the other hand, in which dissimilatory changes are sup-— posed to be predominant, should manifest negativity as their characteristic response ; moribund tissues, in contrast with the actively growing, might also be expected to exhibit respon- sive negativity. In actual fact, however, the very reverse is the case. For in vigorous tissues, normal response is by galvanometric negativity ; and it is the over-fatigued or - moribund which characteristically exhibit the positive re- sponse. It would be difficult again to conceive of assimilation and dissimilation in the case of inorganic matter. Yet even in inorganic matter we find reproduced all the various types met with in the response of living tissues: namely, uniform response, the staircase effect, and fatigue. Response being really due to molecular upset from a condition of equilibrium, we can see how different forms of responsive expression will occur, according to the various molecular conditions of the 88 COMPARATIVE ELECTRO-PHYSIOLOGY substance at the time being. One of the most important factors, then, in determining the character of response is the molecular condition of the substance itself. The numerous anomalies hitherto encountered in our interpretation of responsive phenomena are all traceable to our failure to take this factor of molecular condition into account. For a full exposition of the modifying influence which it exercises on response, however, though I shall here state some of the principal conclusions which I have arrived at, the reader is — referred to Chapter XLII. From the fact, that every type of response is to be obtained from inorganic matter, where chemical assimilation and dissimilation are obviously out of the question, it is clear that the fundamental phenomenon must be dependent on physical or molecular, and not on such hypothetical chemical changes. It must, however, be remembered that though re- sponse phenomena and their modifications are undoubtedly in the first place physical or molecular, yet in the borderland between physics and chemistry there is no sharp line of demarcation. For example, yellow phosphorus becomes converted, under the stimulus of light, into the red, or allotropic, variety. This molecular change, however,cis also attended by a concomitant change in the chemical activity, phosphorus in its allotropic condition being less active than in the yellow. Under certain circumstances, further, it is possible to have a secondary series of chemical events follow- ing upon a condition of unequal molecular strain. A homo- geneous living tissue, when unstimulated, is iso-electric. When stimulated, however, an electro-motive difference is induced, as between the stimulated and unstimulated parts of the tissue. . The result is an electrical current attended by electro-chemical changes. As a consequence of such volta-chemical action, when prolonged, by-products (fatigue stuffs?) may be accumulated, and these may have a de- pressing effect on the activity of the tissue. Hence, just as, after very prolonged activity of a voltaic combination, it is necessary to renew the active element and change the VARIOUS TYPES OF RESPONSE 89 electrolyte, surcharged with by-products, so after sustained activity of a living tissue, the process of renewal, or renova- tion, will be necessary. It is thus seen how upon the funda- mental molecular derangement, a chain of very various chemical events may follow, as its after-effect. And it is only by going in this way to the very root of the pheno- menon that we can avoid the many contradictions with which we are confronted by the chemical theory. In studying various response phenomena, our conclusions are necessarily based upon the observation of the amplitude of responses. It is therefore important at this point to draw attention to the danger of hasty inferences. On finding, for instance, that the amplitude of response in a given case is diminished, we are apt to infer that the responding tissue has undergone depreciation. But this is not invariably the case. In the entire process of response, while stimulus induces molecular upset, we must remember that there is also an internal factor, which brings about molecular restitu- tion. Now, if this force of restitution be inany way enhanced, it is easy to see that the responsive distortion of the mole- cules will find itself opposed, with consequent diminution of amplitude. We shall thus often find that a rise of tem- perature, by enhancing the force of recovery, actually causes a diminution of response. That this is not due, however, to any depreciation of the tissue is seen from the fact that the same rise of temperature enhances another excitatory pro- perty of the tissue—namely, the speed of its conduction. I shall now give a brief account of the modifying influence exercised on response by the molecular condition. It will be shown, in the Chapter (XLII) on the Modification of Response under Cyclic Molecular Variation, that a given response is not determined merely by the nature of the responding substance, but also by the amount of the energy which it possesses. Starting from the lowest condition of sub-tonicity, a substance undergoes progressive molecular transformation by the action of the impinging stimulus itself. Five stages may be roughly distinguished in this transformation. In the gO COMPARATIVE ELECTRO-PHYSIOLOGY first, or A, stage of extreme sub-tonicity, we have absorption without excitatory response. By this absorption the sub- stance passes into the next, or B, stage, which is the stage of transition, where response is converted from the abnormal to normal. Above this stage the rate of molecular transforma- tion is very rapid. From the residual after-effect of stimulus, the substance now passes from the stage B to the stage 0, which is a condition of more or less stability. Further | stimulation carries the substance to stages D and E. Here the molecular distortion from the normal equilibrium is very great. Stimulation applied in this condition has little further effect in inducing response. That is to say, excit- ability is here reduced to a minimum. In this extremely distorted position, moreover, the substance has a strong tendency to revert to the position of normal equilibrium. In the A condition of extreme sub-tonicity, since there ‘is absorption without excitation, the response which we obtain is abnormal positive. Intense or long-continued stimulation carries the substance into the B stage, with its normal negative response often preceded by diphasic. An example of this has already been given in fig. 54, obtained from the sub-tonic petiole of cauliflower. We shall meet, however, with numerous other examples in a great variety of tissues. Arriving at the B stage, the substance is still somewhat sub-tonic, and the rate of molecular transformation here is rapid. From the after-effect of stimulus the mole- cules of the somewhat inert substance become incipiently distorted in the same direction as that of normal response. A proportion of the incident stimulus is thus utilised in inducing a favourable molecular disposition. A repetition of the original stimulus will now give rise to a greater excitatory reaction than before. Thus at the B stage we obtain a stair- case increase of response. This fact—that by the after-effect of previous stimulation the molecules may be incipiently dis- torted in a direction favourable to excitatory response—finds ‘illustration in stimuli individually ineffective being made effective by repetition, The result here is evidently made VARIOUS TYPES OF RESPONSE QI conspicuous by the summation of the after-effects of all the preceding stimuli with the direct effects of their successors. The staircase effect is seen in the two accompanying records. In fig. 55 is given a photographic record of the staircase increase.in the electrical response of a vegetable nerve! in somewhat sub-tonic condition, In fig. 56 we have a second example of this effect, seen in the electrical response of the petiole of Sryophyllum, rendered artificially sub-tonic by cooling. We next arrive at the C stage, which is, as has been said, one of more or less stability. Expenditure is here, for a certain length of time, balanced by income. The molecular condition of the tissue being thus constant, the responses are uniform. I give below records of such uniform re- sponses to uniform stimuli, ex- Fig. 56. Staircase Increase in Electrical Response of Fic. 55. Photographic Re- Petiole of Bryophyllum, cord of Staircase Response rendered sluggish by in Vegetable Nerve cooling hibited by different tissues. In fig. 57 are seen uniform electrical responses to uniform mechanical stimuli, given by the root of radish. Fig. 58 shows uniform electrical responses to uniform thermal stimuli, given by the petiole of fern. The C€ is succeeded by stages D and E, representing a condition of over-strain. In fig. 59, a, are shown uni- form responses to uniform stimuli, applied at intervals " An account of the discovery of certain vegetable tissues, with the function of nerves, will be found in Chapter XXXII, 92 COMPARATIVE ELECTRO-PHYSIOLOGY of one minute. An inspection of the record shows that there is in such cases a complete recovery, at the end of which the molecular condition is the same as before stimula- tion. Hence, successive responses are exactly similar to each other. The stimulation-rhythm was now changed, to intervals Fic. 57. Photographic Record of Uniform Responses (Radish) of half a minute instead of one, while the stimuli were main- tained at the same intensity as before. It will be noticed (fig. 59, &) that these responses are now of much smaller Fic. 58. Photographic Record of Uniform Response in Petiole of Fern amplitude, in spite of the equality of stimulus. An inspec- tion of the figure also shows that, when greater frequency of stimulation was introduced, the tissue had not had time to effect complete recovery from previous strain. The mole- cular swing towards equilibrium had not yet abated, when VARIOUS TYPES OF RESPONSE 93 the new stimulus with its opposing impulse was received. There is thus a diminution of height in the resultant (a) (4) (<) Fic. 59. Record showing Diminution of Response, when sufficient Time is not allowed for Full Recovery : : ake ed : ; Fic. 60. Fatigue in In (a) stimuli were applied at intervals of one Celery minute ; in (4) the intervals were reduced ; - : to half a minute ; this caused a diminution Vibration of 30° at in- of response. Jn (c) the original rhythm: is tervals of half a minute. restored, and the response is found to be enhanced (Radish). response. The original rhythm of one minute was now restored, and the succeeding records (fig. 59, c) at once show increased response. Residual strain is thus seen to be one of the principal reasons of reduced response or fatigue. This is also shown in a record which I have obtained with a petiole of celery (fig. 60). It will be noticed there that, owing to imperfect molecular recovery, during the Fic. 61. Fatigue in Leaf-stalk of time allowed for rest, the heights Cauliflower of succeeding responses undergo Stimulus : 30° vibration at interval ; rier . ‘ f one minute. acontinuous diminution. Fig. 61 gives a photographic record of fatigue in the petiole of cauliflower, and fig. 62 of fatigue in inorganic response. ! It is evident that residual strain, other things being equal, will be greater if the stimuli have been excessive. This is 94 COMPARATIVE ELECTRO-PHYSIOLOGY seen in fig. 63, where the first set of these responses, A, is for an intensity of mechanical stimulation of 45° vibration, and the second set, B, of augmented amplitude, for an intensity of go° vibration. Fic. 62. Photographic Record showing Fatigue in Tin Wire which had been stimulated for continuously Days On reverting, in C, to the first stimulus- intensity of 45°, the re- sponses are seen to undergo a great diminution, as com- pared with the first set, A. This change is due to the over-strain of the previous excessive stimulation. But we should expect that the effect of such over-strain » would disappear with time, and the responses regain their former height, after a period of rest. In order to verify this, therefore, I re- newed stimulation (at the intensity of 45°) fifteen ‘minutes after c. It will be seen from the record D how far fatigue had been removed in this interval. 45 Os a Fic. 63. 90 B Effect of Over-strain in producing Fatigue 45 45 C , D Successive stimuli applied at intervals of one minute. The intensity of stimulus in C is the same as that of A, but response is feebler owing to previous over-stimulation. Fatigue is to a great extent removed after fifteen minutes’ rest, and the responses in D are stronger than those in c. The vertical line between arrows represents ‘05 volt. (Turnip leaf-stalk. ) One peculiarity that will be noticed in these curves is that, owing to the presence of comparatively little strain, the first response of each set is relatively large. The succeeding VARIOUS TYPES OF RESPONSE 95 responses are approximately equal, where the residual strains are similar. The first response in fig. 63, A, shows this, because there had been long previous rest. The first of B shows it, because we are there passing for the first time to an increased intensity of stimulus. The first of C does not show it, because of the strong residual strain from the preceding excessive stimulation. And the first of D, again, does show it, because the strain has now been removed, by the interval of. fifteen minutes’ rest. Of the antagonistic elements of positivity and negativity which are present in response, we have seen that the positive becomes predominant when the excitability of the tissue is in any way depressed. And since a tissue under fatigue has its excitability lowered, it follows that in this condition it may be expected to exhibit a tendency towards positive response : that is to say, expansion in the case of mechanical. and galvanometric positivity in the case of electrical, response. Thus, when a tissue is subjected to continuous stimulation, the first effect will be the maximum negative response, contraction and galvanometric negativity. But on the setting- in of fatigue, the positive effect will predominate, inducing a fatigue-reversal of the response. In cases where such fatigue is very great, as, for instance, in certain muscles, the top of the tetanic curve undergoes rapid decline (fig. 64, a). The normal contraction now exhibits a reversal, or relaxation. In the sensitive plant, 1/zmosa, similarly, continuous stimula- tion by electrical shocks gives rise to results which are essen- tially the same. It will be noticed that after the responsive fall of the leaf it returns to its former erect position, in spite of the fact that stimulus is still being continued. Here also, as in the corresponding case of muscle, we have the usual sequence, of (1) normal contraction and (2) fatigue relaxation (fig. 65). In electrical response, also, under continuous stimulation, the normal galvanometric negativity, owing to the increasing positive effect, undergoes decline or abolition. © This is seen in fig. 64, 6, which exhibits the decline of electrical response 96 COMPARATIVE ELECTRO-PHYSIOLOGY under continuous stimulation in the petiole of celery. The fatigue in the mechanical response of muscle under similar conditions is given in @ for the purpose of comparison. The effect of rest in inducing molecular recovery, and hence in the removal of fatigue, is illustrated in the following set of photographic records (fig. 66). The first of these shows the curve of electrical response, obtained with a fresh plant. It will be seen that under a continuous stimulation of two minutes the response first attains a large amplitude, after which it declines, in a fatigue-reversal. Another two minutes were now (a) (6) Fic. 65. Photographic Records of Normal Mechanical Response of Mimosa to Single Stimulus: (upper ’ ‘ figure), and to Continuous Stimu- Fic. 64. Rapid Fatigue under Con- gt s tinuous Simutation in (az) Muscle ; lation (lower, agure) ‘ } (6) Leaf-stalk of Celery (Electrical In the latter case the leaf is erected in Response) spite of continuous stimulation. allowed for recovery, and we observe that a partial recovery takes place. Stimulation was now repeated throughout the succeeding two.minutes, to be followed once more by two minutes’ rest. The response in this case is seen to be decidedly smaller than at first. The same effects are seen in the third response. A period of rest of five minutes was next given, and the curve subsequently obtained: under the VARIOUS TYPES OF RESPONSE 97 same two minutes’ stimulation as before shows greater response than the preceding, owing to the partial removal of residual strain. | There is one aspect of the subject of fatigue-reversal which now demands our attention. Wehave seen that under continuous stimulation, a maximum contraction is induced, which is attended by the depression of the leaf of A/zmosa. Fic. 66. Effect of Continuous Vibration (through 50°) in Carrot In the first three records, two minutes’ stimulation is followed by two minutes’ recovery. The last record was taken after the specimen had a rest of five minutes. The response, owing to removal of fatigue by rest, is stronger. This is followed, however, by a reversal—namely, expansion, with re-erection of the leaf. According to the chemical theory of assimilation and dissimilation, the fatigue-effect is assumed to be due to an explosive dissimilatory change, with consequent run-down of energy. Inthe case of Wzmosa, however, it is difficult to understand how, by a mere run- down of energy and consequent passivity of the tissue, an active movement of erection—involving the performance of work in lifting the weight of the leaf—could be brought H 98 COMPARATIVE ELECTRO-PHYSIOLOGY about. Now we have seen that the diminution of normal response may be brought about by the augmentation of the internal factor, tending to enhance the force of restitution, and the necessary augmentation of the internal factor may be the result of an increase of internal energy. Thus while the plant is the recipient of a continuous income, its responsive expression is alternately one of emis- — sion and absorption of energv. Thus negative and positive succeed each Fic. 67. Oscillatory Re- other or vice versa. Such a phasic sponse of Arsenic acted ; : pe -on Continuously by alternation is widely present, as we Hertzian Radiation - shall see, in the response, not only Taken by method of con- * oe ‘ ‘ ductivity variation. of various living tissues, but also of inorganic substances. The follow- ing record (fig. 67) exhibits this oscillatory response in arsenic under the continuous stimulation of electric radiation. In the case of Wzmosa, under continuous stimulation, we obtain Fic. 68. Alternate Fatigue (2) in Electrical Responses of Petiole of Cauliflower; (4) in Multiple Electric Responses of Peduncle of Biophytum ; (c) in Multiple Mechanical Responses of Leaflet of Bio- phytum ; and (ad) in Autonomous Responses of Desmodium a single alternation, and a certain period must then elapse, before the response can be repeated. In other cases, how- ever, continuous stimulation may give rise to two, or three, or a large number of similar alternations. VARIOUS TYPES OF RESPONSE 99 In connection with this subject of phasic alternation I may describe a certain curious phenomenon, which I have often noticed ; I refer to the periodic waxing and waning of both mechanical and electrical responses. The simplest example of this will be a case in which the responses are alternately large and small. But others are to be found in which the groupings are more complex. In fig. 68a@ is seen such a simple alternation, in the electrical response of the petiole of cauliflower, under successive uniform stimuli. In 6, c, and d@ are shown similar alter- nations in multiple and autonomous responses. I give alsoa photographic record (fig. 69) of a similar alterna- tion in the automatic pulsations of the leaflet of Desmodium gyrans. IANA ATAVATANLE Fic. 69. Photographic Record of Periodic Fatigue in the Auto- Fic. 70. Periodic Fatigue in matic Pulsation of Des- Pulsation of Frog’s Heart modium gyrans (Pembrey and Phillips) Similar alternations are sometimes observed in the beating of frog’s heart (fig. 70). | In the following record of mechanical response (fig. 71), taken from the style of Datura alba, we find that fatigue, as already understood, would not explain the phenomenon observed. For here, under the continuous action of stimulus, without any intervening period of rest for the so-called ‘assimilatory’ recuperation, we see that a second response occurs. I shall later give other instances in which pulsating responses, with their alternating negative and positive phases, are given, under the action of continuous stimulation. We pass here imperceptibly from the ordinary phenomenon of H2 TOO COMPARATIVE ELECTRO-PHYSIOLOGY individual response to individual stimulus, into that of multiple response, either to continuous, or to a single strong stimulation. The excess of energy derived from impinging stimulus is in the latter case held latent in the tissue to find subsequent expression in phasic alternations of negative and positive variations in series (cf. Chapter XVII). There can be no doubt that these effects of periodic alternation of phase are due to two antagonistic reactions, becoming effectively predominant by turns. Thus the con-— tinuous impact of stimulus on a tissue may first give rise to the negative phase of response. But by the continuous absorption of incident stimulus, the internal energy is in- creased, with its. opposite reaction of _ positivity. Hence, the negativity will be gradually diminished, and the _ positive phase become predominant. The existence of these’ two antagonistic factors will be understood, from an inspec- “Fre. 71. Photographic Record of tion of the top of a tetanic Periodic Fatigue under Continuous curve. Here, the more or Stimulation in Contractile Response ‘ , (Filament of Uriclis Lily) less horizontal line repre- | sents a state of balance between the two opposite forces of excitatory response by contraction, with galvanometric negativity and recovery or expansion, with galvanometric positivity. When this state of balance is disturbed, by a sudden cessation of the hitherto continuously acting stimulus, a brief overshooting of the response in the negative direction is sometimes seen, followed by recovery. We shall meet with examples of this in, among others, the responses of retina and certain vegetable tissues under light. Such facts it has been suggested afford a demonstration of the two antagonistic processes of assimilation and dissimilation, characteristic of living tissues. But that they are really to be accounted for VARIOUS TYPES OF RESPONSE IO! from molecular considerations will be seen from the fact that effects exactly similar are met with in the response of inorganic matter (cf. figs. 258 and 383.) In the case of responses exhibiting fatigue from over- strain, we have a diminution of normal response, which may ultimately culminate in reversal. We may imagine a spiral spring, undergoing increasing compression from a gradually augmenting force. The responsive compression will at first be considerable. But this will soon reach a limit, beyond which added force will seem to have but little power to induce further responsive distortion. In a somewhat similar way, we may visualise the condition of the responding molecule at the stage D or E. Here, molecular distortion has almost reached its limit. It follows that added stimulus can induce Fic. 72. Fatigue in the Contractile Response of India-rubber Note the periodic alternation and the reversal at the end. little further distortion. But the maximally distorted mole- cule has now a great tendency to revert to the position of equilibrium, and the shock of stimulus, instead of inducing excitatory action, induces the reverse. That this is to be ex- plained by molecular rather than chemical considerations, is seen in the following record (fig. 72) of the contractile response of india-rubber to thermal stimulation. This represents the last part of a long series of responses, whose amplitude was already undergoing a progressive decline. Further symptoms of growing fatigue are seen in the periodic alternations of amplitude, and in the final reversal of response to one of expansion. I shall later give another record in which the normal negative response is seen reversed to positive through an intermediate diphasic. 102 COMPARATIVE ELECTRO-PHYSIOLOGY The fact that the normal response of living tissues may be reversed under fatigue, I am here able to show by an experiment of an unexpected character. It is usually supposed that fatigue is typical of such tissues as muscle, and absent from nerve. But I shall show with regard to all the various types of response, that there is none of these which is distinctive of any one tissue. The difference is one of degree and not of kind. The same intensity and duration of stimulus which is efficient to cause fatigue in muscle will not be enough to do so in the case of nerve. But even nerve will display fatigue when ex- cessively stimulated. In the record given in fig. 73, a particular nerve of frog had been previously fatigued, by over- stimulation, and on now taking individual responses to individual stimuli, it was found that they had become reversed to positive. Thus a particular type of response is the result of a particular condition of the responding substance, and there is none which is exclusively characteristic . ' of any one tissue. Were it otherwise, Fic. 73. Reversed Re- ordinary muscle, in which the explosive sponse of Fatigued ; Neve molecular change is supposed to be so predominant, should typically show only the fatigue, and never the staircase effect. But the following record (fig. 74) shows that this is not the case. For at first it exhibits a characteristic staircase effect ; the responses are then for a time uniform; and lastly, we see fatigue, in a manner exactly corresponding to the theoretical considera- tions which we have anticipated in stages B,C, and D. The staircase response is thus not peculiar to cardiac muscle, but is to be seen, under appropriate conditions, in skeletal muscle, in nerve, and even in inorganic substances. In fig. 75 is given a series of responses of Galena to Hertzian VARIOUS TYPES OF RESPONSE 103 radiation, which in its various phases of staircase, uniform and fatigue-decline, is parallel to that just seen in muscle. The phasic change, due to molecular transformation, which I have already pointed out under continuous stimulation, is seen in both these records in the shifting of the base-line. In fig. 64. under continuous stimulation, we see the mechanical response of muscle passing from a condition of growing contraction into one ofrelaxation. In the record of individual responses given in fig. 74, the same is seen to take place: A similar phenomenon is ob- served in the mechanical re- sponse of Mimosa (fig. 65). When the mode of record, however, is electro-motive, in- Fic. 75. Preliminary Staircase, In- crease, followed by Fatigue, in the Fic. 74. Preliminary Staircase, Response of Galena to Hertzian followed by Fatigue, in the Radiation Responses of Muscle (Brodie) (Resistivity variation method) stead of mechanical, the increasing galvanometric negativity which corresponds to increasing contraction, is found gradually to give place to positivity (fig. 64 4). | And finally, when the mode of record is by resistivity-variation, we find, by the shifting of the-base line in fig. 75, that the residual negative variation of resistance at first waxes and then wanes. Instances have been given, in which a portion of the in- cident stimulus has been seen to be held latent to do internal work. And from this it is clear that the current assumption that response must always be larger than stimulus is quite un- 104 COMPARATIVE ELECTRO-PHYSIOLOGY tenable. There are cases, again, in which a large portion of the incident stimulus is held latent for a time, to find subsequent manifestation externally. This I have been able to demon- strate by the discovery of multiple response in plants. Thus while a single moderate stimulus in such cases evokes a single response, a single strong stimulus is found to give repeated or multiple responses. This I have shown, not only in mechanical, but also in electrical response, and the latter subject will be taken up in detail in a subsequent chapter. And, lastly, it follows from what has been. said, that incident stimulus need not always cause depreciation of the energy of the tissue, but that, on the contrary, it may actually raise it above par. I shall now describe an example in which incident -Fic. 76.- Photographic Record of . ' Responses of Style of Datura alba stimulus was seen to find in which Growth had come toa bifurcated expression. In Temporary Stop f 63 : h The up curve shows contraction. As 8 ps fey ees ee rien long as the base-line is horizontal, graphic record of contractile growth is seen to be at standstill. ; ; ‘ ty] £ Renewal of growth at sixth re- responses in the style o sponse, after which growth-elon- Datura alba, in which growth gation is shown by the trend of : 5 the base-line downwards. had previously been in a state of standstill. The first five responses of this series are seen to be uniform. A portion of the stimulus applied must, however, from the first have been absorbed and held latent in the organ, thus increasing that internal energy, or tonic condition, on which growth depends. For at the sixth response we find that growth recommences, and the stimulus now finds bifurcated expression, in maintaining response and in renewing growth, as seen in the trend downwards of the oe ty ee ee ee ‘a di tale _ VARIOUS TYPES OF RESPONSE TO5 hitherto horizontal base-line. This bifurcation causes the first contractile response of the now growing organ—sixth of the series—to be smaller than usual. But, as a favourable tonic condition is gradually established by the absorption of energy and the molecular mobility of the responding organ is increased, the contractile response becomes larger, and growth goes on at a certain steady rate. This constitutes an instance in which stimulus, so far from lowering the energy of the responding system, has actually raised it above par. It would thus appear that while the theory of assimilation and dissimilation is insufficient for the explanation of the various characteristics of response, the difficulties there en- countered are, on the contrary, satisfactorily explained, on taking full account of the influence on response of the molecular condition of the responding substance. From the chemical hypothesis of an explosive molecular change, with its attendant dissimilation and run-down of energy, it would follow that previous stimulation should always induce a depression of the subsequent responses. Instead of this, however, it is found that previous stimulation sometimes exalts, and at other times depresses, the subsequent re- sponses. This apparent anomaly we have seen to be ex- plained by the consideration of molecular transformation. From the sluggish condition A, we have seen tissues trans- formed, by the impact of moderate stimulus, to condition B, with its greater excitability. It is only when the molecular condition has been brought to D or E, that the responses undergo a diminution or reversal. The molecular condition, then, undergoes a continuous transformation, in consequence of the action of stimulus, from the extreme of sub-tonicity A to the overstrained molecular conditions D and E. In the A stage, there is no true ex- citatory expression, response to stimulus being here by the abnormal positive variation. The substance is next trans- formed into stage B, where response exhibits a staircase character. In the next stage C, the responses are uniform. 106 COMPARATIVE ELECTRO-PHYSIOLOGY Under over-stimulation, the stages D and E are reached, characterised by diminished amplitude of response, or actual reversal into positive. There are thus two conditions under which we obtain abnormal positive responses. One of these is that of sub-tonicity, and the other, the reversal due to fatigue. There is, again, no tissue which is exclusively characterised by any specific type of response. All these—staircase, uniform, and fatigue—will occur in muscle, nerve, plant, and even inorganic matter, under certain definite and ap- propriate conditions. In a future chapter, we shall study in detail the characteristic molecular curve, from which light will be thrown on the internal molecular condition of the tissue, and the influence of that condition on response. Ne fi teat tn Oo el os CHAPTER IX DETECTION OF PHYSIOLOGICAL ANISOTROPY BY ELECTRIC RESPONSE Anomalies in mechanical and electrical response—Resultant response determined by differential excitability—Responsive current from the more to the less excitable—Laws of response in anisotropic organ—Demonstration by means of mechanical stimulation—Vibrational stimulus—Stimulation by pressure— Quantitative stimulation by thermal shocks. IT has been customary, as we know, to ascribe the varied movements of plant-organs under external stimulus, to the presence of different specific sensibilities ; and, indeed, it would seem at first sight impossible to reduce such highly complex and apparently unrelated phenomena, to the terms of a single fundamental reaction, common to all alike. There is no denying, for instance, that certain plant-organs, when acted on by light, bend towards it, and others away. I have elsewhere shown,' however, that all these diverse movements are clearly traceable to one fundamental excitatory reaction, and that the different effects observed are due merely to the differential excitabilities of various parts of the structure ; and that the resultant movement is in all cases brought about by the greater contraction of the more excited side. Passing next to the electrical response of living tissues, animal and vegetable, we encounter many anomalies. Not only will one tissue give positive, and another negative response, but we find also that the same tissue will give sometimes one and sometimes the other. ‘These apparent inconsistencies are often due, as we shall find, to the dfferentzal excitability of anisotropic structures—a factor in the problem which has not hitherto been recognised. An investigation on 1 Bose, Plant Response. 108 COMPARATIVE ELECTRO-PHYSIOLOGY this subject, then, demands that we first discover some means of determining the relative excitabilities of different parts of a tissue. As the simplest example of an anisotropic structure, we may take a compound strip of ebonite and stretched india- rubber, glued firmly together throughout their length. Of these, the india-rubber is the more contractile, and when the strip as a whole is subjected to periodic thermal stimulation, response takes place by the greater contraction induced in > the india-rubber. Ifthe strip be held, with the india-rubber below, response will be by the induced concavity of the lower side. -In fig. 77 is shown a series of these responses of the compound strip, taken on a smoked surface by means of a recording lever. In anisotropic motile organs, such as the pulvinus of J/zmosa, response takes place by differential contraction, the more excitable side being that which under diffuse stimulation becomes concave. If we apply very moderate stimulus AG 21. DiRerenge locally on the upper half of the pulvinus, sponse of Artificial we shall find that, by the excitatory con- sh traction of this half, the leaf is raised. A. similar contractile effect, though of greater intensity, is induced when the lower half of the pulvinus is stimulated locally, the leaf in this case undergoing a depression. When both upper and lower halves, then, are excited simultaneously, the resulting fall of the leaf shows that the contraction of the lower half must in this case be the greater, or, in other words, that this half is the more excitable of the two. This experi- ment may be carried out very easily by using the stimulus of light. Fig. 78 gives the results observed (a), showing the up movement consequent on stimulation of the upper half; (¢) that caused by equal stimulation of the lower half; and (c) the resultant fail when the two are excited simultaneously. In the case of mechanical response, then, we find it true that response is by the greater contraction of the more excitable. DETECTION OF PHYSIOLOGICAL ANISOTROPY fore We shall next observe what is the electrical mode of response for.a tissue which is anisotropic, or unequally ex- citable on two sides. For this purpose we may again take the pulvinus of A/zmosa, and make electrical connections at two diametrically opposite points on the upper and lower halves of the pulvinus respectively. It is to be remembered that electrical response takes place on excitation, whether the leaf be free to move, or physically restrained. We may, therefore, hold it in a fixed position; and indeed this is advisable, in order to avoid that shifting of the electrical contacts which might possibly take place if it were allowed to fall. The two contacts are made with two fine straws filled with kaolin paste, moistened in normal saline. On now applying a series of thermal stimuli, on the petiole, near the pulvinus, I obtained the responses given in fig. Fic. 78. Responses of AZ/mosa to Sunlight of ; not too long Duration 79. It will be seen : (a) Light acting on pulvinus from above ; (64) light that the responsive acting on pulvinus from below ; (c) light acting current flows in the simultaneously from above and below. Dotted 3 line represents recovery on cessation of light. tissue from the rela- tively more excited lower, to the less excited upper, half of the organ. We thus arrive at a comprehensive law of the mechanical and electrical response of anisotropic organs: Diffuse stimulation induces greater contraction and galvanometric negativity of the more excitable side. The laws of electric response in the anisotropic organ may then be detailed ‘as follows :— 1. On simultaneous excitation of two points, A and B, the responsive current flows in the tissue from the more to the less excited. IIo COMPARATIVE ELECTRO-PHYSIOLOGY 2. Conversely, if under simultaneous excitation the responsive current be from B to A, then B is the more excitable of these two points. These form only an instance of the general law that the responsive current always flows from the more to the less excited. For when a point, B, is excited locally—-this point, that is to say, being the more excited—the responsive current is found to flow away from it to a neutral or in- different point, A, for which any distant point will serve, provided the tissue be non-conducting. Should it be con- ducting, the neutrality of A is maintained by interposing a Fic. 79. Transverse Response of Pulvinus of AZimosa The petiole is securely held to prevent movement, and diametric electric contacts made in the upper and lower surfaces of pulvinus. Re- sponsive current is from lower to upper surface. block. Should the stimulus, however, not be local, but diffuse, a resultant response may still be obtained by injuring or killing the point A, and thus diminishing or abolishing its excitability. On stimulation, the point B is now necessarily the more excited, and the responsive current is still away from B, towards A. And finally, owing to physiological anisotropy, B may be naturally more excitable than A, and 6n stimulation the responsive current will then be found to flow from the more excited B to the less excited A. The comparison of the excitabilities of the two points A and B, therefore, reduces itself to the application of similar DETECTION OF PHYSIOLOGICAL ANISOTROPY III stimuli to the two points simultaneously, and then ascertaining the direction of the responsive current. For this purpose we might employ any form of stimulus, and it is extremely interesting to find that, however diverse the. stimuli, the results obtained by them are always identical And here we have not merely a means of qualitative demonstration, but in some cases one of quanti- tative also. i If we take an erect stem of Cucurbita, it being radial and isotropic, all its flanks will be found equally excitable. Hence, if two diametrically opposite contacts are made, there Fic. 80. Diametric Method of Stimulation of an Anisotropic Organ Diametrically opposite contacts are made at A and B, and tissue subjected to vibrational stimulus. will, on diffuse stimulation, be no resultant response. But when such a stem becomes recumbent, the upper side, being now constantly exposed to light, becomes fatigued by over- stimulation, with consequent diminution of its excitability. This is true only when the stimulus has been excessive and long continued ; for we have seen moderate stimulus may sometimes enhance the excitability. By the unilateral action of light, then, the organ has been converted from radial into anisotropic, the lower side being that which we shall expect to find the more excitable. On mounting such a stem in the vibratory apparatus (fig. 80), and making diametrically opposite contacts on the two anisotropic surfaces, we find that on applying vibration 112 COMPARATIVE ELECTRO-PHYSIOLOGY both sides are subjected to similar stimulus simultaneously ; and the responsive current is now found to flow across the tissue, from the lower to the upper side. The lower is thus, as we expected, the more excitable. Since we can by means of vibration apply measured stimuli, it will be seen that we have here a quantitative method of investigation. Moreover, as the stimulus is applied directly, it is applicable not only to conducting but also to non-conducting tissues. If we next take a radial stem or petiole of Cucurbita, and slit it longitudinally, we obtain, in either of the halves, a specimen having an inner and an outer surface. As one of these has been exposed to light and the other protected from it, we should expect to find, on examination, that there has been an induction of physiological anisotropy. As such a specimen is not very well adapted for vibrational stimula- tion, we may use that of pressure. Two moistened rags, in _ connection with non-polarisable electrodes, pass through two pieces of cork, adjusted on the two surfaces—outer and inner—at diametrically opposite points. When the inter- posed tissue is now subjected to sudden pressure its two surfaces are excited simultaneously, and the responsive - current is found to flow from the inner concave to the outer convex surface, proving that the former was the more excitable. | We might again use the chemical form of stimulation, and the results obtained by this method will be described in the course of the next chapter. But these forms of stimulus —by pressure, or by chemical means—are not capable of exact measurement. For quantitative observations, then, it is necessary to employ some other form of stimulus, and the electrical offers us in this respect many advantages. There are, however, in this case many possible disturbing influences to be considered, all of which must be carefully eliminated before the method can be used without misgiving. How this may be done will be shown in a future chapter. For the present I shall describe another method of stimulation which I have been able to bring to great perfection, by which ee DETECTION OF PHYSIOLOGICAL ANISOTROPY 113 two points of an anisotropic organ may be simultaneously excited, under a series of stimuli of uniform or increasing intensity. This mode of excitation, by thermal shocks, will be found in every way satisfactory and convenient. The Thermal Variator, by which stimulation is effected, consists of a spiral of german-silver wire, the diameter of the spiral being about 3 cm. The electrical circuit, through which the heating- current is sent, is closed periodically for a definite length of Fic. 81. The Thermal Variator The anisotropic tissue-petiole of J/wsa is held in ebonite clip, c. 8, &’, electrodes connected with opposite sides. Specimen after adjustment pushed inside heating-spiral, T, by slide, s. Spiral heated periodically by closure of electric circuit by metronome, M. time, by means of a metronome (fig. 81). The thermal variation within the coil can be controlled by a suitable adjustment of the battery-power, or by the duration of closure, or both. The experimental tissue is held in an ebonite clip, C, fixed on a slide, S, on the same stand as the heating-spiral. This slide is pulled out for the purpose of adjustment. Square or circular pieces of wetted muslin make contacts with equal areas on two opposite sides of the experimental tissue, these pieces of cloth being connected with non-polarisable electrodes, E and E’ After the adjust- y IIl4 COMPARATIVE ELECTRO-PHYSIOLOGY ment is made, the slide is pushed in, till the tissue is well in the centre of the coil. When the circuit is completed, for a brief period, both the sides A and B are subjected to the same sudden variation of temperature, which, as we know, acts as a stimulus. As the two contacts are thus in practice raised to the same temperature, there will be no thermo-electrical disturbance. The responsive current, therefore, will be determined by any difference of excitability which may exist as between A and B. The spiral also gives out heat-radia- tion, which acts as a contributory stimulus. That it is the thermal variation, and not the temperature, which acts as the efficient external stimulus, is seen from the fact that when the tissue is subjected to the higher temperature con- tinuously, the galvanometric deflection obtained is opposite in direction to that induced by the thermal shock. This is because the absorption of heat, as such, increases the internal energy, and thus induces an electrical effect opposite to that caused by external stimulation. As experimental tissue, we may use the sheathing petiole of Musa. The required piece is cut and mounted in the apparatus, the concave surface being taken, say, as B, and the convex as A. I have mentioned J/usa as suitable for this purpose, because I find it, when fresh, to show practically no sign of fatigue in its responses. There are many other sheathing petioles, which would doubtless answer the same purpose more or less perfectly. | In obtaining records with this specimen, it is found that the responsive current flows across the petiole, from the inner concave surface B to the outer convex surface A, showing that it is the inside which is more excitable. Uniform stimuli of short duration were applied at intervals of one minute, and the responses obtained are seen to be fairly uniform (fig. 82). The specimen was next subjected to the anesthetic action of chloroform. This, it will be seen, in- duced a very great depression of the response. It has thus been shown that just as the greater contrac- tion and concayity of a motile organ enables us to discrimi- DETECTION OF PHYSIOLOGICAL ANISOTROPY I15 nate which side of two is the more excitable, so here also the more excitable side is that which, on diffuse stimulation, exhibits galvanometric negativity relatively to the other. From this it becomes possible to determine the relative excitabilities of any anisotropic organ, even though it be non-motile, and therefore incapable of exhibiting any con- spicuous mechanical response. The difficulty of applying equal and quantitative stimulus on two sides simultaneously Fic. 82. Responsive Current in Petiole of Musa from Concave to Convex Side First series, normal ; after application of chloroform subsequent depression. has now been overcome by vibrational stimulation, and by the perfection of the method of thermal shocks. Thus a definite resultant response has been shown to be determined by the differential excitabilities of two parts of an experi- mental tissue. And that from this consideration it becomes further possible to resolve many of the remaining anomalies of electrical response will be fully demonstrated in a sub- sequent chapter. CHAPTER X THE NATURAL CURRENT AND ITS VARIATIONS Natural current in anisotropic organ from the less to the more excitable—External stimulus induces responsive current in opposite direction—Increase of internal energy induces ‘positive, and decrease negative, variation of natural current— Effect on natural current of variation of temperature—Effect of sudden variation—Variation of natural current by chemical agents, referred to physiological reaction—Agents which render tissue excitable, induce the positive, and those which cause excitation, the negative variation—Action of hydrochloric acid—Action of Na,CO,—Effect modified by strength of dose— Effect of CO, and of alcohol vapour—Natural current and its variations— Extreme unreliability of negative variation so-called as test of excitatory reaction— Reversal of natural current by excessive cold or by stimulation — Reversal of normal response under sub-tonicity or fatigue. WE have seen that when the pulvinus of A/zmosa is excited by an external stimulus, there is a relatively greater expulsion of water from the more excitable lower half, with a con- comitant greater contraction. Conversely, the lower half of the pulvinus is capable of absorbing more water, and of expanding to a greater extent, than the upper. Increased internal energy, in contrast to the action of external stimulus, has the effect of causing a greater expansion of the lower half of the pulvinus, and thus raising the leaf. This we saw exemplified when the plant was subjected to a gradually rising temperature, so as to increase its internal energy, its leaves being thereby made to show increased erection (p. 72), Hence the more excitable tissue in the pulvinus of Wzmosa is characterised, both by greater power of absorption and by greater emission of energy, according to circumstances. In this we see a close analogy to the action of inorganic bodies, in which also we find the greatest power of emission to be associated with a correspondingly great power of absorption of energy. THE NATURAL CURRENT AND ITS VARIATIONS I17 We have thus seen that in order to maintain a high state of excitability, absorption of energy is necessary. On excitation, emission of energy occurs. In this latter case, of emission, we observe a concomitant galvanometric negativity of the more excited lower side. Since to have maintained its excitability the opposite process of absorption would have been necessary, it follows that the more excztable lower side must under normal conditions be galvanometrically positive. This is found to be the case. For when the leaf is in an excitable condition, there is an electro-motive difference between the upper and lower halves of the pulvinus, in con- sequence of which a current flows across the tissue, from the less excitable upper to the more excitable lower half, which is thus galvanometrically positive, in relation to the upper. We have here, then, an additional instance of the opposite effects of internal energy and external stimulus. Internal energy, maintaining a greater excitability of the lower half of the pulvinus, induces in it a relative galvanometric positivity. External stimulus, on the other hand, gives rise to precisely the opposite effect—namely, the relative galvanometric negativity of the lower half. Under typical conditions, then, we may expect the more excitable point to be galvano- metrically positive; and the more excited to be galvano- metrically negative. Turning next to non-motile tissues, we find the same conclusions to hold. good. We saw that in the case of the sheathing petiole of M/usa, the concave was more excitable than the convex side. The concave is thus normally positive to the convex side, and the natural current flows across the tissue from the convex to the concave. While the natural current flows from the more excitable to the less excitable, external stimulus gives rise to a responsive current in the opposite direction, from the more excited to the less excited, constituting a negative variation of the current of rest. . Let us next consider what would be the effect of an increase of internal energy on the natural current. Since the action of internal energy is opposite to that of external stimulus, we should expect it to induce a positive variation of 118 COMPARATIVE ELECTRO-PHYSIOLOGY the natural current. Diminution of internal energy on the other hand might be expected to cause a negative variation. These effects are diagrammatically represented in fig. 83, which also exhibits the parallelism between the electric responses of motile pulvinus and non-motile anisotropic organ. : We next proceed to subject the question of the effect of increased or diminished internal energy on the natural current to experimental verification. As regards the increase ~ of internal energy, we have already seen that this can be secured by a gradually id Than rising _ temperature, its ¥ diminution being, con- eas 2G, trariwise, secured by a 2 falling temperature. In the case of Mzmosa, we Fic. 83. Parallelism of Natural Current . in Pulvinus of Mimosa and Sheathing 54W that the former in- Petiole of Musa duced an erection of the Upper and less excitable surface of former Jeayes and the latter a corresponds with outer or convex sur- ‘ face of latter. The natural current, N, gradual depression. In is in both from the less to the more ex- citable. In both excitatory current, E, order, then, to observe the is in opposite direction, z.e. from the effect of increase or de- more to the less excitable. In Musa ae increase of internal energy (+ }) in- Crease O internal energy duces a positive; and diminution of on the existing current of internal energy (— *) a negative, varia- tion of the natural current. rest, we have only to sub- ject the specimen to gradual thermal ascent or descent, and record the consequent variation of current. The specimen of Zusa is placed in a chamber and two diametrically opposite contacts are made, with the internal and external surfaces, and led off to the galvanometer. To take first the effect of cooling: a stream of ice-cold water is sent through a hollow tube in the chamber: this gradually lowers the temperature, say from 30° C. to 27° C. It will be seen from left-hand curve of fig. 84 that this has the effect of diminishing the natural current of rest in the tissue, as represented by the dotted arrow |}. When the chamber is THE NATURAL CURRENT AND ITS VARIATIONS I1I9Q allowed to’ return to the temperature of the room, this diminution of current is annulled. To study the effect, on the other hand, of a rising tempera- ture, the chamber is gradually heated, by means of the electric heating-coil already described. In thus raising the temperature, it is found (fig. 84, right-hand curve) that the natural resting-current undergoes an increase. On cooling again to the original = temperature, this in- crease is annulled. That these effects are due to induced elec- tro-motive variations, and not to any changes of resistance, is demonstrated from the fact that the effect described takes place even when the original E. M. F. is exactly balanced by a poten- tiometer. Fic. 84. Effect ot Variation of Temperature It ‘all on Natural Current, {, which in Petiole of was specially Musa flows from Convex to Concave Side stated that these ob- Effect of cooling from 30° C. to 27° C., seen servations with regard on left, induces negative variation of natural current. Restoration to original value on tothe effect of varying return to surrounding temperature. Warm- t | ing induces positive variation (see record to emperatures apply right). In this and subsequent figures in only to steady varia- the present chapter { indicates the direction of the natural current of rest. tions. In the case of thermal ascent, we have seen that a steady rise brings about an increase of the existing current. But since sudden variation of tempera- ture acts as a stimulus, we shall, in the preliminary stage, obtain an excitatory reaction, which will cause a transient diminution of the current of rest. This will be followed, when the rise of temperature is steady, by am increase of the current of rest. I give here (fig. 85) a photographic 120 COMPARATIVE ELECTRO-PHYSIOLOGY record of these contrasted effects. In the first part of the curve we observe a sudden movement of the record upwards corresponding to the sudden rise of temperature. This is so great as to carry the curve out of the photographic field. We have here, then, a sudden excitatory diminution of the natural current. In the next stage, while the temperature is steadily ascending, we find a reversal of the curve, and the natural current is enhanced above. the normal. On now allowing the chamber to cool down to the original temperature of the room, the natural current was found to return more or less to its normal value. We shall next study the effect of chemical agents on the natural current. The mode of procedure is to apply the given agent on both the contacts at the same time. If Fic. 85. Photographic Record showing effect of Sudden, followed by steady Rise of Tem- perature on Natural Cur- rent, ¥, in A/usa the substance be liquid, it can be applied by a pipette. If it be gaseous, the specimen is placed in a chamber through which the gas or vapour is allowed to stream. ' During sudden variation of temperature an excitatory negative variation of natural current: takes place, as shown by first up curve; when rise of - temperature becomes steady there is a positive variation, as shown by the down curve ; on re- turn to surrounding tem- perature, the normal cur- rent is restored to its original value. In observing the effects of various agents we obtain results which are at first sight very perplexing. For example, certain substances will be found to induce a diminution of the natural current, and others an increase. The effect, moreover, is found to be modi- fied by the strength of the dose. Thus an agent which, in a given strength, will cause a diminution of the natural current, may often be found to cause an increase, when sufficiently diluted. This inquiry is of great importance, since it is directly connected with many equally obscure problems in medical practice, where the effect of a drug THE NATURAL CURRENT AND ITS VARIATIONS I12I is well known to be modified by the amount of the dose. Much light appears to be thrown on this subject, when we consider the electrical reactions of the chemical agents as due to their physiological action. If a drop of hydrochloric acid be applied to the pulvinus of J7/zmosa, the leaf falls, showing that the more excitable side has undergone a greater excitatory contraction. We have also seen that when a drop of this acid is applied on any tissue in the neighbourhood of, but not directly touching, an electrical contact, it induces an excitatory galvanometric negativity. If now we apply it in solution, say, of 10 per cent. on the two diametrically opposite contacts of J/usa, we shall expect that the greater excitatory reaction induced on the concave side will give rise on that side to a relative galvanometric negativity, resulting in a negative variation of current of rest. On the application of the reagent this is found to be the case, the responsive current flowing in a direction opposite to that of rest: that is to say, it flows from the more excited concave to the less excited convex. It is by considering chemical agents from the point of view of their physiological reaction, that we are able to explain their diversity of effects, according to the strength of the dose and the duration of application. We have seen that while a strong stimulus induces the excitatory effect of negativity, a feeble stimulus will bring about the opposite, or positivity. This abnormal positive response, however, by the continued action of moderately feeble stimulus becomes converted into normal negative. Now a chemical substance which in a certain strength acts as an efficient excitatory agent, may, when sufficiently diluted, act as a feeble stimulus, inducing a positive response. If the same agent again were applied in a slightly greater concentration, its immediate. effect might be positive, to be succeeded under continued application by the normal negative. We might thus expect, using a strong salon of a given chemical reagent, to obtain a negative variation of the current 122 COMPARATIVE ELECTRO-PHYSIOLOGY of rest; using a dilute solution, to obtain a positive varia- tion ; and, lastly, applying a dose of intermediate strength, to discover the very interesting case in which the reagent would give rise immediately to a positive variation, and after a longer or shorter continuance of its action, to a reversed, or negative variation, of the current of rest. These inductions are found fully verified in the experiment which I am now about to describe. 1 | i ‘ ‘ Vv Fic. 86. Action of 7 per cent. Solution Fic. 87. Effect of CO, on of Na,CO, on Natural Current of M/zsa Natural Current of AZwsa Preliminary positive variation represented Preliminary positive seen to be’ by down curve followed by reversal, succeeded by negative variation 50 seconds after application. 5 minutes after application. ; Applying a strong solution of sodium carbonate —10 per cent. or above—at the electrical contacts on Musa, the result is a negative variation of the natural current. If nowa dilute solution of I per cent. be applied on a similar specimen, we obtain a response by positive variation. And if, lastly, we use a 7 per cent. solution, we obtain, as will be seen from the record (fig. 86) the preliminary positive, succeeded, under the continued action of the agent, by reversal to the negative, variation. We pass next to the question of the effect of gases. In fig. 87 is given a record of the action of carbonic acid on i MN i a THE NATURAL CURRENT AND ITS VARIATIONS 123 the natural current in /usa. It will be seen here that in the first stage there was an enhancement, or positive variation, of the existing current. In a later stage, however, this is followed by a reversal, the resting-current now undergoing a diminution. We have here an effect parallel to that of the intermediate dose of sodium carbonate. Vapour of alcohol also exerts an effect very similar ; that is to say, it induces a preliminary exaltation, followed by a depression of the natural current. In connection with this subject, of the changes induced in the natural electro-motive difference between the two surfaces, by the action of a chemical reagent, it is well to distinguish between the effects of two different factors: namely, the electrical variation caused by the chemical sub- stance as such, and that brought about by the excitatory reaction. Let us suppose both the electrical contacts to be made on iso-electrical surfaces, with normal saline solution; there will then be no difference of potential, as between the two. But this state of things will be disturbed, by the appli- cation of another chemical solution, say acid, on either one of the two contacts. The resulting disturbance may be dis- tinguished as due to heterogeneity of chemical application. But if the same chemical agent be applied at both the contacts, no such chemical heterogeneity will ensue. If, then, any electro-motive difference be induced, it must be due primarily to some induced physiological change. The contact which has been rendered more excitable will become increas- ingly positive ; that which is more excited, on the other. hand, will become increasingly negative. That the induced electro- motive variation under such circumstances is indicative ot a variation of excitability or excitation, was seen in the fact that the same chemical agent—for example, Na,CO,— caused a positive variation when dilute, a negative when strong, and positive followed by negative under the continued action of an intermediate dose. This conclusion—that the variation of the existing current, by the simultaneous application at the two contacts of the same chemical reagent, is due 124 COMPARATIVE ELECTRO-PHYSIOLOGY to a physiological reaction, the positive variation being a sign of relatively increased, and the negative of decreased, excitability—will be verified by an independent mode of in- quiry, to be described in the following chapter. | It follows from the experimental demonstration which has just been given that the phenomena of the natural current and its variations may be summarised in general as follows : 1. Under normal conditions, the current of rest flows in the tissue from the less to the more excitable. In other words, the more excitable is galvanometrically positive to the less excitable. 2. Increase of internal energy induces an increase or. positive variation of the existing current ; and diminution of internal energy induces a negative variation. 3. External stimulus induces a negative variation of the true or natural current of rest. The natural current and its variations under normal con- . ditions have now been studied. We shall next proceed to trace out those conditions under which abnormal results may occur. Excessive cooling, by diminishing internal energy, may thus reverse the normal current, which reversal may become more or less persistent. It has been shown, moreover, that in an anisotropic organ, external stimulus gives rise to a current opposite in direction to the natural current. . By this excita- tory reaction the more excitable side, hitherto positive, is rendered negative, and if the excitatory reaction be great, it may remain fora considerable period in this reversed condition of galvanometric negativity. We have seen that under normal conditions, the direction of the natural or true current of rest is from the less to the more excitable, and that external stimulus causes a responsive current in the opposite direction, which thus constitutes a negative variation of the current of rest. This state of things we shall distinguish as the primary condition. It frequently happens, however, in consequence of previous stimulation, with its after-effect, that extremely varied effects, appearing at first very anomalous, occur, with regard to the ‘Le ee THE NATURAL CURRENT AND ITS VARIATIONS 125 direction, not only of the current of rest, but also of the current of response. We shall be able. to obtain a clear understanding of these effects, on subjecting the underlying phenomena to close analysis. As a concrete example, we may take for our investigation the various effects to be observed in the pulvinus of Mzmosa. In this anisotropic organ, the directions of the resultant current of rest and the current of response are determined, as we have seen, by the differential excitability and differential excitation of the two sides of the organ. We shall fix our attention, however, for the sake of simplicity, on the changes which occur in the more effective lower half. I shall here succinctly describe the various post-primary phases in the changing effect, culminating in the onset of fatigue from over- stimulation. In the primary condition, as we have seen, the lower half of the pulvinus is positive to the upper, the direction of the resting-current being down ¥. On stimula- tion, the lower half becomes negative and. the response current is up t. Response thus takes place by a negative variation of the resting-current. We may now suppose the pulvinus to be in a state of slight excitation, its molecular condition at or about the B stage. This existing state of moderate excitation will annul the previous positivity, and the current of rest will now be zero. At this stage, however, as we have seen, the excit- ability of a tissue is enhanced. Hence, on stimulation, the lower half of the pulvinus will exhibit responsive negativity, and the direction of the response current will be up ft: We are, however, unable to describe this variation in terms of the current of rest, since that, as we have already seen, is zero. A condition of still stronger excitation, bringing the tissue to the C condition, will induce galvanometric negativity of the lower half. The so-called current of rest is thus upwards t. But as the excitability of the lower half is. still relatively greater than that of the upper, it follows that external stimulus will bring about a responsive current whose direction is upwards t, This normal excitatory response, 126 COMPARATIVE ELECTRO-PHYSIOLOGY then, in this particular case, appears as a positive variation of the resting-current. And, finally, we may imagine the pulvinus to have been strongly excited, so as to be in the condition Dor E. The resting-current will in this case be upwards ft. But the ex- citability of the lower half, owing to fatigue, has now become depressed, a condition which, as we have seen, tends to give rise to the abnormal positive response, the responsive current being thus downwards ¥. As the modified current of rest | is upwards, this abnormal current of response will appear as a negative variation of it. All these cases are conveniently tabulated as follows : TABULAR STATEMENT OF THE RELATIVE DIRECTIONS OF THE CURRENT OF REST AND THE RESPONSIVE CURRENT UNDER VARIOUS CONDITIONS. Current of rest. Current of re- | Variation of current of rest. ndition. Co sponse. Negative variation Primary condition , | Feebly excited Moderately excited Strongly excited and | fatigued . : * t fi. :, + Positive variation 1 Negative variation | > -o< The various conditions mentioned may be induced accidentally in the responding organ, or may be brought about by the excitatory effect of experimental prepara- tion. I give here the records of certain experiments performed on J/zmosa, in which some of these changes were seen to occur as the result of stimulation (fig. 88). The normal natural current is seen to be from above to below, as represented by the dotted arrow. The first strong stimulus, applied at the moment represented by the thick dot, gives rise to a responsive current whose direction is from below to above, Owing to the strong intensity of the stimulation, there is here a slight indication of multiple response. As an after-effect of stimulus, we observe that the normal resting- current has undergone a reversal, the lower surface, which was formerly positive, having now become relatively negative, A second stimulus now gave rise to a response — oe —— THE NATURAL CURRENT AND ITS VARIATIONS 127 similar to the first. But after this, owing to the greater fatigue with loss of excitability induced in the lower half of the pulvinus, the succeeding responses are seen to be reversed, the responsive current being henceforth from above to below. From the table given on the previous page, it will be seen that hardly could any standard have been devised for the study of excitatory reaction, so likely to be prolific of confusion as this, of the so called variation of the resting- current. For in the first three cases displayed, we see one identical excitatory effect, appearing now as a negative, again as doubtful, and a third time as a positive variation of the current of rest. In the fourth case, again, it is actually the abnormal response’ which appears as the normal nega- tive variation! But while these responses appear to be so various, the underlying Fic. 88. Variation of the Transverse Natural and Responsive Currents in Pulvinus of Wzmosa Natural current } which -is normally down, reversed in consequence of strong external stimulus. The first two responses are normal, z.¢. current being from below to above. Strong stimulus is here seen to induce mul- reaction is nevertheless con- stant. The direction of the responsive current is always from the more to the less tiple responses. After the second response on account of the greater fatigue induced in the lower half of the pulvinus, the direction of the responsive current is seen to be reversed. Thick dots represent excited. moment of application of stimulus. It has thus been shown | in the course of the present chapter that under normal conditions the current of rest flows in the tissue from the less to the more excitable; that increase of internal energy causes a positive variation of the current of rest , while its diminution gives rise to a negative variation ; that reagents which increase excitability induce a positive, and those which cause excitation a negative, variation of the resting-current ; and, finally, that external stimulus induces a negative variation of the resting-current. While these are 128 COMPARATIVE ELECTRO-PHYSIOLOGY the normal reactions, however, under abnormal conditions, they may be reversed. Thus, excessive cooling or strong external stimulation may reverse the normal current of rest. . There are, moreover, two different conditions, those, namely, of sub-tonicity (cf p. 106) and fatigue, which may be effective in bringing about a reversal of the normal direction of the responsive current. In this way, by means of induced varia- tions of the resting-current and of the responsive current, many very varied effects become possible. Al ett i od _— Te eee —o CHAPTER XI VARIATIONS OF EXCITABILITY UNDER CHEMICAL REAGENTS com : Induced variation of excitability studied by two methods: (1) direct (2) trans- mitted stimulation—Effect of chloroform—Effect of chloral— Effect of formalin —Advantage of the Method of Block over that of negative variation—Effect of KHO—Response unaffected by variation of resistance—Stimulating action of solution of sugar—Of sodium carbonate— Effect of doses—Effect of hydro- chloric acid— Di-phasic response on application of potash—Conversion of normal negative into abnormal positive response by abolition of true excitability. IT has been said in a previous chapter that the electrical response is a true physiological response. This is demon- strated by the fact that, while a vigorous specimen gives strong electrical response of galvanometric negativity, the same specimen, when killed, whether by heat or by poison, ceases to respond. This particular electrical response is thus seen to be a concomitant of physiological efficiency. It follows that, whatever diminishes physiological activity will, parz passu, modify the amplitude of the response. But in cases in which the death of the tissue is brought about by steam or by poison, it is the last stage only, namely the abolition of response, that can be observed. It is also impor- tant, however, to be able to trace the growth of physiological changes through the concomitant modification of response. In this way it is possible not only to study the gradual onset of death, as induced by a poison, but also the action of other chemical agents, some of which might be of such a nature as to induce exaltation, others depression, and still others, like the narcotics, a temporary abolition of the electrical response. K. 130 COMPARATIVE ELECTRO-PHYSIOLOGY An essential condition of this investigation is first to obtain a uniform series of responses. Having once done this, those subsequent changes in the response which are due to the appli- cation of a given reagent can be demonstrated in an unmis- takable manner. I have already explained in Chapter III. that this may be done by either of two different methods: namely, those of direct and of transmitted stimulation. Inthe first of these we employ vibrational stimulus, using the Method ql i Before 4 After Fic. 89. Photographic Record of Effect of Chloroform on Responses of Carrot Stimuli of 25° torsional vibration at intervals of one minute. of Block. In the second, the stimulus of thermal shocks is used, the excitation of the proximal contact being due to transmitted stimulation. We shall investigate the effect of chemical reagents by both these methods. And first I shall give results obtained by the employment of the Method of Block, the tissue being subject to direct stimulation. In cases where the effect of gaseous reagents, like chloroform, is to be studied, the vapour is blown into the plant-chamber (see fig. 21). In EXCITABILITY UNDER CHEMICAL REAGENTS 131 cases of liquid reagents, they are applied on the points of contact A and B, and in their close neighbourhood. The experiment is carried out by first obtaining a series of normal responses to uniform stimuli, applied at~ regular intervals of time, say one minute, the record being taken the while on a photographic plate. Then, without interrupting this procedure, the given agent—say, vapour of chloroform— is applied, by being blown into the chamber. It will be seen from fig. 84 how rapidly chloroform induces depression of response, and how the effect grows with time. If the speci- men be subjected for a short time only to the anesthetic, the depressing action proves transient, passing off on the reintroduction of fresh air. But too strong or too pro- longed an application induces a permanent abolition of response. I give below (figs. 90, 91), two sets of records, one of which shows the effect of chloral and the other formalin. : A A — \ ' \ \ A £ a Ne NAA Before + After Fic. 90. Photographic Record showing Action of Chloral Hydrate on the Responses of Leaf-stalk of Cauliflower Torsional vibration of 25° at intervals of one minute. These reagents were applied as solutions on the tissue at the two leading contacts and adjacent surfaces. Both are scen to induce a rapid decline of the response. In the K 2 I 32 COMPARATIVE ELECTRO-PHYSIOLOGY normal responses, shown in fig. QI, is seen a very interesting instance of alternating fatigue. In order to bring out clearly the main phenomena, I have postponed till now the consideration of a point of some difficulty. To determine the influence of a reagent in modifying the excitability of a tissue, we rely upon its effect in exalting or depressing the responsive E.M. Variation, and we read this effect by means of changes induced in the galvanometric deflection. Now as long as the resistance of the circuit remains constant, an increase or decrease of galvanometric deflection will accurately indicate a heightened or depressed E.M. Variation, due to augmented or lowered AAA Sy Me, a Before t After Fic. 91. Photographic Record showing Action of Formalin (Radish) excitability, induced by the reagent in the tissue. But by the introduction of the chemical reagent the resistance of the tissue may undergo a change, and, owing to this cause, modification of response, as read by the galvanometer, may be induced without any E.M. Variation; The observed variation of response may thus be partly owing to some unknown change of resistance, as well as to that of the E.M. Variation. This difficulty may, however, be obviated by interposing a very large and constant resistance in the external circuit. The variation in the tissue then becomes negligible, the galvanometric deflections being now proportional to the electro-motive variation, An actual experiment will make EXCITABILITY UNDER CHEMICAL REAGENTS 133 this point clear. Taking a carrot as a specimen, I found its resistance f/us the resistance of the non-polarisable electrodes to be 20,000 ohms. The application of a chemical reagent reduced this to 19,000 ohms. The resistance of the galva- nometer used was 1,000 ohms, and the high constant external resistance interposed was I million ohms. The variation of resistance induced in the circuit by the application of the reagent was thus 1,000 in 1,020,000, or less than one part in a thousand. : In studying the variation of excitability in animal tissues, the method of negative variation is employed. But I may here draw attention to the advantage which is afforded by the employment of the Method of Block instead. For, in the method of negative variation, one contact being injured, the chemical reagents act on injured and uninjured unequally. It thus happens that by this unequal action the resting difference of potential is indefinitely altered. But the intensity of response in this method of injury may to a certain extent be dependent on the resting difference. It is thus seen that, when this method is employed, a factor is introduced which may give rise to complications. According to the Block Method, however, the two contacts are made with uninjured surfaces, and the effect of the reagents on both is similar. Thus no advantage is given to either contact over the other. The changes now detected in the response are therefore due to no adventitious circum- stance, but to the reagent itself. If further proof be desired of the effect ascribed to the action of the reagent, we can now obtain it by the alternate stimulation of the two ends A and B. I give below (fig. 92) a record of responses obtained in this way from the petiole of turnip. This petiole was somewhat conical in form, and owing to this difference between the A and B ends, the responses given by one were slightly smaller than those given by the other, though the stimuli were equal in the two cases. A few drops of a 10 per cent. solution of NaOH were applied at both ends. The record shows how quickly this reagent abolished the 134 COMPARATIVE ELECTRO-PHYSIOLOGY response of both. In the next figure (fig. 93) is given a photo- graphic record, showing the marked depression of response induced by a strong solution of KOH, and in order to show that under the given experimental conditions, the variation of resistance does not in any way affect the responses, the deflection produced in the galvanometer by the application of an E.M.F. of ‘1 volt to the circuit is shown at the beginning and end of the record. The equality of these two deflections shows that the resistance in the circuit has remained practically the same throughout the experiment. Before t After Fic. 92. Abolition of Response at both A and B Ends by the Action of NaOH Stimuli of 30° vibration were applied at intervals of one minute to A and B alternately. Response was completely abolished twenty-four minutes after application of NaOH. Therefore, the change in the amplitude of the E. M. responses recorded may be taken as due entirely to the variation in the excitability of the tissue. In the experiments just described, the stimulus was applied directly at the responding point. By the application of a chemical reagent, not only was the responsive excitability of the tissue modified, but its receptivity, or power of receiving stimulus, also underwent a change. It will be shown later that the receptive excitability and the responsive excitability are not necessarily the same. The records which have just been given show what is, strictly speaking, the EXCITABILITY UNDER CHEMICAL REAGENTS — 135 effect of the reagent on both receptivity and responsivity jointly. If, however, we wish to study the effect of the reagent on responsive excitability alone, it will be necessary to separate the receptive from the responding point, and apply the reagent on the latter. This may be done by the method of trans- mitted stimulation described previously. Successive uniform Before + Afier Fic. 93. Photographic Record showing the nearly complete Abolition of Response by strong KOH The two vertical lines are galvanometer deflections due to ‘1 volt, before and after the application of reagent. It will be noticed that the total resistance remains unchanged. stimuli applied at a given point cause excitatory response at the separate responding point, the record of which is taken ; after this, the chemical reagent is applied locally at the responding point. It will be seen that the receptive excitability and the conductivity of the intervening tissue remain unaffected, changes being induced at the responding area alone. I shall now describe effects obtained by this method. I 36 COMPARATIVE ELECTRO-PHYSIOLOGY The specimen employed was the petiole offern. The thermal stimulator was at a distance of 1°5 cm. from the proximal electrode. In fig. 94 is shown the stimulating action of a Fic. 94. Photographic Record showing the Stimulatory Action of Solution of Sugar 2 per cent. solution of sugar, inducing a continuous enhance- ment of response for some time. Another stimulating agent is a dilute solution of Na,Co,. This when applied in 1 per cent. solution induces an Fic. 95. Photographic Record showing Continuous Action of 2 per cent. Na,CO, Solution Preliminary exaltation followed by depression. enhancement of amplitude of response, but when given in strong solution, induces depression. An intermediate strength of solution shows preliminary enhancement followed by de- pression (fig. 95). EXCITABILITY UNDER CHEMICAL REAGENTS 137 While pursuing another line of inquiry on the effect of various strengths of solution of Na,Co, on the natural current, I obtained results which were parallel (p. 122). It was there shown that dilute solution of Na,Co, induced a positive variation of the natural current ; a strong solution, a negative variation, and that a solution of intermediate strength induced a preliminary positive followed by a negative variation. Thus the positive variation in the last-named experiments, already shown to be indicative of increased excitability, was here seen to correspond with heightened amplitude of response, while the negative variation on the other hand is seen to coincide with depression of excitability. The application of a strong solution inducing excitation, carries the molecular condition of the tissue to the stage E, where, as we know, the excitability is depressed. Another fact elucidated by this and similar inquiries, which I have pursued elsewhere,' lies in the fact that the difference between stimulants and poisons, so called, is often one merely of degree. Thus a stimulatory reagent, if given in large quantities, will be found to induce a profound depression, whereas a poisonous reagent in minute quantities may be found to act as a stimulant. In carrying out a similar investigation with regard to growth response, | found that sugar, for instance, which is stimulating in solutions of, say, I to 5 per cent., becomes depressing when the solution is very strong. Copper sulphate again, which is regarded as a poison, is only so at 1 per cent. and upwards, a solution of ‘2 per cent. being actually a stimulant. The difference between sugar and copper sulphate is here seen to lie in the fact that in the latter case the range of safety is very narrow. Another fact, which must be borne in mind in this connec- tion, is that a substance like sugar is used by the plant for general metabolic processes, and thus removed from the sphere of action. Thus continuous absorption of sugar could not for a long time bring about sufficient accumulation to cause depression. With copper sulphate, however, the case 1 Bose, Plant Response, p. 488. i138 COMPARATIVE ELECTRO-PHYSIOLOGY is different. Here, the constant absorption of the minimal stimulatory dose would cause accumulation in the system, and thus ultimately bring about the death of the plant. Fic. 96. Photographic Record showing the Depressing Action of 5 per cent. HCl Acid The effect of very dilute acids is often to induce an enhancement of excitability, while strong solutions induce depression and abolition. In fig. 96 is shown the depression Fic. 97, Photographic Record showing Effect of I per cent. KHO Note the preliminary positive twitch at the fourth response after application. and abolition induced by the rene. of a 5 per cent. solution of hydrochloric acid. In dealing with the question of electrical response, we have seen that two opposed electrical effects occur in the EXCITABILITY UNDER CHEMICAL REAGENTS 139 tissue subjected to stimulation. One of these is the positive effect, and the other, the true excitatory change of galvano- metric negativity. As the latter is, under normal conditions, predominant, the simultaneous effect of both is a resultant negativity. The positive effect may, however, be unmasked, as we have seen, by abolishing the true excitatory effect of negativity (p. 66). This positivity may also be un- masked, if, by the action of a chemical reagent, the time- Fic. 98. Photographic Record of Effect of 5 per cent. KHO Note the complete reversal of response to positive at the beginning, and its subsequent abolition. relations of the two responses are changed, so that instead of occurring simultaneously, the one is made to lag behind the other. This case will be seen very strikingly illustrated in fig. 97, which exhibits the effect of a 1 per cent. solution of KHO, on response to transmitted stimulation in the petiole of fern. In the normal responses here given, we observe the resultant response of galvanometric negativity. The application of KHO is first seen to reduce the excit- ability, as indicated by the reduced height of the responses. Later, we observe that the true excitatory effect is delayed. 140 COMPARATIVE ELECT RO-PHYSIOLOGY Hence the positive effect is no longer completely masked. Its existence is now seen as a preliminary downward twitch in a di-phasic response, in the case of the fourth and succeeding records, after the application of KHO. In fig. 98, a stronger, namely a 5 per cent. solution of KOH, was used. And here, by the almost complete abolition of the excitatory factor, the response has undergone an apparent conversion to positive; this positive response is, however, subsequently abolished by the death of the plant. os Seer ae - CHAPTER XII VARIATIONS OF EXCITABILITY DETERMINED BY METHOD OF INTERFERENCE Arrangement for interference of excitatory waves—Effect of increasing difference of phase—Interference effects causing change from positive to negative, through intermediate di-phasic—Diametric balance—Effect of unilateral application of KHO—Effect of unilateral cooling. I HAVE explained how the variations of excitability brought about by various agencies may be determined, by recording the corresponding amplitudes of response, I shall now pro- ceed to describe a new and interesting method of making such determinations, by means of which it will be found possible to elucidate certain questions which without it must remain obscure. This method is, moreover, of extreme delicacy, enabling the investigator to detect the slightest variation of excitability, induced by any agent. Let two points in the experimental tissue, say A on the right, and B on the left, be suitably connected with the galva- nometer, and let the occurrence of excitation at A on the right be represented by an ‘up’ response record, the excita- tory effect at B, on the left, being represented as ‘down.’ If now the two points, A and B, be excited simultaneously, the resultant electrical response will be due to the algebraical summation of the two excitatory electro-motive effects E, and Ey, these standing for the individual electrical effects at the two points A and B, Now if the intensities of the two effects be the same, and if their time-relations be also the same, it is evident that these two excitatory electrical waves, being of equal amplitude and having the same ‘phase but of opposite signs, will, by their mutual interference, neutralise 142 COMPARATIVE ELECTRO-PHYSIOLOGY each other. Under such balanced conditions, therefore, on simultaneous excitation of A and B, the resultant response will be zero. If now, under the modifying action of any external agency, the excitability of A be enhanced, it is clear that the resultant response will be ‘up, showing the greater excitability of the right-hand point. A similar effect will also be produced if the excitability of B be depressed. | Similarly the depression of the excitability of A, or enhance- ment of B, would cause a resultant response which would be ‘down.’ If, again, the two waves of excitation be not of the same phase, we shall obtain various di-phasic effects resulting from the algebraical summation of the constituent response- curves. The resultant zero-response may thus be converted into di-phasic, by the action of any agency which is capable of changing the time-relations of either of the constituent responses. _ I shall now proceed to describe the experimental arrange- ments by which two points in connection with E and E’ may be excited, and the resulting electrical disturbances made to interfere with each other. For this purpose we may use the vibrational stimulation which has already been described, with certain necessary additions .(fig. 99). The angle of torsional vibration which regulates the intensity of excitation is determined by two stops, P and Q. An elastic piece of brass, B, projects from the torsion-head. When a single stroke is given to this, a quick to-and-fro vibration is induced, the backward pull being supplied by the attached spring, s. The amplitude of this vibration remains always the same, as determined beforehand by the setting of the stops P and Q. The stroke is given by the striking-rod R, set in motion by the turning of a handle. What has already been said about the excitation of the right-hand side of the specimen applies equally to the left-hand, arrangements for the purpose being a duplicate of those just described. After deciding on a suitable angle of torsional vibration for the right, and taking the response at that point, we proceed to adjust the torsional angle on the left, so that the response there may be exactly EXCITABILITY DETERMINED BY INTERFERENCE 143 the same as that on the right. If the excitability of the two points had been exactly the same, equal amplitudes of vibra- tion would have resulted in the equal stimulation of both. But in practice the excitabilities are found to be slightly different and the angle of vibration of the one must, therefore, be so adjusted as to induce an excitatory effect exactly equal to that of the other. The two striking-rods, one on the right, R, and the other on the left, R’, can be adjusted so that both are in the same E a a us rt ie B \ 4 P ee < = Nee” : Fic. 99. R, R’, striking-rods for stimulation of two ends of specimen ; B, elastic brass tongue projecting from torsion-head. For producing phase-difference R is adjustable in azimuth. . vertical plane, or so that one is in advance of the other. The left rod is permanently fixed to the rotating axis, but the right can be set at any angle that is desired, with the other. When the right striking-rod is set, pointing to zero of the scale, the two rods are in the same vertical plane, and the rotation of the handle causes equal vibrational stimulus by the two at the same moment. The excitatory reactions on right and left are now, therefore, of the same phase and of equal intensity, but opposed to each other. In fig. 100, a, are reproduced the two separate and equal constituent responses given by a specimen of stem of Amaranth. The 144 COMPARATIVE ELECTRO-PHYSIOLOGY ‘down’ curve was given by the individual excitation of the left, and the ‘up’ by the right. On the simultaneous excita- tion of the two points, the resultant response was zero (6). But if the excitation of one—say, the right—be increased by increasing the angle of vibration, the resultant differential response is found to be ‘up.’ It is obvious that’ a similar effect would have been observed had the stimulation of the right been kept the same, while its excitability was increased . by any external agent. In these cases we have two opposed excitatory waves of similar phase, and of the same or unequal intensities, interfering with each other. Fic. 100. (a) Isolated response of left side (down) and right side (up) ; (4) null-effect when excitations are simultaneous ; (c), (d@), (e) di-phasic responses obtained with increasing difference of phase. We shall next take some simple instances in which, while the stimulation is maintained constant, there is an increasing difference of phase. If the right-hand striking-rod R, instead of being set at zero, be set to the right, or at a p/us angle, the rotation of the handle will cause a slightly earlier excita- tion of the right than of the Jeft. If, on the other hand, the rod be set at a mznus angle, the excitation of the right will be later than that of the left. Under these circumstances, instead of the null-effect due to continuous balance, we shall have a di-phasic response. It is also clear that as the phase difference is increased, the neutralisation of -effects will become. less and less perfect, the separate constituent respon- ses being thus rendered increasingly apparent, In fig. 100, ¢, EXCITABILITY DETERMINED BY INTERFERENCE 145 is seen the di-phasic effect which was induced when the excitation of the right was made to lag slightly behind that of the left, by the adjustment of the striking-rod at a small mznus angle. The first of the two twitches, which is downwards, indicates the relatively earlier excitation of the left-hand contact. As the phase-difference was increased progressively as in (d) and (e), it is seen that the constituent elements of the di-phasic response are increased corre- spondingly. It is also clear from this that, having obtained the null-effect, if any agents were afterwards applied locally which would make the excitation of the one point earlier than that of the other, we must then expect the null-effect to be modified to di-phasic. An earlier ‘up’ twitch would now indicate that the right-hand contact, having had its re- action quickened, was the first to respond ; an earlier ‘down’? twitch the opposite. 3 We thus see how the conversion of the null-effect into a resultant ‘down’ negative or ‘up’ positive, could .be utilised as a test of the excitatory or depressing nature of a given reagent. We alsosee how the conversion of this null into a di-phasic effect would give us indications as to the change of time-relations induced by the reagent. I shall here, before going on to describe the results obtained with plants, give a photographic record (fig. 101) of certain positive, nega- tive, and di-phasic effects obtained in the electrical response of the inorganic substance, tin, under appropriate modification of the excitability of its two contacts by various chemical reagents.’ Turning now to the question of the determination of the effects of the various reagents by the Method of Interference, we may, as we have seen, cause simultaneous excitation of right and left, by means of the apparatus which has just been described, and which I shall distinguish as the Longitudinal Balance. There is, again, another and simple method of accomplishing the same object, by means, namely, of the Diametric Balance, the diagram of which has already 1 Bose, Response in the Living and Non-Living, p. 115. L 146 ' COMPARATIVE ELECTRO-PHYSIOLOGY been given in fig. 80. Using this arrangement, the specimen is clamped at one end, the vibration-head being at the other. Electrical connections are now made with the two dia- metrically opposite points, A and B, of which one, say A, is the upper, and B the lower. Ina tissue -which is isotropic, vibrational stimulus will induce equal and simultaneous excitation at the two points A and B. The effect of any given agency is tested by applying it locally, say at A, and observing the resultant variation of the response. I shall (a) (4) (c) Fic. 101. Photographic Record showing Negative, Di-phasic, and Positive Resultant Responses in Tin under appropriate modifications of excitation of the two contacts here give examples of results obtained by both these methods, thus affording an indication of the extent of their applicability in various investigations. , We have seen in the previous chapter that the application of strong solution of potash will abolish the excitability of a tissue. Using the Longitudinal Balance, I took a petiole of Bryophyllum and first made such adjustments that the right ‘up’ and left ‘down’ responses were almost equal. On now producing simultaneous excitation of the two ends, a di-phasic response was obtained, due to the fact that the left-hand point was the quicker to respond. Strong solution EXCITABILITY DETERMINED BY INTERFERENCE 147 of potash was next applied on the right-hand point, and from the record it is seen that the ‘up’ part of the di-phasic response, due to the excitation of the right-hand side, was thus completely abolished, the ‘down’ response being at the | same time increased. by the suppression of this opposing response (fig. 102). In order to demonstrate the use of the Diametric Balance Method, I undertook to investi- gate by its means the influence of the lowering of tempera- ture on excitability. For this Fic. 103. Photographic Record of Response of Petiole of Cauliflower Fic. 102. Photographic Records. by the Diametric Method (a) Di-phasic response of petiole A contact was naturally more excitable, of Bryophyllum, the up compo- hence resultant ‘up’-response. Ex- nent being due to the excitation citability of A being depressed by of right side. Strong application local application of ice, the re- of KHO on the right abolished sultant response became converted this responsive component, giving to ‘down’; normal ‘up’-response rise in (4) to enhanced down was restored on allowing the tissue response to return to surrounding temperature. purpose, I took a petiole of cauliflower. In this instance, the natural excitability of the upper contact, A, was greater than that of the lower, B. Hence the resultant response was not zero, but ‘up.’ The point A was now cooled locally by ice. This process so lowered its excitability that that of B was now relatively the greater, hence the resultant response was found to be reversed or ‘down. The point A was next L:2 148 COMPARATIVE ELECTRO-PHYSIOLOGY allowed to return to the surrounding temperature of the room, records of the response being taken meanwhile, at intervals of one minute. It will be seen how, by means of the gradual restoration of the original excitability of A, the resultant response changes gradually from negative to zero, and then again from zero back to positive, indicating the restoration of the naturally greater excitability of A (fig. 103). We have thus studied two different methods, both of which depend on interference, for the determination of the variations of excitability induced by different external agents. In a subsequent chapter we shall study a modification of this method, by means of which it is possible to demonstrate the variations not only of excitability but also of conductivity under various reagents. e CHAPTER XIII CURRENT OF INJURY AND NEGATIVE VARIATION Different theories of current of injury—Pre-existence theory of Du Bois- Reymond—Electrical distribution in a muscle-cylinder—Electro-molecular theory of Bernstein—Hermann’s Alteration Theory—Experiments demon- strating that so-called current of injury is a persistent after-effect of over- stimulation—Residual galvanometric negativity of strongly excited tissue— Distribution of electrical potential in vegetable tissue with one end sectioned—Electrical distribution in plant-cylinder similar to that in muscle- cylinder—True significance of response by negative variation—Apparent abnormalities in so-called current of injury—‘ Positive’ current of injury. IF a section be made of an uninjured nerve or muscle, the transverse contact will be found to be galvanometrically negative, as compared with an uninjured longitudinal contact. I shall have occasion in the present chapter to give a simple explanation of this phenomenon and of the excitatory nega- tive variation of the current of injury. It is, therefore, only necessary to recapitulate briefly the three theories which have hitherto been proposed on this subject. The Pre-extstence Theory of Du Bois-Reymond supposed that the smallest particle had the same electro-motive characteristics as the entire tissue, each such electro-motive molecule consisting of two bi-polar portions, the positive poles of any two molecules being always face to face with each other. This theory was based upon the fact that a muscle-cylinder, for example, exhibited a peculiar distribu- tion of electrical tension. There are in such a cylinder, one longitudinal and two transverse surfaces. Midway in the cylinder is the equatorial zone of the longitudinal surface, and this zone is positive to all the rest. Thus the electro- motive difference between one electrode placed on the I50 COMPARATIVE ELECTRO-PHYSIOLOGY equator, and the other, is increased as the latter is moved further and further away, say towards the right transverse section. The distribution of electrical tension on the left side of the equator is symmetrical with this (fig. 104). On these facts was based the theory of Du _ Bois- Reymond; but this has Fic. 104. Distribution of Electrical : me ‘nite hed Tension in Muscle-cylinder. since been found to be in- adequate. I skall later return to the explanation of the particular distribution of electrical tension involved. According to the theory of Bernstein, known as the Electro-chemical Molecular Theory, the fundamental attribute of the molecule is chemical. Its poles are supposed to attach to themselves electro-negative groups of atoms, while its sides attach oxygen, and stimulation is supposed to be attended by explosive chemical changes. According to Hermann’s A/teration Theory, finally, all the _ electro-motive activities of living tissues are supposed to be due to chemical rather than molecular changes of the substance. In amplification of this theory, Hering attributes all electro- motive phenomena to the disturbance of equilibrium by up and down chemical changes. It is my intention to show in the course of the present chapter that the current of injury is an after-effect of over-stimulation. And since excitation is fundamentally due to molecular upset, we shali best understand the electro-motive changes concomitant with it, if we first study it and its after-effect under the simplest conditions, namely those of inorganic substances. For here the action of such complicating factors as assimilation and dissimilation is clearly out of the question. We have found for example that a piece of well-annealed wire was iso-electric throughout its length. In the first CURRENT OF INJURY AND NEGATIVE VARIATION I5I place, when a portion of it was subjected to any molecular disturbance, an electro-motive difference was induced, as between the molecularly disturbed or excited and the un- disturbed areas. The intensity of this electro-motive change, in the second place, was seen to increase with intensity of excitation. And, thirdly, the recovery from excitation was seen to be delayed, where the intensity of stimulus was strong (fig. 105). This is shown in the electrical ° ° ° me) ° -o -° 5 Io Is 20 25 30 35 45 Fic. 105. Photographic Record showing Persistent Electrical After-Effect in Inorganic Substance under Strong Stimulation. Note the tilt of base-line upwards The vertical line to the right represents ‘1 volt. response of tin as a persistent after-effect, the sign of which is the same as that of the excitatory electro-motive change. A similar state of things is exhibited mechanically in a torsioned wire. When the torsion is moderate, and the molecular distortion slight, the released wire quickly re- covers its original position of equilibrium. But when the torsion is excessive and the wire strained beyond a certain limit, it remains for a long time in a torsioned condition, 152 COMPARATIVE ELECTRO-PHYSIOLOGY even after it has been set free. Recovery is thus, in such a case, indefinitely delayed. In other words, a molecularly over-strained substance exhibits a persistent after-effect. Turning next to plant response, we find a similar per- sistence of the after-effect to occur in consequence of over- stimulation. And first we shall take the simplest case— that in which the tissue is directly stimulated. Here the specimen was petiole of cauliflower, and increasing stimuli 24° eC 74° 10° 123° Fic. 106. Photographic Record exhibiting Persistent Galvanometric Negativity in Plant Tissue after Strong Stimulation Stimuli applied at intervals of three minutes. Vertical line = ‘1 volt. were applied, at intervals of three minutes, by means of a gradually increasing angle of torsional vibration. It will be noticed that whereas the electrical recovery from moderate stimulation—as seen in the first of the series—is complete, it becomes, with increasing stimulus, more and more in- complete (fig. 106). In other words, the tissue, after strong stimulation, is seen to exhibit an after-effect of residual galvanometric negativity, which is really due to incomplete molecular recovery, in consequence of over-strain. In the cases just given, stimulation was applied directly. CURRENT OF INJURY AND NEGATIVE VARIATION 153 We shall now, however, take an instance in which excitation is transmitted and observe the persistent negative after-effect, due to strong stimulation. We know that a cut (mechanical section) or the application of a hot wire (thermal section) acts as a strong stimulus, and the effective intensity of such stimulation will obviously decrease with increasing distance from the point of stimulation. Hence, if we observe the persistent excitatory change of galvanometric negativity, which is induced as between an indifferent point—say, the surface of a leaf—and points increasingly near to the zone of section, we shall find that the electro-motive change is greatest at the point of section, and is progressively lessened as we recede from it. This induction may be verified experimentally by taking readings of the persistent negativity, as between an indifferent point, B, and points such as the contacts a, 0, c, d, A (fig. 107), which are further and further removed from the point of section. For this purpose we may employ a capillary electrometer, whose indica- tions are independent of the varying resistance of the interposed tissue. The magnifying power of the observing microscope was so adjusted that ‘1 volt gave a reading of 100 divisions of the micrometer. In carrying out an experiment on the leaf of Colocasza I found the electrical distribution, as between an indifferent point on the lamina and points on the sectioned petiole, at increasing distances from the section, to be as shown in the following table : TABLE SHOWING ELECTRICAL DISTRIBUTION IN SPECIMEN OF Co/ocasia. [The sectioned end was negative. 100 divisions = ‘1 volt. | Tiintaie thom section E.M. difference between indifferent and given points *5 cm. 50 divisions I 99 40 ” 2 9 33 99 3 9° 29 99 4 99 27 cd It will thus be seen that points near the sectioned end are more negative than others further away. 154 COMPARATIVE ELECTRO-PHYSIOLOGY I shall next describe the more sensitive galvanometric method of investigation. The resistance is here maintained constant by having the permanent. contacts at A and the indifferent point B (fig. 107). The specimen is a stem of Calotropis gigantea. A thermal section is made at first, say, at a distance of 3 cm. from A. The persistent galvanometric negativity of A will now be due to the after-effect of stimula- tion by section. The thermal injury is now repeatcd at | LL of ih cai 5 3 2 15 3 Fic. 107. Experimental Arrange- Fic. 108. Records showing in- ment for determining Electrical creasing Persistent Galvano- Effect due to Section metric Negativity, according as injury is caused nearer to proximal contact A, z.e. moved from 3 to'5 cm, distance decreasing distances from A. I give a series of records (fig. 108), from which it will be seen that when the stimulus of thermal section occurs at some distance, there is no persistent after-effect, recovery being complete. But as the injury is made nearer and nearer A, the permanent after- effect becomes greater and greater. From observations made . in the course of a similar experiment, I obtained the following results, given in tabular form, which show the increasing value, with lessening distance, of this persistent galvano- metric negativity. eee CURRENT OF INJURY AND NEGATIVE VARIATION 155 TABLE SHOWING PERMANENT GALVANOMETRIC NEGATIVITY AT DIFFERENT DISTANCES FROM POINT OF INJURY, Distance from section Galvanometric negativity 25 cm. 220 divisions 5» 180; IO ,, 120 os | 5% FINS | 2°0 35, 49 ” | | 370 5, inst Sb | In fig. 109 we have a curve which illustrates these results, and explains why the maximum negativity is at the zone of section, diminishing rapidly as we recede from it. It is obvious that if these sections had been made to the right as Fic. 109. Curve showing the Electrical Distribution in Stem with one Sectioned End Ordinate represents galvanometric negativity ; abscissa, the distance from sectioned end. well as to the left of A, the result would have been a duplicate series of changes of galvanometric negativity in reference to A, on. that side also. Such a series is represented in fig. 110, by means of dotted lines. It will also be seen from this figure that the greatest electro-motive difference exists 156 COMPARATIVE ELECTRO-PHYSIOLOGY as between the equatorial point A and the two terminal sections a and a’; that symmetrical points cc’, 0 0’, a a’, are equipotential ; and that a point relatively nearer the terminal section is galvanometrically negative, in reference to one further away from it. It will also be seen that this electrical distribution is exactly the same as that seen in a muscle- cylinder, with terminal sections, as given in fig. 104. Thus, without the postulation of any electro-motive mole- cules so-called, these experimental results afford a simple and direct explanation of the so-called current of injury, as the excitatory after-effect of strong stimulation. Fic. 110. Electrical Distribution in Plant-cylinder with Opposite Ends Sectioned The Current of Injury is simply therefore an excitatory after-effect, due to incomplete recovery from over-strain. But even after strong stimulation a slow recovery may occur, and the Current of Injury will thus undergo a progressive diminution. This will probably account for Engelmann’s observation that in medullated nerves the E.M.F. of the artificial cross-section fell, by as much as from 25 to 60 per cent., in the first two hours after section, and disappeared altogether within twenty-four. The renewal of the cross- section he found to renew the original difference. This is an obvious case of renewal of the effect by re-stimulation. The disappearance of negativity, owing to recovery, only CURRENT OF INJURY AND NEGATIVE VARIATION 157 | takes place when the injury has not been excessive. If, however this has been too great, the injured tissue will then pass gradually into a condition of permanent death. But the electrical change concomitant with death is one of positivity, as I shall show in the next chapter. Thus the subsidence of the galvanometric negativity of an injured point may be brought about by either of two processes, which are exactly opposite—namely, recovery or death. Turning next to the subject of the Negative Variation of an existing current of rest, as a reliable index to the state of excitation, two different questions arise. First: why, in order to obtain response to diffuse stimulation, is it necessary previously to subject one of the contacts to injury? And secondly: why is the responsive action-current opposite in direction to the resting-current, thus constituting a negative variation of it? With reference to the first of these questions, we have already seen that when two points, A and B, are simul- taneously excited, the resultant electro-motive response is equal to E,—E,. If, then, the excitabilities of these two points are the same, it is clear that the resultant response will be zero. From this we can see that, in order to obtain a resultant response, we must depress or abolish the excita- bility of one of the two contacts. This inference may be verified by the employment of the Method of Block and of longitudinal balance. Two equal and opposite responses are first obtained at A and B. Then one end, say B, is injured by thermal section. The specimen being now replaced in the vibratory apparatus, it is found that, whereas the A half gives strong response, the end B gives none. Or the B end of the specimen may be injured by a few drops of strong potash, the other end remaining uninjured. The end A is then stimulated, and a strong response is obtained. The end B is next stimulated, and there is little or no response. The block between A and B is now removed, and the specimen stimulated throughout its length. Though the stimulus now acts on both contacts, 158 COMPARATIVE ELECTRO-PHYSIOLOGY yet, owing to the irresponsive condition of B, there is a resultant response, and the direction of this action-current is found to be from A to B. 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 injured, by the action of the same stimulus. ; When the point B is injured, there is generally speaking a more or less persistent current set up which flows from | Bto A. But we saw that the direction of the action-current was opposite—that is to say, from Ato B. This will explain the reason why the action-current causes a diminution or negative variation of the current of injury, so called. One method of doing this is to cause injury to one of the two points. If this be such as to kill the tissue, then its excitability is permanently abolished. Or by causing the excessive stimulation of injury, we may simply depress the excitability of the tissue for a longer or shorter time. I shall now give a few instances of response in plants by negative variation, Taking the petiole of turnip, we injure an area on its surface, say B. A current is now observed to flow in the petiole from the injured B to the uninjured A. The induced difference of potential depends on the condition of the plant, and the season. In the experiment here described, its value was ‘13 volt. A sharp mechanical tap was now given to the petiole, between A and B, and a sudden diminution, or negative variation, of current occurred, the resting potential difference being decreased by ‘026 volt. A second and stronger tap induced a second response, causing a greater diminution of potential difference by ‘047 volt. In another experiment, the specimen employed was a petiole of cauliflower (Brassica oleracea). ‘The first up-line to the right indicates the current of injury. The three re- sponses which succeed are induced by a given intensity of stimulus, the next series of six, being in response to stimulus nearly twice as strong, exhibit signs of fatigue (fig. 111). The current of injury generally undergoes a diminution with time. This is often, as has been explained, on account CURRENT OF INJURY AND NEGATIVE VARIATION 159 of slow recovery from the excessive stimulation of injury. Response by negative variation is then found to undergo a decline. It is in general vaguely accepted that, in order to obtain a response by negative variation an‘antecedent current of injury is necessary, by whose induced variation we may be able to record responsive effects. In cases of the dis- appearance of the current of injury, it is supposed that response must necessarily vanish, since its antecedent con- dition no longer exists. But I have already shown, and shall sayy Fic. 111. Record of Responses in Plant (Leaf-stalk of Cauliflower) by Method of Negative Variation The first three records are for stimulus intensity I ; the next six are for in- tensity twice as strong; the successive responses exhibit fatigue. The vertical line to the left represents ‘I volt. The record is to be read from right to left. have occasion again to show in the next chapter, that these suppositions are altogether erroneous. For we may obtain the usual response when the current of. injury is zero, or even positive. In fact, the only essential condition for the obtaining of resultant response is that at one contact the excitability should be in a state of relative depression. In that case in which response becomes enfeebled, with the gradual decline and vanishing of the current of injury, a simple explanation is often applicable. When the tissue is injured, it does not necessarily die. In fact, I have often 160 COMPARATIVE ELECTRO- PHYSIOLOGY found that, in order to ensure death—in the case for instance of thermal section—a prolonged application of the fatal temperature is necessary. In ordinary cases of injury caused by the application of heat, I find that we have merely exces- sive stimulation of the point, with depression of excitability. But after a long interval, excitability is more or less restored, with the gradual passing away of the effect of injury. The subsidence of the current of injury thus also denotes the restoration of excitability to a greater or less extent. Hence that differential action between the uninjured and injured contacts, which determines the amplitude of the resultant response, will become correspondingly diminished. And when response has undergone diminution from this cause, a fresh injury is found to renew its amplitude. This is due to the reduction of excitability now freshly brought about at one of the contacts. € There are, however, two other additional factors which may further contribute to the enhancement of response after a recent injury. We have seen that, as a general rule, the resultant response will be E,—£E, where E, means the excitatory electrical change induced at A, and E, that induced at B. It would therefore appear that this value will be at its maximum when the excitability of B is totally abolished by reason of injury, the resultant effect being due to the unopposed electrical excitation at A. But we have seen that when the true excitatory negative variation of a point is abolished, it may nevertheless exhibit a positive electrical variation, due to hydro-positive action. When this happens to be the case, this positive effect at B, conspiring with the true excitatory effect at A, may bring about a response larger than we should have supposed to be maximum. Again, though over-stimulation of a point diminishes its excitability, yet moderate stimulation often enhances it. The effect of this, in enhancing resultant response, is well seen in the case of conducting nerves. Thus, when the point B is injured, the excitation caused by injury reaches A, and causes moderate stimulation of that point. As an after-effect of this CURRENT OF INJURY AND NEGATIVE VARIATION IOI moderate stimulation, A often becomes more than normally excitable.! It is thus seen how, after a recent injury, these two factors—of a hydro-positive effect at the injured, and of increased excitability at the uninjured contact, in consequence of moderate transmitted stimulation—may act to enhance the response. We have seen that the common effect of injury is to induce a galvanometric negativity of the point injured. We have further seen that in such a case the response to external stimulus is by a negative variation of the current of injury. We have next, then, to take up various instances which appear highly anomalous, cases, that is to say, in which the injured point, relatively to the uninjured, is, for some hitherto unknown reason, galvanometrically positive. As a result of this and other causes, there are, in addition to the cases already described in a previous chapter, instances in which response is found to take place, not by a negative, but by a positive, variation of the current of rest or of injury as the case may be. The first point to be considered in connection with such abnormal responses is whether the experimental tissue is physiologically isotropic, that is to say, of equal excitability throughout, or anisotropic, possessed of unequal excitabilities at different points. The discussion of the first of these cases, the isotropic, I propose to defer to the following chapter. The anisotropic will be touched upon here, though its detailed consideration will be entered upon in the next. As an example of the anisotropic organ, we may take the pulvinus of MWzmosa, in which the lower side is more excitable than the upper. In animal tissues also, such aniso- tropy is not uncommon. For example, we may have a _ muscular tissue terminating in a glandular. Owing to this anisotropy, the muscular and glandular surfaces are unequally excitable, and it will be shown in a later chapter that, generally speaking, it is the glandular which exhibits more intense excitatory galvanometric negativity. When such a ‘ For further details, see Chapter XLII. M 162 COMPARATIVE ELECTRO-PHYSIOLOGY preparation is made, by cutting across the muscle, it is found that an electrical current flows from the uninjured gland to the injured muscle. From this it has been supposed that such a current was not the current of injury at all, but something of an unknown nature, essentially different. The consequent perplexity is the result of a failure to understand on the one hand that there is no such thing as a current of injury fer se, except as the after-effect of strong stimulation, and on the other, that the current induced in the tissue is always from the more excited to the less excited. In the present case of muscle-and-gland preparation, the excessive stimulation due to section becomes diffused all over the tissue, and since the glandular surface is the more excitable, its excitatory galvanometric negativity is greater than that of the sectioned muscle, which thus becomes relatively positive. We have here a striking demonstration of the necessity for regarding the electrical reaction as the sign, not of injury, but of the excitation caused by injury. In the case described, for instance, the physical injury is obviously incapable of transmission, and it is the consequent excitation which is con- ducted to the gland. _ The account of an experiment on a sensitive leaf of Mimosa will serve to elucidate the foregoing argument. If one contact, A, be made with the upper half of the pulvinus, and the other, C, with a distant and indifferent point, then, on giving a prick near A, we shall find that that contact, owing to excitation by injury, becomes galvanometrically negative. If, next, we make two contacts at diametrically opposite points of the pulvinus, A on the upper, and B on the lower, surfaces, it will then be found, on causing injury at the upper point A, that that point, relatively to B, becomes galvano- metrically positive. This is because the stimulus caused bv the injury has become diffused throughout the pulvinus, witn the effect of causing greater excitation and consequent sreater galvanometric negativity at the more excitable B. It has been seen that a mechanical or thermal section acts as a strong stimulus. It has also been shown that CURRENT OF INJURY AND NEGATIVE VARIATION 163 recovery from a strong stimulus is very protracted. Hence, after such stimulation, there is persistent galvanometric negativity as an after-effect. As the intensity of this after- effect depends upon the intensity of stimulation, it will be seen that the galvanometric negativity near the section will be greater than at a distant point, where the transmitted effect of stimulation is feeble. From this it follows, that the so-called current of injury will flow in the tissue from the neighbourhood of the cut, to the distant and relatively un- excited end. The current of injury is thus an after-effect of strong stimulus. The peculiar electrical distribution which occurs in a muscle-cylinder is also found in a plant-cylinder, and both are equally explicable from the fact that the greatest excitatory after-effect occurs at the two sectioned ends, and that this decreases progressively towards the equator. The over-stimulated area of injury has its excit- ability depressed or abolished ; diffuse stimulation, causing sreater excitation of the uninjured contact, induces in it a greater excitatory effect of negativity, and this gives rise to a diminution of the existing difference of potential, as between the injured and uninjured. This is the explanation of response by the so-called negative variation. In an anisotropic tissue the excitation caused by injury, when diffused, induces greater galvanometric negativity of the more excitable part. If this be the distal end, the re- sultant persistent current will be from the distal uninjured to the proximal injured. An apparently anomalous case: will thus arise of a ‘ positive’ current of injury, so-called. CHAPTER XIV CURRENT OF DEATH—RESPONSE BY POSITIVE VARIATION Anomalous case of response by positive variation—Inquiry into the cause— Electric exploration of dying and dead tissue : death being natural—Determi- nation of electric distribution in tissue with one, end killed—Dying tissue shows maximum negativity, and dead tissue, positivity to living —Explanation of this peculiar distribution—Response by negative or positive variation, depending on degree of injury—Three typical cases—Explanation by theory of assimilation and dissimilation misleading— All response finally traceable to simple fundamental reactions. WE have seen in the last chapter that, in order to obtain response by negative variation, it is customary among investigators on animal physiology to kill one end of the experimental tissue, say by scalding. It is generally sup- posed also that dead tissue is negative to living. On stimu- lation, the induced negativity of the living contact, now superposed on the existing P.D. of the unilaterally killed tissue, causes a negative variation of it. This mode of investi- gation, by means of the negative variation, is one which has hitherto, as we have seen, been universally regarded as reliable. In the course of my investigations on the response of vegetable tissues, by this mode of negative variation, however, I have sometimes found response to take place by the positive variation. Taking, for example, a stem of Lalsam, I killed one end by immersion in boiling water. On now subjecting this to diffuse vibrational stimulus, the responsive action was- found to induce a positive variation of the existing current. On further investigation, I found that the excitatory electrical variation at the living contact had remained normal; that is to say, the direction of the responsive current was away from the excited living, and towards the killed end. I next a ee ee a Lt gO ae ee I Nae RESPONSE BY POSITIVE VARIATION 165 found that the so-called ‘current of injury’ had in this case, owing to some hitherto unknown cause, undergone a reversal, and was now from the living to the dead, the latter being galvanometrically positive to the former, to the extent of ‘08 volt. The abnormality of the response lay, then, in this fact, that the current of reference had become reversed, and that the responsive current, due to excitation, was now con- cordant with it, instead of antagonistic, thus constituting a positive variation (fig. 112). Later on, I discovered many instances in which the killed end was positive to the unkilled. Since, then, it is possible for the current of reference itself to undergo such obscure and spontaneous reversals, from un- known causes, it is easy to see how uncertain the study of re- sponsive phenomena must become, if we are to depend upon the negative variation as our only Fic, 112. Response by Positive reliable means for their investiga- Variation of Resting Current tion. I next, therefore, turned my acti a aaeys howe Py attention towards an inquiry into reversed, the killed end having the causes of these anomalous Dans cathe a aise si reversals. » The subject therefore resolved itself into an investigation as to what conditions determined the negativity or positivity of a tissue at the onset of death. My first attempt, then, was to study a case in which the approach of death was natural, and not the result of any sudden or violent change, such as might conceivably give rise to abnormal reactions. And in ‘ my search for suitable specimens, I noticed that often, owing to local mal-nutrition or other causes, the leaves of plants exhibited spots or areas, from which, as centres, death pro- ceeded in constantly widening circles. Thus, in the leaves of Colocasia, for example, we find such dead and dying areas in otherwise fairly healthy leaves. The innermost of these 166 COMPARATIVE ELECTRO-PHYSIOLOGY patches may be quite dark and discoloured, while, as the living tissue is approached, this dark passes imperceptibly into yellow colour. And beyond this, again, we find the discolouration of yellow passing into the vivid green of living tissue. Proceeding thus in a radial direction inwards, towards the centre of such a patch from the living green, we shall find all possible stages of death, from its initiation, somewhere on the border-line between green and yellow, to its phase of completion, in the dark central area. On testing the electrical conditions of these different parts, I found that the border between green and yellow was negative to the living green surface. But the same point was also negative to the dead central area, and more negative to this than to the living tissue. Hence the dead was relatively positive to the living. Or if we make one fixed contact on the living tissue, and if the second exploring contact be made with various points _ successively on a radial line passing from this to the centre of the dead area, these contacts will pass in succession through the living, the dying, and the dead. The variation of elec- trical potential will be found to be at its greatest along this line. The electro-motive difference between the point which has been fixed on the living tissue, and the exploring second contact, will at first be found to increase. The maximum difference is attained on reaching the border-line between green and yellow, or very little beyond this, this point being galvanometrically the most negative. On now passing further inward from this point, the maximum difference is found to decrease, till we come to a point in the dead tissue which is iso-electric with the living. On now again passing inwards, to the still more completely dead tissue of the central area, we find that we are approaching points which are more and more galvanometrically positive, as compared with the living tissue. The dying point on the border-line between green and yellow is thus the most negative, and points to the right or left of this are positive in comparison with it, the dead, however, being more positive than the living. It has been said that the electro-motive variation is most rapid along the CURRENT OF DEATH 167 radial line. On the other hand, we obtain series of equi- potential surfaces whose outlines closely follow those of the boundaries of the different degrees of discolouration. [shall next proceed to give quantitative measurements. The first point to be considered is that of the choice of a definite electrical level, which is to be used as a standard. If this point be selected in the living tissue, we shall find that our standard of comparison is extremely variable, since the tonic condition, on which its electrical level depends, is itself subject to change. The only condition which cannot be modified in any way is that of complete death. This may be taken, then, as the standard level. The method of experi- ment will thus consist in selecting a series of equidistant points, abcd,and so on, 5 mm. apart, along a radial line, passing outwards from the central area, which is completely dead, to the green tissue. The non-polarisable contacts E and E’ are first placed on a and 4, then on @ and ¢, ¢c and d, and so forth. The external circuit contains a high resistance, compared with which any difference of resistance, as between any 5 mm. of interposed tissue, becomes negligible. Hence, the successive deflections of the galvanometer indicate the electro-motive difference that exists between a and @, 0 and «¢, and so on. One difficulty which is experienced, in these measure- ments of small electro-motive differences, lies in securing the iso-electric condition of the non-polarisable electrodes them- selves. Whatever precautions are taken in the construction of these, a small electro-motive difference will sometimes be found to exist between them. The existence of such a difference is easily tested by bringing the kaolin ends of the two electrodes in contact, or by dipping both of them close together in a vessel of normal saline solution. Any electro- motive difference of the electrodes, however small, will now give rise to a large galvanometric deflection. This difficulty may be overcome by first taking special precautions as to the purity of zinc rods and the chemicals employed, and secondly, by keeping the electrodes for a long time short-circuited, with their ends dipped in normal 168 COMPARATIVE ELECTRO-PHYSIOLOGY saline. In very obstinate cases, however, I succeeded in eliminating all differences by subjecting the electrodes to cyclic variations of alternating electro-motive force. By means of a Pohl’s commutator, without cross-bars, the electrodes were put in connection with an alternating source of E.M.F., and with the galvanometer intended to test the resulting variation in the E.M. difference, by turns. — A small hand-driven alternating-current generator was used for this purpose. The speed of rotation of this machine was gradually raised to a maximum, and afterwards as gradually slowed down. Thus at each cycle the electrodes were subjected to ascending and descending intensities of alternating electro-motive variations. The effect of such cyclic changes, in diminishing the existing electro-motive difference between a pair of electrodes, specially selected for carelessness of preparation, will be clearly seen from the following tabular results: Condition at starting Galvanometric deflection E.M. difference Original difference . , 360 divisions 009 volt After first cycle : F 40 Js 52?) After second cycle . ; fe) ie One, After third cycle. ; fe) - ee It will thus be seen that, after a very short time of this treat- ment, the two electrodes were rendered iso-electric. I next proceeded to determine the distribution of elec- trical potential in the various portions, living and dead, of the leaf, In order to remove any accidental strain, the leaf was placed in tepid water, and kept there for about half an hour, till the water was cooled to the surrounding temperature. The experiment was then carried out, in the manner already described, and the following tabular statement shows the results obtained. The electrodes, it will be remembered, were placed successively at points 5 mm. apart from each other, along a radial line proceeding from the dead tissue to the living, the first point being taken as zero; CURRENT OF DEATH 169, * Position of Electrodes | Calapaner Deflection | o— 5mm. e) division 5 ane ei E. =~ 1D 9 IO i568 5 igs e520. 1 255 15 — 20 55 ® i 45 9 20— 25 ,, 225400055 25— 39 5, — 140 29 30 — 40 ,, | + TIO +95 40 — 45 9 ‘+ 20 5) It will be observed that as we proceed from the dead to the dying, the negativity of the latter rapidly increases, the maximum being at 30 mm. from the zero-point taken on the 5 10 15 20 25 30 35 40 45 | : HM vr Wh te tI 400 ee Fic. 113. Distribution of Electric Potential in Lamina of Co/ocaséa along a radial line from dead to living through intermediate stages. Ab- scissa gives distance in mm. from chosen centre in dead tissue, ordinate represents galvanometric negativity in divisions. Dead tissue repre- sented dark, dying shaded, and living white. dead tissue. This point of maximum-negativity almost coincides with the visible border-line between the yellow and the green. Beyond this, however, there is an electrical 170 COMPARATIVE ELECTRO-PHYSIOLOGY reversal, the living becoming increasingly positive, as com- pared with the dying. An inspection of the curve (fig. 113) shows that while there is a point in the tissue between the dying and the dead, which is equipotential with the living, the completely dead tissue is positive to the living. I next carried out an experiment in which death was artificially induced, by immersing a portion of the tissue in boiling water. In connection with this, I may say that it is extremely difficult to ensure the complete death of a thick — tissue. It is only the outside layers which undergo death easily, but the interior tissues, from their protected position, are extremely resistant, and it is only after prolonged immersion in boiling water that death can really be ensured throughout. In the present experiment, however, where only a part of the tissue is to be killed, such prolonged immersion would cause death to encroach upon those portions of the tissue which were intended to be kept alive. This difficulty was met by choosing a specimen, the inside of which was accessible to boiling water. The peduncle of the water-lily (Nymphea alba) in transverse section appears extremely reticulated, and there is thus no difficulty in exposing all its parts to the direct action of the hot water. The upper end of the peduncle was kept surrounded by a cloth moistened in ice-cold water, the lower end being immersed in boiling water for ten minutes. The specimen was then placed.in tepid water, and allowed to cool down slowly. In this way a length of the peduncle was ob- tained, in which one end was completely killed, whereas the other remained fully alive, the intermediate portions showing all stages of the transition from the living to the dead condition. In order to determine the electrical distribution in its different parts, I now employed the potentiometer method of balance. One electrode was per- manently connected with that dying point which by a previous test had been found to exhibit maximum nega- tivity. The second electrode was placed at successive points, I eS Ee oS CURRENT OF DEATH 171 each of which was nearer than the last by 5 mm. to the dead end, which was to the left. The same process was now re- peated, the successive | readings however being taken towards the right or living end. At each point, the electro-motive difference was balanced by the potentiometer. This straight form of potentiometer had a Fic. 114. Straight Form Potentiometer scale divided into one x8 isa stretched wire with added resistances, Rand R’. Sis a storage cell. When the thousand parts (fig. 114), key, K, is turned to the right, one scale and when its terminal division = ‘ooI volt, when turned to the . left one scale division = ‘or volt. P is the electro-motive force was plant. adjusted to 1 volt, each } division of the potentiometer was equal to ‘oor volt. The following table gives the results obtained : Distance from maximum . * Towards left or dead end, : : Towards right or living end ; ; t t = ; ; , E.M. difference in yo55 volt “ee ee, iene C + (—) or E.M. difference in y;55 volt I*2 *5 cm 9 5"0 FO 5, 2°5 18°2 I"5 55 4°7 22°0 rig! ae 6°8 23°0 HES 10°0 23°3 7 hee 12°8 ee 3°55» I 5 6 —— 4°O' 754 16°8 a: 4°55 17°5 — BD igs 18°'0 Here, also, as in the case of natural death, we find a point in the dying tissue which is most negative. From the curve given in fig. 115, it will also be seen that as we pass away from this point in either direction towards the living or dead area, we find an increasing positivity ; the curve for the dead portion is, however, much steeper than that for the living. Thus two points, one 1'5 cm. to the left in the dead tissue, and another 5 cm. to the right in the living tissue, are iso-electric. But while the maximum positivity of the living 172 COMPARATIVE ELECTRO-PHYSIOLOGY is ‘O18 volt, that of the dead is 0233 volt. Hence the dead tissue is here positive to the living, to the extent of 0053 volt. We have seen that the prevailing idea is that the dead is negative to the living. But from the results here shown, we can see that this is not a complete statement of the case. Since then the electro-motive variation, instead of showing a 25° ' ‘ t i ! i Pi ——— + -\ 1. Lesne= i] i i i i { j he ee ee ew ee Rn ee we we ee oes = oe a «. 2 ee me ee ee fe me me me ee ee ee oe ee ee ee ee es ee ee ee ee ee ee ee es eee ee es es he a a ee ee ee ee a Ca 2 3 4 +e) Fic. 115. Distribution of Electric Potential in Petiole of Vymphea alba, one end of which has been killed. The point of maximum negativity is taken as zero, distances to the left or towards the dead taken as mznws, to the right or living, as Aplus. Ordinate represents potential difference in thousandths of a volt. progressive change from the living to the dead, exhibits a maximum difference, followed by a reversal, it may be asked, what is the reason of this anomaly ? Much light is thrown on this subject from the results given by another line of inquiry, to be explained in detail in Chapter XVI. _ It is there shown that the plant-tissue on the first onset of death exhibits a sudden contraction, indicative CURRENT OF DEATH B73 of a strong excitatory reaction. This corresponds with the rigor mortts of the animal, and by means of suitable apparatus, the concomitant mechanical response can be recorded. An electrical record of the same phenomenon may also be obtained, in the form of an electrical spasm of galvanometric negativity. Succeeding to this rigor of the dying tissue, a post-mortem relaxation takes place, with a concomitant change from galvanometric negativity to positivity. Now in a tissue which has been killed unilaterally only, it will be understood that all possible gradations are to be expected. Passing from the completely dead to the fully _alive, we must necessarily pass through various zones, beginning with the abnormally relaxed, through the inter- mediate highly contracted. and rigored tissue on the death- frontier, to the living, which is not so contracted as the dying, and not so relaxed as the dead. At the point where the onset of death-.is recent, the rigor, or excitatory contraction and galvanometric negativity, are at their maximum, Compared with:this, the slightly tonically con- tracted living is positive, but not so positive as the abnormally relaxed dead. : The death-frontier, however, is not fixed. It is con- tinually encroaching on-the living. The line of maximum rigor and galvanometric negativity is thus also shifting in the same direction. Along with this, however, the opposite process of post-mortem relaxation is proceeding; so that a point which was, in consequence of rigor, maximally negative, becomes gradually converted to positive. This positivity of dead tissue as compared with living, which has here been demonstrated in the case of the plant, I find to be also true of animal tissue, in those cases which I have investigated. ‘Thus, while an injured.and dying area in a frog’s nerve is negative, an already dead area is positive, relatively to the living nerve. There is, moreover, an intermediate area, between the dying and dead portions of the nerve, which is iso-electric to the living, 174 COMPARATIVE ELECTRO-PHYSIOLOGY Hence, having one contact fixed on a living area and the other on (1) the dying, (2) the intermediate, and (3) the dead tissue, we shall obtain three different types of what is known as the ‘injury-current.’ In the first of these the second contact will be negative, a condition which has hitherto been assumed to be the sole characteristic of the current of injury. But there are two other cases to be considered. Of these, when the second contact is made at a point intermediate between the dying and dead tissues, we shall find it to be iso-electric with the first, or living contact. And thirdly, when the second contact is on a dead area, the latter will be positive to the first, or living contact. We thus find three cases of the current of injury— the first being negative, the second zero, and the third positive. Taking the first of these—that in which the injured contact is negative—the action-current, in response to stimulus, will bring about a negative variation of the so- called current of injury. In the second, the result will be indeterminate, since the injury-current is zero. In the third, the response will be by a positive variation of the current of injury. I give below three photographic records in illustration of these three cases, obtained with vegetable nerve. I may state here that I have often observed results precisely similar in the case of frog’s nerve also. In the first record, in fig. 116, the thermal injury was moderate. The injured point was thus negative, and the current of injury is represented here by an up-line. The responses are seen to be by negative variation. In the second record the injury was greater, and the injured point was almost neutral; that is to say, on making contact there was a slight up-twitch, which subsided to zero. There is here, then, no current of injury. The subsequent responses are, however, down, the action-current being away from the living contact. In the third record the injury was so great as completely to kill the injured point, which thus became positive to the living. The RESPONSE BY POSITIVE VARIATION 175 reversed injury-current is represented as down, the subse- quent excitatory responses are also down, and constitute a positive variation of the current of injury. It will thus be seen that an identical excitatory reaction of the living tissue appears to give rise to directly opposite Fic. 116. Photographic Records of Responses of Vegetable Nerve, one end of which has been injured In the first injury was slight; current of injury represented up, response by negative variation. In the second, injury greater; injured point neutral, response down. In the third, injured point killed; injury current reversed down, response by positive variation. effects—namely, a negative or a positive variation of the injury-current. : I give below a short summary of the diversities of response which may occur when either the natural, or the injury-current, is taken as the current of reference. (a) (6) < Cc >C B— m , Br —iD pj >R —>R Fic. 117. Typical Cases of Variation of Current of Rest and Action- Current. Specimen originally isotropic (a) A, end slightly injured and negative; Cc, current of injury; R, action- current, a negative variation of Cc. (4) A, end killed and positive ; C, current of injury; R, action-current, a positive variation of c. First—we take the case where the point A is slightly injured (fig. 117,@). The current of injury, Cc, is A> B, and the responsive current, Rk, is B- A, constituting a negative variation. 176 COMPARATIVE ELECTRO-PHYSIOLOGY But when A is killed, the current of injury C is B> A, the responsive current is also BA, constituting a positive variation (fig. 117, 0). Second —we take an instance where, owing to some physio- logical difference, an intermediate point A is less excitable than B or B’ (fig. 118, a). The primary natural current will here be from the less to the more excitable : that is to say, C will be A>B’ and A+B. If stimulus be now applied at x onthe right, an identical excitatory current R, flowing away from the excited point from right to left, will cause seemingly opposite effects: that is to say, a negative variation of A+B’ and a positive variation of A> B. (a) (6) ~< c a >C < Bop al ‘sas Xp! Fic. 118. Typical Cases of Variation of Current of Rest and Action- Current ; intermediate point naturally less or more excitable than either of terminal. (a) Intermediate A, less excitable, shown by vertical shading ; current or rest A>B and A->B’; when right-hand point x excited, action-current R from right to left, gives rise to negative variation of As’, and positive variation of A>B. (4) Intermediate B, more excitable, shown by horizontal shading ; current of rest A>B and A’->B ; action-current on excitation at x, from right to left, giving rise to positive variation of a’/—>B and negative variation of AB. _ Again, we ‘may have the intermediate point B naturally more excitable than A’ or A. The natural current C will be A>B and A’>B (fig. 118, 4). Stimulation at x will now give rise to an excitatory current R, from right to left. The results here will, however, appear to be exactly the reverse of those in the last case: that is to say,.an identical current, R, will give rise to a positive variation of A’ > B, and negative variation of A>B. Instances of these effects will be given in Chapter XVIII. And, lastly, we may have a typically anisotropic tissue, composed of two halves, which are unequally excitable—as, for instance, the upper and lower halves of the pulvinus of Mimosa, or the muscle and gland in a muscle-and-gland -RESPONSE BY POSITIVE VARIATION 177 preparation. Under normal conditions the primary or natural current C is from the less excitable A to the more excitable B, represented by A > B (fig. 119, a). The action-current R, being in the opposite direction B > A, constitutes a negative variation. - But owing to the after-effect of excitation, such as may occur in isolating the specimen by section, the normal resting current C is reversed toB > A (fig. 119, 4). Here the end B may still be the more excitable of the two, hence the action-current B- A will constitute a positive variation of the current of rest. But when B becomes fatigued, its excitability is reduced below that of A; hence the action-current is from the relatively more to less excitable, ze. A>B. In this case, (a) (6) : (c) ——_>C es ta F A B A oon - ae LIB R<——_ R <———- ———>R Fic. 119. Typical Cases of Variation of Current of Rest and Action- Current. Anisotropic organ, B end originally more excitable than A - (a) Current of rest A->B ; action-current, R, in opposite direction ; response by negative variation. (4) Owing to excitatory after-effect, current of rest reversed to B—>A; B nevertheless more excitable than A; action- current, R, is B—>A; response by positive variation. (c) Current of rest reversed BA; action-current also reversed AB, by depression of excitability of B, owing to fatigue ; response by negative variation. on account of the reversal of both the current of rest and action-current, the latter appears to constitute a negative variation of the former (fig. 119, c). It will thus be seen how intricate and diverse are the responsive variations of the resting current, induced by stimulus. Sometimes negative, sometimes positive, it would appear as if there were no guiding principle to regulate these phenomena. The so-called explanations hitherto attempted have consisted in assigning the positive variation to a hypothetical process of assimilation, and the negative to dissimilation. Such explanatory phrases:reach the climax of absurdity when we find ourselves compelled to ascribe | one identical excitatory reaction now to assimilation and then to dissimilation. N 178 COMPARATIVE ELECTRO-PHYSIOLOGY Indeed it must be said that, however suggestive the general theory of assimilation and dissimilation may have been found, its abuse has often stood in the way of physio- logical inquiry. The inquirer, when faced with any difficulty, instead of attempting to surmount it by patient inquiry, was tempted rather to evade it by invoking the aid of an hypothesis which could be made with equal ease to explain a given fact or its direct opposite. We must remember that in the — investigation of obscure problems, the danger is always, instead of seeking an underlying law, to become satisfied with the mere registration of phenomena, and by naming these to imagine that they have been explained. The resulting chaos in the present case has served to deepen the impression that vital phenomena must always remain capricious and mystical. But when we come to survey the facts that have been described, we find the phenomena of response, however diverse they may at first sight appear, to be in no way governed by chance or caprice. ‘They are, on the contrary, definite and uniform under definite conditions. As regards the so-called current of rest in a naturally isotropic tissue, of which one end has been subjected to injury, we must remember that the effect of injury is one of excitation, its sign, within limits, being contraction and galvanometric negativity. But we have seen that when a point is over-stimulated, fatigue-changes appear which give rise to a reversal of its normal sign of response, from con- traction to expansion, from negative to positive (cf fig. 64) The change at death, in which contractile rigor passes into post-mortem relaxation, is analogous to this. ‘Thus when one end of the specimen is merely injured, that end becomes more or less persistently galvanometrically negative, the current flowing away from it. But when the same end is actually killed, the electrical change may be reversed, to one of galvanometric positivity. In an isotropic tissue, then, we may, by moderate injury, bring about a state of anisotropy, under which the uninjured RESPONSE BY POSITIVE VARIATION 179 _ end is rendered relatively the more excitable, and galvano- metrically positive, compared with the inexcitable injured end. In a naturally anisotropic organ, we have a state of things which is analogous. In this case, in the primary condition, the more excitable surface is galvanometrically positive. But under the excitation due to preparation, or accidental dis- turbance, this more excitable surface becomes the more excited, and, relatively to the other, gaivanometrically negative. These varying changes in the direction of the so-called resting current, or current of reference, are the cause of the existing anomalies in the interpretation of response by the positive or negative variation. But the direction of the action-current under normal conditions is always the same. On diffuse stimulation it is always from the more excited B to the less excited A. The differential excitability or anisotropy, may be either natural, or artificially induced, as by injuring one end of an isotropic tissue. There are two different conditions under which the normal effect may undergo reversal, those, namely, of great sub-tonicity or excessive fatigue. But the statement that the responsive current is always from the more excited to the less excited, remains universally true. Numerous illustra- tions, in verification of the cases laid down, will be met with in the course of subsequent chapters. CHAPTER XV EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE General observation of effect of temperature on plant—FEffect of fall and rise of temperature on autonomous response of Desmodium —Effect of frost in abolition of electrical response—After-etfects of application of cold, in EZucharis, Ivy and Holly—Effect of rise of temperature in diminishing height of response— This not probably due to diminution of excitability—Similar effect in auto- nomous motile response of Desmodium—Enhanced response as after-effect of cyclic variation of temperature—Abolition of response at a critical high temperature. WE have now seen that the physiological activity of a living tissue may be gauged by means of its electrical response. We know further that the influence of temperature is of importance in the maintenance of a proper physiological _condition. There is a certain range of temperature which is favourable to this, and above or below these limits physio- logical efficiency is diminished. If the plant be kept too long at or above a certain maximum temperature, it is liable to undergo death. Similarly, there is a minimum point at which physiological activity is arrested,and below which death is apt tooccur. The plant has thus two death-points, one above the maximum and the other below the minimum temperature. Some can resist these extremes better than others, and length of exposure is also a factor which should not be for- gotten in the question of the ultimate survival of the plant under the given unfavourable conditions. Certain species are hardy, while others succumb easily. An unmistakable indication of the effect of temperature on physiological activity is found in the variations induced by it in the autonomous motile pulsations of the telegraph plant, Desmodium gyrans. Here, too great a lowering of the OE OO EE EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE 181 temperature abolishes the pulsation. In fig. 120 are seen (1) the records of normal pulsations ; (2) their arrest under the application of ice-cold water; and (3) their revival, as the plant regains the temperature of the room. In fig. 121 is shown the effect on similar pulsations of a rising tempera- ture. The records in this case were obtained with a different Fic, 120. Photographic Record showing Effect of Rapid Cooling, by Ice-cold Water, on Pulsations’of Desmodium gyrans Normal pulsations recorded to the left. Effect of application of ice-cold water is seen in the production of diminished amplitude and abolition of pulsation. Gradual return to the temperature of the room revives the pulsation in a staircase manner, the period remaining approximately constant. Note that cooling displaces the pulsation in a downward or contracted direction. Gradual warming, conversely, is seen to produce the opposite displacement towards expansion. Up-records represent the fall of the leaflet, down-records its rise. specimen, and it is seen that the pulsations are diminished | in amplitude while their period is quickened, with rise of temperature. When the temperature is raised still higher, they come to a stop altogether. _ We shall next proceed to observe the effect of temperature on the electrical response of plants. As regards the influence of cold, for example, I have found, during the course of a research carried out in England, that after frosty weather, 182 COMPARATIVE ELECTRO-PHYSIOLOGY the electrical responses undergo an almost complete aboli- tion. During a certain week, for instance, the temperature was 10° C., and the electrical responses then obtained from radish (Raphanus sativus) were considerable, giving an E.M. response which varied from ‘o5 to ‘1 volt. Two or three days afterwards, however, as the effect of frost, I found the electrical response of this plant to have practically dis- appeared. A few specimens were found nevertheless which were somewhat resistant. But even in these the average E..M. response had only a value of ‘003 volt, instead of the normal mean of ‘075 volt. That is to say, their average sensitiveness had been reduced to one twenty-fifth. On now Fic. 121. Photographic Record of Pulsations of Desmodium during Continuous Rise of Temperature from 30° C. to 39° C. warming these radishes to 20° C. there was an appreciable revival, as shown by their increasing response. But in those specimens which had been frost-bitten, warming effected no restoration. From this it would appear that frost killed some, which could not be subsequently revived, whereas others were reduced to a condition of torpidity from which, on warming, there was a revival. I have also investigated the effect of an artificial lowering of temperature on the electrical response of plants. The Eucharis lily is particularly sensitive to cold. In this case I took the petiole, and obtained response at the ordinary temperature of the room, which was at the time 17°C. I then placed it for 15 minutes in a cooling chamber at a EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE 183 . temperature of —2°C. On now again trying to obtain response, it was found that it had practically disappeared. The same specimen was next warmed to 20° C., and this induced a revival of response (fig. 122). I was next desirous of studying the after-effect of lowered temperatures on different plants. For this purpose I chose three specimens (1) the petiole of Eucharts Lily, (2) the stem of Ivy, and (3) Holly. I took their normal responses at 17° C.,, and after- wards placed them in an ice-chamber at a temperature of o° C. for 24 hours. The specimens were then taken out, and their responses under stimu- lation once more re- corded (fig. 123). From these it will be seen that while the respon- siveness of the delicate (h) Eucharis Lily was com- | | pletely abolished, that eagnss of the hardier plants, 110,128, Diminuton of Response in Holly and Ivy, exhibited (z) Normal response at 17° C. complete revival. (6) The response almost disappears when plant ; : f is subjected to —2° C. for fifteen minutes. One interesting fact (c) Revival of response on warming to 20° C. which I have noticed is that when a plant approaches its death-point, by reason of excessively high or low temperature, not only is its re- sponse, of galvanometric negativity, diminished to zero, but it is even occasionally reversed to positive. This effect is due to the unmasking of the positive, by the abolition of the true excitatory component. (a) (Cc) 184 COMPARATIVE ELECTRO-PHYSIOLOGY We shall next study the effect on the electrical response of the plant of a rise of temperature. The great difficulty of this investigation lies in raising the plant-chamber to the various determinate temperatures required. I was able, however, to accomplish this by means of electric heating. . Stimulation of lamina at x gives rise to responsive current, R, inducing negative variation of leaf- and positive variation of stalk- currents; (c) Leaf- and stalk-currents of C7ztrus decumana, opposite to those of Ficus and Dionea, > A<-. Stimulation at x induces positive variation of leaf and negative variation of stalk-currents. to flow in the midrib, from the end proximal to the stalk to the distal end. This he designated as the ‘normal leaf- current.’ He further found that if electrical connections were made, so that one contact was near the lamina, and the other away from it, the stalk-current was opposite in direction to the leaf-current (fig. 147 (a) ). On stimulation of the lamina, these resting leaf-and-stalk currents were found to undergo responsive variations. But these changes were exactly opposite to each other. That is to say, the leaf-current underwent a negative, and the stalk- RESPONSE OF LEAVES ik eee current a positive, variation. No explanation has as yet been offered, regarding either the existence of these opposite- directioned currents of rest, or the. apparently anomalous result, that an identical stimulus would induce, in one case a-negative, and in the other a positive, variation of them. As regards these peculiar currents of rest we have seen (p. 176), that if an intermediate point be physio- logically less excitable than either of the two terminal points, then a resting current will flow from the less to the more excitable. This is the particular current-distribution in the leaf of Dzonga. It is not a unique phenomenon, for I have noticed other such instances in ordinary leaves. The point of junction of the petiole with the lamina of Ficus religiosa, for example, is galvanometrically the most negative point in that petiole-and-midrib. _The currents here also, then, as in the case of Dzon@a, flow outwards from the point of junction—the leaf-current towards the tip of the leaf, and the stalk-current in the opposite direction (fig. 147 (0) ). _ We also saw, however, in the same place, that there may be instances in which an intermediate point is more excitable than either of the two terminal. When this is so, the currents of rest will be reversed in direction, and flow inwards. This I find to be the case in the leaf of Cztrus decumana (fig. 147 (c) ). Next with regard to the excitatory variation of these resting-currents in leaf and stalk, we must remember that the effect of stimulation is to give rise to a true excitatory current, flowing away from the excited. If then there be already a resting-current, the responsive current will be added to this algebraically. When the lamina to the right is excited, the responsive current flows from right to left. This would naturally, in the case of Dzonea, induce a negative variation of the leaf-current, and a positive variation of the stalk-current (fig. 147 (a) ). The same thing is seen on stimulating the lamina of Ficus religiosa, where also the excitatory current, being of opposite sign to the leaf-current, and of the same sign as the stalk-current, induces a negative Q 226 COMPARATIVE ELECTRO-PHYSIOLOGY variation of the former, and positive variation of the latter (fig. 147 (6) ). The same stimulus thus induces effects which are apparently opposite. Or an interesting variation of the phenomenon may be obtained, on repeating the experiment with the leaf of Cztvus. Here, on stimulating the lamina, we observe a positive variation of the leaf-current, and a negative variation of the stalk-current (fig. 146 (c)). This is because the currents of reference or resting-currents are the _ opposite of those in Dzonea and Ficus religiosa. Another series of variations exactly the reverse of these, and therefore at first sight anomalous, is caused by simply changing the point of application of stimulus, from the right end on the lamina, to the left end on the stalk. The direc- tion of the excitatory current is thus reversed, being now from left to right (fig. 147 (a) ). By algebraical summation, there now occurs a negative variation of the stalk-current, and a positive variation of the leaf-current, in Dzon@a and Ficus religtosa, while the very opposite takes place in Cztrus. I shall here draw attention once more to those errors to which an investigator becomes liable when he infers that positive and negative variations must necessarily be the expression of assimilatory and dissimilatory processes. For we have just seen that the same responsive current, by alge- braical summation with two opposite-directioned resting- currents, may appear to be both positive and negative, at one and the same time. Again, with a single resting-current, it is possible to obtain either a positive or a negative varia- tion, according as the same stimulus is applied to the right or the left. It is now abundantly clear that the one uni- versal effect of stimulus is to give rise to a responsive current which flows from the more to the less excited portions of the tissue. If there be already an existing current, the responsive current is added to this algebraically, and induces, according to circumstances, either a positive or a negative variation. Much confusion, and many erroneous inferences would be avoided, if instead of looking at these variable indications attention were centred on the one constant criterion, namely RESPONSE OF LEAVES 227 that the excitatory current always flows from the more to the less excited portions of the tissue. Another effect observed by Burdon Sanderson was, that on cutting the petiole across, the existing normal leaf-current was increased, the amount of this increase being determined by the length of the petiole cut off, in such a way that the shorter the petiole left, the stronger the leaf-current became. In Nature (vol. x. p. 128), he suggested an explanation of this phenomenon. In the leaf of Dzonga, as already said, there is a resting-current in the stalk, opposed in direction to that in the leaf. Thus ‘the electrical conditions on opposite sides of the joint between stalk and leaf are antagonistic to each other ; consequently, so long as the leaf and stalk are united each. prevents or diminishes the manifestation of electro- motive force by the other.’ He thus inferred that the pro- gressive removal of the antagonistic element, by section of the stalk, would serve to enhance the intensity of the leaf-current. Taking the ordinary leaf of Fzcus religiosa, | have myself been able to obtain results precisely similar to those described in Dzonea, by making successive sections of the petiole, at shorter and shorter distances from the point of junction. The leaf-current at each section underwent an increment. The parallelism of the two sets of effects will be seen from the following table. Ficus LEAF. DION#A LEAF (BURDON SANDERSON). =e eh Sy a ae ' Length of stalk Galvanometric deflection | Length of stalk | Galvanometric deflection om. | 16 divisions 2°5 cm. 40 divisions ty Stee 4 >» 36 re) | 1°25 5, ; 50 2” 2 » 5° ” | 06 ,, 65 ” | I 5, | 60 ;; bid AOS 5 opal re 90 5; Burdon Sanderson’s suggested explanation that the suc- cessive augmentations of the leaf-current were due to suc- cessive removals of the antagonistic element, by section, is Q2 228 COMPARATIVE ELECTRO-PHYSIOLOGY quite untenable. He failed to see that the effect was, on the contrary, due to the increasing excitatory action of the sections themselves. Similar results may be obtained, even without the bodily removal of the supposed antagonistic element, if, instead, we apply an increasing intensity of stimulus, as say, by contact of a hot wire at points nearer and nearer to that of junction. In the case of the trans- verse section, the cut acts as a stimulus, and the respon- sive current flows from the left to the right... Algebraical summation of this with the existing leaf-current, which is also from left to right, causes an increase, or positive variation of it, ina manner exactly the converse of the negative varia- tion induced in the leaf, when the stimulus was applied on the lamina. - As the section is made nearer and nearer to the point of junction, the degree of stimulation, and the con- sequent positive variation of the resting-current, must become greater and greater. And lastly, in the case of the longitudinal lesfieasPauk Burdon Sanderson found that if a current from a battery were directed through a leaf-stalk, at the same time that the two ends of the midrib were led off to the galvanometer, the difference previously existing between the ends of the midrib would be increased, if the current led through the leaf-stalk were in the same direction with the leaf-current, and diminished, if it were in the opposite direction. A similar effect, as seen in the conducting tissues of ordinary plants, will be studied in detail, when we take up the question of the extra-polar effects’ induced by electrotonic currents (Chap. XXXIX.). | We have already seen that, by means of induced varia- tion of the longitudinal stalk-current, under the stimulation caused by section of the petiole, it is easy to obtain an un- mistakable indication of the nature of the true excitatory electrical change. Burdon Sanderson, however, laboured under the disadvantage, as already said, of having failed to recognise that a section acts as a stimulus. His _ investi- gation, therefore, on the character of the excitatory variation, RESPONSE OF LEAVES 229. was chiefly carried out by means of experiments on electrical variations induced in the lamina. These depended (1) on variations in the cross-difference of existing potential between the upper and lower surfaces, according to his ‘fundamental experiment, and (2) on electrical variations in the led-offs of symmetrical surfaces of contact on the under-side of opposite lobes. The results which he obtained, however, by these methods, appear to the reader to have been very conflicting, and in fact the experimental methods described by him would seem to have been open to many sources of complica- tion of which he himself was unaware. Fic. 148. Burdon Sanderson’s Funda- Fic. 149. Parallel Experiment in mental Experiment on Dzonea Leaf Sheathing Petiole of Musa Electrical stimulus applied on distal Thermal stimulus applied on distal lobe, 7, induces responsive effect side induces responsive effect on on led-off circuit fw. Upper or led-off circuit. Upper or ‘internal’ internal surface, f, more excitable surface more excitable than lower. than lower, 772. I shall deal first with Burdon Sanderson’s ‘fundamental experiment, of which the excitatory electrodes are seen on the left lobe, and the led-off on the right in fig, 148, In fig. 149 is given a diagram of a parallel experiment carried out by myself on the petiole of Musa. ‘According to Burdon- Sanderson, as the result of excitation, a + current is induced in the right lobe of Dzonea (fig. 150). This means, of course, that the upper or more excitable surface of the right lobe has become positive to the lower. This current, how- ever, he termed ‘excitatory,’ regarding it as the analogue of the ‘action-current’ known to animal physiology. After this first phase, when a certain interval had elapsed, he 230 COMPARATIVE ELECTRO-PHYSIOLOGY observed a second phase to set in, in which the upper surface became relatively negative to the lower. This negative change, which he called the ‘after-effect,’ he described as taking place at that moment at which the mechanical effect of excitation also made itself evident. This negative phase—called by him the ‘after-effect’— Burdon Sanderson regarded as connected with those electrical changes which had been observed by Kunkel to be induced by movement of water in the tissues. The first effect on the ‘an Fics. 150,151,152. Recordsjof Electrical Responses of Different Leaves of Dionea according to Fundamental Experiment of Burdon Sanderson HATTA | | Fig. 150. Positive response of certain leaves of Dzonea. Time-marks 20 per second (Burdon Sanderson). Fig. 151. Diphasic response of leaf of Droxea ‘in its prime.’ Positive followed by negative. Time-marks Io per second (Burdon Sanderson). Fig. 152. Positive response of same leaf when ‘ modified’ by previous stimulation. Time-marks Io per second (Burdon Sanderson). The above récords were obtained with capillary electrometer. contrary, which immediately preceded this, and was charac- terised by relative positivity of the upper surface, he regarded, as already mentioned, as the true excitatory or action-effect. The following is from his summary : ‘The first phase of the variation--the effect which immediately follows excitation, and has an opposite sign to the after-effect, and a much higher electro-motive force—does not admit of a similar explanation: for it cannot be imagined that a change which spreads over the whole lamina in less than one-twentieth of a second can be dependent on migration of water. The excita- tory disturbance which immediately follows excitation RESPONSE OF LEAVES 231 is an explosive molecular change, which by the mode of its origin, the suddenness of its incidence, and the rapidity of its propagation, is distinguished from every other phenomenon except the one with which I have identified it—namely, the corresponding process in the excitable tissues of animals. Of the nature of this preliminary disturbance (to which alone the term ex- citatory variation ought to be applied, it alone being the analogue of the ‘action-current’ of animal physio- logy) we know nothing. ... The direction of the ex- citatory effect in the fundamental experiment is such as to indicate that in excitation, excited cells become positive to unexcited, whereas in animal tissues excited parts always become negative to unexcited. The ap- parent discrepancy will probably find its explanation in the difference of the structural relations of the electro- motive surfaces.’ } _ From this quotation it will be seen that Burdon Sanderson had fallen into the basic error of mistaking what I have demonstrated to be the hydro-positive, for the true excitatory effect, and wece versa. In a subsequent Paper again (Phz/. Trans. vol. 179, 1889) Burdon Sanderson published certain results, which differed from those referred to above. He had previously found that usually speaking the upper surface of each lobe was negative to the lower. Later, however, he came to the conclusion that in the leaf of Dzonga in its ‘prime, the upper surface was positive to the under. On repeating his ‘fundamental experiment’ moreover, with these vigorous leaves, he found that instead of the pronounced positive response which he had previously observed, he now obtained a short-lived positive effect succeeded by a strong negative (fig. 151). He was unable to offer any definite explanation of this difference between the two sets of results, but suggested that it might arise, in some way, from changes of the resting-current. ’ Phil, Trans. 1882, vol. 173, p- 55: 232 COMPARATIVE ELECTRO-PHYSIOLOGY ‘In the leaf, observed facts show most conclusively that the two sets of phenomena—those of the excited and those of the unexcited state—are linked together by indissoluble bands: that every change in the state of the leaf when at rest conditionates a corresponding change in the way in which it responds to stimulation, the correspondence consisting in this, that the sign, that is the direction, of the response is opposed to that of the previous state, so that, as the latter changes sign in the direction from + to |, the former changes from | to +.’ } In making this statement, Burdon Sanderson was _ prob- ably guided by the prevalent opinion that response takes place by a negative variation of the existing current of rest. We have seen, however, that this supposition is in fact highly misleading. For, owing to such fluctuating factors as age, season, previous history, or excitation due to prepara- tion, the so-called current of rest may and frequently does undergo reversal. Thus a single excitatory effect might, as we have seen (pp. 175-177) under different circumstances, appear either as a positive or a negative variation of the existing current. The assumption of the universality of response by negative variation is thus seen to be unjustifiable. Indeed, it would appear from the description of some of the experiments actually related by Burdon Sanderson him- self, that response did not, even in these cases, always take place by negative variation of the existing current. For instance, while in the leaf of Dzon@a in its ‘prime’ (upper surface positive) the response is negative, and while this latter becomes reversed to positive, as he tells us, in conse- quence of ‘ modification’ due to previous excitation (fig. 152), yet headmits that even in these circumstances the upper surface had first returned to positivity (zbzd. p. 447). Thus, though the responses of the leaf in its ‘prime, and of the ‘ modified ’ leaf are opposed, yet the antecedent electrical condition of the modified leaf has not in this case undergone reversal. Phil. Trans. 1889, vol. 179, p. 446. RESPONSE OF LEAVES 233 The suggestion, therefore, that the reversal. of response is due, in some way unexplained, to a reversal of the electrical condition of the leaf, cannot hold good. Nor does the use of the term ‘ modification’ in any way of the phenomenon. A satisfactory explanation of this reversal of response, then, still remains to be found. So much for the ‘fundamental experiment. The next experi- mental arrangement employed by Burdon Sanderson consists of a leaf which is led off by symmetrical contacts on the under surfaces of its two lobes (fig. 153). If now the right lobe was excited, by touching assist in the elucidation FIG, 153. Experimental Con- nections with Dzonea ac- cording to the Second Experimental Method of Burdon Sanderson one of the sensitive filaments (on the upper surface) with a camel’s-hair pencil, in the neighbourhood of the leading-oft contact, it was found that the under-surface of the right lobe became first positive, and subsequently negative (fig. 154), relatively to the left (zdzd. p. 440). Mn i Fic. 154. Response of Under-surface of Leaf of Dzon@za, with Electrical Connections as in Fig. 153 {I Mechanical excitation of upper surface of right lobe. shows relative positivity of under surface of same right its relative negativity (down curve). (Burdon Sanderson). lobe (up curve), followed by Time-marks 20 per second Summarising these various observations, then, we find results which are very much at variance. First, according to the ‘fundamental experiment,’ certain leaves are seen to give rise to the positive response; other leaves, in their prime, give diphasic response, the upper surface becoming 234 COMPARATIVE ELECTRO-PHYSIOLOGY first positive and then negative. These latter again, after previous excitation, become so modified as to show only positive changes. And lastly, using the experimental arrangement of symmetrical contacts, a diphasic variation is obtained—positive followed by negative—on the under- surface, instead of the upper, of the lobe excited. No theory is advanced, however, by which a comprehensive explanation might be afforded of these apparently anomalous results. But from the generalisations which I have already esta- blished, regarding the electrical signs of the hydro-positive and true excitatory effects respectively, and from the results of certain experiments on ordinary leaves which I shall presently describe, it will be found easy to arrive at a true explanation of the various observations related by Burdon Sanderson, which would otherwise have appeared inexplic- able. The fact that hydrostatic disturbance induces galvano- metric positivity, and that true excitation induces negativity, has already been clearly demonstrated under conditions from which all possible sources of complication had been elimi- nated (p. 61). The experimental arrangement adopted by Burdon Sanderson, however, laboured under the double dis- advantage, not only of a liability to confuse the hydro- positive and true excitatory effects, but also of the com- plexity arising from the differential excitability of the responding organ. It is only indeed by the closest analysis that it is possible to discriminate, in his results, between such as are due to true excitation and those arising from the hydro- positive effect. The various electrical phenomena which are possible in an anisotropic organ in consequence of the hydro-positive and excitatory effects respectively, may be clearly exhibited, as I have already shown, by means of the mechanical response of the leaf of MW/zmosa. With regard to this, we have seen (pp. 59, 60) that direct stimulation of the pulvinus induces a negative mechanical response, or fall of the leaf, by the greater contraction of the more excitable lower half of the organ. The corresponding electrical variation would RESPONSE OF LEAVES 235 thus consist in the greater galvanometric negativity of this more excitable lower, in relation to the less excitable upper half. If the stimulus, however, be applied at some considerable distance, so that true excitation cannot reach the responding point, then we have an erectile or positive mechanical response of the leaf. This is brought about by the relatively greater expansion of the more excitable. The corresponding electrical response will be the galvanometric positivity of this more excitable, in relation to the less excitable half of the organ. Between these two extremes lies that experi- ment in which stimulus is applied at some intermediate point, the consequence of which is that the hydro-positive wave, with its greater velocity, reaches the responding organ earlier than true excitation, thus bringing about a pre- liminary erectile or positive response, followed by the ex- citatory negative or fall of the leaf. The corresponding electrical response would therefore be diphasic, positive followed by negative. But the occurrence of this second or negative phase is only possible when the conductivity is so great as to allow the wave of true excitation to reach the organ. We may imagine that in a very vigorous plant, with its great con- ductivity, we have found a point, at the maximum distance from which the true excitatory effect of a given stimulus is capable of transmission to the organ. With such a speci- men, in its ‘prime,’ we shall observe a diphasic effect—pre- liminary positive followed by negative. But if we took a less vigorous specimen, and applied the stimulus at the same distance from the responding point, the true excitatory wave would fail to reach the responding organ, and we should see there, only the positive effect due to hydro-positive action. Hence, two different specimens, treated in exactly the same way, may exhibit two different effects, one diphasic, and the other positive alone; this difference being due to their unequal vigour, and concomitant inequality of excitability and conductivity. This will account for the diphasic and positive responses which were exhibited by the more and 236 COMPARATIVE ELECTRO-PHYSIOLOGY less vigorous leaves respectively of Dzonga, when stimulation was applied on the distal lobe, according to the fundamental experiment of Burdon Sanderson. We must next refer to the reason why a leaf that origin- ally gives diphasic response—positive followed by negative —undergoes such ‘ modification, in consequence of: previous excitation, as thereafter to give only positive response. We have seen that the negative element of the diphasic response is due to the arrival at the responding point of the true excitatory wave originated at the distant point of stimula- tion. Now it has been shown (p. 65), that if by any means the conductivity of an intervening region should become diminished, we may expect that the hydro-positive effect will continue to be transmitted, although the passage of true excitation is partly or wholly blocked. By-means of this selective block, I was able to unmask the hydro-positive component present in resultant response (cf. fig. 49). I have shown elsewhere! that the conducting power of a tissue will be impaired by the fatigue consequent on previous stimulation. Thus, in the petiole of Bzophytum, | found that while the plant, when fresh, had a conductivity measured by the velocity of transmission of excitation, at a rate of 1°88 mm. per second, the same plant, when partially fatigued by four successive stimulations, had its conductivity dimi- nished, the velocity of transmisson being now only 1°54 mm. per second. The diminution in this case, then, was about 18 per cent. I shall moreover show in a later chapter that in consequence of growing fatigue the passage of true excitation may at a certain stage be arrested, the hydro- positive effect alone being then transmitted. It is thus easy to explain how it was that in Burdon Sanderson’s experi- ment, of stimulus applied on the distal lobe, the wave of true excitation became blocked, and the ‘ modified’ leaf gave positive response alone. These considerations will be found as I think, to offer a satisfactory explanation of the conflicting results arrived at by Burdon Sanderson, 1 Plant Restonse, Pp. 244. RESPONSE OF LEAVES 237 I shall now, however, proceed to describe a series of ex- periments exactly parallel to the ‘fundamental experiment’ on Dionea, carried out on ordinary plants. We have seen that the inner or concave surface of the sheathing petiole of Musa is relatively more excitable than the outer or convex. Thus it corresponds with the ‘internal’ or upper surface of the leaf of Dzonga. The more excitable internal surfaces of both these, again, correspond with the more excitable lower half of the pulvinus of AZzmosa. In fig. 149 is shown an experi- mental arrangement with a specimen of JZusa which will be seen to be parallel to that of Burdon Sanderson’s funda- mental experiment on Dionea. In order to avoid any such disturbance as might conceivably arise from current-escape, if the electrical form of stimulus were used, I employed the thermal mode of stimulation. A momentary heating-current passed through a thin platinum wire gave the thermal varia- tion required, and was found to furnish a very satisfactory form of stimulus. The led-off circuit was at first placed at a distance of 16 mm. from the point of stimulation. As the stimulation was moderate, and as the conductivity of the tissue was not great, the effect induced at the respond- ing circuit was hydro-positive, the more excitable concave surface becoming positive (fig. 155 (a) ). This response is the same as the positive responses given by the ‘unmodifiable leaf’ of Dzonea (fig. 150), as well as that of a vigorous leaf which had been ‘modified’ by fatigue (fig. 152). On next taking a second pair of led-off points, at the shorter distance of 8 mm., the hydro-positive effect reached the led-off points earlier, and was followed by the true excitatory wave. This is seen as a preliminary positive response, followed by the excitatory negative (fig. 155 (2)). This again is the same as the di-phasic response of a Lzonea leaf in its ‘prime’ (fig. 151). Inthe experimental arrangement with J/usa the led-off circuit was now brought still nearer to a distance of 4 mm. There was now little interval between the arrival at the led-off points of the hydro-positive and true excitatory effects; and since the latter is of predominant electrical 238 COMPARATIVE ELECTRO-PHYSIOLOGY expression, the former is masked by it, and we obtain here only the excitatory negative variation (fig. 155 (¢) ). It only remains to consider the responses which Burdon Sanderson obtained with symmetrical contacts (fig. 152) on the under-surfaces of the two lobes. In the next figure (fig. 153) is reproduced his record of electrical response, obtained on mechanical stimulation of a sensitive filament situated on the upper surface of ‘the right lobe, vertically above the right-hand led-off. This response is, as will be seen, di- Fic. 155. Photographic Records of Positive, Diphasic, and Negative Responses ot Petiole of A/usa depending on the Effective Intensity of Transmitted Stimulus (az) Here stimulus was applied at a distance and hydro-positive effect alone transmitted ; (6) Stimulus was applied nearer, and the positive effect was succeeded by the true excitatory negative; (c) Stimulus was applied very near, with the result of true excitatory negative response. phasic, its first phase being one of relative positivity of the under-surface of the excited lobe, and the second representing its subsequent relative negativity. This first phase is clearly due to the earlier transmission of the hydro-positive or indirect effect of excitation, from the stimulated point on the upper surface. It was supposed by Burdon Sanderson that the second phase of this re- sponse represented the later arrival of the same positive effect at the distal second contact, which would thus induce reversal. But it appears much more probable that this second phase of negativity is due to the arrival at the RESPONSE OF LEAVES 239 under-surface of the wave of true excitation, initiated vertically above. This relative negativity of the under- surface may or may not be helped by the induction of positivity at the distal, due to the transmission of the hydro- positive effect. This view is supported by the fact that in a corresponding experiment on an ordinary leaf, in which the second contact was at a distance too great to allow of the effective transmission of any hydro-positive wave, the stimulation of the upper surface induced a similar diphasic response at a point diametrically opposite, on the under side. In this case the second or negative component of the response could not be due to anything but the subsequent arrival of the true excitatory wave with its concomitant negativity. It is now clear that among the various results obtained from the study of the electrical responses of the leaf of Dzonga, there are some which do not represent true excitation at all, while in others it is only one of the two phases which is significant of this, the other being due to the hydro-positive effect. We have also seen that Burdon Sanderson at starting fell into the error of wrongly identify- ing the true excitatory electrical effect with that which was due to the hydro-positive effect, and vice versa. We have seen that there is not a single response given by the so-called excitable leaf of Dzong@a, which cannot be obtained under similar conditions from the leaves of ordinary plants also. In fact it has been by means of experiments carried out on the latter that we have been enabled to unravel all the intricacies which were offered by the recorded responses of the lamina of Dzonea. : It has further been shown in the course of the present chapter that the leaf and stalk currents observed in Dzonga are also found in, for instance, the leaf of Ficus religiosa. These have been shown, moreover, to be due to physiological differences between an intermediate and the terminal points. The negative variation of the leaf-current, and the positive variation of the stalk-current, on the stimulation of the 240 COMPARATIVE ELECTRO-PHYSIOLOGY _ lamina, were both alike shown to be the result of the alge- braical summation of a definite excitatory current with the two opposite-directioned resting-currents. The positive variation of the leaf-current, again, on section of the petiole, has been traced to the same cause, namely the stimulatory action of mechanical section, giving rise to an excitatory current which was summated with the existing leaf-current. Finally the positive response of the concave surface of Dionega has been shown to arise, not from any specific difference between plant and animal response, but from the fact that in this particular case it was the indirect hydro- positive effect of stimulus that was transmitted, inducing an action opposite to that of true excitation. CHAPTER XIX THE LEAF CONSIDERED AS AN ELECTRIC ORGAN Electrical organs in fishes—Typical instances, Zorfedo and Malepterurus— Vegetal analogues, leaf of Pterospermum and carpel of Déllenta indica or pitcher of Mefenthe—Electrical response to transmitted excitation — Response to direct excitation—Uni-directioned response to homodromous and hetero- dromous shocks—Definite-directioned response shown to be due to differential excitability— Response to equi-alternating electrical shocks—Rheotomic ob- servations-—Multiple excitations—Multiplication of terminal electromotive effect, by pile-like arrangement, in bulb of Uyzc/zs lily. IT has been shown that by a study of the peculiarities of electrical response in plants, it is possible to obtain an insight into the obscurities of similar responses in the animal tissue. Among animal structures, there is one—the elec- _trical organ of certain fishes—the explanation of whose action offers unusual difficulties to the investigator. But I shall attempt to show in the course of the present chapter, that there are also, on the other hand, vegetable structures, the study of which will be found to elucidate the electro-motive action here involved. Taking that of the Torpedo as type, we find that the electrical organ is disposed in the form of columns, each column consisting of. numerous electrical plates, arranged in series, one over the other, like the plates in a voltaic pile. Each electrical plate consists of a rich plexus of nerve-fibres imbedded in a gelatinous mass. There are thus two surfaces, one nervous and the other non- nervous. Each disc then becomes electro-motive under the impulse from the nerve. Though the induced electro-motive force in each plate is small, yet in consequence of their serial arrangement in columns, the elements are coupled for inten- sity, and the resulting E.M.F. of discharge becomes high, R 242 COMPARATIVE ELECTRO-PHYSIOLOGY Fritsch estimates the total number of these plates in some of the Torpedos to be over 150,000. From the point of view of their development, these electrical organs in general constitute modified muscles, containing nerve-endings, The electrical fish known as Matepterurus of the Nile is an exception to this rule, inas- much as morphological evidence goes to prove that in its ~ case it is glandular, rather than muscular, elements which have been so modified. The peculiar characteristic of the discharge of electrical organs in general, is that it takes place in a definite direction at right angles to the plates. It was Pacini who tried to establish the generalisation that the direction of the dis- charge would be found to be dependent on the morphological character of the organ. He found that as a general rule the discharge takes place in a direction from that surface of the disc which receives the nerve (henceforth to be referred to as the anterior surface) to the opposite non-nervous, or posterior, surface. Thus in the Zorfedo, where the plates are horizontal, and the anterior or nervous surface constitutes the ventral aspect of the disc, the discharge is from the ventral or anterior, to the dorsal or posterior surface. In Gymmnotus again, the plates or discs are vertical to the long axis, The anterior or nervous surface is here towards the tail-aspect, and the discharge is from tail to head. If these cases had been all, Pacini’s generalisation, as regards the direction of discharge—from the anterior nervous to the posterior non-nervous—would have been complete, and from it some attempt might have been made to offer an explana- tion of the phenomena. Unfortunately, however, this is not so, since Malepterurus presents a hitherto inexplicable ex- ception to the rule. In this fish, though the anterior or nervous surface is towards the tail-aspect as in Gymnotus, yet the discharge is in the opposite direction towards the head : that is to say, from the posterior surface to the anterior. The difficulties in the way of an explanation of the activity of these electrical organs of certain fishes are thus seen to be THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 243, very great. Is the activity something specific occurring in these fishes alone, and unrelated to other electro-motive phenomena in the animal tissues? Or is it related to the electromotive action already observed in excited muscles? In support of the latter view, it is urged that most of the electrical organs consist of modified neuro-muscular elements, Against this argument, however, as we have just seen, is the instance of Malepterurus, in which, from a morphological standpoint, the organ is to be regarded as a modified gland, and therefore not muscular in character, There are certain peculiarities, further, about the action of these organs which call for elucidation. Among these is the question of the character of the natural current of rest, about the significance of which there have been differences of opinion. There is also the fact that the organ, under a single strong excitation, gives rise not to one, but to a series of electrical responses. We have seen that the apparently unique character of this group of organs constitutes an added difficulty in arriving ata correct theory on the subject. But it is clear that if we could succeed in discovering among vegetable organs any cases which showed similar characteristics, we should then be so much the nearer to the determination of that fundamental reaction on which the phenomenon in animal and vegetable alike depends, In the typical case of Zorpedo, it has been seen that the conducting nerve, when entering into an electrical plate, breaks into an extensive ramification, and thus forms the nervous surface, in contradistinction to the jelly-like sub- stance in which it is imbedded, forming the opposite, and here indifferent surface of the plate. Now this arrangement is closely imitated by many ordinary leaves, in which the vascular elements break, on reaching the lamina, into a pro- fuse arborisation. | I must here anticipate matters to say that I have discovered in the fibro-vascular bundles of plants (see ei hap. XXXII.) elements which are in every way peel eres to the nerves of R2 244 COMPARATIVE ELECTRO-PHYSIOLOGY animals. For an exact vegetal analogue to the electrical plate of Zorpedo, we may take certain leaves in which the ventral, or anterior, surface is formed of a prominent network of highly excitable nervous elements, while the upper consists of an indifferent and relatively inexcitable mass of tissue. An example of this may be found in the leaf of Pterospermum subertfolium (Rox.) whose lower surface is characterised by | a remarkably perfect venation, while the upper or posterior is dry and leathery. Thus the nerve passing into an elec- trical plate of Zorvpedo corresponds with the petiole attached to the leaf just described, since in the two cases alike, it is the ventral surface which contains the highly excitable nervous elements. In the exceptional JMJalepterurus, on the other hand, - it is, as we have seen, a modified gland, and not a modified muscle, which forms the posterior surface of an individual electrical element. Morphologically speaking, the vegetal analogue is found in such organs as the carpellary leaf of Dillenta indica, or the pitcher of Nepenthe, both of which are glandular on their upper or inner surfaces. In point of structure, then, these leaf-organs are analogous to single discs or elements of the electrical organs of TZorgedo and Malepterurus respectively. But we have still, in the course of the present chapter, to inquire whether the electrical reactions are equally correspondent—that is to say, whether, on stimulation, the excitatory current in the type of vege- table organ represented by the leaf of Pterospermum is or is not, from the lower or anterior surface to the upper posterior, as in the electrical plate of Zorpedo; and, con- versely, whether in the type represented by the carpel of Dillenia or the pitcher of Wefenthe the excitatory current is from the posterior to the anterior surfaces, corresponding with the discharge in the electrical element of MWalepterurus, from the posterior glandular to the anterior non-glandular surface. While dealing with the theory of the action of electrical organs, I shall be in a position to show that the characteristic THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 245 reaction of each of these two types is governed entirely by the question of the relative excitabilities of the two surfaces. The physiological anisotropy on which the distinctive effect of the type depends is very pronounced in the representa- tive cases of the vegetal analogues which have been named. In many other cases, however, though the results under normal conditions are fairly definite, and approach one or other of the two types, yet the characteristic responses are liable to be reversed under the physiological modifications induced by age and surrounding conditions. In this way it may be said of the leaf of water-lily (Vymphea alba), of Bryophyllum calcineum, and of Coleus aromaticus that when vigorous, and in their proper season, their responses are of the first of these two types, while those of the bulb-scale of Uviedis lily, with its glandular inner surface, are of the second type. The electrical organ of the fish may be excited indirectly by means of stimulus transmitted through the nerve; or direct stimulation may be applied, as by means of induction- shocks. Under either of these conditions the excitatory discharge is definite in its direction. In the case of Jorpedo, as already mentioned, this is always from the ventral and anterior to the dorsal or posterior surface. Turning then to the corresponding vegetable organ of the first type, I shall show that transmitted stimulus induces an effect exactly similar ; and I shall demonstrate this experimentally by means of the leaf of Vymphea alba. Suitable galvanometric connec- tions were made with the ventral anterior and with the dorsal posterior surfaces of the lamina. Thermal shocks, by means of the electro-thermic stimulator, were applied on the petiole, close to the lamina, at intervals of one minute, records being taken photographically of the resulting responses. It should be remembered here that excitation is transmitted to the lamina by the conducting nerve-like elements present in the petiole. The records (fig. 156) show that the effect of this periodically transmitted stimulation was a series of respon- sive currents, whose direction was like that of the discharge in Torpedo, from the anterior surface to the posterior. 246 COMPARATIVE ELECTRO-PHYSIOLOGY Of great importance was the investigation carried cut by Du Bois-Reymond on the effects induced in the electrical organ by the passage of currents in different directions. Polarising-currents in the direction of the natural discharge of the organ are distinguished, in the terminology introduced by Du Bois-Reymond, as homodromous, and those in the opposite as heterodromous. Polarisation-effects in the direction of the natural discharge he distinguishes as ‘absolutely positive polarisation, and against that direction ‘as absolutely negative.’ A polarisation-current in the same direction as the polarising- current he calls ‘relatively positive,’ and in the opposite direction ‘rela- tively negative’ polarisation. It was found by him that polarising- currents of fair intensity and short duration, whether homodromous or heterodromous, would always give rise to polarisation-currents in the same direction as the natural dis- mea, re6. Mice charge. He believed this to be due of Lamina of Vympheaalba to the occurrence in the electrical due to Transmitted Excita- % . ors. ah an Prole organ of two different polarisation- Direction of responsive current effects, positive and negative. This incaat ttl avper serace will be understood from his own dia- grammatic representation (fig. 157) of the effect which he supposed to take place immediately on the passage of the polarising-current. In the upper figure the ascending arrow represents the homodromous polarising-current. This gives rise, according to Du Bois- Reymond, to two opposite polarisation-effects. The de- flection seen in the galvanometer is the resultant of these, represented by the shaded part of the figure. The resultant of a homodromous current, then, is positive polarisation, both absolute and relative. The heterodromous current, on the other hand, induces absolutely positive and relatively THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 247 negative polarisation. According to Du_ Bois-Reymond, further, heterodromous shocks induce no relatively positive polarisation, or only infinitely little (see down curve in lower part of figure). from Saxton’s. machine, he obtained only the absolutely positive _ polarisation - effect. This he accounted for by supposing the relatively nega- tive polarisations in both directions to cancel each other; the heterodromous positive to be so small as to be practically negligible ; and the homodromous posi- tive. therefore to be alone effective. Du Bois-Reymond failed to recognise the element of excitation. in. these nomena. . What he positive polarisation has been shown by subsequent workers to be due to local polar ex- citation. But the question as to how polarising-currents in both directions could give rise to a_ single-directioned responsive effect has not up to the present, so far as I am aware, been explained fully and satisfactorily. The ex- phe- calls On sending congruent wireless currents Fic. 157. Diagrammatic Representa- tion. by Du Bois-Reymond for Ex- planation of Electrical Response in Organ of Torpedo. - The natural discharge is here supposed to be from below to above. A ’ homodromous current + (upper half -of figure) is supposed to, induce two opposite polarisations, positive » and negative. The resultant, repre- sented by shading in "figure, is absolutely and relatively positive. A heterodromous current |, on the other hand, is regarded as inducin a resultant absolutely positive and relatively negative polarisation (lower part of BEUrE ja: periments carried out on leaves, which I am sidan to describe, will, however, throw much light on this subject. It has already been shown, from anatomico-physiological considerations, that there are certain leaves which approxi- mate to the character of single plates of such electrical organs 248 COMPARATIVE ELECTRO-PHYSIOLOGY as that of Zorpedo. One such leaf, already mentioned, was that of Pferospermum. When induction-shocks are sent in both homodromous and heterodromous directions through such a leaf, between upper and lower surfaces, the leaf being, it is understood, in a normal condition, a responsive current is found to be evoked, always in one direction—that is to say, from the lower or anterior to the upper or posterior surface. This is strictly parallel to the electrical reaction observed by Du Bois-Reymond in Zorfedo. That this result is really due to the excitatory effect is proved by the fact that the same is found to occur when other forms of stimulation are used. Thus, if we place the leaf of Coleus aromaticus within a surrounding thermal helix, suc- cessive thermal shocks, acting simultaneously on both surfaces, give rise to responsive currents which are, as in the last case, Fic. 158. Photographic Records from the lower anterior to the pete silat Site se Seat upper posterior surface. Fig. 158 ae te Thema Pee gives a series of such responses. Resultant responsive current from From the fact which has already more excitable anterior toless been fully established, that on sa rca a the simultaneous excitation of two points the responsive current is always from the more to the less excitable, it is quite clear that in the present case it is the lower or anterior surface of the leaf which is the more excitable. These responsive currents, obtained under a non- electrical form of stimulus, and similar to those evoked by electrical shocks, completely demonstrate the fact that the result is brought about, not by polarisation, either positive or negative, but by the afferential excitability of the tissue itself. The response of electrical organs in general, then may be summarised in the following law: The excitatory discharge is determined by the physiological anisotropy of the organ, its definiteness of direction being deter- THE LEAF CONSIDERED AS ‘AN ELECTRIC ORGAN 249 mined by the fact that the responsive current is always from the more to the less excitable of the two surfaces. Referring once more to the definite-directioned _after- current which we have seen to be induced as the result of polarising-currents, whether homodromous or heterodromous, it is now clear that these currents act as an _ electrical form of stimulus. The intensity of the after-current here seen in the galvanometer, however, is not wholly due to the excitatory electro-motive change, but in part also to physical polarisation, which is added to it algebraically. Thus, an exciting homodromous shock gives rise to an electrical after-effect, in which the excitatory current is opposed by a counter-current of negative polarisation. Under a hetero- dromous shock, on the other. hand, the excitatory electrical change becomes summated with the negative polarisation, which is now in the same direction as itself. In these cases, though the preponderating nature of the excitatory effect determines the definite direction of the after-effect, yet it is difficult to know how much of the latter is actually due to excitatory action as such, and how much to ordinary polarisation helping or opposing this. Very much greater complexities ensue again in practice rom the difference between anodic and kathodic actions on the two unequally excitable surfaces. In Torpedo, for instance, according to Du Bois-Reymond, the electrical organ responds better to a homodromous than to a heterodromous exciting current, while in J/alepterurus, according to Gotch, the reverse is the case, the heterodromous being more efficient than the homodromous. Such diversity of results is prob- ably to be accounted for by the considerations to which I have referred. If we take, tor example, the simplest case, that in which the anterior surface is more excitable than the posterior, and if we suppose an induction-current of moderate intensity to be sent in a homodromous direction, we may assume that Pfliiger’s Law—the kathode excites at make, and the anode at break—will hold good. We shall here, for the sake of 250 . COMPARATIVE ELECTRO-PHYSIOLOGY simplicity, neglect any effects that may accrue from anode- make and kathode-break. Under a homodromous induction- shock, then, two different excitatory electrical changes will be induced, on the lower and upper surfaces respectively, the consequent currents through the tissue being in opposite directions. On these, moreover, will be superposed again the polarisation-current. Calling the effect induced by anode- break as A, and that of kathode-make as K,, we shall obtain a resultant consisting of A,on the more excitable anterior surface, mznus K,, on the less excitable posterior, mznxus the negative polarisation-effect. Under a heterodromous shock, on the other hand, we shall have K,, on the more excitable anterior surface, mznus A’ on the less excitable posterior, plus the negative polarisation-effect. Even this, however, does not exhaust the possibilities of complication. _ For I shall show in a subsequent Chapter, and have already shown elsewhere, that under a high E.M.F. Pfliiger’s Law does not apply. The relative excitatory values of anode and kathode may indeed undergo one or more reversals, according to the intensity of the acting electro-motive force. Thus, under a moderately high E.M.F. in what I have designated the A stage, both the anode and kathode are found to excite at make, and either kathode or anode at break. In the B stage, under a still higher E.M.F., it is the anode which excites at make, and the kathode at break. It will thus be seen what a number of complicating factors may be present when an organ is excited by currents of varying direction and intensity. If, then, we wish to study the purely excitatory reaction of an organ, as dependent solely upon its individual characteristics, uncomplicated by defects inherent in the method of excitation, we must see first that the applied stimulus is equal on both surfaces, and, secondly, that such factors as are not excitatory—that is to say, negative or counter-polarisation—are eliminated. These ends may be accomplished by subjecting the responding organ to symmetrical and alternating equal and opposite shocks, THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 25I following each other in rapid succession. For the resultant negative polarisation will in practice be neutralised, if the primary polarising currents are similar, equal, and opposite. The stimulus applied on the two surfaces, moreover, will be equal, if the two rapidly succeeding and opposite-directioned shocks be so symmetrical as to be interchangeable. Which- ever may. be the factor of excitation will then act equally on both surfaces. The response, therefore, will now be determined solely by the natural difference of excitability as between the - two surfaces. | It has been said that in order to accomplish these experi- mental conditions, the two opposite shocks should be equal in intensity and in point of time-relations. An ordinary make- and-break Ruhmkorff’s shock does not fulfil this condition, since the break-shock is there the quicker'and more intense of the two. Moreover, owing to the varying residual magnetisation in the iron core, successive shocks may not be equal. These defects are overcome by sending round the primary, with a constant rapidity, two equal and opposite currents in alternation. During one semi-cycle, then, the primary current varies from + C to — C,and during the next from — C to + C, and since these two changes are effected with the same rapidity, the induced currents are. symmetrical, equal, and opposite. | Such reversal of current is accomplished by means ofa rotating reversing-key. The key R is wound up against the tension of a spring S, being maintained in this set position by the electro-magnet E, acting on the armature. When the current in the electro-magnet is broken, the alternating double shock from the induction coil I is passed through the experimental leaf L, by means of non-polarisable electrodes N, N,. In the case just described the sequence of the current through the. primary coi] was, say, right-left-right. In the next experiment, by means of the Pohl’s commutator, K,, this sequence may be made left-right-left (fig. 159). Empioying this method, I have carried out rheotomic observations for determining the time-interval after the shock fr } \ { 252 COMPARATIVE ELECTRO-PHYSIOLOGY at which the E.M.F. attained its maximum. The general arrangement here is similar to that described in Chapter IV. (cf. fig. 37). C is the compensator by which any existing electro-motive difference is compensated at the beginning of each experiment. The striking-rod A breaks the current in the electro-magnet E, by which the rotating reverser R is actuated, which brings about equal and opposite shocks to the leaf. The galvanometric after-effect, at any short All lis = Tc = bt > Sh on See Fic. 159. Experimental Arrangement for Rheotomic Observations A, B, striking-rods attached to revolving rheotomic disc; K,, key for electro-magnetic release of rotating reverser R; K,, key for unshunting the galvanometer when pressed by rod, B, for a definite period; ky, key for preliminary adjustment ; E, electro-magnet with its armature by which rotating reverser, R, is set against antagonistic spring, S ; K,, Pohl’s commutator; Cc, compensator; P, primary, and 1, the secondary, of the exciting induction-coil ; N,, N,, non-polarisable elec- trodes, making electrical contacts with posterior and anterior surfaces of leaf. interval after excitation, is obtained by the un-shunting of the galvanometer, caused by the striker B impinging against the key K, (fig. 159). We have seen that, owing to the presence of various complicating factors, as well as to the occurrence of negative polarisation, successive responses to homodromous and heterodromous shocks are unequal. By the employment of equi-alternating induction-currents, how- THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 253 ever, we obtain true excitatory effects, unmodified by any such elements of uncertainty. In order to show how perfect the results obtained by this method become, I give here (fig. 160) the records of two successive excitatory responses obtained from a leaf of Bryophyllum calycinum, the responsive current being from the lower or anterior surface to the upper or posterior. In this mode of stimulation, by equal and opposite shocks, as already said, no advantage is given to either surface over the other. Neverthe- less, I thought it well to take two successive records under shocks, in which the alternating currents in the primary circuit were first right-left-right, and then left- right-left. In the electrical organ of TZorpedo Gotch found the maximum electromotive change to be attained in about ‘oI second after the application of the excitatory shock. In leaves, again, I find the rapidity with which the maximum effect is at- . Fic. 160. Records of Two Successive tained to depend on the Responses in Leaf of Bryophylium nature of the tissue. and calycinum under Equi-alternating ‘ Electrical Shocks also on the intensity of the exciting shock. In sluggish specimens this may be as long as ‘2 second. It should be remembered that in the case of mechanical stimulation of moderate intensity also, this period was, similarly, about *2 second (p. 51). With very vigorous leaves of Vymphaea alba, however, and employing a stronger electrical stimulus, the maximum effect was 254 COMPARATIVE ELECTRO-PHYSIOLOGY attained in a much shorter time —that is to say, in about ‘03 second. I give below a table showing the rheotomic observations made on such a leaf at gradually increasing intervals after the exciting shock. It should be remembered TABLE OF RHEOTOMIC OBSERVATIONS. Mean interval after the shock | Galvanometric deflection | ‘ol of a second ‘20 divisions | °03 9° 99 | 63 99 | "O§ 9° > I 7 Je | °O7 3° +] I 5 9 | I 99 39 20 99 °2 9° bi] 9 23 | ‘ 99 ” 8 oe) | *h 29 rm) 5 ? that the recording galvanometer was un-shunted for ‘ol second, The curve given in fig. 161 has been plotted from these results. The maximum electro-motive change took place, as already pointed out, in ‘03 second after the application of stimulus. This curve shows multiple apices, as was also the case, it will be remembered, after a strong mechanical stimulation (cf. fig. 40). This point will be referred to in greater detail in the next chapter. In the course of half a second after the shock, the . excitatory electro-motive change had subsided to about one-twelfth of the maximum, Fic. 161. Response-curve from It has been said that the scp teeer epee onLeaf excitatory current depends for Ordinate represents galvanometer its definiteness of direction on deflection; abscissa,: time in the physiological anisotropy of hundredths of a second. the organ. In_ those leaves in which the physiological differentiation of the upper and lower surfaces is not strongly marked, the differential I CU THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 255 excitability of the two is liable to undergo reversal, under the changing conditions of age, season, and fatigue induced by previous stimulation. In the leaf of Pzerospermum, however, which I have here taken as the type corresponding with Zorpedo, the normal differential excitability is generally very persistent. Here the excitability of the posterior surface, which is leathery, is slight, and practically negligible. But the anterior surface, with its rich and prominent venation, is highly excitable, The excitatory discharge of such a leaf is thus from the anterior to the posterior. I give in fig. 162 a series of its responses to equi-alternating electric shocks, It will be seen that these are very uniform, and exhibit practically no signs of fatigue. We have thus found a vegetable organ whose re- sponses are exactly parallel to those of a single plate of the electrical organ of Zorpedo and its type. We shall next ens study the responsive pecu- TiC; 162. Series of Responses, given liarities of the vegetable organ folium to Stimulus of Equi-alternat- Base responses correspon d ng eectneal Shocks at Intervals ot with those of the organ of Malepterurus. \t has been mentioned that the posterior surface of each single element of this electrical organ is regarded as consisting of a glandular, rather than a muscular, modification. Among corresponding leaf-organs, then, the carpellary leat of Dzllenta indica might, as we also saw, be taken as the ‘type, its posterior surface: being glandular. Or the analogy will be still more perfect if we take as the vegetal type the pitcher of Vepenthe. Here the internal or posterior surface is richly provided with glands. -The next point to be deter- mined is whether, in these cases also, on excitation the responsive current is from the posterior surface to the anterior, as in the electrical element of Madepterurus. And on sub- jecting them to equi-alternating electrical shocks, I found 256 COMPARATIVE ELECTRO-PHYSIOLOGY this to be the case. The responsive current here flowed from the glandular posterior to the non-glandular anterior surface. From this experiment we see that a glandular surface is exceptionally excitable, a conclusion which will be found to be supported by the numerous experiments on glandular organs in general, to be described in Chapter XXIV. I give in fig. 163 a series of photographic records, obtained on excitation of Dzllenza indica. In the next record (fig. 164) are seen the responses given by the pitcher of Wepenthe. Fic. 164. Photographic Record of Normal Responses given by ; ic Record of Re- ; saat Fic. 163. suis ge Gy rae Pitcher of Mepenthe, under Equi- sponses 0 a alternating Electric Shocks Natural current from posterior to an- ‘ ene terior, and responsive current from sie scare aca woes harden anterior to posterior surfaces. hg nae he donee glandular surface. Note ten- dency to multiple response. An interesting fact to be noticcd in the latter is the tendency to multiple response. ' Similar results were also obtained on taking any single scale of the bulb of Uvzclzs lily about the time of flowering. In each of these the lower or outer surface is invested with a more or less dry and glistening membrane, while the upper or concave is moist and glanduloid. The moisture observed inside each scale is in fact exuded from this inner surface. On subjecting one of these scales, then, to the electrical THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 257 excitation already described, it is found that a very strong responsive current is obtained, whose direction is, as in the last case, from the glanduloid to the non-glanduloid surface. The effect of the serial arrangement, again, in enhancing the electro-motive force—as seen in the pile-like arrangement of the electrical organ of fishes—may be exemplified, in the parallel instance of the plant-organ, by means of the superposed scales of the bulb, as found in nature. The bulb may be divided longitudinally into halves, of which the right-hand half is mounted, for experiment, with the scales vertical. It will be understood that all the glanduloid surfaces here face the left, while the non-glanduloid are turned to the right. Thus the left aspect of this pile corresponds to the head aspect of the organ of JZalepterurus. The latter, on excitation, responds by a current in the direction of head to tail—that is to say, from glandular to non-glandular ; and similarly, in the pile-like half-bulb of Uricls lily, the responsive current is from glanduloid to non- glanduloid—that is to say, from left to right. Another interesting way to perform the same experi- ment is without making any section of the bulb. We take a bulb of Uvzclzs, with the peduncle rising out of the middle. When this hollow peduncle is cut across, it allows of an electrical connection being made with the centre of the interior of the bulb. An equatorial belt makes the second, or outer, connection. On subjecting this to equi-alternating shocks, the resulting response will be found to be from the inner surface to the outer, through the numerous intermediate scales, the individual effect in each being concordant and additive: . We have thus seen how the response of a leaf gives us an insight into the action of a plate of an electrical organ ; how the differential excitabilities of the two surfaces give rise on stimulation to an induced E.M.F. as between the two; how a nervous and indifferent-tissued surface will give rise toa response in one direction, and a glandular and non-glandular S 258 COMPARATIVE. ELECTRO-PHYSIOLOGY in the other; and finally how, by a serial arrangement, the terminal electro-motive effect becomes enhanced. The light thus thrown on the two types of response, known to occur in the electrical organs of fishes, is evident. Further con- siderations, relating to the theory of electrical organs, will be given in detail in the next chapter. EE a i et EA ee CHAPTER XX THE THEORY OF ELECTRIC ORGANS Existing theories—Their inadequiacy—The ‘blaze-current’ so called— Response uni-directioned, to shocks homodromous or heterodromous, characteristic of electric organs—Similar results with inorganic specimens — Uni- directioned _response due to differential excitability—Electrical response of pulvinus of | Mimosa to equi-alternating electric shocks—Response of petiole of Musa— Of plagiotropic stem of Cucurbita—Of Eel—The organ-current of electric fishes—- Multiple responses of electrical organ — Multiple responses of Biophytum. ONE of the most perplexing problems in connection with the phenomena of electrical organs is the question as to whether the activity of such organs is specific—that is to say, peculiarly characteristic of them—or-falls into line with the other electro-motive reactions observed in animal tissue. Many arguments have been brought forward for and against the identity of these phenomena with the excitatory reactions of the nerve and muscle. : From the experimental results which I have Aéecribert however, it would already appear that such reactions as these of the electrical organ are not specifically characteristic, even of the animal structure, but may equally well be observed in plant tissues. It is therefore essential, if we are to determine that basic reaction which is common to all alike, that we should find a wider generalisation than has hitherto been contemplated. This basic reaction, as we have already seen, depends upon the differential excitability of an anisotropic organ, and this aspect of the case we are now. about to study in greater detail. Before doing this, however, we shall briefly glance at various theories which have been suggested, but are generally admitted to be inadequate. | $2 260 COMPARATIVE ELECTRO-PHYSIOLOGY Bell, for example, thought it might be possible to explain ‘the discharge of the electrical organ solely by the negative variation of the nerve-current, concomitant with innervation. In this arrangement the dorsal surface of the electrical plate (of Zorpedo) would, at the moment of innervation, become positive, the ventral surface negative, as actually occurs.’ As against this, it was pointed out by Du Bois-Reymond that this hypothesis in the first place predicates the existence of a current of rest, caused by the ‘natural’ cross-sections (acting like artificial sections) of the nerves in the plates, and accordingly heterodromous to that of the discharge. Instead of this permanent current—which must correspond in E.M.F. with the discharge, if the nerve-current is to disappear in the negative variation—there is only an inessential P.D. during rest, and the resulting ‘organ-current’ is always homodromous with the discharge.! | Even had these objections not existed, however, Bell’s hypothesis would have failed to explain the electrical action of Malepterurus. Du Bois-Reymond himself tried to explain the action of the electrical organ, ‘not by the negative variation of the nerve current, but by a process in the electrical plates transformed from muscles, comparable with the negative variation of the muscle-current, as set forth from the standpoint of the pre-existence theory.’ Here, however, it is perhaps sufficient to point out that the pre-existence theory, on which the hypothesis was based, is now held to be invalidated. There remains only the Chemical, or Alteration Theory, which associates all electrical changes with the corresponding chemical processes of assimilation and dissimilation. But it has not been made clear in what way these can bring about the characteristic discharge of the electrical organ. There is another point, not altogether unrelated to this subject, which may be dealt with on the present occasion, I allude to the so-called ‘blaze current’ of Dr. Waller. By this is meant an after-current in the same direction as the ' Biedermann, Z/ectro-Physiology (English translation), vol. II. p. 462. THE THEORY OF ELECTRIC ORGANS 261 exciting current. It is, in, fact a new name for that phe- nomenon which Du Bois-Reymond indicated as ‘ positive polarisation-current. Du Bois-Reymond had also shown that this particular effect was most markedly exhibited when the functional activity or ‘livingness’ was at its highest. Under opposite conditions, again, it would disappear. The intensity of this homodromous after-effect was thus dependent on the degree of vitality of the tissue under experiment. Hermann and Hering, however, afterwards showed that what Du Bois-Reymond called ‘ positive polarisation’ was in reality excitatory reaction. These excitatory effects are known to be caused by either the anode or the kathode!; and I have, in the course of the last chapter, demonstrated the fact that it is the differential excitability of a tissue which determines such uni-directioned response. It is difficult, therefore, to see the necessity of a new name for these phenomena. Dr. Waller himself, however, offers the following as an important reason : ‘The great mass of living things, whatever else they may give and take from their surroundings, take oxygen and give carbonic acid ; they may live slowly or they may live quickly—sluggishly smoulder or suddenly blaze. A muscle at rest is smouldering: a muscle in its contraction is blazing ; the consumption of carbohydrate and the production of CO,, never absolutely in abeyance, even in the most profound state of rest, are sharply intensified when the living machine puts forth its full power, and there is then a sudden burst of heat, and an electrical discharge... .’? This amounts to another way of saying that the cause of the excitatory galvanometric effect is some explosive dis- similatory change, a view which I have already shown in 1 ‘Within a given ‘ physiological ” range of strength of current the negative kathodic must, equally with the positive anodic, be designated an ‘“‘irritative ” after-current, due entirely to ‘‘ polar current-action.” ’—Biedermann, Zéctro- Physiology (English translation), vol. I. p. 448. | * Waller, Signs of Life, p. 74. 262 COMPARATIVE ELECTRO-PHYSIOLOGY previous chapters to be quite untenable. I shall presently describe experiments which will further show that galvano- metric responses, not to be distinguished from this, take place when there is no possibility of any consumption of carbo- hydrates or production of CO,. , The fact, however, that the excitatory after-effects de- scribed, disappear on the death of the tissue, has led Dr, Waller to put forward the generalisation that this so-called ‘blaze-current’ is the final distinction between living and non-living matter. His formula, with regard to this, is, ‘ If the object of examination exhibits blaze in one or in both directions, it is living.’ He admits, nevertheless, that a sub- stance which is undoubtedly living will not always exhibit the ‘blaze-current.’ -But it is contended that the occurrence of ‘blaze’ is an undoubted ‘sign of life, and that thus a strong distinction is to be made between vitalistic and non-vitalistic, or physical, reactions. Hence, as there is supposed to be no excitatory reaction possible in non-living or inorganic matter, it would follow that electrical shocks passed through such a substance, in either direction, should give rise only to those counter-polarisation currents which are known to physicists. In such cases, on reversing the direction of the shock, the direction of the after-current is also reversed ; but in the living substance, it is maintained, the case is quite different. If the direction of the shock be here reversed, the after-current will still appear, with direction unchanged, because in this latter instance it is not generated by the shock, but is, on the contrary, an inexplicable function of the living material, set in action by it, in the same way as a loaded gun is fired by pulling the trigger. The possibility of obtaining from the given substance such a uni-directioned after-current, independently of the direction of the shock, is thus to be taken as the test and token of ‘ vitality.’ _ Now, while it is certainly true that.the domain of physio- logical phenomena has not yet been so thoroughly explored as that of the physical, it is nevertheless equally true that no one could venture to claim that even physical phenomena THE THEORY OF ELECTRIC ORGANS 263 had up to the present been exhaustively studied. It is, then, somewhat hazardous to declare that because a particular phenomenon has not yet been observed to occur in inorganic matter, it is by that fact demonstrated to be hyper-physical in its nature, and must be relegated to the different and mystical category of the exclusively vitalistic. The very foundation of such a statement would be swept from under it, the moment it was shown that the same phenomenon followed, under the same circumstances, in conditions which were admitted to be purely physical. I have shown, it will be remembered, in the previous chapter, that the uni-directioned response to electrical shocks in either direction was due to the differential excitability of the structure. The response of any aniso- tropic organ would always be from the more to the less excitable, the more excitable becoming relatively galvano- metrically negative. There may here be various cases of excitation, all giving results of the same type, say, a respon- ‘sive current from B to A. The first is that in which, on excitation, both B and A become galvanometrically negative, A being the less so of the two. In the second case, the excit- ability of A being slight, or negligible, B alone becomes negative. And in the third ‘case, excitation induces positivity of A and negativity of B. In all these cases the relative negativity of B being greater, the responsive current will flow from B to A. The resultant current is made up, : in the first case, by subtracting the galvanometric negativity of A from that of B; in the second case, it consists of the galvanometric negativity of B, that of A being zero; and in the third case, it is produced by the addition of the effect at A to that at B. Examples of the last of these will be found in certain animal and vegetable skins, described in Chapter XXII. These being the conditions, then, for the induction of the uni-directioned responsive current, it appeared to me probable that the same result could be obtained with inorganic substances, provided that the specimen were so 264. COMPARATIVE ELECTRO-PHYSIOLOGY prepared as to be anisotropic, one side having a greater potentiality of galvanometric negativity under excitation than the other. In that case, further, it was clear that the strongest resultant current would be obtained, if one surface of the structure became galvanometrically positive, and the other negative, on excitation. I have already stated, in Chapter I., that different inorganic substances give electrical responses of opposite signs. Thus the response of lead is positive, while that of brominated lead is negative. If, then, we take a lead wire A B, clamped in the middle at C, as represented in the upper diagram (fig. 165), and stimulate the right-hand end B, say by mechanical vibration, a responsive - current will be induced, Fic. 165. Responsive Currents in Lead Wire which will flow. to- Upper figure—Excited wire, galvanometrically : positive. Simultaneous excitation of both wards the stimulated, ends balance each other ; resultant response B thus becoming gal- ‘-Z6ro. . : : Lower figure—Left portion, lead wire, right vanometrically posi- portion, brominated lead wire, shown as tive. The same will shaded. Response of first positive, of second A negative. Simultaneous excitation of the be the case with 4, erg andes, fella reponse which“ on stimulation. When both A and B are simul- taneously stimulated, it is evident that the two responsive currents, being antagonistic, will cancel each other. But if the right-hand half B’ of the wire consist of brominated lead (lower diagram, fig. 165), while the left-hand half a’ is of lead like that used in the first case, then stimulation of B’ will cause a responsive current to flow away from the right-hand excited end, B’ thus becoming galvanometrically negative ; A’, on the other hand, will give rise to a positive response towards the excited. Simultaneous excitations of A’ and B’ will not then be antagonistic, but additive in their effects. The resultant response will thus be from the negative b’ to A, in the same direction as the break shock, which was the actual result. In any case, whatever may have been the cause of this, it is clear that the employment of such unequally exciting shocks of make and break would be fatal to any attempt to determine accurately the natural difference of excitability as between the two points. I may state here, that when I have employed absolutely equal alternating shocks on a specimen DETERMINATION OF DIFFERENTIAL EXCITABILITY 279 of nerve, I have obtained no resultant deflection whatever, showing that such shocks induce exactly equal excitations in an isotropic tissue. But if the excitability of one of the two points be first abolished by killing, then a definite resultant responsive current is obtained, from the excitable living to the inexcitable dead. So perfect were in fact the results secured by means of these equi-alternating electric shocks, that I was desirous not only to detect, but also to record photographically, the responses thus obtained. In this a certain difficulty is experienced, inasmuch as the alternating shocks are apt to render the recording spot of light tremulous, and thus to spoil the photographic im- pression. This may, however, be overcome by making the alternation frequency so high, in reference to the period of the needle or suspended coil of the galvanometer, that the unsteadiness of the deflection ceases. I shall now describe the practical means employed to obtain equi-alternating shocks of any frequency that may be desired. This I have been able to do in several ways, and, among others, by using a Rotating Reverser. This consists of an ebonite disc, on the periphery of which there are strips of metal of equal breadth, and separated from each other by equal distances. The odd strips (1, 3, 5, and so on) are connected together and led to a metallic ring on the left of the disc. The same is done with the even strips, which are led to the right. The two electrodes of a battery are led through a key, K, to these two metallic rings and are con- nected with them by means of brushes. Thus one ring, with all the odd strips, is connected, say, with the positive, and the other, with all the even strips, with the negative pole of the battery. The current is led off by a second pair of brushes, placed diametrically opposite to each other on the disc, in the primary circuit, P, of an induction coil (fig. 171). Let us suppose the upper brush to be connected with an odd strip, the lower will then be connected with an even. The current in the primary coil now flows in one direction. When the disc is rotated, so as to bring the next pair of strips in 280 COMPARATIVE ELECTRO-PHYSIOLOGY contact with the brushes, the upper will then be connected with the even strip and the lower with the odd. Thus the direction of the current will be reversed, and rapid rotation of the disc will give rise to equi-alternating currents in the primary of the induction coil. This will in turn induce equi-alternating induction currents in the secondary, the intensity of which can, as already said, be varied within wide limits by appropriate changes of distance between the primary and the secondary. The number of strips in the apparatus used is fifty, and when the disc is rotated, by Fic. 171. Method of Direct Effect of Excitation by Equi- alternating Shocks R, rotating reverser, in circuit with primary coil, P. Duration of stimula- tion determined by metronome, M._ 8, secondary coil in series with ' specimen and galvanometer. means of an electrical motor, at a rate of one revolution per second, there will be fifty alternations of current in a second. The duration of the application of the stimulating shock to the tissue is regulated by a metronome, which completes the primary circuit for a definite short length of time. When the metronome, M, is so adjusted as to complete the circuit for *5 second, then a stimulus of that duration will be imparted at each stroke. A second interrupting key, not shown in the figure, is included in the circuit. When this key is closed, a single beat of the metronome gives a stimu- lating shock of *5 second’s duration. ‘The key is now opened DETERMINATION OF DIFFERENTIAL EXCITABILITY 281 for one minute for recovery. In this way, records of response and recovery are obtained, at intervals, say, of one minute. Another very effective means of producing equi-alter- nating shocks is by the employment of an alternating- current dynamo, driven by an electrical motor, M (fig. 172). The alternating current is led to the primary of a Ruhm- korffs coil in the usual manner. The motor is driven by an electrical supply from the street mains, its speed being adjusted by a regulation of the current, which is effected by TO THE MAIN Fic. 172. Excitation by Equi-alternating Shocks M, motor, rotating armature of alternating-current dynamo, D; R, liquid rheostat, in circuit with street-mains, for regulating speed of rotation of motor; Pp’, idle coil; P, primary coil; I, resonating index; s, secondary coil, in series with specimen and galvanometer. Duration or excitation determined by pressure of key, K. an electrolytic rheostat, R. As the dynamo is provided with a permanent horse-shoe magnet, the intensity of the alter- nating current is determined by the speed of rotation of its armature. If the speed be kept always constant, the number of alternations will also be constant, and the ex- citing value of the electric shocks will depend simply upon the distance of the primary from the secondary. It is thus possible day after day to use the same intensity of stimu- lation, and thus to compare the relative excitabilities of 282 COMPARATIVE ELECTRO-PHYSIOLOGY different tissues. The constancy of the speed of rotation of the alternating-current dynamo is secured by means of the resonating index, I. This consists of a short steel spring with a long index. When the frequency of alternation is the same as the natural period of vibration of the spring, the resonator is thrown into strong sympathetic vibration. At first the rheostatic resistance, which determines the speed of the motor, is made slightly too large. The movable plate is now gradually brought nearer, till the proper speed has been arrived at, and this point is at once indicated by the induced vibration of the resonator. | . A further difficulty has to be overcome in the main- tenance of the uniformity of speed. When the open circuit of the alternating dynamo is closed, by the interposition of the primary of the Ruhmkorff’s coil, the speed undergoes a sudden diminution, owing to the work which the dynamo has now to perform. In order to avoid this fluctuation, then, the dynamo circuit is kept closed by means of an idle primary coil, P’, which is a duplicate of the primary, P, of the Ruhmkorff’s coil. When the key, K, is pressed, the alter- nating current is transferred from P’ to P. There is thus no fluctuation in the speed of the dynamo, and the duration of the closure determines that of the stimulus. I may mention here, that instead of employing a separate motor to drive the alternating-current dynamo, I have sometimes used, with equal success, a motor transformer, giving rise to alter- nating currents. It is easy to construct a very compact and portable form of this latter apparatus. In this manner we may apply uniform stimuli of equi- alternating shocks at regular intervals of time, say of one minute. The usual preliminary test of the successful elimination of all sources of disturbance may here be made in the following way. The kaolin ends of the non-polaris- able electrodes are connected with each other, without the interposition of a specimen, and alternating shocks from the secondary are passed through the circuit. These should give rise to no deflection in the galvanometer. It may be Seg ON ee ie ae a. DETERMINATION OF DIFFERENTIAL EXCITABILITY 283 said here that I use a D’Arsonval type of galvanometer, in which, instead of a suspended needle, we have a suspended coil. There is thus here not even the remote contingency of disturbance which might arise from the demagnetisation of the magnetic needle. Having thus tested, by null action, the symmetry of the electrodes and the galvanometer, the differentially excitable tissue, say the sheathing petiole of Musa, is interposed, with its concave and more excitable surface upwards. On now: applying excitation by equi- alternating shocks, the responsive current will be found to flow downwards, from concave to convex, giving a deflection of the galvanometer, say to the right. And this deflection will continue to be to the right, even if the battery current (fig. 171) be reversed by means of key K. The direction of the excitatory current, moreover, depending solely, as it does, on the relative excitabilities of the two surfaces of the specimen, will remain constant, even if the connections with the secondary coil, S, be reversed. The zinc rod, N, of the non-polarisable electrode in connection with the concave surface (fig. 172) has thus, up to the present, shown induced galvanometric negativity, the galvanometric deflection being to the right. But if we exchange the zinc rods of the non- polarisable electrodes, it will then be N’ which will be con- nected with the more excitable concave surface, and it will now be this electrode N’ which will show galvanometric nega- tivity. This reversal of the galvanometer deflection with the reversal of the electrodes affords additional confirmation of the greater excitability of the concave surface of the specimen of Musa. | In these experiments the existing current of rest may be balanced previously by a potentiometer. But this is not absolutely necessary. I give below a series of records obtained with a specimen of the sheathing petiole of Musa (fig. 173), in which we know the inner or concave surface to be more excitable than the outer or convex. The responsive current is seen under this form of electrical stimulus, as we found to be the case under mechanical and 284 COMPARATIVE ELECTRO-PHYSIOLOGY thermal stimulation, to flow from the more excitable concave to the less excitable convex. In order next to demonstrate the physiological character of these responses, I subjected the tissue to the action of chloroform, and the record in the second part of the figure shows the consequent Bepresion of the response. The great delicacy and pliability of this mode of applica- tion of stimulus enable us to attack many difficult problems, on the difference of excit- ability between two points in a tissue, with perfect ease. To how many distinct in- vestigations it can be suc- cessfully applied will be set forth in detail in succeeding chapters. As there is nothing to prevent the two exploring . electrodes from being applied on any two points, however distant, of the same organism, ‘Fic. 173. Photographic Record of Re- sponse of Petiole of usa to Equi- alternating Electric Shocks, before and after Application of Chloroform. it is seen that we have here a means of determining, not only the differential excit- ability of any two points of the same organ, but also that of any two organs of the same specimen. For the present I shall, however, content myself with giving a few instances only in illustration of the ex- treme delicacy of this method in detecting physiological differences as between two points. We shall first turn our. attention to those physiological modifications which are due to the a-symmetrical action of the environment on the organism, and here we shall select the case of the plagiotropic stem of Cucurbita. We have seen that in the recumbent stem of this plant the tissue of the upper side is rendered relatively fatigued by the con- tinuous action of sunlight, and thus becomes permanently less excitable than the lower side. We have also found that DETERMINATION OF DIFFERENTIAL EXCITABILITY 285 while the natural resting-current was from the less excitable upper to the more excitable lower side, the responsive cur- rent under mechanical stimulation was in the opposite direc- tion—namely, from the lower to the upper (p. 112). Using now the electrical form of stimulus, we obtain results which are identical. Fig. 174 gives a series of such responses under equi-alternating electrical shocks. Curiously enough, as pointed out in the last chapter, I have detected a similar plagiotropy in the case of the eel. The head of the fish was cut off, and voluntary action thus eliminated ; electrical connections were then made, after a period of rest, with the dark dorsal upper surface, and the colourless skin of the ventral or lower. A natural current was now found to flow from the upper Fic. 174. Photographic Record of Responses of Plagiotropic Fic. 175. Electrical Responses of Stem of Cucurbita to Equi- Eel to Equi-alternating Electrical alternating Electric Shocks Shocks Direction of responsive current from Current of response from ventral ventral to dorsal surface. surface to dorsal. surface to the lower, as in the case of the plagiotropic stem of Cucurbita. Electrical excitation was now applied, and the result was a responsive current from the more excitable lower to the less excitable upper surface again, as in the case of Cucurbita. In fig. 175 is seen a series of records in illustration of this. Another investigation which I thought might be interest- ing had reference to the variegated colouring of certain foliage leaves, A striking example of this is found in the 286 COMPARATIVE ELECTRO-PHYSIOLOGY tropical elephant creeper (Pothos), the rich green of which is barred by longitudinal streaks of milk-white. This dis- tribution of colour is found even in the youngest and most vigorous leaves. The question whether such colouring was accidental or associated with physiological differences could, I thought, be determined by the delicate mode of investiga- tion which was now at my disposal. On making electrical . connections, then, with the green and white portions of a leaf, I found that the natural current of rest was from white to green through the tissue, and, on further testing the differ- ential excitability in the usual manner, the responsive current was observed to flow from the green to the white. This showed that pallidity was here associated with a depressed physiological condition, | CHAPTER XXII RESPONSE OF ANIMAL AND VEGETAL SKINS Currents of rest and action—Currents in animal skin—Theories regarding these —Response of vegetal skin—Stimulation by Rotary Mechanical Stimula- tor—Response of intact human skin—Isolated responses of upper and lower surfaces of specimens—Resultant response brought about by differ- ential excitability of the two surfaces—Differences of excitability between two surfaces accounted for— Response of animal and vegetal skins not essentially different—General formula for all types of response of skin— Response of skin to different forms of stimulation gives similar results— Response to equi-alternating electric shocks : (1) Method of the After Effect ; (2) Method of Direct Effect—Response of grape skin—Similar response of frog’s skin—Phasic variation of current of rest induced as result of successive stimulation in (a) grape skin ; (4) frog’s skin ; (c) pulvinus of Mimosa—Phasic variation in autonomous mechanical response of Des- modium gyrans—Autonomous variation of current of rest—True current of rest in skin from outer to inner—This may be reversed as an excitatory after effect of preparation—Electrical response of skin of neck of tortoise — Electrical response of skin of tomato —Normal response and positive after- effect — Response of skin of gecko—Explanation of abnormal response, IN this and the next few chapters it is my intention to make an inquiry into the responsive peculiarities of the skin, epithelium, and glandular tissues, alike in plant and animal. By the study of such simple cases as are found in plants, it should be possible to obtain’a clear insight into the various factors which go to make the corresponding phenomena in animal tissues so complicated and obscure as to be difficult of reconciliation with each other. It is not possible in a short space to give any but the briefest summary of the work hitherto done on this extended subject in animal physiology. All that can be attempted is to indicate some of the leading theories and_results, at the same time drawing attention to those outstanding questions which still remain open. Some of the methods which I have 288 COMPARATIVE ELECTRO-PHYSIOLOGY employed in the investigation of plant phenomena, moreover, have proved so highly satisfactory that records will be given of the results obtained by their means in the case of animal tissues also. And this will, I hope, show the great reliability and simplicity which it is thus possible to intro- duce into the investigation as a whole. With regard to the electrical effects in animal skin, epithelium, and glands, the inquiry resolves itself into the determination of, (1) the direction of the current of rest ; (2) that of the excitatory current ; and, lastly, (3) a consideration of theories regarding these. The first of these, the current of rest, was found by Du Bois-Reymond and Engelmann in the skin of frog to be ‘ingoing ’—that is to say, passing from the outer surface to the inner. Hermann also found a similar current in the skin of eel. He regarded the source of electro-motive action as lying in the partial mucin-metamor- phosis of single cells. From the fact that in the toad, where the ingoing current is specially strong, the skin glands are vigorously developed, and from the discovery by Rosenthal that in the mucous glands of the stomach the current is also ingoing, it was assumed that the observed electro-motive forces were due to the glandular nature of the tissues. The skin current of the frog and of the fish, and the glandular current of the stomach, are thus usually regarded as due to the same cause. There is, however, a serious discrepancy in this view, _ inasmuch as, while local stimulation of the upper surface of the frog’s skin induces.a positive change, a similar stimula- tion of an unmistakably glandular surface is found to bring about a negative. If then the electrical effect on the skin of frog be the same as on a glandular surface, the dis- crepancy of their responsive reactions becomes inexplicable. As regards the excitatory change, very diverse results have been recorded when stimulus has been applied indi- rectly —that is to say, through the nerve. This fact is not to be wondered at, since the responsive effects are subject, as will be shown, to numerous modifying influences. It is generally Fo a ee ee RESPONSE OF ANIMAL AND VEGETAL SKINS 289 — supposed, in the preparations made for these experiments, that it is one surface only which is electro-motive. I shall show, however, that the responsive effects are brought about by the differential excitability of the two. This response, again, is modified by relative changes induced in the two surfaces. And, in addition to these, still further compli- cations are introduced when the stimulus is indirect—that is to say, applied through the nerve. In this case, the relative excitations of the two surfaces will be determined by the particular distribution of the nerve-endings. Again, we shall see that, in an isolated preparation, the nerve itself is liable to undergo certain changes by which its trans- mitted effect may be modified even to reversal (p. 530). Thus, so long as it remains highly excitable, the transmitted effect is one of true excitatory galvanometric negativity. But with physiological depression, the conductivity of the nerve is very much lowered, and the effect transmitted becomes reversed to positivity. For all these reasons, if we wish to study the specific reactions of skin, epithelium, and gland preparations, it is better to do so by observing them under direct stimulation. Engelmann, in studying the responsive reactions to direct stimulation of frog’s skin, found a negative variation of the current of rest. Since the latter was naturally ‘ingoing,’ as regards the upper or’ epidermal surface, this meant that the responsive current was ‘outgoing.’ Reid, again, work- ing on the skin of the eel, obtained ingoing response, or positive variations of the resting-current, by single induction shocks in either direction. Biedermann, in the mucous membranes of the tongue and stomach, obtained both positive and negative variations of the current of rest, Waller, using single induction shocks in either direction, found in the digestive mucosa both ingoing and outgoing responses, the former being much predominant. Even under the simple conditions imposed by direct stimulation, then, the results obtained are seen to be in- consistent. They would appear to show both that the U 290 COMPARATIVE ELECTRO-PHYSIOLOGY responsive effects in the different preparations are different and that, even in the same preparation, they may be reversed under unknown changes of circumstances. It appeared to me, as already said, that much light might be thrown on the questions thus raised by means of an investigation carried out on plants. The most perfect method of experiment here would consist in observing the separate responsive effects on upper and lower surfaces of the preparation. Waller employed single induction shocks for this purpose, observing the after-effect. But in this case, the action of polarisation was not excluded. It would thus be more satisfactory, in order to eliminate this unknown element, to employ either a non-electrical mode of stimulus or an electrical form which would leave no resultant polarisation effect. The latter condition, as we have seen, was fulfilled by the employment of rapidly alternating currents, whose alternating components were absolutely equal. As regards the application of a non-electrical form of stimulus, both thermal and mechanical forms may theoreti- cally be employed. Engelmann and others used heated metals in the proximity of one of the electrodes, for the production of thermal stimulus. This, however, has the disadvantage of thermo-electrical variation, due to unequal heating of the two contacts. Besides this, there is also the effect of a rising temperature, which, as we have seen, is opposite to that of sudden variation, the latter alone consti- tuting the excitatory effect. I have already explained how these difficulties may be overcome by using thermal shocks in which a sudden thermal variation is made to act on both contacts at once. The resultant response thus obtained was shown to be determined by the differential excitability of the two contacts under examination. As regards the mechanical mode of stimulation, previous observers have employed pressure or friction. Such stimulus, however, is at best merely qualitative. If it be applied at the contact itself, objections may be taken to the effect, as Rae a A meh RESPONSE OF ANIMAL AND VEGETAL SKINS 291 due to, or modified by, the variation of contact resistance. ‘And if to avoid this the mechanical stimulus be applied, not at the electrode, but at a neighbouring point, the results will be quite different, according as the conductivity of the intervening tissue is great or slight. In the former case they will consist of the transmitted effect of true excitation ; in the latter of the indirect effect, whose electrical sign is the exact opposite. Fic. 176. Rotary Mechanical Stimulator Specimen of skin pinned on hinged platform which is pressed against electrodes by elastic india-rubber. Electrodes rotated by cord, c c’. S, antagonistic spring, made of elastic. Enlarged view of electrode seen to the right. T, outer fixed brass tube ; T', inner rotating tube, holding non-polarisable electrode. P, pumice-stone. A perfect method of direct mechanical stimulation has been described in Chapter III., the stimulus being vibrational. But for investigations on limp structures, such as skin, this method is not practicable, and the modification which I am now about to describe is necessary, in order to meet the difficulties of the case. The apparatus consists of a hinged platform, P (fig. 176), on which the specimen is securely pinned. The two electrodes, E and E’, rest with a definite pressure on the two points A and B, whose excitatory re- actions are to be studied. These electrodes have at their U2 292 COMPARATIVE ELECTRO-PHYSIOLOGY lower ends projecting pumice-stone cylinders of equal sec- tions, soaked in normal saline. When the electrode E is rotated, the mechanical friction induces local excitation of the point A. B may also be subjected to similar isolated excitation in the same way. In order that such successive excitations may be quantitative and uniform, it is necessary first that a definite area at A or B should be stimulated. In. other words, there must be no lateral slip. For this reason | the electrodes are passed through tubular holders which, from the description presently to be given, will be seen to allow rotation about a definite vertical axis. The extreme bases of the pumice-stone cylinders are, as has been said, of equal section. The glass electrode tube is tightly fixed, by means of a cork, inside a brass rotating tube. The latter, again, plays inside an outer brass tube, which is fixed. The inner brass tube is provided with two collars, one below and one above, by means of which rotation can take place without up or down movement. A string is also wound round it, by pulling which rotation is produced. The electrodes are perpendicular to the plane of the platform which carries the -specimen. It will thus be seen that any variation of the surface subjected to stimulation is prevented. The next difficulty to be overcome is that of liability to variation in the pressure of the contact. It will be remembered that the platform is hinged. It is further held up against the electrodes by the tension of an elastic piece of india-rubber or a spiral spring of steel. This pressure can be regulated to a suitable value, and kept constant. The final difficulty is to apply successive stimuli of equal value, and to render them capable also of graduation from low to high values. This could be secured by rendering the successive rotations of the exciting electrodes equal in number and ‘in time of execution. The intensity of stimulus might then be increased by increasing the number of rotations or the pressure of the electrodes on the specimen. In order to apply successive rotations of definite number, one end of the string wound round the ‘inner brass tube is a a Sea hile A rea RESPONSE OF ANIMAL AND VEGETAL SKINS 293 — attached to a piece of stretched india-rubber, which is fixed by its other end to the apparatus. The second end of the string is tasselled, after being passed through a fixed ring. This position of the string is adjusted by means of a knot, so that the india-rubber at its other end is already in a state of tension. When the tassel is now suddenly pulled and let go, it gives rise to a number of rotations in the positive, followed by an equal number of rotations in the opposite direction, the latter work being performed by the stretched antagonistic spring. It should be remembered that a mechanical rotation, whether p/us or mznus, gives rise to the same excitatory reaction. Next, to make the number of rotations definite, let us suppose the inner brass tube to have a circumference say of I cm. If the string be now pulled through a distance of 5 cm., and let go, there will be five rotations in the positive, followed by five rotations in the negative direction. A second knot in the string, at the distance of 5 cm. from the first, exactly limits the length of the pull; and increase or decrease in the intensity of the stimulus.can be brought about by a change in the distance of the regulating knot. The distance between the two electrodes being always the same, the resistance of the interposed tissue remains approximately constant. To nullify any accidental variation, a high and constant external resistance is interposed in the galvanometer circuit. When the excitatory electro-motive variation of the specimen is very great, it is possible to use an external resistance as high as one million ohms. It should, however, be remembered that even if there be any unavoid- able variation of resistance, it will not in any way affect the discrimination of sign of the characteristic electro-motive response. For the excitatory effect at either electrode may be tested by repeating the experiment with the other. The experiments which will be described afforded definite and characteristic records, which were found capable of repetition. The physiological character of such responses was further demonstrated by repeating the experiment, after killing the 294. COMPARATIVE ELECTRO-PHYSIOLOGY tissue with boiling water, when these electro-motive variations were found to disappear. How very reliable these responses can be rendered is shown by the photographic record in fig. 180, which is of very special interest, giving as it does the record of responses afforded by the intact human skin. Turning now to the nature of the response of. the skin, it has been found by Engelmann and others, as already said, that in the frog, while the natural resting current is from the — outer surface to the inner, the responsive current is from inner to outer. Dr. Waller, again, undertook to analyse the constituent elements of this response, by passing induction shocks along each of the surfaces, first upper and then lower, and in both directions. He then observed the after-effect at one of the excited points, in relation to an indifferent point. In this way he found that an excited point on the upper surface becomes galvanometrically positive, the current being thus outgoing. The inner surface, however, he found to be ineffective. When an induction shock is passed across the tissue, the resultant response from lower to upper is thus, according to Dr. Waller, due to induced positivity of the upper surface. With vegetable specimens, however, such as the outer skin of apple, the results obtained by him were opposite to those of the frog’s skin. ‘The responsive currents were here found to be ingoing, the excited point being galvanometrically negative. The explanation offered, in regard to these results, is that living tissues have the peculiarity of responding by ‘blaze currents’ to electrical shocks. The use of this phrase, however, as already said, offers no real explanation ; but even apart from this point, the question remains, Why should the blaze currents, so called, be directly opposed in the cases of frog’s skin and of the particular vegetable skins which are mentioned, respectively? In answer to this, the hypothesis put forward by Dr. Waller is, that the difference arises from the different natures of animal and vegetable protoplasms.' ' ¢ Vegetable protoplasm is in major degree an instrument of synthesis and accumulation, in minor degree the seat of analysis and emission, Animal a = BOS Ae hk Pe ESS Satna, yt RESPONSE OF ANIMAL AND VEGETAL SKINS 2905 — I shall, however, be able to adduce facts and considera- tions from which it will be possible to arrive at a simpler and more conclusive explanation of these phenomena, on the basis of the differential physiological excitability of the two surfaces. I shall show, moreover, that the difference between animal and vegetable protoplasm, thus assumed to exist, has nothing to do with the question. We have seen that when the physiological activity of a tissue is in any way impaired, its normal excitatory re-action of galvanometric negativity is depressed. This may even go so far as to cause an actual reversal of the response, to galvanometric positivity, as we found in the case of depressed tissues (p. 84). Taking a vegetable specimen, then, say a hollow petiole or peduncle, we find that the outer surface, which is habitually exposed to the manifold influences of the environment, becomes histologically modified, being much more cuticularised than-the inner. Thus these outer and exposed cells generally become reduced in size, and thick- walled, with little protoplasmic contents. Hence, as regards functional activity, these epidermal cells are in a_physio- logical sense very much degraded. We should then expect their excitability to be proportionately lowered in comparison with, say, the inner surface of the same tube, protected as that has been from outside influences. And the variation of physiological excitability thus induced may involve not only the surface, but also the subjacent layers to a certain extent. Theoretically, then, the induced galvanometric negativity of the outer would be less than that of the inner surface,! and simultaneous excitation of both, by whatever means produced, should give rise to a resultant responsive current protoplasm is in major degree an instrument of analysis and emission, in minor degree the seat of synthesis and accumulation. The vegetable, in most immediate contact with inert things, combines, organises, and accumulates, The animal, in less immediate contact with inert matter, disrupts, utilises, and dissipates in their fragments organic compounds that it has received ready made from other animals and from plants.’—Waller, Signs of Life, p. 85. 1 This refers to normal skin, and not to that in which the surface is typically glandular. 296 COMPARATIVE ELECTRO-PHYSIOLOGY from inner to outer. The degree of this diminution of excitatory negativity in the outer surface, moreover, cul- minating as this may in actual positivity, will depend upon the extent of its transformation. In connection with this it should be remembered that, in order to bring out the differential excitabilities of the two surfaces, it is necessary to apply localised stimuli of an intensity not too excessive. For, if the stimulus be very strong, there is always a possibility of its affecting deeper layers of the tissue and thus causing complications in the resultant excitatory changes. The intensity of stimulus which may be safely used without bringing about 3 y such complications will depend b- a zl on the conductivity of the Pd A creme tissue. Epidermal cells are, ee Gar pas generally speaking, feeble con- os | ductors, but in this matter it ee must be understood that the ; differences in this respect be- Fic. 177. Diagram Representing ‘ : Different Levels of Excitability, tween different tissues are not Pika: sels ease eee ' absolute, but a question of Diagram to right of figure shows ; degree, and may to a certain how resultant up response (inner to outer) may be obtained when extent be modified under dif- induced change at A is plus, and at B minus, or when induced ferent circumstances. Thus a eee less negative than feebly conducting tissue, under a favourable condition of tem- perature and strong intensity of stimulation, will become to a certain extent conducting. Highly conducting tissues like nerve, on the other hand, under unfavourable circumstances may, as I shall show later, be converted into very feeble conductors. Returning now to the question of the responsive reactions of skin, we see the theoretical possibility of the following typical reactions. Let the scale of excitabilities be repre- sented by diagram to the left of fig. 177. Now, if the trans- formation of the outer epidermal surface, A, be maximum, the sign of its reaction will exhibit the greatest extent of deviation ee RESPONSE OF ANIMAL AND VEGETAL SKINS 267 from the normal negativity. That is to say, its response will become absolutely positive, as represented by a above the zero line. The response of the inner surface, B, may be normal and strongly negative, as represented by e below the zero line. When both these surfaces, then, are simultaneously excited, the excitatory positive variation, or ‘outgoing’ current at A, will conspire with the ‘ingoing’ current at B and the resultant electro-motive difference will be B, + A,, the direction of the responsive current being thus from inner to outer. But the same resultant up-response will also be induced, even if the reaction of both surfaces be negative, provided only that that of the outer, A,, be less negative than that of the inner, B,, as explained by the diagram to the right of fig. 177. The responsive current will then be represented as B,—A,, that is to say, as proceeding from the more negative B to the less negative A. We have thus examined the two extreme cases possible under the following formula, in which the arrows show the direction of the responsive current, from the more to the less induced negative: end>-co> boa. I shall next proceed to demonstrate the existence of these two extreme types, taking vegetable skins as the experimental specimen. It was supposed by Dr. Waller, as will be recalled here, that owing to characteristic differences between animal and vegetable protoplasm the response of vegetable skin was opposite to that of animal skin: that is to say, the former was ‘ingoing’ and the latter ‘outgoing.’ That this generalisation is not, however, justified, will be seen from the experiments which I am about to describe, carried out on the skin of grape. These results, it should here be pointed out, are not dependent upon any one method of inquiry, for each problem was subjected to attack and analysis by four different modes of experiment. The first of these (1) was by the Rotary Method of Mechanical Stimulation. This method has the great advantage that by it the absolute 298 COMPARATIVE ELECTRO-PHYSIOLOGY response of each surface is displayed separately, without either being affected by the other. There is here, moreover, no complication due to the polarisation factor, inevitable when uni-directioned induction shocks are employed for excitation. Thus, after the individual responses of each surface have been analysed, we are able to arrive at.a definite conclusion as to what would be the character of the resultant response if both the surfaces were simultaneously excited. | This conclusion is then submitted to three other tests. Thus, (2) the two surfaces of the specimen are subjected simul- taneously to the same thermal shocks, according to the method already described. Again, (3) the Method of the After Effect under equi-alternating shocks is employed. And, finally, (4) the Direct Effect of these equi-alternating shocks of moderate intensity is recorded. The results obtained by all these diverse methods are in complete concordance with each other, and fully support the theo- retical inferences which have already been made. I took the skin of a ripe muscatel grape, such as are available in Calcutta. On making the galvanometric con- nections with the outer and inner surfaces, a resting current, -C, was found to flow in the skin from the outer to the inner, just as in the skin of the frog (right-hand diagram, fig. 178). The grape skin was now mounted in the rotary stimulating apparatus, first, for the stimulation of the outer or epidermal surface, with the outer layer placed upwards. The distance between the two electrodes was always the same—namely, 2 cm. On now stimulating one of the two contacts, response took place by the induced galvanometric positivity of that point. That is to say, the current was ‘outgoing, into the galvanometer circuit, from the surface of the skin. When the second point was now stimulated the deflection previously obtained was reversed, the second contact thus also exhibiting galvanometric positivity on excitation. The position of the skin in the apparatus was now changed, the inner surface being placed upwards. In this way points diametrically opposite to those in the last case eT ee Pw a cn rt i i es ti. RESPONSE OF ANIMAL AND VEGETAL SKINS 299 — were subjected to excitation. It was now found that the responses of the inner surface were normal—that is to say, of galvanometric negativity. I give here (fig. 178, a) records of two successive sets of responses obtained from the external and internal points A and B. These records clearly demon- strate that the resultant up-response, on simultaneous exci- tation of the outer and inner surfaces, is brought about by the induced galvanometric positivity of the outer added to the induced negativity of the inner surface. As the resist- ance of the circuit in the two successive experiments was maintained approxi- A B mately the same, the . + bs amplitude of these re- Pile F sponses gives a fairly el t a . One sf \ accurate idea of the ta oe relative electrical effects F 4 induced on the two sur- Fic. 178. Electrical Response of Grape- faces. The positive or skin to Rotary Mechanical Stimulation (a) A, positive response of outer surface ; B, negative response of inner surface ; ‘outgoing’ effect of the outer surface is here (6) c, current of rest, from outer to inner ; ; R, excitatory response from inner to outer, slightly greater than the consisting of summated results of positive ‘ ingoing’ effect. The pig aes of outer with negative response diagram in fig. 178, 3, shows how the individual effects conspire to give rise toa responsive current from the inner to the outer. In order to test the reality of the correspondence between this response of the grape skin and that of the frog, I now repeated these experiments, employing the same apparatus for mechanical stimulation, on the skin of the frog. From the records given in fig. 179 it will be seen that the isolated response of the outer surface is positive, or ‘outgoing,’ that of the inner being negative, or ‘ingoing. The amplitude of the former was, however, much greater than that of the latter. These responses disappeared altogether when the tissue had been killed by immersion in boiling water. From isolated responses obtained by means of induction shocks, Dr. Waller had been led to regard the outer surface of frog’s 300 COMPARATIVE ELECTRO-PHYSioLOGY skin as alone active, the inner being, to his thinking, in- effective. This particular result may possibly be accounted for by supposing that he used a stimulus intensity which was not sufficiently strong. In my own experiments I obtained clear demonstration of the effectiveness of both surfaces in opposite ways electrically, though the effect obtained from the outer was undoubtedly the more intense of the two. By comparing these two experiments, then, on the grape skin and skin of frog, it will be seen that the inference that the vegetable protoplasm reacts in any way A B o = c R A B A ae ee es B —e v f b a a Fic. 179. Electrical Response of Frog’s Skin to Rotary Mechanical Stimulation (a) A, positive response of outer ; B, negative response of inner; (a’) A and B exhibit abolition of response in skin on boiling ; (4) Cc, current of rest from outer to inner ; R, excitatory response from inner to outer, being summated effect of positive response of outer and negative response of inner. essentially different from that of the animal is quite unjus- tified. How widely applicable is the method of mechanical excitation by rotary stimulus will be seen in an attempt, successfully carried out, to determine the very difficult ques- tion of the characteristic response of the intact human skin. This will be seen in the following record of the results obtained with the skin of a forefinger. The responsive elec- trical changes represented by the down records, exhibit induced galvanometric positivity of the excited surface (fig. 180). I shall next describe the results obtained by simultaneous excitation of the inner and outer surfaces of grape-skin. The responses now given, under stiniulation by thermal EE ee RESPONSE OF ANIMAL AND VEGETAL SKINS 301 shocks, are seen in fig. 181, the resultant current being seen to be ‘ up ’—that is to say, from the inner to the outer. On observing the excitatory after-effect of equi-alternating shocks, the results were found to be the same, the responsive current being now once more from the inner to the outer. I next took a series of records of the direct effect of equi-alternating shocks, the results of which were precisely the same as before. On applying stimulation, by exactly equal and alternating shocks, we, as already explained, Fic. 180. Photographic Record of Electrical Responses of Fic. 181. - Photographic -Record of Upper Surface of Intact . Electrical Responses of Grape-skin Human Forefinger to Rotary to Thermal Shocks at Intervals of a Mechanical Stimulation. Minute Down responses here indicate Responsive current from inner to outer, induced galvanometric posi- tivity. obtain a result which is due solely to the differential excita- tion of the two opposite surfaces. This is not complicated in any way by the factor of polarisation, although the latter could not have failed to be present if the exciting shocks had been one-directioned. Under the conditions of these equi-alternating shocks, then, a certain effect is often seen, in the phasic variation of the base-line, which is ex- tremely characteristic. We have already seen (p. 98) that when a tissue is subjected to repeated or continuous stimula- tion, its condition undergoes a phasic or periodic variation. Thus from a neutral or positive condition, it may pass into one of maximum contraction or galyanometric negativity, to 302 COMPARATIVE ELECTRO-PHYSIOLOGY be subsequently reversed to positive once more. Such phasic changes, moreover, may be repeated. They find visible indications in appropriate shiftings of the base line of the record. Similar effects are also shown in the differential response as seen in the records given in fig. 182; this feature ; is very noticeable. We here ob- tain the resultant response of the two surfaces of grape-skin, from . the inner to the outer. As the result of the series of stimuli applied, the existing current of FIG. 182. Photographic Re- cord of Electrical Responses of Grape-skin to Stimula- tion by Equi-alternating Electrical Shocks at In- tervals of a Minute Fic. 183. Photographic Record of Series of Electrical Responses of Frog’s Skin to Equi-alternating Electrical Shocks applied Responsive current from inner to outer. Note periodic variation of resting-current, at Intervals of One Minute causing shifting of base-line, Direction of responsive current from inner to down and up. outer. Note also variation of base-line. rest undergoes a periodic variation. If this had remained constant, the base-line would have been horizontal. In the present case, the original current of rest was from outside to inside. This, at first, underwent an increase; then a decrease ; to be followed, later, by another increase. Thus, in the course of about ten minutes, it exhibited an alterna- tion of almost one whole cycle. In the next figure (fig. 183) I give a series of results obtained RESPONSE OF ANIMAL AND VEGETAL SKINS 303 with frog’s skin in direct response to equi-alternating shocks. Here we find the usual ‘up’ responses, showing that, as before, the direction of the responsive current is from within to without ; and here also we see the existing current of rest undergoing a periodic change. It has now been fully demonstrated that the response of skin is determined by the differential excitabilities of its two surfaces, upper and lower, that of the lower being. the greater. That the resultant responsive current from lower to upper, is in such cases brought about by the greater excit- ability of the lower, has been fully shown, in a previous chapter, by experiments on the pulvinus of J/zmosa. I next made records of a long series of responses given by the last-named specimen, with the object of finding out whether or not these also exhibited a periodic variation of the resting-current similar to those just observed in the anisotropic skins of grape Fic. 184. Photographic Record of Trans- and of frog. Electrical verse Response of Pulvinus of A/imosa : to Equi-alternating Electrical Shocks connections were made : ; . . The direction of the responsive current is with diametrically opposite from the more excitable lower to the ; less excitable upper. Note the cyclic points on the Upper and variation of the current of rest. lower surfaces of this organ, and they were subjected to equi-alternating shocks. Owing to the conducting power of the tissues, it was not now the upper and lower skin surfaces merely, but the upper and lower halves of the organ that became excited. And the responsive current was from the lower to the upper, as already demonstrated. In the particular record seen in fig. 184, the general resemblance to the responses of skin is sufficiently obvious. The interesting feature of this record is the periodic changes in the resting- 304 COMPARATIVE ELECTRO-PHYSIOLOGY current, which exhibit a complete cycle in the course of thirteen minutes. Thus, as a consequence of the after-effect of stimulus, a cyclic variation of relative conditions is induced, as between any two anisotropic surfaces, such as those of skin or pulvinus. This cyclic variation of relative conditions is indicated by the concomitant variations induced in the resting-current, shown in the shiftings of the base line. I have been able, further, to demonstrate the interesting fact that such phasic variations are capable of exhibition | even through mechanical response. I have already ex- plained that autonomous pulsations, such as those of the lateral leaflets of Desmodium gyrans, may be regarded as the after-effect of stimuli previously absorbed and held latent by the tissue. In taking the record of a series of such pulsations, I have often found phasic variations to occur, similar to those obtained with long-continued response of skin or pulvinus. If, for example, the lower half of the pulvinus of the lateral leaflet of Desmodium undergoes an increase of turgidity above the average, that half will become more convex, and the base-line of the record will be correspondingly tilted. The converse will take place under the opposite change. Thus the phasic variations shown in the record (fig. 185) clearly indicate that the relative turgidities of the two surfaces of an anisotropic organ may undergo a periodic change. The corresponding electrical expression of this we have seen in the variation of the current of rest. This variation may sometimes be so great as actually to reverse the normal current of rest. Thus, while under normal standard con- ditions the resting-current in the pulvinus of Mzmosa is from the upper half to the lower, across the organ, this normal direction may sometimes be found to be reversed. It may now be asked, What is it, in the case of the skin, which determines the respective directions of the resting- current and the current of response? We have seen that the current of rest in the frog’s skin, from outer to inner, is generally attributed to the possession of glands by the outer, RESPONSE OF ANIMAL AND VEGETAL SKINS 305 a supposition seemingly supported by Rosenthal’s discovery, already referred to, that an apparently similar ‘ingoing’ current was to be observed in the mucous coat of the frog’s stomach. Against this may be urged the conclusion, to which Hermann drew attention, that the skin glands are nor- mally nearly closed to the external surface, and cannot there- fore have any external galvanic relation. There are, moreover, other arguments. First, a similar current is observed in the case of grape-skin, where there is no special glandular layer. Second, the specific response of a glandular surface is HE MH i Ahi lyf iH i Wi iH if! Hii yy iii TAA), }! itt ALE My Hill Ih) Nyy AWE Mii Wi 6 P.M. 9 P.M. I2 nA AAV aaa wt WW) iyo WV VV" 12 3 A.M. 6 A.M. Fig. 185. Continuous Photographic Record of Autonomous Pulsaticn of Desmodium gyrans from 6 P.M. to 6 A.M. The lower record is in continuation of the upper. Note phasic variation. definite, and is by galvanometric negativity, whereas the response of the outer surface of frog or grape skin on excitation is by galvanometric positivity. And, thirdly, we shall see that the current observed in the mucous membrane of stomach is most probably not the natural current of rest, but the excitatory after-current. It will be remembered, however, that we have always found the natural current to flow ‘in the tissue from the less to the more excitable, and the current of response in the opposite direction. In the skin, owing to physiological and iS 306 COMPARATIVE ELECTRO-PHYSIOLOGY histological modifications, the outer surface is reduced in excitability. The epidermal layers have little protoplasmic contents, and may be transformed in various ways, becoming corneated or cuticularised. The extent of such transforma- tion may be small or great, but the external layer will as a general rule become less excitable than the inner tissue. Hence, under normal conditions, we have a current of rest from without to within. If the inner layer be only moderately excitable, or if its power of recovery from excitation be great, then the dis- turbance caused by the prepara- tion of the specimen will be slight, or will pass off quickly. It is to be remembered that as the inner surface is the more excitable, the responsive current due to the mechanical stimulus of preparation wil! be from inner to outer; and therefore its after-effect, proving in certain Fic. 186. Photographic Record cases persistent, may give rise of Electrical Responses in Skin to g current apparently the re- of Neck of Tortoise to Stimulus PP y of Equi-alternating Electrical verse of the true normal current. aera at Intervals of One Thus the direction of the current The direction of the responsive of rest, which we should have current was from inner to inferred theoretically to be from outer. The so-called current ‘ of rest was also in this case, the less to the more excitable, owing to the excitatory after- may occasionally be found re- effect of preparation, from inner ; ; to outer. versed, owing to the excitatory after-effect of preparation. The current of rest, moreover, is liable to autonomous periodic variation, as we have seen. The most satisfactory method of determining the relative excitabilities of two surfaces, then, lies in subjecting them to simultaneous excitation, and observing the direction of the responsive current. In the skin, unless the tissue was fatigued, I have always found this to be from the more RESPONSE OF ANIMAL AND VEGETAL SKINS 407 excitable inner to the less excitable outer, even in those cases where the normal direction of the resting-current had been reversed, as an excitatory after-effect of preparation. This fact is well illustrated in the following record, taken with the skin of the neck of tortoise. As an after-effect of preparation, the resting-current so called was here reversed, flowing from inner to outer. But the excitatory responsive current was nevertheless from the more excitable inner to the less excitable outer (fig. 186). It was stated at the beginning of this chapter that the resultant response from inner to outer merely expresses the general fact that the vs excitability of the inner is greater than that of the outer. And this will a still remain true, even A : when the transformation ae of the external layer is — iN Se 3 not so great as actually e : 4 to reverse its individual g Fic. 187. Isolated Responses of Upper and galvanometric response Lower Surfaces of Skin of Tomato to Rotary from negativity to posi- Mechanical Stimulus an - (a) A, negative response of feeble intensity in tivity. The experi- rs outer ahce : “ negative response of iach mental results obtained greater intensity in inner surface ; (4) Cc, cur- ‘ : ‘ rent of rest from outer to inner. Resultant with the skin of ripe excitatory response from inner to outer, due tomato form a case in to greater induced galvanometric negativity point. The natural ndeoat | current of rest is here, as usual, from the outer to the inner, and the excitatory responsive current in the opposite direction. But from the analysis of individual responses, on the outer and inner surfaces, obtained by means of the rotary apparatus for mechanical stimulation, it will be seen (fig. 187) that both the surfaces alike give the normal excitatory response of galvanometric negativity. This responsive negativity of the inner, B, is, however, very much greater than that of the outer. The resultant response, then, representing as this does the difference in ; b dy 308 COMPARATIVE ELECTRO-PHYSIOLOGY degree between two negativities, is still from inner to outer, owing to the greater excitatory reaction of the inner. That the direction of the resultant response is actually from the inner to the outer is seen in the series of records given in fig. 188. The stimulus consisted of equi-alter- nating electrical shocks, applied at intervals of one minute. The record shows negative responses, followed appa- rently by the positive after-effect. In order to observe the peculiarities of this response in greater detail, the record was taken on a faster-moving drum (fig. 189). From this figure it will be seen that there was a short latent period of no responsive reaction. Response then rose to a maximum, and again sub- sided. After now reaching the zero position, the record proceeded in the positive direction, and again reverted back to zero. In_ similar records, the occurrence of Fic. 188, Photographic Record of Series of Responses in Skin of Tomato under Equi-alternating Electrical Shocks applied at In- tervals of One Minute Direction of resultant current from inner to outer followed by feeble opposite after-effect. this latent period, and _ posi- tive after-variation, has been adduced by certain physio- logists as affording visible demonstration of the exist- ence of opposite processes of assimilation and dissimilation. It has been supposed that the various features of the response were the outcome of a sort of tug-of-war between the two opposed forces, the preliminary pause being the expression of a short-lived balance, while the subsequent negative and positive variations were to be regarded as indicating the predominance, now of the one process, and then of the other. That in the present case such an assumption is unwarranted will be evident when we observe the isolated responses of the upper and lower surfaces separately (fig. 187). In each of RESPONSE OF ANIMAL AND VEGETAL SKINS 309 these we see the normal response of galvanometric negativity, followed by recovery, without evidence of any antagonistic process, such as might give rise to subsequent positivity. The difference between these two responses lies simply in their time-relations. On simultaneous excitation of the two, the predominant negativity of the inner gives the first half of the negative response. The persistence of the excitatory reaction of the outer, on the other hand, after the subsidence of the effect on the inner, gives rise to the apparently Fic. 189. A Single Response of Skin of Tomato to Equi-alternating Shock recorded on Faster Moving Drum positive after-effect. Thus, here the supposed tug-of-war between two opposite processes of assimilation and dis- similation is, in reality, between two normal responses having ‘different time-relations. It is from a failure to recognise the fact that the excitatory reaction is not con- fined to one, but takes place on both surfaces, that such erroneous assumptions as that referred to have often been occasioned, 310 COMPARATIVE ELECTRO-PHYSIOLOGY The result which I have described—namely, a greater responsive negativity of the inner than of the outer, giving rise to a resultant responsive current from inner to outer—is that which occurs in the majority of cases with tomato. But, as establishing a continuity between this response and that of grape-skin, | may mention the interesting fact that in a few instances I obtained records in which, while the inner surface on excitation exhibited a strong negativity, the outer, under the same stimulus, exhibited a feeble positivity. The normal response of skin is sometimes, however, found to be reversed, and no explanations have yet been Fic. 190. Photographic Record of Series of Normal Responses in Skin of Gecko Responsive current from inner to outer surface. offered to account for this. But I have shown two definite conditions of universal application, which are liable to bring about the reversal of normal response. These are, on the one hand, sub-tonicity, and, on the other, fatigue. Should the condition, in a given case, be the former of these, then the impact of stimulus will of itself, by raising the tonic condition, restore the normal response. ‘Thus in a case of abnormal positive response due to sub-tonicity, an inter- vening period of tetanisation will tend to convert the ab- normal response to normal. An abnormal positive will thus pass into diphasic, and thence into the normal negative. RESPONSE OF ANIMAL AND VEGETAL SKINS 311 For the following experiments, I took the skin of gecko, which can be detached from the body with very little injury. This animal offers remarkable facilities for many electro- physiological experiments. Its isolated tissues can be main- tained in a living condition for a very long time. Its sciatic nerve affords us a specimen about 15 cm.in length. Thus for electro-physiological investigation, it provides much greater advantages than the frog. Fic. 191. Photographic Record of Abnormal Diphasic Responses in Skin of Gecko, converted to Normal, after Tetanisation Taking a specimen of gecko skin, which was in a favour- able tonic condition, I obtained the series of normal responses to equi-alternating shocks, which is given in fig. 190. The responsive current here flowed from the inner to the outer surface. I next took another specimen, which was in a less favourable tonic condition, and obtained records of its responses, here seen (fig. 191) to be diphasic. An intervening period of tetanisation is seen, however, to restore the normal response. CHAPTER XXIII RESPONSE OF EPITHELIUM AND GLANDS. Epidermal, epithelial, and secreting membranes in plant tissues—Natural resting-current from epidermal to epithelial or secretory surfaces—Current of response from epithelial or secretory to epidermal surfaces—Response of Dillenia—Response of water-melon—Response of foot of snail—The so- called current of rest from glandular surface really due to injury— Misinterpretation arising from response by so-called ‘positive variation’ —Natural current in intact foot of snail, and its variation on section — Response of intact human armpit—Response of intact human lip—Lingual response in man—Reversal of normal response under sub-minimal or super- maximal stimulation—Differential excitations of two surfaces under different intensities of stimulus, with consequent changes in direction of responsive currents, diagrammatically represented in characteristic curves—Records ex- hibiting responsive reversals, HAVING now seen how the responsive peculiarities of the epidermis may be elucidated by the responses of similar tissues in the plant, we shall next take up an inquiry as to the parallelism between the responses of epithelium and glands in animal and in vegetable tissues. And here, as in the last case, we shall find the obscurities of the one made clear by the study of the other. If we take the hollow peduncle of a Uviclis lily, and, cutting this into longitudinal halves, take a portion from the upper end of one, we shall observe noticeable differences between the investing membranes of the outer and inner surfaces. On the outer, as we have seen elsewhere, the cells are dry, thick-walled, and cuticularised. This surface then is naturally distinguished as epidermal. The internal mem- brane of the hollow tube, however, is very thin, and its cells very little differentiated (fig. 192). The internal membrane may thus be distinguished as epithelial. If now we examine this inner membrane continuously A ote ate 34K =] RESPONSE OF EPITHELIUM AND GLANDS 313 from the top to the bottom, at the point where the peduncle rises from the bulb, we shall find that the epithelial layer of the upper end passes imperceptibly into a markedly secret- ng (glandular?) layer at the lower. By this, secretion is constantly taking place, filling up the hollow tube with fluid. In one instance which I measured, the amount of this secretion was as much as IO grammes in the course of the day. These secreting cells in this, which may be called the glanduloid layer, are very thin- walled and excessively turgid, and, from an evolutionary point of view, these gradual transitions from epidermal to epithelial, and from epithelial to secretory layers, observed under conditions of such great simplicity, are extremely interesting. | When we come to test the electrical reactions of these tissues, we find, on making electrical con- nections with the external epi- dermis and the internal epithelium, that a natural current flows in the tissue from the external surface yc, 192, Transverse Section of to the internal: This would indi- tissue of Hollow Peduncle of : ‘ Uriclis Lily cate that the internal was the Cells of epidermis are small and more excitable of the two. This thick-walled, those of inner : . surface large and thin-walled. conclusion is confirmed on the application of simultaneous excitation to outer and inner ; for the direction of the responsive current is found to be from the internal surface to the external. _ If, next, electrical connections be made with the.epidermal and secretory layers, a current of rest is once more observed from the external to the internal. On excitation, a very strong electrical response is given, its direction being from the highly excitable secreting layer to the less excitable epidermal. From these experiments we see that the 314 COMPARATIVE ELECTRO-PHYSIOLOGY epidermal cells are, generally speaking, the least, and the secreting cells the most, excitable. I shall show, moreover, that all the responsive character- istics of these secretory cells are to be found repeated in those admittedly glandular layers which occur in the lining of the pitcher of Vepenthe, and cover the upper surface of the leaf of Drosera. Before, however, entering upon the consideration of these highly differentiated organs of Nepenthe and Drosera, - which are further characterised by some of the digestive functions, I shall first discuss in detail the reactions of a simpler type of vegetable organ. This is exemplified by a single unripe carpel of Dz/lenia indica, already referred to, When this is carefully removed from the inside of the pseudocarp, and opened, the inside is found to be filled with a gelatinous secretion. This is gently removed, and electrical connections are made with the inner and outer surfaces. It must be borne in mind that these vegetable organs, being not highly excitable, admit of experimental preparations being made with little or no excitatory effect of injury. Allowing now for a period of rest after making the preparation, it will always be found that the current of rest is from the outer layer to the secreting inner layer, which latter is thus, relatively speaking, galvanometrically positive. From the fact which we have generally observed, that the natural current of rest is from the less to the more excitable, it would appear, then, that the inner layer is here the more excitable. This conclusion, moreover, is in agreement with the inference already arrived at, in connection with the tissues of the Uriclis lily, that secreting cells as a rule are relatively the most excitable. This inference may, however, be subjected to the test of direct experiment. I first tested the response of the same specimen by means of thermal shocks, applied to both surfaces simultaneously. The definite direction of the responsive current, from the inner to the outer, across the tissue, proved conclusively that * the inner surface was the more excitable, becoming as it did, galvanometrically negative in relation to the outer, A similar RESPONSE OF EPITHELIUM AND GLANDS 315 effect was obtained as an after-effect of equi-alternating shocks. I next took records of the direct effect of equi-alter- nating shocks. The direction of the responsive current was found, as before, from the inner to the outer. In the fruit of water-melon we obtain another specimen whose interior cavity is filled with secretion. On making a suitable preparation of this specimen, and arranging electrical connections with the outer epidermal and inner secretory surfaces, I found the responsive current, under equi-alter- nating electrical shocks, to be from the inner secretory to the outer epidermal. Fig. 193 gives a photographic record of these responses. From the typical responsive effects thus obtained with vegetable specimens under the simplest conditions, we are enabled to see that the effect of localised stimulus depends on the characteristic response of the surface layers of the organ. When dealing with this question of the electrical reaction of epi- thelium and glands in animal tissues, Biedermann rightly Fic. 193. Photographic-Record of : , Responses of Water-melon to came to the conclusion that it Equi-alternating Electric Shocks was the surface epithelial layer Responsive current from internal which was, in an electro-motive stale to external epidermal sense, most effective, the term, in its widest sense, including the epithelium of glands and papillz. One complicating factor present in the electrical reactions of animal epithelia and glands, but relatively absent under the simpler conditions of the plant, is the effect of injury caused by the process of isolation. The very fact of making the neces- sary section involves a stimulus of great intensity, and unless the effect of this has thoroughly subsided, the after-effect of such stimulation may be so strong as to reverse the normal current of rest, and otherwise modify the excitability of the tissue, This is seen, for example, in an experiment carried 316 COMPARATIVE ELECTRO-PHYSIOLOGY out by Dr. Waller,’ on the isolated paw of a cat. The current of rest was found by him to flow from the surface of the pad to the section. From this he was led to the conclusion that this current could not have been due to injury, since in that case it would have flowed from the sectioned to the uninjured surface, and not in the opposite direction, as was found to be the case. This misconception arises from a failure to realise that. the so-called ‘current of injury’ is, in fact, an after-effect of excitation. In the case under consideration, the section, acting as an intense stimulus, simply induces greater excita- tory reaction of the more excitable, which in this case happens, as we should have expected, to be the glandular surface. The injury-current here, then, is necessarily from the more excited glandular to the less excited non-glandular. A precisely similar result was obtained in the case of anisotropic plant-organs, where excitation caused by injury of the less excitable side, becoming internally diffused, induced greater galvanometric negativity of the more ex- citable distal point (p. 162). For a typical experiment on a glandular preparation, showing the principal effects, and the complications that may arise owing to injury, we may take the detached foot of the pond-snail, the lower surface of which, as is well known, secretes a slimy fluid. On allowing ‘for the necessary period of rest, and then making electrical connections, we observe a current of rest, so-called, which flows from the glandular to the sectioned end. This is not to be mistaken for the true natural current of rest, being in fact the after-effect of a greater galvanometric negativity at the more excited glandular surface, consequent on section. An independent experiment, in support of this induction, will be described presently. On now simultaneously ex- citing the two surfaces, by equi-alternating shocks, the responsive current is found to flow from the gland inwards, the more excitable gland becoming thus galvanometrically negative. The responsive current is in this case in the same ' Waller, Signs of Life, p. 101, RESPONSE OF EPITHELIUM AND GLANDS 317 direction as the so-called current of rest, constituting a positive variation of it. From these experiments it is clear that the responsive current is due to the greater intensity of the induced gal- vanometric negativity at the more excitable glandular surface. It must, however, be noted here that this definite understanding of the phenomenon has been arrived at by fixing our attention on the relative excitatory reactions at the two contacts. If, instead of this, we had regarded it from the usual point of view, of variations of the resting-current only, we must have interpreted it as apparently an abnormal positive variation ;! for the so-called resting-current, in such a case, on account of the excitatory after-effect of injury, must also, as we have seen, flow from the more excited gland to the less excited muscle. Great confusion, and resultant misinterpretation of observations, have arisen from not sufficiently recognising these facts, that the resting-current may be originated in either of two distinct ways, and that the excitatory effect may consequently be summated with it in different manners. The resting-current in the primary condition is, as I have demonstrated elsewhere, the natural current. This originates in the natural differences of ex- citability between different points, and is, in the intact specimen, through the tissue from the less to the more ex- citable. External stimulus now gives rise to a responsive current, which is in the opposite direction, and therefore constitutes a negative variation of this, This takes. place because the more excitable point, which was naturally positive, has now become negative. But we may have a current of rest which is due to previous excitation, or injury, such as may be caused by the shock of the pre- paration. This current, though usually regarded as the resting-current, is not the true natural current of rest. It is really, as it were, the responsive current. become persis- tent. Succeeding stimuli, inducing responsive galvanometric 1 We shall find in Chapter XX VII. that similar misinterpretations have arisen with regard to the responsive current in the retina, p. 417. 218 COMPARATIVE ELECTRO-PHYSIOLOGY negativity of the more excitable, will now give rise to a current in the same direction as this resting-current, thus constituting a positive variation of it. It is only when fatigue has set in at the more excitable, and induced great depression of excitability there, that the response-current may undergo a reversal, its direction now being from what was. originally the less excitable, to the originally more excitable (p. 177). An example of this I found in the sectioned foot of the large Indian garden-snail. Here the excitatory action on the glandular surface, due to the shock of preparation, was ex- tremely great, as evidenced by the profuse secretion which occurred iinmediately. Owing to this over-stimulation, fatigue was induced, with consequent great depression of ex- citability. Hence the responsive current was now found to be reversed, having, with reference to the glandular surface, become outgoing instead of ingoing. It has been stated above that the ingoing current of rest, observed at the glandular surface under preparation, was not the true natural current, but due to the excitatory after-effect of injury. ‘This I was able to verify by observing the current of rest under natural conditions, without excitation. The snail was allowed to crawl on a glass surface, in the middle of which was a strip of linen moistened in normal saline. This brought the glandular surface into electrical connection with one of two non-polarisable electrodes. When the snail had of its own accord come to a temporary standstill on this piece of linen, the other electrode was quietly placed against the skin of the upper side of the protruding body. The natural current of rest was now found to be outgoing, as regards the glandular surface of the foot, the more excitable being thus galvanometrically positive. The absolute electro-motive difference was found to be + ‘0013 volt. The foot was now sectioned, and the difference of potential between the same points was found to have undergone a reversal. The supposed resting-current was now ingoing, through the glandular surface. Thus, owing to the excitation consequent on preparation, the more excitable surface, originally positive, 7). ee ee ee 4064 cee ( RESPONSE OF EPITHELIUM AND GLANDS 319 had become negative. The induced variation from the original condition, in the present case, was from + ‘OoI3 volt to — ‘0020 volt. It will thus be seen that any irritation is liable to change the natural positivity of a highly excitable glandular surface to negativity. The supposed similarities between the ingoing responsive currents of frog’s skin, and the glandular surface of the stomach, are therefore not real. That the two cases are quite different is proved indeed by the fact that local stimulation of the surface of the skin induces galvanometric positivity, whereas a similar stimulation of the glandular surface induces negativity. In experimenting on animal tissues, it is therefore ad- visable, wherever possible, to use intact specimens. The numerous experimental difficulties with which we are in that case confronted, may be overcome by the method of simul- taneous and equi-alternating shocks which has been described. How practicable this method has been rendered will appear from the experi- ments which | have yet to describe on human subjects. We have seen that a protected sur- face is likely, other things being equal, to be more excitable than an exposed one. Partly owing to this fact, and partly also to its richer possession of imbedded glands, it appeared to me probable that the inner surface of the armpit would prove electrically more pig. 194. Photographic excitable than a corresponding area, on, Record of Electrical Responses of Intact say, the upper and outer surface of the Human Armpit same shoulder. In the records which I Responsive current from succeeded in obtaining (fig. 194), this “Pit to shoulder. supposition was fully borne out. Equi-alternating shocks of one second’s duration were applied at intervals of one minute, and the direct effect photographically recorded. The re- sulting responses were found to be ingoing as regards the armpit, thus proving that that surface was the more excitable. 320 COMPARATIVE ELECTRO-PHYSIOLOGY In order next to show that epithelial cells in the animal are relatively more excitable than epidermal, as we have already found to be the case in vegetable tissues, I performed the following experiment on the human lip. Here it was important that the electrical connections should be main- tained steady. A light spring-contact key was therefore made, as seen in the lower part of fig. 195. The lower. contact of this spring-clip consisted of an amalgamated plate . of zinc leading to the lower electrode. Over this were tied four thicknesses of blotting- paper soaked in zinc sulphate solution. On this again were placed three more thicknesses of blotting-paper, soaked in normal saline. The zinc plate which formed the upper limb of the clip, in connection with the second electrode, was similarly covered with separate layers of blotting-paper, soaked in zinc sulphate and normal saline re- spectively. The protruded lower lip was now placed in the clip, as shown in the upper figure, in | such a way that the latter made : ee eS of Towne a gentle but secure contact. A Lip. galvanometer and a source of Lower figure gives an enlarged view equi-alternating currents were oe also placed in the circuit. Of the two electrodes, the upper was in connection with the epithelial, and the lower with the epidermal surfaces. The natural current was now found to flow in the tissue, as in the corresponding cases of plant specimens, from the epidermal to the epithelial. The perfect steadiness of the contact was evidenced by the stillness of the deflected galvanometer spot of light. On now applying the alternating excitatory shock, the responsive current was found to be in the oppo- RESPONSE OF EPITHELIUM AND GLANDS 321 site direction to the natural current, thus demonstrating the fact that the epithelial layer was here, as in the plant, the more excitable of the two. The regularity of this effect will be seen from the series of photographic records given below (fig. 196), in which is exhibited a slight staircase effect. We next proceed to deal with the response of the glan- dular organ, the tongue. The tongue of the frog has formed the subject of a very extended series of researches, by Engelmann and Biedermann. On_ very careful isolation, entailing as little injury as possible, it was found by these workers that the natural current was ‘entering’ that is to say, it flowed across the tongue from the upper surface to the lower. Both electrical and mechanical stimulation was found by these observers to cause a negative variation of this natural current. As isolation of such a highly excitable organ as the tongue may, however, give rise to unknown excitatory after-effects, it ap- peared to me very desirable that an investi- gation on this subject should be carried out * pei Se prides on the intact human tongue. In connection Electrical Response with this, I must point out that both the Sere pen surfaces of the tongue are excitable. Our Responsive current inquiry, therefore, is into the relative excit- ‘Tom epithelial to epidermal surface. abilities of its upper and lower surfaces. Here the experimental difficulty lies in this very high excitability of the organ, on account of which—except when in a quies- cent state and with a very steady contact—the galvanometer spot of light is apt to be erratic in its movements. Much of this difficulty is overcome, however, by holding the pro- truded tongue lightly clamped between the teeth. The upper and lower surfaces may then easily be held in the clip-key already described. From this double support of the clip and the teeth it is, with a little practice, possible to arrange matters in such a way that the galvanometer spot is Y 322 COMPARATIVE ELECTRO-PHYSIOLOGY practically stable. The current of rest in the intact human tongue is then found to be from the upper to the lower surface, as in the frog. This, according to our previous results, would indicate that the upper surface is the less excitable. This inference finds independent verification, when we subject the organ to the stimulus of equi-alternating shocks. A very strong responsive current is now found to flow through the tongue, from the lower to the upper surface. The tongue is so extremely sensitive that its characteristic response can be evoked even with very feeble stimulus. I have already explained that the alternating currents induced by speaking before a telephone are not exactly equal and opposite, the current being slightly stronger in one direction. Hence, if such currents be made to play upon an organ in which the excitability is only moderately differential, the preponderance of one of the two elements of the alternating shocks is then likely to mask the true excitatory effect. But the differential excitability of the tongue is so great that the responsive current is always from below to above, whether the exciting current be made to act in a favourable or unfavourable direction. Thus, if one speak, even in a very ordinary voice, into an exciting telephone, which is in series with the rest of the circuit, with its poles direct or reversed, a definite lingual current. is induced in response. This, as already said, is always in direction from the lower surface to the upper—surely a curious instance of the speech of one inducing lingual response in ariother, by direct, and not by provocative action ! The results which have been described are the normal effects given in response to stimulus of moderate intensity. By moderate stimulus is here meant that intensity of current which is obtained when the primary coil is slightly within the secondary. By feeble, on the other hand, is meant the intensity produced when the primary is at a distance from the secondary. Excessively strong stimulus again occurs when the primary is pushed fully within the secondary. I shall now proceed to describe occasional variations which a ee RESPONSE OF EPITHELIUM AND GLANDS 333 may be observed when the stimulus is either very feeble or excessively strong. We have seen (p. 83) that when the intensity of stimulus is below the critical degree which is sufficient to induce response, its effect is to increase the internal energy of the tissue. We have also seen that the sign of this increased internal energy is galvanometric positivity, being thus opposite to the excitatory effect. Hence, in a dif- ferentially excitable tissue, we may expect to find instances in which stimulus that falls below the threshold of true excitation will act by inducing a greater galvanometric positivity of the more excitable, whereas, under normal intensity of stimulus, the more excitable would have become galvanometrically negative. We can thus see the possibility of response being reversed under very feeble stimulus. It must be remembered that the excitability of both the contacts is a factor in the response, which has hitherto been overlooked. A second very important factor, which has not yet been taken into consideration, is the difference between the characteristic curves of the tissues at the two different surfaces. By characteristic curve is here meant the curve which shows the relation between intensity of stimulus and response. This difference will be better understood from the diagram of the theoretical curves given below (fig. 197). This exhibits all the cases that can possibly exist. : . Let the curve A aa’ a" represent the characteristic curve of the surface A. Let the curve B 0 0’ 6” similarly represent the characteristic curve of the surface B. Of these two surfaces, B is under moderate stimulation, normally the more excitable. In the middle portion of the curve, representing response under moderate intensity of stimulus, the induced galvanometric negativity of B is thus greater than that of A. Under moderate excitation, therefore, the current is d’>a! through the tissue in the direction from B to A. But below the threshold of true excitation, B would be positive, and A ¥2 324. COMPARATIVE ELECTRO-PHYSIOLOGY relatively negative to it. Hence there would here be a reversal of response, the direction of the responsive current a> through the tissue being now from A to B. This current will be recorded by the galvanometer, provided the induced difference between A and B be sufficiently great. Having thus inferred the different effects possible under sub-minimal and moderate stimuli, we shall next consider the differential effect which may sometimes be induced by | excessively strong stimulus. In the middle part of the curve, | - ie 4 | o , b é b z “1 a A @ ped STIMULUS | 6 Fic. 197. Possible Variations of Responsive Current, as between Two Surfaces A and B, shown by Means of Diagrammatic ‘Representations of Characteristic Curves A, a, a’, a”, characteristic curve of surface A; B, 4, 6’, 6", that of B. Under moderate stimulation, B is the more excitable, its induced galvanometric negativity being greater, and the direction of current from 4’ Zo a', as in the middle part of the curve. Under sub-minimal and super- -maximal stimulation the direction of the responsive current is reversed to a > 6 and a" - 6” respectively. B40! b” is seen to be very much steeper than Aad a’ tae that is to say, the excitatory effect increases very rapidly with the stimulus, in the more excitable of the two surfaces. But this increase may sooner or later reach a limit, that curve tending to become horizontal, aided in this process, possibly, by growing fatigue. The curve A a@a' a’, however, though not so steep, may yet continue to rise throughout a longer abscissa, representing increasing intensity of stimulus. In such a case, there would be a second crossing-point, and Mint thas do rn MMe 2 gee ae m . RESPONSE OF EPITHELIUM AND GLANDS 325 a second reversal of normal response into a@’’>0", under excessively strong stimulation. We are thus enabled to see the theoretical possibility of the reversal of normal response under the two conditions of sub-minimal and super-maximal stimulation. All these phases may not be displayed in the same specimen; but it may be possible to find different specimens exhibiting one or the other. In some cases the difference a—d is too small to allow of an appreciable galvanometric effect, and in their higher parts the curves do not cross. In such specimens, then, there is no response under sub-minimal stimulus, and only normal response under increasing intensities, however strong. The only exception to this will take place when fatigue supervenes, a case which will be dealt with presently. I find that this type of response is the most common. We have next to consider those cases in which in the - sub-minimal region, the difference a—é is appreciable, the reversal to normal 6’>a’ taking place under higher in- tensities of stimulus. There need not in such an instance, be any second reversal. Here, then, the normal response under moderate or strong stimulus is reversed when the stimulus is sub-minimal. An example of this will be given presently. Lastly, there may be a type of response in which in the sub-minimal region the difference a—Jd is slight, and the normal 6’-» { >R Fic. 248. Experimental '. Arrangement for Deter- mination of Differential © _. Excitability of Optic — ; Nerve and Cornea Fic. 249. Series of Photographic Records of ‘Excitatory Responses in Frog’s Eye to Equi-alternating Electric Shocks at Inter- _ vals of One Minute C, injury current, or so-called current of rest; R, re- sponsive current. Current of response from nerve to cornea. as the existing current, and thus constitutes a positive varia- tion of it. Thzs positive variation of the current in the eyeball thus indicates a true excitatory reaction of the optic nerve. From the fact that the nerve is more excitable than the cornea, it is clear that the sectioning of it for isolation of the eyeball, acting as an intense stimulus, will result in its excita- tory negativity, which will persist for a time and slowly dis- appear. Owing to this fact, a current flows from the more excited nerve to the less excited cornea. That this current E E —A18 COMPARATIVE ELECTRO-PHYSIOLOGY is not the true resting-current, but rather an excitatory effect consequent on preparation, is supported by the known fact that it undergoes a decline more or less rapid. On the other hand, from the fact just demonstrated that the nerve is the more excitable, we should expect that, under natural or primary conditions—that is to say, inthe absence of excitatory disturbance—the resting-current would be from the less to the more excitable, or in other words, from cornea to nerve, This | conclusion I was able to verify by carefully dissecting away the socket of the frog’s eye, and making connections with the longitudinal surface of the un- detached nerve and the cornea. Under these ideal conditions the true resting-current was detected, and was, as expected, from the cornea to the nerve. In order, next, to determine whether the current, observed to flow, in a nerve-retina prepara- < tion from retina to nerve, is a ‘ee true: resting-current, or merely C R Fic. 250, Experimental Arrange- an excitatory after-effect, I pro- ment for Demonstration of ‘ i Differential Excitability as bee ceeded to determine, in the tween Retina and Optic Nerve — manner already described, which c, so-called current of rest; R, re- sponsive current. of the two surfaces was the more excitable. Under the excita- tory effect of equi-alternating shocks, the responsive current was found to flow from the retina to the nerve, thus proving that the retina was the more excitable (fig. 250). The first series of responses in fig. 251 gives a record of these effects with a moderate intensity of stimulation, while the second series shows the responses under an intensity nearly twice as great. The so-called current of rest observed in the nerve-retina preparation is thus to be taken as due to that after-effect of preparation which is inseparable from the isolation of such a highly excitable tissue. /¢ well also be RESPONSE OF RETINA TO STIMULUS OF LIGHT 4I9 noticed that the true excitatory effect on the retina ts tn the same direction as the existing injury-current, and thus constitutes a positive variation of tt. . Thus, as regards forms of stimulus other than light, such as, for example, the electrical, the responsive reaction of the retina is by induced galvanometric negativity. This at once disposes of the doubt that the general reaction of the retina might be of a different sign from that of any other tissue. But we have still to determine whether or not the stimulus of light, in particular, induces the same normal negative change, The next question to be taken up, then, is that of the true nature of the responsive variation induced in the Fic. 251. Series of Photographic Records of Excitatory Responses in Frog’s Retina to Equi-alternating Electric Shocks at Intervals of One Minute Responsive current from retina to nerve. First series show response to stimulus of moderate intensity ; the second series to stimulus of intensity nearly twice as great. retina by light. We have seen that the effect recorded as normal by numerous observers, whether in the eyeball or in the isolated retina (Kiihne and Steiner) was a positive varia- tion. But since we now know that retinal response to stimu- lation in general is not unlike that of other tissues, and since, with regard to the stimulus of light'in particular, we have seen it induce true excitation in vegetable tissues, we might expect the responsive reaction of the retina to light to take place by galvanometric negativity. We must then accept one of two conclusions. Either the positive change is a misnomer for the phenomenon observed in the eye, or the inference which we have drawn from the analogy of vegetable tissues is not justified. 420 COMPARATIVE ELECTRO-PHYSIOLOGY As, in reference to this latter point, however, it may be urged that the retina is exceptionally sensitive to light, while the reactions of vegetable tissues are generally slug- gish, it may be worth while to point out here that vegetable tissues are not so insensitive as is generally supposed, but are often, on the contrary, highly susceptible to the: action of light. It. was, for instance, found by Darwin that the coty- ledons of Phalaris canariensts were, in the course of some _ hours’ exposure, curved towards a small lamp, placed ata distance from them of 12 feet.. The intensity of the stimulus of light was in this case extremely feeble. I have myself observed, again, the remarkable sensitiveness to light of the terminal leaflet of Desmodztum,.which, on the mere striking of a match in its vicinity, was thrown into a state of pulsatory movement. I shall, in the course of the present chapter, describe certain definite effects on the retina, which will prove, in an - unmistakable manner, that, when exposed to light, it under- goes a change of galvanometric negativity. It is now there- fore necessary to show clearly that what has been described as the positive variation is really due to the excitatory nega- tive change of the retina. What has to be demonstrated, then, is the way in which this simple underlying reaction of negativity comes to appear as a positive variation of the opposite-directioned currents of rest in the a and isolated retina respectively. As regards experiments on the eyeball, with contacts at nerve and cornea, we have seen that. the existing injury- current is from nerve to cornea, and that this undergoes a positive variation when the nerve is stimulated in any way. This is because the added. negativity induced in the nerve gives rise to an increase, or positive variation of, the existing current (fig. 248). Now, when light falls on the eye it -acts on both the cornea andthe retina. The former, however, is relatively inexcitable, especially to so moderate a stimulus as that of light. But the retina is excited, and its excitatory condition is rapidly transmitted to the optic nerve, which eee RESPONSE OF RETINA TO STIMULUS OF LIGHT 421. thus becomes galvanometrically negative. The so-called positive» variation observed under such an experimental arrangement, then, is really the result of the true excitation of the retina conducted to the optic nerve. In experiments- on nerve-and-retina preparations, with contacts on the nerve and the retina, the existing injury- current is from retina to nerve.- When do¢/ nerve and retina are excited simultaneously, by equi-alternating electrical shocks, we have seen that, on account of the greater ex- citability of the retina, the resultant responsive current, here differential. is from retina to nerve, constituting a positive variation of the existing injury-current (p. 419). In the case of stimulation by light, however, it is the retina which is directly excited. The added negativity thus induced in the retina gives rise to an increase or positive variation of the existing injury-current (fig. 250). Hence, in all these cases, the so- called positive variation really indicates the normal excitatory negative effect. The apparent anomaly involved in the supposition that the response of the retina to light was positive, and thus of opposite character to that of other ex- citable tissues, is thus seen to be due to a misinterpretation of observed results. It is unfortunate that, as a consequence of this misinterpretation, the effects described by different observers, of the response of the eye as ‘ positive,’ are really to. be understood as ‘negative, and vice versa. When quoting these results, therefore, I shall always give the actual effect indicated in italics and in parentheses, Another observation which lends independent support to the view that the retina exhibits the true excitatory re- action, is found in the fact—noted by Van Genderen-Stort and Engelmann—that the cones exhibit a motile effect by retraction under light. It has. been supposed from this that the optic nerve contains not merely sensory, but also retino- motor fibres. But I shall show that it.is not that the endings only of the optic nerve, but also that nerve itself, which exhibit true excitatory contraction under stimulation (cf. figs. 324,404). All nerves, in fact, will be shown in a later 422 COMPARATIVE ELECTRO-PHYSIOLOGY chapter to exhibit normal excitatory contraction, and it will be by the study of these motile responses in nerves, and their variations under different condition, that we shall be able unerringly to relate the abnormal responses sometimes seen in the retina to those changes of condition to which they are due. : With regard to these abnormal responses, I have already shown that various tissues exhibit them under the two different conditions of sub-tonicity and fatigue. With regard to nervous tissue in particular, however, I may refer here, by anticipation, to results which will be given in detail in Chapter XXXV. concerning the mechanical response of nerve and its variations. In normal conditions of ex- citability the nerve gives response by contraction, and this is its true excitatory response, concomitant to the electrical response of galvanometric negativity. This excitatory re- sponse, then, whether by contraction or by negativity, will here, as in preceding chapters, be designated ‘negative.’ We have seen that the maintenance of the normal condition of a highly excitable tissue depends on its supply of energy. Hence, when such a tissue is isolated from the organism of which it forms a part, it is liable to fall below its normal tonic level. This depressed condition, however, does not connote any permanent chemical depreciation, but only a temporary depression of its fund of energy. Under such an induced lowering of the tonic condition, the response is reversed to positive. But under continuous stimulation, excitability is again enhanced, and the abnormal positive is converted to normal negative. Thus we obtain, in a somewhat sub-tonic tissue, the following results : (1) Under a short-lived or instantaneous stimulus, whose effective value falls below the true excitatory level, response is positive (expansion), (2) Under the continuous action of stimulus the effective value is at first below, but after a time rises above, excitatory efficiency. In consequence of this we obtain a first phase of RESPONSE OF RETINA TO STIMULUS OF LIGHT 423 . response which is positive, followed by a second which is negative (expansion followed by contraction). The second condition to induce a reversal of the normal response occurs in consequence of the fatigue due to previous over-stimulation. (3) A reversed positive response (expansion) in conse- quence of fatigue. | | The various anomalies which occur in the response of the eye will all be found resolvable into one or other of these cases. I shall first describe certain experiments which will demonstrate the reversal that is brought about by induced sub-tonicity. We have seen that the normal response of an eyeball, with two contacts at nerve and cornea, consists of a current from the nerve to the cornea. I have already given records of such normal responses, obtained by sub- jecting the preparation to equi-alternating electric shocks (fig. 249). In certain cases, however, in which the isolated eyeball of the frog had fallen into a sub-tonic condition, the response was found to be reversed, the nerve, under excita- tion, becoming relatively positive instead of normally nega- tive. It has already been said that such a reversal is due to great depression in the condition of the nerve. In dealing with these cases, therefore, it occurred to me that it ought to be possible to restore the normal response by the application of some exciting reagent—say, dilute Na,CO,—to the nerve in its depressed condition. As the result of this application I found the reversed response to be restored to the normal. I obtained results precisely similar to these with isolated retina of the frog. The normal responses—a current from retina to nerve (fig. 238)—under equi-alternating shocks, were here found, in a depressed specimen, to be reversed. But the application of Na,CO, solution on the retinal surface brought the responses back to the normal. These abnormal responses, then, rectifiable to normal, are those due to sub- tonicity. And under fatigue finally, induced by long- continued, or over stimulation, I find the normal response of the eye to be reversed. a2a COMPARATIVE ELECTRO-PHYSIOLOGY This is the place in which to refer to various anomalous effects observed. by previous investigators, and to offer satis- factory explanations of them from the results which I have already demonstrated. I shall therefore give a brief sum- mary of these from the admirable account of Biedermann. (a) ‘In light, frogs—z.e, such as have been exposed for hours to the full effect of daylight—the positive fore-swing of the negative variation concomitant~with the impact of © light is entirely wanting, or appears as a trace only.’ ‘ Since this posztzve varzation of the existing current really means, as I have already shown, the ‘true excitatory negative, and the negative variation conversely, the occurrence of positive response, this observation means that a frog’s eye, previously exposed for a long time to light, gives positive response. This, then, is a simple instance of the reversal of response from negative to positive under fatigue, which I have already dealt with above as case (3). (0) ‘The fact that the three phases of the retinal action current, due to transitory illumination, appear in sensitive preparations, even when, as with the electric spark, the impact of light is momentary, shows that the medium nega- tive (fosttzve) phase must not be regarded merely as the consequence of permanent illumination, since it is just this phase which alone appears in less excitable preparations with instantaneous light stimuli.’ ‘With regard to this it may be said that the medium positive phase here referred to, as given by. the excitable retina under continuous stimulation, is not the same as that positive response which ‘alone appears in less excitable pre- parations with instantaneous light stimuli. The former is due to fatigue-reversal, while the latter is an instance of the abnormal positive response of a sub-tonic tissue to feeble stimulus. This will be understood from the following con- siderations. In the retina, under continuous stimulation, the first phase of response is the true excitatory negative. This gives place to a second, or positive, due to _fatigue-decline. ' Biedermann, Zéectro- Physiology (English translation), vol. ii. pp. 474-477. RESPONSE OF RETINA TO STIMULUS OF LIGHT 425 - i g And this is again succeeded bya transitory negative effect on the sudden cessation of: light. These constitute the three phases of retinal action-current just referred to, under con- tinuous stimulus. This sequence is wrongly represented in symbols as (+ — +), since the actual changes concerned are (—+-—). ; . Now in highly excitable. tissues, under instantaneous stimulation, we observe a sequence of response apparently similar, the first being normal_ negative, the second positive, owing- partly to recovery and: partly to the positive after- effect ; and the last phase representing a return from this positive. These three phases, therefore, though apparently similar, are not really the same as those just referred to under continuous stimulation, where the ‘medium negative (postteve) phase’ was the result of fatigue-reversal. The so- called negative (fosztive) effect which alone appears on the instantaneous stimulation of relatively inexcitable tissues is, again, the positive response of a sub-tonic tissue to a stimulus deficient in true excitatory value, already described (p. 422) as case (1). Similar positive responses of vegetable tissues in a sub-tonic condition under the action of light were seen in fig. 240. We come next to the question whether or not we may discover multiple responses in the retina analogous to those which have already been demonstrated in the case of vege- table tissues. The occurrence of such an effect has not hitherto been suspected. We have seen that, under the continued action of light, vegetable tissues exhibit multiple responses ; and since we have found a general close analogy to exist between the responses to light of the retina and of these, we should expect that similar multiple responses would be found in the eye also. The reason why these were not hitherto detected lay in the inevitable depression of excit- ability in the isolated retina or eyeball. In the retina of certain fishes, where the excitability does not appear to decline so rapidly, I have often obtained records of multiple responses For example, in the retina of Wallago attu fish the stimulus of ° nee’ COMPARATIVE ELECTRO-PHYSIOLOGY light applied for three seconds gave as its after-effect multiple responses which lasted for ten minutes, the average period of each oscillation being twenty seconds. I have also obtained such multiple responses from the eye of vigorous bull-frogs, a photographic record of one of these results being given in fig. 252. We shall also see at the end of this chapter that it is quite easy to detect the occurrence of these multiple responses in the intact human eye under stimulus of light. As we have seen that multiple response is the expression of energy previously absorbed, and held latent in the tissue for a time, and since, as has been stated, the retina itself exhibits multiple response, it is easy to see that this organ, on the cessation of light, will show after-effects. In my experiments on the effects of light on vegetable tissues I found, as has already been said, three different types of direct- and after- effect. The first of these related to those highly excitable tissues which under continuous stimulation gave normal responses (—~+—+). In Fic. 252.—Photographic Re- gych cases, if the stimulus was cord of Multiple Response ; of Retina of Frog under stopped on the attainment of Continuous Action of Light 14.imum positivity the immediate after-effect was an increase of positivity. The formula was thus (—+ ++). In the third type, with sub-tonic tissues, the sequence, under continuous stimulation, was (+ —-+-—), and on the stoppage of stimulation at maximum negativity this negativity became suddenly augmented. The formula here was thus (+ —---). In the second or inter- mediate type, again, the formula of the direct and after- effects was either (— + -+-) or (— -:-). I shall now discuss in some detail the various types of after-effects met with in the retina, corresponding, as I shall be able to show, with those met with in vegetables tissues. After-effects like those of Type I., had not hitherto been noticed in the retina for the reason that their demonstration ‘RESPONSE OF RETINA TO STIMULUS OF LIGHT —<— | can only be obtained in a tissue of normal high excitability, and not in one which has undergone depression in con- sequence of isolation. I was fortunate enough, however, to meet with a species of fish, Ophiocephalus marulius, whose vitality is so exceptional that it lives for days when taken out of water. When the fish is pithed, its heart continues beating vigorously for many hours. I made a preparation of the eye of this fish and carried out experiments on it under the action of light. | In fig. 254 is given a record obtained with this specimen during the application of light and on its cessation. It will FIG. 253. FIG. 254. FIG. 255. FIGs. 253, 254, 255. Parallel Records of Responses given by Plant and Retina, during and after Illumination, illustrative of Type I (— + +). In all these cases up-curve represents induced galvano- metric negativity ; down-curves, positivity. White background in this and following records represent light, and shaded, darkness. Fig. 253. Response of petiole of Aryophylium. Light was cut off on attainment of maximum positivity in the second of the multiple responses. Fig. 254. Similar effect in response of retina of Ophzocephalus fish. Fig. 255. The same with another specimen. Light. was here cut off after the first oscillation. be seen that during the application of light the sequence was (—+—+). It will be noticed that, after completing two oscillations, and after the response-curve was even slightly reversed at its maximum positive phase the light was with- drawn. The immediate effect was a sudden increase of posi- tivity, followed by a series of after-effect oscillations. In the next figure (255), obtained with a different specimen of the same fish, light was withdrawn at the exact moment of maximum positivity, and the result is seen to be similar to the last—namely, an immediate enhancement of positivity, - ageiRfe. 428 COMPARATIVE ELECTRO-PHYSIOLOGY followed by an after-oscillation. The essential similarities between these and corresponding records obtained on a fast- moving drum, of the response of the petiole of Sik wi det under light (fig. 253), are sufficiently obvious. When the excitability of the tissue is not so high, we may obtain after-effects of Type II., in which the formula is —-+-+--) or (—---). This was exemplified in vegetable tissues (cf. fig. 245 @).. In Ophziocephalus, 1 was able to obtain — this result also, when the specimen was slightly fatigued (fig. 256). With the eye of the frog, Kiihne and Steiner obtained .the record given in fig. 257, which is seen to be parallel to that given in fig. 256, its true significance being shown in the formula (— +---). | Fic. 256. FIG. 257. Fics. 256, 257. Parallel Records given by Plant and Eye; during and after Illumination, as illustrative of Intermediate Type II. (— + ---) Fig. 256. _ Response of retina of Ophzocephalus when slightly fatigued. Fig. 257. Response of frog’s eye (Kiithne and Steiner). A sub-case of Type II. is represented again, by (—-+--), where on the sudden cessation of light, there is a transient increase of excitatory response, This, as we saw, was due to the abrupt withdrawal of the antagonistic influence of a reversing force. I may state here that I have been able to demonstrate an exactly parallel effect with nerve of frog, where the excitatory negative effect during stimulus under- goes a brief and sudden augmentation on its cessation (p. 5 36). This sudden augmentation on the stoppage of stimulus has been taken as a proof of the existence of antagonistic pro- cesses of assimilation and dissimilation, rather than as due to molecular-derangement by external stimulus and its after-effect. RESPONSE OF RETINA TO STIMULUS OF LIGHT 429 That, for its explanation, however, it is not necessary to postulate the two processes of assimilation and dissimilation is clearly seen from the fact that I have obtained: an exactly similar effect in inorganic. substances, suchas silver bromide, a record of whose response is seen in fig. 258. | We next turn to what has been- designated as Type III.,-in which the sequence of responses, owing to the depressed. condition of the -tissue, is. reversed, the formula here. being (+—+-—), while the direct and after- effects are represented by (+ —--:). asiecih —— This result was already obtained in the f sub-tonic tissue of the petiole of cauliflower, a record of this being given in fig. 259. Iwas able to detect similar effects in a, retina of Ophzocephalus, in => oom ee we wee eee eee —_—_—_— which response had become reversed under the sub-tonicity- due to long isolation (fig. 260). These results will explain the somewhat anomalous re- sponse which Kiihne and _ Steiner obtained with the isolated retinz of certain fishes (fig. 261). Returning now from the question . rieet . Fic. 258. After-effect of multiple excitations during and after OF bight “on “Silver the exposure to light—in prepared speci- Bromide mens, where results must. be modified The thick line represents response during light to.an unknown extent by the effects ~ (half a minute’s ex- ' \ ' t ' ' ' ' ' ' 1 \ \ { \ ‘ ‘ \ \ \ \ : eee VELOCITY OF TRANSMISSION OF EXCITATION 449 same specimen. The distance through which the transmis- sion was observed was 27 mm. TABLE SHOWING VARIATIONS OF VELOCITY OF TRANSMISSION AND. OF AMPLITUDE OF RESPONSE WITH INCREASING FATIGUE Intervals of rest Time igen aenaae = Velocity The plant fresh. . | 14°3 seconds 34 divisions 1°88mm. persec. 3 minutes . : or} BS SeL 55 20 a 1°86mm. ,, 2 minutes , , ta ye We See Oe eee I°72mm. ,, I minute ; : Ag eh eee he SURI 1°64mm. ,, = minute ; : SPSS Lr tes 154mm. ,, It will thus be seen that the fatigue due to having only half a minute’s rest reduced the normal velocity of the specimen by 18 per cent. The effect of intensity of stimulus on velocity of trans- mission was next studied. The stimulus employed was that of condenser discharge, increased intensity being obtained by an increasing voltage of charge. In this way it was found that velocity increased with increasing intensity of stimulus. This fact is shown in the following table, which gives the results of an experiment on a petiole of Liophytum. TABLE SHOWING INCREASE OF VELOCITY WITH INCREASING STIMULUS Specimen I.—Centripetal T; ransmisston The distance traversed by stimulus was 27 mm. Stimulus Time | Velocity ‘o1 Microfarad charged to 8 volts 14°9 seconds | 1°8 mm. per second > $9 I2 >> 14°4 29 I°9 mm. >? en BULSIOL 5 TAB * 55 | 2° mm. Pe Spectmen 11.—Centrifugal Transmission The distance traversed by stimulus was 38 mm. Stimulus Time Velocity ‘ol Microfarad charged to 8 volts 11°6 seconds 3'27 mm. per second | » » 16 ,, 10'2 ;; 3°72 mm. 9 os Ps 24; ROE 25, 3°76 mm. = ee ” oo) 32 4 9°9 ” 3°83 mm. ” 450 COMPARATIVE ELECTRO-PHYSIOLOGY With regard to the effect of temperature, I found that cold reduced the velocity of transmission. Thus, in one experiment, slight cooling reduced it to one-third, and when carried still further, it abolished the conductivity altogether. A rise of temperature, on the other hand, had the effect of enhancing velocity of transmission. The following table shows that a rise of temperature from 30° C. to 35° C. doubled the velocity, and that at 37° C. the rate was. almost three times that at the first temperature. The velocity was in this case determined in the centrifugal direction. TABLE SHOWING THE EFFECT OF RISE OF TEMPERATURE ON VELOCITY. Distance traversed by stimulus 41 mm. Temperature Time | Velocity 307¢), II seconds 3°7 mm. per second 35° C. 5 33 7°4 mm » 37° C. 4°5 9 | g*t mm. ry) Transmission of excitation, as I have shown elsewhere, and shall show again, is depressed or abolished by the action _of anesthetics. We shall also see, further, that the polar effects of currents on the velocity of transmission are the same in the plant as in the animal, being opposite, accord- ing as it is the anode or kathode. In the case of a so-called ‘sensitive’ plant, by taking advantage of the motile indica- tions afforded by the leaf or leaflet, it is possible to determine the velocity of transmission of excitation and its modifica- tions. With ordinary plants, however, no such indications being available, it is obvious that we must find some other means of detecting and observing the excitatory wave during transit. Onesuch I have described elsewhere as the Electro- tactile Method. It is found that the passage of the excitatory wave, even through an ordinary tissue, brings about minute form-changes. These give rise to pressure-variations as between two enclosing contacts. And this variation of pressure, in turn, can be recorded by means of a sensitive electrical device. VELOCITY OF TRANSMISSION OF EXCITATION 451. There is, however, a more direct way of detecting the excitatory wave during its passage through a vegetable tissue. In this—the Electro-motive Method—the galvano- meter takes the place of the motile leaflet. It has been shown that. when the plant tissue is directly excited, the state of excitation is invariably accompanied by an electro- motive variation, the excited point becoming galvano- metrically negative. Hence any excitatory wave which is transmitted through the tissue will always have an electro- motive wave as its strict concomitant. The moment, there- fore, at which excitation reaches any given point, may always be determined by observing the arrival at that point of the excitatory electrical disturbance of galvanometric negativity. In order to prove that the arrival of excitation at the given point is attended by this specific electrical response, we may perform an experiment on a plant such as Biophytum, which is provided with motile leaflets. One of the indicating leaflets is attached to the optic lever, its base being connected with one of the electrodes of the galvanometer, while the second is attached to a distant point on the leaf. The two spots of light, one from the optic lever indicating the mechanical response, and the other from the galvanometer, indicating the electrical, are so adjusted as to lie one above the other, on the same revolving-drum. On now applying a stimulus, say thermal, at.a distant point, it will be found, after the lapse of a definite interval; that both spots of light are deflected at the same time, showing that both alike give an outward indication of that state of molecular disturbance which is synonymous with excitation. These manifestations, of both kirids, would therefore take place at an identical moment, if only the inertia of the two indicators were absolutely the same. But, just as the same impulse would be indicated at slightly different times, if one indicating-lever were light, and the other heavy, so here also there may be a slight difference as regards time between the appearance of the mechanical and electrical GG2 452 COMPARATIVE ELECTRO-PHYSIOLOGY responses, according as the virtual inertia of the one indicator exceeds that of the other. In determining velocity of transmission by the Electro- motive Method, a previous experiment gives us the loss of time due to the inertia of the galvanometer. This, deducted from the observed interval between the application of stimulus and response, gives the time required for trans- mission through the given distance. In this manner I have been able to determine the rate of transmission of excitation in ordinary plants. I give below a table which shows these velocities as determined by me in the case of sensitive plants, and of ordinary plants, and for the purpose of comparison, those obtained by other observers, in the nerves of some of the lower animals, from which it will be seen that all these are more or less of the same order. TABLES GIVING VELOCITIES OF TRANSMISSION OF EXCITATORY WAVE (a) Animal. Subject Velocity Nerve of Anodon : . | IO mm. per second | | Nerve of Eledone (observed by Uexkiill) ‘5 to 1 mm. Ms (6) Sensitive Plants. Subject | Velocity | eens Mimosa pudica: petiole. : : ; | 14 mm. per second Neptunia oleracea: petiole . : ; . | I°I mm. ie Biophytum sensitivum : | Petiole of, direction centripetal . 7 2°I mm. Petiole of, direction centrifugal . 3°38 mm. os Peduncle of . F : : ; | 3°7 mm. ze (c) Ordinary Plants. Subject | Velocity = = - po LiLE Fern: isolated nerve of . , . 2 50 mm. per second Ficus religtosa: stem. : ; ; a 9°4 mm. ‘3 Cucurbita : tendril ; ; | 5 mm. ¥3 Jute: stem P e ‘ : ‘ - | 3°5 mm. Pe Artocarpus: petiole . ; ; ; Fae *54 mm. ae VELOCITY OF TRANSMISSION OF EXCITATION 453. Since the conduction of excitation takes place by the transmission of protoplasmic changes, it is evident that it must occur most easily along those paths in which there is greatest protoplasmic continuity. It is clear, then, that certain elements in the fibro-vascular bundles will furnish the best conducting medium. Cells of indifferent tissue, on the other hand, like the parenchyma of the leaf, are divided from each other by more or less complete septa, the fine filaments, by which neighbouring cells may be protoplasmically connected, being so minute that the conduction of stimulus through such imperfect channels must be comparatively feeble. Such tissues are, therefore, indifferent conductors of excitation, the stimulus remaining more or less localised in them. Plant-organs, then, which contain fibro-vascular elements, such as the stem, peduncle, and petiole, are for that reason relatively good conductors. Conductivity in such an organ, again, is,as we should expect, much greater along the length than across. I shall now describe an important method by which the relative conductivity of a tissue in different directions may be experimentally determined, verifying by its means the difference in the power of a tissue to transmit stimulus longitudinally and transversely. For this purpose I took a thick peduncle of J/usa, and made two electrical con- nections, of which one was at a fixed point B, transversely situated as regards C, the point of application of stimulus. The second point, A, was longitudinally above Cc, and its distance from it could be varied in successive experiments (fig. 273). If we now take a point, A, in such a position that CA is equal to CB, then, on account of the better conductivity along CA, the excitation will reach the A contact earlier than that at B, making that point galvanometrically negative. The direction of the first responsive current, therefore, will be from A->B in the tissue. If, next, the longitudinal contact be moved to A”, that is to say, so far that the excitation reaches the B contact first, then the responsive current. will 454 COMPARATIVE ELECTRO-PHYSIOLOGY be reversed, flowing now from B>A”. A point of transition, or of balance, A’, may now be found by searching, at which the movement of the exploring contact, nearer or further, will give rise to opposite responsive currents. The con- ductivity along the longitudinal direction will then be, to that in the transverse direction, as the balancing-distance CA’ is to CB. With a given specimen of the peduncle of Musa the transverse distance CB was 3°7 cm., and the longitudinal balancing-distance CA” was determined at 10°4 cm. Hence the longitudinal velocity was 2°8 times that in the transverse direction. Fic. 273. Experimental Arrangement for Comparing the Relative Conductivities in Transverse and Longitudinal Directions C, point of application of stimulus ; B, permanent transverse contact ; A, A’, A’, exploring points of longitudinal contact for obtaining balance, It has been shown that different tissues in the plant may possess extremely different powers of conducting stimulus. In animals there are specialised channels of conduction known as nerves, and in plants also I have been able to discover similar conducting tissues, which can be isolated for the study of their responsive peculiarities. Experiments on this subject will be related in detail in Chapter XXXII. It may be said here, however, in anticipation, that the velocity of transmission of true excitation through these nervous channels is, generally speaking, fairly high, being at the rate of about 50 mm. per second in the case of isolated _ —— VELOCITY OF TRANSMISSION OF EXCITATION 455 _ nerve of fern. This, for the relatively sluggish vegetable tissue, is undoubtedly very high. In connection with this question of velocity of trans- mission, a fact not hitherto taken into account is, that there are two distinct kinds of nervous impulses, travelling with different velocities—namely, the hydro-positive and the true excitatory negative. Of these the velocity of the former is greater. In the nerves of higher animals, where the velocity of transmission of true excitation is also great, it is not generally easy to distinguish one from the other, so rapid is their succession. But their occurrence as distinct waves, even in animal tissues, I shall be able to demonstrate in a subsequent chapter. In plants, however, where the velocity of transmission of true excitation is not very high, it generally lags perceptibly behind the positive wave (p. 59). Burdon Sanderson, in his determination of the velocity of trans- mission of excitation in Dzonea, arrived at the exceptionally high result of 200 mm. per second. I have shown, however, that the wave whose velocity he measured was not of true excitation, but of hydro-positive disturbance (p. 231). In the present chapter it has been my object to demon- strate the reality of true excitatory propagation in plants similar to that in the animal. The examples given will be found more fully described on referring to my book on ‘ Plant Response.’ I shall, however, in the course of the present work describe new and extremely delicate means by which the modifications of conductivity may be studied in plants unde- varying physiological conditions, 7 CHAPTER XXXI ON A NEW METHOD FOR THE QUANTITATIVE STIMULATION OF NERVE Drawbacks to use of electrical stimulus in recording electrical response— Response to equi-alternating electrical shocks—Modification of response by decline of injury—Positive after-effect—Stimulation of nerve by thermal shocks — Enhancement of normal response after tetanisation—-Untenability of theory of evolution of carbonic acid—Abnormal positive response converted into normal negative after tetanisation—Gradual transition from positive to negative, through intermediate diphasic—Effect of depression of tonicity on excitability and conductivity—Conversion of abnormal into normal response by increase of stimulus-intensity—Cyclic variation of response under molecular modifica- tion. IN the study of the electrical effects of excitation on the nerve, the chief experimental difficulty lies in the selection of a form of stimulus which can be made quantitative. In such investigations it is usual to employ the electrical form of stimulus, because of the great facilities which it offers. A marked drawback to its use, however, lies in the fact that unless extraordinary precautions are taken it is liable to lead to serious error. It must be remembered that for the detec- tion of responsive variations in the nerve an extremely sensitive galvanometer has to be employed. The excitatory effect which is to be detected being indicated by the relatively feeble electrical response, and the form of stimulus being also electrical and being of high intensity, the results are liable to be disturbed in an unknown manner by leakage of the stimu- lating current. In some cases it is possible to take the bold step of including the experimental nerve itself in a circuit in which the exciting coil and the galvanometer are in series. Under these circumstances, and employing strictly equi-alternating QUANTITATIVE STIMULATION OF NERVE 457 shocks, we have seen that the resultant response is due to the differential excitabilities of the two nerve-contacts A and B. If, for instance, we wish to obtain the responsive reaction of one point only, say A, uncomplicated by that of 8, it is” only necessary to abolish the excitability of the latter. This can be done to a greater or less extent by injury, as, say, by making a transverse section, or by scalding. Response will then take place by the induction of relative galvanometric negativity at A. In fig. 274 is seen a series of records obtained in this manner. The responses here apparently indicate growing fatigue of the nerve. They also exhibit the positive after- effect. With reference to the method of obtaining response by injuring one con- tact, commonly employed, it may be said that the assumption that the ex- citability of the injured point is totally abolished is not justified; for I have found that though recent injury causes a great depression of excitability, yet py. 274. Response of after a lapse of time the injured point — Frog’s Nerve under ‘ F ‘ar Simultaneous Excita- tends to recover its excitability to a tion of both Contacts, greater or less extent. In such a case by Equi - alternating . é Electrical Shocks, one we may expect two different effects to Contact being Injured be exhibited in the responses. The re- Note the positive after- sultant response being due, as we have i 3 seen, to the differential excitability of A and B, the gradual restoration of the excitability of B will progressively diminish the amplitude of the resultant response, thus giving it the appearance of fatigue. Under these conditions, and after a sufficiently long interval, response may almost disappear. This appears to me to be the true explanation of the gradual fall in the amplitude of response, when the specimen is a nerve, having one contact at the transverse section. It also explains why, in such a nerve, a fresh section, causing 458 COMPARATIVE ELECTRO-PHYSIOLOGY renewed depression of excitability, is necessary in order to obtain renewed amplitude of response. The second effect due to this depression, without abolition of the excitability of B, is seen in the diphasic character of the responses. The positive after-effect observed in the record shown in fig. 274 may thus be ascribed to the later induction of negativity at the depressed point B. The electrical re- sponse of the nerve is apparently liable in this way to great _ variations, when the method of record employed is differential. But it must be remembered that true characteristic variations of the response as determined by physiological modification can only be obtained by finding some means which shall be strictly independent of this differential factor. With this object, I have succeeded in devising a new mode of observing and recording the direct effect of stimulus on the nerve, uncomplicated by the differential factor. In a subsequent chapter we shall, using this method, be able to determine the conditions which induce the characteristic variations in the response of nerve, from the staircase increase to the fatigue- decline, or even reversal, through the intermediate phase of uniform reponses. The method which. has just been described, of exciting the nerve at both contacts by equi-alternating shocks, is not applicable, however, where the object of investigation is the conductivity of an intervening tract of nerve between the exciting and the led-off circuits. Here the employment of electrical shocks as exciting stimulus gives rise to disturbing unipolar effects, which persist even when the physiological conductivity of the intervening tract is destroyed as, say, by ligature or by crushing. Thus— ‘If the nerve of a frog’s leg is laid across two electrodes connected with the poles of a secondary coil, so as to close the induction circuit, a ligature being then applied to the myopolar tract, tetanus may still be observed in the isolated leg, on making the lead off from it at a certain distance of coil... These unipolar effects QUANTITATIVE STIMULATION OF NERVE 459 may obviously be very disturbing, and are indeed pro- ductive of fallacies in vivisection and also in experi- ments with the galvanometer, if not avoided by due precautions. Hering has pointed out that in experiments such as the investigation of the negative variation of nerve-currents, in which galvanometers and exciting circuits are separated by a long tract of nerve, the most complete insulation of the two circuits is no guarantee against the overflow of induced electricity through the interpolar part of the nerve into the galvanometer circuit... . This kind of unipolar stimulation is an obvious danger in all experiments on action-currents and negative variation in nerve, while it shows what narrow bounds restrict the intensities of current that may be safely used in these experiments.’ ? From this it will be seen how important it is to have at our command some non-electrical form of stimulation, when the response to be recorded is electrical. Heidenhain. em- ployed a mechanical form of stimulation, by which the nerve was subjected to blows from an ivory hammer, which was kept vibrating by means of an electro-magnetic arrangement. The employment of this mode of stimulation would there- fore eliminate all that uncertainty—arising from the possible escape of current—which is inseparable from the use of electrical stimulus. Though this method must be regarded as one of great value, yet it is impossible to say how far the excitability of a given point in a structure so delicate as nerve will remain unmodified under the repeated action of such blows. In any case, it appeared desirable to inquire whether there was no other non-electrical form of stimulus that could be rendered practicable. Besides the mechanical, the only remaining non-electrical forms of stimulus are the chemical and the thermal. Of these, the former is obviously incapable either of repetition or * Biedermann, Z/ectro- Physiology (English translation), 1898, vol. ii. pp. 222- 223. 460 COMPARATIVE ELECTRO-PHYSIOLOGY of being rendered quantitative. As regards the latter, I~have already shown its practicability for experiments on excitatory phenomena in vegetable tissues. Thus a single loop of platinum wire may be made closely to surround the experi- mental tissue. A definite current sent through the platinum loop for a given length of time will now subject the encircled area to a sudden thermal variation, which acts as a stimulus. Successive closures of the circuit for a definite length of time are ensured by means of a key actuated by a metro- nome. The intensity of stimulus may be graduated in a pre- determined manner by the adjustment of the heating-current. Excitation may then be caused either by one or by a summated series of thermal shocks. I was now desirous of determining whether this form of stimulation would prove advantageous to experiments on the nerve, and in the course of the investigation I found it to be extremely convenient and appropriate. With good speci- mens of nerve I have been able, using thermal stimulus, to obtain long-sustained records of perfectly regular responses. As regards its pliability and facility of application this form of stimulus is quite unique. How many difficult problems -are made possible of attack by its means will be realised in the course of the two following chapters, where the responsive variations of different conducting tissues under changing conditions are subjected to investigation. In order to obtain the electrical responses of animal nerve—that of frog, for example—the distal contact is killed and appropriate electrical connections made with the galvano- meter. The heating current is then adjusted for the desired amount of excitation.: The thermal variation, it must be remembered, should not be so great as to injure the tissue in any way. The platinum loop is not in this case in contact with the specimen, and this is the mode generally employed. Should a more intense stimulation be desired, however, the nerve may be allowed to rest on the platinum loop. In such a case care must be taken to see that the rise of temperature is not so great as in any way to injure the QUANTITATIVE STIMULATION OF NERVE 461 tissue. The nerve, as usual, must be enclosed in a moist chamber, a convenient form of which, as employed i in 1 practice, will be seen in fig. 291. | I shall next give a few records in illustration of the ease and efficiency with which this mode of stimulus may be applied. These records will show the characteristic varia- tions of response given by the nerve under different con- ditions. When making records of electrical responses with frog’s nerve, under electrical stimulus, Dr. Waller obtained responses of three different types. The first of these was the normal, and consisted of negative responses ; the second was diphasic ; and the third was the abnormal positive. This last he regarded as characteristic of stale nerve. These normal negative responses of the first of the three classes were found by him to undergo enhancement after a period of tetanisation ; while the third, that of the abnormal response of stale nerve, underwent a change into diphasic, or a reversal to normal, after tetanisation. From the fact that carbonic acid enhances the normal negative response of nerve, Dr. Walier has suggested that the enhancement of response in normal nerve after tetanisa- tion, and the tendency of the modified nerve to revert to the normal, are results of the hypothetical evolution ot carbonic acid in the nervous substance, due to metabolism accompany- ing excitatory reactions. It must be said, however, that no trace of the presence of carbonic acid has yet been detected in such cases. I shall be able to show, moreover, that these effects are in no way due to the evolutions of carbonic acid, but take place in consequence of molecular changes induced in the responding tissue, which find concomitant expression in changes of conductivity and excitability. I shall now give records of responses of these various types obtained under the action of thermal stimulus. In order to exhibit the effect of tetanisation I give, in fig. 275, a series of normal responses by induced _galvanometric negativity, given by nerve of frog in its normal excitatory condition. ‘This nerve was then subjected to tetanic thermal 462 COMPARATIVE ELECTRO-PHYSIOLOGY shocks, after which its responses to individual stimuli of the former intensity were recorded once more. The subsequent responses show, as is seen in the record, an enhancement of amplitude. . The next series of responses, in fig. 276, exhibits abnormal galvanometric positivity. It may be mentioned here that ; these abnormal responses are not, as supposed by Dr. Waller, exclusively character- istic of the stale condition of the nerve. For employing other and more delicate methods of record I have found even fresh nerves, under certain conditions, to exhibit this effect. Neither is this positive response due in general to any chemical degradation. Instead of this, as we shall see in the present and succeeding chapters, it may be attributed to the run-down of the latent energy of the specimen, a process Fic. 275. Enhancement of Amplitude of Response, as After-effect of which becomes accelerated in Thermal Tetanisation, in Frog’s . ; Notice , 5° isolation. When such a de- The first three responses are normal. pressed specimen is supplied Brief thermal tetanisation is here again with the requisite applied, and the responses subse- quently obtained under original energy, it becomes normally, stimulation are seen to be en- added: or even supernormally, ex- citable. The first part of the following record (fig. 276) gives a series of abnormal positive S §: #/9) § p responses obtained from a specimen of frog’s nerve, which was in a somewhat sub-tonic condition. After the appli- cation of tetanic thermal shocks it will be noticed that the responses in the second part of the figure have become converted into normal. — QUANTITATIVE STIMULATION OF NERVE 463 Between these two extremes of normal negative and abnormal positive responses there lies the intermediate diphasic. All these—positive, diphasic, and negative—may be exhibited in the same specimen, in the course of a sus- tained record of responses to single stimuli, without tetani- sation. This fact is illustrated in fig. 277, where the first series shows the unmixed abnormal positive. then passes by a gradual transition into diphasic— positive followed by negative —and this phase, lastly, is succeeded by a series of purely negative responses. We come next to the ex- planation of these phenomena. We have seen that on account of isolation the tonic condition of a highly excitable tissue will undergo a graduai decline. On account of this its ex- citability and conductivity will fall below par. We have also seen that in this de- pressed condition the normal The response Fic. Conversion of Abnormal 276. response by negativity tends to be reversed to positivity. With regard to the con- duction of excitation it may Positive into Normal Negative Re- sponse after Thermal Tetanisation to left into normal’ negative on right, after intervening tetanisa- tion. Abnormal positive response converted be said that this condition of depression will lower the power of the tissue to conduct true excitation. Thus a stimulus of given intensity, capable under normal conditions of transmission to a certain distance, will, when the tissue is thus depressed, fail of conduction to the same distance. It will now, therefore, be the hydro-positive effect of stimulus which will make its appearance alone at the distant responding point. And the electrical expression of this will be galvanometric positivity. 464 COMPARATIVE ELECTRO-PHYSIOLOGY We have also seen that a tissue which is not in the highest tonic condition may have its tonicity increased by the action of impinging stimulus, with consequent enhance- ment of its excitability. I shall also demonstrate, in Chapter XXXIV, that the effect of an impinging stimulus on a sub-tonic tissue is a similar enhancement of con- ductivity. The result of this will be either (1) that a tissue which has already conducted a moderate intensity of ot — FIG. 277. Gradual Transition from Abnormal Positive, through Diphasic, to Normal Negative Responses in Frog’s Nerve Cf. similar effect in response of skin of gecko, fig. 191. stimulus to a distant point will show, after continuous stimu- lation, an enhanced power of conduction ; or (2) that in a very sub-tonic tissue, in which true excitation has at first failed to reach the responding point, the true excitatory negative is subsequently transmitted instead of the hydro- positive alone. Under actual experimental conditions, where the stimulus is applied at a distant point, the twofold effects of exaltation of excitability and conductivity under tetanisation both come into play. In normally responding nerve, the increased con- QUANTITATIVE STIMULATION OF NERVE 465 duction of excitation, and the enhanced excitability of the responding-point, give rise to an increased amplitude of response after tetanisation, as already seen in fig. 275. Ina depressed nerve, as the transmitted effect is positive, and the tendency of the responding point itself, owing to sub-tonicity, is to the abnormal positive, the record will exhibit the ‘abnormal positive alone, as in fig. 276. But under a series of successive stimuli, the conductivity and excitability of the tissue are both gradually raised, and the effect of this is seen in the consequent gradual restoration of the normal negative response, through the intermediate diphasic (fig. 277). Or, if we do not wish to trace out the intermediate steps of transi- tion, we may tetanise the depressed nerve for a certain length of time, and record only the terminal change to the restored normal negative, as is seen in fig. 276. Taking one of the extreme cases—say that in which the response to transmitted stimulus is positive, and is converted into normal negative after tetanisation—we see that the first result is due to inefficient conductivity, allowing only the hydro-positive effect to cause response. After this, increasing conductivity, making an increasing transmission of true exci- tation possible, gives rise to a diphasic, and ultimately to the normal negative response. This result is analogous to the three types of responses—positive, diphasic, and negative —which we have already obtained with the imperfectly con- ducting tissue of the petiole of cauliflower and the tuber of potato (figs. 47, 48). We there saw that where excitatory efficiency of transmitted stimulus was sufficiently great, it gave rise to the normal negative response. When this, how- ever, was not so great, we obtained ‘the diphasic. Finally, when the true excitatory effect could not be transmitted, only the abnormal positive response appeared. That gradation by which the transmitted stimulus was made fully, partially, or non-effective, to induce true excitation, was simply and most conclusively carried out in the case of the potato, by removing the point of stimulation to an increasing distance from the responding point. In the cases H H 466 COMPARATIVE ELECTRO-PHYSIOLOGY described, then, the three types of response are exhibited by the same tissue, in indubitable relation to the variation of its effective conductivity. If, then, results exactly parallel can be demonstrated to occur in the case of nerve also, it. follows that there is no necessity there to make any such hypothetical assumption as that of the evolution of carbonic acid, suggested by Dr. Waller, in explanation of the conver- sion of abnormal response to normal. In order to show how a varying conduction will give rise to these three types of responses, I shall now describe an Fic. 278. Abnormal Positive Response convérted through Diphasic to Normal Negative under the increasingly Effective Intensity of Stimulus, brought about by Lessening the Distance between the Responding and Stimulated Points experiment which I carried out with a frog’s nerve in some- what subtonic condition. Here, when the stimulator was placed at some distance from the responding point, the response was the abnormal positive (fig. 278). When the effective intensity of transmitted stimulus was now slightly increased by moving the point of application a little nearer, the response became diphasic ; and finally, when the stimu- lator was placed still nearer, the response became normal negative. Thus with an identical specimen we may obtain at will either negative, diphasic, or positive response, by making changes only in the effective intensity of stimulus employed. We have also seen, moreover, that if we kept QUANTITATIVE STIMULATION OF NERVE 467 the stimulator at a certain distance from the responding point, such as at first to cause only positive response, succes- sive stimulations would then act to enhance conductivity gradually, and thus give rise to the appropriate changes, diphasic and negative in the response. The ultimate cause of these variations must therefore lie in the molecular condition of the tissue. Under varying cir- cumstances, this undergoes a cyclic change, the responsive reaction at any given moment constituting an indication of the particular molecular condition of the tissue. A more complete demonstration of this, carried out by an altogether different method, will be given in a subsequent chapter. My principal object in this chapter has been to prove the efficiency of the thermal shock as a mode of stimulation of nerve. Its wider applicability, in the case of other related investigations, will be treated in the two succeeding chapters, HH 2 CHAPTER XXXII ELECTRICAL RESPONSE OF ISOLATED VEGETAL NERVE Specialised conducting tissues—Isolated vegetal nerve—Method of obtaining electrical response in vegeta] nerve—Similarity of responses of plant and animal nerve: (a) action of ether—(4) action of carbonic acid—(c) action of vapour of alcohol—(d) action of ammonia—(e) exhibition of three types of response, negative, diphasic and positive—(/) effects of tetanisation of normal and modified specimens—Effect of increasing stimulus on response of modified tissue. IT has been shown in the previous chapter that the state of excitation is transmitted to a distance in vegetable tissues. It has also been proved that such transmission is not due to the propagation of hydrostatic disturbance but to that of protoplasmic changes, precisely as in the case of animal tissues. It is obvious, further, that such transmission will be the more perfect the less the interruption of protoplasmic con- tinuity. Hence tissues like stems and petioles, which contain fibro-vascular elements, are found to be good conductors of excitation, whereas indifferent tissues, such as those of leaves and tubers, are relatively feeble as regards this power, excitation in their case remaining somewhat localised. Even with regard to stems and petioles themselves, a contrast is found to exist in this respect between the fibro- vascular elements and the ground tissue. Thus, in the case of a petiole of cauliflower, I made two experimental prepara- tions. In the first, the ground tissue was cut away, leaving the fibro-vascular elements ; and in the second, a column of ground tissue was left outstanding, denuded of fibro-vascular elements. The former of these was found to transmit excitation to a certain distance, whereas in the latter the transmission was practically absent. In the case of a third RESPONSE OF ISOLATED VEGETAL NERVE 469 preparation I bifurcated the specimen, stripping away from one of the two limbs the fibro-vascular elements, and from the other most of the ground tissue. Galvanometric connec- tions were now made with the free ends of the fibro-vascular and ground tissues respectively, and stimulus was applied by means of transverse cut, or by application of a hot plate across the area of union. The transmitted effect was now perceived as galvanometric negativity, at the end of that strip which was composed of fibro-vascular elements. In studying this | subject of conduction, I found the transmitted effect of excitation to be universally well ex- hibited in the petioles of ferns, successive re- sponses, obtained at a distance from the point of stimulation, being in their case singularly perfect and uniform. From this I was led to the conclusion that the disposition of the. conductors must here fic. 279. Frond of Fern with Conducting hie par ticularly uel} Nerves N exposed in Enlarged Figure to Right adapted to their purpose. I had long been desirous of isolating whatever elements in the vegetable tissue were to be regarded as performing the function of nerves, and it appeared to me that I had here found a good subject for this investigation ; and accordingly, on carefully breaking the hard casing of the petiole, and pulling it away in both directions, I was able to isolate the conducting fibro-vascular threads, which were long, soft, and white in colour, remarkably similar in their appearance to animal nerves (fig. 279). These threads vary in number with different species of ferns, and resemble animal nerves in general appearance. It is sometimes 470 COMPARATIVE ELECTRO-PHYSIOLOGY possible to detach one of them having a length of 20 cm. or more. Now the essential feature of a nerve is its protoplasmic continuity, which is ensured by its fibrous structure. And in what I have called the vegetable nerve we find.the same characteristic to hold good. On viewing this structure, as it appears on making a transverse section of the petiole, we find it enclosed within sheath-like sclerenchyma. It © mainly consists in itself of a bundle of fine fibres with a few vessels in the centre. But however remarkable these external resemblances may seem, they are by no means so startling as the more fundamental similarities which are demonstrated so soon as we proceed to subject this vegetable structure to those tests of electrical response which are characteristic of animal nerve. It may be said that for the following investigation the nerves of the common maiden- hair fern (Adtantum) and Nephrodium molle were found most suitable. In obtaining a plant nerve for purposes of experiment it is possible to dissect it out and at the same time to avoid injury. It is then placed in normal saline solution for about half an hour, so as to remove all traces of excitation due to handling. When the external temperature is not high, the excitability of the isolated plant nerve is found to remain relatively unaffected for a considerable period, but in the hot weather it undergoes rapid decline; and the only way in which I could overcome this difficulty was by placing the specimen in normal saline solution which was ice-cold. The experimental precautions to be taken are precisely the same as those observed in corresponding experiments with animal nerve; that is to say, the specimen should be placed in a moist chamber. For the process of drying is found to induce a transient increase of excitability followed by a permanent abolition of responsiveness, in the one case as in the other. In order to obtain responses, one end of the specimen may be killed by the local application of hot salt solution. The galvanometric connections are then made, one with the killed, RESPONSE OF ISOLATED VEGETAL NERVE 471 and the other with the unkilled portions of the specimen higher up. In order to ensure that the electrical indication be a true responsive reaction, it is well to use a non-electrical form of stimulus. One of the most perfect forms—as we have seen in the previous chapter, on excitation of animal nerve—is the thermal, and this may be applied in precisely the same manner, that is to say, by means of a platinum wire, surrounding, but not necessarily in contact with, the given area of the specimen, this wire being heated periodically in the manner previously described, by means of a metro- nome closing an electric circuit. With a good specimen, a single thermal shock, lasting for less than a second, will be found sufficient to induce a considerable electrical response, or a response of still greater amplitude may be obtained by the summated effects of several such stimuli. One of the most noticeable differences between this plant nerve and other vegetable tissues lies in its greater excitability. For example, while a single thermal shock of less than one second’s duration is sufficient, as has been said, to evoke immediate and considerable response from the isolated nerve, we find that, in order to evoke similar response from the petiole of the fern as a whole, it is necessary to submit it to the same stimulus some twenty times in succession, the response even after this taking place with relative sluggishness. | A still further characteristic is its indefatigability. A long series of responses to uniform stimuli, such as would in the case of ordinary tissues bring about marked fatigue, will in that of nerve induce little or none. Rapidly succeeding tetanising shocks, moreover, such as in other tissues induce rapid’ decline, induce, generally speaking, but little of such an effect on the response of nerve. In the case of this vege- table nerve also the same statements hold good. A long continued series of responses shows little fatigue. After tetanisation, moreover, we find that the responses of nerve, whether animal or vegetable, become enhanced. In the matter of the effects induced by chemical re- agents on animal and vegetable nerves, a further remarkable A472 COMPARATIVE ELECTRO-PHYSIOLOGY parallelism is to be observed. The completeness of this may be seen in greater detail in the next chapter. I shall, at the present point, confine myself to giving a few typical cases. Ether, for example, when acting on animal nerve, induces a preliminary exaltation of excitability, which is followed under its long continued action by depression. On blowing off the ether vapour again the original state of excitability is restored. In fig. 280 are seen the similar effects of this reagent on vegetable nerve, where (@) exhibits the normal response, (0) the immediate exaltation due to ether, (c) the Fic, 280, Photographic Record of effect of Ether on the Electrical Response of Plant-nerve (a) Normal response: application of ether at point marked with ¢; (4) Enhanced response in first stage of action of ether; (c) Subse- quent depression ; (2) Restoration of normal response after blowing-oft of ether. . subsequent effect of depression, which becomes marked after continuous action during twenty-five minutes, and (d) the restoration of the original condition on the blowing-off of the ether. Carbonic actd is known, in the case of animal nerve, to have the effect, in the first stage, or in small quantities, of inducing exaltation, which passes under its prolonged action, or, in the case of a stronger application, into depression. A similar effect is seen in fig. 281, where (a) shows the normal response of a vegetable nerve, and (0) the preliminary exalta- tion due to carbonic acid introduced into the vegetable nerve- RESPONSE OF ISOLATED VEGETAL NERVE 473 chamber. This is seen to increase continuously for some twenty minutes in (c). But after the expiration of half an hour depression makes its appearance (¢). This becomes still more marked, after the fortieth minute, in (e), | Fic. 281. Photographic Record of Effect of CO, on Electrical Response of Plant-nerve a, normal responses ; 4 and ¢, enhanced response during first stage of action ; @ and e, subsequent growing depression. Alcohol vapour in strong, or long-continued applications, induces marked decline of response in animal nerve. Parallel effects are seen in the case of vegetable nerve in fig. 282. The effect of ammonia on animal tissues is character- istically different, according as the subject of experiment is Fic. 282. Photographic Record of Abolition of Response by Strong Application of Alcohol nervous or ordinary tissue. While the excitability of the muscle, for example, is but little affected by its application, that of nerve is quickly abolished. In order to see whether the same characteristic difference would be exhibited, as A74 ~ COMPARATIVE ELECTRO-PHYSIOLOGY between ordinary vegetable tissues and vegetable nerve, I first studied its effect on the ordinary tissue of the petiole of Fic. 283. Photographic Record of Effect of Ammonia on Ordinary Tissue of Petiole of Walnut Note that the effect of ammonia here is practically negligible. walnut. It will be seen from fig. 283 that ammonia here induced a Digs teayy no change in the excitability. But when the same reagent was applied to the isolated nerve of fern the response underwent depression, followed by total abolition, in the course of five minutes (fig. 284). One very curious charac- teristic of the _ electrical response of frog’s nerve is the occurrence, as referred to in the last chapter, of three distinct types of re- sponses, according to its Fic. 284. Photographic Record of aye : Effect of Similar Application of condition. Thus, as_ has Ammonia on Plant-nerve already been said, while The response here is rapidly diminished highly-excitable nerve é€x- and finally abolished. sae ; hibits the normal negative response, the same nerve, when it has become sub-tonic, will give a mixed or diphasic response; and a nerve which is RESPONSE OF ISOLATED VEGETAL NERVE A75 modified to a still greater extent will show a purely abnormal or positive electrical response. Inthe case of vegetable nerve, J find exactly the same three types of response repeated, under the same conditions. This will be seen in the three sets of records given in fig. 285. The normal responses, which are negative, are here represented as ‘up, while the abnormal positive is represented as ‘ down.’ : Still more remarkable is the parallelism observed between the effects of tetanisation, on animal and vegetable nerve, both normal and modified. In the case of fresh frog’s nerve the responses are, as we have seen, enhanced, after Fic. 285. Photographic Record of Exhibition of Three Types of Response, Normal Negative, Diphasic, and Abnormal Positive, in Nerve of Fern under Different Conditions a period of tetanisation. The effect of tetanisation on vegetable nerve is precisely similar, as is seen in fig. 286. In the case of the modified frog’s nerve, moreover, it is-found that the abnormal positive response tends, after tetanisation, to become normal. This is seen in the abnormal response, whether positive or diphasic, being converted to the normal negative type. I have obtained exactly parallel effects in the case of modified vegetable nerve. In fig. 287 we see the abnormal diphasic response of vegetable nerve converted, after tetanisation, into normal negative. Thus, as in the response of animal nerve, so also in that of the vegetable, tetanisation is found to have the effect of enhancing the normal, or converting the abnormal into 476 COMPARATIVE ELECTRO-PHYSIOLOGY normal response. The abnormal response of nerve we found to be due to the joint depression of conductivity and excita- bility, on account of which the positive alone, instead of the true excitatory negative, was exhibited. In experimenting with frog’s nerve we saw that abnormal! response might, at will, be converted into normal through the intermediate diphasic by appropriately increasing the effective intensity of stimulation. A simple means of effecting this was to bring the stimulator gradually nearer the responding point. Fic, 286. Photographic Record of Effect of Tetanisation in Inducing Enhancement of Normal Negative Response in Nerve of Fern The first series of responses seen to he enhanced after intervening tetani- sation, T. In the response of vegetable nerve effects exactly parallel are to be observed. With a given specimen of vegetable nerve, the stimulator had at first been placed at a distance of 2 cm. from the proximal galvanometric contact, and the responses then taken were found to be of the abnormal positive type. The — stimulator was now brought nearer, the distance being reduced to I cm., and the next pair of responses is seen to be diphasic, consisting of a positive twitch followed by the RESPONSE OF ISOLATED VEGETAL NERVE 477 normal negative response. The distance was next reduced still further, namely, to ‘5 cm., with the result that the Fic. 287. Photographic Record of Conversion of the Abnormal Diphasic into Normal Negative, after Tetanisation, Tr, in Nerve of Fern Fic. 288. Photographic Record showing how the Abnormal Positive ' Response is converted through Diphasic into Normal Negative, by the Increasing Effective Intensity of Stimulus, due to Lessening the Distance between the Responding and Stimulated Points responses now became normal negative (fig. 288). It is thus seen that there is a continuity of response in the same 478 COMPARATIVE ELECTRO-PHYSIOLOGY tissue, as between the abnormal and normal, through the intermediate diphasic. From the various experiments, then, which have been given in this chapter, it will be seen that the response of the isolated vegetable nerve is in every respect similar to the corresponding responses of animal nerve. And we shall also see how, by means of the study of this vegetable nerve, we are enabled to elucidate many obscurities in the responses of the corresponding animal tissue. We shall in the next chapter enter in detail into the question of the modifications induced in the conductivity and excitability of vegetable nerve under the action of various external agencies, and these will be found to exhibit the strictest parallel with corresponding variations induced in the animal. . CHAPTER XXXIII THE CONDUCTIVITY BALANCE Receptivity, conductivity, and responsivity—Necessity for distinguishing these— Advantages of the Method of Balance—Simultaneous comparison of variations of receptivity, conductivity, and responsivity—The Conductivity Balance—Effect of Na,CO, on frog’s nerve—Effect of CuSO,—Effect of chemical reagents on plant nerve—Effect of CaCl, on responsivity—Responsivity variation under KCl—Comparison of simultaneous effects of NaCl and NaBr on responsivity —Effects of Na,CO, in different dilutions on conductivity—Demonstration of two different elements in conductivity, velocity, and intensity—Conductivity versus responsivity—(a) effect of KI—(4) Effect of Nal— Effect of alcohol on receptivity, conductivity, and responsivity—Comparison of simultaneous effects of alcohol—(a@) on receptivity versus conductivity—(2) on receptivity versus responsivity, WE know that when any point in a tissue is acted on by external stimulus, it receives the stimulation and is thrown into a state of excitation. This excitation is then conducted along the length of the tissue, and may be made outwardly manifest at some distant point by means of a suitable in- dication such as motile or galvanometric response. There are thus three different aspects of the excitatory effect to be distinguished from each other, namely, first the excita- tory effect at the point of reception of stimulus, which I have elsewhere designated receptive excitability, or simply Receptivity : secondly, the power of transmission of excita- tion, or Conductivity: and thirdly, the excitatory effect evolved at the distant responding region, which I shall henceforth term Responszvity. ‘Though these three aspects of the excitatory reaction are all alike dependent upon the molecular derangement caused by stimulus, it is nevertheless important to consider them separately, since their variation is not always the same under the same circumstances. We 480 COMPARATIVE ELECTRO-PHYSIOLOGY have seen, for example, that a rise of temperature, by in- creasing molecular mobility, enhances conductivity. But this increase of molecular mobility and internal energy also goes to augment the force of recovery, and, owing to this, the amplitude of excitatory response may be decreased. Thus, while a rise of temperature increases conductivity, it may appear to decrease responsive excitability. So much for the necessity of a distinction between conductivity and | responsivity. The term ‘excitability’ is commonly used for receptivity and responsivity indifferently. But I shall show in the course of the present chapter that it is important to make a distinction between these, since ‘the same external agent may effect the two differently.’ In the ‘following investigation, receptive excitability, or receptivity, will be represented by R, conductivity by cC, and responsive ex- citability, or responsivity, by E. In determining the effect of any external condition such as the application of a chemical reagent on responsive ex- citability, in the case of animal nerve, it is usual to take a series of normal responses, and then to record the modified responses after the application of the reagent. By com- paring a number of such series of records, representing the action of various reagents on different specimens, the relative effect of each chemical may be inferred. The drawback to this method lies, first, in the fact that by the addition of the chemical reagent the resistance of the electrical circuit undergoes an unknown change, thus inducing a variation in the amplitude of response, which is not necessarily due to the excitatory electromotive change fer se. It is true that this difficulty may to a greater or less extent be obviated by interposing a high external resistance in the circuit, but this, by reducing the deflection, necessarily reduces the sensitive- ness of the method also. Different specimens again cannot but be characterised by slight individual peculiarities, and the experimental arrangements therefore can only be considered to be perfect when we are able to compare the effects of two ! See also Bose, Plant Response, pp. 215-230. THE CONDUCTIVITY BALANCE 4381- agents on an identical specimen. Again, in a series of chemical compounds which differ but slightly in effect from one another, an arrangement has to be devised by which the most minute excitatory variations will be conspicuously displayed. The same delicacy of experimental adjustment also becomes necessary when we wish to investigate the varying effects of time and quantity in the application. Similar considerations are involved when we attempt to observe the effects of various agents on conductivity and receptivity ; and still more complicated are the difficulties to be overcome when we have to study the property of con- ductivity versus responsivity or receptivity, or of receptivity versus responsivity, under the action of the same external agent. The methods hitherto available are neither perfect nor delicate enough for a complete and satisfactory determina- tion by their means of the various problems which arise in this connection. I' shall now, however, describe a very perfect and delicate method carried out by an experimental arrangement which I have devised, and shall designate as the Conductivity-Balance, by which the variation of an affected region may be continuously compared with a normal area as regards each of the three different aspects of the ex- citatory reaction, namely, receptivity, conductivity, and responsivity. In this method, moreover, the result is un- affected by any variation of resistance in the circuit that may be induced by changed conditions. It also enables us to solve the various difficulties encountered in comparing the relative changes induced in conductivity with those induced in receptivity or responsivity, or in the two last in respect to each other, under the influence of a given reagent. In fig. 289 is given a diagrammatic representation of the principal parts of this Conductivity-Balance. The thermal stimulator produces stimulation of the enclosed area of the specimen. The excitatory wave travels along both arms of the balance, through the conducting region C and c’, and induces excitatory electromotive effects at the two responsive points Eand E’. The excitatory electrical effects at E and E’ IT 482 COMPARATIVE ELECTRO-PHYSIOLOGY are opposed, and when these are equal, and balance each other, the galvanometer indication is then reduced to zero. E and E’ are usually at a distance of about 4 cm. from each other. When the stimulator is brought too near to the left contact E’, the excitatory effect of galvanometric negativity which is induced there is relatively greater than at E. The balance is thus dis- turbed, and the resultant responsive deflection is then, say, downwards. When the stimulator is placed, on the other hand, too near the contact E, to the right, the resultant galvano- metric deflection will be up.! By suitable movement of the stimulator, to and fro between these two ex- tremes, a point may be found where the excitatory effects at E and E’ will exactly balance each other. I give here (fig. 290) a record taken Fic. 290. Photographic Re- cord made during Pre- liminary Adjustment for Balance of Nerve of Fern The first two down-responses show over-balance, when S is too near the left, E’ being relatively more Fic. 289. Diagrammatic Representa- tion of the Conductivity Balance excited. The up-responses s, thermal stimulator; c and c’, the indicate over - balance conducting arms of the balance ; caused by s_ being too E and E’, responding points. Dif- much to the right. The ferential excitatory electrical effects horizontal record shows at E and E’ recorded by galvano- attainment of — exact meter, G. balance. during this preliminary stage of adjustment. The first two down-responses were obtained when the stimulator was too far away from the balancing-point to the left. The next two 1 It is to be understood that what is said here refers to nerve in a normal condition of conductivity. THE CONDUCTIVITY BALANCE. 483 up-responses were obtained when it-was contrariwise too far to the right. More careful adjustment reduced this up- movement, as seen in the next two responses, and finally, when the exact balancing-point was reached, the effect was null, as seen in the horizontal record. In studying the question of the variation of responsive excitability induced by any given reagent, the agent is applied at the point E to the right. Any variation of excit- ability will then upset the balance. If the reagent be of a stimulatory character we shall obtain a resultant up-response, but if it be of a depressing nature, E will be rendered rela- tively the less excitable of the two points, and the response will consequently be down. It will thus be seen that that upsetting of the balance by which either up- or down-responses are induced is due simply to the relatively excitatory or depressing effect of the reagent, and is completely inde- pendent of any variation of resistance which might be brought about by its application. In the course of the following investigation, it is to be understood that the elec- trical connections are so made that the greater excitation of the right-hand contact is always represented by up-response, and vice versd. If it be desired to make a comparison between the excitatory reactions of two reagents, then the two are applied simultaneously, one at E and the other at E’. The resulting record then affords us a continuous graphic illustration of the relative and varying effects of the two. If, again, it is the influence of any agent on conductivity that is to be studied, we first take a balanced record and then apply the given reagent on an area of about I cm. at Con the conductingarm. In this case, the responsive excitabilities of the two points E and E’ are the same, but if the effect of the agent have been to induce increased conductivity of Cc, then the excitation transmitted to the right-hand side, E, will be greater, and the response caused by the upsetting of the balance will be upwards. Conversely, a down-response will indicate that the effect of the agent has been to depress the conductivity. Again, we can compare the relative effects in II2 484 COMPARATIVE ELECTRO-PHYSIOLOGY conductivity-variation induced by two different agents which are applied simultaneously, one on the arm C and the other enc, It is possible again to compare the variation of con- ductivity with that of responsivity, by applying one agent at a responding region, say E, and the other on the opposite arm of the balance atc’. The mode of investigation of receptivity changes will be described presently. : In fig. 291 we have the complete apparatus. The animal or vegetal nerve, N N, rests on non-polarisable electrodes of E. E2 Es; E 4 Fic. 291. Complete Apparatus of Conductivity Balance The nerve N supported on electrodes E,, E,;. The two other electrodes E, E, are not used in this experiment, but are employed for experiments on electrotonus; T, thermal stimulator, the relative lengths of the arms of the balance being adjusted by the slide s. a U-shape. For the present experiments, two electrodes, E, and £,, are sufficient, their mutual distance being capable of any variation by movement along a sliding-bar. The same apparatus might be used for experiments on electrotonus, in which two additional electrodes would be required. The position of the electrothermic stimulator T is capable of very careful adjustment for purposes of balance, by means of the sliding-rod s. A glass cover, not shown in the figure, fits into the groove which is represented by a double dotted line sur- rounding the apparatus, and thus enables the chamber con- taining the nerve to be kept in a properly humid condition. THE CONDUCTIVITY BALANCE 485 In all these experiments by balance, it is to be borne in mind that adjustment is always made for perfect balance at the beginning of the record, and represented by a short, more or less horizontal, line. te In order to show the typical effects of induced variations of excitability, in upsetting the balance, I shall first give records of experiments carried out on the nerve of frog. Dilute sodium carbonate is known to be an agent which enhances excitability. A long-continued application, or the application of a stronger dose, may, however, bring about a depression. When a dilute solution of Na,CO, was ap- Fic. 292. Effect of Na,CO, Solution on Responsive Excitability of Frog’s Nerve In this and following records the hori- zontal line at the beginning indicates exact balance. The upsetting of the balance in the up-direction repre- sents either the enhanced respon- sivity of the right-hand responding eg _E, = the Leer a con- uctivity of the right-hand arm c, Riowascueeal eee ont correspond- Fic. ASS SEM Se SRR On Et0g's ing absolute or relative depressions. Nerve Na,CO, applied to E is seen to exalt The down record shows depression of the responsivity of that point. excitability. plied at the responsive point E on the right side, the up- setting of the balance upwards immediately indicated the greater excitability induced by the reagent. The long- continued action of this reagent, however, showed that the enhanced excitability was undergoing a gradual decline (fig. 292). In order to exhibit the characteristic upset caused by a depressing agent, I employed on another specimen a toxic solution of copper sulphate, applying it at E on the right. The previous state of equilibrium is seen by the horizontal line at the beginning of the record, and the 486 COMPARATIVE ELECTRO-PHYSIOLOGY subsequent depression of excitability at E is shown by the upsetting of the balance downwards (fig. 293). I shall next take up the determination of the changes induced by chemical agents on the excitability of plant nerve and shall begin by describing the different effects which occur on the application of calcium and potassium salts. For this purpose, deci-molecular solutions were employed. Fig. 294 shows the effect of CaCl, on. vegetable nerve, the solution being applied at E on the -right-hand side. It will be noticed that this caused an upset of the balance, showing an increase of excitability that becomes considerable after the expiration of five minutes. In the case of KCl, however, this effect was re- versed, that is to say, a de- pression was induced. This , is seen in fig. 295, where the _ Fic. 294. Photographic Record show- balanced record gives way, ing Enhancement of Responsivity Gat te diphasic, and :atter- by Application of CaCl, CaCl, applied to E is seen to exalt wards to a down-response, the responsivity of that point. indicating an effect of de- | pression at E. These two experiments show the effect of the basic moiety in in- ducing changes of responsive excitability. I shall next describe experiments by which the simul- taneous effects of two different reagents on the responsivity of a given tissue may be compared. For this purpose, one agent is applied at one end of the balance E, the other being administered at E’. In the case of animal nerve, it was shown by Griitzner, that both NaCl and NaBr induce ex- citatory effects, that induced by NaBr being relatively the greater. But the continued action of either of these reagents THE CONDUCTIVITY BALANCE 487 induces depression, which sets in earlier in the case of NaBr. The effect of these two reagents on vegetable nerve is pre- Fic. 295. Photographic Record showing Depression of Responsive Excitability by Application of KCl cisely the same, as will be seen from an inspection of the record given in fig. 296. The NaBr was applied on the Fic. 296. Photographic Record exhibiting Comparative Effects of NaCl and NaBr on Responsivity NaCl was applied on E’ and NaBr on £, the formula being E’yaciEnapr- The record shows the greater and earlier effect of NaBr at E in causing relative excitation followed by relative depression. right-hand side E, and NaCl on the left-hand E’,a process which is expressed, for the sake of brevity, by the formula E'wacil’wapr =0Lhe greater and earlier. excitatory effect of 488 COMPARATIVE ELECTRO-PHYSIOLOGY NaBr, applied on the right-hand side, is shown by the resultant up-responses. But after a time, E being now depressed by. the continued, action of NaBr, the effect of NaCl, applied on the left, becomes relatively predominant, a fact demonstrated by the upset of the balance in the oppo- site direction, with concomitant down-responses. We shall next take up the subject of variations induced in conductivity. We have seen that dilute solutions of Na,CO, have the effect of exalting responsive excitability. FIG. 297. Photographic Record of Effect of Dilute (+5 per cent.) Solution of Na,CO, on Variation of Conductivity Reagent applied on right arm c. Record shows immediate enhancement of conductivity giving rise to up-curves, followed by depression, seen in down-curves. Note the appearance of a down-twitch at the be- ginning of the sixth response due to the later arrival of excitation at E. Note further the replacement of up- by increasing down-responses. Long-continued applications, or strong solutions, however, have the effect of inducing a depression. Similarly, I find that this reagent has the effect of enhancing conductivity, provided the solution is sufficiently dilute. In the case of the petioles of ferns, a 2 per cent. solution was found to induce a preliminary exaltation of excitability, followed by a depression (p. 136). In dealing with the conductivity- variation in certain isolated vegetable nerves, however, a 2 per cent. solution was found to induce a depression of con- ductivity, but a °5 per cent. solution caused an enhancement THE CONDUCTIVITY BALANCE 489 of conductivity, followed, after long-continued action, by depression. These facts are illustrated in an extremely interesting manner in the records given in figs. 297 and 298. In both these cases the solution was applied on the right arm of the balance at C, the difference being only that in the first experi- ment the strength of solution was ‘5, and in the second 2 per cent. An inspection of fig. 297 shows that the application of the first induced a great and immediate enhancement of conductivity, causing resultant up-responses, which were par- ticularly marked during the first four minutes. This increased Fic. 298. Photographic Record of Effect of Stronger Dose (2 per cent.) of Na,CO, Solution on Conductivity. The solution was applied on the right arm of the balance c. Note grow- ing depression and appearance of diphasic effect. conductivity is then seen to undergo a continuous decrease and reversal into growing depression, as seen in the substi- tution of increasing down-responses. This record deserves special attention, inasmuch as it affords us an insight into a phenomenon which could not otherwise have been suspected. Greater conductivity is usually associated with increased velocity of transmission. It would appear, however, that the term conductivity really covers two different phenomena which may not always be concomitant. That is to say, an increase of conductivity may mean either a greater speed of transmission of excitation or a greater intensity of the 490 COMPARATIVE ELECTRO-PHYSIOLOGY excitation transmitted. In the first four records of the present series the induced enhancement of conductivity is shown by the occurrence of up-responses only. The fifth record, how- ever, shows a marked preliminary twitch in the negative direction, followed by an up-response of some amplitude. This shows that the excitatory effect reached the. right end E later than the left, though the intensity still remained greater. The continued action of the reagent subsequently ~ reduced the intensity also, so that this diphasic ultimately became converted into a purely monophasic down-response, gradually increasing to a maximum. In fig. 298 we observe the depression of conductivity by a stronger dose of 2 per cent. solution of Na,CO,, applied on the right-hand side at C. Here, again, we can see the separated effects of the two elements of conductivity—that is to say, the intensity of the effect transmitted and the speed of transmission. In the first ‘few responses of this series we see the diminished intensity of transmission to the right giving rise to resultant responses which are entirely downwards. Later, this transmission of enfeebled excitation becomes delayed also, and by the phase- difference thus induced we obtain the growing diphasic effects which have already been fully explained on p. 144, fig. 100. Owing now to this growing difference of phase, the two opposed effects no longer neutralise each other to the same extent as before, and we obtain increasing amplitude of both the constituent phases. The down-curve in the diphasic response represents the earlier arrival, and relatively greater intensity, of effect at the left contact E’. And the up-curve shows the later arrival of the less intense effect at the right- hand contact: E. It is thus clearly seen that conductivity includes two different elements of speed and intensity which may not in all cases be coincident. I shall next describe experiments which will demonstrate the variation of conductivity versus that of responsive excit- ability under the action of the same reagent. In animal nerve responsive excitability is diminished by the action of strong solutions of neutral salts, and potassium salts induce greater THE CONDUCTIVITY BALANCE 491 depression than corresponding sodium salts. But neutral salts, generally speaking, affect conductivity to a much slighter extent than responsivity. There is, however, a very curious exception to this rule in the case of animal nerve, where 6'1 per cent. of Nal is found to affect the conductivity to a much greater extent than the responsive excitability. I find a remarkable parallelism to these effects in the case of vegetable nerve, which is capable of striking demonstration by the comparative method of simultaneous variations of conductivity and excitability already de- scribed. In order to demonstrate these con- trasted effects of KI and Nal on conductivity and excitability, I shall here give an account of two different experi- ments. In the first, after obtaining the pre- liminary balance, KI was applied at ton Fic. 299. KESPONSIVITY versus ie pia ; CONDUCTIVITY under KI SHE Sie eee, SOS saat This photographic record shows the effect of reagent being also ap- KI on responsivity and conductivity when Tiead th ee reagent applied at £’ and C simultaneously. pile at € end E o The formula is E’x;Cx;. Record shows the left arm, this pro- greater depression of responsivity than of ; conductivity. cess being represented by the formula E’,..C,,.. The record seen in fig.'299 shows, by its resultant up-responses, that a greater depression of responsivity at E’ than of conductivity at c has been induced. In the next experiment (fig. 300) Nal was applied instead of KI, on C to the right, and E’ to the left, the formula thus being E’,..C.., The resultant responses were now down- wards, showing that there was a relatively greater depression 492 COMPARATIVE ELECTRO-PHYSIOLOGY of conductivity than of responsivity. In respect of conduc- tivity and responsivity, therefore, the effects of these two drugs, KI and Nal, are seen to be opposite. In order to observe the effect of alcohol on nervous tissue, by means of the conductivity balance, I first experimented on the nerve of frog. A 5 per cent. solution was applied at the responding point E. This is seen (fig. 301) to induce a depression of responsivity. A more dilute solution generally induces a preliminary exaltation followed by depression. We said in the previous chapter that when alcohol vapour was passed into the chamber of the vegetable nerve the responses underwent a rapid abolition. This result, however, FIG. 300. RESPONSIVITY versus CONDUCTIVITY under Nal The formula in this case is E’ya1Cnar. Photographic record shows an effect opposite to that of KI as Fic. 301. Effect of Alcohol on the Responsivity of Frog’s previously described, there being Nerve now a relatively greater de- Upsetting of the balance in the pression of conductivity than of downward direction shows responsivity. depression. was due to the joint action of the variations of receptivity, conductivity, and responsivity, some of which may possibly have been in the positive and others in the negative direction. In order to determine the effect of each of these we must, then, perform separate experiments. Such a deter- mination I have made, using the method of the so-called ‘negative variation, in which the proximal galvanometric THE CONDUCTIVITY BALANCE 493 contact was on an unkilled, and the distal on a killed area. The first of these experiments was on variation of receptivity. The thermal stimulator was provided with mica shields, so that the receptive area was strictly circumscribed at the centre of the thermal platinum loop. Normal responses were first taken; the receptive area was next touched with I per cent. solution of alcohol, and the modified responses were recorded. The results are seen in fig. 302, which gives Fic, 302, Photographic Record of Effect of Alcohol Vapour on Receptivity The three normal responses to the left are seen to be exalted after applica- tion of ether onsthe receptive point. a striking demonstration of the increased receptivity induced by dilute alcohol. The effect on conductivity, however, is in curious con- trast to this, On applying I per cent. solution in the conducting region between the stimulator and the proximal contact, a very great diminution of the conducting power is observed, as seen in fig. 303. It may be stated here that a similar enhancement of receptive excitability, and depression of conductivity, are found to be the result of the action of alcohol in animal nerve also.. In the next ex- periment, it is the variation of responsivity under the action of dilute alcohol which is tested. After taking the normal 4904 COMPARATIVE ELECTRO-PHYSIOLOGY a responses as usual, a I per cent. solution of alcohol was applied at the proximal contact. It will be seen from the record in fig. 304 that the immediate effect was a depression Fic. 303. Photographic Record of Effect of Alcohol on Conductivity The three large responses to the left show the normal effect of transmitted excitation. Responses almost abolished, as seen on the right, by depression of conductivity. of the amplitude of response. This subsequently becomes converted into a diphasic response, consisting of a preliminary positive followed by the normal negative; and finally the Fic. 304. Photographic Record showing Effect of Alcohol on Responsivity a, normal responses, depressed, after application of alcohol, to d@; and converted later to abnormal positive responses c. response was totally reversed to positive, by the abolition of the true excitatory effect. It is thus seen that while dilute alcohol exalts the recep- tive excitability, it induces a depression of both conductivity THE CONDUCTIVITY BALANCE 495 and responsivity. I shall now describe further experiments by which the. relative effects of alcohol are compared, as between conductivity and receptivity, and as between recep- tivity and responsivity. : For the purposes of such a comparison, a new balancing arrangement has to be employed (fig. 305). Here, two electro-thermic stimulators are in series, so that ex- citations may be produced at two different points simultaneously. The gal- vanometer contacts E’ and Fic. 305. Diagrammatic Repre- sentation of Experimental Ar- rangement for Demonstration of RECEPTIVITY versus CON- FIG. 306. RECEPTIVITY versus RESPON- DUCTIVITY, or of RECEPTIVITY SIVITY under Alcohol versus RESPONSIVITY Alcohol was applied at the receptive point s and s’ are exciting thermal loops to the left R’, and the responsive point in series ; R and R’, the enclosed to the right E. The formula was receptive points ; C and Cc’, con- R'aic.Eatc, The photographic record ducting arms; E and E’, the shows the relative enhancement of responsive points. receptivity. E are made with two points intermediate between the stimu- lators. The distance of one of the two stimulators is kept constant, at, say, 2 cm. to the left of E’, while the other is moved nearer to, or further from, E, until a balance is obtained. A 1 per cent. solution of alcohol is then applied to the left receptive point, R’, and the right conducting area, C, the formula now being R’,.C,,... The fact that the receptive excitability is heightened by this reagent, and conductivity depressed, receives independent confirmation “from the upset of the balance, giving rise to a downward response. 496 COMPARATIVE ELECTRO-PHYSIOLOGY The next experiment consists of a comparison of the simultaneous variations of receptivity and_ responsivity. Alcohol is applied at R’ and E, the formula thus being RlacEace .And we find here in confirmation. of our previous results that, on account of the opposite effects of this agent on the receptive and responsive excitabilities, the resultant response is downwards (fig. 306), showing that the receptivity has been relatively exalted. Thus the experi- ments which I have here described show that the same agent may have different effects on receptive and _ responsive excitability, and thus accentuate the necessity of clearly distinguishing between the two. CHAPTER XXXIV EFFECT OF TEMPERATURE AND AFTER-EFFECTS OF STIMULUS ON CONDUCTIVITY Effect of temperature in inducing variations of conductivity : (2) by Method of Mechanical Response ; (4) by Method of Electric Balance—Effect of cold— Effect of rising temperature—The Thermal Cell—After-effect of stimulation on conductivity—The Avalanche Theory—Determination of the after-effect of stimulus on conductivity by the Electrical Balance—After-effect of moder- ate stimulation—After-effect of excessive stimulation. IN studying the effect of temperature in inducing variations of conductivity, we may use either of two different methods— in the first place the method of mechanical, or in the second that of electrical response. For the first of these it is neces- sary to have what is generally known as a ‘sensitive’ plant, the leaves or leaflets of which afford conspicuous motile indications of the arrival of the excitatory wave from a distance. In such a case the time-interval between the application of stimulus and the response of a leaflet at a known distance gives us a measure of the velocity of con- duction ; and if we carry out successive experiments at different temperatures we have a means of determining the effect of temperature on conductivity. Employing this method, I have elsewhere given a, determination of the effect of temperature on the velocity of transmission in Biophytum sensitivum. It was there shown that lower- ing of temperature reduced the velocity of transmission even to the extent of abolition, when the cooling was suf- ficiently intense. With moderate cooling the velocity was found to be decreased to about one-third. ‘The effect of rise of temperature was, on the contrary, an increase of KK 498 COMPARATIVE ELECTRO-PHYSIOLOGY velocity. When it rose from 30° C. to 35° C., for example, the velocity was doubled. By employing the electrical method of response, however, we are rendered independent of the use of sensitive plants, and by means of the Conductivity Balance we are enabled to demonstrate the slightest variation of conductivity, as between the left arm of the balance, which is maintained at standard temperature, and the right, which is subjected to the given | change. , Thus in a definite experiment on a nerve of fern the temperature of the room was 30°C. After first obtaining the balanced record, the temperature of a portion of the right arm of the balance was lowered. This one-sided cooling was effected by supporting the right arm of the nerve, through a certain length, in the concavity of a U-tube through which cold water at 15° C. was passed. Stimuli were now applied at intervals of one minute. Previously, as will be understood, such stimuli, owing to balance, had induced no resultant effect. But now, on account of the depression of conductivity on the right side, brought about by cooling, the balance was disturbed, and the resultant down-response seen in fig. 307 shows the diminished con- ductivity of the right arm. On the ‘gessation of the flow of cold water the balance was gradually restored, in concomit- ance with the return to the original temperature. I next investigated the results of a rise of temperature, and here I specially desired to observe the conductivity variations, not at any one degree, but throughout a graduated and con+ tinuous rise. I was confronted at the outset of this investi- gation by the difficulty arising from the fact that there was no convenient and satisfactory means for the local variation of the temperature of the nerve, in definite and known degrees. In connection with this there was also the further difficulty that a sudden variation of temperature will, in itself, act as a stimulus. Hence, in studying the effects of temperature per se, it is essential that there should be no such sudden variation. These difficulties were overcome by EFFECT OF TEMPERATURE ON CONDUCTIVITY 499 the employment of an electrical arrangement to bring about the graduated and continuous rise of temperature. A certain length of the vegetable nerve on the right arm of the Conductivity Balance was thus raised continuously in temperature, and its conductivity compared with that of the left arm of the balance, the latter being maintained at the temperature of the room, which happened at the time to be 33°C. The device by means of which this was accomplished Fic, 307. Photographic Record showing Effect of Cooling on Con- ductivity of Plant-nerve Balance was obtained at starting, when temperature of both arms was 30° C. On cold being applied on right arm, the balance was dis- turbed, showing diminished conductivity on that side. On restoration of normal temperature, the balance is seen at the end of the record to be again restored. will be understood from fig. 308. A piece of cork has a small chamber cut into it measuring I cm. each way. In this is placed moist blotting-paper, which keeps it damp, and across it passes a. length of 1 cm. of the right arm of the vegetable nerve in the Conductivity Balance. This cork- chamber has inlet and outlet tubes ¢ and #.. The first of these contains a spiral, H, of platinum, which can be heated to a suitable degree by means of an electrical current, the KK 2 500 COMPARATIVE ELECTRO-PHYSIOLOGY intensity of which is capable of careful adjustment. The cork chamber is closed with a cover, through which passes a thermometer, T, for the indication of the temperature within, The tube Z’ is connected with an aspirator, and air is thus sucked in by 4, and, passing through the platinum spiral, is warmed, and raises the temperature of the nerve in the chamber. This rise of tem- perature is adjusted (1) by regu- + lating the electrical current which | heats the spiral, and (2) by con- trolling the inflow of air... As regards the first of these two processes, the electrical heating- circuit has a carbon rheostat interposed, by which the rate of rise of temperature may be regulated. The movement of the current of air, on the other hand, is controlled by adjusting the stopcock of the aspirator. By the joint manipulation of both these the rate of rise of temperature t inside the chamber may be made perfectly uniform, and in my yoga ee Rouing ate experiments this rate was approxi- Temperature of one Armof mately 1° C. per minute. ene As already said, I selected a A and B, the two halves of the - , chamber ; T, thermometer ; piece of vegetable nerve and took at ia cap aerate a balanced record. After this the heating. temperature of the thermal cell on the right-hand side was raised continuously, the response-record being taken at each degree of the rise, till a temperature of 50° C. had beenat tained. From the record given in fig. 309 it will be seen that the conductivity was always greater at temperatures up to 47° C. than it was on the left-hand side, which was all the time maintained at the constant temperature of 33°C. At 48°C, EFFECT OF TEMPERATURE ON CONDUCTIVITY 501 however, the reversal of response showed that the conduc- tivity was now being depressed. And at still higher tem- peratures it was found to undergo a very great depression, as is seen by the abrupt downward movement of the curve. It is thus seen that, by means of the Method of Balance, this very difficult problem of the variation of conductivity under variation of temperature is made capable of exact study. I shall next describe the results of an investigation into the after-effects of stimulus on conductivity and excitability, Fic. 309. Photographic Record Showing Effect of Rising Péapelatons on Conductivity Balance obtained at starting at 33° C. Successive responses recorded at each degree C. of rise of temperature. Record shows increasing conductivity up to 472 C. A depression of conductivity is seen by reversal of curve to set in at 48° C., and this becomes extremely pro- nounced at 50° €. a subject of much difficulty and of considerable theoretical importance. It has been found in Animal Physiology that the sciatic nerve of a frog, for instance, is not equally excitable throughout its length. When such a nerve, with its attached terminal muscle, is cut off from the spinal cord, it is seen to be more excitable the further from the muscle is the point on the nerve that is subjected to stimulation. From this fact that excitation increased with the distance of the point excited from the motor organ, Pfliiger was led to 502 COMPARATIVE ELECTRO-PHYSIOLOGY the ‘ Avalanche Theory,’ namely, that during the passage of excitation down the nerve it. actually gathers strength. But it is clear that this cannot be true, since we have seen that, other things being equal, excitation is always greater the nearer the point of stimulation to the responding region, and on this fact have depended all those experiments already described, which involved a delicate balance of equal excitations. It follows that the observed enhancement of excitability of a point on the nerve which is distal from the muscle, and in the neighbour- hood of a section, must be ascribed to some other cause. In reference to this Heidenhain, indeed, explained the greater excitability of higher tracts of divided nerve by the proximity of the artificial section. For the lower end of the nerve at once exhibits the same marked activity as the upper end if a section be made lower down. Excitability is, in fact, raised near the section, wherever the section may be. The distance travelled by the excitation could not, therefore, be the determining factor in the magnitude of effect. For so far from increasing it, this, as a matter of fact, causes diminution. It is to be remembered that though the excitability is increased near the point of section, yet at the section itself it is almost abolished, otherwise there could not have been any response by'so-called negative variation. The question now arises, Why should the excitability be raised near: the point of section ? It has been supposed that this was due to certain electri- cal changes induced by section, which in turn gave rise to electro-tonic variations of excitability. We shall see, in Chapter XL, that the passage of an electrical current through a living tissue induces changes of excitability. And this phenomenon is known as the electro-tonic effect.. Now any ‘injury, such as a mechanical or thermal section, is known to induce galvanometric negativity, or anodic change, at or near the point of section. But it is the kathode-effect which is excitatory. And the observed greater excitability of the nerve near a point of section is supposed to be due to kat- electrotonus, produced within a certain tract from the cross- OE i at ty ok de ie AFTER-EFFECT OF STIMULUS ON CONDUCTIVITY 503 section by internal short-circuiting of the nerve-current. That this explanation, however, does not meet all the requirements of the case will appear from certain experi- ments which I shall describe, where, under exactly similar electrotonic changes due to section, a result directly the opposite of this, that is to say, of depression, is seen to be induced. . All these various facts will be found fully reconcilable, however, on the basis of a proposition which I shall establish, namely that zz a nerve, moderate stimulation enhances ex- citability and conductivity, while excessive stimulation has the opposite effect of bringing about the depression of both. It is indeed natural to expect that while moderate stimulation, by increasing molecular mobility, would bring about one effect, excessive stimulus, by inducing overstrain, would result in exactly the opposite. Before proceeding to give an experi- mental demonstration of this hypothesis, we shall first consider the explanation which it affords of the peculiar excitatory changes observed in the case of cross-sectioned nerve. In the first place we know that a cut acts as a stimulus. And since we found that the effect of stimulus decreases with the distance from the point of stimulation, it would appear that at the section itself the stimulation would be excessive ; moderately strong at a certain distance from it; and practically negligible when very far away. In complete accordance with this is the resulting increase of excitability which has been observed near the point of section, while at the point itself the nerve is relatively inexcitable. The fact that stimulation, when not excessive, increases the conductivity and excitability, we found illustrated in the staircase increase of electrical response, and in the enhance- ment of amplitude after tetanisation, in vegetable and animal nerves (figs. 275 and 286). The same fact will be demonstrated later by means of the mechanical response of nerve. I shall now describe certain experiments which demonstrate it once more in a new and interesting manner. 2 504 COMPARATIVE ELECTRO-PHYSIOLOGY A vegetable nerve was adjusted for balance, with the ends projecting some distance beyond the electrodes. In order to show that the effect of injury is due to stimulus as such, and not to any particular form of it, I now made a thermal instead of mechanical section, by applying salt solution heated to about 60° C. in the region A, at a distance of I cm. to the right of E (fig. 310). The effect of this stimulation was to induce a moderate excitation of the right | arm of the balance, relatively to the left. If this moderate stimulation were to induce any increase of excitability and conductivity, that fact would be demonstrated by Fic. 311. Photographic Record Showing Effect of Moderate Stimulation in Enhancing Conductivity and Excita- Fic. 310. Experimental Arrange- ment for Studying After-effect of Stimulus on Conductivity and Excitability The stimulator adjusted to obtain balance between Eandk’. Stimulus of moderate or strong intensity is applied to a point on the right of E. Upsetting of the balance in an _upward direction shows an en- hancement, and in a downward direction, depression, of con- ductivity and excitability. bility otted line at beginning shows the resting-current, as a per- sistent effect of stimulation. The upsetting of the balance upwards constitutes a positive variation of the resting- current, and indicates en- hanced conductivity and excitability. the upsetting of the balance, the resultant response being upwards. That this is what actually occurs will be seen from the records in fig. 311. It will be noticed that in consequence of stimulation to the right of E, that point became, more or less permanently, galvanometrically negative. This is represented by the dotted line upwards at the beginning of the record. It must be remembered that before the application of the thermal section, the right and left hand excitations, proceeding from the electro-thermically stimu- AFTER-EFFECT OF STIMULUS ON CONDUCTIVITY 505 — lated point in the middle, were exactly equal and balanced. The fact that after this application, however, there are resultant responses which are upwards, shows, as already said, that by the moderate stimulation of the right-hand side, both excitability and conductivity have been increased. The resultant upward response here is, then, in the same direc- tion as the so-called ‘ current of injury, and forms, as it were, a positive variation of it. In another experiment, in which I wished to try the effect of excessive stimulation, instead of applying a hot solution at 60° C., I produced greater injury and consequent excessive stimulation, by scorch- ing the nerve at the same point as before, witha red-hot platinum wire. In this case resultant response was downwards, show- ing that the excitability and conductivity of the right-hand Fic. 312. Photographic Record side of the balance had been showing Effect of Excessive ; P Stimulation in Depressing Ex- depressed by over-stimulation. citability and Conductivity I was next desirous: of Up-line at starting shows the rest- : . ing-current due to after-effect of demonstrating that the excita- stimulation. The upsetting of bility of the over-stimulated or balance in a downward direction : ‘ constitutes a negative variation excited point undergoes depres- of the resting-current, and shows sion. For this purpose I took depression of conductivity and excitability. a fresh specimen and first ob- tained a state of balance. Similar excitation of E’ and E produced a balanced or null effect. The point E was then injured by touching it with a hot platinum wire. On now proceeding to take records, it is seen that the responses were downwards, showing the depression of excitability at the injured E (fig. 312). The fact that galvanometric negativity had been induced at E, by reason of injury, is demonstrated at the beginning of the record as an up-line. The subsequent resultant responses due to simultaneous excitation of E and E’ are 506 ~~. COMPARATIVE ELECTRO-PHYSIOLOGY -seen to be a negative variation of the resting-current due to injury. It is thus seen that while simultaneous-excita- tions of two normally excitable points E and E’ are prevented by balance from giving rise to any response, the excitatory response becomes manifest when the balance is disturbed by the injury of either point of galvanometric contact ; and that, under these circumstances, the response is a negative variation of the current of injury. This experiment is | important as giving a theoretical insight into the so-called response by negative variation. It also shows how limited is the applicability of the assumption that response is always by negative variation. For, in the similar experiment, previously described, under moderate injury, the response was by positive variation of the resting-current. It is further seen from these experiments that the enhancement of excitability, under the stimulation due to moderate injury, could not be caused by the suggested electrotonic effect. For the same anodic change induced by injury at E causes, in the case of moderate injury, an enhancement, and under greater injury a depression, of excitability. It is thus clear that the modifying influence is the effective intensity of stimulation. This fact, that moderate stimulation enhances, and excessive stimulation depresses excitability, will be further demonstrated ina future chapter, by the independent method in which the effects of electrotonus are completely eliminated. ) CHAPTER XXXV MECHANICAL RESPONSE OF NERVE Current assumption of non-motility of nerve—Shortcomings of galvanometric modes of detecting excitation—Mechanical response to continuous electric shocks—Optical Kunchangraph—Effect of ammonia on the mechanical response of nerve—Effect of morphia—Action of alcohol—Of chloroform— Abnormal positive or expansive response converted into normal contractile through diphasic, after tetanisation—Similar effects in mechanical response of vegetable nerve—Mechanical response due to transmitted effects of stimulation—Determination of velocity of transmission—Indeterminateness of velocity in isolated nerve—Kunchangraphic records on smoked glass— Oscillating recorder—Mechanical response of afferent nerve—Record of mechanical response of nerve due to transmitted stimulation, in gecko— Fatigue of conductivity—Conversion of normal contractile response into abnormal expansive, through diphasic, due to fatigue. I HAVE already referred to the distinctions which are com- monly insisted on, as between the reactions of different animal tissues. Certain of these are regarded as motile and others as. non-motile. From an evolutionary point of view, however, it is difficult to conceive of such a hard-and- fast distinction. It would be easier, believing -in continuity, to suppose that a certain responsive reaction, characteristic of the simplest living substance, had become accentuated in some tissues, and not so accentuated in others, according to their different functional requirements. Thus the belief held so implicitly by physiologists that nerves exhibit no motile response whatsoever’ becomes questionable, and is seen to require investigation. After submitting it to this, moreover, one finds it difficult to understand how such an ‘ ‘Nerves are irritable; when they are stimulated, a change is produced in them ; this change is propagated along the nerve, and is called a nervous impulse ; there is no change of form in the nerve visible to the highest powers of the- microscope.’ (Kirke’s Handbook of Physiology, 15th edition, p. 105.). 508 COMPARATIVE ELECTRO-PHYSIOLOGY idea ever gained currency, unless, indeed, it was due to the tyranny imposed on our thought by these arbitrary classifi- cations themselves. Before entering, however, on the question whether the excitatory reaction in nerve finds motile expression or not, we shall first examine the only method at present available for the detection of the condition of excitation. Since ex- cited nerve has hitherto been supposed to exhibit no visible change, it followed that the only method possible for the detection of the excitatory change was the electrical. In- vestigations on nerve, therefore, had perforce to be carried out by this means, through the medium either of the capillary electrometer or of the sensitive galvanometer. But the elec- trical method labours under certain inherent disadvantages, and first of these is the objection which it raises to the free employment of the most convenient form of stimulus, that, - namely, by induction shocks. For we have seen that unless extraordinary precautions are taken, we have here, owing to the possible escape of current, an element of error and un- certainty in the results. If, on the other hand, it should become possible to obtain mechanical response from the _ nerve, this particular form of stimulation might be employed without misgiving. | The second limitation which the electrical mode of detection imposes upon us is that arising from the differ- ential character of the response which it indicates. For stimulus induces electrical changes at both the contacts— proximal and distal-—the record made being finally due to the algebraical summation of the two. It is true that the excitability of one contact is artificially depressed by injury. But it is often difficult to say how far this injury has been effective in completely abolishing the excitability of this point. The depression of excitability, due to partial injury, will sometimes disappear to a certain extent, with lapse of time, and much uncertainty sometimes occurs as to whether a certain curious variation in the response of the nerve— negative followed by positive—is due to this or some other edd A St at a MECHANICAL RESPONSE OF NERVE 509 cause. With mechanical response, however, provided this could be rendered practicable, no such difficulty need arise. For in that case it would be the direct effect of the exci- tatory change, uncomplicated by any other disturbance, which would be recorded. Finally, as regards the detection of the excitatory change itself, the galvanometer is unable to indicate any change below a certain high intensity of excitation. Thus it gives no indication when excitation is due to one or to a few shocks: it can only detect an excitatory effect which is much stronger than this, having been brought about by the super- posed effects of tetanic shocks of a certain duration. In order to obtain even such effects, a galvanometer of very high’ sensitiveness is necessary. That of a fairly delicate instrument, detecting a current of about ‘ooI ampere, will have to be exalted some ten millions of times before it can give efficient indications of excitatory effects in nerves ; and in such a degree of galvanometric sensitiveness we approach a limit which cannot be very much exceeded. Returning now to our original question, we have first to determine whether excitation causes any motile effect in nerve. Under observation, it is easily seen that when the nerve is excited by tetanic electrical shocks it increases in thickness and at the same time shortens in length. We have here a phenomenon in every way analogous to the thickening and shortening of muscle under excitation. The contraction which occurs in nerve, moreover, is of an order by no means microscopic. I give here a record (fig. 313) of the contractile response of nerve under continuous stimulation by fairly strong tetanising electric shocks. This record was obtained by means of the ordinary lever-recor@er, the magnification employed being only three times. The induced contraction in this particular case was about 14 per cent. It will also be seen that this contraction reached a limit, at which state of maximum contraction the nerve remained for a considerable time. After this we observe a tendency 5 £0 COMPARATIVE ELECTRO-PHYSIOLOGY to decline, owing to fatigue. In some other cases, moreover, I have obtained a contraction of as much as 20 per cent. If we wish to obtain a series of successive responses, however, it is desirable to avoid over-stimulation of the tissue. In order, then, to obtain a response-record under moderate stimulation, we have to employ a higher magni- fication.. This magnification, if made about 200 times, is more than sufficient for all practical purposes, and the photo- graphic records given in the course of the present chapter are of this order. With long ‘specimens of nerve, however, a magnification of fifty times would be enough, and in the Fic. 313. Record of Contractile Response in Frog’s Nerve under Continuous Electric Tetanisation. Magnification, three times. course of the next chapters, I shall give certain records on this scale, obtained directly on a smoked glass surface. The apparatus used for the purpose was the Kunchangraph (Sanskrit, Aunchan, contraction), which I had already devised afd employed in recording the contractile responses of plant- tissues. This apparatus, as adapted for the purpose of recording mechanical response in nerves, consists of, first, a nerve-chamber, N; secondly, a modified Optical Lever, 0 ; and thirdly, a photographic recorder, D (fig. 314). _ Of these, the nerve-chamber consists of a small rectangular ebonite box, the front of which is closed by a semi-cylindrical N, nerve chamber containing nerve with electrical connections, E E’, MECHANICAL RESPONSE OF NERVE Sil FIG, 314. Optical Kunchangraph for Record of Mechanical Response of Nerve Thread tied to lower end of nerve, and attached to short arm of optic lever, O. Beam of light from L reflected from mirror of optical lever, oO, falls on recording-drum, D. Adjustment of reflected spot of light made by micrometer screw, Ss. Periodic electric stimulation at intervals of one minute is automatically made by means of key regulated by clock-work. Air bubbles through water at w, and is led on by india-rubber tubing, T, to nerve-chamber, thus kept humid. By proper manipulation of stop-cock any vapour—as chl oroform—con- tained in vessel V, may be passed through nerve-chamb er, subsequent responses showing effect. S12 COMPARATIVE ELECTRO-PHYSIOLOGY glass cover. The nerve is placed vertically within this, and held, at its upper end, by a clamp. The lower end of the nerve is connected with the short arm of the Optical Lever by means of a thread, which passes through a hole in the floor of the chamber. A second thread of cotton moistened with saline solution hangs loosely from the end of the nerve, and is connected with the electrode E’.. When the electrodes E and E’ are put in connection with the secondary of an induction coil R, the entire length of the nerve is subjected to. direct excitation. When, on the other hand, we wish to study the effect of transmitted excitation, the nerve is lightly clamped at B (fig. 315). Excitation is then induced in the portion of the nerve A a, and after transmission through the inter- vening tract, causes the motile effect in the responding portion of the nerve B C, : One precaution which I find to be very necessary is the maintenance of the properly humid condition in the i ._,_nerve-chamber. This is_ specially IG. 315. Diagrammatic , . ; Representation of Ar- important in the warm weather which rangonen irae characterises the greater part of the Stimulus, 1, indicating year in India. The usual means of Sai keeping the chamber moist, by a large quantity of blotting-paper soaked in water, is not sufficient to bring about the maintenance of the normal excitability of the nerve for any length of time. This need was met by keeping moist vapour in uniform circulation through the nerve-chamber. An air-bag is kept under suitable pressure, and the air, bubbling through water in the vessel W, is made to enter the nerve-chamber through an entrance-pipe, and to escape by an exit-pipe. In warm weather it is well to keep fragments of ice in the water-vessel. By proper mani- pulation of the stop-cock of the air-bag, a gentle stream of cooled and humid air is kept in constant circulation through MECHANICAL RESPONSE OF NERVE 513 the chamber. Observing these precautions, I have been able to obtain responses from a given nerve for as much as three hours continuously, whereas, without this care, they would have come to a stop in a very short time. By a modification of this arrangement, we are also enabled to study the effect on the excitability of the nerve of various gases and vapours contained in a second vessel, v. A series of responses is first taken, under normal conditions—that is to say, when the nerve is surrounded simply by a moist atmosphere. On now turning a three-way tap in a given direction, the water-vapour can be made to: pass through the vessel V, filled with the given gas or vapour, before reaching the nerve-chamber. The series of responses then obtained will show either the immediate or the after-effect of the reagent at will. For it is easy, by means of the three-way cock, to shut off the gas and re-establish the first or normal condition, after which the responses will afford an indication of the nature of the after-effect. _ The lower end of the nerve, as has been said, is attached to the arm of the lever which passes through the fulcrum-rod. A light .mirror is fixed on the fulcrum-rod, its face being downwards. The pull caused by the excitatory contraction of the nerve causes rotation of the fulcrum-rod, and this in turn gives rise to a deflection of the spot of light reflected from the mirror. A responsive relaxation of the nerve would give rise, on the other hand, to a deflection of the spot of light in the opposite direction. The long arm of the lever, it will be noticed, is here the ray of light. The responsive movement of the spot of light is recorded on a moving photographic plate vertically below the mirror, and whose movement, regulated by clockwork, is in a direction at right angles to that of the spot of light. The photographic plate, or the film wrapped round the drum, moves under a fixed wooden cover, not shown in the figure, which is provided with a narrow incised slit. The length of this is parallel to the direction of the movement of light, and at right angles to that of the plate or film. The advantage of having the plate LL 514 COMPARATIVE ELECTRO-PHYSIOLOGY vertically below the mirror lies in the fact that a lighted candle may be placed in the dark room without spoiling the record by diffuse illumination. The only way in which such diffuse light could now find access to the plate would be by reflection from the ceiling. But if the ceiling of the experimental room is blackened, or a black cover placed over the nerve-chamber at a certain height, even this possibility is eliminated. The advantage which the observer enjoys, when, instead of groping in semi-darkness, he can work in a fairly well-lighted room is obvious. By making the arm of the lever to which the nerve is attached sufficiently short, and by placing the recording plate sufficiently far away, a wide range of magnification, from several hundreds to several thousands, may be obtained. It may sometimes be desirable to subject the nerve to a certain amount of tension, and this is secured by placing a small weight on the arm of the lever. With high magnification, due adjustment, which is very troublesome, lies in bringing the spot of light con- veniently over the recording plate. This difficulty is obviated, however, by means of a fine micrometer screw S which moves the whole nerve-chamber up or down, in relation ‘to the Optical Lever. The adjustment of this screw in a right- handed manner then moves the spot of light in one direction, say to the left, while its left-handed rotation moves it to the right. This movement can be made very fine, and the spot adjusted to any part of the photographic field. It remains to deal with the possible disturbances inci- dental to the high magnification employed. Apprehension, in this matter, is often more fanciful than real. Disturbances might no doubt occur, however, when proper conditions are not secured for the experiment. If the nerve-chamber, for example, be supported on a different stand from that of the Optical Lever, then the slightest tremor of the common pedestal would result in relative movements of the two supports, causing constant disturbance of the spot of light. Under these conditions, heavy stone pedestals, erected on steady foundations, afford no security against the ground- MECHANICAL RESPONSE OF NERVE 515 vibrations of a busy city. But when both the nerve- chamber and the Optical Lever are fixed to the same supporting-rod, relative movements, due to external disturb- ance, are practically eliminated. This common supporting- rod may be screwed securely to a wall. With these precautions, I have been able to take records, without the least dis- turbance from the adjacent electric tram line. Asa matter of fact, when the magnification required is only of a few hundred times, nothing but gross carelessness could allow any source of disturbance to remain. It is only when the magnification has to be pushed to the order of a hundred thousand that unusual care is necessary to avoid errors of disturbance. One precaution which should, however, be taken, is that arising from disturbance of the mirror by convection currents of air. The remedy for this is obvious, namely; a suitable glass cover. This is the order of magnification which is necessary for the recording of response under a degree of stimulation - usual in making observations of excitatory electrical variation with a very sensitive galvanometer. But while the sensitive- ness of the galvanometric method of detecting response is here nearing its limit, that of the mechanical method is in its first stage only, and how greatly the sensitiveness of the latter may be exalted when required will be shown in the next chapter. I shall: ‘flow “explain how easy it is to study the aiisin: logical variations induced in the animal nerve under various agencies by means of the mechanical response. The following experiments were performed on specimens of the sciatic nerve of frog. A well-known reagent for abolition of ex- citability of the nerve is ammonia. Its effect on mechanical response is seen in fig. 316. In all the following experiments, the stimulus applied was by fairly strong tetanising electrical shocks, which were usually of two seconds’ duration. Two series of records were taken, successive responses being recorded at intervals of one minute, before and after the application of the chemical reagent. In fig. 316, the normal L L 2 516 COMPARATIVE ELECTRO-PHYSIOLOGY responses seen in the first series are found to be abolished when the nerve has been subjected to strong vapour of ammonia for some time. It should be mentioned here that this abolition takes place under the action of a strong dose. When highly diluted with air, the vapour ey cause a temporary exaltation. In the next figure (fig. 317) is shown the effect of szorphia. After the application of this solution for a certain length of time, the response is seen to ‘be abolished. The strength of application which brings about this abolition I find to vary according to the condi- Fic. 316. Photographic Record of Effect of Ammonia. on Mechanical Response of Frog’s Nerve FiG.. “317: Photographic First series of responses are nor- Record showing Abolition mal. Second series show effect of Mechanical Response of ammonia in practical aboli- of Frog’s Nerve by Action tion of response. of Solution of Morphia tion of the nerve. Another agent by which the mechanical response of the nerve is found to be abolished is aconite. And it is of special interest to note that I have often found this to act as an antidote, for the revival of response previously almost completely abolished by morphia. ‘The condition of the nerve here also appears to be a determining factor in the mutually antidotal action of these two poisons. A strong application of alcohol after long-continued action MECHANICAL RESPONSE OF NERVE 517 abolishes the response of nerve. But its preliminary effect is often one of exaltation, as seen in fig. 318. I shall next describe the effect of chloroform, which dis- plays many interesting features. We have seen that when a tissue is excited by impinging stimulus, two opposite effects are induced : one of these is the increase of energy, by the absorption of stimulus, and the other is the expenditure of energy by excitatory response. The former, as we have seen, finds expression in galvanometric positivity and expansion. The latter, on the other hand, is exhibited: as galvanometric negativity and contrac- tion. In the record of excitatory response, the former of these elements is generally masked by the predominant negative or contractile effect. We have also seen that this hidden positive may be unmasked. in either of two: ways: first, by retarding the expression of one effect in relation to the other ; or, second, by abolishing the excitatory negative altogether. In the first of these cases, the negative response is converted into diphasic, say positive followed by Fic. 318. Photographic : Record showing Pre- negative. In the latter, the response limitiary Bimaltation it becomes positive, by the suppression Mechanical Response : . of Frog’s Nerve after of the negative. An example of this Application of Alcohol unmasking of the positive element, by suppression of the negative, we have already seen to occur under the action of chloroform (cf. fig. 49). This demon- stration was made on a vegetable tissue, the test employed being electrical. The experiment which I am now about to describe is interesting from the fact that effects parallel to those there seen in a vegetable tissue are in it shown to occur also in the highly specialised animal nerve. The unmasked ‘electro-positive effect, moreover, is here seen to correspond with an expansive 518 COMPARATIVE ELECTRO-PHYSIOLOGY response of the tissue. A record of the various phases in the effect of chloroform on the mechanical response of nerve is found in fig. 319. It will be seen here that the first effect of chloroform was to cause a great enhancement of ex- citability, which in this case lasted for about a quarter of an hour. I have given only two responses of this series. After this, the responses began to decline, and another very Fic. 319. Photographic Record showing Effect of Chloroform on Mechanical Response of Frog’s Nerve First pair of responses, normal; second pair, preliminary exaltation on application of chloroform; last series exhibit subsequent effect of chloroform in unmasking the positive component as diphasic response. Expansion is here followed by contraction. Note regular waning of both components with growing aneesthetisation. interesting reaction made its appearance. The impinging stimulus had hitherto induced only an immediate contractile response. But by the action of the chloroform the excitatory effect was delayed, and the positive, or mechanically ex- pansive response was unmasked in the form of a preliminary downward twitch. Response was now, therefore, diphasic— positive followed by negative. Immediately on the applica- MECHANICAL RESPONSE OF NERVE 519 tion of stimulus, as may be seen from the record, there is a sudden expansive movement downwards, followed by an equally rapid reversed movement of contraction upwards, and this followed again by a slow recovery. Each of the successive stimuli evokes the same diphasic responsive sequence. It must be noted that the downward twitches are the preliminary, and not the after-affect. It is also interesting to note, as the tissue approaches death, under the continued action of chloroform, how regularly in both negative and positive directions the responses decrease in amplitude. We shall next undertake an independent investigation into the causes which bring about the three types of response —abnormal positive, diphasic, and normal negative—known to be exhibited in the electrical response of the animal, and already demonstrated as occurring also in that of the vege- tal nerve. While discussing these three types of electrical response and their variations in Chapter XXXI. it was stated that the differences of effect involved were due to changes in conductivity and excitability, brought. about by varying tonic conditions. It was also explained, in the same place, that the continued isolation of so highly excitable a tissue as nerve, from its accustomed supply of energy, would be sufficient of itself to depress its tonic condition below par, with concomitant depression of its conductivity and excitability. The result of this depression of excitability will be to render inefficient a stimulus which was formerly efficient, to evoke the true excitatory reaction of galvano- metric negativity. The absorbed stimulus will now induce only a responsive positivity. The depression of conductivity also would cause the transmission: of the hydro-positive, instead of the excitatory negative, wave. Owing, then, to the joint action of these two factors, stimulus induces a positive response—the so-called ‘abnormal ’—at a distant responding point, when the tonic condition of the tissue has become depressed. Absorption of stimulus, however, by supplying the requisite energy, raises the tonic condition, with con- sequent restoration of conductivity and excitability. As 520 COMPARATIVE ELECTRO-PHYSIOLOGY a result of this, the abnormal positive will pass into normal negative response, through an intermediate diphasic, after the impact of a series of stimuli, or after tetanisation. The enhancement of conductivity and excitability thus conferred on the tissue by the absorbed stimulus will now act by still further tetanisation, to bring about the enhance- ment of the normal negative response. Starting thus, with the most depressed condition of the tissue, and sub-. jecting it to continuous action of stimulus, we obtain four typical stages : (1) the abnormal, passing after short tetanisa- tion into (2) the diphasic ; this in its turn giving place to (3) the normal negative alone ; which finally becomes (4) the enhanced negative. | In studying electrical response, both of animal and vege- tal nerves, under appropriate experimental conditions, we have already seen various examples of these different types of response and their transformations. But under such modes of experiment as have been described, the effects were, as already stated, due to joint changes in excitability and con- ductivity. I shall now, however, describe a still simpler experimental arrangement, in which the stimulus is applied directly on the tissue, and the responsive variations are, therefore, due to variations in the excitability alone. These changes, moreover, will be recorded by means of their direct mechanical expression, namely, contraction, or its opposite expansion. With regard to abnormal response, I have already stated that this is brought about, not by ‘staleness,’ or the moribund condition, with its concomitant chemical changes, but by the run-down of the energy of the tissue in isolation. On investigating this subject, by means of mechanical response, with its superior sensitiveness, this conclusion finds inde- pendent support of the strongest character. On taking even the freshest specimen, I generally find that its responses at first are the abnormal positive. These gradually pass into moderate negative through diphasic. This is due to the raising of the tonic condition by the absorption of MECHANICAL RESPONSE OF NERVE 521 the stimulus, and after a series of stimulations, the isolated tissue, which was originally depressed, has its tonic condition so much heightened, that the responses are enhanced to an unprecedented magnitude. A specimen, in fact, which was at first almost irresponsive, may generally be brought to any state of exalted excitability desired, with concomitant increase in amplitude of response, by merely subjecting it for a certain length of time to the action of impinging stimulus. Fic. 320. Photographic Record showing Abnormal Positive converted into Negative Response after Tetanisation First series, abnormal positive ; second series, persistence of this positive after very brief tetanisation ; third series, conversion to negative, after a tetanisation of longer duration. I shall now describe in detail some of the principal experiments, Selecting a specimen of frog’s nerve, I took a series of responses to electrical shocks, of three seconds’ duration, at intervals, in each case, of one minute. The testing stimulus was kept always the same throughout the experiment, except for certain intervening periods of tetani- sation. The variations seen in the responses thus give a visual demonstration of the variations in excitability. The record of these is given in fig. 320. The responses in 522 COMPARATIVE ELECTRO-PHYSIOLOGY the first series are by the abnormal positive variation; that is to say, by expansion. The tissue here being sub-tonic, the impinging stimulus could not induce the true excitatory effect. The tissue. was now subjected to short-lived tetanisation. But the absorbed stimulus was not yet sufficient to induce the normal responsiveness. The next series of. records, = therefore, still exhibited the abnormal positive response. Tetanic shocks of longer duration were next applied. This gave rise to a short- lived positive twitch down- wards, succeeded by large contractile response upwards, After the cessation of the second tetanisation, the absorbed energy is seen to have brought the tissue to a condition of more or less normal responsiveness. This is seen in the third series, where the first responses are diphasic, but the positive component (the downward twitch) becomes perceptibly Fic. 321. Photographic Records show- smaller and the negative ing Gradual Disappearance of Positive larger, in each of the succeed- Element in Diphasic Mechanical . Tt. wheal Responses of Frog’s Nerve and INS responses. shou Plant-nerve also be noticed that che Note also the staircase increase. recovery from positive ts much quicker than trom negative response. This fact is important, in connection with certain psycho-physiological phenomena to be described in a later chapter. The effect of successive stimuli, in enhancing normal response, when the nerve is not yet in maximum. tonic condition is illustrated in a still more striking manner in the record given in fig. 321, obtained with a different specimen MECHANICAL RESPONSE OF NERVE 523 of frog’s nerve. In this, also, the first series of responses was purely positive. But the record shown here begins at the point where, in consequence of previous tetanisation, response has become diphasic. Here it will be noticed that the true excitatory effect of contraction is undergoing a con- tinuous increase, while the abnormal positive is decreasing. The excitatory response, indeed, becomes so great as to be incapable of record within the plate. _ I have already shown how similar in every respec are the responsive characteristics of the vegetal nerve to those of the animal. This fact finds an interesting illus- tration in the various phases of its mechanical response. That is to say, plant nerve in a sub-tonic condition gives positive, passing into diphasic and normal negative response, under tetanisation. On arriving at this second stage of diphasic response, successive responses undergo enhance- ment in a manner precisely the same as holds good in the corresponding cases with frog’s nerve. This is sufficiently illustrated in the two records given side by side in fig. 321, the first of which, as already said, is of frog’s nerve, and the second, of nerve of fern. We see here again, as already in numerous cases before, how the responsive pecu- liarities and their modifications in the one are in every respect paralleled by those of the other. The only differ-— ence between them lies in the degree of their excitability, that is to say, two stimuli of equal intensity will in general induce a more intense excitatory effect in the nerve of frog than in that of fern; or in order to obtain from both an equal intensity of response, we must, in the case of fern, employ. a stronger stimulus. We have seen that in con- sequence of the absorption of stimulus, not only does the abnormal positive phase disappear, giving place to the normal negative, but the subsequent negative responses themselves also show an enhancement in a staircase manner. I give here (fig. 322) another record showing the mechanical response of frog’s nerve to undergo this staircase enhance- ment. From this effect then it is easy to understand that an 524 COMPARATIVE ELECTRO-PHYSIOLOGY intervening period of tetanisation will markedly enhance the negative response. We have now seen that, by the direct mode of investiga- tion afforded in mechanical response, we are able to trace out the causes which determine the three types of response found in nerves. It has been shown that all ‘these are brought about by the varying tonic condition of the tissue. From this it is easy to understand that the three types of | electromotive responses in nerve are also due to the same cause. In the experimental method there employed, the variations of con- ductivity appropriate to the tonic condition are superposed on parallel modifications of the excitability. Thus not only is the responsive change of a sub-tonic responding point positive, but the effect which is transmitted to it through sub-tonic conducting tissues is also positive; after tetanisation, how- ever, the tonic condition of the tissue is raised. The power of transmitting true excitation, previously in abeyance, is now not only restored, but gradually ~ enhanced to a degree, depending within aes pices ces limits, on the amount of tetanisation. case Effect in Me- The excitability also undergoes a similar chanical Response of : Frog’s Nerve transformation, from the abnormal positive to normal negative, which latter again becomes enhanced to a degree that depends, within limits, on previous excitation. These effects, seen in electrical response to transmitted stimulation applied at a distance, I find repeated also in the mechanical response of nerve, under similar circumstances. That is to say, an isolated nerve, by the very fact of its being cut off from its normal sources of energy in the body of the intact animal, is apt to be rendered sub-tonic, and under these conditions no true excitation is transmitted, and it is only when the tonic MECHANICAL RESPONSE OF NERVE 525 condition of the tissue has been raised, by the application of fresh energising stimulus, that the conducting power can be gradually restored. 2 This leads me to what is theoretically a very interesting mode of determining the velocity of transmission in nerve, by the mechanical response of the nerve itself, which will be understood from the diagram already given (fig. 315). In that figure, A B C is the nerve, so clamped at B as to prevent any mechanical slip, but not tightly enough to obstruct the transmission of excitation. The nerve, when brought to a normal excitatory condition, is first excited at A a by a pair of electrodes in connection with an induction coil. The transmitted excitation, reaching B C, induces a contractile mechanical response there, observed by the highly. magnify- ing optic lever. Records of the transmitted effect of stimulus obtained in this manner. will be given later in the chapter. The interval of time, 7, between the application of stimulus and the initiation of response is accurately determined by the usual methods. Stimulus is next applied at B 4, and the interval of time 7’ between stimulus and response again determined. The difference (¢—7’) is the time required for the stimulus to travel the intervening distance a 4. By this means, I found the velocity of transmission in a certain specimen of nerve of fern to be 50 mm. per second. It is thus easy, by means of two successive experiments, to eliminate from the observation the element of the latent period. It is to be understood that the molecular change, ultimately to be expressed as contraction, begins to be initiated as soon as excitation reaches the responding area. As the contractile effect exhibited by the nerve is relatively small, we can see that a certain time will elapse before it becomes sufficient to be perceptible, unless the magnification employed is very high. With a magnification of the order of 100,000 times, however—which, as I shall show, is quite practicable—this loss of time is much lessened. It was while working out this investigation that I realised how indefinite must be any determination of the velocity of 526 COMPARATIVE ELECTRO-PHYSIOLOGY transmission in an isolated nerve. The conductivity, even in the intact organism, we have seen to be liable to modifica- tion from various factors such as fatigue, and it is easy to understand that it will become still more fluctuating when the conducting tissue is isolated. The inevitable changes consequent on separation from the natural sources: of energy at once begin totake place. As the result of this sub-tonicity, even a typically conducting tissue, like nerve, will cease to. be the conductor of true excitation, and there will then be, properly speaking, no physiological distinction between such a structure and a non-conducting tissue. By the absorption of stimulus, however, a transformation sets in, and the non- conducting becomes gradually reconverted, first, into a feebly, and then into a very highly conducting structure. The possible variations in conductivity, therefore, are not a matter of some few units per cent. quantitatively, but even considered qualitatively range from non-conductivity to the highest conductivity. And even, further, when the nerve has been once more rendered conducting, its velocity of transmission will vary greatly with the tonic condition conferred by previous stimulation. Over-stimulation, again, by inducing fatigue, diminishes the power of conduction of true excitation. This fact I shall be able to demonstrate by special experiments. That such changes are not peculiar to the isolated nerve, where the manifestation can be traced unmistakably to its true cause, is seen in those cases of living animals where, owing to mal-nutrition, or for other reasons, the tonic condition of the nerve falls below par, with growing non- conductivity and paralysis as the effect. And here it may be said that the transformation again from non-conducting or feebly-conducting to the normal state of conductivity may in general be brought about by the same means as are employed with the isolated nerve, namely, by the frequent repetition of tetanising electric shocks. The photographic method of recording the response of nerve, employed in the Kunchangraph, has the advantage ~~ ee MECHANICAL RESPONSE OF NERVE 527 that, as the record is made by the moving spot of light, the recording-point, as it were, encounters no friction, and the characteristic form of the response curve is thus unmodified. But prolonged work in the photographic dark-room is very fatiguing to the observer. I was, therefore, desirous of so perfecting the ordinary mode of record by the movement of the tracing-point of a lever over a smoked surface, that it would be adequate for most purposes. The difficulties involved in carrying this out lie, first, in the obtaining of a sufficiently high magnification, and, second, in the overcoming of friction at the writing point. A long lever, such as is necessary for high magnification, entails a heavy weight. But this can be obviated by employing a light and thin aluminium wire, 50 cm. in length. The fulcrum-rod, to which the lever-index is attached, has a diameter of 2 mm. A thread attached to the contracting nerve is wound once round this fulcrum-rod. The radius of the latter being 1 mm., the magnification produced by this arrangement is 500 times. The magnification may in this manner be raised as high as 1,000, by taking a longer lever. For the tracing point the end of the lever is bent at right angles, and a fine bristle attached. Even this degree of magnification is not always necessary, as I have already said. The records which immediately follow have a magnification of only fifty times. The next difficulty, as already stated, lies in the friction to be overcome. The friction offered by a writing-surface of smoked paper is too great to be employed. A surface of plate-glass, coated with a thin and uniform layer of smoke, offers considerably less resistance. But even this retards the free movement of the tracing-point. I was therefore led to the construction of my Oscillating Recorder. The glass plate, on which the record is made, is carried on a primary frame, which is moved at a uniform rate, regulated by clock- work, on wheels, over rails. The plate is mounted on this primary frame in a secondary frame, which is held away from the primary, at a certain fixed distance, by means of spiral springs. This secondary frame, by means of an electro- 528 COMPARATIVE ELECTRO-PHYSIOLOGY magnetic arrangement, can be maintained in a state of to- and-fro oscillation, always strictly parallel to the primary. The recording-index moves in a vertical plane, and the smoked plate backwards and forwards, at right angles to this, the extent of its oscillation being about 1 mm. The recording point is adjusted, barely to touch the smoked » surface. Thus the oscillation of the plate brings it periodi- cally in contact with the tracing-point, which is thus practi- cally free to execute its movements unimpeded. When the oscillation frequency of the plate is sufficiently high, and the speed of the recording-surface low, the curve of record Fic. 323. Pho ographic Reproduction of Record of Mechanical Re- sponses of Frog’s Nerve (left-hand record) and Plant-nerve (right-hand record) obtained on Smoked Glass Surface of Oscillating Recorder appears as continuous. In other experiments, where the determination of time-relations is important, a high speed can be given to the plate by the regulation of the clockwork, and the record will then appear as a succession of dots. From these, and a knowledge of the oscillation-frequency of the plate, the time-relations of different parts of the curve can be determined with accuracy. I give here two different series of uniform mechanical responses recorded with this instrument, obtained from the nerves of frog and of fern respectively (fig. 323). I have also been able, by means of this instrument, to demonstrate a very important fact, namely, that the responses MECHANICAL RESPONSE OF NERVE 529 of the afferent or sensory nerves are in every way the same as those of the efferent, or motor. The numerous records already given are of the latter. For the demonstration of the former I took the optical nerve of Ophzocephalus, and recorded its responses to uniform electrical stimuli, on a smoked surface. The following (fig. 324) is a photographic reproduction of the record. Owing to sub-tonicity, the first response is seen here to be abnormal positive. Successive stiniulation converts this, through diphasic, into normal negative, in a manner exactly the same as has already been observed in the sciatic nerve of frog. Another interesting record obtained with the optical 3 nerve is given later (fig. 404). I also give in: the next figure (fig. 325) a series of effects of transmitted. stimulation, which show.in avery interesting manner the effect of fatigue in the modi- fication of the conductivity of a nerve. Itis customary to suppose Fic. 324. Record of Mechanical that the nerve is indefatigable. Responses to Electrical Stimu- But I shall be able to show that lus obtained on Smoked Glass, : gs ds and given by the Optic Nerve not only is the conductivity of a of Fish Ophiocephalus nerve liable to fatigue, but its Note the abnormal positive re- _excitability also. The demon- natch a ree ed stration of the latter will be given in a succeeding chapter. For the demonstration of the effect of fatigue on conductivity I selected a length of 10 cm. from the sciatic nerve of gecko. This was attached for experiment to the Kunchangraph, in the manner diagrammatically represented in fig. 315. The length Bc, which showed contraction, in response to stimulus trans- mitted from A, measured 5 cm. The two exciting elec- trodes, A a, were 2 cm. apart. The intervening tract, through which excitation was transmitted, was, therefore, 3 cm. At the beginning of the experiment, owing to the depression of tone which the nerve had undergone, from MM 530 COMPARATIVE ELECTRO-PHYSIOLOGY isolation, its conductivity was below par, and the responses obtained were positive. After a series of stimulations, however, the true excitatory wave was transmitted, with the concomitant negative or contractile responses. In order to demonstrate the effect of fatigue on conductivity, the recording of this series was commenced only after many normal responses had already been given. In the series recorded we can see that the responses at first exhibit periodic fatigue. The accentuation of fatigue is then mani- fested by a rapid decline in the amplitude of the responses. A remarkable change next begins to appear. It has been Fic. 325. Record, obtained on Smoked Glass, ot Transmitted Effect of Stimulation on Nerve of Gecko Note here the progressive effect of fatigue, seen first as periodic fatigue ; second as diphasic effect ; and third as reversal into abnormal positive. shown that the true excitatory negative response contains a masked positive element. Owing now to growing fatigue, the exhibition of the negative is delayed, and the positive thus shows itself as a preliminary down-curve in a diphasic response. Afterwards, the excitatory negative is completely abolished, and the positive response by expansion alone remains, as seen in the last of the series. Ultimately, when the nerve is killed, by excessive stimulation, even the positive response disappears. We may notice here the interesting fact that nerve, which is regarded as a conductor, par excellence, will sometimes MECHANICAL RESPONSE OF NERVE 531 become a non-conductor. Conduction, therefore, is not alone dependent on anatomical structure, but requires also a certain molecular condition. A nerve, whose continuity remains uninterrupted, may nevertheless undergo paralysis and cease to conduct. Recovery may then, in many in- stances, be brought about by tetanisation. Thus, by means of mechanical response, obtained with a magnification of only fifty times, we have been able to demonstrate not only those results which may be observed by the most sensitive galvanometer, but also others which were never so detected. The magnification thus employed in the Kunchangraph, however, is here, as already stated, only in its lowest terms. When this is further exalted, still further and important phenomena regarding the exci- tatory changes in nerve are revealed, and some of these will be described in the next chapter. CHAPTER XXXVI MULTIPLE RESPONSE OF NERVE Great sensitiveness of the high magnification Kunchangraph—Individual con- tractile twitches shown in tetanisation of nerve—Sudden enhancement of mechanical response of nerve on cessation of tetanisation—Secondary excita- tion—Multiple mechanical excitation of nerve by single strong stimulation — Multiple mechanical excitation of nerve by drying. WE have already seen that, in order to detect the excitatory _ changes in nerve by the electrical method, the moderate sensitiveness of an ordinary galvanometer has to be exalted more than a million times. Galvanometric indications, more- over, are liable, as we have seen, to be complicated by the occurrence of differential effects at the two contacts. In - the Kunchangraphic method of record, however, there is no possibility of such complications, for the response curve here represents the direct effect of stimulus. We also saw that, according to this method, a very moderate magnification would give us all the variations that could be detected by the most sensitive galvanometer, and, besides this, owing to its simplicity, it makes it possible to observe other phenomena, whose occurrence the galvanometer could not satisfactorily have demonstrated. Such a magnification, however, as I have already said, is in its first stage only. With due precautions it is possible to obtain a Kunchangraphic magnification of a hundred thousand times. It will easily be seen that this places at our disposal an instrument of incomparable sensibility, by whose aid many of the phenomena of the nervous change, hitherto beyond our power of observation, may be brought within the sphere of investigation. a 21 et dhe Ot TS i i, eee ——— a ae ee ee ee MULTIPLE RESPONSE OF NERVE 533 This magnification, of the order of a hundred thousand times, may be accomplished in either of two different ways. A magnified image of the end of the long lever may, in the first place, be thrown on a distant screen. By this compound magnification the sensitiveness of the record may be raised to the extent desired. Or, in the second place, we may employ a battery of two levers in series. The first of these gives a magnification, say, of five hundred times, and is connected with a second optical lever, by which a multiplying magnification of two hundred times is easily obtained. It is unnecessary to point out that special care should in this second case be taken to ensure the steadiness of the support. With due precautions it is, however, not difficult to secure the entire elimination of all disturbing elements. When the spot of light from the second lever is thus thrown on a distant screen, it is very interesting to watch the various changes induced in the nerve by the environmental conditions. An isolated nerve in a moist chamber, cut off from its natural sources of energy, becomes increasingly sub-tonic. This process is attended by an abnormal relaxa- tion, which causes a steady movement of the spot of light in one direction. When the nerve has become very sub- tonic, the effect of stimulus, as that of electric shocks, is to enhance the tonic condition, and by this the downward drift of the spot of light is retarded or arrested. In cases of extreme sub-tonicity there is no further response, beyond this arrest. But where the sub-tonicity is less pronounced, stimulus will induce the abnormal positive response by a sudden positive variation of the drift, which is followed by recovery in the opposite direction. The after-effect of absorption of stimulus is further effective in causing the gradual retardation and final arrest of the downward drift. By such absorption of stimulus the tonic ' The abnormal positive response is also obtained from ‘nerve in ordinary tonic condition, it should be remembered, by the application of excessively feeble stimulus. 534 COMPARATIVE ELECTRO-PHYSIOLOGY condition is raised, and the normal excitability consequently enhanced. From this point onwards the responses are con- tractile or normal negative. At this stage the response of the nerve exhibits the staircase increase, the nerve itself showing a certain amount of tonic contraction. The excitability of the nerve then attains a maximum, and the successive responses become uniform. Long and intense stimulation will, after this, bring on fatigue. This stage is characterised, again, by a growing relaxation of the nerve as a whole, and its responses may become, first, diminished in amplitude, second, of a diphasic character, and, thirdly, reversed to the abnormal positive, according to the amount of fatigue which supervenes. We may thus, for the sake of convenience, distinguish four stages in the response of nerve. The first of these is the initial phase, SUB-TONIC RELAXATION, and the characteristic response to individual stimuli is here abnormal positive. The second phase is that of the TRANSITION to normal response. The characteristic responses to individual stimuli here show a staircase increase, with more or less permanent contraction as its after-effect. If at this stage the nerve is allowed to remain long without stimulation, it slowly reverts to the first stage of sub-tonic relaxation, with its growing relaxa- tion and abnormal positive response. Stimulation, how- ever, brings it back once more to the second or transition stage. In the third stage of UNIFORM responsiveness, the responses are normal and take place by equal contraction. In the fourth, or FATIGUE stage, there is a tendency, as already said, to relaxation on the part of the nerve as a_ whole, and it thus outwardly mimics the stage of sub-tonicity. The responses now, therefore, diminish in amplitude, and show the diphasic or the abnormal positive character. Further characteristics of these four stages, and_ their relations to each other, will be treated in detail in Chapter XLI. A few words may be said about the mechanical response of the nerve, when it is in a favourable condition of excitability. MULTIPLE RESPONSE OF NERVE 535 We have seen that in order to obtain a galvanometric record of the electrical response of nerve, one or even a few shocks will not be sufficient to induce the necessary electromotive change. For this, tetanic shocks of a certain duration are necessary, and the responsive electromotive change is not immediately perceptible. In consequence of this intensity of stimulation, moreover, complete electrical recovery can only take place after a perceptible interval. With the low magnifi- cation Kunchangraph, too, tetanic shocks of something like a second in duration are necessary, and complete recovery here also requires a period of about one minute. But with the greater sensitiveness available in the highly magni- fying apparatus, response with a highly excitable specimen of nerve is obtained with even so short-lived a stimu- lation as that of two or three vibrations of the vibrating interrupter of the secondary coil, lasting less than one-tenth of asecond. The responsive contraction of this short-lived stimulus, and its recovery, are also quick. It is in conse- quence of the rapidity of this response and recovery that the responsive contractions due to the rapidly intermittent tetanising shocks do not become fused, but show themselves in the response-curve as consisting of successive twitches, corresponding to the component shocks. Owing to the high amplitude of these responses, and the trend of the base-line either up or down, it is difficult in practice to obtain photo- graphic records of these effects. But it is easy enough to obtain definite visual demonstration of various characteristic effects in the response by the employment of the following device. The spot of light from the optic lever is made incident on a revolving mirror, and reflected from it to a large white screen at some distance. During a period of repose the quiescent spot traces a more or less horizontal line of light. This may trend either in a downward or an upward direction continuously, according as there is induced a continuous sub-tonic relaxation or a growing contraction, due to the after-effect of stimulus. Somewhere between these two extremes may be obtained a condition of more or less 536 COMPARATIVE ELECTRO-PHYSIOLOGY stability, where the record made by the spot of light appears as a horizontal line. Under normal conditions, then, the response to excitation is a sudden movement, due to con- traction, say upwards, followed by recovery down. In the response-curve projected on the screen, the vertical movement or ordinate represents the amplitude of the re- sponse, and the horizontal abscissa the time. Under tetani- sation a series of curves corresponding in frequency to the | frequency of the shocks is observed as serrations. Another very interesting observation often made in the mechanical response of nerve is that of the after-effect on the cessation of continuous stimulation ‘by tetanic shocks. It has been found, it will be remembered (p. 428), that the response of the retina to the action of continuous light often shows on its cessation a sudden transient increase. This phenomenon has been regarded as peculiar tothe retina. But I have found exactly parallel effects to occurin the mechanical response of nerve. Under continuous stimulation there is a tendency to the attainment of a maximum contraction, which suddenly, on the cessation of stimulation, overshoots, to be followed by the usual recovery. I have already referred to the two different effects of an opposite character caused by incident stimulus, namely, the effect of negativity, and its converse positivity. In the case of mechanical response, it is the former which is effective in inducing contraction, while the latter is associated with expansion, and is a factor in re- covery. It will also be seen, in a general way, that by the - antagonistic action of these two elements, and by the differ- ing relative intensities of their after-effects, many diverse results may be exhibited. In the case of the after-effect in question, which occurs by a sudden positive variation of the contraction, the excitatory effect would appear to be pre- dominant. Even when, after this brief positive variation, recovery is taking place, the excitatory element, with its contractile tendency, appears to persist; for if a second stimulus be applied, some time before the recovery is com- plete, the consequent contractile response takes place almost MULTIPLE RESPONSE OF NERVE 537 instantaneously. But when the recovery is once complete, a similar stimulation will not induce a similar immediate response. Instead of this there will be a brief period of hesitation or latency before its initiation. Another interesting phenomenon, which I was first able to observe by the help of the highly magnifying Kunchan- graph, was the occurrence of multiple response in nerve under intense stimulation. I was led to this discovery by an investigation which I had undertaken for the demon- stration of the identity of response in animal and vegetable nerves. After showing the extended parallelism which exists between the two, under similar conditions and varia- tions of conditions, as already described, I was desirous of seeing whether a plant nerve could be substituted in certain experiments for the animal nerve. In accordance with this I used the vegetal nerve in the experiment known as secondary contraction. Here a nerve-and-muscle preparation of frog is taken, and a second piece of frog’s nerve is suitably laid, with one end lying upon the end of the other nerve. On excitation of this second detached nerve, say by electric shocks, excitatory electrical variation is found to cause responsive contraction in the muscle of the first preparation. In my own rendering of this experiment I employed, instead of the second piece of: frog’s nerve, a length of nerve of fern. In order that the experiment should not be open to any objection arising from the escape of stimulating current, I employed a non-electrical form of stimulus. This was done by touching the plant nerve with a strongly heated wire. The terminal muscle would then, under favourable conditions, begin to respond by strong spasmodic contraction. When this had subsided, a new series of tetanic contractions began ; and this was repeated at short intervals, for nearly half an hour. When this series of spasms had come to a stop, I have often succeeded by a fresh application of the hot wire to the vegetal nerve in obtaining a second series of such repeated responses. It thus appeared that the strongly excited plant nerve gave rise to a series of multiple 538 |. COMPARATIVE ELECTRO-PHYSIOLOGY excitations, the indications of which were afforded by the nerve-and-muscle preparation. The only perplexing feature of these responses was the abnormally long period of ten to fifteen seconds which was generally found to elapse between the application of the strong stimulus to the plant nerve, and the response subse- quently given by the terminal muscle. Here it must be remembered that the excitation applied at one end of the plant nerve has to travel the entire length before its excita- tory electrical variation can be communicated to the nerve of the frog-preparation. The transmitted excitatory varia- tion in the primary has, moreover, to reach a certain intensity before it can effectively excite the secondary preparation. We know, further, that an isolated piece of nerve is liable to fall into a sub-tonic or depressed condition, in which its conducting power is much lowered, to be gradually restored again under strong or long-continued stimulation. These considerations will probably be found to account for the delay in the occur- rence of the first of these responses. It would thus appear from the last experiment that a nerve, when subjected to a single strong stimulus, will give a multiple series of responses. In order to test this by direct experiment I employed the highly magnifying Kunchangraph, and subjected an experimental nerve of frog to a single strong thermal stimulation. This gave rise, at first, either to an abnormal positive response or to a moderate negative. But there followed, after a longer or shorter pause, a series of multiple contractile responses, which generally grew in intensity for a considerable time. There were in the series a number of short pauses, each followed by a veritable storm of excitation, in which individual responses were so rapid that the up or down movement of the spot of light appeared as brief flashes, in which all distinctness was obliterated. This experiment conclusively shows that the nerve, like certain other tissues, is susceptible of multiple excitation. If the nerve in a nerve-and-muscle preparation be allowed to dry, the muscle is seen to be thrown into a series MULTIPLE RESPONSE OF NERVE of spasmodic contractions. caused by multiple excitations induced in the nerve. 539 This also we may regard as And the correctness of this supposition I have been able to verify by experiment. As the individual responses in these multiple series were of fairly large amplitude, I ex- pected to be able to obtain a record of such a series by an ordinary magnification on smoked glass. In order to* obtain this record under normal conditions a stream’ of air, bubbling through water, was passed through the chamber at a uniform rate. Owing to the run- down of the latent energy in the nerve, we are able to observe a_ consequent growing relaxation. By the manipulation of a stop-cock the air is passed through a calcium chloride tube, in- stead of a vessel containing water. In this way the nerve is quickly subjected to dry air instead of moist vapour. This substitution is repre- sented in the record by an upward arrow 7, and it will be noticed how at this point Initiation of Multiple Re- sponse by Drying of Nerve FIG. 326. The nerve, owing to growing sub- tonicity, was showing a growing relaxation, as seen in the first part of the record. Air passed through CaCl, tube, and, thus dried, was now passed through nerve-chamber at point marked with upward arrow *. This gave rise to a large con- tractile response, followed by sub- sequent multiple responses. Original record on smoked glass here reduced photographically to 4. the relaxation is suddenly converted into excitatory con- traction (fig. 326). Under this process of drying, this single contractile movement is followed by a long-continued series of multiple responses, here seen to fall into a somewhat irregular periodicity. CHAPTER XXXVII RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY Variation of resistance in Dionea, by ‘ modification’—Excitatory change, its various independent expressions—Characteristic difficulties of investigation— Morographic record by variation of resistivity—Inversion of curves at death- point—Similarities between mechanical, electro-motive and resistivity curves of death—The true excitatory effect attended by diminution of resistance — Response of plant nerve by resistivity variation—Independence of resistivity and mechanical variations—Responsive resistivity variation in frog’s nerve, and its modification under aneesthetics. IT was noticed by Burdon Sanderson that leaves of Dionga after ‘modification’ exhibited a diminished electrical resist- ance; and this ‘modification’ he found to be most easily induced after the passage of an electrical current through the tissue. Subsequent observers have also noticed a diminu- tion of resistance in many cases when a tissue has been subjected to electric shocks. These diminutions of resistance are observed as more or less permanent after-effects. The experiments in these cases depend on obtaining the galvano- meter deflections caused by a small E.M.F., before and after the modification. The larger deflection due to the same E.M.F. after modification shows that the resistance of the tissue has undergone a diminution. This method, however, is open to several objections. The passage of constant or induction currents through the tissue would not only give rise to polarisation effects, but would also induce an unknown electromotive variation at the two contacts on the surfaces of the tissue, to an extent depending on their differential excitability. The observed deflection by a small testing E.M.F. is thus affected, not Oo ty ihe fan. BP RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 541 only by .the variation of resistance, but also by varying polarisation and. excitatory electromotive effects. The question still remains, What is the nature and significance of this induced variation of resistance? As the effects which have been referred to are generally seen to be induced after excitation, and to constitute its after-effect, does it follow that the diminution of resistance takes place as a remote consequence of other excitatory changes? Or is it but a different manifestation of that fundamental molecular change, induced by excitation, of which the electromotive variation and change of form are other and independent expressions? I showed in the first chapter of this book that one identical molecular change may be detected in different ways, according to the method of observation. Thus the same excitatory change is shown both in change of form -and in electromotive variation. That either manifestation takes place in entire independence of the other is shown, for instance, when the mechanical response of A/zmosa or Desmodium is restrained, under which condition the electro- motive response proceeds as before. Excitatory changes, similarly, may express themselves independently either by electromotive variations or by changes of electric resistance. It was, in fact, by means of the latter method, that of the variation of resistance, that I first demonstrated the responsive molecular changes which take place in inorganic matter.! If living tissues, therefore, really respond to excitation in a manner similar to the inorganic, it should be possible to obtain from them response-records by a new method, that of Resistivity Variation alone. In order to demonstrate this inference, it will be necessary to show that such varia- tion of resistance takes place immediately on excitation, and not as an after-effect. We ‘must, however, ascertain whether this method of Resistivity Variation does or does ' Bose, De la Généralité des Phénomines Moléculaires produits par ? Elec- tricité sur la matidre Inorganique et sur la Maticre Vivante. (Travaux du Congrés International de Physique. Paris, 1900.) 542 COMPARATIVE ELECTRO-PHYSIOLOGY not give us those two opposed effects, positive and negative, which we have already seen to be exhibited by living tissues in other forms of response whether mechanical or electro- motive. Of these, again, supposing them to occur, it will also be necessary to determine whether it is the increase or decrease of resistance which corresponds to the negative and positive mechanical and electromotive responses respectively ; and finally it must be determined what are the effects of the. various physiological modifications, induced by different agencies, on the response by resistivity variation. In this investigation many serious experimental difficulties have first to be overcome. These will be dealt with in series in the detailed description of the method to be employed. It will be well, however, to see in what important respects the conditions for the obtaining of response here are unlike those of the electromotive variation. In the latter case, it we employ an isotropic tissue, diffuse stimulation will induce similar excitatory electromotive variations in every part of the tissue. The differential electromotive variation, there- fore, on which the recording of response depends, will, under _ these circumstances, be impossible. In this case, therefore, it is necessary to injure or kill the tissue at one of the two contacts. Such artificial induction of anisotropy would not, however, be necessary under an experimental method which was not dependent on any differential action. Thus an isotropic tissue would give response by longitudinal con- traction when the stimulus was diffuse. Similarly, though an isotropic tissue fails to give an electromotive response under diffuse stimulation, yet we may expect it to exhibit response by variation of resistance. The recording of excitatory response by resistivity variation has thus one advantage over that of the electromotive variation, inas- much as the record is not affected by complications due to differential action, but is the expression of the direct effect of excitation. The question which we have next to deter- mine, then, is whether or not the excitatory variation of the living tissue is attended by any variation of its resistance, i. ae os fe RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 543 and whether, if so, such variation is or is not of two opposite signs, according to the tonic condition of the tissue con- cerned. In subjecting this question to experimental investi- gation, it is well to employ a non-electrical form of stimula- tion, in order to avoid any possible disturbance of the galvanometer record from polarisation or current escape. The first point to be decided is the character, positive or negative, of that resistivity variation by which the true excitatory change finds expression. We have already seen that when a tissue is subjected to a gradually rising tem- perature it exhibits response, which is expressed mechani- cally as increasing expansion, and electrically as increasing positivity. When the temperature, however, has reached the definite critical point. of death, we have seen that there is a sudden excitatory effect induced, attended by a reversal of the sign ‘of response. This is expressed mechanically by a sudden contraction, and electrically by a change to galvanometric negativity. I have already ex- plained in Chapter XVI. that, in mechanical and electrical morographic curves, the abrupt point of inversion represents the death-point. I have also shown that this death-response is a true physiological response; that the temperature at which it takes place is definite in all phanerogamous plants, being at, or very near, 60° C. in normal specimens; and that it displays depression, by transposition te a lower tempera- ture, when the tissue is physiologically depressed by such influences as fatigue.' From these facts we might expect, if a tissue sfioied response by variation of resistivity, that up to 60° C., or so, there would be a continuous one-directioned change of resistance, succeeded on reaching 60° C. by an abrupt reversal to the opposite-directioned change. In that case, it would be the second of the two, which would be indicative of true excitation. To carry out this experiment I took a radial and physiologically isotropic pistil of, Wzb¢scus, and mounted it on two non-polarisable electrodes. The specimen 1 Bose, Plant Kesponse, p. 177. 544 COMPARATIVE ELECTRO-PHYSIOLOGY was now made the fourth arm of a Wheatstone’s bridge (fig. 327), by which electrical resistance is usually determined. The plant specimens employed generally possessed high resistance, of the order of several hundreds of thousands of ohms. In the Wheatstone’s arrangement employed by me, P and Q represented the ratio-arms; R a standard. megohm, lic. 327. Diagrammatic Representation of Experimental Arrange- ment for Recording Response by Resistivity Variation P Q, ratio arms of Wheatstone’s bridge; R, standard 1 or *5 megohm; S, specimen. or half-megohm; and s the specimen whose variations of resistance were to be determined. It is now evident that Cpa? when the bridge is balanced, S = ~ R. P The ratio-arms, P and Q, consist of resistance-boxes, which allowed a variation of from I to 10,000 ohms. In order to obtain balance, of course, the ratio of the two had to be suitably adjusted. A highly sensitive galvanometer was used, and the electromotive force employed to obtain balance was only ‘o5 volt. This low E.M.F. was obtained by the use of a suitable potentiometer slide. It will be seen that, owing to the very low E.M.F. and the high resistance in the circuit, the current flowing through the specimen was rendered extremely feeble. This was done in order to avoid RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 545 any complication such as might result from the passage of a strong current. 7 4 In order to subject the specimen to a gradual and continuous rise of temperature, it was placed in the thermal chamber, which has already been described (fig. 131). Before the gradual raising of the temperature is initiated, an exact balance is first obtained, the galvanometer spot of light being thus adjusted to zero. This position can be maintained for an indefinite length of time, provided the specimen is subjected: to no variation of temperature. We have already seen that no, resultant electro-motive variation is induced, in consequence of stimulus, in a physiologically isotropic tissue. Any change now recorded under a gradual rise of temperature, by the movement of the galvanometer spot of light, must, therefore, be due toa resulting variation of resistance. The movement of the galvanometer spot of light is recorded in the usual manner, on a photographic plate, a down-record representing an increase of resistance, and an up-record a diminution. In order that the curve should also give indica- tions of different temperatures, light is cut off for a short time at every 2° C. of rise of temperature. Thus each of the successive gaps in the record indicates a temperature-ascent of 2° C. Taking now the specimen of pistil of Wzdzscus, balanced as described, it was seen, on beginning gradually to raise the temperature, that the balance was upset, while the growing deflection of the galvanometer spot indicated an incréasing resistance. The method of experiment, which has been described, proved now so delicate that it was impossible to record the entire curve within the range of the photographic plate. It was, therefore, necessary to choose for record only that part of the deflection which included the interesting and significant point of inversion. The photographic record thus commences at 56° C., it being understood that there has been, before this, a larger and continuously growing deflection downwards, indicative of increasing resistance. During record the deflection continues to increase, till the NWN 546 COMPARATIVE ELECTRO-PHYSIOLOGY critical point is reached. And here, though the temperature still goes on ascending at the same rate as before, we see a sudden reversal in the characteristic curve of resistivity, showing that the hitherto increasing has suddenly become a decreasing resistance. This abrupt inversion represents the Fic. 328. FIG. 329. FIG. 330. Fic. 328. Photographic Record of the Morographic Curve taken by Method of Resistivity Variation in Pistil of Azdéscus. Critical point of inversion at 60°8° C, Fic. 329. Photographic Record of the Morographic Curve taken by Method of Electro-motive Variation in Petiole of Musa. Critical point of inversion at 59°6° C. Fic. 330. Photographic Record of the Morographic Curve taken by Method of Mechanical Response in Filament of 7ass¢flora. Critical point of inversion at 59°6° C excitatory effect which occurs at the point of initiation of death, and is in the present case at 60°8° C. (fig. 328). It is astonishing to find that the morographic curves obtained from different specimens, by three methods so different as the mechanical, the electro-motive, and that of RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 547 resistivity, should bear so strong a resemblance to each other, as is here seen to be the case, in the three records given side by side (figs. 328, 329, 330). The excitatory effect may thus be manifested by contraction, galvanometric negativity, or diminution of resistance. We have already seen that the electromotive is not a consequence of the mechanical re- sponse, but is exhibited independently, when physical move- ment is restrained. The response by resistivity variation likewise, is, as we shall see, an independent expression of the fundamental molecular change due to excitation. Having thus established the fact that true excitatory response is exhibited by diminution of resistance, we‘ have next to ascertain whether this method of resistivity-variation is capable of being employed in the study of excitatory phenomena in general, with as great facility as those mechanical and electro-motive methods with which we are already familiar. In order to determine this question I employed the same Wheatstone’s bridge arrangement as before. As it was important, for reasons previously given, to use a non-electrical form of stimulus, I employed those thermal shocks which we have already found to be so reli- able. The thermal loop of platinum wire enclosed the specimen as before, without being in contact with it. A short-lived passage of heating-current, controlled by a metro- nome, would now give rise to that sudden thermal variation which we have seen to be effective in causing stimulation It should be remembered that the rise of temperature, as such, induces a responsive increase of resistance. But as, on the other hand, the sudden thermal variation acts as a stimulus, it should induce the excitatory response, by a transient diminution of resistance. In the following experi- ments, I employed the physiologically isotropic nerve of fern. The resistance of this tissue, when balanced, was found to be 400,000 ohms. It should be stated here that this specimen was in a very good tonic condition, and might be expected therefore to give normal response. It was now subjected to a series of stimuli of uniform intensity, at intervals of five NN2 548 COMPARATIVE ELECTRO-PHYSIOLOGY minutes. The consequent responses are seen to be uniform, and to take place by that diminution of resistance which we already know to constitute the normal mode of response (fig. 331). In order to obtain some idea of the magnitude of these resistance variations the balance was upset at the end of the response record, to the extent of 4,000 ohms. The deflection seen to the right of the figure represents the effect of this variation of resistance. The normal resistance of the tissue, including that of the non-polarisable electrodes was, as stated before, 400,000 ohms. The resistance of the electrodes themselves was 50,000 ohms. That of the tissue FiG. 331. Response Records by Resistivity Variation, in the Nerve of Fern ; Stimuli at Intervals of Five Minutes Kesponse to stimulation is by the negative variation or diminution of resistance. The record to the right shows deflection due;to variation of resistance of 4,000 ohms. alone was thus 350,000 ohms. The variation of resistance induced by stimulus, therefore, was, in the present case, approximately I per cent. In order. next to determine whether the resistance variation was a consequence of the responsive change of form, or an independent expression of the fundamental molecular change, I clamped a nerve of fern suitably, at its two ends, to prevent any possible change of length, the two non-polarisable electrodes being led off in such a way as to include a certain length of the specimen. On carrying out the experiment in this manner I obtained response by diminution of resistance, exactly as in the last RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 549 case. It is thus seen that the response, by resistivity variation, is an independent expression of the excitatory variation. . a In taking records of the responses of animal and vege- table nerves, by the methods of mechanical and electro- motive variations, we saw that, while the normal response was negative, this was liable to become reversed to positive, under two different conditions—namely, sub-tonicity and the fatigue due to excessive stimulation. Similar reversals are observed under similar conditions, when the method of resistivity variation is employed. We saw, further, that the abnormal positive response, due to sub-tonicity, could be gradually converted into normal negative, through inter- mediate diphasic, by tetanisation—further tetanisation acting, moreover, to exalt this feeble into enhanced negative response. Parallel results are observed in the case of resistivity variation. The initial abnormal response, by increase of resistance, is found, after short tetanisation, to be converted into diphasic—an increase of resistance or positive response preceding the true excitatory or negative effect of diminution of resistance. Further tetanisation brought about the disappearance of this preliminary positive, and the enhancement of the negative, response. — I used the same method, finally, for the observation of response and its modifications, by means of anesthetics in animal nerve. For this purpose I took a nerve of frog, and subjected it to chloroform. It will be remembered that in studying the effect of anzsthetics by the electro-motive variation method, we found it, first, to reverse the normal response to positive, and finally to’ induce an abolition, which might prove to be either temporary or permanent. The same thing is seen under the resistivity variation method. In the first series of records, given in fig. 332, we find normal responses by diminution of resistance, to a series of stimuli applied at intervals of two minutes. After the application of chloroform, the normal responses are seen to have disappeared. Stimulus now evokes 550 COMPARATIVE ELECTRO-PHYSIOLOGY either no response or an occasional flutter, in the positive direction. We have thus seen, in the course of the present chapter, that, in addition to the mechanical and electro-motive modes of response, there is also a third mode available—namely, that by Resistivity Variation. We have also seen that the results obtained under these three methods are identical. It has been shown that the normal excitatory effect is in AW WW Vi FIG. 332. Effect of Chloroform seen in Modification of Resistivity Variation in Frog’s Nerve The normal responses seen to the left by diminution or negative variation of resistance were evoked by stimuli at intervals of one minute. Those to the right exhibit the effect of chloroform. The normal response is thus abolished, and we have either no response or only an occasional flutter in the positive direction. all three cases negative, consisting of mechanical contraction, galvanometric negativity, or diminution of resistance, as the case may be. In recording the morographic curve by these three methods, we find that up to the critical point of death, at or near 60° C., we obtain expansion, galvanometric posi- tivity, and increasing resistance. At that point, however, there is a sudden reversal of the curve, indicating conversion to negative, contraction, galvanometric negativity, and de- crease of resistance. CHAPTER XXXVIIi FUNCTIONS OF VEGETAL NERVE Feeble conducting power of cortical tissues—Heliotropic and geotropic eflects dependent on response of cortical tissues only—Phenomenon of correlation —FExcitability of tissue maintained in normal condition only under action of stimulus—Physiological activities of growth, ascent of sap, and motile sensibility, maintained by action of stimulus—Critical importance of energy of light—Leaf-venation a catchment-basin—Transmission of energy to remotest parts of plants—Plant thus a connected and organised entity. IN the animal body, different kinds of tissues are possessed of different degrees of conductivity, the nerve being specialised for the rapid transmission of stimulus. And it is now seen that in the plant also we have a similar state of things, cortical tissue, for example, though excitable, having feeble conductivity, whereas the vegetal nerve possesses this power in high degree. The question next arises: What is the function subserved in the economy of the plant by a tissue so highly specialised for the rapid conduction of stimulus ? The various growth curvatures, by means of which plants place themselves under the directive action of light and gravity, are of advantage to the organism. But in bringing about these movements, the plant-nerve takes little or no part. And this is the case, even when the responsive curvature takes place at a certain distance from the point of stimulus. Here the transmission takes place slowly, through the feebly-conducting cortical tissues. For example, in Avena, curvature in consequence of such transmitted effect is observed, even when the fibro-vascular bundles have been cut across. , If, indeed, the highly conducting nervous elements ha been concerned, these curvatures in response to unilateral 552 COMPARATIVE ELECTRO-PHYSIOLOGY stimulus could not well have taken place. This will be clear if we consider the case of a radial organ, such as the stem, unilaterally acted on by light. Here a positive heliotropic movement is induced, by which the growing organ is placed in the most favourable position as regards illumination. The peculiarity of this phenomenon lies in the responsive contraction of the side acted on by stimulus, with consequent concavity and curvature towards light. This heliotropic | movement continues until the organ has placed itself in the direction of incident radiation. When this orientation has become perfect there is no further movement, because the proximal and distal sides are now equally stimulated. Had the cortical tissue, on whose differential responsive action the curvature depended, been as highly conducting as the vegetable nerve, this particular-directioned movement would have been an impossibility, for the stimulus, instead of remaining localised on one side, would in that case have become diffused, with the result of inducing antagonistic effects on the proximal and distal sides, under which there could have been no resultant curvature. Indeed this neutral- ising action of conduction, in nullifying responsive curvature, is seen even when unilateral stimulus is excessively strong. For under these circumstances stimulus is conducted transversely, through the imperfectly conducting tissue, with the result of undoing the previous curvature. And it is obvious that had the conductivity of the tissue been higher, this neutralisation would have taken place, even under feeble stimulation. I have also shown elsewhere that, in the responsive movements of leaves, conduction through nervous elements plays little or no part. For the blade of the leaf may be acted on by light without showing any responsive movement. Hence the lamina is not to be regarded as the perceptive organ. The organ by which, on the contrary, the responsive movements of the leaves are determined is the pulvinus or pulvinoid. This is at once perceptive and motile. When such an organ, then, is acted on directly and locally by light, FUNCTIONS’ OF VEGETAL NERVE 553 a responsive movement is\induced. These are facts which can be demonstrated by shielding the lamina and pulvinus alternately from the action of light. When the lamina alone is exposed there is no action; but when it is the pulvinus to which light is admitted, there is an immediate responsive movement. The lamina, it is true, is provided with a fine fibro-vascular network containing the nervous strands. But the stimuli received by this extensive system are ultimately conducted along the thicker channels of which it forms the terminal ramification, and serve to stimulate the plant as a whole. When such stimuli reach the petiole, then, they cannot act in that direct and unilateral manner in the motile organ which is required for the responsive movement of the leaf. The petiole, it is true, from its dorsiventral character, is unequally excitable on its two sides. But since,in the process of the transference of stimulus from the nervous to the ordinary elements there is a great loss, and since, moreover, the motile tissues in the case of most petioles are very sluggish, the diffusely transmitted stimulus induces practically no directive effect. Nor could there, in any case, have been any com- parison between the effective strength of an external stimulus acting directly and unilaterally, and a transmitted stimulus acting diffusely. It will thus be seen that conduction through specialised nervous elements is by no means the essential factor in bringing about those numerous directive curvatures which subserve so many important functions in the life of the plant. The question, therefore, as to what is the part in the economy of the organism played by the vegetable nerve still remains to be answered. One very obscure problem in connection with Vegetable Physiology is that of Correlation. Thus various complex activities may be set up in one part of the plant, when another part, more or less distant from it, is subjected to the variation of some excitatory influence. In this way every part of the plant-organism would appear to be ez rapport with 554 COMPARATIVE ELECTRO-PHYSIOLOGY the rest, and this intimate connection between outlying areas becomes comprehensible, when we are made aware of the easy communication afforded by the existence of specialised conducting elements. I shall now proceed to deal with. the importance ot stimulus, and its conduction to the interior of the plant, as the essential factor in sub- serving the various life-. activities of the organism. That the reception of stimu- lus is important, in main- taining the excitability of a plant, is easily seen in the case of Mzmosa, when de- prived of light, for example. Under these conditions, its motile excitability is found to disappear. And this is only restored on re-exposure to light. We have seen again, in the course of the last chapter, that the isolated vegetable nerve, deprived, as it is, of normal favourable RiGcsrin Pilostanhins Recmdcc! conditions, becomes sub-tonic Effect of Tetanisation in En- or moribund, and then its hancing Mechanical Response of Plant-nerve ordinary responsive power is The first series of responses heightened abolished or even reversed. to second series, after intermediate Under these ‘clvcumatantes tetanisation. the normal excitability is found to be restored by the continued action of stimulus. Abnormal positive response is thus found to be converted into normal negative. Again, after an intervening period of stimulation, response of ordinary amplitude is found, as in fig. 333, to become enhanced. It is thus seen that a tissue, when cut off from the supply of stimulus, loses its normal excitability, and that a@ more or less continuous supply of FUNCTIONS OF VEGETAL NERVE 555 stimulus ts essential to the maintenance of the proper excitatory condition of a tissue. | | It is known that in the animal, when the conduc- tivity of a nerve is abolished by nerve degeneration, the connected muscles also rapidly waste away. Thus the maintenance of the proper excitability of various tissues is dependent on their constant reception of stimulus or energy through the mediation of the attached nerve. It is therefore highly probable that the excitability of the indifferent vegetable tissues is kept at its normal level by the reception of energy | of stimulus through the conducting nerve. | I shall next briefly refer to a fact which I have demonstrated fully elsewhere, that all the principal physio- logical activities of the plant, such as autonomous movement, ascent of sap, and growth are fundamentally excitatory phenomena. Thus, for example, the autonomous rhythmic movements of the lateral leaflets of Desmodium gyrans come to a standstill when their store of latent energy is exhausted. And it is only by the accession of fresh stimulus from outside that these multiple responses can be renewed. We describe the state of the plant, when its internal energy is below par, by saying that it is sub-tonic, the normal tonic condition, or health of the plant, being dependent on the sum total of stimulation previously absorbed by it. Turning next to the question of the ascent of sap, I have shown that the most important factor in bringing this about is the multiple rhythmic activity of certain interior tissues of the plant. Under such circumstances as cause the tonic condi- tion of the tissues to fall below par, the rate of the ascent of sap will be lowered, or it may possibly even be brought to a standstill, owing to the depression of excitability induced. On now supplying fresh stimulus, we find the excitability to be renewed and the normal rate of ascent restored (p. 383). Another instance of this is seen in the fzleus of Coprinus which droops when kept too long in the dark, but recovers its normal turgidity on exposure to light. Growth, again, I have shown to be a result of multiple 5 56 COMPARATIVE ELECTRO-PHYSIOLOGY rhythmic excitation. When the tonic condition of the plant falls below par, growth is arrested, however large the amount of formative material present. But if stimulus be applied, while the plant is in this state of growth-standstill, there is a renewal of responsive growth. The importance of the absorption of stimulus of light to the response of growth is seen in the development of certain seedlings. These, when grown in the dark, become diseased | and perish. The growth and the development of organs cease, even though the cotyledons still contain considerable quantities of unused formative substance. They become moribund, as the expression of their loss of tonic condition, which, as we have seen, depends upon the supply of stimulus from outside. And in the present case the critical element is the stimulus of light. This fact that the stimulus of light may enhance the ex- citability of a tissue, is shown in the following photographic records of the mechanical response of vegetal nerve. The first three responses show the extent of normal response to a given electrical stimulus applied in the dark. The specimen was then subjected to the light of an electrical arc lamp, and the next series show the consequent enhancement of response, under the same stimulus as before. Light was now cut off, and after an interval response once more taken. This is seen to have been of the same amplitude as at the beginning (fig. 334). Thus light is seen to enhance excitability. In the cases which we have just been considering we have, for the sake of simplicity, confined our attention to a single factor—namely the photo-tonic—among the many which finally determine the general tonic condition of the plant. And we have found that when the organism is deprived of this source of stimulus, its motile activity, its suctional activity, and its response of growth, all disappear. When the plant, however, is restored to the direct action of light, all these various activities reappear. Now it is clear that this illumination cannot. directly penetrate to many of those interior tissues, whose activity is nevertheless essential to the oe Pei Ba) Ras FUNCTIONS OF VEGETAL NERVE 557 maintenance of life. How, then, is the external stimulus conveyed to these? It is evident that this can only be accomplished through the agency of the nervous elements. This fact, of the transmission of the excitatory effect of an external stimulus from one part of the plant to another at a distance, there to maintain the tonic condition, is again still more clearly seen in the well-known experiment on the sensitiveness of Wzmosa when partially kept in the dark. If one branch of this plant be covered by a dark box, while the rest of it is exposed to light, it is found that the leaves of the FIG. 334. Photographic Record showing Enhancement of Excitability under Action of Light in Nerve of Fern First series, normal mechanical responses to electrical stimuli, in dark ; second series, the same, taken under light; third series, taken after withdrawal of light. first undergo no loss of motile sensitiveness. It is thus evident that the photo-tonic stimulus has been transmitted from the illuminated to the unilluminated portions of the plant, through conducting channels, in order to maintain the normal excitatory condition. | Next comes @ie very interesting experiment of Sachs, in which a long shoot of Cucurbita was made to grow inside a dark box, the rest of the plant being exposed to light. The covered part of the plant, under these circumstances, showed normal growth of stem and leaves. Normal.flowers and a large fruit were also produced in the same confinement. The tendrils inside the box, moreover, were found to be fully 558 COMPARATIVE ELECTRO-PHYSIOLOGY as sensitive as those outside. The transmission of stimulus by the plant, in such a way as effectively to maintain such complex life-activities as motility and growth, even in the absence of direct stimulation, is. thus fully demonstrated. And we may gather an idea from this fact of the funda- mental importance, to the life of the plant, of those nervous elements by which this is rendered possible. One of the most important functions of the venation ot the leaf, not hitherto suspected, is now made clear to us: Among external stimuli, none perhaps is so essential, or so universally and easily available to green plants, as energy otf light. And we now see that the fine ramification of fibro- vascular elements over as wide an area as possible in the leaf, provides a virtual catchment- basin for the reception of stimu- lus. The expanded lamina is Re Sages STistginurine ore Ties thus not merely a specialised vascular Elements in Single structure, for the purpose of Bevan heel ot hapaye photo-synthesis, but also a sen- There are at least 20: such layers eb ‘ engirdling the stem. sitive area for the absorption of stimulus, the effect of which is gathered into larger and larger nerve-trunks, in the course of its transmission downwards into the body of the plant. And even in the interior of the plant the distribution o1 these is such that no mass of tissue is too remote to be ex- cited by the stimulus conducted through the nervous ele- ments buried in them. How reticulated they may be, even in the trunk, is seen in the accompanying photograph of the distribution of fibro-vascular elements in the main stem of Papaya (fig. 335). This network, of which only a small portion is seen in the photograph, girdles the stem through- out its whole length, and in this particular case there were as Many as twenty such layers, one within the other. crawls, ‘aomsn mei; pooner STONE es Pe ee le el ae: FUNCTIONS OF VEGETAL NERVE 559 It is thus seen how all parts of the plant are, by means of nerve-conduction, maintained in the most intimate communi- cation with each other. It is, then, in virtue of the existence of such nerves, that the plant constitutes a single organised whole, each of whose parts is affected by every influence that falls upon any other. | CHAPTER XXXATX KLECTROTONUS Extra-polar effects of electrotonic currents on vegetal nerve—Electrotonic variation of excitability—Bernstein’s polarisation decrement —Hermann’s polarisation increment—Investigation into the law of electrotonic variation of conductivity —Investigation on variation of excitability—Conductivity en- hanced when excitation travels from places of lower to higher electric potential, and depressed in opposite direction—When feeble, anode enhances and kathode depresses excitability—All electrotonic phenomena reducible to combined action of these factors—Explanation of apparent anomalies. WHEN an electrical current is Jed through a portion of a nerve— entering, say, at A, and leaving by K—it is found that electro-motive changes are induced by it in the extra-polar AD aS = FIG. 336. FIG. 337. Extra-polar Kat- and An-electrotonic Effects Fig. 336 shows kat-electronus, E near K being galvanometrically negative. Fig. 337 shows an-electronus, E near A being now galvanometri- cally positive. regions. On the kathodic side, the electric potential near K is found to be lowered in reference to a point further away. On the anodic side similarly, the electric potential of a point near A is found to be raised. These changes induced in the electric potential are indicated by the galvanometric nega- tivity of the point near the kathode, and positivity of that near the anode (figs. 336, 337). In the tissue itself the current is assumed to flow in a direction contrary to that in > ELECTROTONUS 561 the external galvanometric circuit, as indicated by the dotted arrow.' In the medullated animal nerve, the electrotonic currents increase with the intensity of the polarising current. In the vegetal nerve, I have obtained exactly similar results. Taking afresh and vigorous specimen, the polarising elec- trodes were placed at a distance of 2°5 cm. from each other, the pair of extra-polar electrodes, where the electrotonic effects are observed, being separated from these by 2 cm. and divided from each other by 2 cm. also. The value of the acting polarising E.M.F. could be varied by the use of a Fic, 338. Extra-polar Electrotonic Effects under an Acting E,M.F. which rises from °6 to 1°4 Volts A, an-electrotonic deflections seen to left ; K, kat-electrotonic to right. potentiometer arrangement. In order to induce in the extra- polar electrodes, an-electrotonic and kat-electrotonic effects alternately, the current in the polarising circuit can be sent in one direction or the other by means of a reversing-key. The record of the galvanometer deflection, in the extra-polar circuit, gives a measure of the electrotonic effect induced. In fig. 338 is seen such a record of. effects both an-electro- tonic and kat-electrotonic, taken while the acting E.M.F. was increased from ‘6 to 1°4 volt, by steps of ‘2 volt at a time. ' Certain considerations, which need only be referred to here, cast some doubt on the validity of this assumption. But as it is so widely current in physiological literature, I shall confine myself, in dealing with the subject of the electrotonic current and its variations, to those indications in the external circuit which are afforded by the galvanometer. OO 562 COMPARATIVE ELECTRO-PHYSIOLOGY I give here a table which shows the galvanometric deflection corresponding to each particular E.M.F. TABLE OF GALVANOMETRIC DEFLECTIONS AND CORRESPONDING E.M.F. Volts | An-electrotonic effect Kat-electrotonic effect 6 _ §0 divisions 58 divisions - 8 65 9 78 9 | ae) 107 ) IIO -s 1‘2 126 ee 124 - 1°4 150°; | 148s, In this particular experiment, it will be seen that the an-electrotonic and kat-electrotonic effects are practically equal. But, to be more accurate, the an-electrotonic are slightly lower with low E.M.F., and slightly higher with high, than the corresponding kat-electrotonic deflections. A constant electrical current is thus seen to induce electro- motive variations, outside its poles, in the vegetal nerve. We next turn to the question of the variation of excitability induced in a tissue, by the passage of a con- stant current. On this subject the most important con- tributions have been made by Bernstein and Hermann. Bernstein, experimenting on the sciatic nerve of frog, found that excitation induced a polarisation decrement. This experiment is illustrated in the following diagram (figs. 339, n —— eceet —o Tah FIG, 339. FIG. 340. Figs. 339, 340. Diagrams illustrating Bernstein’s Electrotonic Decrement Fig. 339 shows decrement of kat-electrotonic, and fig. 340 of an-electro- tonic currents, under stimulation at s. In this and following figures the inside thin arrow indicates direction of polarising current, the outside thick arrow the direction of responsive current. 340). In fig. 339 the kathodal effect is seen induced in the extra-polar circuit. When the nerve is now excited by tetanising electric shocks, a diminution of the extra-polar current is induced. When the anodal effect is induced in ELECTROTONUS ; 563. the extra-polar circuit, by reversal of polarising current, the an-electrotonic current, opposed in direction to the former kat-electrotonic, also undergoes diminution on excitation of the nerve (fig. 340). It has been suggested that this diminution of electrotonic current was due to a supposed diminution, during excitation, of the susceptibility of the nerve to polarisation. But this explanation is negatived by an experiment of Hermann, showing the occurrence of polarisation increment during excitation. In figs. 341 and 342 we havea polarising _ and exciting circuit in series, excitation being caused by the ot eh = Yo a a aEEERRREaEned A pea af K K <—__—_—_ A Fic. 341. FIG. 342. Figs. 341, 342. Diagrams representing Hermann’s Polarisation- increment under Tetanising Shocks Inside thin arrow indicates the direction of polarising current ; the outside thick arrow, the direction of excitatory current. secondary coil of an inductiorium. With such an arrange- ment, the polarising current, whether from left to right or from right to left, is found, during excitation, to undergo an augmentation. Hermann refers these facts to alterations of intensity in the negative wave of excitation, during its passage through the nerve, when the latter is polarised. ‘ It is, indeed, more pronounced at any point of the nerve, the more strongly positive and weakly negative the polarisation of the latter, ze. it increases when it is becoming algebraically more positive, and diminishes when it advances upon more negative points’ (Hermann’s Law of the ‘ Polarisation Increment’ of excitation).! It would thus appear that the observations hitherto made, as to the effects of electrotonus on excitatory response, are of ! Biedermann, Blectro- -phystology (Engl. transl. ), vol, ii. p. 315. 002 564 COMPARATIVE ELECTRO-PHYSIOLOGY a somewhat discordant character. I shall, however, be able to show that their complexity is due to the combination of the different effects of the polarisation current on conductivity and on excitability. These separate effects may, according to circumstances, either conspire or act antagonistically. Hence the great variety of results, which appears at first sight incapable of a consistent explanation. In order, then, to discover the laws by which an electric. current induces a variation of conductivity and excitability, we must first determine the pure effect of the current on conductivity, apart from any excitatory variation; and, secondly, its effect on excitability, uncomplicated by any variation of conductivity. | | To take conductivity first: the ideally perfect arrange- ment would be to have the polarising electrodes, in relation to the region whose conductivity-variation is to be tested, at a distance so great that they could exert no predominant an- or kat-electrotonic influence upon it. In a led-off circuit, moreover, a differential action, unless proper,pre- cautions are taken, is exerted on two electrodes placed side by side. It is, therefore, desirable to remove one of these outside the sphere of action. Such, then, being the con- ditions to be observed, in order to eliminate the effect of the poles themselves, and thus determine the influence of the direction of current on conductivity alone, I took a petiole of fern 20cm. in length, and connected its ends through a reversing-key with a Daniell cell (E.M.F.= 1 volt). The responding galvanometer-circuit had one electrode about the middle of the petiole, near the insertion of a certain lateral leaflet, the other electrode being connected with the lamina of the same leaflet, whose midrib, however, was cut across to prevent transmission of the excitatory effect (figs. 343, 344). It is thus seen that the led-off electrodes are at a relatively great distance from the polarising electrodes, and further, owing to one electrode being placed out of the way, on the lateral leaflet, and the other symmetrically between anode and .kathode, it is clear that anodal or kathodal action is ee eS ee rae eee eee eee eee ELECTROTONUS 565 reduced to wz. The excitation from the stimulator is transmitted across the intervening conducting region, either along the slope of a falling electrical potential, that is to say, from-a galvanometrically positive to a galvanometrically negative point, or against that direction, namely, in an electrically uphill manner, from the galvanometrically negative to the galvanometrically positive. Now, if the direction of an electrical current have an effect on the conduction of excitation, this fact will be detected by the modification induced in the normal response during the passage of the current. : The results of the present experiment will be found to determine this question. Excitation was induced by means Fic. 343. : Fic. 344. Figs. 343, 344. Experiment with Petiole of Fern demonstrating Variation of Conductivity by Polarising Current of the thermal stimulator, and the normal responses taken, shown in fig. 345 a, as ‘up. The polarising current was now sent from left to right; hence excitation will now be transmitted through the intervening conducting region in an electrically downhill manner, or in the direction of the falling potential—that is to say, from the region of the anode to that of the kathode. It will be seen presently that conduction is retarded or abolished when excitation is made to travel elec- trically downhill from the anode to the kathode.' If this be so, we shall expect to detect the fact by the diminution of the amplitude of the normal response, or even by its actual reversal. For we have seen that when the excitatory re- action of galvanometric negativity is sufficiently retarded, its opposite, the positive effect, often makes its appearance alone. 1 These remarks apply to a feeble or moderate rate of fall of potential. 566 COMPARATIVE ELECTRO-PHYSIOLOGY In fig. 345 4, this is seen to have actually occurred. There will be other cases where, the depression of conductivity induced being not too great, it will be possible to watch the gradually lessening amplitude of response until it ends in actual reversal. We have next to determine the effect on conductivity, of the passage of excitation in an uphill direction—that is to say, from the kathodic to the anodic region. For this purpose the polarising current was reversed Fic. 345. Photographic Records of Responses taken in last Experiment, when Excitation was transmitted with and against the Polarising Current a, Normal response of petiole of fern to transmitted excitation; 4, Reversal of response when excitation was travelling electrically downhill or with the current; c, Normal response once more ; @, Enhanced response due to increase of conductivity when excitation travels electri- cally uphill, or against the polarising current. . Upward arrow 4 indicates that polarising current is in same direction as normal response. Downward arrow { shows polarising current in opposite direction. The same in the two following figures. by means of a reversing key, the left-hand end of the petiole being now made the kathode. Before doing this, however, I stopped the current, and took a second set of records of normal responses. It will be seen that by reason of the cessation of the previously acting left-to-right current, leaving an after-effect, these were slightly enhanced above the first normal responses (fig. 345 ¢c). On now reversing the current, conductivity was found to be enhanced, as seen in the greater amplitude of response (fig. 345 @). aan ELECTROTONUS 567 I next undertook an investigation into the effect on conductivity, of variations of intensity in a moderate polaris- ing current. This is shown in fig. 346, in which excitation travels electrically downhill—that is to say, from the anodic to the kathodic region. In a we have the normal response before the passage of the current. In 4 we have the re- sponses reduced by the diminution of conductivity con- sequent on the application of ‘1 volt for polarisation. On the application of *5 volt in c, there was a tendency towards Fic. 346. Photographic Record of Modification of Conduction during Passage of Excitation from Anodic to Kathodic Region, under Increasing Intensity of Polarising E.M.F. a, Normal response ; 4, Diminished response where terminal E.M.F. was "I volt; c, Response still further diminished and rendered diphasic under *5 volt ; @, Response reversed under I volt. reversal, the response being now diphasic, positive followed by negative. Finally, on the application of 1 volt in -d, we see the response reversed to positive, the conduction of the true excitatory effect being here altogether abolished. In a second set of experiments, carried out on a fresh specimen, I investigated the effect of an increasing intensity of the polarising current, when the excitation was made to travel, electrically uphill, from the kathodic to the anodic region. It will be seen, from figure 347, that the application of a polarising E.M.F. of 1 volt increased the conductivity, as seen in the heightened responses shown in 4, as compared 568 COMPARATIVE ELECTRO-PHYSIOLOGY with the normal responses in a. The application of higher polarising E.M.F. of °5, 1, and 1°5 volts respectively, now - induced appropriate increments of conductivity, as seen in ¢, d, and e. I was unable to use an E.M.F. of higher than I'5 volts because the galvanometer spot of light became unsteady. It is to be borne in mind that the specimens in these experiments were 20 cm. long, and the maximum potential gradient employed was only ‘07 volt per cm. In experimenting on electrotonic effects, it must be remembered that the E.M.F. employed is, generally speaking, feeble. Fic. 347. Photographic Record showing. Enhanced Conduction from Kathodic to Anodic Region a, Normal responses; 4, c, d, ¢, Responses gradually enhancing under increasing polarising current. From the results described, then, we arrive at the follow- ing law of the effect of a moderate or feeble constant electric current on conductivity. A moderate polarising E.M.F. induces variations of conduc- tivity. The conductivity is increased in the direction from the kathodic to the anodic region, and depressed in the opposite, Having thus demonstrated the pure effect of a constant electric current on conductivity, we have next to study the unmixed effect of polarisation on excitability. We. have seen that when two equally excitable points in the same circuit are simultaneously excited by an identical stimulus, there is no resultant response, since the two excitatory * eLECTROTONUS 569 effects balance each other. The galvanometric effect is then zero. But if one of the two have its excitability en- hanced in any way, this balance will be disturbed, and a resultant current will flow through the circuit, the more ex- citable contact becoming galvanometrically negative. I now took a long piece of isolated vegetal nerve and connected it with the galvanometer at E and E’,, a secondary coil, giving equi-alternating electric shocks, being also in the circuit (fig. 348). The two longitudinal con- tacts E’ and E being more or less equally excitable, there was at first no. resultant re- sponse to stimulation. E’ was now made the anode, an E.M.F. of +1 volt being used for the purpose, and a perma- nent current was found to flow in the galvano- meter in the direction of E’GE shown by the thin inner arrow, E’ being galvanometrically FIG, 349. Experimental Arrangement to Exhibit the Enhancement of Excit- ability at Anode, and its Depression at Kathode, when the Acting E.M.F. is feeble Figs. 348, 349. positive. On now ap- plying equi-alternating shocks, the balance was Fig. 348 shows enhancement of excitability at anode; Fig. 349, the depression of excitability at kathode. Inside thin arrow indicates direction of tantarins ing current. Outside thick arrow, direction of excitatory current. Note that in both thereis a so-called polarisation-decrement. found to have been dis- turbed, and the re- sponsive. current to be in the opposite direction, namely, EGE’, as shown by the thick arrow; E’ now undergoing an excitatory negative variation. This shows that the ex- citability of E’ has become enhanced by being made anode. E’ was next made kathode, in consequence of which the permanent current in the galvanometer was now in the direction of EGE’ (fig. 349). E’ is now the kathode, E 570 COMPARATIVE ELECTRO-PHYSIOLOGY in relation to it being anode. On excitation the responsive current was in the opposite direction to the permanent current, in consequence of the induced depression of the kathode E’ or the induced enhancement of excitability at the relative anode E. In fig. 350 are given the records of these effects. Two different experiments were carried out, on two different specimens of plant nerve, whose records are given in a and 4, fig. 350. In each of these we observe, first, Fic. 350. Photographic Records of Response, illustrating the Enhance- ment of Excitability at Anode, and Depression at Kathode, under Feeble Acting E.M.F. in two Specimens of Nerve of Fern a and 6 Before application of polarising current there was no resultant response in either case. When E’ was made anode, there was an up-response, indicating enhanced excitability of that point.. The dotted arrow ¥ seen below shows the direction of polarising current. The responsive current is then opposite in direction to the polarising current. When E’ is made kathode the resultant response is down, showing depression of the excitability of the point. The responsive current is here also opposite in direction to the polarising current. the enhanced excitability due to E’ being made anode, which gives rise to up-responses, opposite in direction to the permanent current, shown by the dotted arrow below. The second pair of responses in each case shows the depression of excitability at the kathodic point E’, which is tantamount to enhancement of excitability at the relative anode E. An inspection of figs. 348 and 349 will show that the responsive current is always in a direction opposite to that of the existing polarising current, thus constituting the so-called polarisation + FOO OO ee eee ee oe TGR conse pL SS ee Seb er aN ea ee nace -2t WwW | ELECTROTONUS S71 decrement. But we shall presently find that the direction of the responsive current is the only constant factor here, de- termined as this is by the relative excitabilities of the. two electrodes. An identical variation of excitability may, as I shall show, appear under different circumstances, either as a polarisation-increment or as a decrement. I have obtained results precisely like the foregoing, with the sciatic nerve of frog. It should be mentioned here that such effects are obtained without much difficulty in the first stages of polarisation. But, if this be prolonged, there is a certain liability to reversal. From the experiments which have been described on variations of excitability by the polar action of currents, we arrive at the following law: A feeble E.M.F. induces modifications in the excitability of a tissue: the anode enhances and kathode depresses excitability. This result is startling, contravening, as it does, Pfliiger’s Law. A factor that had not been taken into account was the range of E.M.F., within which this law might be applicable. In the present case, the acting E.M.F. is relatively feeble, and we shall see later that Pfliiger’s Law does not apply above or below a certain medium range. Having thus obtained the isolated effects of electric currents on conductivity and excitability respectively, I next took up those more complex cases in which both effects were present in various combinations. This problem was attacked by means of the Conductivity Balance. In this experiment, carried out on the petiole of fern, the led-off points E and E’ were at a distance of 6 cm. from each other. The distance of each of the polarising electrodes A and K outside the led-off circuit E’ and E was 2 cm. (figs. 351 and 352). The thermal stimulator S was so adjusted before the passage of the current that the excitations at E’ and E were exactly equal, as seen in the balanced horizontal record n fig. 353a. It should be mentioned here thatthe galvano- meter connections were so arranged that an _ increased excitability of the left-hand contact E’, would be shown by 572 COMPARATIVE ELECTRO-PHYSIOLOGY means of ‘down’ and that of the right hand contact E by means of ‘up’ responses. An E.M.F. of *5 volt was now eens Gorrtey rep fa = Ame fl A E’ E K K; E E H noe FIG, 351. FIG. 352. Figs. 351, 352. Experimental Arrangement demonstrating the Joint Effects of Variation of Conductivity and Excitability by Polarising Current employed to induce polarisation, the anode being in the first case to the left. Fic. 353. Photographic Record of Response under the Arrangements given in Figs. 351, 352 in Nerve of Fern a, Balanced record before passage of polarising current. 4, Resultant response downwards when polar- ising current is from left to right, as shown by arrow —. This shows excitability of FE’ and conductivity in direction SE’ to be relatively enhanced. c, Resultant response upwards when polarising current is from right to left <. This shows excitability of E and conductivity in direction SE to be relatively enhanced. Here we have a greater excitability induced at E’ by the proximity of the anode, that of E being depressed by the proximity of kathode. Of the two waves of ex- citation, moreover, which proceed in opposite di- rections from the stimu- lator S, that towards E’ is moving electrically uphill, or towards the anode, and owing to increased conductivity in that direction the excitation is better con- ducted than in the case of the second wave, which is _ proceeding electrically downhill to- wards the kathode at E. It must also be remembered that not only is the intensity of excitation which reaches E’ greater than that which reaches E, but also that the point E’ is itself rendered more excitable by the ELECTROTONUS 573 contiguity of the anode, while E is depressed by that of the kathode. Hence, by the concordant action, at each end of the balance, of conductivity and excitability changes, and owing to the opposite nature of these changes at opposite ends, the original balance is disturbed, and we obtain resultant down responses, showing the greater excitation and galvanometric negativity caused at E’ than at E, when anode is to the left and kathode to the right. This is exhibited in the first pair of down responses in figure 353 4. When, however, the polarisation current is reversed (fig. 352), the excitation at the right-hand side, E being now near the anode, is relatively the greater, and we find the resultant responses to be upwards, as seen in the third record in fig. 353. To go back to the question of the relative directions of electro- tonic and responsive currents, we find in that case, when the anode is to the left, that E’ is galvanometrically positive, while the excitatory change makes it galvanometrically negative. This means that the excitatory response takes place by the so-called polarisation decrement. When the anode again is to the right, the galvanometrically positive E tends by excitation to become galvanometrically negative. This will be clearly understood from the arrows which accompany the diagram, in figs. 351, 352. The inner and thin arrows represent the direction of the polarising current, and the thick outer arrows the responsive current. These results are tantamount to an example of the so-called polarisation- decrement. In order to show, however, that the. same excitatory reaction might appear as a polarisation-increment, I shall describe another experiment. The experimental tissue is here the isolated nerve of fern, and the method employed is again that of the Conductivity Balance. In this case, however, it will be noticed (figs. 354, 355), that the galvanometer is included in series with the polarising E.M.F., instead of being placed as a shunt, as in the lastcase. The stimulator was first adjusted at halance. The left electrode was now made kathode, the right being anode, the E.M.F. employed being °2 volt (fig. 354). On account 574 COMPARATIVE ELECTRO-PHYSIOLOGY of the increased excitability of A at the anode, and also of the greater intensity of excitation conducted towards it, the balance was disturbed, and the resultant response ‘took place by the enhanced galvanometric negativity of that point. The responsive current thus constituted an increment of the polarisation-current, as seen from the arrows; of which the thin inner represents the polarisation and the thick outer the responsive current. On now reversing the current again; the right-hand end being made anode and more excitable, the resultant response was found to take place by the enhanced negativity of that point, thus again constituting a polarisation increment (fig. 355). I give here two different Fic. 354. T'IG. 355. Figs. 354, 355. - Experimental Arrangements for Showing so-called Polarisation-increment by the Joint Effect of Increased Excitability at Anode and Enhanced Conduction of Excitation electrically Uphill sets of photographic records, obtained with the nerves of fern and frog respectively. Balance was first obtained at the beginning of the record, but on the passage of the polarisation current, this balance was found to be disturbed. When the right end of the balance was made anode, the resultant response on excitation was up, demonstrating the enhanced excitability of the anodic point. When the right- hand end, however, was made kathode, the balance was upset in the opposite direction, that is to say, down, showing that the left-hand anodic point was now the more excitable. Fig. 356 gives a record of these responses as obtained from the nerve of fern, and fig. 357 from the nerve of frog. The responsive currents in these cases, it should be noted, are in the same direction as the polarising current. ELECTROTONUS - 575 On referring to the experiments on polarisation increment and decrement which have just been described it will be noticed that the excitatory reaction is the same in both cases, taking place by the enhanced galvanometric negativity of the more excitable anodic point. The seeming difference in the electrotonic variation in the two cases lies simply in the fact of the different dispositions of the galvanometer. This occupied, in the first case, the position of a shunt in the polarisation-circuit, while in the second it was placed in series. From the investigations which have been described, we shall now find ourselves in a position to explain the various FIG. 356. FIG. 357. Fic. 356. Photographic Record of Responses in Nerve of Fern, under Anodic and Kathodic Action, as described in Figs. 354 and 355. The upsetting of the balance is upwards, when the right-hand end of the balance is made anode, proving the enhanced excitability thus induced. Resultant response downwards when the right-hand end of the balance is made kathode. Fic. 357. Photographic Record of Similar Effects in Nerve of Frog. experiments of Hermann and Bernstein, and to show that these, although apparently conflicting, are really mutually consistent. First, then, to take Hermann’s experiment, and referring back to figs. 341 and 342, in which the galvanometer is placed in series in the polarisation-circuit, we find this to be an instance in which we have to deal almost exclusively with the effect of anode and kathode on excitability. Simultaneous excitation of the anodic and kathodic points by alternating induction currents, induces greater excitation, and consequent enhanced negativity of A. The responsive 576 COMPARATIVE ELECTRO-PHYSIOLOGY current, being thus concordant with the electrotonic current, causes an increase of it, the so-called polarisation-increment. In Bernstein’s experiment on polarisation-decrement, we are confronted with a question of greater complexity, for here we have to deal with changes of conductivity and excitability at the same time. We shall first take the -case (fig. 339) in which one electrode of the led-off circuit E is under kat-electrotonus. EE’ is therefore relatively anodal, and consequently more excitable. The excitation from the stimulator S which reaches E’ is in this case impeded in reaching E by the fact that it has to travel electrically downhill—that is, from the anodal E’ to kathodal E. Thus, owing to the greater excitation which reaches E’, and owing also to the greater excitability induced in it by the fact that it is relatively anode, excitation induces a relatively greater galvanometric negativity of that point. The thick arrow in the figure indicates the excitatory current, which is opposite in direction to the polarisation current, which latter is indicated by the thin arrow. In the second case, when the polarisation current is reversed (fig. 340), E is anodal, and _ therefore relatively more excitable, and E’ kathodal, and there- fore less excitable. Unlike the last case, the excitation from s, in order to reach FE, has now to travel electrically uphill from the kathodal to the anodal points. The excitation of E therefore is in this case not impeded. Hence greater excit- ability of E makes that point, on stimulation, galvanometrically negative, and the responsive current, represented by a thick arrow, brings about a diminution of the polarisation-current. It has thus been shown, in the course of the present chapter, that the same electrotonic effects are exhibited in the case of the plant, as in that of animal, nerves. It has been shown that various apparently anomalous results may be brought about by simple combinations of two different factors. Thus, the so-called polarisation increment and decrement are not mutually conflicting. They are, on the contrary, due to the distinct and definite effects induced by electrotonus on conductivity and excitability respectively, ELECTROTONUS SGe- As regards conductivity, it has been shown that excitation travels best in the direction electrically uphill—that is to say, from a place of low to one of high electric potential. In consequence of this fact a moderate excitation becomes enhanced when travelling from the kathodic to the anodic region. Conductivity is depressed, on the other hand, from anode to kathode. An excitatory impulse is thus retarded in travelling electrically down-hill. For these reasons, a normal negative excitatory effect may, during transmission, undergo either diminution of intensity, or actual reversal to positive. With reference, again, to electrotonic variations of excita- bility, we have seen that under feeble E.M.F. it is the anode that exalts, and the kathode that depresses. This conclusion. is obviously opposed to the generalisation known as Pfliiger’s Law, the extent of the applicability of which will be discussed in detail in the following chapter. P,P CAP LER INADEQUACY OF PFLUGER’S LAW Reversal of Pfliiger’s Law under high E.M.F.—Similar reversals under feeble E.M.F.—Investigation by responsive sensation—Experiments on _ living wounds—Under moderate E. M.F., intensity of sensation enhanced at kathode, and depressed at anode—Under feeble E.M.F., sensation intensified at anode and depressed at kathode—Application of electrical currents in medical practice. IN studying polar variations of excitability in nerves, in the last chapter, we found that, during the passage of the current, it was the anode which enhanced excitability and the kathode which induced depression. Now this conclusion, as will be remembered, is directly opposed to what is known as Pfliigers Law, the universal applicability of which has hitherto been regarded as beyond dispute. Pfliiger’s Law lays it down that the kathode excites at make, and the anode at break; and that, moreover, during the passage of a constant current, excitability is raised at or near the kathode, and depressed at or near the anode. We are next, then, led to inquire: Under what conditions is this law applicable, and when does it fail to hold good? Now, as regards the effects at make and break, I have shown elsewhere, in the course of experiments on plants, that these are not determined by anode and kathode alone, but also by the intensity of the acting electro-motive force. Thus, in the case of the sensitive Biophytum, in a given experiment it was found that, using the moderately strong E.M.F. of 24 volts, the excitatory wave at make was found to be initiated at kathode, and to travel in both directions, causing depression of nine pairs of leaflets. The forward half of this wave of excitation, stopped only at i i as ET A A _ ' Sn . ————— ST INADEQUACY OF PFLUGER’S LAW 579 one pair of leaflets before the anode. There was no action at the anode itself at make. After a suitable interval, during which the leaflets re-erected themselves, the current was interrupted. There was now no action near the kathode at break; but excitation was induced at the anode, as was shown by the fall of three pairs of leaflets in its vicinity (fig. 358), The experiment was now repeated by reversing the direction of the current. The poles being thus reversed, eight pairs of leaflets fell at the new kathode, in and out. There was no effect, however, at the new anode at make. But at break, excitatory reaction was _ ini- tiated at the anode, and none at the kathode. These are the normal effects, falling under Pfliiger’s Law, which holds good within a certain medium range of E.M.F. But when the E.M.F. is much higher, I find that these normal effects become Fic. 358. Make-kathode and Break- reversed. Thus, employing anode Effects in Bzophytum EMF. of lts-j Upper figure shows effect at make, an i.M.I'. Of 220 volts, it was excitation being produced at found that excitation took kathode. Lower figure shows effect at break, excitation being place at the anode at make, now produced at anode. the excitatory depression of | the leaflets passing slowly thence towards the kathode. At break, excitatory action was initiated at the kathode, the wave of excitation then passing towards the anode. I thus found, by the employment of a very high E.M.F., that the normal polar effects were completely reversed. Intermediate between these two extremes of normal and reversed action, I obtained a transitional phase, in which both anode and kathode were seen to excite at make. At break also there was here occasional excitation, at either anode or kathode. Similar reversals and transitional effects have also been noticed, in the case of certain protozoa by Kiihne and Verworn. Thus Pelomyxa is excited by the anode at make, PP2 580 COMPARATIVE ELECTRO-PHYSIOLOGY and by the kathode at break. Actinospherium, again, shows excitation on make, at both anode and kathode, and on break at the kathode only. Having thus demonstrated the fact that an excessively strong E.M.F. induces a reversal of the normal polar effects, it may not appear improbable that there should be a similar reversal of these effects when the intensity of E.M.F. is varied in the opposite direction, that is to say, when it is | very weak. I have already drawn attention, in many places, to the importance of this factor of intensity in determining the excitatory effect of a stimulating agent. A chemical reagent, for instance, when administered in moderate or very dilute doses, will induce one effect, say that of exaltation, and, in greater quantities, the very opposite, or depression. A poisonous reagent, again, which usually induces depression, will, if given in sufficiently minute quantities, have the effect of exaltation. These reversals, under varying intensities of the external agent, are noticeable again in different physico- chemical phenomena. Thus it is well known that in the formation of the photographic image, while a moderate _ intensity of light gives us the normal ‘negative,’ a stronger intensity will produce a ‘ positive,’ and a still more intense light, bring about a re-reversal. We may thus have a series of recurrent reversals. - Returning, then, to the question of polar action on excitability, we find that the typical results of Pfliiger with nerve and muscle preparations, were obtained when using a moderately strong E.M.F. In this, which is sometimes distinguished as the third stage, excitatory contraction of the muscle is induced, only on the closure of the descending current, or opening of the ascending. In the former case, the kathode is nearest the muscle, and as there is no inter- mediate block the excitation is clearly due to the make-action of the kathode. In the second case, similarly, the break of the anode, which is now near the muscle, causes excitation. With very weak E.M.F., however—that is to say, in his first stage—Pfliiger found that excitation took place by the make INADEQUACY OF PFLUGER’S LAW 581 of both ascending and descending currents, but not at the break of either. Extending the clear inference of the previous case to cover this, it was supposed that here, too, the kathode—at one time near to, and at another far from, the responding muscle—excited at make. But this is not so conclusive, since the anode might equally well be regarded here as causing the excitation at make. Indeed this supposition that a very weak anode might cause excitation at make derives some support from Heidenhain’s experi- ments. For, using a weak E.M.F., he found make-excitation to occur in the first stage only, when the current was ascending—that is to say, when the anode was near the responding muscle. This result would tend to show that there was a possibility of the reversal of normal polar effects when thé acting E.M.F. was weak. With regard to this particular effect of minimal currents, there are considerable differences of opinion. The obtaining of such an effect is probably only possible when the nerve-muscle preparation is in an exceptionally favourable condition of excitability, a state of things not always possible to secure in the isolated specimen. It therefore occurred to me that the effect of a feeble anode in enhancing excitability might be demon- strated conclusively in the case of the vigorous intact animal. With this consideration in view, I carried out a number of experiments on certain of my students and myself. If we make a slight wound, say one square cm. in area, on the back of the hand, and apply a solution of salt, which is not too strong, a constant sensation is induced which cannot be called painful, but may best be described as smarting or irritating. If now we apply one non-polarisable electrode on this wound, and the other on a distant and indifferent point, then, on applying an E.M.F. to the circuit, charac- teristic variations of sensation will be induced, depending on whether the wound-spot is made anode or kathode (fig. 359). Employing an E.M.F. of 2 volts, it will be found that when the spot is made kathode, the sensation, which was previously one of mere general irritation, becomes 582 COMPARATIVE ELECTRO-PHYSIOLOGY intensely painful. This is because the kathode, at make and during its continuation, induces an enhancement of the excit- ability of the wound-spot. On the cessation of the current, the painful sensation disappears, and the normal smarting is restored. The wound-spot was next made anode, with Fic. 359. Effect of Anode and Kathode on ROSES Sensation in Human Hand By means of reversing key, R, E in connection with the esha: -spot may be made anode, and E' kathode, and wice versa. By alternately pressing the keys, K’ and kK, feeble or moderately strong E.M.F. may be em- ployed. the same E.M.F. as before. The sensation now experienced was one of soothing, the sense of smarting irritation having disappeared. On the stoppage of this current the original irritation was again restored. In these experiments we have typical instances of the kathode inducing increase of excitability, and the anode INADEQUACY OF PFLUGER’S LAW 583. depressing it, during the continuation of the current, a verification, by means of responsive sensations, of Pfliiger’s Law. Having thus, with moderate E.M.F. obtained the excitatory effect at kathode, and depressing effect at the anode, by means of the contrasted sensations of intense irritation and soothing, I was next desirous of seeing whether, with low E.M.F., these effects would be reversed. I therefore undertook investigations on a dozen different individuals, to determine the effect of anode and kathode, as the E.M.F. was gradually increased from *3 to 2 volts. It should be mentioned here that the subjects of the experiments were totally ignorant of the object of the investigations, and were simply asked to describe their sensations at different points. Their ages varied from eighteen to twenty-five. As the critical point may undergo some variation with the season, it may be worth while also to mention that the experiments were carried out in summer, in the month of August. The following case may be taken as typical : PoLAR EFFECTS OF E.M.F. oF VARIOUS INTENSITIES ON RESPONSIVE SENSATION Acting E.M.F. | Effect on wound-spot when kathode Effect on wound-spot when anode *3 volt Slightly soothing Marked increase of irritation So _ Slightly soothing Marked increase of irritation os eee Increase of irritation Indifferent ES 155 Increase of irritation Slightly soothing 2°0 volts Painful Soothing It will thus be seen that the kathode, which, at the moderately intense E.M.F. of 2 volts, induced a painful sensation, owing to the increase of excitability, induced the very opposite effect of depressing excitability at the low E.M.F. of -3 volt. Precisely the reverse, moreover, was the case with the anode. Here, with ‘3 volt, excitability was found to be enhanced, causing increase of irritation, while, with the moderately strong E.M.F. of 2 volts, it induced the opposite effect of soothing, by depression of excitability. 584 COMPARATIVE ELECTRO-PHYSIOLOGY The critical point of reversal would in this instance appear to be slightly below 1 volt, in the case of the kathode, while in that of the anode, it was at 1 volt, or slightly above. The effect observed at the extreme points were the same in all cases. Individual differences were concerned only with the exact point of reversal. Thus the point of reversal for the kathode varied in different cases between ‘6 and 1 volt; whereas with the anode it varied from 1 to 1°5 volt. Ina. subsequent chapter, this phenomenon of reversal of sensation under varying intensities of E.M.F., when other forms ot stimulus are applied, will be studied in more detail. It may be stated here, however, that though the critical point of reversal varies to some extent with different individuals, and under different forms of stimulation, yet the law holds good that the excitatory effects induced by moderate E.M.F. are exactly reversed under feeble. The main results regarding this opposition of the effects of feeble and strong E.M.F. may be still better demonstrated by the method of successive contrasts. In the last experi- ments, a long course of observations on the same individual, would be liable to fatigue the tissue. Moreover, the fine gradation of the changes induced is not calculated to exhibit the contrasts involved in their full intensity. Having, then, determined, from the previous experiments, that an E.M.F. of ‘5 volt and another of 2 volts were opposed in their excitatory effects, I now made special arrangements for applying these two intensities of E.M.F. alternately. For this purpose, I arranged a potentiometer which gave an E.M.F. of 2 volts between L and N (fig. 359), and of ‘5 volt between Land M. The end, L, was connected with the wound-spot by means of a non-polarisable electrode. A distant indifferent point, say on the surface of the finger, was connected with a double key KK’. When kK’ was pressed, ‘5 volt was applied, and when K, 2 volts. Further, by means of a reversing-key, P, the wound-spot could be made either anode or kathode at will. In this way, first making the wound-spot anode, I applied alternately the INADEQUACY OF PFLUGER’S LAW 585 __ E.M.F. of ‘5 and of 2 volts respectively. The lower voltage now gave rise to intense excitatory pain. On the cessation of the current the normal smarting sensation, due to salt, was restored, and on now applying 2 volts, this slight irritation was superseded by a sensation of soothing. This result was found to be repeated many different times. The kathodic effect was next put to the test, and found to induce responsive sensations exactly the reverse. The application of *5 volt caused a soothing sensation, due to depression of excitability. An E.M.F. of 2 volts, on the other hand, induced an increase of excitability, with con- sequent pain. | These results are shown in the following table : METHOD OF SUCCESSIVE CONTRASTS TO SHOW REVERSAL OF SENSATION UNDER POLAR CURRENTS Wound-spot anode Wound-spot kathode E.M.F. ‘5 volt _ E.M.F. 2 volts E.M.F. of ‘5 volt E.M.F. of 2 volt Intense pain Soothing Soothing Painful From these experiments, then, it will be seen that during the passage of the current, and when the E.M.F. is low, it is the anode which increases the excitability, and the kathode which depresses. Pfliiger’s Law is thus seen not to be universally applicable, but to be true only within certain limits, the very reverse of this law holding good, in the case of excessively high, and in that of low E.M.F. The demonstration which has just been given of the latter of these two facts, is independently borne out by the results of electrotonic variations of excitability in nerves, described in the last chapter, where we saw that, with moderately feeble E.M.F., excitability was enhanced by the anode and depressed by the kathode. It will thus be seen that polar variations ot excitability are not always the same, but differ in character, according as the intensity of the acting E.M.F. is moderate or low. The great significance of this fact is apparent, with regard to the 586 COMPARATIVE ELECTRO-PHYSIOLOGY medical application of electricity, since the failure to recog- nise that reversal of effects which is to be expected under a feeble E.M.F. might here lead to a result the very opposite of that intended. It has thus been shown that Pfliiger’s Law of the Polar Variation of Excitability is not universally applicable. It fails when the E.M.F. is either too high or too low, the effects observed under these circumstances being precisely. the opposite of those enunciated by Pfliiger. Under a low E.M.F. then, it is the anode which enhances the excitability, depression being induced by the kathode. This important fact, and the further fact that with low E.M F. conductivity is increased in the direction of the rising electrical potential, and depressed in that of the falling potential, will be found to explain all the varied electrotonic phenomena of nerves described in the previous chapter. SD ADM) 5 nent Bek eee » one A ae min em meee om mn = Aan «et i, A , - ” Aron rn te — pa a ae RA oes See ret YAR 0884 = \ i oe hl ar. ee aaa ae ore mete Me > cia. ae —— a Sree Syst? nah Wea SIL F wg & - CHAPTER XLI THE MOLECULAR THEORY OF EXCITATION AND ITS TRANSMISSION Two opposite responsive manifestations, negative and positive—Such opposite re- sponses induced by polar effects of currents of different signs—Arbitrary nature of term ‘excitatory ’—Pro-excitatory and anti-excitatory agents—Molecular distortion under magnetisation in magnetic substances—Different forms of re- sponse under magnetic stimulation—Mechanical, magneto-metric, and electro- motive responses— Uniform magnetic responses—Response exhibiting periodic groupings—Ineffective stimulus made effective by repetition—Response by resistivity-variation—Molecular model—Response of inorganic substance to electric radiation—Effect of rise of temperature in hastening period of re- covery and diminishing amplitude of response—Sign of response reversed under feeble stimulation—Conduction of magnetic excitation—The Magnetic Con- - ductivity Balance—Effect of A-tonus and K-tonus, on excitability and con- ductivity— Conducting path fashioned by stimulus—Transmission of excitation temporarily blocked in iron wire, as in conducting nerve—Artificial nerve- and-muscle preparation, IT is admitted that the excitation of living tissues is brought about by some kind of molecular disturbance, and that the passage of this molecular disturbance from point to point zs the transmission of excitation. As we do not possess the power of molecular vision we have perforce to be contented with the vagueness of the ideas which these terms connote, complicated as they are by the concomitance of other apparently mysterious properties of living tissues. If re- sponse and its variations, however, be in truth mainly de- pendent on the molecular condition of the tissue and its upset, then, from molecular considerations alone, it must be possible to explain why, under certain conditions, the responding substance is increased in excitability, and under others depressed. It has hitherto been found impossible to determine what is the nature of the antecedent molecular 588 COMPARATIVE ELECTRO-PHYSIOLOGY conditions to which these differences may be due: what it is that so determines the Zone, that the excitability of a tissue is made to undergo a profound change during the action of a particular stimulus or on its cessation; and what finally causes the fact that one identical stimulus, say that of tetanising shocks, will sometimes act to exalt, and at others to depress, the excitability of the same tissue. It is the caprice which has seemed to preside over these phenomena. that has forced observers upon the postulation of a hyper- physical ‘vital force. In the course of the present work, however, it has been shown that not only the simple pheno- mena of response, but all their complex variations also, are to be met with in the inorganic as in living matter, and that their explanation, therefore, must be sought for in the nature of antecedent molecular changes. As in the inorganic, the conditions of investigation are less complex than in living tissues, it follows that the study of molecular transformations and their after-effects there, is likely to throw much light upon that phenomenon of response which we have thus seen to be universal. | Taking first the response of living tissues, we find that the responsive change is of two kinds. This may be illus- trated by the following experiment, carried out on the pulvinus of Erythrina indica during the season of its greatest sensitiveness. The stimulus employed was that of a con- stant electrical current. When the upper half of the pul- vinus was made anode, response was found to take place by local expansion. This is seen in the up-record of figure 360. On the break of the anode, we observe a movement of recovery in the opposite direction. The pulvinus was next subjected to kathode-make, and we observe a_ responsive contraction. At kathode-break, however, we have a recovery by expansion. We have thus observed two opposite re- sponsive effects, according to the different polarities of the stimulating agent—namely, expansion at the make of anode, and contraction at that of kathode. Since responsive effects must be due to molecular upset, THE MOLECULAR THEORY OF EXCITATION 589 or to new conditions of alignment, it is clear that contraction must be brought about by a one-directioned, and expansion by the opposite-directioned, change. This is evident in the present case, since the polar stimulating agents are opposite in their characters, and the opposition of their effects must correspond to this. Now it is necessary to distinguish these two responsive effects by opposite terms, which must needs be somewhat arbitrary. The contractile effect has thus been taken as the normal excitatory and negative. Having once adopted such a nomencla- ture, it is of course im- portant that it should be strictly adhered to. Thus, if contraction be the nor- mal response, then any- thing which tends to Up-curve represents expansion and con- vexity. Down-curve represents con- traction and concavity. Continuous curve represents the action at make. Fic. 360. Polar Effects of Currents due to Localised Application on Upper Half of Pulvinus of Zryihrina indica enhance it must be re- garded as excitatory, and anything which opposes or retards it as depressing. The dotted curve shows the effect at break. Am = convexity induced at anode-make. Ad = responsive con- cavity at anode-break. Km =induced concavity at kathode-make. Ké = expansion induced at kathode-break. The time-marks represent minutes. This word ‘depressing’ is, however, unfortunate, since by it might be indicated a permanent depreciation of the tissue, while diminution of the normal response is possible without such depreciation. Moderate rise of temperature, for example, with its expansive tendency, will lessen the contractile response without necessarily depreciating the tissue (p. 187). Revert- ing once more to the kathodic mode of stimulation, we know that a certain intensity of kathode is necessary, for the visible initiation of contractile response.’ Should the intensity employed be just short of this, there will be an 1 These kathodic and anodic effects refer to the normal moderate range of E.M.F, within which Pfliiger’s Law is applicable. 590 COMPARATIVE ELECTRO-PHYSIOLOGY incipient molecular distortion, in the same direction as that which precipitates the excitatory response, hence kat-electro- tonus should prove to be excitatory. But a moderate anode, with its incipient molecular distortion in the opposite direction, will retard the normal response, and thus appear to be depressory. I must here point out that these terms excitatory and depressing have ordinarily speaking no ab- solute meaning, and can only acquire a definite significance when we have first fixed on that form of response which is to be regarded as normal. If, instead of contraction, we had regarded expansion as the normal response, then the effect of anode would have been regarded as excitatory, and that of kathode as depressing. We must therefore recognise that the very fact of contractile response being taken as excita- tory, entails as a consequence the designation of all agencies, such as K-tonus, which predispose the tissue to contraction, -as excitatory, or better pro-excitatory, while those which, like an-electrotonus, oppose this, must be regarded as depressory, or better anti-excitatory. From what has been said, it will be understood that it is the direction of the molecular derangement which determines ‘the character of the response. That molecular upset, which expresses itself as excitatory contraction, we may call the K-effect, and the reversed molecular movement, expressed as expansion, the A-effect. ‘Thus, under anode, in fig. 360, the molecular distortion in one direction induces the expan- sive A-effect. On the cessation of this, the rebound of recovery causes a movement in the opposite direction, which may carry the molecules back, not merely as far as the equilibrium position, but beyond this. This movement, however, is in the same direction as that induced by K-make. Hence we may understand how excitation is caused, not only by K-make, but also by strong A-break. We may also understand how it is that the excitatory effect is much enhanced when A-break is immediately followed by K-make. We also see, in a general way, that a particular-directioned molecular movement would have the most intense excitatory Ss RO —— I enaataetiiar otal Se al ea THE MOLECULAR THEORY OF EXCITATION 591 value when the molecular distortion was proceeding at a rapid rate, and not so much when a condition of permanent distortion had been attained. It is for this reason that, usually speaking, the excitatory effect is most pronounced at either kathode-made or anode-break,! and not so much during the continuation of kathodic action. To recapitulate some of the principal facts enumerated above, the term ‘excitatory’ being applied to a particular- directioned distortion or K-effect, then anything which induces an incipient molecular distortion in the same direc- tion, tending to aid the K-effect, and therefore to enhance that response, will be known as K-tonus. Anything, on the other hand, which induces an incipient distortion in the opposite direction, will oppose or retard the normal K-effect, and will, therefore, be known as inducing A-tonus. In the examples given, the opposite K- or A-effects - observed were the outward manifestations of the aggregate molecular effects induced. And from these we inferred the opposite-directioned changes which must have been their antecedent cause. In working with inorganic substances, however, and particularly in dealing with magnetic bodies, our power of molecular scrutiny is much keener. A rod of iron, for example, is known to consist of magnetic particles, each one of which is-a true magnet, possessed of polar properties. Under ordinary circumstances these magnetic molecules are in close chains, but under the action of magnetising forces they become distorted in a directive manner. Under north-magnetising force they are distorted in one direction, and under south polar induction in the reverse. The intensity of the induced magnetisation is a measure of the degree of molecular distortion, and can be gauged by the deflection of the freely suspended needle of a magnetometer in the neighbourhood. Increasing magnetising force is thus seen to induce greater magnetometric deflections, ! It is conceivable that there should be occasions in which the final condition of distortion is not attained quickly, but slowly ; or where it is Huctuating instead of stable. Under such circumstances the excitation induced would be more or less persistent or tetanic. 592 COMPARATIVE ELECTRO-PHYSIOLOGY and on the cessation of the inducing force there is usually a molecular recovery, with a concomitant return of the magneto- metric indicator to its original position. Here, then, we have a means of recording the molecular distortions induced in a substance under a given external force. We are able also to study the relation between the acting force and the distortion induced, while it is increased or diminished in a known manner. And further, keeping the acting force the same, we are here able to study the effects of various modifying agents on the response, as recorded by the magnetometer, In all these cases, then, we have a strict parallel to the excitatory molecular changes and their variations induced in a living tissue under stimulus. But besides this local action we have also, in the living tissue, nerves possessing the property of transmitting the state of excitation—that is to say, the molecular disturbance—to a distance ; and this trans- mission is modified appropriately by the various modifica- tions which may be induced in the conducting nerve. Simi- larly I shall be able to show that, in an iron wire, excitatory magnetic disturbance is propagated to a distance; this con- duction likewise being modifiable by the molecular changes induced in the conducting wire. Thus, in those particular cases where molecular scrutiny is possible, we are enabled to visualise with considerable accuracy those molecular events on which excitation and its transmission depend. Afterwards, discarding this illustrative class of magnetic substances, I shall refer to other methods, by which the responsive manifestations of ordinary substances under stimulus, and the modifications of these responses under various conditions, will be recorded. From so compre- hensive a study we shall find that whatever be the mode ot record, and whatever the experimental substance employed, the fundamental reaction, and its variations under particular conditions, are curiously similar. It will then be realised that the response of living tissues is not alone of its own kind, but falls under a wide generalisation, THE MOLECULAR THEORY OF EXCITATION 593 But before proceeding further with the magnetic responses, we must call to mind two different responsive manifestations of living tissues. We have observed these under the polar action of electric currents, one being the K- and the other the A-effect. Similarly in magnetic substances also, under the action of the magnetising forces, we observe two different effects brought about by opposite polar changes. One of these is the result of north and the other of south polar in- duction ; and of these, for the sake of convenience, we shall fix our attention on the effect induced by the north pole as the normal negative or K-effect. The fundamental molecular change induced may here, as in the case of living tissues, be recorded in various ways. In the present case, of the response of magnetic substances under magnetic stimulation, the methods of record may be classified as mechanical, magnetometric, and electro-motive. Joule discovered that a rod of soft iron undergoes a change of length on magnetisation. Though this variation is very small, I find it comparatively easy to demonstrate and record the responsive change concerned by means of the following device. One end of the iron rod is fixed, and the free end, carrying a wooden disc, rests on a tambour covered with stretched indiarubber. The tambour chamber is closed except at the point where a capillary tubing of glass enters it. This tube contains a short index. On now suddenly inducing magnetisation by a magnetising coil, the rod under- goes instantaneous elongation, and the resulting expulsion of air from the tambour causes a corresponding movement of the index outwards. Cessation of the magnetising current is attended by immediate recovery. It need only be men- tioned here that by making the diameter of the tambour sufficiently large, and that of the capillary tube sufficiently small, and by optically magnifying the movement of the index, it is easy to obtain for this mode of experiment a very high degree of sensitiveness. 5 It is much easier, however, to record responsive molecular changes by the usual magnetometric, or by the induction or QQ 594. COMPARATIVE ELECTRO-PHYSIOLOGY electro-motive method. According to the former of these, the magnetising coil, C, is placed broadside on, in reference Fic. 361. Experimental Arrangement for Magnetometric Method of Record Fic. 362. Photographic M, magnetometer ; C, magnetising coil ; Record of Uniform B, balancing coil; A, ammeter; -R, Magnetic Responses rheostat ; K, key actuated by metro- , of Iron nome. to a freely suspended magnetic needle with its attached mirror (fig. 361). Fic. 363. Photographic Record of Periodic Groupings in Mag- netic Responses A second balancing coil, B, is placed on the other side, and so adjusted as to nullify any disturbance of the needle by the magnetising coil. The experi- mental rod of iron is then introduced inside C, and the responsive molecular action induced by the exciting current is recorded in the usual manner by the deflected spot of light from the mag- netometer, M, thrown on a revolving drum. The intensity of the exciting current, measured by the ammeter, 4, is capable of adjustment by means of the rheostat, R. The duration of appli- cation of the exciting current is deter- mined by a metronome, and thus kept uniform in successive experiments. In fig. 362 is seen a series of records obtained in this manner, employing stimulation of moderate intensity. In fig. 363 is seen a curious instance of periodic groupings THE MOLECULAR THEORY OF EXCITATION 595 in magnetic responses, similar to those obtained in living tissues. In the next figure (fig. 364) is shown the effect of strong stimulation, which gives rise to responses, not only of greater amplitude, but also of prolonged recovery. Under the strong stimulation here employed, owing to persistent molecular strain, the recovery did not become complete. This is analogous to the contracture in strongly excited -muscle. Such persistent strain may be removed by miole- cular vibration, the hastened recovery in the present record 4 being the result of a tap. Magnetic stimuli, individually ineffective, become effective by repetition. In fig, 365 is Fic. 364. Photographic Record or Response and Recovery of Steel under Moderate and Strong Mag- netic Stimulus First pair of records show response and recovery under moderate stimulus. FIG. 365. spare sie ay Record In the next two, stronger stimulus sabes: neffective Stimulus induces response of greater ampli- made Effective by Repetition tude and incomplete recovery. Molecular vibration by tap, at point marked by down-arrow |, hastens recovery. Asingle brief magnetic stimulation induced little or no effect, but when rapidly repeated thirty times it became effective. seen a record of this. Tetanisation also induces the maxi- mum effect of fusion—as will be seen in the following chapter. Tetanisation, again, induces interesting after-effects in mag- netic responses, precisely the same as those seen in living tissues. Under certain conditions, moreover, to be fully described later, tetanisation, as we shall see, enhances the subsequent responses, while under. other conditions, by in- ducing fatigue, it brings about their depression. I have already mentioned the fact that in addition to QQ2 596 . COMPARATIVE ELECTRO-PHYSIOLOGY the mechanical and magnetometric methods of studying response in magnetic substances, there is also a third .means available, in the Induction or Electro-motive Method, to be fully described at the end of the present chapter. I have now explained how the extent of molecular distortion induced in a magnetic substance by an external force can be gauged or measured by magnetometric or electric indications. For the detection of similar changes, however, in matter which is not pronouncedly magnetic, it is necessary to devise a method of record of more universal application. Such a method we have, as already said, in the record by resistivity-variation. It is here desirable, however, to give. a more detailed account of this and the principle involved. | | Our object being the detection of the molecular changes induced by stimulus, let us briefly consider certain well- known cases of molecular transformation induced by various stimulating agencies. Thus, when sulphur is subjected for a certain length of time to the action: of light, there is no visible sign of any change. Its solubility in carbon disulphide, however, has been altered, and we can dis- criminate-the portions acted upon from those unacted, by means of this ‘developing’ solution. But such discrimina- tion is only possible when the molecular or allotropic modification has gone so far as to be somewhat stable—that is to say, when the after-effect of stimulus is persistent. The development of any after-effect would have been impossible had the substance in the meanwhile exhibited self-recovery. Between the original condition A, again, and the terminal modification D, the substance must have passed through many gradations of condition, of a more or less impermanent stability. This case is analogous to that of a piece of iron under the action of magnetising forces, with their consequent molecular modifications. When the acting force is moderate, and the specimen has the power of self- recovery, the induced molecular distortion—that is to say, the induced ‘magnetisation—is fugitive, and there is no after- THE MOLECULAR THEORY OF EXCITATION 597 effect on the cessation of the force. But, under intense magnetisation, the molecular transformation is more or less persistent, and we observe an after-effect in the induced permanent magnetisation. To revert here to the illustration of sulphur, it is only because the persistent terminal change is the most easily distinguishable that we single it out for the name of ‘allotropic change. As a matter of fact we see that this is but the climax of a series of changes, and so incomplete a view has been made current by the fact that we had no means of recording the intermediate changes while they were in progress. The next question is as to the possibility of making such records of molecular transformations, or of induced varia- tions in the state of molecular aggregation, while they are taking place. This may be accomplished, as I shall show, by the concomitant variation of electrical conductivity. It is to be borne in mind that the state of molecular aggrega- - tion plays an important part in determining the conductivity of a substance, and as an example we may take the case of carbon, which exhibits wide differences of conductivity in its two allotropic conditions of graphite and diamond. Let us imagine a piece of carbon in an intermediate or neutral state between these two. We-may suppose that an external force distorts it to a small extent towards the more con- ducting state of graphite. This distortion would be attended by an increase of conductivity, from which latter the extent of molecular distortion or upset involved might be inferred. Now, during the distortion from the equilibrium position, a force of restitution will tend to restore the carbon to its original neutral condition. If the’ distortion does not proceed beyond the elastic limit, then, on the cessation of the external stimulus, it will recover its original state, and this will be evidenced by the restoration of its original con- ductivity. But if the distortion be of a sub-permanent or permanent type, the recovery will be very much protracted, or will not take place at all. Such more or less permanent distortion, known as allotropic transformation due to stimulus 598 COMPARATIVE ELECTRO-PHYSIOLOGY of light, is seen in the production of red phosphorus from the yellow variety, and the insoluble from the soluble variety of sulphur. It will thus be seen that the conductive aspect of a given substance is not definite, but variable, the conductivity being dependent on the particular molecular condition of the sub- stance. This peculiarity may be represented in the accom- panying model (fig. 366), if we give the cylinder representing the sensitive molecule three main-conducting aspects A B C. The non-conducting aspect is represented by c. With the sensitive substance in this particular condition, inter- posed in the electric circuit, the current in the galvano- meter would be zero. A is the semi-conducting aspect of the substance, under which we may imagine the corresponding deflection of the galvanometer to be 50. B is the highly conducting aspect, the corresponding galvanometer reading being 100. Fic. 366. Molecular Model The model representing the sensitive substance has its surface divided into six parts, the opposite sextants being put in electric communication. The opposite sextants CC are coated with shellac to represent the non-conducting aspect ; the sextants AA are coated with graphite to repre- sent the semi-conducting aspect; and the highly conducting aspect is represented by the sextants BB coated with tinfoil. The three main aspects of the sensitive substance are thus represented in the model; it is to be understood that with sensitive substances, under the action of stimulus, the transi- tion from one aspect to the next is gradual, and not abrupt, as represented. ‘The sensitive substance is interposed between THE MOLECULAR THEORY OF EXCITATION 599 — two electrodes. The torsion of the wire by which the cylinder is suspended represents the force of restitution. The galvanometer coil, by its deflections, exhibits indirectly the molecular strain produced in the substance by the action of stimulus. Let us suppose that we start with the substance in its normal state A, with moderate conductivity, and let the corre- sponding galvanometer deflection be 50. Let the substance belong to the negative class which exhibits an increase of conductivity, or diminution of resistance, under the action of stimulus. The stimulus will therefore distort the substance to a state of increased conductivity, the increased conductive aspect BB being brought opposite the electrodes. The enhanced current thus produced causes a deflection of, say, 100 in the galvanometer. If the strain has not been excessive, the substance will return, on the cessation of stimulus, to its original position of equilibrium, and the galvanometer deflection will fall from 100 to the original value 50. If the substance belong to the positive class, the distortion will be in the opposite direction, and the effect of stimulus will be to induce a responsive increase of resistance. The coil of the indicating galvanometer thus moves in perfect response to the varying molecular strain induced in the sensitive substance by the action of stimulus. The invisible molecular distortions are thus revealed by the visible deflections of the galvanometric indicator—the effect on one is merely the reflection of the effect on the other. A curve of the molecular effect, induced by the action of stimulus, may thus be obtained with the galvanometer de- flection as ordinate, and the time as abscissa. It is thus seen that these response-curves faithfully represent the in- visible molecular strain-effect due to the stimulus, and the subsequent recovery. = I shall now describe how in practice, by this method of resistivity variation, we obtain responses of various sub- stances to the stimulus of visible or invisible radiation. The 600 COMPARATIVE EILECTRO-PHYSIOLOGY sensitive substance may be made the fourth arm of the Wheatstone’s bridge, and the responsive galvanometric de- flection and subsequent recovery of the spot of light—by the upsetting of the balance, under the action of stimulus of radiation—is recorded in the usual manner, on a moving photographic plate. Or the sensitive substance may be placed in series with a galvanometer, a small E.M.F. giving a steady permanent deflection. Taking first selenium as the. sensitive substance, the molecular change induced by the action of light, with its concomitant variation of resistance, causes a deflection of the galvanometer spot of light. On the cessation of the stimulus, molecular recovery takes place, and the deflected spot of light returns to its original position. A series of such responses will be found on referring to page 3, fig. 3. The parallel method employed in recording the responsive resistivity varia- tion of masses of metallic par- ticles of various kinds, under the stimulus of electric radia- : tion, will be understood from Fic. 367. Method of Resistivity "8+ 367. On obtaining records Variation of the responses given under Sensitive metallic particles placed in this method, I find, as I pointed tube in series with galvanometer 5 and E.M.F. This gives a steady out in the first chapter, that permanent deflection. Stimulus the responding substances are ‘of electric radiation induces a ; responsive variation of resistance of two different types. The with. concomitant variation of first, of which aluminium may galvanometric deflection. be taken as the example, re- spond by diminution, or negative variation of resistance. The second, illustrated by potassium or arsenic, respond by an in- crease, or positive variation of resistance. In living tissues also, tested by various modes of response, we have seen two opposite types to occur—highly excitable nerve giving one, say, negative, while skin, on the other hand, gave the positive. In the case of the inorganic substances referred to, we have extreme types, whose response is generally either positive or negative. There are, however, intermediate at ane a THE MOLECULAR THEORY OF EXCITATION 601 cases, where it is liable to change of sign according as the stimulus is feeble or strong. Certain substances, again, cannot quickly recover from the after-effect of stimulus ; while, in others, recovery is fairly rapid. Recovery from intense stimulation is generally, other things being equal, more protracted than from feeble or moderate. Anything, however, which enhances molecular freedom or mobility will tend to hasten recovery. I shall now give several typical records in illustration of the peculiarities of this form of response by resistivity variation, under various conditions. The first example Fic. 368. Photographic Record of Response of Aluminium Powder in Sluggish.Condition to Stimulus of Electric-Radiation. . The first two responses exhibit incomplete recovery, which becomes com- plete on application of warmth. Note that warmth, increasing force of recovery, hastens recovery and also diminishes amplitude of response, as seen in the two succeeding records. given, that of aluminium powder, will» be of the negative type, the response being by diminution of resistance. When the substance tested happens to be in a sluggish condition, recovery is very protracted. There is then a _ response- remainder of persistent negative variation, corresponding to the contraction-remainder in muscle, or persistent electro- motive negativity in other living tissues. But we know that a moderate rise of temperature is favourable to recovery ; and on applying gentle heat, at the end of the second response, with its incomplete recovery, the persistent effect is seen to be removed, and -there is an immediate completion of recovery (fig. 368). This is the place to refer once more to an apparent 602 COMPARATIVE ELECTRO-PHYSIOLOGY anomaly, in the response of living tissues, where a slight rise of temperature increases conductivity, at the same time that it appears to diminish excitability, inasmuch as it brings about a lessened amplitude of response (Chapter XV.). This latter, however, may not really be due to diminution of excitability, since the same effect might equally well be brought about by an enhancement of the force of recovery. This view is supported by the further records given in fig. 368. We see here that incomplete recovery became complete, under the application of gentle heat. The next response given by this slightly warmed substance is seen to Fic. 369. Photographic Record Showing Uniform Response of Alu- miniun Powder to Uniform Stimulus of Electric Radiation. show complete recovery within a relatively short time, this enhanced force of recovery bringing about at the same time a diminution in the height of response. The temperature of the substance was now again raised to a slightly higher degree, and the next response shows a still further diminished height and a considerably quickened recovery. When a substance is in a normal condition of excitability, its succes- sive responses to uniform stimuli are found to exhibit com- plete recovery, and to be of equal amplitude. Figure 369 shows such a series obtained with powdered aluminium. We have seen that the increased molecular mobility con- ferred by warming hastens recovery. A similar hastening of recovery may be brought about by a mechanical tap, as has already been shown (fig. 364) in the case of magnetic response. THE MOLECULAR THEORY OF EXCITATION 603 In fig. 370 is seen an example of the same thing in tungsten, where recovery from the effect of electric radiation is hastened by a tap. It has been shown that the normal response by negativity in living tissues is liable to reversal under very feeble stimulation. This is better observed when the tissue is not highly excitable; because in this case it is easy to adjust the intensity of stimulation, so as to fall below the critical value for excitation. It is very interesting to ob- serve similar opposed effects, under feeble and moderately strong stimulations, in the re- sponse of inorganic substances. For the reason just mentioned, it is desirable to select a sub- stance for this purpose, which possesses a moderate degree of sensibility. Using a mass of tungsten particles, I found that under strong intensity of electric radiation—-brought about by placing the radiator within a short distance of the Fic. 370. Photographic Record of Response of Tungsten substance—the response was ; : The incomplete recovery is hastened by the normal negative varia- by application of tap at points, tion, or diminution of resist- marked with downward arrow. Cf. fig. 364. ance. But when the intensity of stimulus was dimfnished by placing the radiator at a greater distance, then the response was converted to positive. A record of this abnormal effect under feeble stimulation will be given later. Thus, having observed molecular response and its varia- tions by the Magnetic and Resistivity Methods of record, we now proceed to study the transmission of the state of excitation. We have seen that the essential condition of the transmission of excitation in living tissues lies in the 604 COMPARATIVE ELECTRO-PHYSIOLOGY propagation of molecular disturbance from point to point. The characteristics of such propagation must be—(1) that the transmitted molecular disturbance becomes enfeebled with distance, so that at a certain point the transmitted excitation would be reduced to zero; (2) that while a moderate stimulus is transmitted to a short distance, a stronger stimulus would be carried further ; and (3) that the intensity of excitation transmitted would depend on the conducting power of the intervening tract, this conductivity being capable of enhancement by certain agencies, and depressible by others. I shall now proceed to show that in an iron wire a transmission of molecular disturbance takes place which is Fic. 371. Experimental Arrangement for obtaining Response in Iron by Induction Current similar to that at the basis of the transmission of excitatory changes, both, as I shall show, being modifiable by similar circumstances in a similar manner. For these investigations I have employed the Induction or Electro-motive Method of observation. In the experimental arrangement—a diagram- matic representation of which is shown in fig. 371—S is the stimulating or exciting coil appliéd at the point to be excited. The conducting region intervenes between S and R, which is the responding point, over which is wound the receiving coil, placed in series with either a telephone or a galvanometer. When the excitatory molecular disturbance reaches R, it gives rise to an induction current in the coil, which in turn causes a sound in the telephone, or a responsive deflection in the galvanometer. For the purpose of simplicity, we shall take north polar or K-excitation as THE MOLECULAR THEORY OF EXCITATION 605 normal, and the resulting deflection of the galvanometer to the right as the normal response. ~The direct effect of the coil S on the coil R may be regarded as negligible, when they are separated from each other by a sufficient distance, and this would be even more true if the intervening iron wire were bent at an angle of 90 degrees. Employing this mode of obtaining records of response to K- or.A-excitation, we meet with several curious analogies to the responsive effects seen in living tissues, under the electrical mode of stimulation. Electrical excitation of nerve and muscle, for example, is most effective when it is longitudinal, and ineffective when transverse. The same is true of magnetic excitation of iron, where longitudinal excitation is effectively transmitted to a great distance, whereas transverse excitation is relatively ineffective. Again, in the case of the electrical excitation of living tissues, it is at the instant of kathode-make, as we have seen, that excitation is induced. Continued action exhibits in general no effect. The same normal excitatory effect seen at kathode-make, is induced again, but at anode-break. Similarly, in the case of an iron wire, the normal galvano- metric response is seen at the moment of K-magnetic excitation, but not during its continuance. The same excitation is also obtained, at break of A, or south polar magnetisation. . We are led from such close analogies, not only to visualise, but also to obtain some insight into the sequence of molecular events which is the concomitant of excitation. I have already pointed out that excitation and its opposite, depression, being phenomena of molecular. distortion, it is to be expected that a particular-directioned distortional movement should be associated with one of these, and the opposite with the other. We also know the further suggestive fact that it is the sudden change of the environ- ment, inducing a sudden responsive molecular disturbance, that is most effective in bringing about excitation. The latent period, and a slowly-rising excitation, correspond to the 606 COMPARATIVE ELECTRO-PHYSIOLOGY slow initiation of the molecular upset. After this the rate of molecular distortion will be rapid, and in this second period we find that the excitatory reaction also is at its maximum. In any case, it is rather during the period of increasing molecular distortion that we should expect to see the most intense excitation, than when a static condition of derangement has been attained. Thus it is at the moment of K-make that we obtain the excitatory indication, and not afterwards, when the molecules are being maintained in the distorted position. , Returning once more to the iron wire, we find that when the distorted molecules have been set free by the break of kK, there is a sudden movement of recovery in the opposite direction. If now the K-effect, with its particular-directioned molecular movement, be termed the excitatory, then the oppo- site movement must be regarded as one of depression, and it is interesting to note that in a living tissue there is an after- effect of depression at kathode-break. The anode-make, on the other hand, with its opposite molecular distortion, is, as ' one would expect, depressory. But at the break, the direction of the rebound of the released molecules being the same as that brought about by K-make, must be excitatory. The close parallelism which we have thus traced out, forces upon us the conclusion that the molecular actions which underlie the excitation of living tissues may be-polar in their character. The fact that magnetic excitation undergoes diminution during transmission, can be shown by moving the receiving coil R further and further away from S, when the responsive sound in the telephone, or deflection in the galvanometer, will be found to undergo a graduated diminution, till, with a given stimulus, the effect, from being considerable, is reduced at a certain distance to zz/, Keeping this distance the same, however, a stronger stimulus will be found efficient to evoke response, and the responding coil will now have to be moved further, in order again to reduce the response to zero. We shall next study the variation of conductivity induced -_. = THE MOLECULAR THEORY OF EXCITATION 607 by an external agent, as. modifying the intensity of the transmitted effect. In order to study the phenomenon of conduction and its modification, as will be remembered, a delicate form of Conductivity Balance, fully described in Chapter XX XIII. was used. Excitation was here caused by S at a middle point, the transmitted excitatory effects at E’ and E being made to balance, This condition of balance was obtained when one arm, say the left E’, was kept at a fixed distance from Ss, and the other, or right, was moved towards S, or away from it, as required. When E was too far from S the excitatory effect would be smaller than at E’, and this under-balance would be indicated by a response, say downwards. When, again, E was too near to S, there would be an over-balance, the resultant response being upwards. Between these could be found a point of exact balance where the record was horizontal (cf figs. 289, 290). A high degree of delicacy in the study of: similar phenomena in the case of iron wires may be obtained by Fic. 372. Magnetic Conductivity Balance S, magnetising coil, by which north-polar or K-impulses are sent out in two directions as shown by arrows. E BE’, receiving coils, adjusted at balance. M, permanent magnet, by ,which either A- or K-tonus is induced at the responding ends of the iron rod. T, tonic coil, by which A- or K-tonic molecular dispositions may be induced in one arm of the balance. the employment of the Magnetic Conductivity Balance (fig. 372), which I shall now describe. The magnetic stimulator, S, consists of a pair of similar coils wound in opposite directions, When a magnetising current is suddenly 608 COMPARATIVE ELECTRO-PHYSIOLOGY sent through these two coils, in a proper direction, two equal north-polar impulses will be generated simultaneously, and travel, one to the right, towards E, and the other to the left, towards E’. [n order to obtain a balance of the excitatory effects at E and E’, we keep E’ at a fixed distance, and move E backwards and forwards till the balance is found. This process of balancing will be found graphically illustrated in the records given in fig. 373. E was placed at first too near to S, and the over-balance is seen as up-responses. The coil was then moved away very gradually, and the response of over-balance is seen at each step to undergo a diminution or approach towards balance. We next note the attainment of exact balance, where the record is seen to be horizontal. The coil is now moved still further to the right, and the con- Fic, 373. Process of Balancing illustrated by Photographic Record | of Responses sequent increasing under-balance is exhibited by the gradually increasing reversed down-responses. Having thus obtained balance, we are able to record the variations induced in conductivity by a given agent. This is applied on the right arm of the balance, the subsequent upset of which, in one direction or the other, indicates the enhancement or depression of conductivity. Resulting up- responses will indicate enhancement, and down-responses depression. A well-known agent for the enhancement or depression of the conductivity of the nerve is the polar action of the kathode and anode. Moderate kat-electro- tonus enhances conductivity, whereas the anode depresses or inhibits it. The explanation which I have already offered, regarding anodic and kathodic effects on excitability, will also. be found applicable in the case of conductivity. An excitatory or kathodic effect will be facilitated in trans- THE MOLECULAR THEORY OF EXCITATION 609 mission, if the molecules in its path are already incipiently orientated, so that the incident stimulus finds them pre- disposed to respond in that direction and to transmit the excitation. Hence the kathodic effect is more easily trans- mitted through a tract which is in a state of K-tonus, whereas it is retarded or inhibited under A-tonus. We shall now study the corresponding effect in magnetic conduction. Normal excitation in these experiments, it should be remem- bered, is taken as that which is brought about by the north- polar or K-effect. If there is a tonic coil, T, surrounding one arm of the balance, then, by sending a permanent current of moderate intensity round the coil, in one direction or the other, we may induce at will, in that arm, either K-tonus or A-tonus. The molecular disposition induced by the stimulus, and by K- and A-tonus respectively, will be under- stood from the diagrammatic representation given in fig. 372. Local variation of excitability at E may be induced by bringing near to’it either the north or south pole of a permanent magnet M. I shall now exhibit the enhance- ment or depression of magnetic conductivity by K- or A-tonus. A balanced record is first obtained, Fic, 374. Effect of K- and and K-tonus then induced in the A-Tonus on Magnetic Con- right arm. Successive K-make ex- duction aes . . The first series exhibit by citations are now applied, starting resultant over-balance up- from the centre of the balance at wards the effect of K-tonus ‘ ; -% in enhancing ‘conductivity S, and proceeding onwards to left of right arm, The next and right simultaneously. The — series, with resultant down-responses, show de- resulting responses are recorded, pression by A-tonus. records of the break-effect being avoided by timely interruptions of the galvanometer-circuit. It will be seen (fig. 374) from the upsetting of the balance in an upward direction, that K-tonus has induced enhancement of conductivity in the right arm. On now causing A-tonus, by reversing the current in the enclosing tonic coil, T, a de- ¢ RR 610 COMPARATIVE ELECTRO-PHYSIOLOGY pression of conduction is induced, as shown by the upsetting of the balance in a downward direction. - We next turn to the question of the variation of conduc- tivity induced by K-tonus, when moderate or excessively strong ; and it is here important to forecast from theoretical considerations what is to be expected under varying intensities of the polarising force. It is easy to understand that moderate K-tonus, inducing an incipient orientation of the molecules, will predispose them to easy upset in a particular direction, thus greatly facilitating the transmission of excitation from point to point. Thus a moderate K-tonus will enhance con- ductivity. But if the K-tonus in question be excessive, so that the molecules are already distorted to their maximum position, incident stimulus can then induce no further change, and under such circumstances there can be little transmission. Hence, under increasing intensity of K-tonus, we may expect to obtain increasing conductivity up to a certain point. But, beyond this, the conductivity will be decreased, or even actually inhibited. These anticipations are seen fully verified in the accom- panying record (fig. 375), which shows the opposite effects on conductivity of moderate and strong K-tonus. The upsetting of the balance in an upward direction, K, shows the effect of moderate K-tonus. Strong K-tonus was next applied, with the effect of upsetting the balance in the opposite direction, K’. Thus we see that, while under moderate K-tonus the conductivity is enhanced, under a much greater intensity it becomes depressed. This will, I think, be found to explain a somewhat anomalous occurrence, which has been observed in regard to the conduction of excitation through a kathodic region in nerve-and-muscle preparation. A stimulus applied on the extra-polar region in nerve is Fic. 375. Opposite Effects of kK-Tonus when moderate and strong THE MOLECULAR THEORY OF EXCITATION OI found tobe transmitted through the kathodic area, inducing enhanced response of the indicating muscle, if the polarising current be weak. But when the intensity of the kathode is made stronger, even the strongest stimulus will fail to induce response. This is evidently due to the fact that a strong kathode induces a depression or abolition of conductivity. Moderate K-tonus, then; we have seen to induce enhanced conductivity, because of the favourable molecular disposition which it brings about. Even on the cessation of K-tonus this disposition remains, owing to molecular ‘ retentiveness, with its concomitant enhanced conductivity as an after- effect. This induction of a favourable molecular disposition or habit is an interesting phenomenon, which we shall meet with again. : We shall next study the enhancement or depression of local excitability by K- or A-tonus. We saw, in Chapter XXXIIL, that by means of the Con- ductivity Balance we might determine the variations, not only of conductivity, but also of local excitability. In mag- netic experiments the responsive area at the right-hand end of the balance may be made either K-tonic or A-tonic, by bringing near it one or other pole of a permanent magnet. Under induced A-tonus, the molecular excitability is depressed, and Fic. 376. Effects of K- and the balance upset in a down- A-Tonus on Magnetic Ex- . ‘ ae citability ward direction; while under 4 Ae From the resulting upset of the K-tonus excitability is enhanced, balance, A is seen to induce de- the resulting response being up- FF coun SNR EETER Es wards (fig. 376). A still more interesting case is that in which the stimulus itself fashions,:as it were, the path for its own conduction. The receiving coil is placed at such a distance from s RR2 612 COMPARATIVE ELECTRO-PHYSIOLOGY (fig. 371) that, owing to imperfect conductivity of the inter- vening tract, but little excitation reaches it. Excitation at S, however, distorts the molecules in its immediate neighbour- hood, in a certain direction, incipiently distorting others at a little greater distance in the same favourable way. A second stimulus is therefore transmitted a little further, bringing about the same predisposition still further on, Thus an im- proved conducting-path is made, in a substance formerly but. an indifferent conductor, by the action of the stimulus itself. In this way transmitted excitation, at first relatively ineffec- tive, becomes increasingly effective (fig. 377). It is very interesting to note that I have obtained an effect exactly parallel in the case of nervous tissues. For example, when attempting to obtain the transmitted effect of ex- citation by mechanical response, in a vegetable or animal nerve in de- pressed tonic condition, the first series Fic. 377. Gradual Enhance- Of tetanising shocks would induce no RED oe Caen response. It would sometimes be } only after long repetition that con- ductivity would be gradually restored, as seen in the initiation and subsequent enhancement of responses given at the distant responding-point: - It may be that few phenomena connected with the response of living tissues, bring home to us, so effectively aS an experiment on a nerve-and-muscle preparation, the sense of the specific and mysterious character of the responsive manifestations of the living. The nerve, at its central termination, is locally excited by electric shocks, and some obscure impulse then passes through the long conducting tract to the muscle at the other end. Arriving there, this invisible nervous impulse initiates a new Series of events, which find expression in visible motile indications The work performed at the responding end may be out of all proportion to the strength of the stimulus imparted at the centre. It is as if the nervous impulse tapped a relay, and a AR ee php ee EER Bee ae ee eT ee Ne ae a rine nerf mo In pa ym ae | eau THE MOLECULAR THEORY OF EXCITATION 613 set free a local store of latent energy. The conductor, moreover, is seemingly unlike the conductor in an electrical circuit, where the line wire and return wire must be periodically connected with terminals of an electro-motive source, for any message to be transmitted. In the nerve we have only a single conductor, without a return, an arrangement by which it would appear as difficult to send a message, as it would be to apply the two poles of a battery at the end of a single wire, in the expectation of a signal from the recorder at the far end. Inorganic matter again, is popularly regarded as susceptible only of impulses from the grosser physical forces, while the nerve—the vehicle of psychic impulses—is conceived of as_ played upon by forces of a finer order, ‘and as itself modifiable, by subtler influences, notably that of its own previous history,or memory. There are, as we know, some conditions which induce such changes in the nervous channel itself, that messages from outside, previously scarcely perceptible, are accentuated. Under opposite influences, again, the conduction of impulse is interrupted. Similar results are brought about by certain agents of a polar character, like the action of anode and kathode. Under electrotonic action the transmission of impulses through the nerve may be blocked, conduction being renewed as soon as the electric block is removed. Or electrotonic action, again, may be used for the opposite purpose, of accelerating the trans- mission of impulses. Nothing more convincing than such facts could have been urged in support of the hyper-physical character of the phenomena in question. But the experiments which I have described, relating to the conduction of excitatory molecular changes in a piece of iron wire, show that parallel phenomena occur in the physical domain also; and in order to demonstrate this in a striking manner, I cannot do better than describe an arrangement which I have devised, and which may be taken as an artificial nerve-and-muscle preparation. This consists of a thin iron rod for the transmission of magnetic 614 COMPARATIVE ELECTRO-PHYSIOLOGY = - excitation applied at one end, with a responding arrange- ment, to give motile indications, at the other. This latter consists of a secondary coil, which may be slipped over the responding point, being in series with some sensitive metallic powder in circuit with a galvanic recorder, and a voltaic cell as source of energy. The excitatory molecular dis- turbance transmitted through the conducting iron rod gives rise, on reaching the responding-point, to an_ electrical disturbance in the secondary coil connected with the motile indicator. This electrical disturbance causes secondary excitation of the sensitive substance, in consequence of which the electric conductivity of the particles becomes suddenly enhanced. By this ‘relay’ action the stored-up energy of the cell is suddenly released, with a consequent ‘induction of motile response in the galvanic recorder. It is thus seen that this motile response, initiated by the transmitted stimulus, need not be proportionate to its primary exciting cause, since it may possibly be much en- hanced by the amount of energy set free in the responding circuit itself. This transmission of excitation is liable, moreover, as in nerve, to be modified by subtle molecular changes induced in the conducting tract through which it takes place. Excitation may be arrested in the one case by an electrical block ; and in the other, similarly, we are able to stop the transmission of a message, by means of a magnetic block. It is by no gross physical restraint that the impulse is so arrested, but by invisible molecular distortion within the rod. Molecular freedom is next re- stored by the removal of- the magnetic block, and we find that the message, which, though constantly reiterated, was hitherto inhibited, is suddenly allowed to rush onwards and bring about the signal. ; CHAPTER XLII os MODIFICATION OF RESPONSE UNDER CYCLIC MOLECULAR VARIATION . Anomalies of response—Explicable only from consideration of antecedent molecular changes— Continuous transformation from sub-tonic to hyper-tonic conditions—Two methods of inquiry, first by means of characteristic curves, second by progressive change of response—Abnormal response characteristic generally of A or sub-tonic state—Abnormal transformed into normal, after _ transitional B state—B state characterised by staircase response—Responses at C stage normal and uniform—aAt stages D and E responses undergo diminution and reversal— Responsive peculiarities seen during ascent of curve, repeated in reverse order during descent—All these peculiarities seen not only in living but also in inorganic substances, under different methods of observation— Elucidation of effect of drugs—Response modified by tonic condition and past history. WE have seen that, normally, the phenomenon of response in living tissues is very definite’ There are other con- ditions, however, under which it is found to be modified or even reversed. These abnormal effects may be brought about, either by feeble stimulation, or by changes in the responding tissue itself. Thus, though moderate stimulus evokes normal negative response, a feeble stimulus will often be seen to induce the abnormal positive, and this is most easily observed in certain particular modifications of the tissue associated with sub-tonicity. The fatigue-changes due to excess of stimulation are also, curiously enough, effective in bringing about the same abnormalities of response. It is open to-us to regard these anomalies as the result of obscure vital actions, and therefore incapable of further analysis. Or,since the phenomenon of response itself is admitted to be due to the molecular upset caused by stimulus, their origin may be looked for in the antecedent 616 COMPARATIVE ELECTRO-PHYSIOLOGY molecular condition of the responding substance. There is a school of investigators, again, who, appearing to discard the theory of vital action, in accounting for these changes, have substituted for it the hypothetical anabolic, or up-building, and catabolic, or down-breaking, chemical changes. And such assumptions have certainly the advantage of meeting every emergency, whether it be an expected effect or its direct opposite which occurs, for by their means it is always _ possible to make a reference to the one process or the other, whatever be the inconsistency involved. - As regards the interminable controversy on the physical versus chemical nature of response-phenomena, I have already drawn attention to the fact that on the border-line between Physics and Chemistry it is impossible to make any sharp demarcation. Changes, in themselves undoubtedly molecular or physical, may be attended by concomitant changes of chemical activity. An example will perhaps make this clear. We may take, for instance, the photo- graphic action of light on a sensitive plate. This is re- garded as due to chemical dissociation or break-down. If this were so, however, the effect would be permanent. But, instead of this, the latent image is liable to disappear, and in a Daguerreotype plate the after-effect of light—that is to say, the persistence of the image—has a duration of a few hours only. Such images, moreover, due to the action of light, have been found to form themselves even on elementary and inert chemical substances like gold. Here, any chemical break-down, in the ordinary sense of the word, is out of the question. Stimulus in general we have seen to induce molecular distortion, the persistence of which is dependent on the strength of the stimulus, and also on the power of self- recovery characteristic of the given substance. We have further seen a difference of electrical potential to be induced, as between molecularly strained and unstrained areas. When the substance, therefore, thus differentially acted upon, is placed in a suitable electrolyte, volta-chemical actions are CYCLIC MOLECULAR VARIATION 617 necessarily set up, by which material in one part may be accreted, and in another dissolved. In this way a positive or negative image may be developed. We have also seen, in the responses of living tissues, that while moderate stimulation induces one effect, the same stimulation, long continued, may cause the so-called fatigue- reversal, such reversals sometimes, in fact, becoming recurrent. It is interesting to note that in a similar fashion a photographic plate, subjected to various durations of exposure, will give either negative or reversed positive images, or recurrences of these." : From such facts it is clear that for the elucidation of response and its variations, we must look to its molecular antecedents, and not to its secondary chemical or other consequences. If response phenomena in general, then, are determined by molecular conditions, as such, it follows that in order to unravel the anomalies which occur in - the response of living tissues, we must attempt to ascertain those conditions which induce any given variation of response in matter in general. That these phenomena are not peculiar to the response of living tissues, but take place in all matter under similar circumstances, is a fact which has been often reiterated in the course of previous chapters, and which I first pointed out in the course of my investigations on ‘Response in the Living and Non-Living,’ ? In the work in question, referring to the occurrence of abnormalities in response, I said : ‘Calling a// normal response negative, for the sake of convenience, we observe its gradual modification, correspond- ing to changes in the molecular condition of the substance. Beginning with that case in which molecular modification is extreme, we find a maximum variation of response from the normal, that is to say, to positive. Continued stimulation, however, brings the molecular condition to normal, as * Bose, ‘On Strain Theory of Photographic Action,’. Proc. Roy. Soc. 1902. See Response in the Living and Non-Living (1902), pp. 129, 130. 618 COMPARATIVE -ELECTRO-PHYSIOLOGY evidenced by the progressive lessening of the positive response, culminating in- reversion ‘to the normal negative. This is equally true of nerve and metal. In the next class of phenomena the modification of molecular condition is not so great. It now exhibits itself merely as relative inertness, and the responses, though positive, are feeble. Under continued stimulation, they increasé in the same direction as in the last case—that is to say, from less negative to more negative, this being the reverse of fatigue. This is evidenced alike by the staircase effect and by the increase of response. after tetanisation, seen, not. only in nerve, but also in platinum and tin. The substance may next be in what we call the normal condition. Successive uniform stimuli now evoke uniform and equal negative responses—that is to say, there is no fatigue. But after intense or long-continued stimulation, the substance is overstrained. The responses now undergo a change from -negative to Jess negative: fatigue, that is to say, appears. Again, under very much prolonged stimulation, the response may decline to zero, or even undergo a reversal to positive, a phenomenon which we shall find instanced in-the reversed response of retina, under the long continued stimulus of light. ‘We must, then, recognise that a substance may exist in various molecular conditions, whether due to internal changes or to the action of stimulus. .The responses give us indica- tions of these conditions. A complete cycle of molecular modifications can be traced, from the abnormal positive to the normal negative, and then again to positive, seen in reversal under continuous stimulation.’ ! It is the molecular cycle here referred to, with the con- comitant cyclic variation of response, that forms the subject of the present chapter.. I shall attempt to show that the various anomalies in-the response of living tissues, which were referred to in an earlier passage, may be elucidated ' In the above quotation I have, in accordance -with the convention which I now uniformly oe referred to normal response as negative, and abnormal as positive.—/. C. B _ CYCLIC MOLECULAR:VARIATION — 619 by this consideration. I explained, im the first chapter of the present work, the fact that the molecular derangement of matter under stimulus might be studied by recording any one of several concomitant physical changes. -These are: (a) the change of form—contraction or expansion ; (3) the electro-motive change ; and (c) the variation of electric resistivity. By means of the first of these we investigated the responsive effects induced by stimulus in animal and vegetable tissues, and in the inorganic substance indiarubber. By the second, that of electro-motive variation, the excitatory change and its variations were studied in living tissues, animal and vegetable, and in inorganic bodies like metal wires. And, lastly, by variation of resistivity, we have obtained records of excitatory changes in living tissues, as also in masses consisting of metallic particles. In the last chapter, moreover, I have shown that the molecular responses of a magnetic substance may be recorded by means of appropriate magnetometric or galvanometric methods. I shall now take up the question of the nature of those obscure molecular modifications which the response of a substance is found to undergo, and in consequence of which it exhibits variations either of intensity or of sign. The only conceivable reason for such changes would lie in some unknown transformation of the antecedent molecular con- dition. This being so, the next question is, whether we could possibly discover what these transformations are. The properties of a substance at any given moment, we must remember, are not determined solely by the nature of that substance, but also by the energy which it possesses. It is obvious, for instance, that the responsive properties of matter, when its energy is depleted or its condition-is a-tonic, will be different from those of matter in a higher tonic-con- dition, and that there will be many gradations intermediate between the two. Thus, as a substance is gradually trans- formed, from a state of depletion to one of excessive energy, we~can see that, theoretically, there -might - be two possible ways of obtaining an insight into the progressive molecular 620 ' COMPARATIVE ELECTRO-PHYSIOLOGY changes occurring in it. First of these would be the con- tinuous observation of the character of the replies made by the changing substance to the shock of stimulus, with the progressive modification of those replies. And the second method would lie in taking a continuous record of some property of the substance, as a whole, which was undergoing a concomitant change. In the first of these modes of scrutiny the information would be obtained by an inspec- tion of the varying responses. In the second, it would be arrived at by the examination of certain characteristic curves ; z = fe es + oR) eS wi ra a) < = MAGNETISING FORCE Fic. 378. Characteristic Curve of Iron under increasing Force of Magnetisation and finally, if both these methods gave correct indications of the molecular state at the time being, then each particular response of the first method would be found to have its own place in the characteristic curve of the second. This characteristic curve will be best understood from a con- tinuous record of the induced molecular change occurring under the action of an increasing external force. The simplest example of this is afforded by the curve which shows the relation between induced magnetisation and inducing magnetic force (fig. 378). This induced magne- tisation, as will be understood, measures the amount of molecular distortion. A characteristic curve, essentially CYCLIC MOLECULAR VARIATION 621 similar, is obtained from filings of a substance belonging to the negative class under increasing electro-motive force (fig. 379). Taking first the substance in a low or indifferent condition, we find the curve in its earliest stage, A, to be almost horizontal. That is to say, the molecular distortion induced is here very slight. We next arrive, however, at a stage, B, which I shall call transitional, where increasing force induces change at a rapid rate. In the third stage, subsequent to this, there is a decline in the rate of change, the molecules now approaching their maximum distortion, fa Pa Lid A a a O ELECTROMOTIVE FORCE Fic. 379. Characteristic Conductivity Curve of Sensitive Metallic Particles belonging to Negative Class, under increasing Electro- motive Force These principal features are common to characteristic curves in general, slight deviations from the type being met with occasionally. In the cases given, for example, the substance starts from an indifferent condition. But it might have been in a still lower, or a-tonic, condition at starting. Under such circumstances I find that the tendency of the first part of the curve is to fall below the zero-line, crossing it, however, in an upward direction, at the transitional point B. When the curve, again, has reached the highest point, c, it may remain horizontal for a considerable time, or there may be a decline, owing, as we shall see, to fatigue. 622 - COMPARATIVE ELECTRO-PHYSIOLOGY If we take a cyclic curve, recording the effects. under increasing, followed by those under diminishing, force, it will be found that the forward and return portions of the curve do not in general coincide (fig: 380 a). Thus, when an increasing magnetising force starting from’ zero acts on an iron rod, and is brought back to zero, the condition of the rod at the end is not exactly the same as at the beginning. A certain amount of- molecular work, which is not reversible, has been done during the cycle.. A certain molecular distortion persists as an after-effect in residual magnetisation. Similarly, when Fic. 380. Cyclic Curves of Magnetisation (2) and of Conductivity (4) metallic particles. are subjected to cyclic electro-motive varia- tion, an after-effect is found to persist in a change of con- ductivity. In substances belonging to the negative class the after-effect is one of enhanced conductivity ! (fig. 380 4). Referring again to that molecular condition of the substance which is represented by @ in fig. 378, we find that a new increment or accession of force will raise its condition to 4’. In this case the acting force has been continuously operative and continuously increasing. On the cessation of the acting foree, a substance possessing marked self-recovery will fall back from 6’ to 4 But if. there be a certain persistence of after-effect, then a 1 Bose, ‘On the Change of Conductivity of Metallic Particles under Cyclic Electro-motive Variation.’—7he Electrician, September 1901. CYCLIC MOLECULAR VARIATION 623 stimulating force which had raised the substance to - 0’ would, when again applied, after a very brief interval, raise it to J’, and so on. That is to: say, the molecular effect would in this case be additive. Tetanisation - will thus give a curve bearing a great resemblance to the charac- teristic curve. This will be seen from the following record, obtained by magnetic tetanisation of steel (fig. 381), which bears so close a resemblance to the record of electrical tetanisation of nerve (cf fig. 313). Both these curves, again, resemble the typical characteristic curve seen in fig. 378. In Fic. 381. Photographic Record of Magnetic Tetanisation of Steel, exhibiting Transient Enhancement of Response on Cessation In a tetanising shocks were moderate, in 4 strong. all these we find that the curve rises, after a longer or shorter horizontality, in an abrupt manner ; that its rate of rise then undergoes a decline, the curve tending again to become horizontal ; after which fatigue-decline may be initiated. In the. photographic record of the magnetic tetanisation of steel (fig. 331), a remarkably suggestive phenomenon is ob- served. In that part of the tetanic curve which is horizontal the one-directioned molecular distortion, due to stimulus, is exactly balanced by the force of restitution. On the sudden cessation of tetanisation the state-of balance is disturbed, and we obtain here the remarkable occurrence of a_ brief overshooting, Or positive variation, in the curve, followed 624 COMPARATIVE ELECTRO-PHYSIOLOGY by recovery. This is exactly parallel to the sudden enhancement of response in the retina on the cessation of tetanising light, or to the enhancement of response in the nerve when the tetanising electrical shock is suddenly withdrawn (pp. 428, 536). From the present experiment it will be seen that the suggested explanation of the pheno- menon, as due to anabolic or katabolic changes, is gratuitous. In responding substances, where the persistence of after-_ effect is relatively great, the successive shocks for the obtaining of the tetanic curve need not be repeated so quickly as where recovery is rapid. The shifting of the base-line of a series of even such responses as indicate incomplete tetanus, will give an indication of the form of the characteristic curve. The progressive molecular modification of a substance may thus be gauged, as already pointed out, in either of the two different ways—by progressive changes in the character of the response, or by means of the characteristic curve of the substance, And if both these, again, represent correctly the molecular condition of the material, we shall further find that definite parts of the characteristic curve have each their peculiar responsive features. In order to take these records ‘of the characteristic curve and corresponding responses of a substance, moreover, we may adopt any method that is convenient—mechanical, electro-motive, magnetic, or that of the resistivity variation. The feasibility of such records is obviously a matter of the extent of the change induced and the sensitiveness of the recording apparatus. Of the various methods here mentioned, it may be said that there are no particular sources of uncertainty to be guarded against in regard to variations of resistance, of magnetisation, or of length. But in the method of electro-motive variation, as the change to be recorded is relative, being measured against a neutral or indifferent point, some difficulty occurs in securing a point which is invariable. This may be done more or less per- fectly, however, by choosing an injured or killed point on the tissue for the second contact, in order that it may be subject to as little variation as possible from environmental changes. CYCLIC MOLECULAR VARIATION 625 ‘We shall now proceed to the description of the distinctive characteristics of certain. molecular states, We may take first the case of ‘nerve, which gives different characteristic responses under different’ conditions; and here, employing the simplest mode of record—namély, the mechanical—we find, as already said; that, when it is cut off from all sources of energy, the specimen is apt°to fall into a condition of stowing sub-tonicity,, This is indicated in the mechanical Fic. 382. Mechanical Response of Frog’s Nerve to successive equal Stimuli, applied at Intervals of One Minute The sloping line at the beginning shows growing elongation due to sub- tonicity, Stimulus here causes positive response. Fourth, fifth, and sixth responses are distinctly diphasic. Responses become normal and ‘increasingly negative’ after the seventh, with marked staircase increases. Molecular transformation is seen to be very rapid, above the B point of transition. Record is a photographic reduction, half original size, of tracings obtained on smoked glass, record by an increasing abnormal elongation, as in fig. 382, given above. When the nerve is now subjected to the action of stimulus, its. tonic condition is gradually restored, progressing towards a normal excitatory condition. The molecular transformation involved here is at first expressed by growing retardation of the abnormal elongation, and afterwards by gradual contraction. At the point of trans- ition from positive to negative, or from elongation to sS 626 COMPARATIVE ELECTRO-PHYSIOLOGY contraction, that is’to’say, in stagé B,we shall find that the rate of transformation becomes very rapid. The second test, by which we may judge of the progress of molecular transformation in the experimental specimen, consists, as we have seen, in the nature of its reply to stimulus. Thus, in the sub-tonic condition, with its tendency to elongation, the responses are abnormal. positive. From this they pass gradually, with the progress of molecular. transformation, into the normal negative, the intermediate responses being either diphasic or zero. As the process is very rapid after passing the point of transition, the succeeding responses near this point show a staircase increase. Or if we do not wish to record the intermediate series, but merely to observe the terminal transformation into negative, or enhanced negative, due to the ascent of the molecular curve above the transitional point, we may apply a rapid series of stimuli, or tetanisation. We may here, according to circumstances, and the point started from, obtain either (1) abnormal positive transformed to normal . negative responses; or (2) diphasic, passing into normal negative; or (3) feeble, becoming enhanced, negative response. The idea has been put forward, as already said, that tetanisation enhances the responsiveness of the nerve, by some supposed evolution of carbonic acid. That this, however, is erronéous, has been shown by numerous experi- ments already related, and by the fact that even in inorganic substances, under given circumstances, tetanisation enhances response. Nor is it invariably true, in any case, that its effect is always to enhance response. Under certain conditions, it may actually cause depression. The decisive ‘element in the question of its effect lies in that part of the characteristic curve at which it is applied. If this be immediately after the point of transition its result will be an enhancement. Should tetanisation, however,.be applied above the maximum or highest point in the curve, its effect will be the diminution of response by fatigue. ; In order clearly to exhibit the fact that continuous Ne ee i - hs CYCLIC MOLECULAR VARIATION 627 molecular transformation shows itself in two different ways— by a progressive physical change of the substance itself as exhibited’ by the characteristic curve, and also by a pro- gressive variation in the character of the responses—I shall here give a pair of records of the mechanical response of frog’s nerve. In fig. 382 the continuous molecular trans- formation caused by impinging stimulus is shown by the growing contraction, or responsive mechanical negativity of the nerve, as seen in the shifting of the base-line upwards. It is also in- teresting to notice here the continuous trans- formation of the in- dividual responses from the abnormal positive through diphasic to the normal negative. There is also the noticeable additional fact that after the point of transition is passed the response Fic. 383. Mechanical Response of Frog’s undergoes a marked Nerve, showing Conversion of Abnormal . ; Positive into Normal Negative Response staircase increase. In after Tetanisation fig. 383 is given another Note also the shifting of the base-line up- : : wards, and that the individual period of record, obtained with positive is shorter than that of negative frog’s nerve, where, after responses. an intervening period of tetanisation, the abnormal positive response is converted into normal negative with staircase increase. The shifting of the base-line upwards is also very noticeable here. Effects pre- cisely similar are observed in the mechanical response of vegetal nerve. If we now turn to a different ae of observation—-say that by the electro-motive variation—the records will. be found to bear a remarkable resemblance, in every. particular, to those which have just been given. We find here the same SS 2 628 COMPARATIVE ELECTRO-PHYSIOLOGY continuous transition, from abnormal positive to normal negative, :as before, through intermediate diphasic, with: a shifting: of ‘the base-line upwards, exhibiting an increasing negativity. “The gradual transformation of the character of the response may be seen when a long series of successive responses to successive stimuli is taken (cf fig. 277). Or the abnormal positive may be-séen’ transformed: into normal negative, after an intervening period .of tetanisation. (cf fig. 276). Or when the point of molecular transition is passed, ‘the effect of intervening tetanisation is to enhance the ampli- tude of response (cf fig.275). It will thus be seen that the characteristic response in the sub-tonic condition A is abnormal positive ; and that, when the substance ‘is transformed by stimulation, to a point above the transitional B, the response is con- verted into normal negative, and lastly, since the rate of transforma- tion is very rapid above the point B, that successive responses in that region exhibit a. staircase increase, or moderate negative becomes the | enhanced negative, after an_inter- Fic. 384. Photographic Re- yening period of tetanisation.. The cord showing~ Conversion ‘ : q of Abnormal ‘Down’ Re- underlying transformation is thus yee Re aeenites indicated by changes in the response, and also by the shifting of the base- line upwards, in exhibition of the characteristic curve. These changes, which have now been described in the case of nerve, will be found to apply in all other instances of melecular transformation equally, Results in every way parallel are obtained with inorganic substances. In fig. 384 is seen the abnormal electro-motive response, represented as ‘down,’ converted into normal ‘up’ after an intervening period of tetanisation. In the CYCLIC MOLECULAR VARIATION 629 next figure (fig. 385) is shown how this abnormal response in platinum, in consequence of successive ‘stimulation, is Fic. 385. Gradual Transformation from Abnormal to Normal Response in Platinum The transition will be seen to have commenced at the third and ended at the seventh, counting from the left. eradually transformed-into a growing normal, through the intermediate diphasic. In fig. 386 is seen how the normal Fic, 386. Normal Electro-motive Response in Tin, enhanced after Tetanisation 630 COMPARATIVE ELECTRO-PHYSIOLOGY response is enhanced, after an intervening cet, in a specimen of tin wire. We pass next to the third mode of record, that, namely, by the Conductivity or Resistivity Variation. A selenium Fic. 387. Photographic Record of Abnormal Response of Selenium Cell converted into Normal after Tetanisation Stimulus applied was high frequency electric shocks, cell I find to be sometimes in a certain molecular condition in which it will respond to high frequency equi-alternating FIG, 388, Photographic Record showing Moderate Normal Response of Selenium enhanced after Tetanisation Stimulus applied was light. electrical shocks, of the order of a million times per second, by an increase of resistance. ‘Tetanisation is found to induce a transformation, attended by a diminution, or negative variation, of resistance. After. this, the responses are found es ie Se NPE TY ee ee ee FPR RR NTE TT CYCLIC MOLECULAR VARIATION 631- to be converted into normal: that is to say, they now take place by the diminution of resistance. Fig. 387. gives a photographic record of these effects. Selenium cells, again, under normal conditions, respond to light by a diminution of resistance. After tetanisation, or continued application of light, the normal responses, under certain circumstances, undergo an enhancement. The transformation induced by tetanisation, it is interesting to note, also shows itself by the shifting of the base upwards (fig. 388). I have found similar effects, again, to be exhibited by various metallic powders, under the stimulus of electric radiation. The record given in fig. 389 exhibits the abnormal positive response, of increase of resistance, as given by tungsten. After a short period of tetanisation the base-line is. seen to be shifted upwards, the molecular condition being transformed, in a negative direction, and thus exhibiting a permanent diminution of resistivity. The response in this particular transformed condition is seen to be diphasic—positive followed by negative. A further period of tetanisation carries this transformation still further in the negative direction, and the individual responses now seen are augmented normal negative. I give also a second pair of records in which the normal response of moderate amplitude in aluminium is enhanced, after an ee rsning period of tetanisation (fig. 390). gf We have seen, lastly, that molecular response may be recorded by means of the magnetic variation. «And it is interesting to see, by employing this mode of record, that under certain conditions tetanisation will enhance erence response (fig. 391). - 7 In order to make a striking demoristration of Hie fact that the various phenomena described are not the result of some specific property of living tissues, with their hypo- thetical assimilation and dissimilation, but are determined by molecular conditions common to matter both living and inorganic; I shall now give in vertical. columns; several series of records of responses, obtained, under parallel conditions, 632 COMPARATIVE ELECTRO-PHYSIOLOGY from living tissues, animal and: vegetal, and from inorganic bodies. As the methods also, by which these records were Fic, 389. Photographic Record ot Abnormal Response of Tungsten to Electric Radiation, converted after Tetanisation into Diphasic and Normal obtained, were so different as those of the mechanical, the electro-motive, the resistivity and the magnetic variations, it Fic. 390. Moderate Normal Response of Aluminium, enhanced after Tetanisation follows that their similarities under parallel circumstances can only be due to certain fundamental molecular reactions, which are common to all alike. Further, since some of th CYCLIC MOLECULAR VARIATION 633 responding substances were elementary, and the experimental arrangements offered no. possibility of chemical reaction, it follows that similar responses, in other cases like- wise, are determined, not» by some antecedent chemical, but by molecular action, though chemical action may take place as a consequence of. their responsive molecular derangement., _In the first of the series of records in vertical columns (fig. 392) we have: (a) a mechanical record of abnormal response by expansion, FIG. 391. Photographic Record of Enhancement of Magnetic Response after Tetanisation passing into normal response by con- traction, after intervening tetanisation, in frog’s nerve. In (0) we observe a similar transformation, as seen in the electro-motive response of frog’s nerve. The abnormal response by galvano- metric positivity is here converted by tetanisation into the normal megazzve. Turning next to inorganic substances, and taking the method _ of Resistivity Variation, we find in (c) the abnormal postive response of tungsten converted by tetanisation into normal negazzve, Finally (d) where the specimen is tin wire, and the record made by electro- Fig, 392. Vertical Series of a, Records showing Trans- formation of Abnormal into Normal Response after Tetanisation in Living and Inorganic alike in the A phase Mechanical response of frog’s nerve to electric stimulation ; 4, Electro- motive response of frog’s nerve to thermal stimu- lation; c, Response by resistivity variation in tungsten to electric radia- tion; .d@, Electro-motive response of tin wire to mechanical stimulation. 634 FIG. 393. COMPARATIVE ELECTRO-PHYSIOLOGY motive variation, the abnormal response is seen to be converted into normal after tetanisation. It will be noticed, in all these cases, that the antecedent molecular transformation, on which the conversion from abnormal to normal . response depends, is also shown independently, by the shifting of the base-line of the record in the direction of the normal response—that is to say, upwards, In the next series, again, in fig. 393, is shown the effect. of tetanisation in enhancing feeble normal response. This moderate normal response, it will be remembered, is characteristic of the molecular condition, just above the point of transition from abnormal to normal. In (a) is seen the enhancement of mechanical response in nerve of fern. In (6) we have the enhanced electro- motive response of frog’s nerve. In (c) a similar enhancement of electro-motive response is shown in plant nerve. In (@) we see the enhancement of response after tetanisation in aluminium powder by the method of resistivity variation, the stimulus employed being Hertzian radiation. In (e) the method of record is also by resistivity variation, in a selenium cell, under the stimulus of light. And finally, in (7) are given the responses of platinum wire, under the Series showing how Tetanisation enhances Normal Response in the B Phase a, Mechanical response of frog’s nerve; 6, Electro-motive response of frog’s nerve; c, Electro-motive’ response of plant-nerve; @, Response by resistivity variation in aluminium powder; ¢, Response of selenium ; f, Electro-motive response of tin. CYCLIC MOLECULAR VARIATION 635 method of electro-motive variation, before and after mechanical tetanisation. The antecedent molecular transformation to which this enhancement is due may also be gauged, in all these cases, by the shifting of the base-line upwards. We have up to this time dealt with the first part only of the characteristic curve, up to a point slightly above that of transition. The responding substance, however, in con- sequence of the after-effect of stimulation, now passes into FIG. 394. Photographic Record showing Responses corresponding with different parts of characteristic curve in frog’s nerve a, Abnormal subtonic ; 4, Staircase ; c, Uniform ; d@, Fatigue decline ; : ¢, Fatigue reversal, various different phases of molecular condition, These may be short-lived, or more or less persistent. We shall next study all the responsive modifications dué to these induced molecular conditions, from the subtonic A to the post-maximum E conditions,-in order, Selecting as our specimen for this purpose the nerve of frog, the different phases through which this is capable of passing. may, for convenience, be divided into five classes (fig: 394). . In the first of thesé—the abnormal A phase—the nerve is sub-tonic. It is here undergoing a relaxation, and its characteristic 636 COMPARATIVE ELECTRO-PHYSIOLOGY response to -individual stimulus. is abnormal: positive. In consequence- of stimulation, however; we have seen this relaxation to be arrested, and to pass into growing con- traction. ‘The characteristic’ of response at this transitional stage is to be diphasic, passing gradually into the normal negative. On reaching this, the B phase, the responses, as we have seen, commence with feeble normal, and undergo a staircase increase. We may arrive at an idea of the rate of molecular transformation, in this and succeeding phases, from the curve of the mechanical response of nerve under tetanisation (cf fig. 313).. We there saw that in the B, or transitional, phase, the rate of contraction was very rapid ; we also found the individual responses at this stage to show a staircase effect. The rate of contraction next became slower, and the curve was afterwards more or less horizontal. Beyond this, fatigue-relaxation set in. We have now to observe the responsive variations characteristic of these different phases. For this purpose, a high magnification of three hundred times has to be em- ployed. Records so obtained are given in fig. 394. The method of procedure is as follows: We first take two or three test-responses to individual stimuli of definite intensity, at the A phase. This test-stimulus is subsequently main- tained at the same intensity. When the record of the A stage has thus been taken, continuous stimulation is applied for a time, till we arrive at the B stage, when the record of responses to individual stimuli is taken once more. The contraction due to the previous tetanising stimulus employed for the conversion of phase, is now so great that the record- ing spot of light is carried out of the field. At the com- mencement of each phasic record, therefore, the spot has to be brought back to the plate by suitable adjustment of. the reflecting mirror. Thus the first record of each series really shows the effect of the termination of tetanisation, the sub- sequent records showing response to individual stimuli. We may, however, obtain some idea of the characteristic changes occurring in the nerve as a whole, by joining the tops of the a Ae ee as) Noe ne Weer ae Ee CYCLIC MOLECULAR VARIATION. ~ 637 response records, Fromm the inclination of the line thus pro- duced it is possible to. see whether the nerve at each ‘different phase was contracting, had assumed a stable length, or was relaxing. -In the B phase, as here shown, for instance, it will be seen that the nerve, when undergoing an. increasing con- traction, shows a staircase enhancement of response; at C we observe this change to arrive at a climax,: with con- sequent stability of condition and uniformity of response. _ _ The characteristic curve, after this, undergoes a reversal : that is to say, responsive contraction is now diminished, and eventually gives place to relaxation ; and it is curious to find that all the responsive phenomena observed during the ascent are now repeated, but in the reverse order, That is to say, during the ascent of the curve we obtained the se- quence of abnormal positive, diphasic, and increasing normal responses. And during the reversed process we obtain diminishing normal, diphasic, and the culminating abnormal positive response. The cycle of molecular phases, with their attendant variations, is thus complete. An inspection of D shows the change in the condition of the nerve from the contracted to the relaxing state. The onset of fatigue is also seen in the diminishing amplitude of the responses, This process is seen accentuated, to the actual reversal of response, in the last phase E, I shall later give a special record exhibiting the diphasic responses inter- mediate between D and E, | The response of nerve has hitherto been supposed, as already mentioned, to be specifically different from that of ordinary tissues. One characteristic particularly’ insisted upon was its indefatigability, or incapacity for fatigue, the nerve in this respect differing essentially from the muscle. On taking a general review, however, of nerve and muscle- response, we find that there is no essential difference between the two. During the first phase of contraction, both alike show staircase increase. This is followed, in both, by a series of uniform responses. And in the stage of fatigue, in both, the process of contracture gives place to one of 638 COMPARATIVE ELECTRO-PHYSIOLOGY relaxation. Theé’only difference lies in the fact that fatigue — makes its appearance in the one case earlier than in the other. When dealing with the subject of the enhancement of response by tetanisation, I stated that here it was not tetanisation, as such, which formed the determining factor in bringing about the increase of response; this was rather due to a phasic molecular transformation, induced by tetanisation. If the substance happen to be in the transitional B phase, then and then only will tetanisation enhance its response. If, however, it should happen to be in the optimum C phase, then the same tetanisation will have the effect of carrying it into D and E, the phases of fatigue. The response here, Fic. 395. Photographic Record of Response of Tungsten showing Enhancement of Response after moderate Tetanisation, and Reversal of Response, due to Fatigue under stronger Tetanisation instead of being enhanced, will be decreased or reversed. This is seen in the following record (fig. 395) obtained with tungsten when moderate tetanisation enhances response, whereas strong tetanisation, by bringing on fatigue, reverses the normal response. | How universal are these phenomena will be seen from the accompanying series of records, obtained. not only with various living tissues, but also with inorganic substances under parallel conditions, the normal responses being in all these cases reversed by tetanisation, in consequence of the transformation from the C to the E phase. In fig. 396 (a) is seen the normal contractile response of a frog’s nerve reversed to the positive or expansional, after tetanisation. CYCLIC MOLECULAR VARIATION 639 In (6) is seen the reversal of the normal electro-motive response in the digesting leaf of Drosera, after tetanisation, the stimulus here also being electrical. reversal after tetanisation in the elec- tro-motive response of the pulvinus of Mimosa. And in (d) is given a similar reversal after tetanisation, in the response of tungsten powder, the record being here of the resistivity variation, under the stimulus. of Hertzian radiation. These, and other results already given, have _been obtained by the employment. of different forms of stimulation. We may, therefore, regard these charac- teristic transformations as: brought about by all forms of stimulus alike. We thus see that one identical stimulus may give rise to opposite effects, according to the molecular condition of the responding tissue. This molecular transformation, more- over, may be brought about by the previous action of the stimulus itself. These considerations will, I think, be found to elucidate the very obscure question of the effect of drugs, with special reference’ to the opposite actions of large and small doses. Since a chemical substance acts in- a manner. not unlike that-of other stimulating agents, a moderate dose of a given reagent might be expected to induce effects similar to that of the action of moderate stimulation. FI a; [In (¢) we have G. 396. Series showing reversal of Normal Re- sponse by fatigue due to strong Tetanisation in- ducing the E phase Mechanical response of frog’s nerve; 4, Electro- motive response of Dvo- sera; ¢, electro-motive response of pulvinus of Mimosa; ad, Response by resistivity variation of tungsten powder. Hence_its effect in inducing molecular transformation will generally be to en- hance excitability, as from B to ©. Too long-continued action, 640 COMPARATIVE ELECTRO-PHYSIOLOGY ‘however, carrying the substance acted upon ‘to the phase of D or E, will cause depression, Or it is conceivable that the same depression might be more rapidly induced by more intense stimulation—that is to say, by a larger dose. Now that this is what actually takes place has already been shown in several experiments which have been described, We saw, for example (fig. 95) that the continued action of the moderately stimulating agent, sodium. car- bonate, at first induced an exaltation of response, followed later by depression. In the case of vegetal nerve, again (ff. fig. 297), we found that the same agent, in smaller doses, caused at first an enhancement of conductivity, followed later by slow depression. A stronger dose of the same reagent, however, was found to cause rapid depression (fig. 298). Even in the case of poisons, so-called, the same facts make their appearance. Here an agent which’ proves toxic in large, appears as a stimulant when given in minute, doses, Thus in studying the effect of various chemical agents on growth-response, I found that while a one per cent. solution of copper sulphate was toxic, the same reagent proved stimulatory, if given in a solution of ‘2 per cent. _ A more detailed account of these experiments will be found in my work on ‘Plant Response,’ from which I quote the following summing up: | ‘A survey of the effects of drugs, both stimulating and poisonous, reveals the striking -fact that the difference between them is [often] a question of quantity. Sugar, for instance, which is stimulating. when given in solutions of, say, I to 5 per cent., becomes depressing: when the solution is very strong. Copper sulphate, again, which is regarded as a poison, is only so at I per cent. and upwards, a solution of ‘2 per cent. being actually a stimulant, The difference between sugar and copper sulphate is here seen to lie in the fact that in the latter case the range of safety is very narrow. Another fact which must be borne in mind in this connection is that a substance like sugar is used by the plant for general metabolic processes, and thus removed from the ECR ene See ae el ee ee Se IT Oe ee a a i EY INR Peat Pee, CYCLIC MOLECULAR VARIATION 641 sphere of action. Thus, continuous absorption of sugar could not for a long time bring about sufficient accumulation to cause depression. With copper sulphate, however, the case is different. Here, the constant absorption of the sub-tonic stimulatory dose. would cause accumulation in the system, and thus ultimately bring about the death of the plant’? . = From all this it is clear that the progress of medicine may be greatly facilitated when the attention of investigators is drawn to the importance of the molecular aspects of the phenomena with which they have to deal. Thus, in examin- ing the action of drugs, a threefold question is seen to arise. It must first be determined what is the nature of the respon- sive molecular change induced by the given reagent under normal conditions. The second matter of inquiry is, What is the critical dose, above and below which opposite effects may be expected? And, finally, as the nature of the response has been seen to be influenced by the part of the molecular curve, at which the responding tissue has arrived, when the chemical reagent is applied, it rollows that an important element in the problem lies in the determination of the tonic condition of the tissue. How important is this last factor will be seen from an experiment to be described at the end of the present chapter, where an identical course of treatment+‘in one condition of the tissue revives it from inanition, and in another hastens its death. I have shown that when the condition of the substance is transformed from C€ to E, the response ‘also/is reversed from normal negative to abnormal positive. I shall now, therefore, proceed to show that in the course of this transition there is an intermediate stage of diphasic response. Before exhibiting this in the case of nerve, I shall give an interesting record in which the same thing is seen to take place in the mechanical response of fatigued indiarubber. Before the onset of fatigue, the normal'contractile responses were large, but at that stage—that is to say before the record 1 Bose, Plant Response, p. 488. yes iy 642 COMPARATIVE ELECTRO-PHYSIOLOGY commences —they had begun to decline. In the series then recorded (fig. 397) we see how the depressed contractile responses are gradually transformed into’ abnormally expan- sive, through an intermediate diphasic. : ; Fic. 397. Fatigue in Indiarubber giving rise to Diphasic and Reversed Responses In the next series of mechanical records, obtained from nerve of frog (fig. 398), we have results exactly similar. The depressed contractile negative here passes through diphasic to abnormal positive. Thus, during the descent of the characteristic curve we obtain, as has been said before, a Fic. 398. Fatigue inducing Diphasic Variation and Reversal of Normal a Response in Frog’s Nerve a, Diminished normal response; after tetanisation, enhanced fatigue in- duces diphasic passing'into reversed positive response, 4 ; a period of rest after this revived the normal response in c ; after long-continued tetani- sation, response is seen to be abolished in.d, by the death of nerve. repetition, but in reverse order, of all the phenomena seen during the molecular ascent; the sequence of responsive variation was from abnormal positive, through diphasic, to increasing negative. During the descent the sequence is diminishing normal response, diphasic, and abnormal positive. ow wererter os Se SS ee ee ee ee eee CYCLIC MOLECULAR VARIATION 643 The two halves of the cycle are thus strangely alike, one being, as it were, a reflection of the other. The cycle begins with sub-tonicity, due to a deficit of absorbed stimulus, and ends with the abnormality caused by excess of stimulation. The starting-point of the one may be supposed to meet the end of the other in a common fatality. The tissue comes to the same death by inanition on the one hand, through lack of stimulation, and by fatigue, on the other, through over- stimulation. But though the one half thus mimicks the other, there is, as it were, a polar difference between the two, by reason of the difference in their past histories. To revive the dying tissue, in the beginning of the cycle, stimulation is necessary ; to revive it afresh, at the termination of the cycle, a period of rest is essential. TT2 CHAPTER XLIII CERTAIN PSYCHO-PHYSIOLOGICAL PHENOMENA—THE PHYSICAL BASIS .OF SENSATION Indications of stimulatory changes in nerve: 1, Electrical; 2, Mechanical— Transmission in both directions—Stimulatory changes in motor and sensory nerves similar—Responsive molecular changes and the correlated tones of sensation—Two kinds of nervous impulse, and their characteristics— Different manifestations of the same nervous impulse determined by nature of indicator —Electrical, motile, and sensory responses, and their mutual relations —The brain as a perceiving apparatus—Weber-Fechner’s Law—Elimination ot psychic assumption from explanation of particular relation between. stimulus and resultant sensation—Explanation of the factor of quality in sensation— Explanation of conversion from positive to negative tone of sensation after tetanisation—Various effects of progressive molecular change in nerve—FEffects of attention and inhibition—Polar variations of tonus, inducing acceleration and retardation. IT is admitted that the molecular changes induced in the nerve by stimulus, are followed by sensations perceived in the brain. The question as to the nature of these antecedent changes induced in the nerve, and the quality of the sensation that succeeds them, falls properly, then, within the scope of a physiological inquiry ; and it is certain aspects of this which will be treated in the present chapter. I may here point out that the results which I have to describe consist of deductions drawn from direct experiment. They will in some cases lend support to the psychological hypotheses already ad- vanced ; while in others they will be found to be opposed. In such cases, therefore, it is perhaps not too much to hope, from their strictly experimental character, that they will prove of use in deciding between rival theories; while in — others they will be found to introduce facts and considera- — tions which are entirely new. ———— ee, o> yp oer PHYSICAL BASIS OF SENSATION 645 Referring to the excitatory changes on which sensation depends, there has been much discussion as to whether the effects of stimulus in efferent and afferent nerves are of the same or of different natures. The difficulty in deciding this point lay in the fact that the indications of the state of excitation are different in the two cases, one exhibiting it objectively by the motile effect, and the other subjectively by sensation. It has been supposed, as we have seen, that the excitatory changes transmitted by the nerves were un- accompanied during their progress by any direct visible indications. It has been shown, however, in the course of previous chapters, that a change of form does in fact ac- company the transmission of the wave of excitation along the nerve. It was also shown that this mechanical indica- tion could be rendered extremely delicate, ranking, in degree of sensitiveness, between the galvanometer and the brain. Employing this mode of investigation, then, we found not only that the wave of excitation might be trans- mitted in either direction in any given nerve, but also that the changes induced by stimulus were similar in afferent and efferent nerves (p. 529). Regarding the nature of this molecular change, again, it has been supposed that the nerve under excitation exhi- bited a specific variation, known as the xeura/, totally unlike those changes which take place, for instance, in muscle. We have seen, however, that this is not the case, the mechanical and electrical expressions of the molecular changes in excited nerve being of a nature essentially similar to those observed in muscle also.. Even in the matter of conduction, we have seen that non-neural tissues transmit'the state of excita- tion to a certain distance beyond the point of stimulation. The difference in this respect is one of degree, and not of kind. We have next to deal with the question of sensation as induced by molecular changes in the nerve. It is widely admitted that the changes induced in the nerve by stimulus will cause responsive sensations. But the relation between 646 COMPARATIVE ELECTRO-PHYSIOLOGY the responsive sensation and the character of the molecular change that induces it has been regarded as unascertainable. ‘That many of our feelings depend immediately upon the condition of the nervous elements is beyond doubt... . What is the peculiar nature of the excitation upon which the different feelings depend ‘for their differences of quality ? What is the characteristic change in the excita- tion that gives rise to two kinds of tone which the feelings possess, to pleasure and to pain? Physiological psycho- logy can answer none of these questions with much con- fidence.’ ! The fundamental contrast of tone in question raises the inquiry, therefore, whether it may be possible to discover any antecedent nervous changes of opposed character. Taking an instance of response by some simple form of sensation, it is well known that while moderate stimulus produces a feeling which may be described in general as not unpleasurable, or even distinctly pleasurable, an intense stimulus of the same nature will cause a displeasurable or even painful, sensation. These fundamental differences of quality are classified as ‘positive and negative Zones’ of sensation, the term ‘ positive’ being here associated with perceptions which are not un- pleasant, or even actually pleasant, while ‘negative’ refers to the reverse. While the sensations ensuing under moderate stimulus, then, such as moderate pressure or moderate light, are of ‘positive’ tone, those brought about by more intense stimulus are apt to become converted into negative. The positive sensation grows to a maximum, according to the rise of stimulus-intensity within a certain limit. Beyond this point, sensation becomes, first, less and less positive, and then increasingly negative, as the intensity of stimulus continues to be augmented. Ora simple stimulus, suchas a light blow, which evokes a positive sensation, will, when often repeated— that is to say, when employed tetanically induce a negative or painful sensation. It is thus seen that the tone of sensation is in some way associated with the intensity or duration of * Ladd, Outlines of Phystological Psychology (1891), p: 387. ' rhe a i P - cae ee ae ta 2 ab a) Shee ae PHYSICAL BASIS OF SENSATION 647 stimulus. The question, however, remains, whether or not. these opposite sensation-tones could be demonstrated to be dependent upon characteristic nervous changes of opposed characters. lf we should succeed in making such a demon: stration a physico-physiological basis of. psychical effects would have been established which would unquestionably prove to be of great value, Now we have seen, referring to previous investigations on nerves, (1) that a feeble stimulus applied to the nerve is transmitted as a pulse of expansion. This we have designated the positive wave. The propagation of this wave being more or less of the nature of a hydrostatic disturbance, we have seen that its transmission is not affected to any great extent, even when the conductivity of the tissue is diminished. (2) A more intense stimulus we have found competent to give rise to a disturbance of opposite or negative sign—that is to say, toa pulse of contraction. The velocity with which this second, or,as we have called it, the true excitatory wave, was conducted, we found to increase with the intensity of the stimulus. While with feeble stimulus the positive wave alone was transmitted, with stronger, both negative and positive were propagated, but the more intense negative was liable to mask the feeble positive. As the negative wave was dependent on the conductivity of the tissue for its propagation, we have seen that it was possible to separate the two by any means which would diminish the conductivity "of the tissue. By such means the negative could be made to lag behind the positive; or, by its complete suppression, it was even possible to exhibit the positive alone. Thus a tissue which normally gave only negative response, owing to the masking of the positive, might, by the depression of its conductivity, be made to give diphasic, or positive response alone (p. 530). So far then, as regards the detection of two nervous im- pulses of opposite sign by means of the delicate mechanical method. The same facts may also be demonstrated by the less sensitive method of electrical response, according to 648 COMPARATIVE ELECTRO-PHYSIOLOGY which we saw that the two nervous impulses were exhibited by two opposite electro-motive variations—those of galvano- metric positivity and negativity respectively. This reaction of expansion and galvanometric positivity, however, may also occur as the expression of the increase of internal energy, in whatever way produced. Indeed, the positive form of response under moderate stimulation may be regarded as a case falling within this definition. Thus we . see that, beginning with very moderate stimulus, we obtain in the tissue a purely positive effect; and that, as the stimulus is augmented, the true negative excitatory effect also begins to make its appearance in increasing degree, the positive component of the response being now more or less masked. The energy that afterwards remains latent in the tissue goes to enhance the tonic condition. The amount thus held latent depends on the difference between income and expenditure. As a general rule, it will be under intense stimulation that the expenditure of energy will be likely to exceed the income. Thus we have two extreme cases, first, that in which moderate stimulus brings about increase of energy ; secondly, that in which excessive stimulus brings about run-down of energy ; and between the two a large range of variation, within which either one condition or the other may predominate. It must, of course, be under- stood that anything which increases the tonic condition is for the well-being or health of the organism, and is associated with positivity. Similarly, any fall of the tonic condi- tion below par makes for exhaustion and against healthy tone. We have next to take a rapid survey of the changes induced by stimulus in the conducting nerve itself, or any of its attached indicators. Such variations may, for purposes of convenience, be classified as motile, electrical, and sensory. In the nerve itself we have found, as has already been pointed out, by means of the Kunchangraph, that the motile change induced by feeble stimulus was one of expansion, the same change being shown electrically by galvanometric —_- ee ee ee ee ee ee ee ee —— PHYSICAL BASIS OF SENSATION 649 positivity. The change induced by strong stimulus, on the other hand, was of contraction and galvanometric negativity. In the terminal motile indicator also, there are two different modes of response of opposite signs—namely, expansion and contraction. -In the highly excitable muscle, the occurrence of the former of these, brought about, as it is, by very feeble stimulus, is not easy to demonstrate. Bearing in mind, however, the fact that in nerve positive response is more easily obtained when the excitability is depressed, I succeeded in obtaining positive expansional response of the muscle, in a nerve-and-muscle preparation of frog, which had been depressed by the anzsthetic action of chloroform. At a certain stage of anzsthetisation, the response of the muscle under stimulation of the nerve was found to take place by expansion, followed by recovery. Just as in a nerve in a somewhat depressed condition, ee Fic. 399. Abnormal Response of Muscle by stimuli evoke positive Relaxation, followed by Normal Response response converted later af, Contraction ‘ 1 ; The first two responses by relaxation are into normal negative, followed by two contractile responses. so, in the muscle-pre- paration described, the abnormal positive was followed by the normal negative response. In fig. 399 I give a photo- graphic reproduction of the myographic record obtained on a smoked-glass surface. In all these different effects we obtain, by means of the mechanical response of the terminal organ, what is merely a parallel expression of changes occurring in the nerve itself. As in the nerve, so also in the muscle, there are two different kinds of responsive expression—namely, expansion and con- traction. Thus we see that the various manifestations registered by different modes of indication are only so many diverse expressions of the same fundamental molecular changes. 650 COMPARATIVE ELECTRO-PHYSIOLOGY We turn next to the sensory mode of indication, that is to say, to the psychic effects registered in the central perceiving organ by the positive and negative waves conveyed to it along the afferent nerves. We have already seen that the stimulatory changes induced in these sensory nerves are precisely the same as those which occur in the efferent. What, then, are the effects in the central apparatus induced (1) by that positive impulse which is associated with . expansion, and (2) by the negative impulse associated with contraction ? : It is a matter of universal experience, as already mentioned, that feeble stimulus gives rise to sensations of positive or pleasurable tone, while an intense stimulus of the same kind will induce a responsive sensation which is negative or painful. We have also seen, in the course of the present work, that a feeble stimulus will give rise to a wave of expansion and galvanometric positivity, while the same stimulus, when intense, will give rise to a negative wave. We are therefore justified in regarding the positive impulse, associated with expansion and galvanometric positivity, as _pleasure-bearing, and its, opposite as pain-bearing or dolori- ferous. Numerous experiments—some being of a crucial character—will be given, in the course of the present and succeeding chapters, which will be found to lend full support to this conclusion. This fact, that the same stimulus may induce positive sensation in the central and expansion in the motile organ, or the negative painful sensation with muscular con- traction, according only to the nature of the indicator, will furnish grounds of reconciliation to those who hold on the one hand that the motor reaction is secon- dary to the mental, and on the other, that sensation is merely an accompaniment of movements reflexly in- duced.’ ‘Many hold the motor reaction to be secondary to the mental. Of the coarser emotions it has been argued by James that the feeling does not cause, but is caused by, the bodily expression, The bodily changes, according to him, follow directly the perception of the exciting fact, and our feeling of the same Ue ed es ee eee ee eee i pw eal a Eager pment ns eae PHYSICAL BASIS OF SENSATION 651 If the sensation be in fact due to definite and ascertainable physico-physiological changes in the nerve, then the various modifications of sensation must, in like manner, be traceable to corresponding modifications in the physico-physiological process. In that case, the particular relation which is known to exist as between stimulus and sensation—expressed as Weber-Fechner’s Law — must be demonstrable as directly dependent upon molecular changes induced, and not on the existence of some assumed psychic factor. This molecular theory, further, if it expresses a truth of universal applica- tion, ought to be capable of explaining not only the quantitative relation between stimulus and sensation, but also that qualitative variation of which Weber-Fechner’s Law is unable to take account. Should the Molecular Theory prove adequate to this, its truth may be regarded as demonstrated. | We shall, however, subject this theory to further and still more crucial tests. If it be true that our sensations, ‘painful and pleasurable, are due to nervous impulses of opposite character, then any modification of either of these impulses by any given agent should appropriately modify the resultant sensation. We have seen, for instance, that the negative wave is complex, and contains within it the masked positive. We have also seen that by appropriate means these two waves may be made to exhibit themselves separately ; or the positive, by the total suppression of the negative, may be displayed alone. I shall therefore show that, by the employment of the same means, the subjective sensation of painful or negative tone may also be analysed into its component parts, which may thus be made to exhibit themselves in succession; and, on the other hand, that by changes as they occur zs the emotion. Certain experiments furnish evidence— not highly satisfactory—that all pleasurable states of consciousness are accom- panied by bodily movements of extension, and all painful by movements. of flexion. These movements may be very slight. Miinsterberg concludes that the feeling of agreeableness is the mental accompaniment and outcome of reflexly-produced movements of extension, and disagreeableness of the move- ments of flexion.’--Schafer, Zext-Book of Physiology, vol. ii. (1900), p. 975- 652 COMPARATIVE ELECTRO-PHYSIOLOGY the complete obliteration of the negative element an already painful sensation may be converted into pleasurable. Of the scheme thus laid down, the first part will be carried out in the present, and the second in the succeeding, chapters. Turning now to our sensations themselves, it may be well to consider some of the characteristics of the central perceiving | apparatus. Asa detector of nervous changes the brain is undoubtedly the most delicate of instruments, surpassing in this respect not only the galvanometer, but also the Kunchangraph. It fails, however, strictly speaking, as an accurate metrical apparatus. It is not able to discrimi- nate quantitatively, for instance, by means of sensation, through any wide range, between the finer differences of intensity in the nervous impulses it receives. In the pain- and-pleasure series, again, the distinctions which it is able to make are, to a certain extent, of a merely qualitative character, unmistakable only as between the two extremes of the series, the intervening region tending to be somewhat indefinite. The sensitiveness of the physical instruments, Kunchangraph and galvanometer, is always constant and reliable. For example, in the galvanometer, by adjusting the controlling magnet, we can obtain varying degrees of sensibility, which at any particular adjustment will remain constant. But in the perceiving apparatus, not only is the sensitiveness of different individuals widely different, but even in a single individual it undergoes great variation under different conditions. By deliberate attention or inhibition, as by raising or lowering of the controlling magnet in the galvanometer, the sensitiveness of the perceiving field can be almost indefinitely varied. Pursuing this analogy of the galvanometer further, we find that in the brain, instead of a single coil, with its one pair of terminals, there are many coils with many pairs of terminals, receiving impulses from every part of the organism. Confining our attention, moreover, to any single circuit among these, we find again that the impulses it o Sy? sate 22 Rey hae erie Ea 9 Soe i beets a” — Magy eet Mag ee! MEMORY 679 which had lengthened to 5 seconds by 3 P.M.; and was further prolonged to 6°5 seconds by II P.M. | One way of exhibiting the after-images in the retina is, as we have already seen, by means of a stereoscope con- taining two incised slits inclined to each other, instead of photographs. On looking through this at the bright sky for ten seconds, or longer, a composite image is formed of an inclined cross. The eyes are now closed, and the first. effect noticed is one of darkness, due to the molecular rebound. By reason of the Binocular Alternation of Vision, already referred to, one luminous arm of the inclined cross now projects itself aslant the dark field, and then slowly disap- pears, after which the second, perceived by the other eye, shoots out suddenly in a direction athwart the first. This multiple alternation proceeds for a long time, and produces the curious effect of two luminous blades crossing and re- crossing each other. At first the after-images of the cross, seen with the eyes closed, are very distinct, so distinct that any unevenness in the design at the edges of the slanting cuts can be made out clearly. There is here no doubt of the ‘objective’ nature of the strain impressed on the retina, which, on the cessation of direct stimulus of light, gives rise to after-oscillations with concomitant visual recurrences. This recurrence may be taken as a proof of the existence of physical strain in the retina. The recurrent after-image is very distinct at the beginning, but becomes fainter with each repetition. A time comes when it is difficult to tell whether the image is the objective after-effect due to previous strain, or merely an effect of ‘memory.’ There is, in fact, no hard- and-fast line of demarcation between the two—one merges simply into the other. In connection with this, it is interesting to note that some of the phenomena of memory also are admitted to be recurrent. Visual impressions and their recurrence often persist for a very long time. It usually happens that, owing to weariness, the recurrent images disappear, but in some in- stances, long after this disappearance, they will spontaneously 680 COMPARATIVE ELECTRO-PHYSIOLOGY appear at most unexpected moments. Thus in a given case of the present experiment, performed in the afternoon, the subject perceived this recurrence for some time, after which the alternating impressions seemed to disappear, and were completely forgotten. On retiring at night, however, these recurrent images suddenly reappeared. Thinking the matter to be an effect of light, the observer hastily extinguished his lamp. But the recurrent images now became only the more © intense. In another case the recurrence was observed in a dream, about three weeks after the original impression was made, and in this case it was seen as the crossing and recrossing of bright swords. These instances of the revival at night of impressions made in the daytime, when the interference o distracting influences is withdrawn, is significant. Since an intense stimulation of nerve is liable to recur spontaneously, ‘without the action of the will, or even in spite of it, it follows. that any single impression, when very intense, may become dominant, and persist in recurring automatically. Examples of this are only too familiar. We have hitherto dealt with that aspect of memory in which it isa more or less immediate after-effect of sensory stimulation. But we encounter a much more difficult pro- blem when we come to the question of the revival of an image long after it has apparently faded. It has been sug- gested that this process of revival depends upon the existence of some ‘scar, or fixed impression, in the brain, or on a certain persistent disposition or tendency to movement created there. It is perhaps worth while to point out here, however, that though when a blow is recent, the smarting effect will persist for some time, yet; when once healed, no scar could of itself reproduce the original excitation. It is of course recognised that such expressions are merely figurative, and that the entire process is not clearly understood. We are more likely, however, to arrive at a true explanation of the phenomenon if we recognise in it two distinct factors, first, that of molecular change, with concomitant change of MEMORY 681 properties ; and, second, the effect of an internal stimulus, delivered as a blow from within, by an impulse of the will, upon the sensitive surface in which the image is latent. _ We shall now first observe in some detail those changes which remain as an after-effect of previous stimulation. The differential effect caused by primary stimulus fixes the latent image, and it is only by the reproduction of the same differen- tial excitation, that the memory-image can subsequently be revived. We must here recall briefly the results which were estab- lished in Chapter XLII., on the modification of response under cyclic molecular variation. It was there shown that, under the action of stimulus, the molecular condition of a substance undergoes a progressive variation, exhibited in its characteristic curve ; that the forward and return curves do not exactly coincide, because the history behind the two half-cycles has not been the same; and, finally, that on the cessation of stimulus, the original molecular condition is not exactly restored, a certain effect being residual. Owing to this residual effect, the properties of the responding sub- stance are changed. We also saw that, in consequence of this impressed change, the conductivity and excitability of’ the substance might be enhanced. A frequent repetition of a stimulus was thus shown to create a habit or disposition by which the mass of a substance, formerly almost non-con- ducting, might be made a conductor of excitation. These impressed molecular changes may not leave any visible impression behind. But let us look at the responding properties of a given substance at different points on the characteristic curve. In a sluggish A condition, that is to say, before it has even been excited, the power of response of the substance to a given stimulus will be slight or negligible. Let us suppose next that by the action of stimulus the sub- stance is raised above B. On the cessation of stimulus a slow recovery will then take place, whose completion may be indefinitely prolonged. The substance will thus approach very near the point B in the curve, without actually reaching 682 COMPARATIVE ELECTRO-PHYSIOLOGY it. This difference between B and the point actually reached may be so small as to be undetectable by any ordinary mode of inspection. We therefore term the impression latent. But the properties of this B area, formerly acted upon, have been profoundly changed, being rendered more excitable by the impressed effect of previous stimulus. In this sensitive impression-surface will be certain areas in the A and certain others in the B condition, the former sluggish. and the latter characterised by enhanced excitability. By the shock of an internal diffuse stimulus, a differential excita- tion may now be induced, exactly similar to that caused by primary stimulus. This zs.the revival of the memory-image. _ We may carry out a physical experiment exemplifying this process of the rise of a latent impression into vividness under the action of diffuse stimulus. We may take a sensi- tive surface, in which different areas, in consequence of pre- vious excitation, have impressed on them latent variations of excitability. Thus indifferent portions of the surface A, A,, may have their excitability represented by zero, another portion B, whose excitability has been exalted as the after- _effect of stimulatory agents previously applied, will have its normal excitability enhanced. In still a third portion, C, the excitability is artificially depressed or abolished. The responding substance was a tin wire; dilute solution of sodium carbonate, which is an exciting agent, was applied on the area B. The depressing or poisonous reagent, oxalic acid, was applied at c. After a short period of this applica- tion the wire was washed, and there was no outward indica- tion of any difference between the areas A, Bandc. Elec- trically also there was little or no permanent difference between them. One non-polarisable electrode connected with a galvanometer was kept permanently applied on the indifferent surface A,. The second exploring electrode was now moved along the wire, and while it rested on any point. the wire was excited as a whole by vibration. The galvano- meter, under this arrangement, would detect differential excitability. As long as the exploring wire moved over ae MEMORY 683 indifferent areas there was no effect detected in the galvano- meter. But as soon as the exploring electrode rested on the area B, the latent enhancement of excitability there showed itself by a sudden responsive up-movement of the galvano- meter. When the electrode again passed over B and reached an indifferent area, A,, response disappeared. But when it reached C, with its depressed excitability, there was another responsive movement, this time in the reversed or down direction. It is thus seen that the impress made by the Fic. 406. Revival of latent Image in Metal action of stimulus, though it remain latent and invisible, can be revived by the impact of a fresh excitatory impulse (fig. 406). Again, this revival of the latent image by a subsequent stimulation may be exemplified ina simpler and more striking way. We take a card and coat it with some so-called phos- phorescent material, such as luminous paint. This is kept a long time in the dark, till the whole is reduced to a uniform A condition. From a previous experiment we have deter- mined what is that duration of exposure, T, to a given 684 COMPARATIVE ELECTRO-PHYSIOLOGY intensity of light, which will evoke a luminous or phosphor- escent response. A stencilled pattern is now placed on the prepared card, and the whole is exposed to light for the time T. On now cutting off the light and removing the stencil a luminous pattern is seen, which is the primary response. This impression slowly fades out. But the cardboard now contains a latent image, whose revival will be analogous to that of memory. The stimulated areas which have now ceased to respond are still, in virtue of previous stimulation, in the B condition, which is more excitable than the indif- ferent A. A feeble diffuse stimulus should now, by its differential action, prove efficient to revive the latent image. We now expose the whole card to diffuse stimulation of light, of a duration shorter than T. The excitation of the indifferent background will by this means be ineffective, whereas it will be effective wherever the image proper has been impressed. We shall, therefore, obtain a revival of the positive image— that is to say, an image of the same kind as the original. An interesting case occurs here, showing the theoretical possibility of obtaining a negative or reversed ‘memory image.” The possibility of this will be understood, from an inspection of the characteristic curve. We saw that in the region B the substance rises in excitability. But in the region of D and E, where the maximum molecular distortion has already been reached in consequence of over-stimulation, fatigue changes are induced, by which the excitability is depressed below the normal. It follows from what has already been said that an impressed image of this character will be revivable, under subsequent diffuse stimulation, but as a negative, or reversed memory-image. I shall now describe a psycho-physiological version of this experiment. Let the observer stare at the incandescent fila- ment of an electric lamp, preferably with one eye, say the right, the left being kept closed all the time. The right eye is next closed, and is further covered by the hand. Multiple after-images will now be seen for some time, till the impression seems to have completely disappeared. No trace of the ae Se . oe ee, Se Sie eee MEMORY 685 latent image is now perceivable in the field of dark vision. When this point has been reached, the hand is suddenly withdrawn from its position over the closed right eye. The light in the room now percolates through the semi-translucent eye-lid, and suddenly gives a moderate diffuse stimulus to the retina. Under these circumstances, the latent image is revived, as a negative—that is to say,as a very dark filament against a brighter background. Thus the essential condition for reviving the latent impression of stimulus would seem to be the subjecting of the unequally impressed tissue to diffuse stimulation. The revival of the image as positive or negative will then be a question of whether the stimulus have been moderate or intense. I have already shown, by actual experiment on nervous tissues themselves, that the differential excitability induced as an after-effect of moderate stimulus (memory-impression) will give rise, on diffuse stimulation, to one kind of response, and the after-effect induced by strong stimulus to the reverse (cf. figs. 311, 312). In the former case, the moderately stimulated area, on diffuse re-stimulation exhibits induced galvanometric negativity, as compared with the indifferent contact, this being the sign of its relatively greater excitation. In the second case, the sign of response is reversed, the over-stimulated area, on re-stimulation, becoming galvano- metrically positive. The revival of memory-images is thus seen to be due to differential response, evoked by diffuse stimulus, in an organ rendered anisotropic, by the unequal impressions which it contains of previous stimulation, A similar differential effect under diffuse stimulation has been seen in plagiotropic stems. Here the upper surface has a deep impression or memory of over-stimulating sunlight, and on diffuse stimulation this upper surface becomes galvanometrically positive, a respon- sive current flowing from below to above. It will thus be seen that there is a continuity between the impressions made on the sensitive neurile elements, and the physiological anisotropy induced by the differential action of past stimulus. 686 COMPARATIVE ELECTRO-PHYSIOLOGY Diffuse stimulus, moreover, whether internal or external, acting on the differentially excitable tissue, gives rise to a marked indication, which may be either motile, electrical, or psychic. A stimulus is applied to the stem of JM/zmosa. This is transmitted as an excitatory impulse, and reaches the differentially excitable organ, the pulvinus. As-‘far as this organ is concerned, the transmitted stimulus may be re- garded as internal. This internal stimulus, then, gives rise to a conspicuous differential effect, shown in the fall of the leaf. In electrical fishes, similarly, the internal stimulus, delivered by the will of the animal upon the differentially excitable organ, becomes evident as an excitatory discharge In man, again, the revival of memory constitutes a psychic response, due to the play of the diffuse internal stimulus of will upon a sensitive surface rendered differentially excitable . by the presence of a latent image. It will thus be seen that various after-effects of stimulus find expression as the phenomena of memory. The effect of primary stimulus does not disappear at once, but fades gradually, with a concomitant fading of the sensory impres- sion. From the fact that the after-effect of feeble, is less persistent than that of strong, stimulus, we understand that the sensory or memory impression also lasts longer in the latter case than in the former. Very intense stimulation, again, is apt to give multiple responses as its after-effect, and the corresponding psycho-physiological phenomenon is seen in the recurrent after-images in the retina. When a considerable interval has elapsed after the primary stimulus, there is apparently no trace left of the latent image. But the properties of the impressed portions of the sensitive surface have undergone a more or less permanent change in consequence of stimulation. Certain channels have been rendered more conducting, and certain areas more excitable. By an internal diffuse impulse it is now possible to cause differential excitation, and thus to revivify the latent image. CHAPTER XLVI REVIEW OF RESPONSE OF ISOTROPIC ORGANS Laws of response—Opposite responsive expressions of true excitation and increase of internal energy—-Separation of the positive and negative waves— Position in molecular cycle determines character of response—Abnormal sub-tonic positive and reversed fatigue positive—Effect of tetanisation— Similar effects in the inorganic—Phasic alternations—Multiple and auto- nomous response—Unmasking of antagonistic element by overshooting — Different expressions of a single fundamental molecular change —Response by change of form, by secretion or absorption, by variation of electric resistivity, or by electro-motive change—For the last, induction of anisotropy necessary—Perfect modes of stimulation : (a) Torsional vibration ; (¢) Rotary mechanical stimulation ; (c) Thermal shocks; (@) Equi-alternating electric shocks—Accurate determination of the death-point by mechanical and electrical spasms—Current of injury due to after-effect of stimulus— Explanation of characteristic electric distribution in plant and muscle cylinders—Relative positivity of dead tissue—Reversal of current of injury so-called—Unreliability of response by negative variation. IT has been shown, in the foregoing chapters, that all the diverse phenomena of response may be summarised in the two following formule : 1, Excitatory response takes place by contraction and galvanometric negativity. 2. Increase of internal energy induces the opposite effect, of expansion and galvanometric positivity. The first of these effects is simply demonstrated by direct excitation of an excitable tissue. In order to demonstrate the second, stimulus is applied at a distance from the responding point. In consequence jof sudden local con- traction at the receptive area, a wave of increased hydrostatic tension is transmitted with great rapidity. Energy is thus conveyed hydraulically, and at the distant responsive point the transmitted effect induces expansion and galyanometric 688 COMPARATIVE ELECTRO-PHYSIOLOGY positivity. This is followed by the more slowly transmitted wave of true excitation, which on its arrival gives rise to the normal response of contraction and galvanometric negativity. The two responsive effects can thus be exhibited separately, when one lags behind the other. When the intervening tract is short, or the conductivity great, the excitatory negativity masks the hydro-positive effect. But this hydro- positive may again be unmasked, by various forms of. selective physiological block, which depress the conduction of the true excitatory, without interfering to any appreciable extent with the passage of the hydraulic wave. In this way, the positive may be separated from the contained negative, the response being thus rendered diphasic— positive followed by negative. Or, by the complete suppression of the excitatory negative wave, a response originally negative may be converted into purely positive (figs. 45, 47, and 49). As response is an expression of molecular derangement, it is the extent of this which determines its amplitude. The character of response is also modified by the molecular condition of the responding substance, and the different molecular conditions through which a substance may pass are indicated by the characteristic curve. From the study of such a characteristic curve we find that these molecular transformations are not specific, but of general occurrence— alike in inorganic and living tissues. When the energy of the ‘responding substance is for any reason below par, that is to’ say, when it is in the extremely sub-tonic A condition, external stimulus will be absorbed without evoking the normal excitatory expression. Response will then be abnormal, or of opposite sign to the true excitatory effect. By the absorption of impinging stimulus the substance now passes into the next stage B, where molecular transformation proceeds at a rapid rate. At this stage, the previous abnormal response is not only reversed to normal, but successive responses exhibit a staircase increase. At the next or C stage, the responses are uniform. Following this, we arrive at the maximally distorted position D, Stimulus thininiaie, -_ ate ie ~~ ee oe 7 SE ——EE—E———=—— se CUreO REVIEW OF RESPONSE OF ISOTROPIC ORGANS 689 | at this stage induces little further excitatory distortion, while the tendency to recovery is great. In this fatigue-state the amplitude of response undergoes a decline, and in. the succeeding stage E an actual reversal. : _ The various corresponding types of response—sub-tonic abnormal, staircase, uniform, fatigue-decline, and fatigue- reversal—are not exhibited by any one particular kind, but by all forms of tissues. Thus muscle may exhibit a short- lived staircase effect, and nerve, supposed to be indefatigable, not only shows decline, but even reversal of normal response, under extreme fatigue. There are two definite conditions ander which the normal negative response is converted into abnormal positive, with an intermediate diphasic. These are (1) the condition of extreme sub-tonicity, and (2) that of fatigue brought on by over-stimulation. As regards the first, it is to be remem- bered that the normal excitability of a tissue is maintained by the supply of energy from the rest of the organism of which it forms a part. Under isolation, the latent energy or tonic condition of the tissue is liable to fall below par, under which circumstances the response becomes abnormal positive. By the absorption of the energy of stimulus, the substance is transformed from the A to the B condition, with restoration of its normal response. The process of gradual .trans- formation may be seen in a series of records to successive stimuli, when the abnormal gradually passes into the normal, through an intermediate diphasic.. Or, an intervening tetanisation will serve to convert response from the abnormal to the normal. Abnormal or reversed response is also seen to occur under fatigue, but its genesis in the molecular curve is here in reversed order to that of the abnormal response of sub-tonicity. In the latter, during the continuous trans- formation from the A to the © phase, stimulation converted the abnormal response into normal, through diphasic. But now, during transformation induced by stimulus from C to E, the normal negative passes into abnormal positive, through intermediate diphasic. To transform the abnormal positive ¥-Y¥ 690 COMPARATIVE ELECTRO- PHYSIOLOGY into normal negative in the first case, stimulation is necessary. To do the samein the second case, rest is necessary. In the records obtained from different animal tissues, various anomalies are met with, of which there has not hitherto been any satisfactory explanation. Thus the same tissue at different times will be found to give either the normal negative, or di-phasic, or abnormal positive response. Thus it has been shown that in the two extreme cases alike, of sub-. tonicity and fatigue, the response of nerve is abnormal positive (p. 636). Numerous other examples of this fact have been met with in the course of this work, in, for example, the response of skin (p. 311), that of the glandular and digestive organs (pp. 342, 346), and that of retina (p. 423). It will thus be seen how important is the molecular condition of the tissue in determining the nature of response. This is strikingly shown in the fact that the same tetanisation which in the A condition converts the abnormal to normal, in the D will convert the normal into abnormal. Again, if tetanisation be applied at the beginning of the B stage, the subsequent re- sponses are enhanced, whereas the same tetanisation at the _end of C induces a fatigue reversal (figs. 394, 395, and 398). That the explanation of these various results is to be sought for in molecular considerations, and not in that hypo- thetical assimilation and dissimilation which really explain nothing, is fully demonstrated by the fact that precisely similar responsive variations are obtained, in the same cir- cumstances, in the case of inorganic matter, under different forms of stimulus and different methods of record. As an example, may be cited the transformation of abnormal response into normal, in tungsten, after tetanisation (fig. 391), the stimulus employed being electric radiation, and the mode of record, resistivity-variation. Parallel effects have been shown in the case of tin, the response being recorded by the electro-motive variation, and the stimulus employed mechanical (fig. 386). The enhancement of normal response also under tetanisation, when at the B stage, has been shown in tin (fig. 388); and finally, the reversal of normal response REVIEW OF RESPONSE OF ISOTROPIC ORGANS 691 by fatigue was shown in tungsten under electric radiation, while in the contractile response of indiarubber under thermal stimulation it took place with intermediate diphasic: (fig. 397). The characteristic curve has been shown to exhibit the history of molecular transformation under continuous stimulation. In the first part of this curve a progressive change is shown to be manifested outwardly by increasing contraction or galvanometric negativity. In the second part a reversal of this process is seen to occur. This is illustrated in records of response under continuous stimulation. Thus muscle shows increasing contraction, to be followed by fatigue-relaxation (fig. 64). The same thing is observed in Mimosa, as a fall of the leaf, followed by its re-erection (fig. 65). Electrically, this is observed as increasing galvano- metric negativity, followed by reversal to positivity. These phasic alternations may in some cases be exhibited only once, and in others repeatedly. Thus, in a certain style of Datura such phasic alternation is seen to occur twice (fig. 76); and again, in leaflets of Desmodium gyrans, at first quiescent, continuous stimulus of light gives rise to those repeated alternations of negative and positive which consti- tute multiple response (fig. 141). The distinction between the tissue which gives only one such alternation, and others which display it in repeated succession, is not, it should be borne in mind, rigid. Even skeletal muscle, under certain circumstances,.is found to give rise to rhythmic excitations. The fact that multiple response is a phenomenon of wide- spread occurrence, and not specifically characteristic of any particular kind of tissue, has been fully demonstrated in the course of the present work, It would appear that there is a tendency of the incident stimulus, when applied continuously, to find an expression whose predominant characteristics are alternating. We may first have the exhibition of excitatory molecular distortion. But when this has reached a maximum, no further excitatory expression being possible, the incident energy becomes relatively effective in increasing the internal factor,- with YY2 692 COMPARATIVE ELECTRO-PHYSIOLOGY attendant expansion, galvanometric positivity, and enhanced power of recovery. At the maximum point—that is to say, at the top of the tetanic curve—the two forces are balanced ; and at this point, if the stimulus be suddenly withdrawn, the particular state of unstable balance is often manifested by a brief overshooting in one or other direction. This effect’ is often noticed in the retina and in certain vegetable structures under the action of light (figs. 244, 247, 254, and 260), and in nerve under electric tetanisation (p. 536). That it is not primarily dependent on assimilation and dissimilation, but on the molecular factor, is seen in the fact that similar effects are also to be observed, under corresponding circumstances, in the response of inorganic substances (figs. 258 and 383). The phasic molecular alternation so conspicuously ex- hibited under continuous stimulation may also be seen in the record of responses to successive stimuli. . The phenomenon is then regarded as an after-effect and shown by the shifting of the base-line of the record (figs. 208 and 396). Since the effect of stimulus is to induce a molecular upset, the change in question must be attended by various concomitant physical changes. It will therefore be possible to record the excitatory effect by recording the attendant variations of any one of these. The effect of stimulus may thus be recorded by (1) the accompanying change of form, in: contraction or expansion; (2) an attendant secretion or absorption; (3) a variation of electric resistivity by dimi- nution or increase of resistance; and (4) electro-motive changes of galvanometric negativity or positivity. The changes in the responding substance as a whole, may be recorded by any one of the first three methods. But in the last, or that by the electro-motive variation, the method depends on the relative variations of the electric potential at two different points. -For if the substance be isotropic and subjected to diffuse stimulation, the electro-motive change at the two contacts being similar, there will be no resultant effect to record. For the recording of electro-motive response, then, it is necessary to obtain an effect which is differential. REVIEW OF RESPONSE OF ISOTROPIC ORGANS 693 The first way of doing this is to localise the stimulus at one of the two contacts. This may be done by interposing a physiological block between the two, so that the excitation of one does not reach the other. The second method is to select an experimental specimen which is anisotropic, whether naturally or artificially. Artificial anisotropy is induced by injuring one of the two contacts, and so bringing about a relative depression of excitability at that point. The method of resistivity variation which I had pre- viously employed, in observing the response of inorganic substances, proved capable of sufficient perfectibility for the study of similar phenomena in living tissues also. The main difficulty in applying this method had hitherto lain in the disturbing electro-motive variation, consequent on a-symmetrical excitation, or the differential excitability of the structure. A detailed account of the means by which this method was rendered reliable will be found in ' Chapter XXXVII., where it will be seen that records of the excitatory variation obtained by it are in every way similar, to those made by other methods. All the different modes of taking records which have been enumerated are, it must be remembered, independent expressions of a common fundamental molecular change. Thus, on physically restrain- ing that mechanical movement in a motile organ which. is due to excitatory change, the electromotive response of galvanometric negativity continues to be given. Similarly, in a tissue in which, under the experimental arrangements, there can be no resultant electro-motive change and no con- tractile movement, the excitatory change may, nevertheless, be observed by means of the resistivity variation (p. 548). For the obtaining of the electromotive response, the electrical mode of stimulation, unless special precautions are taken, is subject to various disturbing influences, such as current-escape and the occurrence of polarisation. For this reason it was desirable to devise sore non-electrical form of stimulation which should be capable of quantitative appli- cation ; and this I have been able to secure by no less than 604 COMPARATIVE ELECTRO-PHYSIOLOGY three distinct methods. I found that torsional to-and-fro vibration constituted an effective form of stimulus, the amplitude of which could be increased by increasing the angle of vibration. The intensity of stimulus was found to remain constant so long as the period and amplitude vibration were kept constant. The tissue, moreover, was not subject to injury by the use, within limits, of this method (p. 31). My second method was that of Rotary Mechanical Stimulation, in which friction of the terminal area of a pumice- stone electrode constituted the stimulus, whose intensity was determined by the number of rotations (p. 291). The third non-electrical mode of stimulation employed was that of thermal shocks. The area to be stimulated was, in this case, enclosed within a thermal loop of platinum or german-silver wire, the requisite thermal variation being produced by the passage of a heating electrical current round the loop. The intensity of the stimulus could in this case be varied by increasing the intensity or duration of the heating current (p. 38). And finally I have shown that the drawbacks inci- dental to the electrical mode of stimulation might be over- come by the use of equi-alternating shocks, the indefinite polarisation factor being thus neutralised (p. 251). As the intensity of stimulus is gradually increased, it is found that the amplitude of response reaches a limit. Beyond this, increase of stimulus evokes no increase of response. On the application of a very strong stimulus, then, there is an amount of energy which is unable to find expression in the single response given by the tissue. Under such circumstances, the excess of energy is held latent, and often finds responsive expression later in a series of multiple responses. This phenomenon of multiple response to a single strong stimulus I find to be of very extensive occurrence. As examples of the different kinds of tissues in which this may be observed, may be mentioned the stems and petioles of various plants (fig. 138), the digesting leaves of Drosera (fig. 209), the pitcher of Mepenthe heh Bt BES ST =e ee ee See ae ae SE ESE RR Py a ny eS Sate iaike =i fet REVIEW OF RESPONSE OF ISOTROPIC ORGANS 695 (fig. 206), the animal stomach (fig. 213), nerves of animals, and the retina (fig. 252). I have also shown that thers is no strict line of demarcation between the phenomena of such multiple response and autonomous response so-called. Bzophytum, for example, which, usually speaking, exhibits a single response to a single moderate stimulus, and multiple response to a strong stimulus, will, under exceptionally favourable tonic conditions—that is to say, when it has absorbed from its surroundings an excess of energy—exhibit responses which are apparently autonomous. A typically autonomous plant like Desmodium gyranus, again, when deprived by unfavour- able circumstances of that excess of energy which it requires, will be reduced to the condition of a multiply responding plant. merely. It then responds by a single response to moderate, and by multiple responses to strong, stimulus. When the energy imparted by strong stimulus is exhausted, these multiple responses come to a stop, to be once more renewed, on a fresh accession of strong stimulus. Or a lateral leaflet of Desmodium, originally quiescent, may be put into, and maintained in, a state of pulsation by the action of sunlight. It is from the stored-up energy derived from _ its surroundings that the tonic condition of the plant is so raised as to maintain its so-called autonomous activity. From this it will be seen that, strictly speaking, there is no such thing as automatism. Movement can only be produced by the immediate action of stimulus, or by energy previously absorbed. In recording the autonomous pulsation of the lateral leaflets of Desmodium gyrans, it is found that while the down-movement brought about by the contractile action of the lower half of the pulvinule is very rapid, the up-move- ment due to recovery, and to contraction of the upper half of the organ, is relatively slow. The two alternating excitatory impulses, in the lower and upper halves respec- tively, are in the ratio approximately of 1°5 to 1, This 696 COMPARATIVE ELECTRO-PHYSIOLOGY explains the peculiar electrical responses of Desmodium gyrans, which are concomitant with the autonomous mechanical pulsations of the leaflet. I find that, corre- sponding with one complete mechanical pulsation, there are two electrical pulses. Of these the principal electrical wave coincides with the down-movement of the leaflet, and the smaller with the up. The electro-motive intensity of the principal wave is nearly 1°5 times that of the subsidiary. | In a particular experiment, for example, while the value of the former was ‘0024 volt, that of the latter was, ‘oo16 volt. These electro-motive variations are expressions of funda- mental excitatory effects, and not dependent on the mechanical movement of the leaflets. For when the responding leaflet is physically restrained, the electro-motive responses exhibit even greater intensity than before. This will be seen in the simultaneous records of mechanical and electrical pulsations given in fig. 145. An important subject of inquiry lay in the accurate determination of the death-point. This investigation afforded striking demonstration of the fact that it is a single excitatory reaction which is expressed in different ways under different modes of record. It has been shown that when the experimental tissue is subjected to a gradual rise of temperature, there is a definite point at which an excitatory spasm occurs, marking the initiation of death. If a continuous record be taken of the concomitant variation of length, increasing expansion is found to be converted at this point into a sudden contraction. In an anisotropic organ like the pulvinus of Mzmosa the erectile movement of the leaf is abruptly transformed into one of fall. A curled tendril exhibits at this point a sudden uncurling. Taking, again, the electro-motive method of record for the detection of the death-point, the increasing positivity of .the specimen is spasmodically reversed to negativity. Finally, on employing for the record the method of resistivity variation the increasing is seen to become suddenly changed into a diminishing resistance. It is found,. how- OS ae ee ee ae oe a ee ee ie REVIEW OF RESPONSE OF ISOTROPIC ORGANS 697 — ever, employing numerous specimens, that these mechanical and electrical spasms take place, under normal conditions, at the same point. In the case of phanerogamous plants, this is found to be at or very near 60° C. (figs, 328, 329, 330). That these mechanical and electrical spasms, further, constitute a true case of excitatory response, is proved by the fact that induced physiological depression also induces depression of the death-point. Fatigue may thus lower the death-point by as much as 19° C. : The response of contraction, initiated at the death-point, is later converted into fost-mortem relaxation, and galvano- metrically the negativity initiated at the same moment becomes subsequently a post-mortem positivity. With regard to the so-called Current of Injury it. was shown that this arises as the after-effect of strong stimulus. It should be remembered that a cut, or the application of a heated wire, constituting mechanical and thermal sections respectively, will act as a strong stimulus, and, further, that the after-effect of excitatory galvanometric. negativity is persistent when the stimulus is strong.. The excitatory effect, moreover, is transmitted from the point of application to greater or less distances, according to the strength of stimulus and the conductivity of the tissue. As this trans- mitted effect undergoes diminution with distance, it is obvious that the most intense negativity will be induced at the point of section, undergoing a gradual diminution as we move further away from it. If, taking a given length of isotropic tissue, we make two opposite terminal sections, we shall clearly have a symmetrical. distribution of electrical potential as regards the middle or equatorial zone, the two ends being most negative, while the equator is relatively most positive (fig. 110). . Two points symmetrically situated as regards this equator would thus be equi-potential, while a-symmetrical points would show appropriate differences of potential, a zone near the equator being relatively positive to one which is further away from it, or nearer to the terminal section. These considerations, supported as they 698 © COMPARATIVE ELECTRO-PHYSIOLOGY are by experimental results, account satisfactorily for the particular electrical distribution in a muscle-cylinder. It is often supposed that dead tissue is negative to living. But I have shown that this is not the case, the dead being actually positive to the living. It has already been mentioned, in connection with experiments described, on the mechanical and electrical spasms of death, that at the initiation of death, a tissue exhibits excitatory con-. traction and negativity, while the post-mortem effect is one of relaxation and positivity. This explains the peculiar electrical distribution which I have observed, in the explora- tion of tissues, of which some parts were dead, others dying, and still others, again, fully alive. It was there shown (figs. 113, 115) that the greatest negativity occurred on the death-frontier. Proceeding in either direction from this point, whether towards the living or towards the dead, it is found that these points are increasingly positive, or decreasingly negative. But the maximum positivity of the dead portion is greater than that of the living. From this it is clear that the dead is positive to the living. From these facts, that the dying is negativé, and the dead relatively positive to the living, it is clear that the so-called current of injury is liable to reversal. In the case of the former, the current of injury will be from the dying to the living; in the latter, from the living to the dead. This demonstration of the occurrence of a hitherto unsuspected reversal, demonstrates to us the possibility of many complications, and wrong theoretical inferences, For response by the negative variation of the current of injury is usually taken as the concomitant of the chemical process of dissimilation, while the positive variation is held to be associated with assimilation. Now, by the reversal of the so-called current of injury, one identical excitatory reaction may be made to appear, now as a negative, and again as a positive variation. This is. sufficient to indicate the unreliability of the so-called Method of Negative Variation, ane. tae a Orr ee ee A Se Eee SUAS Io ate fi arses eS ES SNR NY A A I NE A AR RR rT _ * Te a REVIEW OF RESPONSE OF ISOTROPIC ORGANS 699 _ an unreliability of which we shall further meet with many glaring instances. Pe ; An assumption more or less current is, that in order to obtain response, there must be an antecedent current, by whose negative variation it can be detected. Hence the supposed necessity of a current of injury prior to response. The real reason, however, for thus injuring one of the contacts is so to depress its excitability that, on diffuse stimulation, the excitatory response of the uninjured may remain unbalanced, and therefore unannulled. That it is this depression of excitability, and not the current of injury as such, which is the essential condition for obtaining resultant response, is seen from the fact that excitatory response may still be obtained, even when the so-called current of injury is zero, or reversed positive (fig. 116). CHAPTER XLVII REVIEW OF RESPONSE OF ANISOTROPIC ORGANS Anisotropic organs—Laws of response in anisotropic organs—Natural current of rest and current of response— Reversal of natural current of rest-—Unreliability of positive and negative variations of current of rest-—Determination of the differential excitability of a tissue—Resultant response of skin due to induced stronger negativity of inner surface and feebler negativity (tomato skin) or positivity (skins of grape and frog) of outer—Response of intact human skin — Response of intact human lip—High excitability of secretory and glandular surfaces—Response of glandular foot of snail—Response of intact human tongue—Response of digestive organs—Phasic alternations of secretion and absorption—Multiple response of digestive organs—Phasic changes induced by previous activity—Response of digestive organs of Mepenthe and Drosera —Electro-motive peculiarities of skin and mucous coat of stomach not similar —Normal response by galvanometric negativity in mucous coat of stomach of frog, gecko, and tortoise— The root as a digestive organ—Excitatory secretion and galvanometric negativity of young roots—Phasic alternations of secretion and absorption — Cognate subject of ascent of sap—.Sap-wood not really dead— Proofs of physiological character of suctional response—Water-movement a mode of excitatory response—Response of electrical organs—Two types, Torpedo and Malepterurus—Vegetal analogues to electric plates of two types, Torpedo and Malepterurus, in Pterospermum and pitcher of MWepenthe—- Multiple character of response of electric organs—Response of electrical organs constitutes an extreme case of differential excitability of anisotropic structures--Similar effects with inorganic structures—Excitatory effect of light on plant tissues—Phasic alternations—Initiation of multiple and autono- mous response by light—Three types of direct and after-effects—Response of retina like, and not different from, that of other tissues—Error introduced by method of negative variation—Multiple responses in retina and their visual correspondences —Binocular Alternation of Vision—Three types of direct and after-effects in retina under light—Geo-electric response. I SHALL next pass in review another class of phenomena, the want of a clear understanding of which is at the root of many supposed anomalies in the response of animal tissues. I allude to the natural anisotropy, with consequent differential excitability, of various organs, i re REVIEW OF RESPONSE OF ANISOTROPIC ORGANS /7oT ~ _ As an example of a differentially excitable organ we may take the pulvinus of J/tmosa, in which the lower half is more excitable than the upper. In this case, strictly localised stimulation of either the upper or the lower evokes con- traction and galvanometric negativity of that particular half, the effect in the lower half being the greater. But if the stimulus be diffused, whether internally or externally, the response will be differential, by the greater contraction or galvanometric negativity of the more excitable. From this we arrive at the general law of the electrical response of anisotropic organs. 1. On simultaneous excitation of two points A and B, the responsive current flows in the tissue from the more to the less ~ excited. 2. Conversely, if under simultaneous excitation, the responsive current be from B to A, B is the more excitable of these two points. The second of these two laws enables us to determine the relative excitabilities of any two points. As a simple example of the anisotropy induced in a tissue by the unequal action of the natural stimuli of the enviroment, we may take a tubular organ, such as the hollow peduncle of Uriclis lily. Here the exposed outer surface, constantly subjected to external stimuli such as light, becomes as it were fatigued, and reduced in excitability. Other histological modifications follow on this, the external cells becoming thus cuticularised and protoplasmically defective. Owing to the depression of excitability on this epidermal surface, the intensity of its normal excitatory change by galvanometric negativity is decreased, a change which, in the case of certain skins, culminates in responsive positivity. The inner surface of the hollow peduncle, which may be regarded as epithelial, being, on the other hand, protected, remains normally excitable and is thus more so than the outer surface. The outer sur- face, however, probably by reason of the action of the external stimuli to which it is constantly exposed, is naturally negative, relatively to the protected and more excitable inner 702 COMPARATIVE ELECTRO-PHYSIOLOGY surface. And it will generally be found true that while this natural cnrrent of rest is from the less excitable A to the more excitable B, the current of response, on the other hand, which occurs on excitation, is from the potentially more excitable, and therefore now more excited B, to the less excitable and therefore less excited A. Such is the course of events in the normal or primary condition. But under the excitation due to preparation, or - accidental disturbance, the more excitable surface becomes the more excited, and relatively to the other, galvanometri- cally negative. In consequence of this, the natural current is reversed, and we have a resting-current due to the after- effect of injury or accidental excitation, flowing from the more to the less excitable. Thus, while the natural current, in the primary condition, was from the less excitable A to the more excitable A, that is to say, A > B, this reversed current of rest, due to accidental excitation or injury, is from B->A. Even now, however, & may be more excitable than- A, hence fresh stimulation will induce a responsive current from B to A. In the primary condition, such a responsive current would have appeared as a negative varia- tion of the natural current AZ. But when the primary condition has been so modified that the natural current is reversed, and has become B-A, the normal responsive current B-+A will appear as a positive variation. Still another variation is possible, when the normal response itself undergoes reversal owing to fatigue, under which condition this abnormal response, relatively to the reversed current of rest, appears as if it were the normal negative variation (fig. 119). It has, however, been shown that if we discard this unreliable test of response, by the variation induced in an antecedent current of rest—the so-called negative varia- tion—it will be found that the responsive current always flows from the more to the less excited. In order to determine which of two points in an anisotropic tissue is the more excitable, it is necessary, as now under- stood, to determine the direction of resultant response, under REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 703 stimulation which is equal and simultaneous. In order to do this, we may employ such a non-electrical form of stimu- lation as the mechanical or the thermal. For this it is possible to employ (1) the Vibratory Stimulator; (2) the Rotary Mechanical Stimulator ; or (3) stimulation by thermal shocks. When results are obtained according to these methods, there can be no uncertainty as to those compli- cations of effects which might conceivably arise when the electrical form of stimulus is employed. The last-named may, however, be used without misgiving, when stimu- lation is effected by equi-alternating shocks, The ordinary Ruhmkorff’s make- and break-shocks are not suitable for this purpose, inasmuch as the effective intensity is unequa] for make and break, besides which the polarisation-effect may not be exactly neutralised. The equi-alternating shocks, from which these defects have been eliminated, are obtained by means of (1) a rotary reverser in the primary coil (fig. 170), or (2) a motor-dynamo (fig. 172). The responses again, under these electrical forms of stimulation, may be photo- graphically recorded as either the direct or the after-effect of stimulus. It was shown, by the employment of all these various methods of stimulus, mechanical, thermal, and elec- trical, that the responsive current to be obtained with an anisotropic organ was definite in direction, being always, under normal conditions, from the more excitable B to the less excitable A. I shall now proceed to recapitulate briefly the results obtained by these methods in various cases of anisotropic tissues, such as skin, epithelium, glands, animal, and vegetal digestive organs, and electric organs generally. Taking first the skin of tomato it has been shown that the separate responses of the outer and inner surfaces are unequal. The outer, owing to cellular modification under the stimuli of the environment, gives only a feeble negative response, whereas the internal surface gives a much stronger normal response by galvanometric negativity. On simul- taneous excitation of both inner and outer surfaces, the responsive current is found to flow from the inner to the 704 ~ COMPARATIVE ELECTRO-PHYSIOLOGY outer. Here the resultant’ current’ is ‘brought about~ by the difference between the stronger responsive negativity of the inner, and the feebler responsive negativity of the outer surface, which © may be represented as” 4 With certain specimens of tomato skin, however, the modification of the outer surface is so great that its individual response is reversed to positive, that of the inner being the normal strong negative. The resultant response, then, is still from inner to outer, but equals the summated effect of the two ne From this we pass to the response of grape-skin, which resembles the latter of these two cases. The response of the skin of frog is also of this type, and it may be said of skins in general that their response is from the. more excitable inner surface to the less excitable outer. This conclusion has been verified by experiments on various skins, both vegetable and animal. Among the latter of these may be mentioned the skin of the neck-of tortoise, and that from various parts of the body of gecko.- When the skin is isolated with very great care, so as to reduce to a minimum the excitatory effect of preparation, it is found-that the natural current of rest is from the less excitable outer to the more excitable inner surface; the excitatory current being in,the opposite direction. Owing to the excitatory effect of preparation; the current of rest of the skin of tortoise-was found reversed. The responsive current, however, was found to flow from inner to outer, thus proving that the inner surface was the more excitable. In illustration of the great practicability of the methods employed, I may refer to the photographic records obtained of the response of the skin of the intact human forefinger (fig. 180). . In describing the differential excitability of the hollow peduncle of Uviclts lily, it was shown that protected surfaces are, as a rule, more excitable than those which are exposed, and have thus undergone a greater degree of modification. On taking the plagiotropic stem of Cucurbita, the lower surface of which is protected from light, it is. found that, apt peiy a SS ee |) h6U lee Le ee ee ae oe REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 705 while the current of rest flows from the exposed upper to the protected lower surface, the direction of the responsive current is opposite, namely from the lower to the upper, proving that the protected lower is the more excitable of the two. Similarly, in the case of the intact human lip, I found that the resting current was from the epidermal to the epithelial, the responsive current being in the opposite direction (fig. 196). . Again, on testing the differential response of armpit and shoulder, I found that the respon- sive current was from armpit to shoulder, the former being thus the more excitable of the two (fig. 194). We have seen that the lining membrane of the inner surface of the peduncle of Uvric/zs lily is very thin, and that, in distinction to the outer or epidermal membrane, it may be regarded as epithelial. As we approach the bulb-end of the peduncle, this inner layer of cells is found to be highly turgid, and secretion is found to take place into the hollow tube. The inner surface of the carpellary leaf of Dzllenta indica, again, secretes a mucilaginous substance. In these two cases there are no definite glands, But definite glands are found to occur on the inside of the pitcher of Wepenthe. In all these cases the secreting layer, whether provided with glands or not, is found to be very highly excitable, and to respond by strong galvanometric negativity. Taking a carpel of Ditllenia indica, it is found that the natural current is from the outer epidermal to the inner secreting surface, the respon- sive current being in the opposite direction. On making very careful connections, with the skin of the protruded body of the snail, and the glandular under-surface of its foot, it is found that the natural current is from the non-glandular to the glandular, but the responsive current from glandular to non-glandular. As an example of the way in which the true natural current of rest may be reversed by the excitatory effect of preparation, I showed that, while in the intact snail the natural current was from non-glandular to glandular— the gland being in this case relatively positive, to the extent of -0013 volt—after the sectioning of the foot, the original ZZ 706 COMPARATIVE ELECTRO-PHYSIOLOGY natural current was reversed, owing to the greater relative excitation induced at the glandular surface, which now became relatively negative, to the extent of —-‘0020 volt. With the intact human tongue, further, I found that a very strong responsive current was induced on excitation, from the lower to the upper surface, thus showing that the lower was the more excitable of the two. The response of digestive organs may now be passed in review. In these, as in glandular organs, excitatory response is supposed to take place by secretion. In connection with this, it must be borne in mind that in the tissue of the pulvinus of J/zmosa, on the removal of the impervious skin, excitation induces secretion of the contained fluid, which, again, is re-absorbed on the cessation of excitation. We know the pulvinus to be contractile, and may therefore regard this secretion as an effect of contraction, causing expulsion of water. Apart from the differential action of the upper and lower halves of the organ, and the magnifying petiolar index, the fundamental contractile action would, in the case of J/zmosa, as in others, have passed unnoticed. This goes to show that it is not impossible that the phe- - nomenon of secretion through a permeable membrane may be associated with excitatory contraction. In favour of such continuity, it may be urged that tissues, hitherto regarded as non-motile, have been shown to exhibit excitatory contrac- tion. In digestion, as a whole, we have to recognise two different processes, those, namely, of secretion, and of sub- sequent absorption. Parallel to these, we find that the electrical response of digestive organs exhibits phasic alter- nations of negativity and positivity. It was shown that the pitcher of Wepenthe—which may be regarded as an open stomach—affords us unique facilities for the observation of the normal responses of digestive organs. In experimenting with the animal stomach, the specimen has to be cut open, in order to make the necessary connections ; and, owing to the highly excitable character of the organ, this gives rise to intense excitatory action, the REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 707 | after-effect of which is necessarily to reverse the normal current of rest, With a pitcher of Mepenthe in a fresh condition, the natural current of rest is from the outer to the inner, the responsive current being in the opposite direction, and the glandular surface, on simultaneous exci- tation of the two, becoming galvanometrically negative (fig. 203). Digestive organs, moreover, tend to -exhibit multiple responses, the response to a single strong stimulus, say thermal, or of mechanical section, consisting, whether in animal or vegetable organs, of a series that may persist for nearly an hour (figs. 206, 209, and 213), When the pitcher of Nepenthe contains a large number of captured flies, that is to say, when it has been subjected to long-continued stimu- lation, it exhibits a phasic change, the responses now becoming reversed to positive (fig. 205). This, as pointed out above, is probably significant of absorption. In Drosera, the normal response of the glandular surface is by induced negativity, but on long-continued stimulation, this is reversed to positivity (fig. 208). In the animal stomach, the sine current of rest is generally from the glandular to the non-glandular surface. From the fact that the skin of the toad, which is also possessed of imbedded glands, gives a current of rest from the outer surface to the inner, it has been supposed that the mucous coat of the stomach of the frog had the same electro- motive reaction as its outer skin, That this, however, is not the case is seen from the fact that on excitation the skin becomes galvanometrically positive, while the mucous mem- brane of the stomach becomes galvanometrically negative. The observed current of rest in the stomach would appear, from WVepenthe, to be, not the natural current of rest, but the reversed current, due to the excitatory effect of preparation. The normal effect of excitation in the stomach, I uniformly find, in such different instances as frog, gecko, and tortoise, to be by galvanometric negativity of the mucous surface (figs. 210, 211, and 212). On applying a strong thermal stimulus to the stomach of frog, I obtained an interesting series of ZZ2 708 COMPARATIVE ELECTRO-PHYSIOLOGY responses, of which the first were negative, the second part diphasic, and the last portion reversed positive (fig. 213). Looking at the phenomenon of digestion, we see that it consists first of a secretory process, by which certain solid substances are dissolved, and secondly of the absorption of these dissolved substances. Similar functions are subserved in vegetable life by the root, by which solid inorganic food- materials are first dissolved by secreted acids, and then absorbed. The proof of the former is seen in the well- known corrosion-figures produced by growing rootlets on a marble surface. I have also been able to demonstrate the phenomenon of excitatory secretion in young roots by allow- ing them to absorb dilute salt solution, and then under exci- tation to secrete it into highly dilute silver nitrate solution: This last was attended by the visible formation of a white precipitate. The electrical response of young roots of Colocasia, moreover, I found to be by induced galvanometric negativity (fig. 214), which, under long-continued stimulation, was apt to show reversal to positivity. The older roots, on the other hand, under the same intensity of stimulation, gave response by galvanometric positivity (fig. 215). The former of these responses, there is every reason to believe, is as- sociated with secretion, and the latter with absorption. This question of the absorption of inorganic food materials by the plant is naturally connected with the subject of the Ascent of Sap, which is regarded as one of the most difficult problems in plant physiology. The non-physiological theories advanced are admittedly inadequate to the explanation of this phenomenon. That the ascent, nevertheless, could not be due to physiological action was held to have been proved by the facts (1) that water-conduction takes place pre- ferentially through sap-wood, assumed to be dead ; and (2) that poisonous solutions, such as would kill a living tissue, have been found to be transported through the roots, or the cut ends of their trunks, to the tops of trees. I have, however, been able to show that these objections are not valid. For in the first place, the supposed dead me PET, mer ae ee a ed aa eee ee se ee ee i % REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 709 | wood, concerned in the transport of sap, through the trunks of trees, can be proved, by electrical tests, to be fully alive. This living wood responds to stimulation by in- duced galvanometric negativity, such response disappearing on the death of the tissue, as, say by drying, after which it cannot be restored. The response of living wood is also depressed by anesthetics, and abolished by poisons (figs. 216, 217). As regards the argument based on the transport of poison, it has been shown that as the active elements concerned in the transport of sap are diffused throughout the length of the trunk, the death of one indi- vidual zone, to which the poison has ascended, does not abolish the suctional activity of the zone above. It is only when the plant has been killed throughout, by the arrival of the solution at its top, that the complete arrest of suction could be expected to take place. And this is found to be the case. Various agents, on the other hand, which are known to induce changes, whether of exaltation or depres- sion, in the physiological activity, are found to induce corre- sponding modifications in the rate of suction. A very delicate means of investigating this question has been shown to be that afforded by the records obtained with the Shoshungraph (fig. 218). Here, under the ordinary method of record, the slope of the curve indicates the normal rate of suction, and the effect of various agencies is immediately shown by the resulting flexure of the curve. This method of record, again, becomes extremely sensitive, when it is carried out under balanced conditions. By means of these records, it has been shown that depressing agents, such as cold or anesthetics, depress or arrest suction, whereas warmth exalts it. It has been shown, further, that just as the multiple activity of the Desmodium leaflet is arrested, when the latent energy of the plant falls below par, so also, under similar circumstances, the suctional activity falls into abeyance, and that, as in the one case, so also in the other, the activity is renewed, by the application of an external stimulus. It has also been shown that the latent 710 COMPARATIVE ELECTRO-PHYSIOLOGY period which elapses, before the initiation of this responsive variation to external stimulus, is longer when the plant is in a sub-tonic condition than in the same plant when its tonic condition has been slightly raised by previous stimulation. Crucial experiments, finally, have been described, showing that water-movement is a mode of excitatory response. A difficult problem in connection with electrical response is that of the discharge from the electrical organs of certain . fishes. In a large number of cases, of which Torpedo may be taken as the type, the discharge takes place in a direction from the anterior or nervous to the posterior and non- nervous surface. Pacini’s generalisation that the responsive discharge is always from the anterior to the posterior surface is negatived by the instance of Malepterurus, in which it is from the modified glandular posterior to the anterior surface. Another peculiarity of the response of electric organs in general is that the responsive current is always in the same direction—that, namely, of the organ-discharge — whether the exciting shock be homo- or hetero-dromous. No theory has yet been found which will fully explain all these peculiarities. I have shown, however, that this phenomenon is not alone of its kind ; nor is it dependent on any specific characteristic of the animal nerve-and-muscle, or gland, of which different electric organs are modifications. The response of the electric organ simply constitutes an extreme case of differential excitability, and follows the general law of response in anisotropic organs—namely, that on diffuse stimulation the responsive current flows from the more to the less excitable. The peculiarity of the organ simply depends upon the fact that owing to the serial arrangement of its elementary aniso- tropic plates the terminal electro-motive effect becomes very large by summation. We find vegetal analogues to the two types of electrical plates of Zorpedo and Malepterurus, in the leaves of Pterospermum, and the pitcher.of Vepenthe. In the first of these, Pzerospermum, as in Torpedo, the anterior nervous surface is relatively more excitable than the mass REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 7II of indifferent tissue on the posterior surface. Hence the current of response is from the more excitable anterior to the less excitable posterior. In the second type—the pitcher of Nepenthe and the electrical plates of Malepterurus—the posterior surface being glandular and therefore exceptionally excitable, the responsive current is from posterior to anterior. In taking rheotomic observations on the response to electrical stimulation in various anisotropic leaves—virtually acting, as has been shown, like electrical plates—it was found that in sluggish specimens the maximum electro-motive value was attained ‘2 second after the exciting shock. This was also the value of the period which elapsed after the applica- _tion of moderate mechanical stimulation. With vigorous specimens, however, such as the leaves of Vymphea alba, the maximum effect was attained in a much shorter time, that is to say, in about ‘03 second. In the electrical organ of Yorpedo the corresponding period has been found to be ‘o1 second. The response of electrical organs is found to be repeated or multiple. In the rheotomic records obtained with leaves, further, the multiple apices of the curve show that the response of vegetable organs also has this multiple character Multiple response, however, is not the peculiar characteristic of the electrical organ, but has been shown to take place in various kinds of animal and vegetable tissues. Again, that this peculiarity—of definitely uni-directioned response, whether the excitation be homodromous or hetero- dromous—is not distinctive of life, with its specific powers of assimilation and dissimilation, but of anisotropy in general, with its consequent differential excitability, was shown by the fact that similar uni-directioned responses to homo- or hetero-dromous shocks were given by an inorganic structure, consisting of prepared lead (fig. 167). We have next to pass in review the question of the response of plant and animal tissue to stimulus of light The various motile responses, induced by light in plants, are so diverse and so apparently incapable of being explained by any single reaction of fundamental excitation, that it 712 COMPARATIVE ELECTRO-PHYSIOLOGY was thought that the effect of this stimulus was different in different cases, the specific reaction in each organ being determined by the ultimate advantage of the plant. But I have been able to show that the excitatory effect of light is normal and like that of any other form of stimulus. The various results induced by it depend, first, on the question whether stimulus has remained localised at the point of application, or been transmitted to distant areas. The effect | is thus modified by the intensity of the stimulus and the conductivity of the tissue. These results, however, may be further modified by the differential excitability of the organ. Here, as in other cases of stimulation, the general rule holds good that response is by greater contraction and galvano- metric negativity of the more excited. As a concrete example may be mentioned the case of the pulvinus of MW/zmosa, when the upper surface alone is subjected to the stimulus of light. Here, owing to local excitatory contraction of the upper, the expelled water reaches the lower half of the pulvinus and induces there the hydro-positive effect of expansion, both of these effects conspiring, in this first stage of response, to erect: the leaf. The electrical variation at the lower half is here, then, found to be positive. But as the excitatory effect itself is gradually conducted to the lower half, it induces there an increasing contraction. The mechanical response is now therefore reversed, from one of erection to one of depression, the electrical variation of the lower half of the pulvinus undergoing at the same time a corresponding change from positivity to negativity (fig. 237). From this experiment it is clear that the electrical response under light exhibits the same stimulatory changes which are also visibly demonstrated by mechanical response. We see, moreover, from this experiment that light in general acts as a moderate stimulus. For while mechanical or thermal stimulus induces a sudden collapse of the leaf of AZzmosa, the application of light brings about only a gradual fall. Owing to this moderateness of the stimulus of light, and to the fact that its application is strictly local, it is easy to eet ne ox eel i's SS att. Pe Tae ee aS ee ee ee ee ee gree ee REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 713 understand the possibility of certain modifications occurring in the response. Thus, in highly excitable and conducting tissues, the responses will be by galvanometric negativity, and the state of excitation will be conducted to a certain distance. But we have seen that in tissues which are not highly excitable, stimulus, falling below the excitatory value, gives rise to positive response. Thus, under the action of light, we obtain in plants two types of response, negative and positive. Moreover, under continuous stimulation of light, these may undergo phasic alternations (— + — +) or (+ — +.—). Asan example of negative response to direct or transmitted stimulation of light may be seen the response of Bryophyllum (fig. 238), the positive response being exem- plified in the record obtained with a petiole of cauliflower (fig. 240). It has been explained how these alternating phasic responses lead us to the phenomenon of multiple and autonomous response. | A leaflet of Bzophytum, or a Desmodium \eaflet in a state of standstill, under the continuous action of strong light, will exhibit multiple mechanical responses. The corresponding multiple electrical responses are seen in the response of the lamina of Bryophylum under the action of continuous light (fig. 242). It has also been shown that these phasic alterna- tions are brought about by the fact that the antagonistic elements in the response become effectively predominant by turns. Either of these antagonistic factors may be unmasked more effectively by the arrest of external stimulus at a particular phasic maximum, Thus, in the case where the normal alternation is (— + -— +), if the stimulus be sud- denly withdrawn at the end of the second phase, or positive maximum, the response overshoots in the positive direction (figs. 243, 244). The characteristic direct and after-effects in this Type I., then, during the application of light and its remoyal are ((— + +). In specimens whose characteristic response under continuous stimulation is (+ — + —), if stimulus be again withdrawn at the end of the second 714 COMPARATIVE ELECTRO-PHYSIOLOGY phase—here negative maximum—the response overshoots in the negative direction (figs. 245, 247). The direct and after-effects in this Type III., therefore, may be represented by the formula (+ —...). Between these two extremes lie instances of an intermediate Type II., which has cases (a) and (6), according as the stimulus is removed at maximum of the first or negative phase, or at maximum of the second or positive phase. The formula of Type II. (a) is thus (— + «.), while that of Type II. (0) is(—... ). The response of the retina furnishes us with the most striking examples of the action of stimulus of light. The true character of this response has been supposed hitherto to be unlike that of other tissues, for while excited nerve and muscle were said to show response by ‘ negative variation, the response of the retina was referred to as by ‘ positive variation.’ This furnishes us with an instance of the confusion which is apt to result from making the so-called resting-current the standard of reference. On testing for the natural current, by making connections with the longitudinal surface of the optic nerve, and with the cornea, in an undetached eyeball of frog, I found that it flowed from the cornea to the nerve. But when the eye is detached, by section of the optic nerve, the after-effect of excitation on the more excitable nerve reverses this current, the nerve becoming relatively galvanometrically negative. The normal effect of transmitted excitation from the retina would now make the nerve still more galvanometrically negative, and this would appear as a positive variation of the reversed natural current. Hence, the responsive positive variation, met with in the eye under light, is in reality the same normal excitatory response, by galvanometric negativity, with which we are already familiar. I have also shown, by means of equi-alternating electric shocks, that under normal conditions the optic nerve is more. excitable than the cornea, and that the retina is more excitable than the optic nerve. The eyeball and retina have often been found by different observers to exhibit pinot Aided ser sommes ee ee ee ed a REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 715 abnormal or reversed response. Now, with regard to reversed response in general I have shown it to be due to either of two different conditions which hold good for all responding tissues. These are in the first place sub-tonicity, and secondly, fatigue. The abnormal response caused by the first has been shown to be converted into normal, in the case of the retina, by the action of an agent which enhanced the excitability. Another phenomenon which I discovered in the response of retina was that of multiple response, induced by the application of strong or of continuous stimulation. These multiple responses have visual correspondences in the multiple after-images seen in the retina, and in the visual fluctuations which occur under the constant stimulus of light. The latter of these facts was demonstrated by a specially devised stereoscope (p. 432). In this connection may be mentioned the interesting phenomenon of Binocular Alternation of Vision. 3 The various types of direct and after-effects observed in vegetable tissues under light I find to have their close correspondences in the responses of the retina. Just as in the highly excitable lamina of Bryophyllum, constituting Type I., we have the formula of (— + -i-), so also, in the highly excitable retina of Ophzocephalus, the same sequences of direct and after-effects is observed. In less highly excitable vegetable tissues, such as the petiole of cauli- flower, affording us Type III., the sequence was shown to be (+ —...). In correspondence with this may be mentioned the response of the isolated retina of fish, observed by Kiihne and Steiner. In this case, as the effect of isolation, the retina must have become sub-tonic, which supposition is borne out by the fact that its response to the immediate action of light was abnormal positive instead of negative. I found a similar sequence to occur in an isolated sub-tonic retina of Ophiocephalus (figs. 260, 261). Finally, in somewhat fatigued specimens, an intermediate Type II. was found, in which the sequence was (— + ...) 716 - COMPARATIVE ELECTRO-PHYSIOLOGY or (—...). Examples of these are afforded by the eye of the frog. These correspondences, between the effects of light in vegetable tissues and in the retina, will be clearly understood from the series of figs. 253 to 261. The next subject to be summarised is that of the electrical response of plants to gravitational stimulus. In an apogeotropic organ like the stem, when laid horizontally, the mechanical response is such as to make the shoot once more vertical. The active factor in this curvature might obviously be, either the responsive contraction of the upper side, or the responsive expansion of the lower. The question to be decided here was whether the response of the plant, to geotropic stimulus, was or was not of the same nature as its response to other effective forms of stimulation—that is to say, by excitatory contraction. An experiment has been described (p. 436) in which this question was subjected to tests. The local application of cold is known to bring about the temporary abolition of the excitatory effect, and in the present case, its application on the lower side of a horizontally laid shoot was not seen to induce any effect on the response, while, when applied on the upper, it retarded - and arrested response to gravitation. This shows that in this response it is the contraction of the upper side which is the active factor. This is independently verified by the test of electrical response, where I find that the upper side, when subjected to gravitational stimulus, exhibits the sign of true excitation—namely, by induced galvanometric negativity. The important Theory of Statoliths offers us a suggestive explanation of the manner in which gravity exercises stimu- lation upon the responding tissue, by the weight of solid particles. When the stem is vertical, in consequence of the symmetry of distribution of the particles on all sides, there is no resultant action; and as soon as this symmetry is disturbed by laying the stem horizontally, response might be expected to be initiated. This, however, is not the case. The shoot first bends down, and it is not until after the is on REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 717 expiration of nearly three-quarters of an hour that the first sign of apogeotropic action appears. This anomaly is probably due to the induced mechanical curvature caused by weight which has first to be overcome. We may, however, regard ourselves as independent of the mechanical indications, when recording the effect of gravitational stimulus by geo-electric response. The excitatory electric effect, as we have seen in other cases, takes place as before, when all responsive mechanical indications are restrained. Proceeding on this principle, therefore, I found that the geo-electric response was initiated within so short a time of subjecting the specimen to gravi- tational stimulus as one minute (fig. 271). This experiment shows of what widespread application is the electrical mode of detecting the excitatory response of tissues, to many different forms of stimulus, CHAPTER XLVIII REVIEW OF RESPONSE OF NERVE AND RELATED PSYCHOLOGICAL PHENOMENA Transmission of excitation in plants—Vegetal nerve—Similar variations of receptivity, conductivity, and responsivity, under parallel conditions in plant and animal nerves—Conductivity balance—After-effect of section on con- ductivity and excitability—Function of vegetal nerve in plant-economy— Laminz of plant form a catchment-basin for stimulus—Motile response of nerve— Molecular cycle and characteristic changes in response of nerve— Effect of fatigue on transmitted excitation—Similarity of excitatory molecular changes in both afferent and efferent nerves—Multiple response induced by strong stimulus in nerve—Multiple excitations in nerve during drying — Individual contractile responses to constituent tetanising shocks—Negative after-effect on abrupt cessation of tetanisation—Extra-polar effects similar in plant and animal nerve —Inadequacy of Pfliiger’s Law— Under feeble E.M.F. excitability enhanced by anode and depressed by kathode—Demonstration by subjective response—Under feeble current excitation travels better against than with it—Response by variation of electrotonic current due to algebraical superposition of excitatory effect—Physico-physiological basis of sensation— Identification of positive tone of sensation with hydro-positive wave and negative tone of sensation with negative wave—Natural and artificial induc- tion of dissociation of sensation—Physical explanation of Weber-Fechner’s — Law—Quality of sensation also a factor—Conversion from painful to pleasur- ‘able and vice versa at will by electrotonus—Memory as an after-effect of stimulus—-Persistent after-sensation— Revival of latent memory-image through differential excitation induced by diffuse stimulation—-Same effects demon- strated in the inorganic. THE next subject to be reviewed is that of the conduction of stimulus. It has been supposed that plants do not con- duct excitation by the transmission of protoplasmic changes, as certain animal tissues are known to do. Even in the well- known case of Mimosa, where stimulus is seen to induce move- ment at a distance, this was supposed to be the result of hy- dro-mechanical disturbance. This conclusion has been shown, however, to be erroneous, for pure hydrostatic disturbance Pa RESPONSE OF NERVE 719 has been proved to occasion an erectile movement of the leaf with galvanometric positivity (figs. 44, 45, and 46). The transmission of true excitation, on the other hand, gives rise to a fall of the leaf and the electrical response of galvano- metric negativity. Again, the transmission of excitation in the plant is modified similarly by those varying physiological conditions- which influence it in the case of the animal. Thus, a strong stimulus is transmitted more quickly, other things being equal, than a feeble. Fatigue, on the other hand, is found to depress the velocity. The application of cold reduces or temporarily abolishes the transmission, while warmth enhances its velocity. Anzsthetics, again, are found to depress conductivity. And lastly, the polar effect of currents, in the plant as in the animal, is to induce opposite changes, according as anode or kathode is applied. I have, moreover, been able to isolate certain tissues specially fitted for the conduction of excitation. These are found in the soft parts of the fibro-vascular bundles, and are particularly easy to isolate in the case of fern. They here possess the relatively high velocity of about 50 mm. per second. It may be said, in view of their peculiar responsive charac- teristics, and the modifications of their response under given conditions, that these structures are indistinguishable from animal nerves, and may therefore be rightly designated vegetal nerves. On isolation, for example, these highly excitable vegetal nerves, like the animal nerve, when isolated, are liable to fall into a state of sub-tonicity, on account of which their conducting power is temporarily impaired. The transmitted effect of stimulus, then, as in the corresponding case of animal nerve, becomes one of abnormal galvano- metric positivity. Continuous stimulation when in this state, however, by carrying the tissue out of the A into the B condition, converts the abnormal positive response into normal negative, through an intermediate diphasic, in the plant as in the animal nerve. When in the B stage, again, tetanisation -has the effect of enhancing response in both, The effects of ether, carbonic acid, alcohol vapour, and 720 COMPARATIVE ELECTRO-PHYSIOLOGY ammonia are the same.in the one case as in the other. The effects of various drugs on the receptivity, conductivity, and responsivity of the vegetal nerve are the same as on those of the animal, and finally, in the action of different salts, the acid and basic moieties exhibit the same characteristic effects in plant and animal nerves alike (Chapters XXXII. and XXXITI.). In order to study the variation of excitatory effects in. nerves I was able to devise a very delicate instrument, the Conductivity Balance: (fig. 291). This apparatus not only enables us to study the modifications of conductivity, excit- ability, and responsivity, induced by a given agent separately, but also to compare relative variations as between any two of these, say, for instance, conductivity against excitability, or receptive excitability against responsivity. It also enables us to compare and contrast the action of two different reagents applied simultaneously in different parts of the same nerve. In this way the factor of uncertainty introduced by the unknown individual differences between two nerves is eliminated. _ The principle on which the Method of Conductivity Balance depends is that of applying stimulus at a point which, in the excitatory sense, is exactly midway between the electrodes E and E’; the excitatory effects at E and E’ exactly balance each other, and the galvanometric deflection is then zero. When the excitability of the right hand, E, or the conductivity of the right arm, C, of the balance is enhanced, the balance is upset and the resultant response is, say, up ; depression, on the other hand, upsets it in the opposite direction. Not only may the effects of various chemical agents be determined by this method, but it is easy also to study by its means the effects of temperature on conductivity. Cold is thus found to depress, and warmth to enhance it (figs. 307, 309). Another important investi- gation carried out by this means was on the curious phenomenon presented by the effect of section in enhancing the excitability of adjacent points. It was shown that this — a Ss re RESPONSE OF NERVE 721 was due to the molecular transformation caused by the stimulus of the mechanical or thermal section. The effect of such stimulus on neighbouring points is to induce moderate . excitation, raising them to the higher excitability of the condition B (fig. 311).. At or very near the section point itself, on account of over-stimulation, the transformation is to condition D or E, and the result should be one of loss of excitability. In accordance with this, it is found that at such points there is depression of excitability (fig. 312). As regards the place of the vegetal nerve in the plant economy, it may be said that the normal excitability of a tissue, by which its proper functions are discharged, can only be maintained fully by a supply of energy, which must be received from the environment. Both animal and vegetal ’ nerves have been shown, when isolated, to lose their normal conductivity and excitability, their response becoming ab- normal or being abolished. It is only by the accession of fresh energy of stimulus that the normal conductivity and excitability are restored. It is known, further, that when the nerve loses its excitability, undergoing consequent degenera- tion, the attached muscle also exhibits rapid decay. It will thus be seen that the various tissues of the organism are maintained in their normal functional activities by means of energy conveyed to them through the nerves. One of the principal forms of energy in maintaining the tonic condition of a green plant is sunlight; when deprived of this, its various normal activities come gradually to a stop, and the plant ultimately dies. But if any portion of the plant be exposed to light even its shaded parts will be found to continue in natural vigour. This is exemplified by the experiment of Sachs, in which an undetached branch of Cucurbita was kept in a dark box, and was found to grow, and produce flowers and fruits, as if under normal conditions. The fact that a plant, when totally deprived of sunlight, dies, shows how essential to its tonic condition is energy of light. The fact that so long as a portion of it is kept in light the whole flourishes, proves the transmission of energy from one 3 A 722 COMPARATIVE ELECTRO-PHYSIOLOGY part to another, a transmission which is now made com- prehensible, being effected through the intervention of the plant-nerves, whose existence I have demonstrated. In the case of trees, again, the interior tissues whose: functions are of great'importance in various ways, are inaccessible to such external energy as that of light. But no part of them:is far removed from the vegetal nerves, whose outer endings are found in the ramified venation of the leaves. The lamine of the plant thus in their aggregation form an extensive catchment-basin for the reception of energy from ‘outside and its ultimate transmission within the plant. An experiment has been described which shows the enhancement of the excitability of the plant-nerve by energy of light (fig. 334). I have next to summarise a new method for the study of’ excitatory reactions in nerves. It has been supposed that in certain respects the reaction of the nerve is specifically different from that of the muscle. It has been regarded as typically non-motile, the highest power of the microscope being incapable, it was said, of detecting any effect in respon- sive change of form. I have shown, however, that this - conclusion was erroneous, there being in this respect a con- tinuity between the responses of muscle and nerve. In a particular case of frog’s nerve the responsive contraction under strong stimulation was as much as 14 per cent. of the original length, and in others, it was as much as 20 per cent. or more. With a magnification of about 200 times, which is afforded by my moderately sensitive Kunchangraph, the observer is able to study all the excitatory phenomena in nerve with as great ease, and much greater accuracy, as by the employment of a very highly sensitive galvanometer. Records of the electrical responses of nerve are obtained by the differential effects of excitation at the two contacts, when one of these has been subjected to injury. It has been shown that such injury does not always completely abolish the excitability of the second contact, for which reason there may be induced a local reaction of feeble negative or reversed RESPONSE OF NERVE 3 723 positive response. The interference of this with the normal response at the uninjured contact is thus apt to give rise to various complications. In contrast with this we have the reliability of the mechanical response of the nerve, in which the effect recorded is direct, and not differential. Again, the electrical form of stimulus, which is almost universally employed for the excitation of nerve, is liable by leakage, unless very great precautions are taken, to vitiate the results obtained by the electrical mode of response. When the response observed, however, is not electrical but mechanical, this source of error is obviously eliminated. } : By means of mechanical response, the molecular trans- formations through which the nerve passes, under the action of stimulus itself, may be observed with the greatest clearness. An isolated nerve, cut off from its natural supply of energy, generally falls into a sub-tonicity indicated in the mechanical record, as an increasing abnormal relaxation; and the application of stimulus induces at this point an abnormal positive response, of sudden expansion. Successive or con- tinuous stimulations, however, transform the nerve from condition A to condition B; the abnormal expansion being arrested and converted into increasing contraction. . During this stage, then, the responses to individual stimuli are trans- formed from the abnormal expansive positive to the normal contractile negative, through an intermediate diphasic. Molecular transformation is here very rapid and the re- sponses show a staircase increase (fig. 382)... An intervening period of tetanisation will now have the effect of enhanc- ing the response (fig. 383). In the clear demonstration thus obtainable of a progressive molecular transformation, with corresponding variations of response at its different stages, we arrive at the true explanation of the change from the abnormal positive to the normal negative, in electrical response, and also of the enhancement of the normal negative after an intervening period of tetanisation (figs. 275-278). The next stage to be reached is C, where the responses are uniform. After this, we arrive at D, where fatigue-decline 3 A 2 724 COMPARATIVE ELECTRO-PHYSIOLOGY begins to make its appearance. Up to this point, the nerve as a whole has been undergoing increasing contraction, the base-line of the series of records being thus tilted upwards. But after D, it begins to show relaxation, and at the stage E, the responses to individual stimuli are actually reversed, the region of transformation from diminishing to reversed response being often marked by the appearance of diphasic (figs. 396 and 400). The entire responsive cycle may thus be viewed as consisting of two halves of which one is the reverse of the other. From the state of extreme sub-tonicity at A with its abnormal positivity, the responses are transformed through diphasic to feeble normal negative at B. They here increase in a staircase manner, till they become uniform at C. After this begins the reversing process, due to fatigue, brought on by overstrain, with its diminishing normal re- sponses at D, through diphasic, to abnormal positive once more,at E. Excessive sub-tonicity and excessive stimulation alike find their extreme case in the abolition of all response at death. The difference between the abnormal positive response of sub-tonicity and the abnormal positive response of fatigue lies in their previous history. The one is due to lack of stimulation and the other to itsexcess. For the restoration of normal response, the treatment in the two cases must be opposite. In the first, the application of stimulus is necessary ; in the second, it is its cessation, or rest, which is required. _ Similar effects are also met with, in the case of trans- mitted excitation. In the sub-tonic condition, conductivity is depressed, and the transmitted effect is abnormal positive. By the action of stimulus, however, the conductivity is gradually restored, and the response to transmitted stimu- lation is converted from abnormal. positive to normal negative through the intermediate diphasic. After this, under increasing fatigue the diminishing responses are con- verted to abnormal positive through an intermediate diphasic (fig. 325). Another important demonstration was that of the perfect similarity of the molecular changes induced by stimulus in the afferent and efferent nerves respectively. RESPONSE OF NERVE 725 The experiments which have just been described were carried out on the efferent gastrocnemius of frog and gecko. With the afferent optical nerves of certain fishes I obtained mechanical responses which were exactly the same as these (figs. 324, 402). That is to say, in a sub-tonic condition the optic nerve gave the abnormal positive or expansive re- sponse, and this was subsequently converted into the normal contractile responses, through an intermediate diphasic. The mechanical response of nerve just described, may be recorded either photographically, by a reflected spot of light, or directly on a smoked-glass surface by means of a writing- point. The difficulties due to friction in the latter case are obviated by the use of the Oscillating Recorder. By means, however, of a battery of levers, and using the optical method of record, it is possible to have a magnification by the Kunchangraph of one hundred thousand times or more, the sensitiveness of the record being correspondingly enhanced. By this means many new phenomena may be brought under observation, one of these being the multiple response induced by strong stimulus in nerve. It is known, again, that nerve becomes highly excitable during the setting-in of ‘drying, and under these conditions, in a nerve-and-muscle preparation, repeated mechanical spasms are exhibited by the attached muscle. In taking the mechanical record of nerve, it is found that the substitution of dry for moist air at once induces a visible contraction. Now this state of partial contraction, bringing the nerve, as it does, into condition B, we know to be significant of enhanced excitability. If the drying of the nerve be now allowed to continue, it is found that there is induced a series of multiple responses (fig. 326). And the multiple spasms seen during drying in the muscle of a muscle-and-nerve preparation undoubtedly have, as one of their factors, these multiple excitations thus demonstrated to take place in the nerve. ; With the highly magnifying Kunchangraph, again, the individual effect of a single shock is demonstrated with the greatest clearness. Under rapidly succeeding tetanising 726 COMPARATIVE .ELECTRO-PHYSIOLOGY shocks, the response shows a serration of the apical line, proving that the individual responses are not completely fused. On the abrupt cessation of tetanising shocks a sudden enhancement of.the contractile effect occurs, followed by the usual recovery. : This is analogous to the sudden enhancement. of response on the cessation of tetanisation, seen in the retina, in magnetic response, and in the response of certain sensitive inorganic preparations under similar circumstances (pp. 536, 428, 383). The next subject to be surveyed is that of electrotonus, and the variations in excitatory effects induced by it. It has been shown that the polarising currents induce extra-polar currents in the plant nerve, exactly as in that of the animal (fig. 338). As regards the effect of electrotonic currents generally on excitability, the results obtained by Bernstein are described as polarisation-decrement, whereas those of Hermann are known as polarisation-increment. That is to say, with one experimental arrangement the induced electrotonic current is seen to undergo a diminution under excitation, and with a different arrangement an. increase. These and other electrotonic variations appear to be very anomalous, and incapable of mutual reconciliation. I have, however, been able to show that all these effects may be regarded as combining the variations of two distinct factors, namely conductivity and excitability, under the influence of an electrical current. One of the principal difficulties in the correct explanation of these phenomena has hitherto lain in the assumption that Pfliiger’s Law, relating to the polar effects of currents, was of universal application. I have shown, however, to the contrary, that it applies only to a certain middle range of electro-motive intensity, the excitatory effect at anode and kathode being, at a very high E.M.F., exactly reversed. Going, again, to the other extreme, of a low electro-motive force, I have shown that, in opposition to Pfliiger’s generalisation, it is the anode that enhances the excitability of a nerve, while the kathode depresses it. This I have been able to demonstrate by a ee ee “pS aa as el Pal a al i ah lt ral a Re ar ON a solr ey, “RESPONSE OF NERVE | 727 numerous experiments (figs. 350 and 353). The fact that under feeble E.M.F. the variation of excitability is opposite to that under moderate E.M.F. can be demonstrated with great simplicity by means of the subjective response of sensation. A wound was made on the back of the hand, and the application of a dilute solution of salt caused a moderate irritation. The application of kathode to this wound now rendered the irritation intolerably painful, while that of the anode at once made it soothing, removing: even the normal discomfort due to the salt. These effects—coming under Pfliiger’s generalisation that kathode enhances excitability, while anode depresses—held good so long as the acting E.M.F. was about 1°5 volt. But when the acting E.M.F. was reduced to ‘5 volt, the kathode was found to induce a soothing sensation, whereas the anode. became painful. I have also found that the passage of a current pro- foundly modifies the conduction of excitation in a directive manner, according as the excitation has to travel with or against it. In the simplest cases, where the polarising elec- trodes are so far apart as to eliminate the direct excitatory effect of the poles, and using a feeble current, I have shown that excitation travels better electrically uphill, that is to say, against the current, than down, or with it. Thus the normal responses to transmitted stimulation are found to be enhanced when the polarising current is against the ‘direction of trans- mission. A polarising current in the same direction as that of excitation, has, on the other hand, the effect of retarding it. The normal responses are then diminished, or even reversed to positive, by the diminution or abolition of the power of true conduction (figs. 345, 346, 347). The various effects described as polarisation-increment and decrement have been shown further to be due to the increased galvanometric negativity of the more excited of two points, the responsive current being algebraically sum- mated with the existing electrotonic current. The greater excitation of one of these two points was also shown to be due to the greater intensity of excitation conducted to it, or 728 COMPARATIVE ELECTRO-PHYSIOLOGY to the greater excitability induced by the action of the anode, or to both. This summary of results will conclude with a brief account of the demonstration of the physico-physiological nature of the basis of sensation. The effect of a single stimulus has been shown to consist of two different waves sent out from the point stimulated, of which the hydro- positive travels with a greater velocity than the true excita- . tory or negative. If the stimulus applied, moreover, be feeble, the positive wave alone will be transmitted. If the stimulus, again, be very strong and the path of conduction short, one wave will be superposed over the other, the nega- tive masking the positive. The two waves, however, may be separated from each other by inducing a depression of the conductivity of the nerve, when the negative will be made to lag behind the positive. By the suppression of the negative, owing to sufficient reduction of conductivity, the positive may be made to arrive at the responding point alone. Nervous impulses have thus been shown to be of two different kinds, positive and negative, and contrary to the universal assumption that the nerve gives no visible indication of its state of excitation, it has been shown that these are accompanied by waves of expansion and contraction respec- tively. In addition to these visible mechanical expressions, we have also the concomitant electrical expressions of galvanometric positivity and negativity. I have been able, moreover, to identify the wave of expansion as the vehicle of that change which gives rise to the positive tone of sensation, which may be described as pleasurable or at least not unpleasurable. The negative or contractile wave, similarly, has been shown to be doloriferous. These two waves we saw to be separable from each other, whenever the conducting nerve was sufficiently long. Thus, when the sole of the foot receives a smart stroke from a rod, two different impulses are sent out, first the positive or sensation of con- tact, which is not unpleasurable, followed by the negative, with its different and painful tone of sensation. In various AES Sea See Ree ee ee RESPONSE BY SENSATION 729 well-known cases of nerve-disease, bringing on diminished conductivity, this dissociation of sensation is met with patho- logically. In paralysis, again, burning coals may be held in the hand and induce only the feeling of contact, without any sensation of pain. One very difficult problem in connection with psycho- logical response is that of the peculiar relation between the intensity of stimulus and that of response. The generalisa- tion known as Weber-Fechner’s law, asserts that stimulus must increase in geometrical, for sensation to increase in arithmetical, progression. Fechner, moreover, regarded this relation, not as due to any physical or physiological factor, but as a particular case of some specific psychological law. On an inspection of the mechanical responses of animal nerve, given in figs. 400, 401, and 402, however, we see that the peculiar relation between stimulus and sensation follows inevitably on the physiological character of those responses. We there see that under feeble stimulus the response is positive, connoting, as we know, a positive tone of sensation. After this, as stimulus increases, the sign of response under- goes a reversal into normal negative. From this point onwards, for some time, the response to increasing stimulus shows a rapid rate of increase; but this increase tends to reach a limit as the maximum molecular distortion is approached. These facts follow naturally from the mole- cular theory of response which has been described, and in such considerations we obtain an explanation of those changes in the tone or quality of sensation of which Weber- Fechner’s law was unable to take account. That these responsive characteristics, again, are not peculiar to the animal nerve, has been seen in the fact that vegetal nerves also show a similar relation between stimulus and response (fig. 403). That this relation indeed is universal, will be understood from the response of an inorganic substance to increasing stimuli, as given in fig. 404. | Another interesting proof of the dependence of the psychological upon physico-physiological changes is afforded 730 COMPARATIVE ELECTRO-PHYSIOLOGY by the ‘polar action of currents. It has been shown that the positive response is short-lived, whereas the negative is relatively more persistent, its persistence increasing with the intensity of the response. Now, by means of the Sensimeter (fig. 405), we can apply a series of stimuli of measured intensity in such a way as to induce the neutral sensation which is neither pleasurable nor painful. The frequency of this stimulation is so adjusted as to appear all but continuous. If we now render the excited point moderately anode, and thus reduce its excitability, the neutral will be converted to the positive tone, and the sensation, moreover, will be rendered strikingly discrete. If, next, the excitability of the stimu- lated point be enhanced by the application of moderate kathode, the neutral sensation will become converted into painful, becoming, further, fused and continuous. It will thus be seen that in the determination of sensation the internal plays as important a part as the external. By the peculiar molecular disposition of the nerve, it is indeed possible, as we have seen, to convert one quality of sensation into another, and such dispositions are to a greater or less ex- tent under the control of the will. It is not external circum- stances, then, which are the dominant factor psychologically, for the impression created by these is capable of indefinite modification in any direction, by the action of habitual induced dispositions, The reader will see for himself what illimitable possibilities are opened up by the line of thought here suggested. Ee) | The last subject to be reviewed is the phenomenon ot memory, which is an after-effect of stimulus. The after- effect of strong stimulus is in general more persistent than that of feeble. Similarly, the memory of a strong sensation is more¥enduring than of a weak one. Very strong stimulus, again, gives rise, as we have seen, to multiple responses. In the retina these are perceived as multiple after-images, which sometimes appear to be renewed spontaneously. This fact will often be found a sufficient explanation of visual phantoms and hallucinations. ' This, however, is not the usual method ta een 0? (iret ae Tee ag ge ae, eee te ee ee Ws = ie OS RESPONSE BY SENSATION ~ 731. of reviving memory-images. Long after every trace of the primary stimulation has disappeared we can revive it by an impulse of the will. Memory-impressions are often likened to scars. Of this metaphor, however, it may be said, that though, no doubt, when the blow is recent the smarting effect will persist for some time, causing an ever-diminishing after- sensation, yet, when the scar has healed, how could it, of itself, reproduce the original sensation? To do this, the original excitation would require to be reproduced, in the absence of the primary exciting cause. If, then, instead of regarding it as a scar, we translate the original impression into shades of light and darkness, we see that such a picture was produced by different intensities of the primary stimulus acting on the sensitive surface—in other words, by means of induced differential excitation. To bring back the picture we have to reproduce, in the absence of prirnary stimulus, the same state of differential excitation as was at first induced by it. Such a revival is possible, as already shown, under the combined action of two different factors. It has been shown that when an isotropic tissue is locally acted upon by stimulus, the excitatory manifestation thus induced disappears after a time. There is now nothing visible by which to. distinguish the stimulated from the unstimulated areas. In consequence of this stimulation, however, there has been a transformation of the molecular condition of the portions acted upon. The tissue, which was originally isotropic, has now become an- isotropic, by the impression of this latent image. On diffuse stimulation, the differentially excitable structure will now exhibit the latent image, by various forms of differential excitation, of which some one particular manifestation will, in the case of any given organ, be the most conspicuous. Thus, in a metallic plate containing latent positive and negative chemical impressions, we shall obtain, on the appli- cation of diffuse stimulus, corresponding positive and negative galvanometric responses. In a phosphorescent plate, again, a small area may be subjected to the action of light. On the 732 COMPARATIVE ELECTRO-PHYSIOLOGY cessation of stimulus this will give luminous response, which may be taken as the immediate effect of primary stimulus. On the fading of this image, if the whole plate be subjected to feeble diffuse illumination for a short time, the latent image will once more appear as a bright patch against a dark back- ground. This is because, as the after-effect of stimulus, the area B has been rendered more excitable. Hence, diffuse stimulation evokes more intense response from it than from | its more inert background. Similarly, the memory-image is capable of revival by the internal impulse of the will, acting as a diffuse stimulus to evoke a differential sen- sation, which reproduces the light and shade of the primary picture. | The responsive phenomena seen in living matter are, _undoubtedly, wonderful and mysterious ; but those shown by the inorganic are no less wonderful. By-ascribing all physiological occurrences to specific reactions, and by con- stantly postulating the intrusion of forces of a new order, the road to the further advancement of knowledge is closed. By the conception of matter itself, on the other hand, as possessed of sensibility—that is to say, of molecular respon- siveness—we attain an immediate accession of insight into those physical interactions which must furnish the terms of any ultimate analysis. We are led by it to the discovery of the impressive fact of continuity as existent between the responses of the most complex living, and the simplest inorganic matter. Limiting ourselves, again, to the realm of living matter, we are impelled to recognise parallelisms, in the response of plant and animal, whose extent could never otherwise have been suspected. All the responsive phe- nomena of the animal are thus found to be foreshadowed in the plant, and this to such a degree that in the common script of the response-record the one is indistinguishable from the other. In both we observe a similar series of excitatory effects, whether these be exhibited mechanically or electrically. Both alike are responsive, and similarly responsive, to all the diverse forms of stimulus that impinge ost SAE Pike CeO te 2 Sere ed ts We RESPONSE BY SENSATION rates upon them. We ascend, in the one case as in the other, from the simplicities of the isotropic to the complexities of the anisotropic ; and the laws of these isotropic and aniso- tropic responses are the same in both. The responsive peculiarities of epidermis, epithelium, and gland; the re- sponse of the digestive organ, with its phasic alternations ; and the excitatory electrical discharge of an anisotropic plate, are the same in the plant as in the animal. The plant, like the animal, is a single organic whole, all its different parts being connected, and their activities co-ordi- nated, by the agency of those conducting strands which are known as nerves. As in the plant-nerve, moreover, so also in the animal, stimulation gives rise to two distinct impulses, exhibiting themselves by twofold mechanical and electrical indications of opposite signs. It is the nature of the indica- tor, again, which determines in any given instance the form of the responsive expression. A single molecular derange- ment may thus find manifestation as change of form, alteration of electrical condition, and subjective sensory variation. The dual qualities or tones known to us in sensation, further, are correspondent with those two different nervous impulses, of opposite signs, which are occasioned by stimulation. These two sensory responses—positive and negative, pleasure and pain—are found to be subject to the same modifications, under parallel conditions, as the positive and negative mechanical and electrical indications with which they are associated. And finally, perhaps, the most significant example of the effect of induced anisotropy lies in that differential impression made by stimulus on the sensory surfaces, which remains latent, and capable of revival, as the memory-image. In this demonstration of continuity, then, it has been found that the dividing frontiers between Physics, Physiology, and Psychology have disappeared. 2 a a CLASSIFIED. LIST OF EXPERIMENTS MOLECULAR RESPONSIVENESS OF MATTER . Mechanical response : PAGE 1. Contractile response in indiarubber ; . : > . ‘ 2 Electromotive response : 2. Response of tin . ‘ . 6 3. Fatigue in inorganic response : 7 4. Action of sce on response of batirnast : - d are 8 5. Action of ‘ poison’ in abolishing response of metal . 9 6. Response in metal by method of negative variation 9 Response by resistivity variation : 7. Response of selenium to light 3 8. Response of galena to electric radiation 3 g. Response of allotropic silver Ag’ to electric vailission 4 FUNDAMENTAL PHENOMENON OF RESPONSE IN PLANTS 10. Simultaneous record of mechanical and electrical response 19 11. Electrical response of pulvinus of Mimosa when physically re- strained . ; 2 . 20 12. Response to sudden sailation of tension 25 13. Response'to sudden compression . ; 25 14. Response to tension and compression . 2 15. Response to mechanical blow ‘ . . : - : e726 16. Response to vibrational stimulus 27 17. Response to chemical stimulus : : : ; 2. 27 18. Response to thermal shock ‘ : : ‘ee ae 19. Influence of sudden variation on efficiency or siirialation * 32 20. Additive effect . ‘ ‘ : ‘ : ; 34. 21. Genesis of tetanus in mechanical response of plants . 43 22. Genesis of tetanus in electrical response of plants 43 23. Rheotomic observation of time relation . ‘ é 48 24. Response to increasing intensity of stimulus of mechanical blows 39 25. Response to increasing intensity of vibrational stimulus ae gies 26. Response to increasing stimulus, with or without complete recovery. 41 COMPARATIVE ELECTRO-PHYSIOLOGY POSITIVE. AND NEGATIVE RESPONSE . Hydraulic response in Mimosa . Positive mechanical response followed by anlative in 5 Wioshysas ¢ . Positive mechanical response followed by negative in AZzmosa. . . Simultaneous record of positive and ign mechanical and electrical response in Bzophytum . . Positive, diphasic and negative Seanoues in petiolé of cauliieer . Positive and negative responses in tuber of potato . Unmasking of positive element in response by selective block : . Effect of stimulus of light on growth . . Effects of steady and sudden variation of Pome on a prowth response VARIOUS TYPES OF RESPONSE . Abnormal positive response in sub-tonic tissue . Staircase response in tissue originally sluggish . Staircase response in vegetal nerve . Staircase response in galena . Uniform response in plant . Fatigue due to rapidly succeeding Tre oem . Fatigue due to overstrain . ‘ ae . Fatigue-decline under continuous stimulation, i in medhanical response of Mimosa. . Fatigue-decline under continuoas ecmueaens in tecnica! response of celery . Oscillatory response in arsenic . Phasic alternation in mechanical dessonne of style of Diiave . Periodic fatigue in electric response of plants . ‘ . Periodic fatigue in autonomous response of Desmodium an . Reversal of normal response in fatigued nerve . : . . Bifurcated expression of response as growth and mechantesl response DETECTION OF PHYSIOLOGICAL ANISOTROPY . Differential response of compound strip . : . Isolated responses of upper and lower halves of ihe inus af Mitosa, with resultant differential response . . Transverse differential electrical response of eee af Mian . Transverse differential electrical response of plagiotropic stem of Cucurbita . Transverse differential dlectrical: reponse i cetiole of Musa NATURAL CURRENT OF REST AND ITS VARIATIONS . Effect of rise of temperature on current of rest . Effect of falling temperature on current of rest . Effect of Na,CO, solution on current of rest . Effect of CO, on current of rest ‘ . Reversal of natural current of rest as after- stint of esimuladion 103 102 104 108 109 1@ fe) III 114 119 119 122 122 127 CLASSIFIED LIST OF EXPERIMENTS 737 EFFECT OF CHEMICAL AGENTS ON EXCITABILITY PAGE 61. Effect of chloroform : : ‘ : ‘ é ; ; - 130 62. Effect of chloral hydrate . ; : ‘ ; RIM faerie an BSE 63. Effect of formalin . : : ; : ; ‘ ; ; . +932 64. Effect of NaOH. ; , ‘ ; : : , , na 5." 65. Effectof KOH . ‘ . i a é ; a : 835 66. Effect of sugar solution . “ ; ; ee ‘ 2. oe ae 67. Effect of Na,CO, solution. ° : ; : ; ; . 136 68. Effect of HCl . ; ‘ ; ; (on Ea 69. Effect of moderate and rong aa of KOH : . P i - 139 METHOD OF INTERFERENCE 70. Responsive effect of variation of phase ; F : ‘ 5 enh el 71. Diphasic response and its variation 4 : ; : : a EAS 72. Diametric method of recording response. ‘ , e . » 147 CURRENT OF INJURY AND NEGATIVE VARIATION 73. Electrical after-effect in inorganic substances under strong stimu- lation . : ‘ I51 74. Resistant saicuaomnisis saath: in vegetable tinea cases sti stimulation . : ‘ , Las oa 75. After-effect of persistent negativity ise to section 2), i aig 5 76. Electrical distribution in plant cylinder. : ; d Sf. age 77. Response by negative variation . : : : : d . 158 CURRENT OF DEATH AND RESPONSE BY POSITIVE VARIATION 78. Response by abnormal positive variation . : : g OS 79. Electric exploration of dying and dead tissue . : ’ ‘ . 169 80. Electric exploration of tissue one end of whichis killed . . . 171 81. Response by negative and positive variations of current of injury . 174 EFFECT OF TEMPERATURE 82. Effect of cold in arresting autonomous pulsation in Desmodium . . 181 83. Effect of warmth on autonomous pulsation of Desmodium : . 182 84. Effect of cold in pezmanent abolition of response , ‘ ote SZ 85. Effect of cold in temporary abolition of response. ‘ - 184 86. Effect of cyclic variation of temperature on electric response site EBS 87. Effect of rising temperature on amplitude of response ; . 186 88. Effect of rising temperature on conductivity pe , o Avca BOF 89. Abolition of response by high temperature ~ . e258 190 90. Effect of cooling on frequency and amplitude of pulsation a Des- : modium , ‘ , : : ‘ : . ° jet OSS 3 8 738 COMPARATIVE ELECTRO-PHYSIOLOGY DETERMINATION OF DEATH-POINT 91. Determination of death-point by abolition of electrical response . 195 92. Determination of death-point by means of thermo-mechanical curve 198 93. Determination of death-point ie means of inversion of electro- motive curve . . : - + 202 94. Simultaneous reversal of fectital curve ea Seen ‘ : . 204 MULTIPLE AND AUTONOMOUS RESPONSE 95. Multiple mechanical response in Biophytum . ; : ae ae a 96. Multiple electrotactile response in Mimosa . : ; ; . 208 97. Multiple electromotive response in Biophytum . : , oe ROO 98. Multiple electric response in various tissues . ; , ‘ . 210 99. Multiple electric response in stomach of frog. j ; ae 8 Ie, 100. Autonomous response in Biophyium - ; eT 101. Initiation of multiple response in Deiwiutint cider light - eee ee 102. Spark record of autonomous pulsation in Desmodium . : 214 103. Simultaneous record of mechanical and electrical response of pul sating Desmodium leaflet . : : 217 ; 104. Record of electrical responses in are ee leaflet nena movement is restrained . : ‘ ; : : : : Shea 105. Multiple response of Seine ; : : : : } gee +f RESPONSE OF LEAVES 106. Effect of section of petiole of /zcus on ihe current of rest : a: Bay 107. Effect of section of petiole of C7¢7ws on the current of rest . S96 108. Effect of stimulation of lamina. : . 225 109. Parallelism between response of J/usa aiid that of es eae OO“. ee ELECTRIC DISCHARGE IN ANISOTROPIC ORGAN 110. Response of leaf of Vymphea to transmitted stimulation ‘ + =2a5 111. Response of leaf of Co/ews to thermal shocks . A ; <4 She 4 112. Rheotomic observations. a ee 113. ‘ Blaze current,’ so-called, in lament pence : : ices etn Response to equi-alternating shocks in : 114. Carpellary leaf of Didlenza . 3 . ; : . 256 115. Leaf of Plerospermum . : : ; : ‘ : Re 116. Pitcher of Nepenthe . , : : ; , : : . 256 117. Pulvinus of AZzmosa : : : : . : : ~ 4 ams 118. Bulb of Mriciis lily. : ‘ . : ‘ ‘ : i SY 119. Prepared strip oflead_. ; ; : : : : < i. Oe 120. Petiole of Alusa . : , : : ‘ .- (283 ‘121. Plagiotropic stem of [ome f : : : : buts eos $22, er. . . ; : : : ; ey ees 123. Variegated leaf of Pothos . . . . ; : ; ~ -« 206 124. 125. ‘126. 127. 128. 129. 130. 131. 132. 133. 134. 135. 136. 137. 138. 139. 140. I4I. 142. 143. 144. 145. 146. 147. 148. 149. 150. 151. 152. 153- 154. 155- 156. 157: CLASSIFIED LIST OF EXPERIMENTS RESPONSE oF SKIN Current of rest in vegetal skin : Isolated responses to mechanical stimulus of id ali tower porbiecs of grape skin . : : : ‘ Isolated responses of frog’s an? Isolated responses of skin of tomato Response of grape-skin to thermal shocks . ‘ Response of grape-skin to equi-alternating shocks Response of frog’s skin to equi-alternating shocks . Response of tomato-skin to equi-alternating shocks Exhibition of positive after-effect . Response of skin of tortoise Response of intact human skin . ‘ Illustrative response of pulvinus of AZmosa waniae sei? variation Illustrative autonomous senanee of Desmodium exhibiting cyclic variation : Normal response of skin of ake: ; A Abnormal diphasic response of skin of gecko, ceerieds to aaian | after tetanisation RESPONSE OF EPITHELIUM AND GLANDS Resting current in foot of snail Reversal of true resting current by injury . Response of water-melon F Response of glandular foot of snail Response of human arm-pit . Response of human lip Response of human tongue . : Normal response of pulvinus of eee révened sue eigntaation Response of Dz//enia and its reversal after tetanisation Reversed response of Dz//enza under feeble stimulation . RESPONSE OF DIGESTIVE ORGAN Determination of natural current of rest in digestive organ of Nepenthe . Excitatory electric deagolise of fash vibe of Nepenthe Response of Wefenthe at intermediate stage — Response of pitcher of Vefenthe with entrapped iseets Normal response of digestive leaf of Drosera and its reversal éter tetanisation Response of frog’s atitibeuth to iiebhaniéed pildautadion Response of stomach of tortoise to electric stimulation Normal response of stomach of ee and its reversal after eebht: sation ° Multiple response to trou Sith ule in sf piteher of Wepenilic thes: fresh . - ‘ : 3B2 739° PAGE 298 299 300 307 301 302 393 308 309 3097 300 303 304 310 311 318 319 315 316 319 320 322 326 328 335 338 339 339 342 345 345 346 341 749 158. 159. 160. 161. 162. 163. 164. 165. 166. 167. 168. 169. 170. 171. T 72: ‘$93. 174. 175. 176. i or 178. 179. 180. 181. 182. 183. 184. 185. 186. 187. 188. 189. 190. gl. 192. 193. COMPARATIVE ELECTRO-PHYSIOLOGY Multiple response in pitcher of Wepenthe with entrapped insects Multiple response in Drosera . , Multiple response in stomach of frog ASCENT OF SAP AND SUCTIONAL RESPONSE Electrical response of young root Electrical response of older root Responsive secretion by root Response of root to chemical stimulation : ; Electrical response of sii wood and its lepresson aniter anses- thetic . Abolition of gedit: pepenae a weed by poison Hydraulic response to stimulus . Effect of cold on suctional response Effect of rise of temperature on suctional responsé Effect of anzesthetic on suctional response Excitatory versus osmotic action Initiation of suctional response and enhanceiient under atcaatite Diminution of latent period as after-effect of stimulus Responsive variation of suction under overbalance. Response to sub-terminal stimulation RESPONSE TO STIMULUS OF LIGHT Transverse transmission of effect of moderate stimulus Transverse transmission of effect of strong stimulus Mechanical response of Mimosa to unilateral light . Electrical response of A/imosa to unilateral light Transmitted effect of stimulus of light Electrical response of Bryophy/lum to light Electrical response of petiole of cauliflower Multiple growth response under light Multiple mechanical response of Biophytum under hone Multiple electrical response in Bryophyl/um under continuous light Normal negative and positive after-effect under light Influence of fatigue on after-effect . Third type of direct and after-effects in alae bac light . RESPONSE OF RETINA Determination of differential excitability as between optic nerve and cornea ‘ Determination of differential away as orcas Gina aoe opéle nerve . Determination of true current 96 ea in ae S aes . ‘ Conversion of abnormal retinal response to normal by escitatocy agents Normal retinal response of Ophiocephatus. 397 401 402 402 405 407 408 409 4II 412 417 419 418 423 427 194. 195. 196. BOP 198. 199. 200. 201. 202. 203. 204. 205. 206. 207. 208. 209. 210. 211. 212. 213. 214. 215. 216. 217. 218. 219. 220. 221. 222. 223. 224. 225. CLASSIFIED LIST OF EXPERIMENTS 741. PAGE Reversed retinal response and after-effect in Ophiocephalus Fecctady Three parallel types of direct and after-effect of light in plant and animal . ; Pau Rab aaas ~ 5p Si 430 Multiple response in hoe’ S aoe , : , , ; 426 Multiple response in retina of Wallago. + . : : ‘ - 433 Multiple response in human retina . : ie ep ae Pulsating response in human retina under juiiaueam Tight : 592 Binocular alternation of vision . , ; : ; “ae i! Analysis of composite image by after- shect ‘ F i . +: 432 GEO-ELECTRIC RESPONSE Response to unilateral pressure of particles : ‘ ; 7 = 37 Determination of excited area under geotropic stimulus . ‘ - 436 Geo-electric response . ; S ~ Sye§40 Geo-electric response of an oad Ghesicaite ae F : - 442 VELOCITY OF TRANSMISSION > Determination of velocity of transmission by mechanical response . 447 Determination of centripetal versus centrifugal velocity . : . 448 Effect of fatigue on velocity of transmission — . ; ; . « 449 Effect of intensity of stimulus on velocity . ‘ ‘ : - 449 Effect of temperature on velocity. .; . 450 Determination of velocity of transmission by pleetroniutive wiethoul 452 Longitudinal versus transverse conduction < : i . eee ELECTRIC RESPONSE OF NERVE TO THERMAL STIMULUS Electrical response of frog’s nerve to equi-alternating shocks . . 457 Normal response of animal nerve to thermal stimulation . . 460 . Enhancement of normal response after thermal tetanisation . . 462 Abnormal positive converted to normal negative after thermal tetanisation . . ‘ 463 Gradual transition oe {honda ester : sonal Woeative through diphasic . P 465 Conversion of abnormal positive to sired eis faust Sige by increasing intensity of stimulus : ; ° : . . 466 ELECTRIC RESPONSE OF PLANT NERVE Effect of ether on electric response of plant nerve . : ; of eaQye: Effect of carbonic acid . 5 ‘ : : . ; a: Cae Effect of alcohol . ; : ‘ 5 F ‘ < «tae Oe Effect of ammonia . - P : spt WEA Effect of ammonia on response of indifferent iSueale:: : ; - 474 Three parallel types of response in plant and animal nerve Ae iak 7A. Effect of tetanisation on enhancement of normal negative response. 475 742 226. 227, 228. 229. 230. 231. 232, 233. 234. mae. 236. 237. 238. 239. 240. 241. 242. 243. 244. 245. 246. 247- 248. 249. 250. 25%. 252. 253: 254. 255. 256. 257: 258. 259. 260. 261. COMPARATIVE ELECTRO-PHYSIOLOGY Abnormal diphasic converted into normal negative after tetanisation Conversion of abnormal positive to normal negative through inter- mediate diphasic under increasing intensity of stimulation . CONDUCTIVITY BALANCE Effect of Na,CO, solution on responsivity of frog’s nerve Effect of CuSO, solution on responsivity of frog’s nerve . Effect of CaCl, on responsivity of ai nerve Effect of KCl ; Comparative effects of NaCl ant N ae on deeds Effect of dilute solution of Na,CO, Effect of stronger solution of Na,CO, Excitability versus conductivity under KI Excitability versus conductivity under NaI Effect of alcohol on responsivity of frog’s nerve Effect of alcohol on receptivity of plant nerve Effect of alcohol on conductivity of nerve Effect of alcohol on responsivity of nerve . Receptivity verses responsivity under alcohol Effect of cold on conductivity . Effect of warmth on conductivity . ; After-effect of moderate stimulation on peaduclivits and excitability After-effect of strong stimulation on conductivity and excitability MECHANICAL RESPONSE OF ANIMAL NERVE Mechanical response of frog’s nerve under electric tetanisation . Effect of ammonia on mechanical response Effect of morphia Effect of aconite . Effect of alcohol Effect of chloroform Conversion of abnormal positive to ‘Homial peace ‘heough sisbacies by tetanisation Occurrence of staircase seer Comparison of mechanical responses in accanl and slit nerve . Mechanical response of optic (sensory) nerve . Fatigue of conductivity in nerve of gecko. ‘ : Transient enhancement of contraction on cessation of tetanisation Multiple mechanical response in nerve as effect of drying . MECHANICAL RESPONSE OF PLANT NERVE Enhancement of excitability after tetanisation Effect of light in enhancing excitability of plant nerve Determination of velocity by mechanical response of plant nerve PAGE 476 477 485 485. 486 © 486 487 488 489 491 492 492 493 493 494 495 499 $01 504 595 509 516 516 516 517 518 521 524 528 529 530 536 539 554 556 525 . . 262. 263. 264. 265. 266. 267. 268. 269. 270. 271. 272. 273: 274. are. CLASSIFIED LIST OF EXPERIMENTS RESPONSE OF LIVING TISSUE BY RESISTIVITY VARIATION Determination of death-point by inversion of curve of goles Excitatory response by resistivity variation Action of anesthetics on response by resistivity iivintod in fido%s s nerve . . . . . . Oo . . *. e ELECTROTONUS Extra-polar effects in plant nerve Variation of conductivity in plant nerve by piece of suse Conduction of excitation with the current 5 Conduction of excitation against the current . Modification of excitability by anode Modification of excitability by kathode . Variation of excitability and conductivity with pélacitiie sisesindes in shunt ‘ Variation of excitability st cinddeivity $ith patiniateg Medtrblen in series . INADEQUACY OF PFLUGER’s LAW Normal effects of anode and kathode on plant . Reversal of normal effect under high E.M.F. Demonstration by subjective response of opposite effects cotaeed by moderate and feeble E.M.F. MOLECULAR THEORY OF EXCITATION Mechanical Response : 276. Mechanical response of pulvinus of Zrythrina indica, by make of kathode and anode Magnetic Response : 277. 278. 279. 280. 281. 282. 283. 284. 285. 286. 287. Uniform magnetic responses Periodic groupings in magnetic response Incomplete magnetic recovery after strong aieniation Additive effect of magnetic stimuli, individually ineffective Magnetic tetanisation, with transient enhancement of effect on cessation . Demonstration of anes raeoene balenas Effects of A-tonus and K-tonus on magnetic comico . Opposite effects of moderate and strong K-tonus on esagrnnite con- duction . Effects of A-tonus and k K- ewe on rielgrietic excitability Enhancement of magnetic G-menen: by successive fongnetic stimuli. ‘ ‘ : ° . : Blocking of trainee of magnetic excitations 743 © PAGE 546 548 549 561 566 567 568 569 579 - 572 574 579 579 582 7A4 COMPARATIVE ELECTRO-PHYSIOLOGY PAGE Response by resistivity variation : 288. Response of aluminium powder to electric radiation . . * <3, OL 289. Persistent after-effect on strong stimulation . : : : . 603 290. Effect of warmth in hastening recovery . > ; gag? at one, OE 291. Uniform responses to electric radiation . apes 602 292. Cyclic molecular variation and concomitant snodification a response —characteristic curves . ‘ ; : ‘ ; : 5: ce GRD Effect of tetanisation at A stage, conversion of abnormal positive to normal negative seen in : 293. Mechanical response of frog’s nerve. ; ; , , « 627 294. Electromotive response of tin . : . 628 295. Conversion of abnormal to normal thioagh dighaiivs in 7 caaioae - 629 296. Response by resistivity variation in selenium. — . : ‘ - 631 297. Response by resistivity variation in tungsten. : ; : «eee Effect of tetanisation at B stage, enhancement of normal response seen in : 298. Mechanical response of frog’s nerve. : : : : - 634 299. Responsive resistivity variation in selenium ; : . . woe 300. Responsive resistivity variation in aluminium powder . . < 63 301. Electromotive response of tin . : ; . : : ~' «O30 302. Magnetic response of iron. ‘ ; ; ‘ ‘ - | 633 Effect of tetanisation in inducing E stage, diminution or reversal of normal response seen in : 303. Mechanical response of frog’s nerve . , : : * . ted. 98 304. Mechanical response of nerve of gecko . ‘ ‘ ‘ é - “he 305. Mechanical response of india-rubber. : ° ; : eh 16GS 306. Responsive resistivity variation in tungsten . ‘ ‘ : . 638 CORRELATION OF PSYCHIC AND PHYSIOLOGICAL RESPONSE 307. Expansive and contractile response in muscle . : . 649 308. Relation between stimulus and response in sciatic nerve ar seks «) g? 309. Relation between stimulus and response in sciatic nerve of bull-frog 658 310. Relation between stimulus and response in sensory optic nerve of Ophiocephalus . ; : : . 659 311. Relation between stimulus anid fespolise in plant i nerve. » s B59 312. Relation between stimulus and response in magnetic substance . 660 EXPERIMENTS WITH SENSIMETER ON ELECTROTONIC VARIATION OF SENSATION 313. Conversion of pleasurable sensation to painful under kathode (mechanical stimulation) . ; ‘ : . . 670 314. Conversion of painful to pleasurable Scaaeepe ar anode (mechani- cal stimulation) . ; : i ; , ; y ae, ST 315. 316. 317. 318. 319. 320. 321. CLASSIFIED LIST OF EXPERIMENTS Positive tone of sensation due to thermal stimulus converted to negative under kathode . Negative tone of sensation due to thermal ainalas. eoaneeed to positive under anode . : ‘ Reversal of normal effects under feeble E. M. F. : ; 671, 672 745 © PAGE 672 672 Differences of fusion in sensation according as it is modified to positive or negative . 5 F : : ; : 671, 672 MEMORY Revival of latent impression in metal under diffuse stimulation é Revival of latent or ‘memory image’ in phosphorescent screen under diffuse stimulation Reversed or negative image . 683 684 685 INDEX ADDITIVE effect, 34, 595 After-effect, persistence of, under strong stimulation, 151-154 Anesthetics, effect of, on excitability, 130 on response of nerve, 472, 518, 673 on response of wood, 362 ~ re on responsive resistivity variation, 549 Sa on suctional response, 375 eieoazons induced by stimulus, in memory image, 686 in metallic plate, 683 bd "e b in phosphorescent screen, 684 3 PR in plagiotropic stem, III Arm-pit, sckpouiee of human, 319 © Ascent of sap, various theories of, 356 Assimilation and dissimilation, 68, 87, 308 Autonomous response, continuity with multiple, 211 * a in Biophytum, 211 is in Desmodium, 212 Reslenche theory, 502 bP) 99 29 BERNSTEIN on polarisation decrement, 562 Biedermann on response of glands, 289 ase riff “ > of stomach, 289 Binocular alternation of vision, 431 Biophytum, mechanical response of, 58 aS multiple response of, 209 Pe positive and negative response in, 59 Blaze current, so-called, in lead, 266 Block, advantages of method of, 133 » method of, 5 Burdon Sanderson, on response of Dione@a, 12 © CHARACTERISTIC curves of conductivity, 621 3 », Of differentially excitable surfaces, 324 pr », of magnetisation, 620 Complex sensation, dissociation of, by lag, 674, 675 ‘4s », obliteration of negative element in, by selective block, » 073s 675 Composite image, analysis of, by after-effect, 432 Conduction of true excitation in plants, 446 748 COMPARATIVE ELECTRO-PHYSIOLOGY Conductivity balance, experiments with : + = sy on condectivny versus receptivity sek alcohol, 495 Wa - ~ on conductivity versus receptivity under KI and Nal, 491-492 - cs - on receptivity under alcohol, 493 ee a me case versus responsivity under alcohol, 495 PP > a on responsive variation under alcohol, 494 re sy rs on variation of conductivity under alcohol, 494 Conductivity balance, experiments with : si », Variation of responsivity by alcohol on frog’s nerve, 492 a * Py re by CaCl, on plant nerve, 486 $5 re ne . by CuSO, on frog’s nerve, 485 ‘“e Fi Pe te by KCI on plant nerve, 487 & Pe ‘ys te by Na;CO, on frog’s nerve, 485 5 ms ‘6 es contrasted effects of NaCl and NaBr, 487 a Pe ‘i conductivity by Na,CO, on plait ne ve, 488- 489 Conductivity balance, experiments with : % effect of cold on conductivity, 499 +3 »» Of electric current, 565-568 - », Of excessive stimulus, 505 ae »» Of moderate stimulus, 504 ‘ », Of warmth, so1 el oa: 553 Corrosion figures, 349 Crescograph, 221 Cucurbita, electric response of plagiotropic stem of, 111, 285 Current of death, 166 Current of injury : anomalous variation in, 165 mA », diminution of response with diminution of, 159 ear i explanation of, 156 = op its decline, 158 a 33 positive and negative variation of, 161 ee various theories of, 149 Current of Reet, effect of CO, on, 122 oe », effect of fall of temperature on, 119 i », effect of Na,CO, on, 122 5 », effect of section of petiole on, 225-227 os », effect of steady rise of temperature on, 119 ‘5 »» effect of sudden variation of temperature on, 120 - »» in animal skin, 288 a o> ©6in Citrus, 224 a », in Dionea, 224 "ys »» in Ficus, 224 9 », in foot of snail and its variation on injury, 318 ” », in frog’s eye, 418 INDEX | 749 Current of rest, in Mepenthe, 335 iz », in vegetal skin, 298 ef ,, natural, and its variations, 317 Bs: »» phasic changes in, 302, 303 se », physiological condition determining, 117 aoe ,» positive and negative variations of, 126 % ,, reversal of, as after-effect of stimulus, 124 “ »» variation of, 175-177 DARWIN on excitatory reaction in Drosera, 331 Dead tissue, positivity of, 170 Death, different Jost-mortem symptoms of, 192 Death-point, accurate methods of determining, 194 ss determination of, by abolition or reversal of response, 195 od = by electric spasm, 202 a 36 by inversion of curve of electric resistivity, 546 a x by thermo-mechanical inversion, 198 Depression, response by method of relative, 9 Desmodium pulsation, electro-motive response of free leaflet, 218 »” » » “ leaflet physically restrained, 220 » ” > ” principal and subsidiary waves it; ; 219 <5 sy initiation of, under stimulus, 212 ” » » Yate of, 215 a ss spark record of, 214 Bens: and McKendrick on retinal current, 415 Differential excitability, determination of: in eel, 285 Yr) $9 ee in Musa, 114, 284 >» 2 Pe in plagiotropic stem, III, 285 ” 2” ” in pulvinus, 303 an. » % in retina, 419 ” » 2 in variegated leaves, 286 Differential excitation, in memory revival, 680 Differential response, of compound strip, 108 e $3 of Mimosa, 108, 303 + laws of, 109 Dicesinie organ, alternating phasic reactions in, 329 i »» current of rest in, 335, 344 Z », multiple response in, 333, 341, 343, 347 ¥5 5, response of, in Drosera, 342, 343 9 99 » in frog, 345, 347 » 99 9 in gecko, 346 a : 5 in Nepenthe, 339-341 sa a Je in tortoise, 345 Digestive organ, response of, : is iy i reversal of, in Dvosera after tetanisation, 342 ia = 4 3 in gecko after tetanisation, 346 Dillenia indica, normal response of, 256 » » » y9 reversal of, under fatigue, 327 750° COMPARATIVE ELECTRO-PHYSIOLOGY Dillenia indica, reversal of normal response, under feeble stimulation, 328 Direct and after-effect, methods of, 275 x 5 of light, in plant, 409-414 ss »5 in retina, 427-430 asoeis tia and delayed pain, 675 ne of complex sensation, by depression of conductivity, 674 2” oe) 29 by lag, 675 Dose, effect of, on excitability, 136 Drosera, response in digestive leaf of, 342, 343 Drugs, modification of effect by tonic condition, 641 », significance of effect of dose, 639, 640 Drying, effect of, on nerve, 539 Du Bois-Reymond on current of rest in frog’s skin, 288 ee “4 on organ current, 260 a se on positive and negative polarisation, 246 - ¥ pre-existence theory of, 149 ; Dying tissue, negativity of, 169, 173 a : EBBINGHAUS, on rate of forgetting, 678 } Eel, electric response of, 285 % Electric discharge under excitation in leaf organ : ; »» In Bryophyllum, 253 F »» in bulb of Uriclés lily, 257. 1 »» in Coleus, 248 3 » in Mimosa, 268 », in Musa, 284 ‘ » in Mymphea, 246 3 in pitcher of Vepenthe, 256 in Pothos, 286 in Pterospermum, 255 Electric distribution, explanation of, in dying and dead tissue, 173 ic. “ in plant and muscle cylinder, 150, 156 Electric organ, anterior and posterior surfaces, 242 = », laws of response in, 248 is », theories of, 260 Electrical response, in absence of mechanical, 20, 220 ey ne laws of, in anisotropic organs, 109 a3 af »» in isotropic organs, 75 Electrotonus, Bernstein’s polarisation decrement, 562 i conversion of qualities of sensation by, 670-672 KA extrapolar effects in plant nerve, 561 ie Hermann’s polarisation increment, 563 ; Ws law of variation of conductivity under, 568 oe ‘ excitability under, 571 Pe iodiication of conductivity by, 566-568 i variation of excitability by, 569 Energy, hydraulic transmission of, 69 Engelmann on current of rest in skin, 288 Equi-alternating shocks: their advantage, 274 INDEX Excitability, variation of, by chloral, 131 9? 9) 29 chloroform, 130 formalin, 132 HCl, 138 KHO, 138 NaHO, 134 Na,CO,, 136 sugar solution, 136 BacBakion: true caoe of, 16 FATIGUE, alternating, 98 in response of metal, 7 reversal of normal response in D2//enza under, 327 9 99 93 99 “= on 93 93 be) _ in Drosera under, 342 in Mimosa under, 326 in nerve under, 102 in stomach of gecko under, 346 transmitted effect in nerve under, 530 under continuous stimulation, 95 under overstrain, 96 Fibro-vascular bundles, distribution of, in stem, 558 Forgetting, rate of, 678 Frog, response in retina of, 418, 426 in skin of, 300, 302 in stomach of, 345, 347 Functions of vegetal nerve, 559 GALENA, response of, 3 Gecko, fatigue of conductivity in nerve of, 530, response in nerve of, 657 in skin of, 310, 311 in stomach of, 346 Geo-electric response, in apogeotropic organ, 440 in organ physically restrained, 442 Gdotrenic action, hydrostatic theory of, 435 statolithic theory of, 435 Geotropic stimulus, determination of area excited by, 436 Gotch on oscillatory character of electric discharge, 270 Growth, effect of stimulus on, 73 ; temperature on, 73 33 be] 9? 59 99 9? 99 Growth pulsation, 221 Gymnotus, electrical discharge in, 242 HAAKE on electromotive difference in plants, 13 Hartig on ascent of poison, 363 Heidenhain on enhancement of excitability by section, 502 Hermann on current of rest in skin, 288 2) on polarisation increment, 563 Holmgren on retinal current, 415 751 : —--- = ' 752 COMPARATIVE ELECTRO-PHYSIOLOGY Human lip, response of, 321 », skin, response of, 300 », tongue, response of, 322 Hydraulic response, 55 INJURY, degree determining sign of action current, 175 _ see Current of Injury . Interference, induced difference of phase causing, 142 af method of: effect of chemical agents determined by, 147 * Be effect of cold determined by, 147 Inversion of thermo-mechanical curve, 198 “f of electro-motive curve, 202 Pr. of curve of resistivity, 546 KUHNE and Steiner on retinal current, 415 Kiihne on polar effects in Protozoa, 579 Kunchangraph, 511 Kunkel on electro-motive variation due to water movement, 13 », on electric reaction in plants, 13 LATENT image, revival in phosphorescent screen, 684 | _ Latent impression, revival of, in metal, 683 : | Laws of differential response, 109 | s» 5, electrical response of isotropic tissue, 75 | s» 3, response in electric organs, 248 +» 9, variation of conductivity under electrotonus, 568 rey) 9 ,», excitability under electrotonus, 571 Leaves, electric response of Bryophyllum, 253 oes 7 i »» bulb of Uriclis, 257 4 ” ” re) », Coleus, 248 » » >». 3, Déllenia indica, 256 % 2 or », Mimosa, 268 ” ” - », Musa, 284 le oe » », Wymphea alba, 246 9 » 3 »» pitcher of Wepenthe, 256 fe 5 a », Lothos, 286 a 5 », LPterospermum, 255 Light, stimulus of : clecticel response of A/zmosa under, 401 Ae ‘ mechanical response of Mzmosa under, 400 op ic: mechanical response under, in pulvinated and growing organs, 394 A a multiple electrical response induced by, in plant, 406, 408 ‘9 19 multiple mechanical response induced by, 407 > » » ” » ” in retina, 426 . multiple visual impulse induced by, 430 transmitted effect due to, 402 Libs influence of fatigue on after-effect of, 411 »» negative and positive responses to, 402, 406 »» phasic responsive alternations under, 408 INDEX 3 753 Light, positive and negative after-effects under, 409, 412 ,», three types of direct and after-effect in plant under, 409-414 ,, three types of direct and after-effect in retina under, 427-429 Lip, response of human, 321 MAGNETIC balance, 607 Magnetic conduction, blocking of, 614 <, 93 effect of A- and K-tonus on, 609 <3 aye enhancement of, by successive stimuli, 612 > cs opposite effects of moderate and strong K-tonus on, 610 3 response, additive effect in, 595 a fe direct effect of tetanisation and transient after- effect, 623 +5 s3 effect of A- and K-tonus on excitability, 611 xe =F induction record, 604 = magnetometric record of, 594 ye ie mechanical record of, 593 Re xi periodic, 594 .* . uniform, 594 Malepterurus, electrical organ of, 242 Mechanical and electrical response, simultaneous record of, 17, 19 Mechanical stimulator, rotary, 291 Melon, electrical response of, 315 Memory, an after-effect of stimulus, 677 4 explanation of revival of, 685 ee persistence, dependent on strength of stimulus, 677 a5 spontaneous revival of, 680 Memory image, negative, 684 P Metal, abolition of response by poison, 9 1 : »» fatigue in response of, 7 »» response of, 6 Mimosa, electrical response of, 20, 110, 127, 268, 326 re electrical response under light, 401 »» hydraulic response in, 55 », hydro-positive and negative response of, 56, 59 »» | mechanical response under light, 400 5, phasic changes in response of, 303 »» teversal of response by fatigue, 326 5, Variation of motile sensibility of, 21 differential response of, 108 etecaiae model, 598 ; Molecular modification, reversal of normal response due to, 7 Molecular response, persistent after-effect in, 597, 601, 603 Molecular theory of excitation, 590 Molecular transformation, external tests of, 620 Morograph, 197 Morographic record by electro-motive response, 202 vs », by mechanical response, 198 ae 43 »» by resistivity variation, 546 Motor transformer, 281 754 COMPARATIVE ELECTRO-PHYSIOLOGY Munk on response in Dionea, 12 Musa, electrical response of, parallel to Dionea, 237 Muscle cylinder, electrical distribution in, 150 Multiple response, electrical in Biophytum, 209 9» wi oe in Desmodium, 218, 220 >» » ” in Drosera, 343 és » - €lectro-tactile in Mimosa, 209 ~ electrical in pitcher of Wefenthe, 341 % $5 re in stomach of frog, 347 re x mechanical, in Biophytum, 208 93 95 se in Desmodium, 212 ” ” 9 in nerve, 539 mf oe rheotomic record showing, 52 re 9 under light in Bzophytum, 407 » »» ” in Bryophyllum, 408 4 as “ in cauliflower, 406 on re ‘5 in frog’s retina, 426 » % 5 in human retina, 430 . és of growth, 221 Nepenthe, current of rest in, 335 a multiple response in, 341 - three types of response in, 338-340 Nerve, excitatory electrical changes in, 508 me sg mechanical changes in, 509 ,, failure to conduct, 530 Nerve of animal, electrical response of, me ay oa . conversion of positive to negative after ~ thermal tetanisation, 463 " % . - conversion of positive to negative by in- creasing intensity of stimulus, 466 * +3 Ra y»» ° employment of electrical stimulus, errors due to, 458 ” . os Pr enhancement of normal response after thermal tetanisation, 462 re 7 e sa gradual transformation from positive to negative through diphasic, 464 > » » 7 to equi-alternating shocks, 457 - 5a e a to injury of one contact, complications arising from, 458 ge +3 “ ay under stimulation by thermal shocks, 460 see also Conductivity Balance. ; Nerve of animal, mechanical response of, » ” +s i constituent twitches during tetanisation in, 535 oe) ry) 2 99 effect of drying on, 539 ” ” ” ” effect of alcohol on, 517 » » » 99 », Of ammonia on, 516 » » » 9 »» Of chloroform on, 518 + | . | . | | INDEX Lip SF Nerve of animal, mechanical response of, effect of morphia on, 516 » ” » » Sg ee tetanising electric shocks, 510 » e 3 ss five stages in, 89, 635 ” » a -3 multiple response in, 538° | os 0» 33 re relation between stimulus and, 657-659 et - e a similarities of, in plant and animal, 528 » ” ” ” % in motor and sensory, 529 ” y *” * three types of, 519 ox a 2 *F transient enhancement of, on cessation of tetanisation, 536 Nerve of plant, discovery of, 470 oe »» response of, conversion of abnormal to normal after tetanisation, 475 ; »» » a conversion of abnormal to normal by increasing in- tensity of stimulus, 476 | a ” >» a3 effect of alcohol on, 473 i 9 > $s effect of ammonia on, 474 ‘ ss st effect of CO, on, 472 9 ¥ 3 effect of ether on, 472 me fe “4 effect of tetanisation in enhancing, 476 $9 ee 4 three types in, 475 F a 5, Similarities of response in, and in animal, 471-478 Nerve at plant, mechanical response of, 528 % » 2 » determination of velocity by, 525 » » ” % effect of light on, 557 » > >» 9 enhancement after tetanisation, 554 Nervous impulse, two kinds of, 647 PS various direct and indirect manifestations of, 648 Noll, Haberlandt, and Nemec, statolithic theory of, 435 5 Nymphea alba, response of leaf of, 246 Ophiocephalus, mechanical response of optical nerve of, 529 $5 response in retina of, 427-429 Oscillating recorder, 527 Optic nerve and cornea, differential excitability between, 417 PAcINI, law of, 242 Pfeffer and Czapek on theory of geotropism, 435 Pfliiger, avalanche theory of, 502 Pfliiger’s law ; its failure with high E.M.F., 579 5 aS oa with low E.M.F., 581 5 », Of polar effects of currents, 578 Phasic reactions, alternating, 100 ,» Variations of current of rest, 302, 303 ns turgidity, 305 Phenoipthalines detection of transport channels by, 360° | Polar effects of currents, demonstration of : s i ay oe os by motile response in plants, 579 “= sy oa “3 . by subjective sensation, 582 g 756 - COMPARATIVE ELECTRO-PHYSIOLOGY Poison, action of, modification of, by dose and tonic condition, 640, 641 a on inorganic response, 9 Positive response of sub-tonic tissue, 83 a unmasking of, from resultant negative, 66 Pterospermum, analogy with Torpedo, 255 Pulvinated and growing organs, similarities of response in, 394 REID, on response of skin of eel, 289 Resistivity variation, determination of death-point by, 546 3 +3 response by, and its correspondence in the other modes of response, 549 v bs s3 experimental difficulties of, 540 ~ a », of metallic particles by, 3, 600-603 a ag », Of frog’s nerve by, 549 ae », of selenium by, 3 Response, bifurcated expression of, 104 - considered as molecular derangement, 590 rs law of differential, 109 = law of isotropic, 75 ‘3 positive, diphasic, and negative in cauliflower, 62 ” =a 29 ” in potato, 64 ‘5 simultaneous record of mechanical and electrical, 17, 19 re various forms of, 2 . Response recorder, 34 Retina, determination of differential excitability of, and optic nerve, 418 . ; 5» excitatory after-effect in, 427-430 - 7 », multiple response in human, 430 : 29 2 9 in frog, 426 . bere es Wallago, 425 Pe raion of, in Ophiocephalus, 427-429 = oy in frog, 418 5, so-called positive response of, .419 Retino-motor effect, 421 Retinal response, conversion of abnormal to normal, 423 oY ue explanation of abnormal, 423 ae ae three types of after-effect in, 427-429 Reverser, oscillating, 276 53 rotating, 280 Rheotome, observations with, 47, 254 Root as digestive organ, 349 », response of young and old, 353, 354 5» responsive secretion of, 352 Rosenthal on currént of rest in stomach, 288 Rotary Mechanical Stimulator, 291 SACHS on growth of Cucurbita in darkness, 557 Schonlein on oscillatory character of electric discharge, 270 Season, influence of, on recovery from stimulus, 45 es o on suctional response, 390 INDEX ; TBR Selenium, response of, 3 Sensation, conversion from positive to negative by tetanisation a 66 5 + different tones of, 646 ks dual elements in, 674 F effect on, of attention and inhibition, 652 are effect on, of molecular disposition, 663, 664 ss effect on, of progressive molecular change in nerve, 661 is identification with opposite nervous changes, 650 4. interchange of pleasurable and painful under electrotonus, 670- Oe », - negative element in, blocked by anesthetics, 673 | a3 positive and negative, 664 ; ny positive simple, negative complex, 665 Sensimeter, 670 Shoshungraph, 368 Skin, abnormal response converted to normal after Seeanie ols, 31 3 », response of, in frog, 300, 302 ' +r A in gecko, 310, 311 Re By in grape, 299, 301, 302 a Ss in intact human, 300 rs - in tomato, 397, 308, 309 i in tortoise, 307 Snail, foot of, response in, 316 aS ets resting current and its variation in, 318 Staircase response, 91, 103, 522,524, 625, 635 Stimulants, action of on inorganic response, 8 Stimulation, by chemical agents, 27 ae by equi-alternating electric shocks, 277 % by taps, 26 “4 by tension and compression, 25 ‘i by thermal shocks, 24 © effect of moderate, on conductivity, 504 a », of strong, on conductivity, 505 a instantaneous mechanical, 47 en response to various forms of, 24-27 re », to increasing intensity of, 40 ae rotary mechanical, 291 $3 vibratory, 27 Stimulator, electro-thermic, 38 ‘ “ vibratory, 30 Stimulus, effect of, on growth, 73 8 importance of, seen in ascent of sap, 382, 555 ” 99 9 autonomous response, 212, 555 29 ” 9 growth, 556 » » »» motile excitability, 554 - opposite effects of, on highly tonic and sub-tonic’ G'tissues, 77 4g relation between, and response : ” » in plant-tissue, 40, 41 2 ‘* in nerve of bull-frog, 658 » 2 in nerve of fern, 659 | e 758 COMPARATIVE ELECTRO-PHYSIOLOGY Stimulus, relation between, in nerve of gecko, 657 9 * in optic nerve, 659 .; ig magnetic, in iron, 660 Strasburger on ascent of poisons, 363 Suctional response, diminution of latent period of, 384 » 3 effect of anzesthetics on, 375 * . effect of poison on, 374: . »» effect of season on, 390 a 4 effect of variation of temperature on, 372 Pe =f initiation of, by stimulus, 382 a9 om osmotic versus excitatory action, 376, 377 x es persistence of, particular zone being killed, 373 = oe under method of balance, 383 - $s ‘5 aa »» * overbalance, 386 = i: », unbalanced method, 388 TABULAR statement : a is electro-motive variation in Desmodium leaflet, 219 9 . heliotropic effects, 394 Be determination of death-point, 205 $9 velocity of transmission in living tissues, 452 Tapper, the mechanical, 26 Temperature, different effects of, on conductivity and excitability, 187 ‘a effect of cold on electric response, 183 ae effect of cyclic variation of, on electric response, 189 9 effect of high, in abolishing response, 190 % effect of low, on autonomous response, 181 » effect of, on growth, 74 * effect of rise of, on autonomous response, 182 ¥ effect of rise of, on conductivity, 450, 501 93 effect of rise of, on electric response, 186 i effect of steady and sudden variation of, 74 Tetanus, genesis of mechanical and electrical, 43 Tetanisation, transient enhancement of response on cessation of : os » ‘3 in brominated silver, 429 » 9 99 in frog’s nerve, 536 » ” 3 in frog’s retina, 428 ” » 9 in magnetic response, 623 Tetanisation, effect of : A stage—conversion of abnormal to normal response, Electromotive response, + - continuous transformation from abnormal to normal in platinum, 629 ‘5 in nerve of fern, 475 1 zi in nerve of frog, 463 5 55 in skin of gecko, 311 Pn ‘ in tin, 628 Mechanical response, an os conversion from abnormal expansive contractile response in frog’s nerve, 627 to normal INDEX a 759 Tetanisation, effect of : Response by resistivity variation, ; as Ai 3 in selenium, 629 aK fe a in tungsten, 630 ’ B stage—enxhancement of normal response, . | Electro-motive response, ot i in nerve of fern, 475 ‘a »» in nerve of frog, 462 = = in response of tin, 630 Mechanical response, 58 ss in frog’s nerve, 634 Pe we in nerve of fern, 554 Response by resistivity variation, sf me in aluminium powder, 632 re Bn in selenium, 630 Magnetic response, 3 $s in response of iron, 632 D stage—/fatigue reversal of normal response, Electro-motive response, 9 ‘ reversal of normal response in Drosera, 342 ” 4 38 a in stomach of gecko, 346 Mechanical response, z ee reversal of normal contractile response in frog’s nerve, 635, 642 9 9 rr rs <3 in indiarubber, 642 oe) ” > ” 9 in nerve of gecko, 530 Response by resistivity variation, a », fatigue reversal in tungsten, 638 Thermal chamber, 200 os cork chamber, 500 ¥ shocks, quantitatiye stimulation of nerve by, 460 3 »» stimulation by, 38 variator, 113 Time-relations, difference of, in different tissues, 45 +s rheotomic observations on, 50 Tongue, response of human, 322 Torpedo, electrical organ of, 241 Tortoise, response of skin of, 307 a me of stomach of, 345 Transportation channels, detection of, by phenolpthaline, 36 VELOCITY of transmission : determination of, by electro-motive Inethed, 452 oe by mechanical method, 447 ss centrifugal versus centripetal, 448 ” effect of fatigue on, 449 *” 760 COMPARATIVE ELECTRO-PHYSIOLOGY Velocity of transmission : determination of, effect of intensity of stimulus on, 449 + effect of temperature on, 450 2 longitudinal versus transverse, 454 Verworn on polar effects of currents on Protozoa, 579 Vibratory stimulator, 30 Vision, binocular alternation of, 431 Visual impulse, pulsatory character, 432 Von Fleisch] on response of nerve, 278 WALLER on ‘blaze current,’ 260 7 on response of green leaves to light, 395 ss on response of skin, 294 oe on three types of response in nerve, 461 Waves, positive and negative : their characteristics, 67 Weber-Fechner’s law : its inadequacy, 656 Wood, demonstration of living characteristics of, 361 »» effect of anzsthetics and poison on pane of, 362, 36 »» effect on, of drying, 361 », normal response of, 361 ZANTEDESCI on organ current, 269 PRINTED BY SPOTTISWOODE AND CO. 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