Comparative Electro-Physiology: A Physico-Physiological Study

“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 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

' * 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). > 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. 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, 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 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-

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. 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 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, —

_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

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. 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

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 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—In- creasing response to increasing stimulus—Effect of fatigue—Tetanus . 29 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

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

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

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

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

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 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 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

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

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! 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

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

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

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

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— 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