Comparative Electro-Physiology: A Physico-Physiological Study

_ 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.

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 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

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

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 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

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 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 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

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 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

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. 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 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

. 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 . Positive, diphasic and negative Seanoues in petiolé of cauliieer . Unmasking of positive element in response by selective block : . Effects of steady and sudden variation of Pome on a prowth . Fatigue due to overstrain . ‘ ae . Fatigue-decline under continuous stimulation, i in medhanical response

. Fatigue-decline under continuoas ecmueaens in tecnica! response . Phasic alternation in mechanical dessonne of style of Diiave . Reversal of normal response in fatigued nerve . : . . Bifurcated expression of response as growth and mechantesl response . Differential response of compound strip . : . Isolated responses of upper and lower halves of ihe inus af Mitosa, . Transverse differential electrical response of eee af Mian . Transverse differential electrical response of plagiotropic stem of

. Transverse differential dlectrical: reponse i cetiole of Musa . Effect of CO, on current of rest ‘ . Reversal of natural current of rest as after- stint of esimuladion 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

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 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

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 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

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 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

Isolated responses to mechanical stimulus of id ali tower porbiecs of grape skin . : : : ‘ Illustrative response of pulvinus of AZmosa waniae sei? variation Illustrative autonomous senanee of Desmodium exhibiting cyclic variation : Abnormal diphasic response of skin of gecko, ceerieds to aaian | after tetanisation Response of human tongue . : Normal response of pulvinus of eee révened sue eigntaation Response of Dz//enia and its reversal after tetanisation

Determination of natural current of rest in digestive organ of Nepenthe . Normal response of digestive leaf of Drosera and its reversal éter tetanisation 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 . - ‘ : Multiple response in pitcher of Wepenthe with entrapped insects Multiple response in Drosera . , Multiple response in stomach of frog Electrical response of sii wood and its lepresson aniter anses- thetic .

Initiation of suctional response and enhanceiient under atcaatite 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 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 .

Determination of differential excitability as between optic nerve and cornea ‘ Determination of differential away as orcas Gina aoe opéle nerve . Conversion of abnormal retinal response to normal by escitatocy agents 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

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 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