Comparative Electro-Physiology: A Physico-Physiological Study

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

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. |

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 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 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

the positive A’. We may next take a flat strip of lead, of which the lower surface B is brominated... On mechanical stimulation of both surfaces by vibration it will now be found that the resultant responsive current flows across the strip, from the negatively-responding B to the positively- molecular disturbance on which excitation depends is caused by a non-electrical form of stimulus—the electrical character of the response obtained is unexcep- Fic. 166, © Flat Strip of Lead, of which

from any complication Response of upper surface positive, of lower y Pi : surface negative. Resultant response Let us next consider what would be the effect of sending induction shocks across such a strip. If inorganic bodies be really inexcitable, then we can here obtain only the counter-polarisation current as the after-effect. That is to say, on sending a shock from below to above in an ascending direction, we should observe only negative polarisation as an after-effect, or a descending current from above to below. A descending shock should, on the other hand, give rise to an ascending after-current. But if inorganic substances should prove to be excitable, and if B were to become on excitation relatively negative to A, as we found in the experiments on mechanical stimulation, then, whatever the direction of the shock, we should have a uni-directioned response, from below to above, exactly like the excitatory discharge of the electrical organ of Zorpedo, from the ventral surface to the dorsal.

‘ In order to brominate this surface as required, it may be held exposed to vapour of bromine. Or an electrical deposit may be made by electrolysis, in a bath of potassium bromide solution. A certain depth of deposit and time of formation are important to the successful preparation of the plate. When these are secured, the proper condition of responsiveness is found to be long-enduring as will be seen from the photographic records. I give below (fig. 167) photographic records of the responsive after-effects actually obtained on carrying out this experiment on the lead strip prepared as described. It is here seen that whatever had been the direction of the ‘shock, homodromous + or heterodromous |, the responsive current was always one-directioned : that is to say, from the more negatively-excitable lower to the positively-excitable upper surface. If the test of the ‘blaze-current’ is to be accepted, then we shall be compelled to refer this. metallic strip to the category of organic matter in a living condition !

Fic. 167. Photographic Records of After-effect of Homodromous *¢ and Heterodromous | Induction-shocks in Prepared Strip of Lead Note uni-directioned response, whatever be direction of induction-shock. Since it is admitted that the electrical response of living tissues is due to molecular excitation, and since we obtain similar electrical effects, as just seen, from the inorganic, it is clear that excitability is the property, not of the organic alone, but of all matter. It is also clearly seen that the one. directioned response of an anisotropic structure—so charac- teristic, among other things, of the electrical organ of certain fishes — depends on its differential molecular excit- ability. “The phenomenon is thus reduced to what are almost its last terms—namely, the molecular. It is therefore un- necessary to call in the aid of such indeterminate factors as vitalism, or assimilation and dissimilation,

In taking these responses to homodromous and hetero- . dromous shocks, the counter-polarisation-current is super- posed upon the excitatory effect. For this reason we see, in fig. 164, that the homodromous response, in which negative polarisation was an opposing factor, is smaller than the heterodromous, in which polarisation conspires with the excitatory current. We have seen, in our experiments on the leaf-organ, that when this negative polarisation is annulled by taking responses under equi-alternating elec- trical shocks, successive responses, giving the true excitatory effect, become equal. ~ I give here (fig. 168) a series of responses of the pre- pared lead strip, under these conditions of equi- alternating shocks, in which they are seen to have become equal, the resulting responsive cur- rent being from the lower surface to the upper, as before.

Having thus demon- sponses to Equi-alternating Electric strated in various ways See et Si of One Minute in epared Lead Strip the nature of that funda- Responsive Current as before from lower mental condition, which to upper surface. determines the excitatory discharge of the electrical, organ, we may next take other organs which are known to be differentially excitable, and observe whether they also, under electrical excitation, give definite uni-directioned responses.

The differential excitability of the upper and lower surfaces of the pulvinus of J/zmosa are well known. On subjecting this organ, then, to equi-alternating electrical shocks, I obtained uni-directioned responsive currents, their direction being from the more excitable lower to the less excitable upper half, of which a photographic record is given in fig. 169. In this particular specimen, owing to growing fatigue, the responses are seen to undergo diminution. In the sheathing petiole of Musa also, we found, as will be remem- bered, that the inner or concave surface was more excitable than the outer or convex. In taking records of the responses of such a specimen to equi-alternating electrical shocks, the direction of the responsive current was found to be from the more excitable inner to the less excitable outer surface.

It is now evident that in the structure of any single element of an electrical organ, the essential question is not ‘as to the corre- spondence of one part or another with muscle, nerve, or gland; but merely that of anisotropy. Any tissue which is anisotropic is potentially an electrical element. Thus a stem of Cucurbita origin- ally radial, becomes physiologically anisotropic when it happens to assume the recumbent posture, owing to the a-symmetrical action Fic. 169. Response of Pulvinus of environmental stimuli. Such

Flectric Shocks an anisotropic organ, when elec- Responsive current from more trically excited, gives a one- from the lower or ventral to the upper or dorsal surface. A similar reaction is, curiously enough, shown by the body of the Eel, which also, on excitation, gives a responsive current from the ventral surface to the dorsal. The responsive peculiarity of the constituent elements of the electrical organ is thus not unique. The extraordinary character of the organ depends merely upon the serial arrangement of innumerable such elements, connected with a nerve-trunk, by means of which a voluntary impulse is enabled to bring about the excitatory discharge of the electrical pile, and so convert it into a weapon of offence.

The most difficult problem with regard to these electrical organs having thus been solved, it remains to say a few words concerning two other points: namely, the natural current of rest and the repeating character of the excitatory discharge. As regards the first of these, Du Bois-Reymond found the current of rest—which he designated as the organ-current —to be in the direction of the electrical discharge. We have found, however, that, as a general rule, in the primary condition, the true natural current flows in the opposite direction to that of excitation, that is to say, from the less to the more excitable. In agreement with this, I find, in the leaf of Pterospermum, the electrical reaction of which is similar to that of the plate of Zorpedo, that while its excitatory current is from the more excitable ventral to the less excitable dorsal, its resting-current is opposite to this—that is to say, from dorsal to ventral. With regard to the electrical organ, then, there can be little doubt that here also the true resting-current would have been found to be opposite in direction to the excitatory, if it could have been observed and recorded under an absolute con- dition of physiological rest. In a highly excitable struc- ture, however, the shock of preparation, as we have seen and shall further see, leaves an after-effect which reverses the natural current of rest. For this reason, the current of rest observed in preparations of the electrical organ has not, in all probability, represented the true current, but rather the excitatory reversal of it. This view is supported by the fact that while in the organ-preparation of Torpedo, this reversed, or ingoing-current of rest is con- siderable, in the intact fish it is negligible. It must be borne in mind that the fish is spontaneously excitable, and also that there must remain a certain residual effect from the organ-discharges. Nevertheless Zantedeschi found a resting- current to occur in the intact fish in the reverse direction to that of the excitatory discharge. This was evidently the true resting-current. This view of the organ-current, of

Du Bois-Reymond, as, in reality, a persistent after-effect of excitation, gathers confirmation from an observation made by Gotch, that it is considerable in 7 orpedo, in which the excitatory effect also is known to be very persistent ; but in Malepterurus, where recovery from excitation is rapid, this particular organ-current is practically absent from excised preparations. | | 7 We may turn now to the repeated or oscillatory character observed in the electrical discharge by both Gotch and Schénlein. This is seen in the multiple apices ‘of its rheotomic curve. Multiple apices are also found, as we have seen, in the rheotomic observations on vegetable organs, given in fig. 40. Gotch attempts to explain these repeated responses of the electrical organ—which he calls ‘auto- excitation ’—by the passage through the tissue of the intense current due to the response; this he regards as exciting the tissue again, and bringing about the repetition of the same effect. With regard to this hypothesis, however, it is un- necessary to suppose that it is the intense electrical current of the first response which is the exciting cause of the second, and so on. For we must bear in mind that multiple response is not exclusively characteristic of these electrical organs, with their high intensity of discharge-current, but is exhibited by tissues of various kinds. These, as we have seen in Chapter XVII., may be thrown into a condition of rhythmic or multiple excitation by any form of stimulus, provided that its intensity be beyonda certain value. It thus happens, as we have seen, that while a single moderate stimulus induces a single response, a single strong stimulus induces multiple responses.

Indeed this fact—that it is not the intensity of the first responsive current, causing a new excitation of the tissue, which is accountable for the second, and so on— becomes quite clear, as soon as we make quantitative obser- vations of response, in those cases in which it receives undoubted visible manifestation, by the orderly fall of leaflets serially arranged—that is to say,in such plants as Biophyium. The sensitiveness of these leaflets is of that order which requires on an average an E.M.F. of 12 volts to cause excita- tion by kathode-make or anode-break. And this value is considerably higher for anode-break than for kathode-make. The lowest E.M.F. which I have found with highly excitable Biophytum to be effective in causing excitation, was 4 volts, and in less sensitive specimens it might be as high as 20 volts. )

Now, on applying a strong stimulus, say by contact of hot wire, on the petiole bearing the sensitive leaflets, an excitatory wave is initiated, which, during its progress, brings about depression of the leaflets in serial order. After an interval of about half a minute, a second wave is found to be initiated from the original point of excitation, causing a second series of responses, shown by the same serial depres- sion of the leaflets as before. And such recurrent excitations may take place from a single stimulus, as often as twenty times. On determining the E.M.F. value of each of these excitatory waves, however, I have found it to be of the order of ‘or volt. This, it will be seen, is only about four one-hundredths of the minimum E.M.F. necessary to induce excitation of the leaflet. It clearly follows that here the original stimulus is the cause of these multiple excitations, and not the first response the cause of the second.

The phenomenon of multiple response then, is, as we have seen, of very extensive occurrence, and not confined to elec- trical organs. We have seen it exhibited even by ordinary tissues, and we shall find in subsequent. chapters that such repeated responses are actually induced in nervous and glandular tissues, under the action of an intense stimulus. This is interesting in view of the fact that the electrical organs of fishes are made up of either neuro-muscular or neuro-glandular elements.

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 ot nerve —Complications arising from use of make and break shocks-—Rotating reverser—Motor transformer—Response of A/wsa 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.

WE have seen, in Chapter IX. that the differential excitability of any two points in a tissue can be detected, by observing the direction of resultant response, when both the points are simultaneously excited by an identical stimulus. It was seen in the same place also that the more excitable point becomes, under diffuse stimulation, relatively galvanometrically negative. I further described the various forms of quanti- tative stimulus which might be employed for this purpose, those, namely, of mechanical vibration and of stimulation by thermal shocks. By employing these non-electrical forms of stimulus the fundamental law of differential response was firmly established, in such a way as to exclude every source of uncertainty.

The electrical form of stimulation is characterised never- theless by many advantages. Its intensity, for instance, is easily graduated. But its principal superiority lies in its sreat flexibility of application. Any two points, however remote or difficult of access they may be, may by this means be subjected to a required stimulus, if we can only apply two electrodal points to them. These qualities, however, are counterbalanced by many serious drawbacks. For the re- sultant electrical change, induced at a given point by an electrical shock, is the sum of a number of changing factors, which may be broadly classified as excitatory and polarising. Let us suppose the induction shock to enter at a point. We shall there have the physiological polar effects of anode-make and anode-break. There is again, on the cessation of the current, a counter-electro-motive force due to polarisation. The physiological reaction, moreover, will depend on the excitability of the point.

Next, as regards the second or kathodal point, where the shock-current leaves the tissue. We have here the physiological effects of kathode-make and break, the factor of the ex- citability of the point, and the counter electro-motive force due to polarisation, all contributing to the resulting electrical change at that point. That relative electrical difference induced between the points A and Bb, which determines the observed electrical variation, thus equals the sum of the fluctuating factors acting on A, mznus the sum of the fluctuating factors acting on B. These elements of variation are sufficiently complicated ; but still another, as already said, is added to them, in the fact that, with regard to the excitatory polar effects of currents themselves, we have not to deal simply with the law enunciated by Pfliiger, that the kathode excites at make and the anode at break. The com- plete law, as will be shown in a later chapter, is complicated by the fact that the result depends on the intensity of the electro- motive force. With feeble and again with excessive E.M.F., the actual facts are the opposite of conclusions arrived at by Pfliiger. Under these circumstances it would appear at first sight impossible that any reliable results could be obtained by the employment of the electrical form of stimulation. I shall now, however, proceed to show in what manner all these difficulties may be overcome, and the electrical form of stimulus made extremely reliable. This will perhaps be best understood if we take a concrete example. Let us suppose

that a single electrical shock of moderate intensity enters an isotropic tissue at the point A, and leaves it at B ; A will then be the anode, and B the kathode. Here the true excitatory effect is found to take place only at the kathode, probably because the anode-break excitation takes place at much higher intensities of E.M.F. than the kathode-make. At these higher intensities, then, the anode-break effect also will occur. At an excessively high E.M.F. again, these relations, for reasons already explained, may undergo reversal. The point of such reversal would depend on the nature and excitability of the tissue. Though, for all these reasons, the relative excitations of A and B remain a matter of doubt, yet we may be sure of the excitation of both points, if two, or any equal . number, of exactly equal shocks be sent through the tissue in opposite directions, in rapid alternation. If, again, instead of two alternate shocks only, we give z alternating shocks, abso- -lutely equal, and if, further, the natural excitability of the two points A and B have been the same, then there will be nothing to distinguish the excitatory effect induced at A from that at B. In other words, the two excitations will be exactly equal. These strictly equal and opposite alternating currents, more- over, can have no resultant polarisation-effects, for the effect arising from an induction shock, in either direction, will be counteracted by that caused by the opposite.