Comparative Electro-Physiology: A Physico-Physiological Study

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- 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, 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

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

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

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 of succeeding responses undergo Stimulus : 30° vibration at interval ; rier . ‘ f one minute.

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 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

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.

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 fifteen minutes’ rest, and the responses in D are stronger than those in c. The vertical line between arrows represents ‘05 volt. (Turnip 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

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 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

Fic. 65. Photographic Records of Normal Mechanical Response of Mimosa to Single Stimulus: (upper 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

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

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

‘ ductivity variation. of various living tissues, but also of ing record (fig. 67) exhibits this oscillatory response in arsenic under the continuous stimulation of electric radiation. In 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.

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.

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

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

| 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

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.

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 ; 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

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-

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