Response in the Living and Non-Living

(a) When there is little friction we get an afteroscillation, to which we have the corresponding phenomenon in the retinal after-oscillation (compare fig. 105). (6 andc) If the friction is increased, there is a damping of oscillation. In (ce) we get recovery-curves similar to those found in nerve, muscle, plant, and metal. (7) If the friction is still further increased the maximum is reached much later, as will be seen in the increasing slant of the rising part of the curve; the height of response is diminished and the period of recovery very much prolonged by partial molecular arrest. The curve (d) is very similar to the ‘ molecular arrest curve obtained by small dose of chemical reagents which act as ‘ poison’ on living tissue or on metals (compare fig. 93, a).

(e) When the molecular mobility is further decreased there is no recovery (compare fig. 93, 0). Still further increase of friction completely arrests the molecular pendulum, and there is no response. From what has been said, it will be seen that if in any way the friction is diminished or mobility increased the response willbe enhanced. This is well exemplified in the heightened response after annealing (fig. 58) and after preliminary vibration (figs. 81, 82).

Possibly connected with this may be the increased responses exhibited by the action of stimulants (figs. 89, Reduction of molecular sluggishness attended (1) by quickened recovery.—Sometimes, after a cell has been resting for too long a period, especially on cold days, the wire gets into a sluggish condition, and the period of recovery is thereby prolonged. But successive vibrations gradually remove this inertness, and recovery is then hastened. This is shown in the accompanying curves, fig. 63, where (a) exhibits only very partial

(a) Slow recovery of a wire in a sluggish condition. (6) Quickened recovery in the same wire after a few vibrations. recovery even after the expiration of 60 seconds, whereas when a few vibrations had been given recovery was entirely completed in 47 seconds (b). There was here little change in the height of response. Or (2) by heightened response.—The removal of slugeishness by vibration, resulting in increased molecular mobility, is in other instances attended by increase in the height of response, as will be seen from the two sets of records which follow (fig. 64). Cold, due to prevailing frosty weather, had made the wires in the cell somewhat lethargic. The records in (a) were

the first taken on the day of the experiment. The amplitudes of vibration were 45°, 90°, and 135°. In(b) are given the records of the next series, which are in every case greater than those of (a). This shows that previous vibration, by conferring increased mobility, had heightened the response. In this case, removal of molecular sluggishness is attended by greater intensity of response, without much change in the period of recovery. In connection with this it must be remembered that

(a) Three sets of responses for 45°, 90°, and 135° vibration in a sluggish wire. (b) The next three sets of responses in the same wire ; increased mobility conferred by previous vibration has heightened the response. ereater strain consequent on heightened response has a general tendency to a prolongation of the period of recovery. It is thus seen that when the wire is im a sluggish condition, successive vibrations confer increased molecular mobility, which finds expression in quickened recovery or heightened response.

Effect of temperature.—Similar considerations lead us to expect that a moderate rise of temperature will be conducive to increase of response. This is exhibited in the next series of records. The wire at the low temperature of 5° C. happened to be in a sluggish condition, and the responses to vibrations of 45° to 90° in amplitude were feeble. Tepid water at 30° C. was now substituted for the cold water in the cell, and the responses under- (a) Responses when the wire was in a sluggish condition at temperature of 5° C. (6) Enhanced response at 30° C. . (c) Diminution of response at 90° C,

went a remarkable enhancement. But the excessive molecular disturbance caused by the high temperature of 90° C. produced a great diminution of response (fig. 65). Diphasic variation.—It has already been said that if two points A and B are in the same physico-chemical condition, then a given stimulus will give rise to similar excitatory electric effects at the two points. It the ealvanometer deflection is ‘ up’ when A alone is excited, the excitation of B will give rise to a downward deflection. When the two points are simultaneously excited the electric variation at the two points will continuously balance each other. Under such conditions there will be no resultant deflection. But if the intensity of stimulation of one point is relatively stronger, then the balance will be disturbed, and a resultant deflection produced whose sign and magnitude can be found independently by the algebraical summation of the individual effects of A and B.

Tt has also been shown that a balancing point for the block, which is approximately near the middle of the wire, may be found so that the vibrations of A and B through the same amplitude produce equal and opposite deflection. Simultaneous vibration of both will give no resultant current; when the block is abolished and the wire is vibrated as a whole, there will still be no resultant, inasmuch as similar excitations are produced at A and B. After obtaining the balance, if we apply an exciting reagent like Na,CO, at one point, and a depressing reagent like KBr at the other, the responses will now become unequal, the more excitable point giving a stronger deflection. We can, however, make the two deflections equal by increasing the amplitude of vibration of the less sensitive point. The two deflections may thus be rendered equal and opposite, but the time relations—the latent period, the time rate for attaining the maximum excitation and recovery from that effect—will no longer be the same in the two cases. There would therefore

a) Records of A and B obtained separately. R’ is the resultant by algebraical summation. (b) Diphasic record obtained by simultaneous stimulation of A and B. By suitably increasing the amplitude of vibration of the less sensitive, the two deflections were rendered The records of A and B were at first taken separately (fig. 66,a). It will be noticed that the maximum deflection of A was attained relatively much earlier than that of B. The resultant curve R’ was obtained by summation.

After taking the records of A and B separately, a record of resultant effect R due to simultaneous vibration of A and B was next taken. It gave the curious two-phased response — positive effect followed by negative after-vibration, practically similar to the resultant curve R’ (fig. 66, b). The positive portion of the curve is due to A effect and the negative to B. If by any means, say by elther increasing the amplitude of vibration of A or increasing its sensitiveness, the response of A is very greatly enhanced, then the positive effect would be predominant and the negative effect would become inconspicuous. When the two constituent responses are of the same order of magnitude, we shall have a positive response followed by a negative after-vibration ; the first twitch will belong to the one which responds earlier. If the response of A is very much reduced; then the positive effect will be reduced to a mere twitch and the negative effect will become predominant.

I give aseries of records, fig. 67, in which these three principal types are well exhibited, the two contacts having been rendered unequally excitable by solutions of the two reagents KBr and Na,CO;.. A and B were vibrated simultaneously and records taken. (a) First, the relative response of B (downward) is increased by increasing its amplitude of vibration. The amplitude of vibration of A was throughout maintained constant. The negative or downward response is now very conspicuous, there being only a mere preliminary indication

of the positive effect. (+) The amplitude of vibration of B is now slightly reduced, and we obtain the diphasic effect. (c) The intensity of vibration of B is diminished still further, and the negative effect is seen reduced to a slight downward after-vibration, the positive up-curve being now very prominent (fig. 67). Fic. 67.—Nraative, DrpHastc, AND Positive Resuurant REsPoNSE Continuous transformation from negative to positive I have shown the three phases of transformation, the intensity of one of the constituent responses being varied by altering the intensity of disturbance.

In the following record (fig. 68) I succeeded in obtaining a continuous transformation from positive to negative phase by a continuous change in the relative sensitiveness of the two contacts. I found that traces of after-effect due to the application of Na,CO; remain for a time. If the reagent is previously applied to an area and the traces of the carbonate then washed off, the increased sensitiveness conferred disappears gradually. Again, if we apply Na,CO,; solution to a fresh point, the sensitiveness gradually increases. There is another further interesting point to be noticed: the beginning of response is earlier when the application of Na,CO; is fresh.

We have thus a wire held at one end, and successive uniform vibrations at intervals of one minute imparted Fic. 68.—Contrnvovus TRANSFORMATION FROM NEGATIVE TO PosITIVE THROUGH INTERMEDIATE DieHasic RESPONSE Thick dots represent the times of application of successive stimuli. to the wire as a whole, by means of a vibration head on the other end. Owing to the after-effect of previous application of Na,CO, the sensitiveness of B is at the beginning ereat, hence the three resultant responses at the beginning are negative or downward.

Dilute solution of Na,OO; is next applied to A. The response of A (up) begins earlier and continues to grow stronger and stronger. Hence, after this application, the response shows a preliminary positive twitch of A followed by negative deflection of B. The positive grows continuously. At the fifth response the two phases, positive and negative, become equal, after that the positive becomes very prominent, the negative being reduced as a feeble after-vibration.

It need only be added here that the diphasic variations as exhibited by metals are in every way counterparts of similar phenomena observed in animal tissues. Fatigue in metals—Fatigue under continuous stimulation—Staircase effect —Reversed responses due to molecular modification in nerve and metal, and their transformation into normal after continuous stimulation—Increased response after continuous stimulation. Fatigue.—In some metals, as in muscle and in plant, we find instances of that progressive diminution of response which is known as fatigue (fig. 69). The accompanying record shows this in platinum (fig. 70). It has been said that tin is

only. Nothing is absolutely indefatigable. The exhibition of fatigue depends on various conditions. Even in tin, then, I obtained the characteristic fatigue-curve many days (fig. 71). While discussing the subject of fatigue in plants, I have adduced considerations which showed that the residual effect of strain was one of the main causes for the production of fatigue. This conclusion receives independent support from the records obtained with metals.

important fact is that the various typical fatigue Fic. 71.—FaticurE sHowN By TIN - ac : ae WIRE WHICH HAD BEEN CONTINU- effects exhibited in living OUSLY STIMULATED FOR SEVERAL substances are exactly re- a produced in metals, where there can be question neither of fatigue-product producing fatigue effects, nor of those constructive processes by which they might be removed. We have seen, both in muscles and in plants, that if sufficient time for complete recovery be allowed between each pair of stimuli, the heights of successive responses are the same, and there is no apparent fatigue (see page 39). But the height of response diminishes as the excitation mterval is shortened. We find the same thing in metals. Below is given a record taken with tin (fig. 72). Throughout the experiment the amplitude of vibration was maintained constant, but m (a) the interval between consecutive stimuli was 1’, while in (0) this was reduced to 30”. A diminution of height immediately occurs. On restore the original rhythm as in (¢), the responses revert to their first large value.

Thus we see that when the wire has not completely recovered, its responses, owing to residual strain, undergo diminution. Height of response is thus decreased by incomplete recovery. If then sufficient time be not allowed for perfect recovery, we can understand how, under certain circumstances, the residual strain would progressively increase with repetition of stimulus, and thus there would be a progressive diminution of height Fic. 72.—Diminution or RESPONSE DUE TO SHORTENING THE PERIOD OF The stimulus is maintained constant. In (a) the interval between two suc-

cessive stimuli is one minute, in (6) it is half a minute, and in (ce) it is again one minute. The response in (b) is feebler than in either (a) or (c). of response or fatigue. Again, we saw in the last chapter that mcrease of stram necessitates a longer period of recovery. Thus the longer a wire is stimulated, the more and more overstrained it becomes, and it therefore requires a gradual prolongation of the interval between the successive stimuli, if recovery is to o maintained

be complete. This interval, however, being constant, the recovery periods virtually undergo a more and more incomplete. These considerations may be found to afford an insight into the progressive diminution of response in fatigued substances. Fatigue under continuous stimulation.—Fatigue is perhaps best shown under continuous stimulation. For example, in muscles, when fresh and not fatigued, the top of the tetanic curve is horizontal, or may even be ascending, but with long-continued stimulation the curve declines. The rapidity of this decline depends on the nature of the muscle and its previous condition.

In metals I have found (a) (b) exactly parallel instances. In 8 tin, so little lable to fatigue, (a The top of response-curve un- : der continuous stimulation in the top of the curve is horitin is horizontal or ascending zontal or ascending ; or it may there is tapid decline owing to = 5 atigue. exhibit a slight decline. But the record with platinum shows the rapid decline due to fatigue (fig. 73). Taking any of these instances, say that in which fatigue is most prominent, it is found that short period of rest restores the original intensity of response. This affords additional proof of the fact that fatigue is due to overstrain, and that this strain, with its sign of attendant fatigue, disappears with time.

Staircase effect.—We shall now discuss an effect which appears to be the direct opposite of fatigue. This is the curious phenomenon known to physiologists as ‘the staircase’ effect, in which successive uniform is seen under particular conditions in the response of certain muscles (fig. 74, a). It is also observed sometimes even in nerve, which otherwise, generally speaking, gives uniform responses. Of this effect, no satisfactory theory has as yet been offered. It is in direct contradiction to that theory which supposes that each stimulus is followed by dissimilation or break-down of the tissue, reducing its function below par. For in these cases the supposed dissimilation is followed not by a decrease but by an increase of functional activity. This ‘staircase. effect’ I have shown to be occasionally exhibited by plants. I have also found it in metals. In the last chapter we have seen that a wire often falls,

a lone time, into a state of Fia. 74.—‘ STAIRCASE ’ EFFECT 5 < ? (a) in muscle (after Engelmann). comparative — sluggishness, (b) in metal. ; and that this molecular inertness then gradually gives place to increased mobility under stimulation. As a consequence, an increased response is thus obtained. I give in fig. 74, 6, a series of responses to uniform stimuli, exhibited by platinum which had been at rest for some time. This effect is very clearly shown here. So we see that im a substance which has previously been in a sluggish condition, stimulation confers increased mobility. Re- sponse thus reaches a maximum, but continued stimulation may afterwards produce overstrain, and the subsequent responses may then show a decline. This

exhibited by muscles, where the first part of the series exhibits a staircase increase followed by declining responses of fatigue. Reversed response due to molecular modification and its transformation into normal after continuous stimulation (1) in nerve.—Reference has already been made to the fact that a nerve which, when fresh, exhibited the normal negative response, will often, if kept for some time in preservative saline, undergo a molecular modification, after which it gives a positive variation. Thus while the response given by fresh nerve is normal or negative, a stale nerve gives modified, 1.e. reversed or positive, response. This peculiar modification does not always occur, yet is too frequent to be considered abnormal. Again, when such a nerve is subjected to tetanisation or continuous stimulation, this modified response tends once more to become normal.

It is found that not only tetanisation, but also CO, has the power of converting the modified response into normal. Hence it has been suggested that the conversion under tetanisation of modified response to normal, in stale nerve, is due to a hypothetical evolution of CO, in the nerve during stimulation.! (2) In metals.—I have, however, met with exactly parallel phenomena in metals, where, owing to some molecular modification, the responses became reversed, and where, under continuous stimulation, though here

1 «Considering that we have no previous evidence of any chemical or physical change in tetanised nerve, it seems to me not worth while pausing to deal with the criticism that it is not CO,, but “something else” that has given the result.’—Waller, Animal Electricity, p. 59. That this phenomenon is nevertheless capable of physical explanation will be shown presently. there could be no possibility of the evolution of CO,, they tended again to become normal.

If after mounting a wire in a cell filled with water, it be set aside for too long a time, I have sometimes noticed that it undergoes a certain modification, owing to which its response ceases to be normal and becomes reversed in sign. I have obtained this effect with various metals, for instance lead and tin, and even with the chemically inactive substance Fic, 75.—ABNoRMAL PosirIvE (tp) Respons—E IN NERVE CONVERTED INTO Normal (powN) Response AFTER Continuous Stimunation T (WALLER) The galvanometer is not dead-beat, and shows after-oscillation.

The subject will be made clearer if we first follow in detail the phenomenon exhibited by modified nerve, eiving this abnormal response. The normal responses in nerve are usually represented by ‘down’ and the reversed abnormal responses by ‘up’ curves. In the modified nerve, then, the abnormal responses are ‘up ’ instead of the normal ‘down.’ The record of such abnormal response in the modified nerve is shown in responses are undergoing a diminution, or tending towards the normal. After continuous stimulation or tetanisation (T), it will be seen that the abnormal or ‘up’ responses are converted into normal or ‘down,’