Response in the Living and Non-Living

fatigue was present. It will be seen that the curves obtained by joining the apices of the successive single responses are very similar. In one case there is no fatigue, the recovery from each stimulus being complete. Every response in the Fig. 34.—ReEsponses TO INCREASING STIMULUS OBTAINED WITH Two SPECI- series therefore starts from a position of perfect equilibrium, and the height of the single responses increases with increasing stimulation. But in the second case,

the strain is not completely removed after any single stimulation of the series. That recovery is partial is seen by the gradual shifting of the base line upwards. In the former case the base line is horizontal and represents a condition of complete equilibrium. Now, however, the base line, or line of modified equilibrium, is tilted upwards. Thus even in this case if we measure the heights of successive responses from the line of absolute equilibrium, they will be found to increase with increasing stimulus. Ordinarily, however, we make no allowance for the shifting of the base line, measuring response rather from the place of its previous recovery, or from the point of modified equilibrium. Judged in this way, the responses undergo an apparent diminution.

Effect of very low temperature—Influence of high temperature —Determination of death-point—Increased response as after-effect of temperature variation—Death of plant and abolition of response by the action of steam. For every plant there is a range of temperature most favourable to its vital activity. Above this optimum, the vital activity diminishes, till a maximum is reached, when it ceases altogether, and if this pomt be maintained for a long time the plant is apt to be killed. Similarly, the vital activity is diminished if the temperature be lowered below the optimum, and again, at a minimum point it ceases, while below this minimum the plant may be killed. We may regard these maximum and minimum temperatures as the death-points. Some plants can resist these extremes better than others. Length of exposure, it should however be remembered, is also a determining factor in the question as to whether or not the plant shall survive unfavourable conditions of temperature Thus we have hardy plants, and plants that are affected by excessive variations of temperature. Within the characteristic power of the species, there may be, again, a certain amount of individual difference.

mine whether the undoubted changes induced by temperature in the vital activity of plants wi affect electrical response. Effect of very low temperature.—As regards the influence of very low temperature, | had opportunities of studying the question on the sudden appearance of frost. In the previous week, when the temperature was about 10° C., I had obtained strong electric response in radishes whose value varied from ‘05 to ‘1 volt. Buttwo or three days later, as the effect of the frost, I found electric response to have practically disappeared. A few radishes were, however, found somewhat resistant, but the electric response had, even in these cases, fallen from the average value of ‘075 V. under normal temperature to ‘005 V. after the frost. That is to say, the average sensitiveness had been reduced to about ,%. On warming the frost-bitten radish to 20° C. there was an appreciable revival, as shown by increase in response. In specimens where the effect of frost had been very great, i.e. in those which showed little or no electric response, warming did not restore responsiveness. From this it would appear that frost killed some, which could not he subsequently revived, whereas others were only reduced to a condition of torpidity, from which there was revival on warming.

I now tried the effect of artificial lowering of temperature on various plants. A plant which is very easily affected by cold is a certain species of Eucharis lily. I first obtained responses with the leaf-stalk of this lly at the ordinary temperature of the room (17° C.). I then placed it for fifteen minutes in a cooling chamber, temperature —2° C., for only ten minutes, after which, on trying to obtain response, it was found to have practically disappeared. I now warmed the plant by immersing it for awhile in water at 20° C., and this produced a revival of the response (fig. 35). If the plant be subjected to low temperature for too long a

I obtained a similar marked diminution of response with the flower-stalk of Arum lily, on lowering the temperature to zero. My next attempt was to compare the sensibility of different (b) lowered temperatures. Fic. 35.—Diinvtion or RESPONSE IN s Kucuaris BY Lowerinea or TEMPERATURE For this purpose I (a) Normal response at 17°C. F b) The response almost disappears when plantfis chose three specimens: subjected to —2° C. for fifteen minutes. ei (c) Revival of response on warming to 20° C. (1) Eucharis lily; (2) Ivy; and (8) Holly. I took their normal response at 17°C., and found that, generally speaking, they attained a fairly constant value after the third or fourth response. After taking these records of normal response, I placed the specimens in an ice-chamber,

temperature 0° C., for twenty-four hours, and afterwards took their records once more at the ordinary temperature of the room. From these it will be seen that while the responsiveness of Eucharis lily, known to be susceptible to the effect of cold, had entirely disappeared, that of the hardier plants, Holly and Ivy, showed very little change (fig. 36). Another very curious effect that I have noticed is that when a plant approaches its death-point by reason of excessively high or low temperature, not only is its general responsiveness diminished almost to zero, but even the slight response occasionally becomes reversed.

Holly Eucharis Fic. 36.—ArrreR-EFFECT OF Comp on Ivy, Houtiy, ann Evcuaris Liny a. The normal response; 0. Response after subjection to freezing temperature for twenty-four hours, Influence of high temperature, and determination of death-point.—I next tried to find out whether a rise of temperature produced a depression of response, and whether the response disappeared at a maximum temperature—the temperature of death-point. For this purpose I took a batch of six radishes. and obtained from them responses at gradually increasing temperatures. These specimens were obtained late in the season, and their electric responsiveness was much lower than those obtained earher. The plant, previously kept for five minutes in water at a definite temperature

(say 17° C.), was mounted in the vibration apparatus and responses observed. The plant was then dismounted, and replaced in the water-bath at a higher temperature (say 30° C.) again, for five minutes. A second set of responses was now taken. In this way observations were made with each specimen till the temperature at which response almost or altogether ceased was reached. I give below a table of results obtained with six specimens of radish, from which it would appear that response begins to be abolished in these cases at temperatures varying from 53° to 55° C.

Electric heating.—Ihe experiments just described were, however, rather troublesome, inasmuch as, in order to produce each variation of temperature, the specimen had to be taken out of the apparatus, warmed, and remounted. I therefore introduced a modification by which this difficulty was obviated. The specimen was now enclosed in a glass chamber (fig. 37), which also contained a spiral of German-silver wire, through which electric currents could be sent, for the purpose of heating the chamber. By varying the intensity of the current, the temperature could be regulated at will. The specimen chosen for experiment was the leaf-stalk of celery. It was kept at each given temperature for

ten minutes, and two records were taken during that time. It was then raised by 10° C., and the same process Amplitude of vibration which determines the intensity of stimulus is measured by the graduated circle seen to the right. Temperature is regulated by the electric heating coil R. For experiments on action of anesthetics, vapour of chloroform is blown in through the side tube. was repeated. It will be noticed from the record (fig. 38) that in this particular case, as the temperature

1 min Fic. 38.—Errect or TEMPERATURE ON RESPONSE The response was abolished at the hot-water temperature of 55° C. rose from 20° C. to 30° C., there was a marked diminution of response. At the same time, in this case at. least, recovery was quicker. At 20° C., for example, the response was 21 dns., and the recovery was not complete in the course of a minute. At 30° C., however, the response had been reduced to 7:5 divisions, but there was almost complete recovery in twelve seconds. As the temperature was gradually increased, a continuous decrease of response occurred. This diminution of response with increased temperature appears to be universal, but the quickening of recovery may be true of individual cases only.

(‘01 Volt = 35 divisions) Temperature Response Temperature Response ee 21 | SO aan Aaa 2) ee 75 | GO ences 3 AN Soar 5:5 In radishes response disappeared completely at 55° C,, but with celery, heated in the manner described, I could not obtain its entire abolition at 60° C. or even higher. <A noticeable circumstance, however, was the prolongation of the period of recovery at these high temperatures. I soon understood the reason of this apparent anomaly. The method adopted in the present case was that of dry heating, whereas the previous experiments had been carried on by the use of hot water. It is well known that one can stand a temperature of 100° C. without ill effects in the hot-air chamber of a Turkish bath, while immersion in water at 100° C. would be fatal.

for five minutesin water at 55° C. This, as will be seen from the record taken afterwards, effectively killed the plant (fig. 38, w). Increased sensitiveness as after-effect of temperature variation.—A very curious effect of temperature variation is the marked increase of sensitiveness which often Fic. 39.--Errect oF Risinc AND FaLuinc TEMPERATURE ON THE RESPONSE oF Scorcu Kae appears as its after-effect. I noticed this first in a series of observations where records were taken during the rise of temperature and continued while the temperature was falling (fig. 39). The temperature was adjusted by electric heating. It was found that the responses were markedly enhanced during cooling, as

compared with responses given at the same temperatures while warming (see table). Temperature variation thus seems to have a stimulating effect on response, by increasing molecular mobility in some way. The second Fic. 40.—Rercorps or Responses IN EucuHaris Liny purinac Rise Anp Faun or TEMPERATURE Stimulus constant, applied at intervals of one minute. The temperature of plant-chamber gradually rose on starting current in the heating coil; on breaking current, the temperature fell gradually. Temperature correspond- K S Miho 5 : E i ing to each record is given below.

ee ere ode eis lieve, ee oes NO spite oo. | cw yell Sock Vela lpr teh CONC S CAA 1510) nay ee ee : Si. wlGy AU e arcs” hes oe — of temperature. Fig. 41 gives a curve of variation of response during the rise and fall of temperature. Point of temperature maximum,—We have seen how, in cases of lowered temperature, response is abolished earlier in plants like Eucharis, which are affected by cold, than in the hardier plants such as Holly and Ivy. Plants again are unequally affected as regards the upper range. In the case of Scotch kale, for instance, response disappears after ten minutes of water temperature of about 55° C., but with Eucharis fairly marked response can still be obtained after such

Fie. 41.—CurvE sHowING VARIATION oF RESPONSE IN EUCHARIS WITH THE RisE AND Fay or TEMPERATURE immersion and does not disappear till it has been subjected for ten minutes to hot water, at a temperature of 65° C. or even higher. The reason of this great power of resistance to heat is probably found in the fact that the Eucharis is a tropical plant, and is grown, in this country, in hot-houses where a comparatively high temperature is maintained. The effect of steam.—I next wished to obtain a continuous record by which the effects of suddenly increased temperatures, culminating in the death of the plant, might be made evident. For this purpose I mounted the plant in the glass chamber, into which steam

could be introduced. I had chosen a specimen which gave regular response. On the introduction of steam, with the consequent sudden increase of temperature, there was a transitory augmentation of excitability. But this quickly disappeared, and in five minutes the plant was eflectively killed, as will be seen graphically illustrated in the record (fig. 42). “N After Fic. 42.._Errect or Steam 1n Kitiinac REsPoNsE The two records to the left exhibit normal response at 17°C. Sudden warming by steam produced at first an increase of response, but five minutes’ exposure to steam killed the plant (carrot) and abolished the response. Vibrational stimulus of 30° applied at intervals of one minute; vertical line='1 volt.

It will thus be seen that those modifications of vital activity which are produced in plants by temperature variation can be very accurately gauged by electric response. Indeed it may be said that there is no other method by which the moment of cessation of vitality are able to judge that a plant has died, only after various indirect effects of death, such as withering, have begun to appear. But in the electric response we have an iminediate indication of the arrest of vitality, and we are thereby enabled to determine the death-point, which it is impossible to do by any other means.

It may be mentioned here that the explanation suggested by Kunkel, of the response being due to movement of water in the plant, is madequate. For in that case we should expect a definite stimulation to be under all conditions followed by a definite electric response, whose intensity and sign should remain invariable. But we find, instead, the response to be profoundly modified by any influence which affects the vitality of the plant. For instance, the response is at its maximum at an optimum temperature, a rise of a few degrees producing a profound depression; the response disappears at the maximum and minimum temperatures, and is revived when brought back to the optimum. Ansesthetics and poisons abolish the response. Again, we have the response undergoing an actual reversal when the tissue is stale. All these facts show that mere movement of water could not be the effective cause of plant response.

Effect of anesthetics, a test of vital character of response—Effect of chloroform—FEffect of chloral—Effect of formalin—Method in which response is unaffected by variation of resistance—Advantage of block method—Effect of dose. THE most important test by which vital phenomena are distinguished is the influence on response of narcotics and poisons. For example, a nerve when narcotised by chloroform exhibits a diminishing response as the action of the anesthetic proceeds. (See below, fig. 43.) Similarly, various poisons have the effect of permanently abolishing all response. Thus a nerve is killed by strong alkalis and strong acids. I have already shown how plants which previously gave strong response did not, after application of an anesthetic or poison, give any response at all. In these cases it was the last stage only that could be observed. * But it appeared important to be able to trace the growing effect of anesthetisation or poisoning throughout the process. There were, however, two conditions which it at first appeared difficult to meet. First it was necessary to find a specimen which would normally exhibit no fatigue, and give rise for a long time to a uniform series

of response. The immediate changes made in the response, in consequence of the application of chemical reagents, could then be demonstrated in a striking manner. And with a little trouble, specimens can be secured in which perfect regularity of response is found. The record given in fig. 16, obtained with a specimen of radish, shows how possible it is to secure plants in which response is absolutely regular. I subjected this to uniform stimulation at intervals of one minute, during half an hour, without detecting the least variation

Before ap After Fic. 43.—Errecr of CHLOROFORM ON NERVE Response (WALLER) in the responses. But it is of course easier to find others in which the responses as a whole may be taken as regular, though there may be slght rhythmic fluctuations. And even in these cases the effect of reagents is too marked and sudden to escape notice. For the obtaining of constant and strong response I found the best materials to be carrot and radish, selected individuals from which gave most satisfactory results. The carrots were at their best in August and September,

after which their sensitiveness rapidly declined. Later, being obliged to seek for other specimens, I came upon radish, which gave good results in the early part of November ; but the setting-in of the frost had a prejudicial effect on its responsiveness. Less perfect than these, but still serviceable, are the leaf-stalks of turnip and cauliflower. In these the successive responses as a whole may be regarded as regular, though a curious alternation is sometimes noticed, which, however, has a recularity of its own.

My second miseiving was as to whether the action of reagents would be sufficiently rapid to display itself within the time limit of a photographic record. This would of course depend in turn upon the rapidity with which the tissues of the plant could absorb the reagent and be affected by it. It was a surprise to me to find that, with good specimens, the effect was manifested in the course of so short a time as a minute or so. Effect of chloroform.—lIn studyine the effect of chemical reagents in plants, the method is -precisely similar to that employed with nerve; that is to say, where vapour of chloroform is used, it is blown into the plant chamber. In cases of liquid reagents, they are applied on the points of contact A and B and their close neighbourhood. The mode of experiment was (1) to obtain a series of normal responses to uniform stimuli, applied at regular intervals of time, say one minute, the record being taken the while on a photographic plate. (2) Without interrupting this procedure, the anesthetic agent, vapour of chloroform, was blown into the closed chamber containing the plant.

Tt will be seen how rapidly chloroform produces depression of response (fig. 44), and how the effect grows with time. In these experiments with plants, the same curious shifting of the zero line is sometimes noticed as in nerve when subjected similarly to the action of reagents. This is a point of minor importance, the Fic. 44.—Errrecr or CHLOROFORM ON RESPONSES OF CARROT Stimuli of 25° vibration at intervals of one minute. essential point to be noticed being that the responses are rapidly reduced.

Effects of chloral and formalin.—I give below (figs. 45, 46) two sets of records, one for the reagent chloral and the other for formalin. The reagents were applied in the form of a solution on the tissue at the two leading contacts, and the contiguous surface. The rhythmic fluctuation in the normal response shown minute of the application of chloral, is also extremely well marked. Fie. 45.—Acrion or CHnoran HyprRATE ON THE RESPONSES OF LEAF-STALK OF

Vibration of 25° at intervals of one minute. Response unaffected by variation of resistance.—In order to bring out clearly the main phenomena, I have difficulty. To determine the influence of a reagent in modifying the excitability of the tissue, we rely upon variation. We read this effect by means of galvanometric deflections. And if the resistance of the circuit remained constant, then an increase of galyanometer deflection would accurately indicate a heightened or depressed E.M. response, due to greater or less excitability of tissue caused by the reagent. But, by the introduction of the chemical reagent, the resistance of the tissue may undergo change, and owing to this cause, modification of response as read by the galvanometer may be produced without any E.M. variation. The observed variation of response may thus be partly owing to some unknown change of resistance, as well as to that of the E.M. variation in response to stimulus.

We may however discriminate as to how much of the observed change is due to variation of resistance by comparing the deflections produced in the galvanometer by the action of a definite small E.M.F. before and after the introduction of the reagent. If the deflections be the same in both cases, we know that the resistance has not varied. If there have been any change, the variation of deflection will show the amount, and we can make allowance accordingly.

I have however adopted another method, by which all necessity of correction is obviated, and the galvanometric deflections simply give E.M. variations, unaffected by any change in the resistance of the tissue. This is done by interposing a very large and constant resistance in the external circuit and thereby making other resistances negligible. An example will make this point clear. Taking a carrot as the vegetable tissue, I found its resistance plus the resistance of the non-