SOCIETY, PHYSIOLOGICAL PROCEEDI NGS. June 6, rod, and held near the bottom of the inside of a cylindrical Dewar flask

Transcription

1 PROCEEDI NGS OF THE PHYSIOLOGICAL SOCIETY, June 6, Improved myothermic apparatus. By A. V. HILL and VIKTOR WEIZSACKER. (Demonstration.) All myothermic experiments made hitherto on isolated muscles have been carried out in air, oxygen or nitrogen. We have developed a method for working on muscles immersed in Ringer's solution, which is thoroughly simple, and offers various advantages. We use a-thermopile of the form described by A. V. Hill (This Journal, XLVI. p ), a "long straight thermopile" with 3.5 pairs of junctions. The thermopile contains muscle holder and stimulating electrodes complete. The thermopile holding the muscle is fixed to a long glass rod, and held near the bottom of the inside of a cylindrical Dewar flask of 40 cm. depth and 8 cm. diameter. Enough Ringer's solution (500 c.c.) is introduced to cover the muscle and thermopile. A wooden stopper holds the glass rod and closes the Dewar flask. Through holes drilled in the stopper go (1) the insulated leading-off wires of the thermopile, (2) wires for electric excitations, (3) a thread to the end of the muscle for recording isometric contractions, (4) a stirrer and (5) a tube for changing the Ringer's solution. The chief advantages and peculiarities of this arrangement are as follows: (1) rapid attainment of temperature equilibrium: (2) easy maintenance of a constant temperature, whether at, above or below the room temperature: (3) possibility of a rapid alteration of physical or chemical conditions, by changing the Ringer's

2 xxxvi PROCEEDINGS OF THE PHYSIOLOGICAL solution: (4) very much better conditions for the muscle, which lives far longer in the Ringer's solution than it ever will do in air. The apparatus has been used to estimate heat-production both in single twitches and in tetani. The heat-capacity of water is some 3000 titnes greater than that of air: its conductivity somewhat greater. Both factors cause a rapid and great heat loss from the muscle to the surroundings, and it is found in practice that the galvanometer deflections are reduced 5 to 10 times by immersing the muscle in the Ringer. Nevertheless, the 100 mm. or so obtained for a sinale twitch is quite sufficiently large, and we have found that we can obtain a sensitivity amply sufficient for all purposes. In consequence of the greater heat-capacity of the convection currents set up in water, the galvanometer is not so steady as when the thermopile is in air. The investigations made therefore have confined themselves hitherto to the initial heat-production. It should be distinctly understood that these experiments are not calorimetrical: the rise of temperature of the muscle immediately warms the thermopile in contact with it: the heat is not collected and measured as in a micro-calorimeter. The effects of various physical and chemical factors on the initial heat-production of muscle. By VIKTOR WEIZSACKER. By the method communicated by A. V. Hill and myself, myothermic experiments can be carried out with muscles immersed in various solutions. The chief results obtained so far by this method are as follows. In the first place it should be noticed that a rapid change of the solution around the muscle can be effected, and it is usually possible within a few minutes of changing the solution to make observations of the heat-production. Thus successive observations on the muscle, under various conditions, are rendered possible before the general condition of the muscle has had time to change appreciably. It has been found that the "initial heat-production " (as represented by the maximum deflection of the galvanometer) is exactly the same in Ringer's solution (a) saturated with, or (b) free from oxygen. Also, when oxidations are prevented by the presence of KCN the initial heatproduction is unaltered. It is therefore very likely that the initial heat-production is entirely due to a non-oxidative process. Thus one is enabled to perform a separate study of each of the two main transformations of energy in the active muscle, namely (1) the non-oxidative contractile process and (2) the oxidative recovery process.

3 SOClETY, JUNE 6, The effects of temperature have been investigated, and it is probable that the method provides the only satisfactory means hitherto invented of carrying out this important investigation. In single twitches increase of temperature, from 0' to 250 C., causes a decrease of the initial heatproduction. The tension developed in an isometric twitch also is slightly decreased from 00 to 200, though in a smaller degree. The " efficiency " of the muscle in developing tension therefore rises as the temperature rises, and at the higher temperatures the rise may be quite obvious. The heat-production in a short tetanus (0'5 sec.) on the other hand seems almost to be unaffected by temperature. The effect of alcohol is, in lower concentrations (2 to 3'5 O/0),-after a short increase-a proportional decrease of heat and tension. At higher, but still reversible, concentrations the development of mechanical energy is extinguished while one third and more of the initial heat is still produced. It is therefore possible to separate two parts in the contractile mechanism, sensu sthictiorn, namely one part which provides free energy, and another which transforms this energy into mecbanical potential energy or work. It is possible not only to influence this latter contractile portion of the mechanism, but also the energy-providing part, viz. by the use of hypotonic Ringer's solution. In this case we find a proportional decrease of heat and tension, both being extinguished (reversibly) at the same time. The same is true for solutions containing an excess of potassium, except that the change produiced is irreversible. It is possible therefore to act upon at least three different parts of the chain of processes in active muscle (1) upon the oxidations (cyanide), (2) upon the initial liberation of energy (temperature, hypotonic solutions etc.), and (3) upon the transformation of this energy into the mechanical response (alcohol, temperature). It is possible that a fourth point in the mechanism can be isolated, viz. the transformation of energy derived from oxidative breakdowns into the restored potential energy of the "recovered" muscle. I have found previously that temperature has an effect on the oxygen used by the heart muscle, directly in the opposite direction to its effect upon the heat-production: the oxygen used for a given mechanical response rises, while the heatproduction falls, with rise of temperature. If this be so we have reached a new point of attack upon the muscular mechanism, the "efficieicy" of the oxidative recovery processes and its temperature coefficient..vi *

4 xxxviii PROCEEDINGS OF THE PHYSIOLOGICAL Binocular vision. By F. W. EDRIDGE-GREEN. (From the Institute of Physiology, University College, London.) The perception of binocular relief and solidity is not dependent upon the combination of images falling upon disparate points of the two retinas though when images do fall upon adjacent disparate points they are combined with an alteration in their projection in space. If two photographs taken from the same negative be placed one on either side of the stereoscope a striking appearance of relief is obtained, though the photographs are not stereoscopic photographs and no double images are formed. When these are carefully compared with the same view taken with stereoscopic photographs combined in the usual way, in most cases the perspective is better with the stereoscopic photographs, but in some cases it is difficult to detect any difference. If an ordinary stereoscopic photograph of a scene be placed in the stereoscope and viewed in the ordinary way the usual striking appearance of relief is obtained. If now whilst the eyes are still looking at the photograph, a sheet of white cardboard be dropped over one of the photographs so as to entirely occlude this photograph and only present a white surface to one eye, a striking appearance of relief remains. This fact may be emphasised even more by altering the experiment in the following way. If the cardboard be placed so that only half of one photograph be occluded a careful comparison can be made between the uipper and lower halves of the combined visual field. It will be noticed that when there is one picture in the stereoscope and a white blank on the other side, the appearance of solidity is greatly diminished when the eye receiving the impression of the white surface is closed. We can also obtain pictures in strong relief by combining two halves of a stereoscopic photograph, that is to say, half of the photograph which is usually presented to the right eye is shown on the right side and half of the left is shown on the left side. This may be done by placing a sheet of white paper of appropriate size in the centre of the field of vision; in this way there is no common object in the field of vision and yet the stereoscopic photographs combine into an object in strong relief. It will be- noticed that the appearance of relief is in some cases even more marked in this way than with ordinary stereoscopic photographs. It would appear that in ordinary binocular vision the right eye dominates for the right side and the left eye for the left of the combined field unless the position of two points in space be noted when one eye,

5 SOCIETY, JUNE 6, x[xxix usually the right, dominates. The mind projects outwards the appearance of a solid object which would give rise to the images falling uipon the retinas. This also applies to those cases in which images falling upon disparate points are combined, as for instance when the images of two daggers are combined in the stereoscope and appear as a dagger standing straight out from the table; the images in the stereoscope are similar to those thrown on the two retinas by a dagger standing straight out from the table. When the mind is not able to project the image of an object in space which would produce the two images, double images or binocular struggle or rivalry take place. Binocular struggle is absent when the half photographs are combined in the above way. Some points in the action of adrenin. By W. BURRIDGE. (Preliminary communication.) Adrenin has a twofold action on the perfused heart of the frog, a primary depressing action and a secondary favouring action. Whether the primary depressing action be observed or not depends on the effective concentration of the calcium salts in the perfusing solution. If the perfusing solution be such that a reduction of its calcium content to one-fifth the original amount, say, does not result in any material reduction in the amplitude of the spontaneous contractions, then a very large concentration of adrenin must be added to the original solution to depress the amplitude of the spontaneous contractions on perfusion. But if the heart be perfused with a solution in which the calcium salts are barely adequate, or slightly inadequate, for the maintenance of the spontaneous contractions at their maximum amplitude, relatively small concentrations of adrenin have a visible primary depressing action. By increasing the strength of adrenin the heart can be stopped in the dilated and electrically inexcitable condition. In general terms it may be stated that the more feebly the heart beats at the time of making the experiment, the less is the concentration of adrenin required to stop it in the dilated condition. This action of adrenin is antagonised by calcium salts. But on washing away the adrenin, the heart not only restarts beating but is capable of maintaining good spontaneous contractions on a solution of much lower calcium content than was the case before tbe adrenin was perfused. If the strength of adrenin be not sufficient to

6 xl PROCEEDINGS OF THE PHYSIOLOGICAL stop the heart in the dilated condition augmentation follows the primary depression. In every case examined it was found that when the augmenting and accelerating action of adrenin was present the heart was capable of maintaiding activity on a solution of much lower calcium content than was the case before treatment with adrenin. This condition of increased sensitiveness to calcium persisted for some time after removal of the adrenin from the perfusing solution. The favouring action of adrenin rnight apparently be as great when the strength employed was 1 in 10,000,000 as it was when the strength was 1 in 250,000 but whereas the latter induced also marked primary depression of the heart, the former was only observed to auigment. If the heart were 'inhibited' by adding potassium salts to the perfusing solution, the addition, now, of adrenin to this solution was followed by resumption of spontaneous beating. Assuming this favouring action of adrenin to reproduce sympathetic nerve stimulation, it would follow that as a result of* sympathetic stimulation the heart has an increased responsiveness to the calcium salts in the solution perfusing it. The persistence of this changed state long after removal of the adrenin from the perfusing solution (15 m.) indicates that a changed state of aggregation of certain heart colloids is an important factor in this process, rather than the local release of calcium salts suggested by Howell and Duke,. Voluntary reversal of the human electrocardiogram by deep respiration. By A. D. WALLER, M.D., F.R.S. At a previous meeting of the Society I summarised the effects of the respiratory movements upon the amplitude of the ventricular spike V1 by the general statement that as a rule with inspiratory descent of the diaphragm the electrical effect is weakened in the strong leads (left superior and right inferior), strengthened in the weak leads (right superior and left inferior). (This rule does not however apply to all sorts of hearts, e.g. in the horizontal heart the right inferior peak VI is increased by inspiration.) The effect of respiration is greater in the cases of the weak than in those of the strong leads. I This Journal, xxxv. p

7 SOCIETY, JUNE 6, As regards the two weak leads the effect of respiration is greater upon the left inferior than upon the right superior, so great indeed that it is possible for a person with a negative left inferior VI (horizontal heart) to render it positive by maximal descent of the diaphragm, and for a person with a positive left inferior VI (oblique heart) to render his V1 negative by maximal ascent of the diaphragm. xli iw l E R :.A 7 4~~~~~~~~~~~~~~~~~~~~~ T Upper line. Left lateral reeord of A. D. W.; the normally negative spike is rendered positive by extreme inspiration. Lower line. Left lateral reeord of J. C. W.; the normally positive spike is rendered negative by extreme expiration. This has been done in the two cases of A. D. W. and J. C. W. respectively. The experiment is one that can be repeated by anyone having the suitable heart, and serves when understood as a caution against admitting too hastily a negative RIII as a sign of left ventricular hypertrophy or of interruption of the right branch of His's bundle. The effect of acetone and aceto-acetic acid on the estimationof creatinine and creatine. By R. A. KRAUSE. Different results have been obtained by different workers, including myself, in trying to determine the manner in which acetone and acetoacetic acid affect the creatinine and creatine determinations, and this applies especially to acetone. I have therefore again examined the effect of adding these substances to a number of normal urines, obtained

8 xlii PROCEEDINGS OF THE PHYSIOLOGICAL from different persons and at different times. So far, my results show that even when using the same sample of acetone, no matter in what percentage, the effect on the colorimetric readings for creatinine is not always the same. It must be remembered that a deepening of the colour reaction tends to mask the presence of creatine, whereas a lightening of the colour reaction would increase the values for creatine and might therefore give results indicating the presence of creatine in a urine which in reality does not contain any creatine at all. With some normal urines the colour readings were lighter after the addition of acetone, more commonly however the colorimetric readings were lower than those found normally for creatinine, and so would give higher creatinine values. In most of these cases the colour did not fade, so that the readings remained stationary; but in the case of some of them the colour faded and the readings eventually became those of the normal urine. This last condition is the one which I observed in my results previously published'. In some cases the readings went even higher, i.e. the solution became lighter. With the urines of three normal persons no difference in the colorimetric readings was obtained after the addition of acetone, even although the urine contained as much as 2%0/ acetone. I have not yet been able to determine the factor in the urine which thus modifies the action of acetone on the colorimetric readings for creatinine. After the addition of aceto-acetic acid to the urine the colorimetric readings were always found to be higher, as Graham and Poulton state. Whether its effect on the colour reaction used for the creatinine estimation shows variations similar to those observed with acetone I have not been able to determine, as I have not examined a sufficient variety of urines. It was found, however, that sometimes the presence of acetone may completely neutralise the effect of aceto-acetic acid. My previously published findings with aceto-acetic acid may have been due to the presence of some disturbing factor of this kind. My observations therefore, while not entirely agreeing with those of Graham and Poulton2, show nevertheless that the presence of acetone and aceto-acetic acid may introduce a fallacy in estimating creatine and creatinine. In my previous observations in which the excretion of creatine in diabetes mellitus and phlorhizin diabetes was demonstrated, it was pointed out specially that the creatinuria may appear in the absence of an acidosis and that, in fact, of the cases of diabetes mellitus I Krause. Quart. Journ. Exp. Physiol. ni}. p Graham and Poulton. Proc. Roy. Soc. B, LxxvU. p

9 SOCIETY, JUNE 6, xiii* examined none showed an acidosis during the period of investigation. There is therefore no justification for the suggestion that the creatinuria in those conditions is only an apparent one. It goes without saying that the fallacy introduced by the presence of the acetone bodies does not enter at all into the consideration of the excretion of creatine by normal women and normal children'. In starvation and in carbohydrate starvation the conditions are more complicated, because in those conditions the onset of creatinunra is practically coincident with the appearance of the acetone bodies. Whether in these conditions the creatinuria observed by Cathcart is an apparent one, as Graham and Poulton state, or a real one, as Cathcart maintains, is at present being investigated. The excretion of creatine in severe and mild cases of diabetes mellitus. By R. A. KRAUSE. The excretion of creatine in diabetes mellitus, which was observed by Krause and Cramer in and which has since been confirmed by a number of workers, takes place, as was pointed out at the time, even in mild cases of the disease, in which there is no acidosis. Since the observations of Graham and Poulton3 have made it possible to exclude the influence of aceto-acetic acid upon the estimation of creatinine and creatine it was of interest to study the degree of error introduced by the presence of acetone bodies in diabetes mellitus. I have recently examined three cases of diabetes: one a severe case with a definite acidosis, secoindly a milder case with only traces of aceto-acetic acid and acetone and thirdly a case without any acidosis at all. In the first two cases the urine was examined both before and after the removal of the aceto-acetic acid according to the method of Graham and Poulton. In all three cases creatine was present. The following Table gives typical results obtained from each case. It is noteworthy that in the mild acidosis case, which gave a negative ferric chloride test and a faintly positive nitroprusside (Rothera's) reaction, the differences in the readings for creatinine obtained before and after the removal of aceto-acetic acid were so small as to fall within the limit of error, in other words the amount of acetone bodies 1 Krause. Quart. Journ. Exp. Physiol. rv. p Ibid. vii. p Krause and Cramer. Proc. Physiol. Soc. July 1910, Journ. of Physiol. xl. Krause. Quart. Tourn. Exp. Physiol. m. p Graham and Poulton. Proc. Roy. Soc. B, Lxxxvu. p

10 xliv PROCEEDINGS OF THE PHYSIOLOGICAL Preformed Preformed creatinine creatinine Total Degree of nitrogen plus nitrogen minus creatinine Creatine acidosis aceto-acetic acid aceto-acetic acid nitrogen nitrogen None Mild Severe ' present did not appreciably affect the creatinine and creatine estimations. This raises the question at what degree of acidosis the fallacy introduced by the acetone bodies becomes negligible. By carrying out observations with normal urines to which varying quantities of acetoacetic acid had been added, it was found that this acid will not appreciably interfere with the creatinine and creatine determinations as long as the ferric chloride reaction is negative or even faintly positive. Incidentally it may be mentioned that the nitro-prusside test, as modified by Roth era, is much more sensitive for aceto-acetic acid than for acetone, as was pointed out by Hurtleyl. The "dead space" in breathing. By J. LINDHARD, Finsen- Institute, Copenhagen. Recently Krogh and J2 published a method of determining the "dead space" in breathing, which is sufficient for most purposes. As the method is rather difficult to manage and requires a special apparatus it would be of great interest to find out some scale, according to which it might be possible to estimate approximately the volume of the "dead space." Usually an approximation will be quite sufficient, but sometimes, e.g. when calculating the alveolar-tensions from the composition of the expired air in persons with a very shallow respiration (tidal air 300 c.c. or less), even the most careful determination, according to any method hitherto published, is not accurate enough. In order to find a suitable basis for such an estimate I have determined the "dead space " on a number of subjects, men as well as women. I have then attempted to compare the results with d -1sat Hurtley. Lancet, cxxv. p Journ. of Phys. mxvn. p

11 SOCIETY, JUNE 6, body measurements (total length, weight, volume of lungs etc.) and found that the best index so far obtainable was the length of the trunk measured in the erect sitting position of the subject from the seat to the angle between the chin and the neck (os hyoideum). For using this I find the following formula for estimating the "dead space": Women Length of the trunk 66 =n cm. 68 n cm. "Dead space" at 370 (moist) n c.c n c.c. In all female subjects except Miss R. the agreement between the observed and the calculated values is as good as might be expected. For her I have four determinations, the first two give 75 c.c., last two 98 c.c. for the " dead space." I have strong reasons to believe that the first figure is right; unfortunately the experiments with Miss R. could not be continued. In the male subjects the difference between the calculated and observed values is wider, and these differences are certainly real, the subjects concerned being well experienced. Only in the case of V. M., however, the use of the calculated "dead space" instead of the determined might occasionally give rise to more serious errors. Krogh and I have previously stated, that the "dead space " is essentially the same at rest and during muscular work, and that Length of trunk (ems.) Table of experiments. "Dead space" observed Subject Miss A. 66 (106)*, 105, 104, 99, 106 average 104 Mrs M , 90-5, 94'5, (98), 93 average 95 Miss B , 72, 100, 96-5 average 87 -Mrs H '5, 67, 78, 65 average 72 Miss M , 48, 71, 62, 66 average 61 A. K.t 69'5 143 K. A. H , 141, 140-5, 118'5, 143, 163 average 141 J. J '5, 99, 119-5, 106, 112-5, 99, 106, 125 average 111 V. M , 95, 91, 94, 86 average at ca. 20 at Men Calculated from formul Q Deviation of obs. value Brackets indicate a small irregularity in the experiment concerned, which has been considered insignificant for the result. t The figures for A. K. and J. L. have been taken from the previous paper. d xliv

12 xlvi xliproceedings OF THE PHYSIOLOGICAL probably the upper or upmost part of the air-passages, especially the nose, constitutes the primary resistance when the ventilation is strongly augmented. In a respiration experiment, the subject breathing through a mouthpiece and having his nose closed by a clip, the air current goes through the mouth and when the ventilation is increased the mouth cannot be kept closed. The cavity of the mouth is much more variable in volume than that of the nose owing to the movable and elastic diaphragma oris; it is possible to hold more than 100 c.c. of water in the mouth with closed lips and without filling up the sutci alveolo-buccales. Alterations in volume of the mouth cavity will alter the "dead space." I have demonstrated this fact in a few double determinations, the one undertaken with " normal " mouth, the other with large mouth. Normal mouth Large mouth J. L. " Dead space " at I have further observed, that in respiration experiments during muscular work I always open the mouth to a certain degree. To see how far this habitual position of the mouth affects~the " dead space " I have made a series of determinations with the following result: J. L. "Dead space" at 200 C. in c.a., 123, 124, 120, 120, 128, 112, 116 5, 119, 129, 109. Average, 120. At 370 C., 132. The experiments show that the "dead space" is increased by 23 c.c. However, especially in work experiments such an increase is for most purposes quite irrelevant. Note on the relation between the eleotrolyte concentration of some neutral perfusion liquids and the frequency of beat of the frog's heart. By MARY D. WALLER, B.Sc. The object of the following series of observations was to determine the relation between the concentration of physiologically effective perfusion fluids and the activity of the heart as measured by the frequency of the beat. The observations were made upon the frog's heart (Rana temporaria) prepared as described by Mr Mines1, at whose suggestion they were undertaken. By preliminary experiments it was ascertained that under constant conditions of temperature and pressure the frequency of beat rises and 1 Mines. Journal of Physiology, xlvi. p

13 SOCIETY, JUNE 6, xlvii falls with rising and falling concentration of the Ringer solution in a remarkably regular way for long periods. Thus e.g. in one experiment (see Fig. 1) the normal frequency with the original solution at concentration= 100 is 36 per minute = 75,, 32 = 50,, 28 = 40,, 24 = 30,, Ca 0 0 PS! 3 xo to r So'l'. iw'1' ICObl, 1.6/ 100% IO go S ' The procedure was as follows:- A normal perfusion liquid (Ringer KCI M/10 2 c.c., CaCl2 M/10 2 c.c., NaHCO3 M/8 1 c.c., NaCl M/8 to 100 c.c.) was prepared; its concentration was taken = 100. This normal solution was diluted by the addition of certain proportions of an isotonic (but physiologically ineffective) solution in which a non-electrolyte, i.e. cane sugar or urea, took the place of NaCI, the other constituents remaining as before. The effects of the more or less concentrated solutions were compared with that of the original solution by observing the beat frequencies during perfusion by the respective liquids. The frequency of beat was counted for half-minute intervals during periods of perfusion of five to six minutes-a time that was found to be sufficient to allow the frequency to settle to its steady value when the perfusion liquid was changed. In considering the relation between alterations of frequency caused by alterations of concentration of the Ringer solution, it is convenient to express the fall as a fraction in which the original frequency is the denominator and the altered frequency the numerator or f/f. Thus in Fig. 1 where the original frequency is 36 and the altered frequency 28, this ratio or quotient is i or 8 when the concentration is 50 0/0.

14 xlviii PROCEEDINGS OF THE PHYSIOLOGICAL The relation between concentration and quotient for experiments with Ringer and cane sugar is given in Fig. 2, to show how the frequency of beat diminishes with diminution of NaCl in the perfusion liquid Concentration Fig. 2. Ringer and cane sugar. (Similar curves were obtained by using a Ringer solution in which the Cl ion was replaced by Br, I and NO3, diluting the Ringer as before by different proportions of the cane sugar and urea solutions.) Excitation of the sudo-motor nerves of the cat's foot by condenser discharges. By W. W. WALLER, M.B. The sudo-motor electrical response was first demonstrated by Luchsinger and Hermann' on the pad of a curarised cat under artificial respiration, and further studied by Waller2 on a decapitated cat post mortem. The object in both cases was to observe only the sudo-motor electrical response of the cat pad, uncomplicated by the electrical effect of muscular contraction and of shifting contact. By reason of the great length of latency of the sudo-motor response it is however possible by means of a string-galvanometer to observe and 1 Hermann and Luchsinger. Pfluiger's Arch. xvii. p A. D. Waller. Proc. Roy. Soc. LXV. p Ibid. LXXIII. p

15 SOCIETY, JUNE 6, xlix record the succesive effects of both muscular and glandular response when both are present; the indication of muscular response serving as a time-signal to the subsequent glandular response. Stimulation by a single condenser discharge was applied by platinum electrodes to the sciatic nerve of a cat killed under chloroform by puncture of the medulla, the circulation being maintained by artificial respiration. The large pads of the two hind feet were led off to the galvanometer by unpolarisable electrodes. Excitation by a condenser was used in order to learn what energy at what rate was required for the muscular and glandular responses respectively. The resistance in the exciting circuit was measured. With a small stimulus (e.g. less than 1 erg) only the muscles contract; there is no electrical response of the Electrical response of a eat's pad to a single condenser discharge (2mF, 20 volts, viz ergs) applied to the sciatic nerve. The small waves at the beginning of the record indicate the muscoular twitch of the limb; the subsequent long wave indicates the electrical response of the sweat glands. The E. is.r. of this response is approximately y6 volt and its direction through the skin is from without inw&rds. Its latent period is 1 7 seconds. pad. With a large stimulus (e.g. above 1000 ergs) the muscles of the leg are 'seen to twitch immediately, and about two seconds later the galvanometer is deflected in a direction indicating an ingoing current of the pad on the stimulated side. As can be seen on the record the two phenomena are separated from each other by an interval of time which is lonag enough to be measurable by stop-watch. It has always been obvious in repeating this experiment that whereas a small energy discharge with a sharp gradient is sufficient to excite musculo-motor fibres in the sciatic nerve, the excitation of its sudo-motor fibres requires a relatively large energy discharge of more gradual gradient.

16 1 PROCFEDINGS OF THE PHYS. SOC., JUNE 6, Further experiments-not yet completed-have been undertaken to determine the numerical relation between the optimal minimal stimulus in the two cases; the following numbers will serve to indicate the order of difference under ordinary conditions, i.e. without regard paid to temperature or moisture or state of nerve: F V 5FV2 V/FRx1O6 T, time of fall R=10,000 ohms capacity voltage energy gradient ol energy to : Muscle-nerves erg sec. Sweat-nerves ergs sec. By the kindness of Prof. Lapique I was able under his control and guidance to obtain some preliminary time-values for the two kinds of nerve-fibres, for excitation by the constant current and by condenser discharges. The characteristic time of excitation (" chronaxie ") came out by both methods as approximately sec. for the sudo-motor response as compared with sec. which is the chronaxial value of musculo-motor nerves as determined by Prof. Lapique. These figures indicate that the response to excitation of musculo-motor fibres in the sciatic nerve is about ten times as rapid as that of sudo-motor fibres.