TEMPERATURE AND THE RESPONSIVE MECHANISM OF CARDIAC...

373

TEMPERATURE AND THE RESPONSIVEMECHANISM OF CARDIAC MUSCLE

I. TEMPERATURE AND THE DURATION OFCONTRACTION

BY DUGALD E. S. BROWN

(Washington Square College, New York University).

(Received ist May, 1930.)

(With Two Text-figures.)

THE responsive mechanism by which a muscle cell reacts to a stimulus consists ofa group of closely associated processes following each other at definite intervals.Three distinct phases may be recognised in this system: (1) a local process occurringin the region of the stimulus; (2) a rapid series of changes referred to as the propa-gated disturbance and indicated by the bio-electric variation; (3) the response of thecell in the region adjacent to the seat of stimulation. Associated with each of thesephases are various processes which, although separately definable, appear to beintegral parts of the whole response. Thus, with the first and second phases areassociated chronaxie, the bio-electric variation, the conduction of the propagateddisturbance, the absolute and relative refractory periods, and other phenomena.With the third phase, comprising the contraction of the muscle, are associated thelatent period of contraction, the duration of the contractile phase, the duration ofthe relaxation phase, the tension developed, and the heat production. Considerableevidence exists that these are inter-dependent processes and not merely independentconcurrent processes (Lillie, 1923; Fulton, 1926). In comparing the velocity ofmovement of different muscles it has been observed that the more rapid is the move-ment of the tissue the briefer are chronaxie, the time for the conduction of thepropagated disturbance, the time for the development of the bio-electric variation,the duration of the refractory period, the duration of the latent period, and theduration of the isometric contraction. It has been shown also that with the increaseof initial tension on the muscle there is associated an increase in chronaxie, in theduration of the isometric twitch, in the total tension, and in the heat production.

Despite this close relationship between the separate processes, it is significantto note that each exhibits its own characteristic temperature coefficient. It is,therefore, essential to determine the effect of temperature upon these processeswith reference to the velocity of the process as a function of temperature, and alsoto d^ermine whether this function for each process may be modified independentlyof H r other processes.

374 DUGALD E. S. BROWN

This paper is the first of a series dealing with these two problems in the ^sive mechanism of cardiac muscle. It presents an analysis of the velocity of con-traction of the auricular muscle as a function of temperature and an analysis of thestability of the system under various conditions. Other phases of the responsivemechanism of auricular muscle will be dealt with in later papers of the series.

METHODS.

Preparation of the tissue.

The tissue used throughout these experiments is prepared either from the heartof the turtle Pseudyms elegans or Chrysemys emarginate. The heart upon excision isimmediately immersed in a modified Ringer solution containing adrenalin i part inIOO.OOO. The adrenalin serves to prevent the tonic smooth muscle contractionwhich otherwise hinders ready dissection of the tissue. The two auricles are severedfrom the ventricle by an incision passing through the auriculo-ventricular junction,and are then separated from each other by an incision around the auricles along theinter-auricular septum. The rhythmic beating of the auricles is stopped by removingthe sinus tissue in which the excitatory impulse originates. To prevent the sub-sequent assumption of rhythmicity by the auricle o-oi per cent. MgCl2 is added tothe Ringer solution (Smith, 1926). The auricle to be used is then placed upon itsposterior surface and opened to form a rectangular strip by two parallel incisionsalong either side from the auricular opening almost to the tip of the auricle. Oneend of this strip is spread upon a small block of ebonite or of paraffined wood andfastened with a silk thread. The other end is secured in the muscle clamp on themuscle holder.

Recording apparatus.

The muscle holder consists of an ebonite disc which carries supported from itslower surface two glass rods; the ends of these pass through an ebonite bar whichhas on its upper surface a small ebonite clamp. One end of the muscle is held bythis clamp, while the other end of the muscle strip is tied tightly to a small eboniteblock attached to the muscle lever by a silk thread. Also suspended from the largeebonite disc are two electrodes consisting of glass tubes, in the ends of which aresealed wires. In the case of platinum electrodes the tubes are filled with mercuryand appropriate contact maintained at the top. In the case of silver electrodes theyare coated with silver chloride and copper-wire connections are made between thesilver and the binding post. Holes in the ebonite disc allow the insertion of athermometer graduated to oi° C. and a tube for oxygenating the chamber.

The ebonite disc with the accessory parts is fastened in position by a clamp insuch a way that it can be raised or lowered, or the muscle chamber can be removedat any time without disturbing the muscle holder.

For recording the isometric contraction of the muscle, an isometric lever is used.The lever is of the torsion wire type. It consists of a piece of fine steel w hspring, 2-5 cm. in length, fastened at either end by clamps which can be adjusted soas to place the band under tension. At the centre of the strip of steel and at right

Temperature and the Responsive Mechanism of Cardiac Muscle 375

to it is soldered the lever arm. A small mirror 5 mm. square is fastened• to the spring at the point of attachment of the lever arm. The lever holder is

rigidly mounted upon an adjustable post so constructed that it is possible to raise,lower or revolve the spring holder in a horizontal plane. The adjustable post itselfcan be turned to any desired position in a vertical plane. The lever used has aperiod of 200 per second which is quite sufficient for the purpose in hand. By meansof a suitable lens the image of the single filament of a 4-volt electric bulb reflectedfrom a mirror is brought to a focus upon the recording surface. The movement ofthe beam of light is recorded upon a moving sheet of bromide paper in an electro-cardiographic camera. The recording system gives a magnification of 75 times.

All observations are made upon muscle immersed in 400 c.c. of a modifiedRinger solution. This is made up from stock solutions of the salts in glass-distilledwater. The salts are present in the following proportion: NaCl 0-59 per cent., KC10-029 Pe r cent., CaCl2 0-017 Pe r cent., and MgCl2 0-049 Pe r cent.

The solution is buffered to a pH of 7-0-7-2 by the addition of NajjHPO,,. Theamount necessary is determined by titration and rarely exceeds o-oi per cent.

Control of temperature.

The temperature is controlled by the use ofDewar flasks. At the beginning ofthe experiment nine of these flasks are filled with modified Ringer solution whichhas been adjusted to the desired temperature, and tightly stoppered. These maintainthe temperature constant to within o-i° C. during the time of recording, and, whenstoppered, within 2° C. at the lower and higher temperatures for from 4 to 5 hours.

Analysis of record and data.

In the analysis of the records, the duration of the contractile phase of the responseis taken as the time from the onset of contraction to the peak of the contraction. Theinvestigations of Wiggers, as well as unpublished data of the author concerning thegenesis of the isometric myogram of this tissue, justify this procedure in that theyhave shown that the values so determined represent the duration of the contractilephase of the first region of muscle stimulated.

In the analytical treatment of the data, the velocity of the process as a functionof temperature is expressed in terms of the Arrhenius equation. This proceduremakes possible the comparison of the results with those of other investigators andfacilitates the comparison of several processes occurring simultaneously in the sametissue. Although it would be more suitable to use a general expression of the sameform to which the theoretical implications of the Arrhenius equation would not beattached, it seems advisable not to introduce any new equation to express thevelocities of the processes as a function of temperature, but rather to emphasise thephysiological factors inherent in the system under investigation, which limit the useof the Arrhenius equation1.

1 A number of expressions have been used by investigators to describe temperature effects onvarious protoplasmic systems, in many cases with a view to obtaining some function common to all.I^Mpossible that for all simple cellular processes the velocity is the same function of temperature,b^^Viere is no theoretical or biological reason for expecting a common function for processes asdivMse as the growth of Drosopkila larvae, the locomotion of Amoeba, and the heat production pergram tension in skeletal muscle. See Belehradek, 1928.


THE RELATION OF THE VELOCITY OF CONTRACTIONTO TEMPERATURE.

When a non-rhythmic auricular strip immersed in Ringer solution is subjectedto an increase in temperature, there results a decrease in the duration of the con-tractile phase of the isometric twitch. If the velocity of this process is considered asthe reciprocal of the duration, the velocity as a function of temperature may beexpressed in terms of the Arrhenius equation. In its integrated form this equation is

lnK2-R\T2 T

where Kx and K2 axe the velocities at the respective temperatures Tt and T2 (T2 > 7\);fj, is a constant independent of the temperature, and R is the gas constant. In agraphical treatment this expression is satisfied if the points obtained by plotting thelogarithm of the velocity against the reciprocal of the absolute temperature lie ona straight line. From the slope of this line the constant /x may be calculated. Theresults are best dealt with by considering a series of representative experiments,shown in the following figures.

In Fig. i, B, are plotted the data given in Table I from a representative experi-ment. Each point represents the average value for the first three or four twitchesexcept where otherwise indicated. The twitches were recorded after a 15-minuteperiod for temperature equilibration; a stimulation interval of 15 seconds wasemployed at the time of recording.

Table I

Exp.no.

i2

3456789

1 0I I12

1314IS161718192O

Time

2.453 0 53.173-353-5°4 0 54.204-357.007-i57-3°7-458.008.158.308-4S9.009-159 3 O9-45

Tempera-ture

0 74-47-6

io-61351651 9 32 1 4I2-I1 5 61 8 62 1 42 4 727-32 9 63 2 935-73 8 216-3195

Stimu-lation

interval(sec.)

15ISISIS15IS151515ISISISISISIS15IS15ISIS

Record 1

—313229179134967967

17t1281 0 28062604939

—21

128—

Duration contraction

Record 2

4563 H229178135947967

179132104

8264574837322 0

125106

Record 3

4 7 2300—I7S132958066

17713410585635849363218

127106

1

Record 4

————132

94>7f68

—132103

826453503532IS

——

The results show that the velocity of contraction as a function of temperaadequately described by this equation from 0-7° to about 200. Above


deviate from the linear relation obtaining below this temperature, and in alion indicating a decrease in velocity (increase in the duration) of the contractile

phase of the response. The data is such that either a smooth curve, with a sharpinflection at 200, or two straight lines intersecting at a point corresponding to 200,may pass through the points. For purposes of calculation, there are advantages inthe latter method of treatment. For purposes of analysis, however, it is sufficient to

log.vel.=log. 4+constant17

1.6

1.5

1.4

1.3

1.2

I.I

1.0

0.9

08

0.7

0.6

05

0.4

03

0.2

\

I0.0032 0.0033 0.0034 0.0036 0.00370.0035

Iabsolute tempgraturg

Fig. 1. Curves A, B and C for auricular muscle. Curve D for gastrocnemius muscle of the frog. Thefirst two points recorded in the experiment are numbered. For subsequent points + indicatesdeterminations at increasing temperatures and © at decreasing temperatures.

assume that the Arrhenius equation adequately describes the relation between thetemperature and the velocity of the underlying process, whatever it may be, and thatthe deviations shown to exist owe their origin either to factors associated with the cellu-lar mechanism itself, or that they are inherent in the experimental methods employed,

such an analysis, it is essential to determine whether the results express theof the contractile process as a function of temperature alone, or as a function


of temperature plus cellular changes likewise varying as a function of temper^y-e.Perhaps the most significant concomitant cellular change which could influenSRieresults is the progressive change in functional state, or "deterioration," which anisolated tissue undergoes when immersed in a physiological solution. To determineif possible to what extent the deterioration of the tissue is modifying the velocity-temperature relation, experiments are performed in the following way: A firstrecord is obtained following a 10-minute exposure of the tissue at 200. The tissue isthen immersed immediately in Ringer solution at a temperature around 50. Recordsare obtained at this temperature and successively at higher temperatures at intervalsof 30 to 300, and then at decreasing temperatures at 30 intervals till io° is reached. InFig. 1, A, are plotted the results of a typical experiment performed by this method.

These experiments show that a deterioration of the tissue, progressing as afunction of the time and resulting in an increase in the duration of contraction, isoccurring at all temperatures. Below 200 the rate of deterioration is so slow that in thetime involved it is not appreciable. At temperatures above 200 the rate of deteriorationincreases rapidly with the temperature. The degree of deterioration at these tempera-tures is obviously sufficient to play an important part in determining the results.

Since this "deterioration" is a function of the time of exposure and of thetemperature, it may be controlled to a considerable extent by experimental treat-ment in the following way. A first record is obtained, following a 10-minuteexposure of the tissue at 200. The tissue is then immersed immediately in Ringersolution at a temperature in the vicinity of 3°. Records of the simple twitch arethen obtained at this temperature and successively at temperatures of 8°, 120, 160

and 200, after a 10-minute equilibration period in every case. Following the 20°record the tissue is immersed quickly in Ringer solution at about 360 to 390. Afteran exposure of 2 to 3 minutes at this temperature, three contractions are recorded,and the tissue immersed in Ringer solution at 150. A record is then obtained aftera 5-minute equilibration period at this temperature.

The results of an experiment performed in this fashion are plotted in Fig. 2, A.They show above 200 a deviation from the linear relationship existing below thattemperature. In the particular experiment of the figure the value obtained at 38°deviates 19 per cent, from the value expected on the assumption that the Arrheniusequation adequately describes the relation for the entire range of temperature. Forpurposes of comparison, the results of an experiment, involving a prolonged exposureto progressively higher temperatures, are plotted in Fig. 2, B. The deviation fromthe expected linear relation in this experiment is much greater than in Fig. 2, A. Itcannot be considered, however, as being similar in origin as it is completelyirreversible. This is shown in Fig. 1, A, where the deterioration which has occurredpermanently alters the subsequent values for the lower temperatures from thosefound before the tissue was exposed to the higher temperatures. This result isdirectly opposite to the results shown in Fig. 2, A, where the deterioration whichoccurred at higher temperatures did not appreciably alter the subsequent values atlow temperatures. These results make it seem very unlikely, therefore, thdeviation from the expected linear relation shown in Fig. 2, A, can be due


d^Boration of the tissue at high temperatures. This conclusion does not precludethe fact that the exposure to high temperatures results in some irreversible changesin the tissue; it may be considered, nevertheless, as showing that such changes asdo occur cannot be recorded as changes in the duration of contraction by anymethods ordinarily employed, but that changes in the system do occur is shown by

log. Vel = log.}+constant

1.7

1.6

1.5

1.4

L3

1.2

I.I

ID

0.9

Q8

Q7

0.6

0.5

0.4

0.3

02

, \

''•x

-_

r i

\ i

V \\

\\

1

\

X*\A\

0.0032 0.0033 0.0034 0.0035I .

0.0036 0.0037

absolute temperatureFig. 2. + indicates determinations at increasing temperatures; © at decreasing temperatures. Thefirst two values recorded in the experiment are numbered.

an irreversible decrease in the total tension of the twitch (as opposed to the durationof contraction) subsequently recorded at temperatures below 200 following anexposure to a high temperature.

The results from experiments involving the use of an isotonic method of recordingsubstantiate the foregoing results. They show that an irreversible progressivedetej^ration occurs, as a function of time, at temperatures above 200. The deteriora-tio^^Pay be partially eliminated as a modifying factor in the results, in this case,also, by proper regulation of the time of exposure to the higher temperatures.


Under the foregoing experimental conditions, which tend to limit the progdeterioration occurring at temperatures above 200, the result may be satisfactorilydescribed by the Arrhenius equation- over a temperature range from 0-7° C. to200 C. A marked deviation is still shown to exist above this temperature. If thedegree of deterioration under-these conditions be considered as negligible,. therelation between the velocity of contraction and the temperature obtained may beconsidered as being jointly determined by two factors: (a) the actual reactionsinvolved in the contraction of the muscle, and (b) associated reversible changes inthe physico-chemical organisation of the cell at different temperatures, whichmight modify the reactions included under (a).

Although there is little direct evidence bearing on the point, we may take it asexceedingly improbable that the fundamental changes underlying the contractionare characterised by discontinuity, e.g. we may be reasonably certain that theneutralisation of lactic acid by the buffer system in the muscles proceeds above 200

in essentially the same way as it does below 200. An intracellular property, however,which has been suggested as accounting for these discontinuities is the property ofviscosity, and the results of investigations upon protoplasmic viscosity certainlyfurnish evidence of a gross physico-chemical reorganisation in the cell progressingas a function of temperature. The viscosity of the protoplasm of the Arbacia egg andAmoeba dubia (Heilbrunn, 1925, 1929), for example, is high at low temperatures,and, as the temperature increases, rapidly falls to a minimum, rises to a maximum,decreases to a second minimum and increases again at very high temperatures. Themaximum in Arbacia is at 15°, and in Amoeba dubia is at 25°. Snyder (1911),Putter (1914), and others have suggested that changes in viscosity may be responsiblefor the deviations from the accepted linear relation between the velocity of biologicalprocesses and the temperature, and Heilbrunn (1925) has emphasised the possi-bility of such changes in the viscosity of protoplasm affecting the velocity of cellularreactions. In the case of muscle, it is possible that in the vicinity of 200 the responseis modified by rapid physico-chemical changes in the system associated with thecondition of maximum viscosity at that temperature, but for reasons which will bedeveloped in a later paper, the viscosity per se is not considered as directly affectingthe system, but rather as one expression of a physico-chemical reorganisation withwhich may be associated those changes in the system responsible for the deviationfrom the linear relation.

The determination of the nature of the changes grouped under (a) would befacilitated if a treatment of the kinetics of the contractile system were available. Theuse of the Arrhenius equation in describing the relation between the velocity andtemperature, however, involves a very elementary treatment of the kinetics of thesystem. Thus, in applying this equation to the data, it is assumed that the reciprocalof the duration of contraction is proportional to the velocity constant of the reactionat each temperature; this assumption implies either that the concentration ofmaterial involved in the reaction is constant at all temperatures or that the vdarityconstant is independent of the concentration of the reacting substances. AflBle-quate consideration of the foregoing factors may account for the deviations from the

Temperature and the Responsive. Mechanism of Cardiac Muscle 381

^ ^ t e d linear relation; it should be emphasised, however, that the results plottedin Fig. 2, A, accurately describe the velocity of contraction as a function of tempera-ture under the conditions established by the experimental methods employed, and,moreover, that any treatment of the kinetics of the system must be in accordancewith the results of such an experiment. In fact, the nature of the intra-cellularchanges associated with the discontinuities referred to are unknown, and mustremain unknown until the kinetics of the system are solved.

CONDITIONS MODIFYING THE VELOCITY-TEMPERATURERELATION.

The tissue deterioration whieh has been shown to increase the duration ofcontraction also results in a decrease in the total tension produced during contrac-tion. This result might be brought about either by the deterioration resulting in adecrease in the quantity of material released at stimulation, or by the deteriorationproducing modification in the method by which the foregoing material is utilised inproducing contraction of the muscle, or by both. In either of the above cases, it ispossible that such alterations due to deterioration would result in a change in thevelocity of the process as a function of temperature.

To determine, if possible, whether deterioration in the tissue results in analteration in the velocity-temperature relation, experiments were performed uponthe tissue in which various degrees of deterioration had been produced. The effectsof such treatment are best shown by a consideration of an actual experiment. InFig. 1, A, are plotted the results of an experiment performed on the same tissueimmediately after removal from the body of the turtle, after an exposure to roomtemperature and after an exposure to high temperature of sufficient duration toproduce a considerable effect. These results show that the velocity as a function oftemperature was not affected by such treatment. However, the slope of the line isgreatest between the points 1 and 2 recorded immediately after removal from theturtle; following an exposure to a temperature of 200 for 3 hours, the slope is less.As the exposure is made longer and longer, the decrease in slope diminishes andreaches a quite constant value. If the slope is expressed in terms of /x, the initialvalues would be about 14,800 ± 500; after an exposure of 2 hours to a temperatureof 200 the value would be 14,000 ± 500, and after prolonged exposure it wouldreach a lower limit of about 13,500 ± 500.

Deterioration due to exposure to alcohol.

The exposure of the tissue to anaesthetising concentration of alcohol similarlyresults in an irreversible deterioration of the tissue which causes an increase in theduMfcon and a decrease in the total tension of contraction. In this case also thedeflftration fails to modify the velocity-temperature relation although it causes adecrease in the slope which expressed in terms of p gives a value of 13,500 ± 500.

.JEB-VIliv 25


Effect of varying the rate of stimulation.

The relation between the velocity of contraction and the temperature shown toexist in the auricular muscle is a special case determined by the stimulation intervalemployed. In these experiments only the first response following a 10-minute restperiod was considered. The magnitude and duration of this response is determinedby the cellular conditions existing during the "steady state" of the resting muscleat that particular temperature. A similar relationship might be obtained underconditions of repeated stimulation, either at a constant or a variable rate, providedthe same relative cellular conditions existed at each temperature, as in the firstresponse following a period of rest, but such a condition is not attained readilyunder conditions of repeated stimulation. If a constant rate of stimulation ismaintained throughout the experiment, the acceleration of the recovery processwith an increase in temperature serves to convert the stimulation interval, constantwith respect to time, into a stimulation interval of variable length with referenceto the cellular processes themselves. Thus, a stimulus occurring relatively early inthe recovery phase at low temperatures would occur relatively late in the recoveryphase at high temperatures. Since the magnitude and duration of the secondresponse depends upon the time at which it occurs during the recovery periodof the first response, the cellular conditions at the different temperatures arenot identical. The situation is complicated further by the fact that these effects ofregular stimulation of the tissue are associated with irregularities in the magnitudeand duration of the successive responses during continuous stimulation. In thelatter phenomenon, known as treppe, the first twitch following a period of rest isusually larger than the second, after which each succeeding twitch increases in sizeuntil a plateau is reached, the height of the plateau depending upon the rate ofstimulation. The slope of the temperature-velocity curve, therefore, depends uponthe particular stimulation interval employed and the duration of stimulation, andthe proper choice of interval and duration can result, over a portion of the tempera-ture range, in a slope practically identical to that obtained when the averageduration of the first few twitches only is used in the calculation. When a variablestimulation interval is employed at different temperatures almost any variation inthe curve may be obtained. This is clearly shown by the results of Clark (1920) onthe effect of temperature upon the duration of contraction of the rhythmicallybeating auricular strip. It is evident, therefore, that in an investigation of theeffects of temperature upon the contractile mechanism, only those results areadequate which are based upon the duration of contraction of the first two or threetwitches following an adequate period of rest, and stimulated at an interval sufficientto allow adequate recovery at all temperatures.

DISCUSSION.

The foregoing discussion should be adequate to show that little significan^pcanbe attached to the values of \L obtained in the sense of their chemical significance.


values obtained for various portions of the curve furnish, however, a con-venient means of. comparing the constancy of the function in various tissues underdifferent conditions. In Table II are plotted some of the values of //. obtained inthese experiments. It should be noted that the /* values for the temperature range0-7° to 200 are highest when experimental methods tending to limit the heat deterio-ration of the tissue are employed. Similarly, for the temperature range from 200 to3 8° the highest values of p were obtained under the same conditions, and thedifference in /A value for these two ranges of temperature is well outside the experi-mental error; the values for the upper range of temperature cannot, of course, beconsidered as accurate as those for the lower range where the deterioration of tissueis practically negligible. For this reason, in comparing the values for the velocityof contraction of the auricular muscle with similarly determined values for thevelocity of contraction of other types of muscle, the most accurate temperaturerange over which to make a comparison is that from 0° to 200, or to that temperatureat which the lower value of JU. is approached.

Table II

Exp.no.

I

2

34

6

I

H from slope ofline o°-2O°

Temp,range

8 8 8

88 1 1 1

14,700

13,3°°14,40014,50°13,600*

H value from first two records obtained

Temp,range

O

10-3-20-510-2-20-3

1-9-20-85-7-18-43-4-20-5

V-

14.74°i5,68of13,ioot

13,670*15.59°I4.95O

Temp,range

21-3-29-617-7-34-8

18-6-32-914-0-35-9

21-9-31-7

11,26010,650

9.5OO11,970*

11,840

• After 2 hours' exposure to 3 per cent, alcohol.Immediately after removal from the turtle,i j hours later.I

The fact that the /x value depends on the experimental methods employedrenders difficult any exact comparison of the values obtained in this investigationwith those of other investigators. The /* value of 14,500 for the auricular muscle ofthe turtle as obtained in this investigation is higher than that found by Eckstein(1920) for frog heart. At the same time the results are more consistent. The value,however, compares favourably with the fi value of 14,000 for the velocity of con-traction of the gastrocnemius muscle of the frog for the same temperature range.This is shown in Fig. 1, D, in which are plotted the values obtained by Fulton (1926)for the gastrocnemius muscle. The complete lines are those applied by the author on

ption that the values obtained at lower temperatures are the most accurate,gives a ft value of 14,000. The //. value of 12,500 obtained by Fulton is the same

as would be obtained for the auricular muscle if points only in the upper temperature25-2


range were considered; the difference between the results of this paper and ^ pFulton disappear, however, if the lower temperature range is used. This procedure,for reasons already stated, is preferable. It should be pointed out that if the value14,000 is selected as best for skeletal muscle on the grounds that the observations inthe lower temperature range of Fulton's data are the most accurate, the /u value isnot in accord with that of 12,500 obtained over the same temperature range, for theheat production per gram tension in skeletal muscle (Hartree and Hill, 1921;Fulton, 1926).

CONCLUSIONS.

1. The velocity of contraction of the auricular muscle strip as a function oftemperature is described adequately from 0-7° C. to about 200 by the Arrheniusequation. Above 200 the results deviate from the linear relationship obtainingbelow this temperature in a direction indicating a decrease in the velocity of con-traction. The cause of the deviation is unknown.

2. The deviations occurring above 200 C. are still present when methods areemployed to reduce to a minimum the progressive deterioration of the isolatedtissue at high temperatures.

3. Deterioration of the tissue due to prolonged exposures to low temperaturesand brief exposures to high temperatures, or due to exposure to alcohol, producesno appreciable alteration in the velocity of contraction as a function of temperature.The n value between 0-7° and 200, however, is slightly lower.

4. The rate of stimulation can profoundly alter the relation between the velocityof contraction and the temperature.

REFERENCES.BBLEHRADKK, J. (1928). Protoplasma, 8 311.CLARK, A. J. (1920). Journ. Pkysiol. 54, 275.ECKSTEIN, A. (1920). Pfltlger's ArMv, 183, 184, 40.FULTON, J. F . (1926). Muscular Contraction and the Reflex Control of Movement. Williams and

Wilkins Co., Baltimore.HARTHEB, W. and HILL, A. V. (1921). Joum. Pkysiol. 65, 133.HBILBRUNN, L. V. (1924). Amer. Journ. Pkysiol. 68, 645:

(1925)- Science, 62, 268.(1929). Protoplasma, 8, 58.

LILLIE, R. S. (1923). Protoplasmic Action and Nervous Action. Chicago Univ. Press.POTTER, A. (1914). Zeitsch.f. allgem. Pkysiol. 16, 574.SMITH, H. W. (1926). Amer. Journ. Pkysiol. 76, 411.SNYDEH, C. D. (1911). Amer.Joum. Pkysiol. 28, 167.WIGGEKS, C. J. (1927). Amer. Journ. Pkysiol. 80, 1, 12.

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