373
TEMPERATURE AND THE RESPONSIVE
MECHANISM OF CARDIAC MUSCLE
I. TEMPERATURE AND THE DURATION OF
CONTRACTION
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 of
a group of closely associated processes following each other at definite intervals.
Three distinct phases may be recognised in this system: (1) a local process occurring
in the region of the stimulus; (2) a rapid series of changes referred to as the propagated disturbance and indicated by the bio-electric variation; (3) the response of the
cell in the region adjacent to the seat of stimulation. Associated with each of these
phases are various processes which, although separately definable, appear to be
integral parts of the whole response. Thus, with the first and second phases are
associated chronaxie, the bio-electric variation, the conduction of the propagated
disturbance, the absolute and relative refractory periods, and other phenomena.
With the third phase, comprising the contraction of the muscle, are associated the
latent period of contraction, the duration of the contractile phase, the duration of
the relaxation phase, the tension developed, and the heat production. Considerable
evidence exists that these are inter-dependent processes and not merely independent
concurrent processes (Lillie, 1923; Fulton, 1926). In comparing the velocity of
movement of different muscles it has been observed that the more rapid is the movement of the tissue the briefer are chronaxie, the time for the conduction of the
propagated disturbance, the time for the development of the bio-electric variation,
the duration of the refractory period, the duration of the latent period, and the
duration of the isometric contraction. It has been shown also that with the increase
of initial tension on the muscle there is associated an increase in chronaxie, in the
duration of the isometric twitch, in the total tension, and in the heat production.
Despite this close relationship between the separate processes, it is significant
to note that each exhibits its own characteristic temperature coefficient. It is,
therefore, essential to determine the effect of temperature upon these processes
with reference to the velocity of the process as a function of temperature, and also
to d^ermine whether this function for each process may be modified independently
of 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 contraction of the auricular muscle as a function of temperature and an analysis of the
stability of the system under various conditions. Other phases of the responsive
mechanism 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 heart
of the turtle Pseudyms elegans or Chrysemys emarginate. The heart upon excision is
immediately immersed in a modified Ringer solution containing adrenalin i part in
IOO.OOO. The adrenalin serves to prevent the tonic smooth muscle contraction
which otherwise hinders ready dissection of the tissue. The two auricles are severed
from 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 the
inter-auricular septum. The rhythmic beating of the auricles is stopped by removing
the sinus tissue in which the excitatory impulse originates. To prevent the subsequent assumption of rhythmicity by the auricle o-oi per cent. MgCl2 is added to
the Ringer solution (Smith, 1926). The auricle to be used is then placed upon its
posterior surface and opened to form a rectangular strip by two parallel incisions
along either side from the auricular opening almost to the tip of the auricle. One
end of this strip is spread upon a small block of ebonite or of paraffined wood and
fastened with a silk thread. The other end is secured in the muscle clamp on the
muscle holder.
Recording apparatus.
The muscle holder consists of an ebonite disc which carries supported from its
lower surface two glass rods; the ends of these pass through an ebonite bar which
has on its upper surface a small ebonite clamp. One end of the muscle is held by
this clamp, while the other end of the muscle strip is tied tightly to a small ebonite
block attached to the muscle lever by a silk thread. Also suspended from the large
ebonite disc are two electrodes consisting of glass tubes, in the ends of which are
sealed wires. In the case of platinum electrodes the tubes are filled with mercury
and appropriate contact maintained at the top. In the case of silver electrodes they
are coated with silver chloride and copper-wire connections are made between the
silver and the binding post. Holes in the ebonite disc allow the insertion of a
thermometer 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 in
such a way that it can be raised or lowered, or the muscle chamber can be removed
at 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 h
spring, 2-5 cm. in length, fastened at either end by clamps which can be adjusted so
as 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 itself
can be turned to any desired position in a vertical plane. The lever used has a
period of 200 per second which is quite sufficient for the purpose in hand. By means
of a suitable lens the image of the single filament of a 4-volt electric bulb reflected
from a mirror is brought to a focus upon the recording surface. The movement of
the beam of light is recorded upon a moving sheet of bromide paper in an electrocardiographic camera. The recording system gives a magnification of 75 times.
All observations are made upon muscle immersed in 400 c.c. of a modified
Ringer solution. This is made up from stock solutions of the salts in glass-distilled
water. The salts are present in the following proportion: NaCl 0-59 per cent., KC1
0-029 P e r cent., CaCl2 0-017 P e r cent., and MgCl2 0-049 P e r cent.
The solution is buffered to a pH of 7-0-7-2 by the addition of NajjHPO,,. The
amount 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 of
the experiment nine of these flasks are filled with modified Ringer solution which
has been adjusted to the desired temperature, and tightly stoppered. These maintain
the temperature constant to within o-i° C. during the time of recording, and, when
stoppered, 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 response
is taken as the time from the onset of contraction to the peak of the contraction. The
investigations of Wiggers, as well as unpublished data of the author concerning the
genesis of the isometric myogram of this tissue, justify this procedure in that they
have shown that the values so determined represent the duration of the contractile
phase of the first region of muscle stimulated.
In the analytical treatment of the data, the velocity of the process as a function
of temperature is expressed in terms of the Arrhenius equation. This procedure
makes possible the comparison of the results with those of other investigators and
facilitates the comparison of several processes occurring simultaneously in the same
tissue. Although it would be more suitable to use a general expression of the same
form to which the theoretical implications of the Arrhenius equation would not be
attached, it seems advisable not to introduce any new equation to express the
velocities of the processes as a function of temperature, but rather to emphasise the
physiological factors inherent in the system under investigation, which limit the use
of the Arrhenius equation1.
1
A number of expressions have been used by investigators to describe temperature effects on
various 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 as
divMse as the growth of Drosopkila larvae, the locomotion of Amoeba, and the heat production per
gram tension in skeletal muscle. See Belehradek, 1928.
376
DUGALD E. S. BROWN
THE RELATION OF THE VELOCITY OF CONTRACTION
TO TEMPERATURE.
When a non-rhythmic auricular strip immersed in Ringer solution is subjected
to an increase in temperature, there results a decrease in the duration of the contractile phase of the isometric twitch. If the velocity of this process is considered as
the reciprocal of the duration, the velocity as a function of temperature may be
expressed in terms of the Arrhenius equation. In its integrated form this equation is
ln
K2-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 a
graphical treatment this expression is satisfied if the points obtained by plotting the
logarithm of the velocity against the reciprocal of the absolute temperature lie on
a straight line. From the slope of this line the constant /x may be calculated. The
results 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 experiment. Each point represents the average value for the first three or four twitches
except where otherwise indicated. The twitches were recorded after a 15-minute
period for temperature equilibration; a stimulation interval of 15 seconds was
employed at the time of recording.
Table I
Exp.
no.
Time
Tempera- StimuDuration contraction
lation
ture
interval
(sec.) Record 1 Record 2 Record 3 Record 4
i
2
2.45
07
305
4-4
3
3.17
7-6
io-6
3-5°
135
165
193
214
4
5
6
7
8
9
10
II
12
3-35
405
4.20
4-35
7.00
7-i5
7-3°
7-45
8.00
8.15
8.30
I2-I
156
186
214
247
13
14
IS
16
17
18
19
8-4S
9.00
9-15
35-7
93O
16-3
2O
9-45
195
27-3
296
329
382
15
IS
IS
IS
15
IS
15
15
15
IS
IS
IS
IS
IS
IS
15
IS
15
IS
IS
—
313
229
179
134
96
79
67
17
t
128
102
80
62
60
49
39
—
456
3H
229
178
135
94
79
67
179
132
104
82
64
57
48
37
32
21
20
128
—
125
106
472
300
—
I7S
132
—
—
—
—
132
95
94
80
7f
68
66
177
134
105
85
63
58
49
36
32
18
127
106
>
—
132
103
82
64
53
50
35
32
IS
—
—
The results show that the velocity of contraction as a function of tempera
adequately described by this equation from 0-7° to about 200. Above
1
Temperature and the Responsive Mechanism of Cardiac Muscle 377
deviate from the linear relation obtaining below this temperature, and in a
lion 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 sharp
inflection 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 in
the latter method of treatment. For purposes of analysis, however, it is sufficient to
log.vel.=log. 4+constant
17
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
0.0032
0.0033
0.0034
0.0035
I
I
0.0036
0.0037
absolute tempgraturg
Fig. 1. Curves A, B and C for auricular muscle. Curve D for gastrocnemius muscle of the frog. The
first two points recorded in the experiment are numbered. For subsequent points + indicates
determinations at increasing temperatures and © at decreasing temperatures.
assume that the Arrhenius equation adequately describes the relation between the
temperature and the velocity of the underlying process, whatever it may be, and that
the deviations shown to exist owe their origin either to factors associated with the cellular mechanism itself, or that they are inherent in the experimental methods employed,
such an analysis, it is essential to determine whether the results express the
of the contractile process as a function of temperature alone, or as a function
378
DUGALD E. S. BROWN
of temperature plus cellular changes likewise varying as a function of temper^y-e.
Perhaps the most significant concomitant cellular change which could influenSRie
results is the progressive change in functional state, or "deterioration," which an
isolated tissue undergoes when immersed in a physiological solution. To determine
if possible to what extent the deterioration of the tissue is modifying the velocitytemperature relation, experiments are performed in the following way: A first
record is obtained following a 10-minute exposure of the tissue at 200. The tissue is
then immersed immediately in Ringer solution at a temperature around 50. Records
are obtained at this temperature and successively at higher temperatures at intervals
of 3 0 to 300, and then at decreasing temperatures at 30 intervals till io° is reached. In
Fig. 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 a
function of the time and resulting in an increase in the duration of contraction, is
occurring at all temperatures. Below 200 the rate of deterioration is so slow that in the
time involved it is not appreciable. At temperatures above 200 the rate of deterioration
increases rapidly with the temperature. The degree of deterioration at these temperatures 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 the
temperature, it may be controlled to a considerable extent by experimental treatment in the following way. A first record is obtained, following a 10-minute
exposure of the tissue at 200. The tissue is then immersed immediately in Ringer
solution at a temperature in the vicinity of 3°. Records of the simple twitch are
then 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. After
an 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 after
a 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 that
temperature. 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 Arrhenius
equation adequately describes the relation for the entire range of temperature. For
purposes of comparison, the results of an experiment, involving a prolonged exposure
to progressively higher temperatures, are plotted in Fig. 2, B. The deviation from
the expected linear relation in this experiment is much greater than in Fig. 2, A. It
cannot be considered, however, as being similar in origin as it is completely
irreversible. This is shown in Fig. 1, A, where the deterioration which has occurred
permanently alters the subsequent values for the lower temperatures from those
found before the tissue was exposed to the higher temperatures. This result is
directly opposite to the results shown in Fig. 2, A, where the deterioration which
occurred at higher temperatures did not appreciably alter the subsequent values at
low temperatures. These results make it seem very unlikely, therefore, th
deviation from the expected linear relation shown in Fig. 2, A, can be due
Temperature and the Responsive Mechanism of Cardiac Muscle 379
d^Boration of the tissue at high temperatures. This conclusion does not preclude
the fact that the exposure to high temperatures results in some irreversible changes
in the tissue; it may be considered, nevertheless, as showing that such changes as
do occur cannot be recorded as changes in the duration of contraction by any
methods 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
''•x
ID
0.9
Q8
Q7
0.6
_
\i
V
\
\
\
\
\
X*
0.5
0.4
\A\
0.3
02
0.0032
r
i
0.0033
1
0.0034
0.0035
I .
0.0036
0.0037
absolute temperature
Fig. 2. + indicates determinations at increasing temperatures; © at decreasing temperatures. The
first two values recorded in the experiment are numbered.
an irreversible decrease in the total tension of the twitch (as opposed to the duration
of contraction) subsequently recorded at temperatures below 200 following an
exposure to a high temperature.
The results from experiments involving the use of an isotonic method of recording
substantiate the foregoing results. They show that an irreversible progressive
detej^ration occurs, as a function of time, at temperatures above 200. The deterioratio^^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.
380
DUGALD E. S. BROWN
Under the foregoing experimental conditions, which tend to limit the prog
deterioration occurring at temperatures above 200, the result may be satisfactorily
described by the Arrhenius equation- over a temperature range from 0-7° C. to
200 C. A marked deviation is still shown to exist above this temperature. If the
degree of deterioration under-these conditions be considered as negligible,. the
relation between the velocity of contraction and the temperature obtained may be
considered as being jointly determined by two factors: (a) the actual reactions
involved in the contraction of the muscle, and (b) associated reversible changes in
the physico-chemical organisation of the cell at different temperatures, which
might modify the reactions included under (a).
Although there is little direct evidence bearing on the point, we may take it as
exceedingly improbable that the fundamental changes underlying the contraction
are characterised by discontinuity, e.g. we may be reasonably certain that the
neutralisation 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 of
viscosity, and the results of investigations upon protoplasmic viscosity certainly
furnish evidence of a gross physico-chemical reorganisation in the cell progressing
as a function of temperature. The viscosity of the protoplasm of the Arbacia egg and
Amoeba 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. The
maximum 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 responsible
for the deviations from the accepted linear relation between the velocity of biological
processes and the temperature, and Heilbrunn (1925) has emphasised the possibility of such changes in the viscosity of protoplasm affecting the velocity of cellular
reactions. In the case of muscle, it is possible that in the vicinity of 200 the response
is modified by rapid physico-chemical changes in the system associated with the
condition of maximum viscosity at that temperature, but for reasons which will be
developed in a later paper, the viscosity per se is not considered as directly affecting
the system, but rather as one expression of a physico-chemical reorganisation with
which may be associated those changes in the system responsible for the deviation
from the linear relation.
The determination of the nature of the changes grouped under (a) would be
facilitated if a treatment of the kinetics of the contractile system were available. The
use of the Arrhenius equation in describing the relation between the velocity and
temperature, however, involves a very elementary treatment of the kinetics of the
system. Thus, in applying this equation to the data, it is assumed that the reciprocal
of the duration of contraction is proportional to the velocity constant of the reaction
at each temperature; this assumption implies either that the concentration of
material involved in the reaction is constant at all temperatures or that the vdarity
constant is independent of the concentration of the reacting substances. AflBlequate 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 plotted
in Fig. 2, A, accurately describe the velocity of contraction as a function of temperature under the conditions established by the experimental methods employed, and,
moreover, that any treatment of the kinetics of the system must be in accordance
with the results of such an experiment. In fact, the nature of the intra-cellular
changes associated with the discontinuities referred to are unknown, and must
remain unknown until the kinetics of the system are solved.
CONDITIONS MODIFYING THE VELOCITY-TEMPERATURE
RELATION.
The tissue deterioration whieh has been shown to increase the duration of
contraction also results in a decrease in the total tension produced during contraction. This result might be brought about either by the deterioration resulting in a
decrease in the quantity of material released at stimulation, or by the deterioration
producing modification in the method by which the foregoing material is utilised in
producing contraction of the muscle, or by both. In either of the above cases, it is
possible that such alterations due to deterioration would result in a change in the
velocity of the process as a function of temperature.
To determine, if possible, whether deterioration in the tissue results in an
alteration in the velocity-temperature relation, experiments were performed upon
the tissue in which various degrees of deterioration had been produced. The effects
of such treatment are best shown by a consideration of an actual experiment. In
Fig. 1, A, are plotted the results of an experiment performed on the same tissue
immediately after removal from the body of the turtle, after an exposure to room
temperature and after an exposure to high temperature of sufficient duration to
produce a considerable effect. These results show that the velocity as a function of
temperature was not affected by such treatment. However, the slope of the line is
greatest between the points 1 and 2 recorded immediately after removal from the
turtle; 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 and
reaches a quite constant value. If the slope is expressed in terms of /x, the initial
values would be about 14,800 ± 500; after an exposure of 2 hours to a temperature
of 200 the value would be 14,000 ± 500, and after prolonged exposure it would
reach a lower limit of about 13,500 ± 500.
Deterioration due to exposure to alcohol.
The exposure of the tissue to anaesthetising concentration of alcohol similarly
results in an irreversible deterioration of the tissue which causes an increase in the
duMfcon and a decrease in the total tension of contraction. In this case also the
deflftration fails to modify the velocity-temperature relation although it causes a
decrease in the slope which expressed in terms of p gives a value of 13,500 ± 500.
.JEB-VIliv
25
382
DUGALD E. S. BROWN
Effect of varying the rate of stimulation.
The relation between the velocity of contraction and the temperature shown to
exist in the auricular muscle is a special case determined by the stimulation interval
employed. In these experiments only the first response following a 10-minute rest
period was considered. The magnitude and duration of this response is determined
by the cellular conditions existing during the "steady state" of the resting muscle
at that particular temperature. A similar relationship might be obtained under
conditions of repeated stimulation, either at a constant or a variable rate, provided
the same relative cellular conditions existed at each temperature, as in the first
response following a period of rest, but such a condition is not attained readily
under conditions of repeated stimulation. If a constant rate of stimulation is
maintained throughout the experiment, the acceleration of the recovery process
with an increase in temperature serves to convert the stimulation interval, constant
with respect to time, into a stimulation interval of variable length with reference
to the cellular processes themselves. Thus, a stimulus occurring relatively early in
the recovery phase at low temperatures would occur relatively late in the recovery
phase at high temperatures. Since the magnitude and duration of the second
response depends upon the time at which it occurs during the recovery period
of the first response, the cellular conditions at the different temperatures are
not identical. The situation is complicated further by the fact that these effects of
regular stimulation of the tissue are associated with irregularities in the magnitude
and duration of the successive responses during continuous stimulation. In the
latter phenomenon, known as treppe, the first twitch following a period of rest is
usually larger than the second, after which each succeeding twitch increases in size
until a plateau is reached, the height of the plateau depending upon the rate of
stimulation. The slope of the temperature-velocity curve, therefore, depends upon
the particular stimulation interval employed and the duration of stimulation, and
the proper choice of interval and duration can result, over a portion of the temperature range, in a slope practically identical to that obtained when the average
duration of the first few twitches only is used in the calculation. When a variable
stimulation interval is employed at different temperatures almost any variation in
the curve may be obtained. This is clearly shown by the results of Clark (1920) on
the effect of temperature upon the duration of contraction of the rhythmically
beating auricular strip. It is evident, therefore, that in an investigation of the
effects of temperature upon the contractile mechanism, only those results are
adequate which are based upon the duration of contraction of the first two or three
twitches following an adequate period of rest, and stimulated at an interval sufficient
to allow adequate recovery at all temperatures.
DISCUSSION.
The foregoing discussion should be adequate to show that little significan^pcan
be attached to the values of \L obtained in the sense of their chemical significance.
Temperature and the Responsive Mechanism of Cardiac Muscle 383
values obtained for various portions of the curve furnish, however, a convenient means of. comparing the constancy of the function in various tissues under
different conditions. In Table II are plotted some of the values of //. obtained in
these experiments. It should be noted that the /* values for the temperature range
0-7° to 200 are highest when experimental methods tending to limit the heat deterioration of the tissue are employed. Similarly, for the temperature range from 200 to
3 8° the highest values of p were obtained under the same conditions, and the
difference in /A value for these two ranges of temperature is well outside the experimental error; the values for the upper range of temperature cannot, of course, be
considered as accurate as those for the lower range where the deterioration of tissue
is practically negligible. For this reason, in comparing the values for the velocity
of contraction of the auricular muscle with similarly determined values for the
velocity of contraction of other types of muscle, the most accurate temperature
range over which to make a comparison is that from 0° to 200, or to that temperature
at which the lower value of JU. is approached.
Table II
Exp.
no.
H from slope of
line o°-2O°
Temp,
range
H value from first two records obtained
Temp,
range
V-
Temp,
range
10-3-20-5
10-2-20-3
14.74°
i5,68of
13,ioot
21-3-29-6
17-7-34-8
11,260
10,650
1-9-20-8
5-7-18-4
3-4-20-5
13,670*
15.59°
I4.95O
18-6-32-9
14-0-35-9
9.5OO
11,970*
21-9-31-7
11,840
O
3
4
6
I
8 8 888 1 1 1
I
2
14,700
13,3°°
14,400
14,50°
13,600*
• 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 employed
renders difficult any exact comparison of the values obtained in this investigation
with those of other investigators. The /* value of 14,500 for the auricular muscle of
the 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 contraction 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 temperature
25-2
384
DUGALD E. S. BROWN
range were considered; the difference between the results of this paper and
^p
Fulton 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 value
14,000 is selected as best for skeletal muscle on the grounds that the observations in
the lower temperature range of Fulton's data are the most accurate, the /u value is
not in accord with that of 12,500 obtained over the same temperature range, for the
heat 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 of
temperature is described adequately from 0-7° C. to about 200 by the Arrhenius
equation. Above 200 the results deviate from the linear relationship obtaining
below this temperature in a direction indicating a decrease in the velocity of contraction. The cause of the deviation is unknown.
2. The deviations occurring above 200 C. are still present when methods are
employed to reduce to a minimum the progressive deterioration of the isolated
tissue at high temperatures.
3. Deterioration of the tissue due to prolonged exposures to low temperatures
and brief exposures to high temperatures, or due to exposure to alcohol, produces
no 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 velocity
of contraction and the temperature.
REFERENCES.
BBLEHRADKK, J. (1928). Protoplasma, 8 311.
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