THE INFLUENCE OF WARMTH UPON THE 
IRRITABILITY OF FROG'S MUSCLE AND 
NERVE. By CHARLES L. EDWARDS, A. M. With 
Plate IV. 
Historical. 
At the suggestion of Dr. Howell the following experiments 
were undertaken to demonstrate the effects of warmth upon the 
irritability of frog's muscle. The historical resume is brief, for 
although a number of investigators have given hints, only two, 
Marey and Schmulewitsch, have given us important results con- 
cerning this phase of muscle activity. 
Helmholtz,w whose classical researches have furnished the 
foundation for the modern investigation of muscle phenomena, 
seems not to have mentioned the influence of warmth, although 
he noticed that of cold, upon muscle contraction. E. J. Marey,(2) 
in 1868, with new and much improved methods, was enabled to 
record very elaborately his results. 
The frog's gastrocnemius was placed in a metallic case sur- 
rounded by a second case, while in the annular space between 
the two warm water was made to flow. The effects of heating 
the muscle he divided into two periods. In the first, the period 
of " excitation of muscular action," the simple contraction is 
shorter and stronger as the temperature rises, provided, however, 
it does not exceed 30° to 35° C. In the second period, that of 
''alteration of the muscle by warmth, and loss of irritability," if 
the warmth be increased from the previous limit of 35° C., the 
height of the* contraction decreases and the muscle does not 
regain its normal length, so that each contraction curve shows a 
marked contracture. If the muscle is warmed by submitting it 
immediately to a temperature of 45° to 50° C. this result of the 
second period may be obtained at once without the occurrence 
of the first period. 
To these two periods a third should be added in the liNuUr 
punkt " of J. Schmulewitsch.(3) Schmulewitsch placed the frog's 
gastrocnemius in a vessel containing 0.65 per cent. NaCl solution, 20 
CHARLES L. EDWARDS. 
over the rim of which the nerve was carried to the stimulating 
electrodes, so that it wras not submitted to the same temperature 
as the muscle. The muscle was warmed by placing the vessel 
in which it was fastened in a larger vessel containing water of a 
constant temperature of from 46° to 47° C., by means of which it 
could be heated to any given temperature. At a certain tem- 
perature, varying with individual muscles from 37° to 41i5° C., 
the muscle loses its irritability--reaches the "Null-punkt" The 
irritability could be restored by bringing the muscle to a lower 
temperature again. The cooling was done in one-half minute 
by means of fresh cool NaCl solution. 
In Marey's results the gradual loss of irritability was associ- 
ated with heat rigor. But the fact discovered by Schmulewitsch, 
and shown in this paper, that a complete loss of irritability can 
be obtained without any heat rigor, thus making the latter quite 
distinct, makes it necessary to add a fourth period, that of heat 
rigor, to the preceding. 
According to Hermann,(4) heat rigor was first observed by 
Pickford. 
Ch. Rouget(6) noticed that the extent of the heat rigor short- 
ening is equal to that of the highest contraction, and he de- 
clared them to be of the same nature.- 
W. Preyer(7) found that after the muscle had gone into rigor 
its irritability could be regained if, in addition to restoring the 
circulation, the muscle was bathed in 10 per cent. NaCl or certain 
other solutions. 
Apparatus. 
The apparatus I used for warming the muscle consisted essen- 
tially of a double-walled brass cylinder, 1) of Plate IV, about 
11.5 cms. long and 6 cms. wide. The distance between the 
outer and inner walls of the cylinder was 1 cm., and through this 
space warm or cool water was made to pass from a reservoir, a, 
in which the water was always kept some two or three degrees 
higher than that to which it was desired to have the cylinder 
heated. In this way the cylinder could be warmed slowly or 
quickly to any given point and, when desired, its temperature 
could be kept constant within half a degree for any length of 
time. The muscle to be warmed was placed within the space WARMTH ON FROG'S MUSCLE AND NERVE. 
21 
enclosed by the inner cylinder. The cover of the cylinder is of 
hard rubber, c, containing binding screws for the attachment of 
the wires, and a small hole through which a thermometer can be 
passed to give the temperature of the interior space in which the 
muscle lies. In the end opposite to that in which the rubber 
cover fits is a narrow slot through which the silk thread attached 
to the tendon of the muscle passes to be fastened to the record- 
ing lever y, the thread passing over the pulley e. The muscle 
used in all the experiments was the gastrocnemius, and was dis- 
sected away from the os cruris in the usual way. It was placed 
horizontally upon an oblong block of wood, enclosed in a bit of 
the reflected skin, and was kept firmly in position by pinning 
the os f&moris and os cruris to the wooden block. This method 
was used whether the muscle was entirely isolated from the rest 
of the body or whether the whole frog was placed in the warm 
chamber; and the muscle could easily be arranged so as to keep 
the circulation entirely uninjured. In one series of experiments 
the whole frog (curarized) was used, but so arranged that only 
the leg with the muscle to be experimented upon, with its circula- 
tion intact, was within the cylinder, the rest of the animal 
being placed upon a support just outside of the cylinder. This 
experiment required, of course, a different cover with a hole of 
sufficient size to allow the leg to fit snugly into it. The warm 
chamber was kept moist by means of filter paper saturated with 
normal NaCl solution, which was placed upon the block of wood 
beneath the muscle. The contractions of the muscle wTere 
registered upon the smoked paper of an ordinary drum kymo- 
graph, upon which also a time marker was made to write, record- 
ing fiftieths of a second. To prevent the great inertia fling of 
the muscle lever, a damper was attached, consisting of a fine 
steel rod attached to the lever and ending below in a disc of 
parchment paper, with a diameter of about 3.5 cms., which 
moved in a beaker of olive oil,/'. For stimulating the muscle, 
one of the'DuBois Reymond induction coils was used, which was 
run with a single Daniells cell. For breaking the primary 
current through the coil, a mercury make-and-break key was 
employed, and the muscle in all the experiments was stimulated 
only by the breaking shocks, the making shocks being short- 
circuited in the usual way by means of a Du Bois Reymond key. 22 
CHARLES L. EDWARDS. 
The stimulus was always a single sub-maximal shock, unless 
otherwise specified. A Centigrade thermometer was used for 
taking the temperature of the warm chamber. 
Experiments. 
In the following experiments the muscle wqs subjected to five 
different conditions. I have therefore tabulated the results as 
Series I, II, III, IV, V. 
Series I. 
In this series only the excised muscles of curarized frogs 
were used ; muscles, therefore, in which there was no circulation 
of blood and the influence of motor nerves was eliminated. The 
muscle was prepared and placed in the cylinder and then 
slowly warmed. Starting from the temperature of the room, 21° 
to 23°, several contractions were taken at given intervals of 
temperature, and the muscle was kept at each temperature for 
about five minutes in order to be certain that the whole muscle 
had been really heated to that degree. 
In this, as in the succeeding series of experiments, the follow- 
ing facts were ascertained whenever possible: 1. The temperature 
of the greatest contraction ; 2. The temperature at which tetanic 
contractions appeared ; 3. The temperature of the loss of irrita- 
bility ; 4. The duration of the loss of irritability; 5. The temper- 
ature of heat rigor, and, 6. The time required for the development 
of heat rigor at a constant temperature. 
In general, the contractions show a gradual rise in height to a 
maximum in the highest simple contraction. At about this tem- 
perature contractions of a tetanic nature (see Plate IV, Fig. 3) 
were obtained in all but No. 2. Then there ensued a gradual dimi- 
nution in the height of contractions until the irritability was lost. 
This condition may last for some time, as in No. 18 for 15 
minutes, or it may give place at once to heat rigor. The latter 
develops slowly or quickly according as the temperature is kept 
at about the point at which the muscle loses its irritability, 
or is raised somewhat higher. In No. 1 the development of heat 
rigor required one hour, the temperature being constant at 38.5°. 
Where in the table the temperature of loss of irritability or of WARMTH ON FROG'S MUSCLE AND NERVE. 
23 
heat rigor is given at a lower point than that of the highest 
contraction, the muscle had been previously heated to the highest 
point given. Plate IV, Fig. 2, gives a typical series of contraction 
curves, and although representing an experiment of Series II, 
may be taken as an illustration of the general effects of warmth 
upon frog's muscle under any one of the five conditions. 
Series I. 
Excised Muscle ; Frog Curarized. 7 Experiments. 
Number of Experiment. 
CO CO CO CO CO CO CO 
<j io io io <* io 
Or cn Or or Or <Or Or 
o o o o o o o 
Temperature of Highest 
Contraction. 
co co co to co 
P Ci to 
io <* <? io io 
Or Or Or Or or 
1° 1° 1° 1° 1° 
co co co CO CO 
GO GO GO 
Or to io 
O or Or Or Or 
o o o o o 
CO 
or 
io 
Or 
1° 
CO 
GO 
io 
Or 
o 
Temperature of Tetanic 
Contractions. 
co co co co co co co 
GO GO CO -Q CD 
• o • • * • o 
to <? to <1 
Or or or Or or 
o o o o o 
Temperature of Loss of 
Irritability. 
15 minutes. 
Duration of Loss of Irri- 
tability. 
: co co co co 
: -7 a o 
• io <? 
: Or Or Or Or 
• o o o o 
38.50° 
Temperature of Heat 
Rigor. 
1 hour. 
Time of Development of 
(.Rigor at a Constant 
Temperature. 
2 hrs. 15 minutes. 
2 hrs. 35 " 
1 hr. 47 " 
1 hr. 45 « 
3 hrs. 7 " 
1 hr. 26 " 
1 hr. 20 " 
Duration of Experiment. 
In this series the highest contraction was obtained between 
36.25° and 38.50°, except in one case, No. 4, which reached this 
point at 33.25°. No. 20 may be taken as an average experiment 
for this series, although from 21.75° to 33.50° there is generally 
a gradual rise in the height of contraction, while in this experi- 
ment the curves for this period present no material difference. 
The maximum contraction is given at 37.75°, while from 36.25° 
to 38.50° the muscle is in a state of great irritability, as shown 
by the tetanic nature of the contractions. At 39°, the tempera- 
ture having reached its highest point, there is a complete loss of 
irritability. Without trying to keep the muscle in this condition 
for more than a few minutes, when it was taken from the case 
and cooled, the irritability was restored when the temperature 
fell to 33.75°. The contraction at this point is slightly higher 
than the contraction taken at about the same temperature 
near the beginning of the experiment. Subsequent warming 
resulted in diminishing contractions until the irritability was 
lost a second time at 38°. 24 
CHARLES L. EDWARDS. 
Series II. 
In this, as in Series I, only the excised muscles were used, but, 
as the frogs had not been curarized, the nerves were still active. 
Although the stimulus was sent directly to the muscle, probably 
the nerves received and distributed it. In this series there were 
no tetanic contractions. 
Series II. 
Muscle-Nerve. 4 Experiments. 
Number of Experiment. 
co co co co 
00 -Q p p 
co io io 
Or CT! Or Or 
o o o o 
Temperature of Highest 
Contraction. 
Temperature of Tetanic 
Contractions. 
36.50° 
36.75° 
37.75° 
Temperature of Loss of 
Irritability. 
21 minutes. 
Duration of Loss of Irri- 
tability. 
CO CO CO 
ppp 
io <? bt 
Or Or O 
o o o 
Temperature of Heat 
Kigor. 
Time of Development of 
Kigor at a Constant 
Temperature. 
2 hrs. 
1 hr. 18 minutes. 
1 hr. 45 " 
2 hrs. 
Duration of Experiment. 
In No. 6 the second contraction at 29.75° was the highest, and 
the contractions then diminished as the muscle was warmed. To 
see if this diminution could be checked, at 36.25° the muscle was 
again cooled, but the irritability was only slightly restored. In 
No. 16, although the highest contraction was obtained at 37.75°, 
there was but a slight loss of irritability until at 39.25°, when 
heat rigor commenced. 
During the first part of the development of rigor, contractions 
gradually decreasing in height were given. In No. 17 there is 
a typical series of contractions (see Plate IV, Fig. 2), gradually 
increasing in height until 38.25°. Then allowing the temperature 
to fall slightly, and keeping it constant at from 36.25° to 37° for 
about twenty minutes, the irritability did not remain constant, 
but steadily fell; even lowering the temperature still further was 
of no avail, and at 28.25° there was a total loss of irritability. 
In all of these experiments there was some development of heat 
rigor, although very small, while the contractions were diminish- 
ing, so that this condition could not be marked off so distinctly 
as in the other series. WARMTH ON FROG'S MUSCLE AND NERVE. 
25 
Series III. 
In this series the muscle was dissected free from the distal 
attachment, but was left with the blood-vessels uncut at the 
proximal end. The whole frog having been curarized, was 
pinned to the block in such a manner that the circulation was 
not impaired, and then w'armed. If the heart had ceased to 
beat when the muscle had lost its irritability, then, when the 
irritability of the muscle was restored by cooling and bathing in 
normal NaCl, the action of the heart was also generally restored. 
In these experiments the loss of irritability was somewhat more 
rapid than in those upon the excised muscles. 
/ 
Series III. 
Muscle with Circulation ; Whole Frog Warmed; Frog Curarized. 7 Experiments. 
Number of Experiment. 
co w ca co os co co 
<? Cl CO CO Cl hU rfi. 
° -i <? to <? io io 
C! O( Cl 3 Cl C! 
o o o o o o 
Temperature of Highest 
Contraction. 
co: 
Cf * 
o : 
l . 
co • 
o • 
6t • 
o 
Temperature of Tetanic 
Contractions. 
co co co co co 
o ci 
° io io io 
Cf C» C C3 
o o o o 
Temperature of Loss of 
Irritability. 
'J? 
Ji 
3 
3* 
- 
•D 
Ji 
1 hour. 
53 minutes. 
7 minutes. 
Duration of Loss of Irri- 
tability. 
39.25° 
39.50° 
CO co 
Ci co 
cl cl 
o o 
Temperature of Heat 
Kigor. 
35 minutes. 
1 hr. 28 min. 
Time of Development of 
Kigor at a Constant 
Temperature. 
to co co 
tr tr &- 
'Ji GO cZ cZ 
co to 
00 OI to 
1 hr. 40 minutes. 
1 hr. 6 " 
3 hrs. 37 " 
Duration of Experiment. 
In No. 7 the maximum contraction was at 34.75°. Raising 
the temperature, the irritability decreased, until at 35.75° only 
the faintest tremor could be obtained. Lowering the tempera- 
ture to 29.25°, only the slightest irritability was shown, while at 
26.75° there was none. Again raising the temperature, heat 
rigor commenced at 33.75°. Substantially the same results were 
obtained in No. 8, except that a loss of irritability came when 
the temperature had fallen to 29.25°, and heat rigor on again 
warming to 36.75°. In No. 9 the loss of irritability lasted for 
one hour, the temperature gradually falling. When the frog was 
taken from the warm chamber and bathed in normal salt solu- 
tion, the irritability of the muscle was restored. 26 
CHARLES L. EDWARDS. 
In No. 10 the loss of irritability was obtained twice-the first 
time at 37.25°, and then the muscle was allowed to cool off slowly. 
After 35 minutes, there being no irritability at 31.25°, the frog 
was taken from the case and cooled still more by bathing in 
normal NaCl. In 20 minutes at 23.75° the irritability was 
restored, and the muscle gave its highest contraction in this con- 
dition at that temperature. Again warming the frog, the irrita- 
bility was a second time lost at 36.25°. Holding this temperature 
constant for 30 minutes, there was neither irritability nor heat 
rigor, but on increasing the temperature 2°, rigor commenced. 
Keeping the temperature constant at 39.25°, the development of 
heat rigor required 35 minutes. 
In No. 11 marked tetanic contractions were obtained from 
37.75° to 39.50°, but only after a rest of from two to five min- 
utes between them, for stimuli sent in upon the next revolution 
of the drum after obtaining a tetanic contraction produced only 
the normal curve (see Plate IV, Fig. 3). In this experiment 
the development of heat rigor while the temperature remained 
at from 38.25° to 39.50° required 1 hour 28 minutes. 
In No. 21 the highest contraction during the whole experiment 
was given at 32.25°, the muscle having been previously warmed 
to 36.25°, where the irritability was lost. The muscle was then 
kept constant in this condition at 36.25° to 37.25° for 36 minutes, 
and again the irritability was restored on cooling. 
Series IV. 
The frog pithed, and not curarized, was placed within the 
cylinder just as in Series III and gradually warmed. The circu- 
lation and the nerves of the muscle were therefore not directly 
impaired. As in the case of the experiments upon the muscle- 
nerve preparation, this series is marked by the absence of any 
tetanic contractions, which phenomenon therefore is no doubt due 
to the presence of the nerve. WARMTH ON FROG'S MUSCLE AND NERVE. 
27 
Series IV. 
Muscle with Circulation ; Whole Frog Warmed ; Frog Pithed. 3 Experiments. 
'JI >4- co 
Number of Experiment. 
co co co 
o to co 
io 
On Or Or 
o o o 
Temperature of Highest 
Contraction. 
Temperature of Tetanic 
Contractions. 
xo co co 
-5 Or <1 
0 to 
Or Or 
o o 
Temperature of Loss of 
Irritability. 
CO 
3 
5* 
d 
2 
21 minutes. 
Duration of Loss of Irri- 
tability. 
Temperature of Heat 
Rigor. 
Time of Development of 
Rigor at a Constant 
Temperature. 
2 hrs. 27 minutes. 
2 hrs. 25 " 
2 hrs. 49 ' ' 
Duration of Experiment. 
In No. 13, when the muscle had lost its irritability at 37.75°, 
although immediately cooled to 23.75°, only the faintest trace of 
irritability was restored, and that after 21 minutes; while heat 
rigor commenced slowly and continued as the muscle was again 
warmed. In No. 14, after the irritability was once lost, it was 
not restored. In No. 15 the muscle was kept at a tempera- 
ture of 36° to 37.75° for 55 minutes before there was a loss 
of irritability, although heat rigor commenced after 27 minutes 
at 37.75°. Allowing the temperature to fall 0.75° in the next 
28 minutes, heat rigor still continuing to a small extent, the 
loss of irritability was obtained. This condition was held for 
37 minutes, during which time the muscle was cooling off, then the 
irritability was somewhat restored, but the muscle all the time 
developed more rigor. Again, as the temperature rose the rigor 
became more marked, but the muscle still retained its irritability 
until very near the end of the period. 
Series V. 
In this series the experiments without doubt were performed 
under the most favorable conditions. The frog was prepared as 
in Series III with perfect circulation, but, instead of warming 
the whole frog, only the leg including the muscle to be experi- 
mented upon was warmed. , 
The remainder of the body, resting upon a small shelf just 
outside of the cylinder, was kept cool by frequent bathing in 
normal NaCl solution. The fact that in No. 22 the muscle was 28 
CHARLES L. EDWARDS. 
subjected to varying conditions of heat for five hours and twenty- 
five minutes without any rigor, shows that, although the muscle 
has lost its irritability and had been kept in this condition for a 
long time, yet if one is careful not to go beyond this point there 
is no apparent injury to the muscle from the influence of warmth. 
Series V. 
Muscle Only Warmed ; With Circulation ; Body Cool; Frog Curarized. 
4 Experiments. 
to to 
Of 4- CO to 
Number of Experiment. 
CO CO CO 
to <7 ° 
Of Or 
o o 
Temperature of Highest 
Contraction. 
CO CO CO 
00 Q P 
C7f *o Wo 
o 1 | 
CO co 
GO O 
Or Or 
o o 
Temperature of Tetanic 
Contractions. 
36.25° 
39° 
38.75° 
Temperature of Loss of 
Irritability. 
30 minutes. 
Duration of Loss of Irri- 
tability. 
JT 
O 
Temperature of Heat 
Rigor. 
50 minutes. 
Time of Development of 
Rigor at a Constant 
Temperature. 
5 hrs. 25 minutes. 
3 hrs. 13 " 
4 hrs. 47 " 
1 hr 1? u 
Duration of Experiment. 
In No. 22 the highest contraction was at 34°, but the following 
contraction at 35.75° was only one-quarter its height. Holding 
the temperature constant at from 35° to 37.12° for 1 hour 6 
minutes, the contractions, taken about every five minutes, were 
almost exactly equal. Then raising the temperature not more 
than 1°, the irritability commenced to diminish until it was lost 
after 30 minutes at 36.25°. The temperature being kept at this 
high point, the state of loss of irritability remained without any 
heat rigor for 30 minutes. Then cooling the muscle, the irrita- 
bility was partially restored immediately. Allowing the muscle 
to rest for 1 hour 10 minutes, the irritability was completely 
restored. Again warming it, tetanic contractions were given at 
36.5° and 36.75° higher even than those given at 34° during the 
first part of the experiment. Again, holding the temperature 
constant at from 35° to 37.75° for 1 hour 45 minutes, the con- 
tractions were not quite uniform, there was a constant though 
slight diminution in the successive contractions until the period 
ended in complete loss of irritability. 
In No. 23 the usual series was given ; the highest contraction WRMTH ON FROG'S MUSCLE AND NER VE. 
29 
at 38.75°, tetanic contractions from 36.37° to 38.75°, and loss of 
irritability at 39°. This was with a sub-maximal stimulus; but 
upon increasing the stimulus to maximal, a tetanic contraction 
higher than any preceding contraction was given. Keeping the 
temperature constant at from 38.75° to 41.25° for 1 hour 43 
minutes, and using a maximal stimulus, the contractions grad- 
ually diminished, losing their tetanic nature after 25 minutes 
until the period ended in loss of irritability, while at the same 
time during this period the muscle had developed a large amount 
of its heat rigor. Now pushing the secondary coil completely 
over the primary, making the stimulus as much supra-maximal 
as possible, an additional small contraction was given, which 
was somewhat increased when the stimulus was sent in as rapidly 
interrupted induction shocks. In 26 minutes from the loss of 
irritability for a maximal stimulus even this enormous supra- 
maximal stimulus was unable to call forth a contraction. 
Putting the frog, still cool and unharmed, aside in normal 
NaCl solution for about 14 hours, the irritability had again been 
partially restored, a maximal stimulus causing a contraction the 
height of the highest contraction, the stimulus being equal to that 
used in the first part of the experiment. Now warming the 
muscle to a high temperature, only a small curve of heat rigor 
was obtained. This would represent about one-third, and the 
curve of rigor obtained in the first portion of the experiment 
about two-thirds of all the rigor registered. But comparing this 
whole curve with the heat-rigor curve of the gastrocnemius from 
the other leg, which curve was considerably higher, shows that 
after taking the muscle from the cylinder some rigor must have 
developed which was not registered. 
In No. 24, using a maximal stimulus from the beginning, a 
regular series of contractions reaching a maximum at 39.25° was 
obtained. From this point the temperature was held constant 
at from 39.25° to 38.75° for 1 hour 40 minutes. In 1 hour 8 
minutes heat rigor commenced. At the end of this period the 
stimulus was made supra-maximal, but with scarcely any effect. 
However, when the muscle was cooled, bathed in normal NaCl and 
set aside for about 2 hours, the irritability was somewhat restored. 
In one experiment upon a frog, not curarized nor pithed, the 
whole animal being warmed, a regular series of contractions 30 
CHARLES L. EDWARDS. 
was obtained reaching a maximum at 36.75°. This highest con- 
traction was also the only one in the whole experiment of a tetanic 
nature. In addition to these contractions caused by the regular 
single sub-maximal shocks there was irregular series of volun- 
tary contractions, increasing in height as the warmth increased 
until they too attained their maximum at 36.75°. But although 
the highest contractions, both voluntary and those caused by the 
electric stimulus, were obtained at the same temperature and 
about the same time, the former were 2J times the height of the 
latter. In this condition of greatest irritability the frog gave a 
number of convulsive voluntary contractions which entirely 
ceased in about 5 minutes, while period B (see below) continued 
as in the other experiments. 
Influence of Warmth upon the Irritability of Motor 
Nerves. 
Three experiments were made upon motor nerves, using the 
same apparatus as in Series V, warming the sciatic nerve and 
registering its condition by means of the gastrocnemius, which 
rested upon the support outside, and was frequently bathed in 
normal NaCl solution. 
In the first experiment with a single sub-maximal induction 
shock, the contractions showed no difference up to about 42.25° 
after having been warmed for 1 hour 23 minutes; then there 
was a slight diminution so that 33 minutes later at 48.75° a con- 
traction wTas only given with rapidly interrupted induction 
shocks, and this irritability soon disappeared. Then, on allow- 
ing the nerve to cool, its irritability was restored. This process 
of warming to loss of irritability and then restoring was repeated 
several times with no apparent injury to the nerve. 
The second experiment was practically a repetition of the 
first except that the diminution in height of the contractions 
commenced at 45.25°, and by holding the temperature constant 
within 1|° for 12 minutes a loss of irritability was obtained. 
In the third, the nerve lost its irritability for a sub-maximal 
stimulus at 48.25°, and on continuing to warm it to 50° there was 
still no irritability manifested, until the stimulus was increased 
by pushing the secondary coil to " 6 "; then a contraction was WARMTH ON FROG'S MUSCLE AND NER VE. 
31 
given. Still raising the temperature, the nerve again lost its 
irritability at 51.25° with the coil at " 6," but at 51.75°, by push- 
ing the secondary coil to " 4," another contraction was obtained. 
On now maintaining the temperature at this point for 4 min- 
utes, irritability was lost for the stimulus "4." On again in- 
creasing the stimulus to " 3J," a contraction of I the height of 
the last was given, but the response to this stimulus soon ceased. 
Next, on warming to 53.25°, pushing the coil to "3" and mak- 
ing the stimulus tetanic, only a very small contraction resulted. 
This soon disappeared, and no further increase of stimulus was 
able to cause a contraction at this temperature, but as soon as 
the nerve was cooled the irritability returned, although some- 
what impaired. 
N. Afanasieff(8) in his paper, " Investigation upon the Influence 
of Warmth and Cold upon the Irritability of the Motor Nerves 
of the Frog," has emphasized several facts. His method was 
to let the nerve rest easily upon two hook-like stimulating 
electrodes placed within a glass tube. The warming was accom- 
plished by bringing pure oil, heated to the desired temperature, 
in contact with the nerve. A minimal stimulus was used. The 
degree of irritability of the nerve was determined by moving the 
secondary coil. Gradually warming the nerve to 35° C. gave an 
increase of irritability. Suddenly warming the nerve to 35°-40° 
caused clonic spasms of the muscle. By warming to 40°-45° 
convulsions of a tetanic nature were produced, as Rosenthal also 
had observed. These convulsions may last for a minute. At 
65° the irritability is destroyed almost immediately. Between 
40° and 50° the irritability is lost, but can be restored upon cool- 
ing. This, Rosenthal and, according to Hermann/9' Pickford 
also, had observed. A condition which Afanasieff calls the 
" apparent death of the nerve," wherein it is absolutely unex- 
citable to the strongest stimuli, is obtained at 50°-65° C. But 
by cooling the nerve the irritability can be restored, though 
incompletely. 
There are several differences between the results of Afanasieff's 
work and those of this paper, the methods being quite unlike in 
the two cases. The highest temperature at which I could get a 
contraction with the strongest stimulus was at 53.25° C., and 
beyond that the nerve went into " the condition of apparent death." 32 
CHARLES L. EDWARDS. 
When the irritability was lost with a sub-maximal stimulus, not 
only was a contraction given at the same temperature by 
increasing the stimulus, but also at a somewhat higher tempera- 
ture. And this process of losing and regaining the irritability 
was repeated at successively higher temperatures until the limit 
was reached. 
Conclusions. 
In general, four periods, representing distinct phases of the 
condition of irritability, were obtained in each of the five series. 
These may be described as, A, gradual increase of irritability to 
the maximum ; B, gradual diminution of irritability to its total 
loss; C, condition of no irritability, and B, development of heat 
rigor. In these separate phases the results of the whole course 
of experiments may be summarized. 
Period A. 
Gradual Increase of Irritability to the Maximum. 
This in general corresponds to Marey's(2) first period " exci- 
tation of muscular action," in which he obtained the highest 
contractions at from 30° to 35°. But my results differ in making 
the maximum contractions at from 32.75° to 39.25°, with only 
one exception, No. 6, Series II, where it was 29.25°, and this no 
doubt was abnormal. Marey also says that if a muscle be pre- 
viously submitted to a low temperature and then warmed, the 
descent of the contraction curve becomes shortened, thus 
marking the transition between the lengthening of movement by 
cold and its acceleration by warmth. This is evidently true for 
this epoch of transition; but from the temperature at which the 
muscle enters into period A, say 22°-26°, there is generally a 
slight increase in the duration of the contraction, so that the con- 
traction lasts .02 or .03 of a second longer in the condition of 
greatest irritability than it does at the beginning of period A. In 
addition to Marey's results, during and near the temperature 
of greatest irritability, I obtained tetanic contractions, the 
stimulus being simply a single sub-maxivial shock. These 
tetanic contractions were obtained in ten experiments included 
in Series I, III and V, but not in either Series II or IV, so that WARMTH ON FROG'S MUSCLE AND NERVE. 
33 
whenever the uninjured nerve was present they were absent. 
As shown in the experiments on nerves, at a period when the 
muscle is in its condition of greatest irritability the nerve is 
scarcely affected by heat. Hence, as the nerve probably received 
and distributed most of the stimulus, this may explain the appa- 
rent anomaly. These tetanic contractions were usually more 
marked after a rest of four or five minutes than in contractions 
observed after a shorter rest, as one or two minutes, and they 
sometimes disappeared entirely in the latter case. 
Period B. 
Gradual Diminution of Irritability to Total Loss. 
In Marey's second period, " alteration of the muscle by 
warmth, and loss of irritability," the phases in periods B and C 
were united, while period D was not brought out at all. 
In period B there is a gradual diminution in both the height 
and duration of the contraction. If one is very careful to stop 
the rise of temperature immediately after the highest contrac- 
tion and at that point keep it constant, this period may last for 
one or two hours. If, however, the temperature rises only one 
or two degrees above that at the beginning of the period, the 
loss of irritability is considerably hastened, and heat rigor may 
commence. Exercising considerable care, however, this period 
may be carried into period C without causing any rigor in the 
muscle. 
Period C. 
Condition of No Irritability. 
This period was pointed out by the investigation of Schmule- 
witsch,(3) whose methods have been described. Schmulewitsch, 
however, did not keep the muscle in this condition as I have 
done, but restored its irritability at once by means of cool 0.65 
per cent. NaCl solution. Normal NaCl is not necessary to restore 
the irritability, although it promotes the restoration. Simple 
cooling is sufficient. 
This period may come at any point within 5° above the tem- 
perature of the greatest contraction (in No. 6, Series II, there 
was a difference of 7°), or it may come at a somewhat lower 34 
CHARLES L. EDWARDS. 
degree if, after period B is well begun, the temperature is allowed 
to fall. I have found that this period may last if the tempera- 
ture is kept constant, as e. g. No. 21, Series III, for 36 minutes 
or more; while, if the temperature be allowed to fall slowly, as 
e. g. No. 9, Series III, it may last for one hour. 
Period D. 
Development of Heat Rigor. 
After the restoration of the muscle's irritability, the extent of 
the contractions is generally smaller than that of those of period A, 
the first contraction being usually the largest; then they diminish 
until a second loss of irritability. To this, however, there are 
marked exceptions, in one or the other particular, or in both, as 
e. g. No. 22, Series V, where the conditions of the experiment 
were more favorable than in the preceding series. This restored 
series may be obtained without any heat rigor, but a loss of irri- 
tability usually comes sooner than in period B. Heat rigor 
commences generally at a temperature from 5° to 1° or 2° above 
that of loss of irritability ; but if in period C the muscle be kept 
sufficiently long at a constant temperature, no further increase 
is necessary to produce heat rigor. The time of development of 
rigor at a constant temperature varies from 35 minutes, as e. g. 
No. 10, Series III, to 1 hour 28 minutes, as e. g. No. 11, Series III. 
The regular series of long contractures which Marey(2) obtained 
during the development of heat rigor I was unable to get. Un- 
fortunately, Marey does not give us the exact method by which 
his curves were obtained. During the first portion of the de- 
velopment of rigor, contractions can be obtained, but they do 
not show long contractures. However, if a period of rest 
intervenes, a contraction then taken may give the long contrac- 
ture; but the curve of the succeeding contraction, taken after one 
revolution of the registering drum, generally, as in the normal 
curve, comes at once back to the base line. The long-lasting 
contracture is exceptional. 
To Dr. W. H. Howell, who designed the apparatus (which w'as 
made in the workshop of the laboratory), and gave me many 
valuable suggestions during the course of these experiments, 
I wish to express my indebtedness and gratitude. WARMTH ON FROG'S MUSCLE AND NERVE. 
35 
BIBLIOGRAPHY. 
1. Helmholtz. Arch. f. Anat. u. Physiol. Berlin, 1850, pp. 
276-364. 
2. E. J. Marey. Du Mouvement dans les Fonctions de la Vie. 
Paris, 1868, pp. 351-358. 
3. Jacob Schmulewitsch.' Jahrb. d. Ges. d. Aerzte in Wien, XV, 
p. 3, 1868. 
4. L. Hermann. Handb. der Physiologic. Leipzig, 1879, I, p. 
100. 
5. J. Schmulewitsch. Compt. rend., tome LXVIII, p. 936, 
1869. 
6. Ch. Rouget. Compt. rend., 1867, I, p. 1232. 
7. W. Preyer. Central-blatt f. d. medic. Wissensch., 1864, p. 
769. 
8. N. Afanasieff. Arch. f. Anat. u. Physiol., 1865, p. 691. 
9. L. Hermann. Handb. d. Physiol. Leipzig, 1879, II, p. 92. 
EXPLANATION OF PLATE IV. 
Figure 1. Apparatus used in warming the frog's muscle (described 
page 20). 
Figure 2. Showing the effect of gradual increase df temperature 
upon the contractions of the muscle. The temperatures indicated 
by the different letters are as follows: 
a, 26.25° e, 37.25° i, 37° m, 31.75° 
b, 30.75° f, 36.75° j, 36.25° n, 30.25° 
c, 34.75° g, 38.25° k, 36.75° o, 29.25° 
d, 36.75° h, 36.25° I, 33.75° p, 28.25° 
Figure 3. Showing the tetanic contractions obtained with single 
induction shocks. The temperatures indicated by the letters are as 
follows: f, 37.25° g, 37.75°. STUDIES FROM BIOL.LAB. VOL. IVPLATE IV 
Fig. 1 
Fj gl 
Fig. 3