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IOWA ACADEMY OF SCIENCE Vol. XXVII, 1920 
When the desired temperature was registered a stimulus was given, 
the record for that temperature labeled, and the drum turned a 
short space for the next stimulation. 
A range of temperature from +10°C. down through 0°C. to 
— 7°C. and then up through 0°C, to rigor caloris was used. It 
was found, however, that in order to reach the turning point 
below 0°C. it was necessary to change the temperature rapidly 
to prevent the muscle from being killed or to produce a period 
of no irritability. A cooling mixture of ice and salt was used as 
the means to produce the desired temperatures below 0°C. and 
when the turning point had been reached a bunsen burner was 
applied to increase the temperature. Records were taken at in- 
tervals of five degrees during the descent to 0°C. ; below 0°C. 
they were obtained at each degree and on recovery the interval 
was usually taken each two degrees until rigor caloris was reached 
when the muscle became non-irritable. 
There were no two muscles that responded alike throughout as 
would be expected but some, were more or less similar or at 
certain points paralleled one another closely. As a whole the rec- 
ords of the muscles fell into one of the two classes ; they showed 
either two maxima or three maxima points. For convenience 
the range of temperature was arbitrarily divided into four per- 
iods. The first period covered from -|-10°C. to — 7°C. ; the 
second one extended from — 7°C. to -|-20°C. ; the third period 
ranged from 22° C. to 42° C. and finally the rigor period from 
44° C. to 50° C., where the majority of muscles went into rigor 
caloris, with complete loss of irritability.* The first maxima 
were found to fall into the first period, in the second came the 
second maxima, the third maxima appeared in the third period 
and the maxima of heat rigor in the fourth period. When only 
two maxima occurred they appeared in the first and third periods 
with the usual heat rigor maximum. 
In the three-maxima class, when different individual records 
were studied, there seems to be two different points for the 
second maxima, one in the range from — 5°C. to — 2°C. and 
the other falling somewhere between -j-8°C. and -|-16°C. This 
might be accounted for in the latter case in some measure by 
exposure to the cold, since this might render the muscle non-ir- 
ritable and a lag in response on recovery might result. 
The first maxima of this group appeared between 10° C. and 
* In the following discussion the rigor maximum was not included as a maximum, 
for other influences enter in and thus it would not compare favorably with those 
which were stimulated by electricity. Rigor caloris is discussed in a later paragraph. 
