70 THE ROYAL SOCIETY OF CANADA 



to an asphyxia from lack of oxygen. His experiments indicate also 

 that frogs (species not stated) whose cerebrum has been removed, will 

 withstand a temperature gradually raised in two hours from room 

 temperature to 39°, and then immediately lowered, without fatal 

 results. Becht further points out that heat paralysis of nerve always 

 precedes heat paralysis of muscle (heat rigor) . 



A large number of experiments have been carried out by numerous 

 observers on the effect of heat on frog's muscle, the majority being 

 directed towards determining the temperatures of coagulability of 

 the different proteins present, and the coincidence of one or other of 

 these with the shortening of muscle produced on heating, the loss of 

 irritability, and the onset of heat rigor. 



A full discussion of these results is given by Vrooman,^ whose ex- 

 periments on R. pipiens in this laboratory are confirmatory of those 

 of Vincent and Lewis^ and others using British frogs, and indicate 

 that striped and unstriped frog's muscle, heated gradually from room 

 temperature, undergo two contractions, the first at about 39°, (38° 

 to 40°), the second at about 50° (49° to 51°); the first contraction is 

 due to the coagulation by heat of the protein present in the muscle 

 fibre during life, the second to changes in the connective tissue elements 

 in the muscle. 



Since the muscle does not recover from heat rigor, such experi- 

 ments indicate that exposure of frog's muscle for a very short period 

 at 40° is fatal. No experiments have apparently been performed 

 in which frog's muscle has been kept for definite periods of time at 

 definite high temperatures. 



Alcock^ has shown that frog's nerve is killed by a short exposure 

 to a temperature of 40° to 42°, while Vernon's experiments seem to 

 indicate that the fatal temperature for frogs' hearts is a degree or two 

 higher still. ^ (for R. temporaria and R. esculenta). J. B. Hofmann 

 quotes the fatal temperature for the frogs' heart as 42°.^ 



Our experiments can be divided into three series: 

 i. Experiments on the intact animal, immersed in water, 

 ii. Experiments on the intact animal, in air saturated with water 



vapour and kept at a constant temperature, 

 iii. Experiments on exsected heart, muscle, and nerve. 



R. pipiens has been employed in all cases except where stated 

 specifically ; R. clamitans was used in a few experiments. Late winter 



1 Vrooman, "Heat rigor in vertebrate muscle," Biochem. J., 1907 vol. ii, p. 363. 



2 Vincent and Lewis, "Observations upon the chemistry and heat rigor curves 

 of vertebrate muscle, involuntary and voluntary," J. Physiol., 1901, vol. xxvi, p. 445. 



^ Alcock, Proc. Roy. Soc. London, 1903, vol. Ixxi, p. 275. 



« Vernon, J. Physiol., 1899, vol. xxiv, p. 250. 



6 J. B. Hofmann, in Nagel's Handbuch der Physiologie, 1909, Bd. I, S. 231. 



