264 THE ROYAL- SOCIETY OF CANADA 



experiments, so that it may be concluded that the much slower rate 

 of heating which takes place in the latter does not affect the result, 

 and since the rate of cooling is similarly slow, that this also is not a 

 controlling factor. 



The cause of death in the experiments appears to be due to a speci- 

 fic temperature effect on the higher coordinative centres of the brain 

 and cord. In our previous communication Mr. Brownlee and I gave 

 evidence to show that the various tissues are not killed until a much 

 lower temperature is attained, and it will be observed that in all 

 the experiments with R. pipiens quoted above the separate tissues 

 (heart, striped muscle, peripheral nerve) were not killed.* In ex- 

 periments 12 and 16 I have compared the gross reflexes obtained by 

 stimulating parts of the brain of the dead frog with those obtained 

 in the living frog under chloroform, and could observe no differences. 

 Apparently only the coordinating centres are affected. It may be 

 assumed perhaps that that controlling lung-respiration is an essential 

 factor in the cause of death. 



The few experiments carried out on R. clamitans and R. spheno- 

 cephala appear to indicate that, while the general result holds, the 

 actual death temperature is a few tenths of a degree higher. More 

 accurate methods would be required to establish exactly the extent 

 of this variation. The range of these frogs is distinctly further to 

 the south than that of R. pipiens, and the difference may indicate a 

 slight degree of adaptation in the different species. 



All the observations on which reliance can be placed, on the winter 

 habits of R. pipiens, confirm the experimental results of this paper. 

 Mr. Reed, Laboratory Steward of the Department of Physiology of 

 the University of Minnesota, from whom the Minnesota frogs were 

 obtained, informed me that during the winter the Indians in different 

 parts of Minnesota who supply him with frogs obtain these in large 

 numbers by digging down to unfrozen springs. He himself, searching 

 for frogs in spring, has frequently found creeks (in which in a pre- 

 viously severe winter the water had completely frozen) containing 

 large numbers of dead frogs. 



The Manitoban material was obtained for me by one of our stu- 

 dents, Mr. E. Rutherford, to whom my thanks are due. He obtained 

 the frogs from springs, in the neighbourhood west of Brandon, in the 

 western part of the Province. These springs remain unfrozen and 

 open at the surface throughout the winter, although the external 

 temperature usually reaches — 40°C. at least once, and may remain 

 below —30° for long periods. The frogs were obtained at the end of 



'We have discussed the cause of death of these tissues in the paper referred to 

 (Trans. 1913, Sect, iv., p. 114). 



