84 THE ROYAL SOCIETY OF CANADA 



although it seems almost certain that such heat-coagulation and 

 heat-rigor would be produced at markedly lower temperatures than 

 those hitherto recorded (about 40°C.) if there were long exposure 

 to such temperatures; some of our experiments showed rigor after 

 exposure to 36°C. Meigs has suggested that the heat shortening 

 of striped muscle tissues is dependent, not on the aggregation of the 

 particles of coagulable protein, but on some other process, not im- 

 probably the formation of a large quantity of lactic acid.^ This 

 suggestion may have some application to our results. 



Our results do not accord with any statements previously pub- 

 lished (that we have been able to find) on the upper limits of temper- 

 ature compatible with life in the frog. 



We must repeat that the results in this paper apply to R. pipiens, 

 late winter and spring specimens, (and to R. clamitans) and may not 

 apply to other species nor at other times to these two species. 



We desire to thank Professor Swale Vincent for the interest he 

 has taken in this work. 



* Meigs, "Concerning the supposed connection between protein coagulation and 

 the heat shortening of animal tissues, "Amer. J. Physiol., 1909, xxiv, p. 13, and p. 184. 



