(From the Departement of Physiology, Tulane University of La.) 



Heat-Coagulation of Muscles of Northern and Southern 



Frogs. 



By 



Ralph Hopkins 



and 



Gustav Mann. 



As a phase of evolution for the protection of the species against 

 death from heat rigor, it was thought that, in regard to the heat- 

 coagulation of muscles, there might be differences between frogs 

 living in colder regions and those whose normal habitat was in a 

 climate, the summer temperature of which often approximates the 

 thermal limit for the viability of muscles. During the heat, therefore, 

 of early summer in the semi-tropical climate of New Orleans some 

 observations were made on the large Bull Frog (Rana Catesbiana) 

 indigenous to Louisiana, with reference to the temperature necessary 

 foi the production of heat-rigor in different types of muscles. 



In the succeeding autumn and early winter, similar observations 

 were made with the same method on the muscles of a variety of the 

 ordinary laboratory frog, Rana Vernalis, obtained from Indiana. 



The temperature necessary for the coagulation of voluntary 

 muscles was found to be somewhat lower in the southern than in the 

 northern frogs: a result, the opposite to what might have been ex- 

 pected from a priori reasoning. For some of the involuntary muscles 

 of both species comparatively very high temparatures were required 

 to produce heat rigor. The results of experiments on 61 muscles are 

 given the in tables at the end of this paper. 



