Section V, 1921 [13] Tr.\ns. R.S.C. 



Further Experiments on Conditions Influencing the Life History of the 



Frog 



By A. T. Cameron, F.R.S.C. 



(Read May Meeting, 1921) 



The following are the chief results outlined in a series of papers 

 by Cameron and Brownlee (Trans., 1913 to 1915): 



1. Frogs {R. pipiens) freeze at a temperature of — 0.44°±0.02°C., 

 in a manner very similar to that of solutions isotonic with their body 

 fluids. The minimum body temperature which they will survive for 

 one hour is — 1.25°±0.15 C.° The cause of death is probably a 

 specific temperature effect on the co-ordinating centres of the central 

 nervous system. Those controlling lung respiration may be specially 

 concerned. Exsected hearts will survive a temperature of —2.5° for 

 one hour, but are killed by a temperature of —3.0° for one hour. 

 Similarly, Brunow has shown that muscle tissue survives —2.9° but 

 is killed by —3.0° (R. fusca) and Garten and Sulze have shown that 

 nerve survives even lower temperatures (R. esculenta). 



It is not improbable that longer exposures to low temperatures 

 would prove fatal to R. pipiens at temperatures higher than —1.25°. 

 There is no climatic adaptation, nor any periodic adaptation due to 

 hibernation. Frogs surviving degrees of cold such as those occurring 

 during a Manitoban winter (usual minimum about — 40°C.) do so 

 below the surface, near the margins of, or submerged in the water of 

 springs, and are themselves never subjected to temperatures below 

 the freezing point of water. 



There seems to be a slight variation in the death temperature 

 from cold of different species of frogs {R. pipiens, clamitans, spheno- 

 cephala) amounting to some tenths of a degree Centigrade. 



2. The highest temperature at which R. pipiens can maintain 

 life continuously under such conditions that its own body temperature 

 cannot be lowered by evaporation of water, is about 18°C., while 

 continued subjection to a slightly higher temperature under these 

 conditions will prove fatal in a few days. The time of exposure 

 required to produce a fatal result decreases steadily with rise of 

 temperature, a few minutes at 40° proving fatal. (All the tempera- 

 tures refer to the actual body temperature of the frog.) The effect 

 appears to be specifically one of temperature. Recovery, when un- 



