20 THE ROYAL SOCIETY OF CANADA 



hibernation under these conditions, I amplanningto cut it off next winter. 



"We rarely have over 20 individuals to a tank, generally fewer, 

 and sometimes we have a few to liberate in the spring. 



"About 12 per cent, sicken and die, the cause being apparently 

 a marked accumulation of gas under the skin, and a distension of the 

 veins on the under surfaces of the hinder parts of the body and limbs. 

 We rarely have a death before the middle of December, and none after 

 about the middle of March. Owing probably to increasing buoyancy 

 affected individuals rise to and remain at the surface, where they 

 die in a few days. . . . 



"The temperature of the tank water is the result of the tempera- 

 ture of the room and the rate of flow, and seldom drops below 54°F. 

 the first two months, but later may fall to 35°F. . . . Probably 

 death from gas accumulation is rare in nature." 



Summary and Conclus (ons 



The experimental data detailed in this series of papers, considered 

 along with the results of other observers which have been quoted, 

 lead to the following conclusions bearing on the life history of frogs 

 living in temperate and cold climates. 



There appear to be slight variations in the temperature limits in 

 different species, though it is doubtful if the maximal temperatures 

 which such frogs can survive vary by more than a few degrees, and 

 the minimal by more than some tenths of a degree Centigrade. 



R. pipiens cannot survive a permanent body temperature higher 

 than 18°C. and it is evident that such frogs as this species can only 

 survive a summer heat for such a time as evaporation of water from 

 their body fluids will permit the retaining of their own temperature 

 below this limit. A temperature of 30° is fatal in six hours, of 32° in 

 two hours, and such summer shade temperatures are often reached 

 in these latitudes. 



R. pipiens and similar species cannot survive body temperatures 

 of — 1.25°C. for more than one hour, under laboratory conditions. 

 During this period super-cooling ceases, and the body fluids and 

 tissues freeze. It is possible that under natural conditions a very 

 slow cooling may induce super-cooling at so slow a rate that death 

 does not occur. It seems almost certain that once tissue freezing 

 commences and lasts for more than the negligible period of one hour, 

 no recovery can take place. Such slow super-cooling could only take 

 place if the frogs were immersed deeply in earth, slime, or water. 

 There is no evidence that they can burrow in earth, or even do so 

 in thin slime. If they are below water the problem does not usually 



