[Cameron] LOW TEMPERATURES ON THE FROG 263 



the lowest temperature reached as the determining factor, one may 

 conclude that exposure to — 1-4°C. for one hour is fatal (experiments 

 6, 7, 9, 11, 15), while exposure to — 1-1°C. for a similar period is not 

 fatal (experiments 2, 5, 14). The death temperature for this species 

 can therefore be taken as— 1 -25°+0- 15°C. Prolonged exposure 

 at slightly higher temperatures may prove fatal. I have been unable 

 to test this point specifically. One may perhaps infer from the uni- 

 formity of the results obtained that this is not the case. There appears 

 to be no variation with time of year, since these measurements were 

 made at periods corresponding to the onset of winter (October-Nov- 

 ember), depth of winter (January-February), and spring (March- 

 April, for Illinois frogs). Age also appears to have no effect since 

 similar results were obtained with full-grown Illinois and Minnesota 

 frogs, weighing 30 grams or more, and half-grown Manitoban frogs, 

 weighing from 10 to 15 grams. 



An objection which might possibly be put forward to these results 

 is that the actual cause of death is not the minimum temperature to 

 which the animals are subjected, but either the initial rate of cooling 

 or the subsequent rate of warming to room temperature. In ex- 

 periments carried out under usual conditions I have always found 

 that recovery, when it takes place, takes place within between one 

 and three hours after the thaw is complete. It takes a little longer, 

 the lower the temperature attained, but the "recovery-point" is 

 fairly sharp. I have carried out two experiments which show the 

 effect of rapid heating. I subjected two Minnesota frogs (R. pipiens) 

 to a temperature of from —0-7° to 0-8°C for two hours. One, al- 

 lowed to warm up gradually, recovered perfectly in two and one-half 

 hours. The other was taken directly from the cooling apparatus at 

 its minimal temperature, and placed in warm water at a temperature 

 of +27°C, and so heated in 8 minutes to a temperature of +15°C. 

 It was then removed and placed in water at room temperature. It 

 recovered in part, but very slowly. After 24 hours all its reflexes 

 were present except that of lung-breathing. It was peculiarly hyper- 

 sensitive Tapping it gently threw it into convulsions. It remained 

 in this pathological condition for five days, when it died, without 

 having resumed lung-breathing at any period. A second less extreme 

 experiment was carried out accidentally. The small frog employed 

 in experiment 14 was allowed to warm up too rapidly in a warm room. 

 It developed the same hypersensitive condition, but to a less degree, 

 and did not breathe for more than seven hours, although it had com- 

 pletely recovered in 20 hours. 



These experiments show conclusively that rapid heating produces 

 an entirely different set of phenomena to those observed in the normal 



