[CAMEROX] HISTORY OF THE FROG 15 



but with a strong heart-beat. It was left in contact with cold water and recovered 

 in 12 minutes. Three other frogs, only a quarter grown, treated in the same way, 

 were quite unconscious with no sign of heart-beat at the end of 15 minutes. They 

 were left in contact with cold water. Two showed hearts feebly beating 30 minutes 

 later, and recovered completely in less than one hour. The third had not recovered 

 in three hours. 



R. esculenta (near St. Ouen, Picardy). May 11th, 1916. Small frogs, 10 to 15 grams. 

 Two frogs were held in my hand for 15 minutes, a thermometer in the hand 

 registering 36.4 C. In each case the heart was beating feebly when the frog was 

 removed, but the animal was unconscious, and did not recover. A third, held in the 

 hand of an R.A.M.C. sergeant, at a temperature of 36.3 C, gave precisely similar 

 results. 



These experiments, though not very accurate, perhaps illustrate 

 the variations in resistance to temperature of different species of 

 frogs; but the difference in results is probably largely due to the 

 difference in size of the animals, and therefore the difference in time 

 of adaptation to the temperature of the hand. 



It was also found that R. esculenta would survive a temperature 

 of 30°C. for one hour (thermometer through gullet in stomach), but 

 would not survive 34°, while tadpoles (presumably esculenta) would 

 survive for one hour at 31-32°, but even 15 minutes at 34°C. was 

 fatal. 



Immersion Experiments. 



The following experiments were carried out in Winnipeg in the 

 winter of 1919-20, advantage being taken of the fact that the Winnipeg 

 water supply had been changed in the interval to a very soft water 

 (lake source), containing (September) only 120 parts of solid per 

 million, as compared with 1,158 in the previous experiments. A rough 

 determination showed that one litre of this water contained 3.2 c.c. 

 of oxygen and 7.8 c.c. of nitrogen. During the winter the hardness 

 slightly increased (separation of ice in the lake supply), calcium and 

 magnesium salts showing a definite increase. 



Experiment i. — Commenced October 17th, 1919. Three male frogs (each 67 

 grams) and three females (each 90 grams) were submerged in running tap-water so 

 that they were retained permanently below the water surface. On the 18th the 

 water flow stopped for some time. One frog became slightly buoyant, but the 

 buoyancy had disappeared on the 19th. On the 26th the water temperature rose 

 to 16°, and two frogs were distinctly swollen. The temperature fell to 10°, and the 

 frogs became normal. The frogs remained quiescent for long periods as if hibernat- 

 ing. On November 7th and 14th, through cessation of water-flow (pressure changes), 

 one female frog breathed air for a short period. The results of the experiment are 

 summarized in the following table: 



