[CAMERON] HISTORY OF THE FROG 21 



arise. Undoubtedly large numbers do survive such winters as are 

 experienced in central Canada below water at the outlets of springs. 

 Others are probably immersed in slews and river water. 



I have shown that R. pipiens can survive complete immersion in 

 fresh running water for a period of 150 to 200 days, and the survivors 

 show no ill effects, and relatively little loss of weight. It seems a 

 normal refîex for a frog, exposed to cold air, to dive beneath water, 

 and in the immersion experiments they take up such a quiescent 

 condition as must be considered to be actual hibernation. 



Under experimental conditions, especially when a large number of 

 frogs are confined together below water in a relatively small vessel, 

 certain of these may become oedematous, and buoyant, nitrogen gas 

 being retained within the body of the frog, and death following from 

 the oedema and gas distension. Such nitrogen gas appears to be 

 normally got rid of in part through the lungs by the expiration from 

 time to time of small bubbles of gas. My experimental methods did 

 not entirely exclude the possibility of some carbon dioxide being also 

 present in small amount, though it could only amount to a very small 

 percentage of the retained gas. It is probable that this water- 

 absorption and gas-retention does not take place to a great extent 

 under natural conditions. The cause of it has not been ascertained. 

 The harder the water the more likely is it to occur, and it may perhaps 

 be induced by an increase in calcium or magnesium ions. It takes 

 place at low temperatures. 



I have made some observations which appear to show that frogs 

 wholly or partially submerged in water which is allowed to rise in 

 temperature above 16°C., or wholly submerged in water in which there 

 is an oxygen deficiency, suffer some change leading to an upset of 

 osmotic regulation, with a resulting oedematous condition. 



References 



The three papers, by Cameron and Brownlee, contain a fairly 

 complete list of references on the subjects dealt with. 

 Cameron, A. T., and Brownlee, T. I., Trans. Roy. Soc. Canada, 1913, 



vii, sec. IV, 107; 1915, ix, sec. IV, 51; 67. [And Quart. J. Exp. 



Physiol., 1913, vii, 115; 1915, ix, 231; 247] 

 Cameron, A. T., ibid., 1914, viii, sec. I\^ 261. [And Quart. J. Exp. 



Physiol., 1915, viii, 341] 

 Brooks, Eleanor S., Amer. J. Physiol., 1918, xlvi, 493. 

 Knauthe, Zool. Anz., 1891, xiv, 109. 

 Willey, A., Trans. Roy. Soc. Canada, 1918, xii, sec. IV, 100. 



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