HIBERNATION AND ALLIED STATES IN ANIMALS 105 



peculiarities, which renders the case, to my mind, all 

 the more instructive when considered in connection 

 with all those states I am now considering. 



II. 



1 propose now to discuss the real nature of hiber- 

 nation and kindred states. 



In the paper on Squirrels read before the Society in 

 1887, I said, speaking of hibernation : " I think it is 

 very probable that, when the matter has been fully 

 investigated, all degrees of cessation of functional 

 activity will be found represented, from the daily 

 normal sleep of man and other animals to the lowest 

 degree of activity consistent with the actual mainten- 

 ance of life." 



As a matter of fact this is the conclusion toward 

 which all my investigations since that time have 

 tended. Though some maintain that in true hiber- 

 nation there is cessation of respiration, it would be 

 hard to prove this, for, as Hall showed, the circulation 

 continues, and the very beating of the heart against the 

 lungs displaces a certain amount of air, and in any 

 event we cannot leave out of account diffusion of gases, 

 which, in all cases of animals with lungs, plays an 

 essential part in the process of respiration. 



It would be interesting to know the condition of the 

 heart in a hibernating frog or turtle ; but in such 

 creatures the skin, as also probably in snakes, has a 

 respiratory function. Live frogs will stay for hours at 

 the bottom of a tank in winter, provided fresh water 

 is flowing over them constantly. In fact, winter frogs 

 kept under these conditions respire largely by the skin. 

 So far as the bat is concerned, it is difficult to observe 

 any respiratory movements ; but in the Woodchuck I 



