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 
