ADAPTATIONS TO HIGH ALTITUDES 51 



income and almost no expenditure ! The heart beats 

 slowly and very feebly, breathing has practically 

 stopped, and the kidneys do not function. There is 

 no sleep so near to death as the winter sleep of the 

 Hedgehog. But it is usually a success. 



It may be that the comparative warmth of the sleep- 

 ing-berth, which several inmates sometimes share, and 

 the closeness of the atmosphere help to keep the 

 sleeper sleepy, and that an accumulation of inevitable 

 waste products in the body brings about a sort of 

 drugging; but we have to remember that the winter 

 sleeping is not an individual experiment it is part of 

 the racial constitution and has been slowly wrought 

 out in the course of ages. It has been engrained in 

 the constitution this habit of hibernation; it is an 

 internal rhythm, which normally corresponds to the 

 external periodicity of the seasons, but does not neces- 

 sarily do so. Thus Woodchucks may go to bed while 

 the weather on the Adirondacks is still warm and 

 pleasant, and unusually severe cold may waken a 

 hibernator. Indeed, there is a good deal of truth in 

 the hard saying of an old investigator of the puzzle of 

 hibernation, that winter sleep is not sleep, and that it 

 has nothing to do with winter. It must be noted that 

 we cannot draw any distinction between the summer 

 sleep of the Tenrec of Madagascar and the winter 

 sleep of the European Hedgehog. 



The winter sleepers differ considerably in the sound- 

 ness of their slumbers. The sleeping Hedgehog may 

 be immersed in water for twenty minutes or sub- 

 jected to noxious gases and yet remain asleep, and the 

 Marmot of the Alps is another heavy sleeper. The 

 Dormouse, on the other hand, is a rather light sleeper; 



