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THE AMERICAN NATURALIST 



ber of ground-squirrels (Citellus t>i<h < < mlnn-atus) to be 



at the onset of hibernation— that the assumption of any 

 theory ascribing the phenomenon of hibernation to a lack 

 of function of all or any one of the ductless glands is not 

 justified. 



From this general summary it will be seen that great 

 diversity of opinion prevails regarding the immediate 

 cause of this extremely interesting condition, and of the 

 sudden transformation from the homoiothermal to the 

 poikilothermal state (and vice versa) so characteristic of 

 hibernating mammals. It is not the author's object, 

 however, to discuss the relative merits of the various 

 theories. Suffice it to say that all of them are based upon 

 insufficient data. To say which of the various conditions 

 associated or occurring simultaneously with winter-sleep 

 are concerned with the production of the lethargy and 

 which are the results of this or some other condition, is 

 extremely difficult. Until certain causal relations are defi- 

 nitely established between the factors concerned, many of 

 these theories are of very little value except as a stimulus 

 to further research. It is thus very evident that we are far 

 from having any adequate explanation of the mechanism 

 of this phenomenon, to say nothing of how it was estab- 

 lished as a more or less variable character in certain 

 animals. 



If hibernation of mammals is only an extreme form of 

 ordinary diurnal sleep of man and other animals, it is 

 especially to be hoped that this subject will continue to be 

 investigated by more modern and adequate means, for no 

 entirely satisfactory theory has yet been advanced to ex- 

 plain the physiological cause of ordinary sleep. Since 

 winter-sleep may also be attended with total abstinence 

 from food and drink for many months, the facts derived 

 from a study of the various conditions associated with 

 this dormant period are of interest also in connection with 

 the subject of inanition in particular and metabolism in 

 general, as is plainly indicated by the frequent reference 



