No. 598] 



THEORIES OF HIBERNATION 



615 



2.5° C. in the body temperature of a hysterical woman. 

 Others have gone much farther in this regard. Thus 

 Liebeault 51 (1866) andForel 59 (1877), especially the latter, 

 consider hibernation similar in nature to hypnotic sleep. 

 To Mares, however, the initial cause of winter-sleep is the 

 ability of the nervous system to loose its specific sensitive- 

 ness to the external cold. This sensitiveness, he thinks, 

 does not belong to the fundamental properties of the 

 nervous system, since it is not found in the young unde- 

 veloped animal. It is a property acquired slowly onto- 

 genetically just as it was slowly acquired phylogenetically 

 by the two highest classes of animals. A similarity be- 

 tween the hibernating and fetal states was noted long ago 

 byTallas 53 (1778), Prunelle 3C ( 1811), Tiedermann" (1815) 

 and Edwards 22 ( 1824) . Tiedermann claimed that in both 

 states there is merely a vegetative existence, hardly any 

 appreciable difference between the appearance of the 

 venous and arterial blood, much serum and little clot 

 when the blood coagulates, a low body temperature, an 

 enlarged thymus (he included the hibernating gland as 

 part of the thymus) containing a fluid, and a secretion of 

 bile. He therefore considered winter-sleep as a periodic 

 return to a fetal state. Pembrey and Hale White 55 

 (1896) regard the evolution of hibernation, not as the 

 acquisition of a new power, but as a retention of one al- 

 ready present, as is evident from the condition of young 

 mammals and birds in whom the heat- regulating power 

 is inefficient. 



Many observers have questioned the value of cold as a 

 factor in the production of this dormant state. Quincke 38 

 (1882) thought that rest and an appropriate temperature 

 generally, though not always, cause torpor, and yet he 

 said that there seems to be some relationship between 

 degrees of lethargy and external temperature. Blandet 25 

 (1864) considered that winter was only occasionally, if at 

 all, the cause; while Horvath 56 (1872-81), with whom 

 Bunge 57 (1901) seems to agree, said that hibernation is 

 not sleep at all and that winter has nothing to do with it. 



