No. 598] THEORIES OF HIBERNATION 617 



Pembrey 65 (1898), while recognizing that want of food 

 and cold seem to be the most important factors in hiber- 

 nation, says that some other condition yet unknown is 

 necessary to explain such lethargy during the summer. 



As a result of the uncertain action of cold, certain other 

 external conditions have been considered the real excit- 

 ing cause of hibernation. The food factor was empha- 

 sized by Mangili 19 (1807), who believed that neither cold 

 nor vitiated air has anything to do with the production 

 of this torpid state. He thought fasting was necessary 

 because, of several animals under the same external con- 

 ditions, those animals that were fed did not become dor- 

 mant, while the non-fed ones did. Marshall Hall 21 (1832) 

 stated that the lack of food predisposes the animal to 

 torpor by rendering it more susceptible to cold. Sacc 01 

 (1858) concluded that, while he could see no relationship 

 between the atmosphere and torpidity, he could see some 

 connection between the fatness of the animal and the 

 length and profoundness of winter-sleep. He, therefore, 

 concluded that obesity, in connection with fatigue, is the 

 cause of hibernation. Claparede 29 (1905) and Forel 52 

 (1887) think that the amount of fat may be an important 

 factor, while Beretta 66 (1902) opposes this idea. Simp- 

 son 67 (1912) finds that feeding woodchucks greatly inter- 

 feres with winter-sleep, at least in captivity. Albini 68 

 (1901) in case of the marmot, and Reeve 16 (1809) in con- 

 nection with dormice and hedgehogs, also confirm the ob- 

 servation of Mangili on the role of food in preventing 

 hibernation. Yet it appears that these animals (mar- 

 mots) may go into winter sleep while plenty of food is 

 available. Thus Mills 62 (1892) found that during the 

 winter of 1890-91 a marmot hibernated in a cage provided 

 at all times with plenty of food; but during the two fol- 

 lowing winters two other marmots, kept in the same room 

 and in the same cage under similar conditions, did not 

 hibernate at all, though the temperature got low enough 

 to freeze the water in the cage. It is also a common ob- 

 servation that some of these animals naturally retire 



