Muller's Arcliiv fiir Anatomie, Pliysiologie, S^c. 46^ 



is regulated very much by that of the surrounding air. For in- 

 stance, when a thermometer placed in the saw-dust which formed 

 their nest indicated 36°, the heat of their bodies was 37°. At other 

 times, the heat of the saw- dust and the animals was respectively, 

 38° . . 50° 54° . . 53° 



60 . . 58 63 . . 63 



56 .. 54 58 . . 61 



Thus it appears that the temperature ef the animals is sometimes 

 higher, and at other times lower, than that of the surrounding me- 

 dium. In order, however, to prove this more clearly, the nest was 

 placed in the open air at night, -when the thermometer stood at 23°, 

 and the respective temperature of the animals and the nest was taken 

 down every half hour. The result showed that the body is more 

 slowly susceptible of change than the saw-dusf, but that when the 

 heat of the day is greatest, that of the animal soon surpasses it, and 

 is longer in cooling down again. The heat of different individuals, 

 however, is subject to variation. They are also so constituted, that 

 they remain some degrees above 32° when the external air sinks below 

 that point. In times of extreme cold, unless they are surrounded 

 by a nest of warm materials, death ensues, and the slowness with 

 which their heat is lowered to that of the air is no doubt a provi- 

 sion of nature to provide for their safety in such cases. 



The author's view of the question is, that hybernation does not 

 proceed from too great a degree of cold, nor from want of nutriment, 

 (since animals fall asleep though kept in a warm place and supplied 

 with abundance of proper food,) nor yet from the want of power 

 to retain a due supply of heat whilst the temperature of the air is 

 becoming lower ; but he regards it as a part of the great system of 

 nature, which exhibits a deficiency of vital energy in every branch 

 of the animal and vegetable world at stated periods. This condi- 

 tion shows itself in some animals when instinct leads them to pro- 

 vide receptacles against the approach of winter, either singly or in 

 societies, then in a state of inactivity, and a desire to sleep, and 

 lastly, in a complete suspension of the action of the nerves, the cir- 

 culation, the digestive organs, &c. or, in other words, which he calls 

 the condition of " vita minima." This condition is represented 

 amongst the Mammalia which do not hybernate by the shedding of 

 fur, &c.; amongst birds by moulting, and by migrations ; by conceal- 

 ment and torpidity amongst the Amphibia and the Invertebrata ; and 

 in the vegetable kingdom by the ripening of seeds, the falling of 

 leaves, branches, &c. The same cause will account for the torpidity 

 during summer of the Tanrec of Madagascar, of the crocodile. 



