490 



THE AMERICAN NATURALIST [Vol. XL VIII 



with the minimum nightly temperature of 48°, 49°, 56° 

 and 53° F., respectively, a much warmer series of nights, 

 it remained inactive, And again, after November 1, dur- 

 ing a warm spell in which the minimum nightly tempera- 

 ture for November 7 was 64° F., the mouse did not appear. 



A study of this chart suggests the question as to how 

 much the temperature has to do with this habit of hiber- 

 nation. 



It is a somewhat general belief that temperature regu- 

 lates the degree of torpidity. 



Barton 1 maintains that 

 the torpid state of animals is altogether an accidental circumstance and 

 by no means constitutes a specific character. The same species becomes 

 torpid in one country and not in another. Nay, different individuals 

 of the same species become torpid or continue awake in the same neigh- 

 borhood or even on the same farm. 



Seton 8 believes that 



while torpor is more or less controlled by temperature, the habit of tor- 

 pidity, like the changing pelage of the white-hare, is so deeply ingrained 

 constitutionally that there is a strong tendency to torpify at a given 

 time without regard to the original cause. 



It is evident from this chart that torpidity develops 

 gradually, at first for only one night at a time. Whether 

 this process is explained by a cerebral anemia, a slow 

 toxemia of the brain centers or some other of the theories 

 regarding sleep, it seems to require about two months in 

 which to become sufficiently developed to control com- 

 pletely voluntary body functions. During that interval 

 the animal occasionally awakens, probably from hunger 

 and habit as much as from any effect in change of tem- 

 perature. 



After torpidity is thoroughly established, 

 temperature may be important external factors, 

 been demonstrated on numerous occasions in pr 

 temporary activity by the application of heat, 

 to say, however, that the temperature is not the 

 ment which influences the length of the period of 

 tion. 



"om hunger 

 age of tem- 



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