110 WONDERS OF ORGANIC LIFE. 



temperature conduces to hybernation, which as 

 in the case of ordinary sleep comes on gradually, 

 with diminished activity, and a diminished 

 sense of hunger. When a hybernating animal 

 feels the drowsiness which ushers in its winter 

 sleep, and is under the influential agency of a 

 certain degree of cold, it is urged by instinct to 

 make preparations of self-defence against an 

 excess of severity, the effects of which would 

 be fatal. It therefore retires to its hyberna- 

 culum, or winter dormitory, closes itself in, 

 falls into a tranquil sleep, which in due time 

 passes away, and is succeeded by a renewal of 

 activity. 



The intensity or profoundness of this sleep 

 varies in different animals ; in all, the pulsa- 

 tions of the heart become feeble and slow, the 

 respiration is also very slow, and frequently 

 intermits for a considerable interval, or even 

 becomes altogether imperceptible. The tem- 

 perature of the body sinks greatly, and in some 

 instances is but little elevated above that of the 

 surrounding medium, perhaps only by two or 

 three degrees. In very profound hybernation, 

 the body feels cold and stiff, the senses are in 

 a state of oblivion, and nervous sensibility is 

 greatly reduced, insomuch that severe wounds, 

 and even electric shocks, are insufficient to 

 awaken the lethargic sleeper to consciousness. 

 During this sleep, a diminished weight of the 

 body takes place, to be restored by food after 

 reviviscence. 



Confining ourselves for the present to quad- 



