6^ THE CANADIAN NATURALIST. 



general those species which survive the winter in the imago 

 state become torpid ; and this negative sort of existence is 

 found in other animals to be a preventive of the ordinary 

 effects of great cold on vitality. 



C. — How is it that animals can remain in a state of 

 torpidity without food, when a few days' fast, in ordinary 

 circumstances, would be fatal ? 



F. — In a state of health, I believe (without knowing 

 much of physiology) the sensible and insensible evacuations 

 continue whether food be supplied or not. But if the supply 

 of nutriment be cut off, the secretions and evacuations going 

 on, with nothing to make up the deficiency, life ceases from 

 absolute exhaustion. In some diseases, in which the secret- 

 ing organs are disordered, though scarce any food be taken, yet 

 hunger is not felt. It is probable that in total torpidity, as 

 in the case of the cold-blooded animals, reptiles and insects, 

 secretion ceases altogether ; while it would seem that in the 

 case of such mammalia as hybemate, as the bear, marmot, 

 dormouse, &c. secretion goes on, but very languidly. To 

 supply the waste occasioned by this secretion, these animals 

 on going into their retreats are very fat ; but on coming out 

 in the spring, they are invariably poor and lean, proving that 

 this superfluous fat has been absorbed into the system, so 

 that it may be considered as a magazine of nutriment. 



C — Do birds ever become torpid ? 

 . F, — From their superior powers of locomotion, there is 

 not the same necessity in their case, as they can, and most 

 of them do, migrate from one country to another at the ap- 

 proach of winter, yet as some species do remain in the coldest 

 countries, at least as far north as Hudson's Bay, this does 

 not altogether account for the difference. The blood of birds 

 is much warmer than that of any other animals, and their 

 peculiar covering is perhaps the most perfect non-conductor 

 of heat, of all known substances. There have not been 



