62 
THE CANADIAN NATURALIST 
general those species which survive the v^inter 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 hybernate, 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 
