338 SOURCES OP ANIMAL HEAT. 



supposed that Bees do not become torpid during the winter ; 

 but this is now known to be a mistake. Bees, like other 

 Insects, pass the winter in a state of hybernation ; but their 

 torpidity is never so profound as to prevent their being aroused 

 by moderate excitement. The temperature of a hive is usually 

 from 5 to 20 above that of the atmosphere ; being kept at or 

 above the freezing-point, when the air is far below it. Under 

 such circumstances, their power of generating heat is most 

 remarkable. In one instance, the temperature of a hive, of 

 which the inmates were aroused by tapping on its outside, 

 was raised to 102; whilst a thermometer in a similar hive 

 that had not been disturbed, was only 48^; and the tempe- 

 rature of the air was 34|. 



412. The evolution of Heat in the Animal body may now 

 be stated with tolerable certainty to depend for the most part 

 on the union, by a process resembling ordinary combustion, 

 of the carbon and hydrogen which it contains, with oxygen 

 taken-in from the air in the process of Eespiration. It has 

 been elsewhere shown that, even in Plants, this union, when 

 it takes place with sufficient rapidity, is accompanied by the 

 disengagement of a considerable amount of heat (VEGET. PHYS., 

 381); and in all those Animals which can maintain an 

 elevated temperature, we find a provision for this union, both 

 in regard to the constant supply of carbon and hydrogen from 

 the body, and to the introduction of oxygen from the air. 

 The supply of carbon and hydrogen may be derived (as already 

 shown, 157), either directly from the food, a large proportion 

 of which is thus consumed in many animals without ever 

 forming part of the tissues of the body ; or it may be the 

 result of the waste of the tissues, especially of the muscular, 

 consequent upon their active employment ( 160), and con- 

 verted into a substance peculiarly adapted for combustion by 

 the agency of the liver ( 366). Or, again, it may be derived 

 from the store laid-up in the system in the form of fat ; which 

 seems destined to afford the requisite supply, when other 

 sources fail. Thus, when food is withheld, or when dis- 

 ease prevents its reception, the fat in the body rapidly 

 diminishes ; being burnt off, as it were, to keep up the 

 temperature of the system. This is the case, too, during 

 hibernation; the animals which undergo this change usually 

 accumulating a considerable amount of fat in the autumn, and 



