CIIAP. v.] NUTRITION. 463 



generated, to the tissues or organs where heat is being lost by 

 radiation, conduction or evaporation, tends to equalize the tempera- 

 ture of the various parts ; and thus maintains a "constant bodily 

 temperature." 



When the production of heat is not great as compared with the 

 loss there is no great accumulation of heat within the body, the 

 temperature of which consequently is but slightly raised above 

 that of surrounding objects. Thus the temperature of the frog, for 

 instance, is rarely more than '04 to '05 C. above that of the atmo- 

 sphere, though in the breeding season the difference may amount 

 to 1. Such animals, and they comprise all classes except birds 

 and mammals, are spoken of as cold-blooded. Exceptions among 

 them are not uncommon. Some fish, such as the tunny, are warmer 

 than the water in which they live, and in a species of Python (P. 

 bii'ittatus) a difference of as much as 12 C. has been observed. 

 Hliber found that in a beehive the temperature rose at times as 

 much as to 40 C. In the so-called warm-blooded animals, birds 

 and mammals, the loss and production of heat are so balanced 

 that the temperature of the body remains constant at, in round 

 numbers, 35 or 40 C., whatever be the temperature of the air. 

 The temperature of man is about 37'6 C. ; in some birds it is as 

 high as 44 C. (Hirundo) and in the wolf it is said to be as low as 

 35-24 C. 



This temperature is with slight variations maintained through- 

 out life. After death the generation of heat rapidly diminishes, 

 and the body speedily becomes cold; but for some short time 

 immediately following upon systemic death, a rise of temperature 

 may be observed, due to the fact that, while the metabolism of the 

 tissues is still going on, the loss of heat is somewhat checked by 

 the cessation of the circulation. The onset of pronounced rigor 

 mortis causes a marked accession of heat, and when occurring after 

 certain diseases may give rise to a very considerable elevation of 

 temperature. 



This mean bodily temperature of warm-blooded animals is, 

 during health, maintained, with slight variations of which we shall 

 presently speak, within a very narrow margin, a rise or indeed a 

 fall of much more than a degree above or below the limit given 

 above being indicative of some failure in the organism, or of some 

 unusual influence being at work. It is evident, therefore, that the 

 mechanisms which co-ordinate the loss with the production of heat 

 must be exceedingly sensitive. It is obvious, moreover, that these 

 mechanisms may act when the bodily temperature is tending to 

 rise, by either checking the production or by augmenting the loss 

 of heat ; and when the bodily temperature is tending to fall, by 

 either increasing the production or by diminishing the loss of heat. 

 As the regulation of temperature by variations in the loss of heat 

 is better known than regulation by variations in production, it will 

 be best to consider this first. 



