810 THE CONSTANT BODILY TEMPERATURE. [BOOK n. 



the tunny, are warmer than the water iu which they live, and in 

 a species of Python (P. bivittatus) a difference of as much as 12 

 has been observed. In a beehive the temperature may rise at 

 times as much as to 40. 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, whatever be the temperature of 

 the air ; hence these have been called homoiothermic, of constant 

 temperature. The temperature of man is about 37"; in some 

 birds it is as high as 44 (Hirundo) and in the wolf it is said to 

 be as low as 35 '24. 



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; conversely when the bodily temperature is tending to 

 fall, they may act by either increasing the production or by 

 diminishing the loss of heat. As the regulation of tempera- 

 ture by variations in the loss of heat is better known than 

 regulation by variations in production, it will be best to consider 

 this first. 



532. Regulation by variations in loss. Heat is lost to the 

 body by the warming of the faeces and of the urine, by the warming 

 of the expired air, by the evaporation of the water of respiration, 

 by conduction and radiation from the skin, and by the evaporation 

 of the water of perspiration. It has been calculated that the 

 relative amounts of the loss by these several channels are as 

 follows : In warming the faeces and urine about 3, or according to 

 others 6 per cent. By respiration about 20, or according to others 

 about 9 only per cent., leaving 77, or alternatively 85, per cent, for 

 conduction and radiation and evaporation by the skin. 



The two chief means of loss then, which are at all susceptible 



