66 HOMOIOTHERMISM 



If there is a sudden rise in the external temperature 

 caused by some factor which diminishes the loss of heat, 

 the temperature of the skin will rise, the end organs will 

 be stimulated, and the sensation of warmth is developed. 

 Conversely a fall in temperature stimulates the recep- 

 tors for cold. The afferent impulses in either case stimu- 

 late the heat center to the proper activity resulting in a 

 regulation through heat dissipation or conservation. 

 Since changes in skin temperature would eventually in- 

 fluence the general body temperature if not compensated 

 for, the temperature sense organ undoubtedly serves a 

 useful purpose in temperature regulation. 



Fever. — One of the most striking aspects of many 

 pathological disturbances is a rise in body temperature, 

 a condition known as fever. This increase in heat may 

 be the consequence of a greater production than can be 

 lost through the normal channels, or of a lack of regula- 

 tion of the loss of heat. Most investigators hold that, 

 although there may be a slight increase in the production 

 of heat in fevers, this is too small to account for a rise 

 of several degrees in the body temperature ; in fact, many 

 physiologists now believe that the rise in basal metabo- 

 lism during fever is to be regarded as a result of the 

 rise in temperature, rather than as a cause. 



Fevers are apparently secondary factors in infec- 

 tions. Toxins act to increase the affinity of protoplasmic 

 colloids for water with the result that the blood volume 

 is reduced. This effect is assumed to be localized mainly 

 at the body surface and leads to a cooling of the periph- 

 ery and the sending of afferent impulses to the heat 

 center. Thus the thermolytic mechanism is brought into 

 play, without regard to the actual heat equilibrium. 



The Endocrines and Temperature Regulation. — The 

 endocrines unquestionably have an influence on the tem- 



