68 APPLIED PHYSIOLOGY 



temperature brought about by muscular exercise- 

 especially when unsuitably clothed in a hot and damp 

 atmosphere. 



INTEKNAL HEAT-BEGULATING MECHANISM. 



In addition to the mechanism already described for 

 regulating the heat production and loss of the body in 

 accordance with variations in the temperature of its 

 surroundings, there must also be a means of regulation 

 in correspondence with variations in the temperature of 

 the blood which arise from within. The increased heat 

 production induced by hard exercise, for example, must 

 be met by some means of increasing heat loss, and we 

 know that this takes place by sweating. The mechanism 

 involved here is apparently not a reflex one, but is a 

 direct action of the temperature of the blood on the heat- 

 regulating centres. There is reason to believe that this 

 mechanism is less delicate and active than the reflex 

 one, and it is probable that disorders of it play a part in 

 the production of fever. Into the subject of fever, how- 

 ever, we can hardly enter, as it is purely a matter of 

 pathology, although one or two statements about it 

 which can be directly deduced from the teaching of 

 physiology may now be pointed out. 



Fever. In the first place, a permanent rise of tempera- 

 ture in the body cannot be due simply to increased heat 

 production, for, as we have seen, even hard exercise, in 

 which heat production is enormously increased, only 

 raises the temperature but a little, and for a short time. 

 Nor can diminished p4^ction alone be the cause of 



