374 HUMAN PHYSIOLOGY 



fever it must make adjustments to dissipate the extra 

 Calories which it is generating. 



Two factors are recognized which are operative both in 

 the adaptation to warm surroundings and to muscular 

 activity. These are the dilation of the cutaneous vessels 

 and the secretion of sweat. But we must note a differ- 

 ence between the skin which is flushed by contact with 

 warm air and that which glows with exercise. In the 

 former the blood is not moving at an unusual rate 

 through the dilated vessels; in the latter the velocity is 

 presumably increased somewhat with the general quick- 

 ening of the circulation. 



Two other factors are discovered during muscular 

 activity which are not clearly present during simple 

 exposure to warm air. One of these is deep breathing. 

 It is only certain species of animals which pant when they 

 are warmed from without* but all animals breathe deeply 

 when they are producing uncommon quantities of heat 

 internally. The primary service of the increased ventila- 

 tion of the lungs is to provide more oxygen and remove 

 more carbon dioxid but the discharge of heat is promoted 

 at the same time. 



Another means of shaking off heat during exercise is 

 found in the constant shifting of contact between the 

 skin and the air. The effect is that of a breeze. It is 

 plain that a man who is riding a bicycle, running, or 

 walking enjoys this favoring condition. The same is 

 true in a measure of the man who is standing in one spot 

 and swinging his arms; he profits by the fanning of his 

 skin. The air which lies against it at one moment and 

 has become warm and moist is replaced a moment later 

 by cooler and drier air. An important detail is the 

 pumping of air from within the clothing and the sub- 

 stitution of fresh portions. When one is resting, the air 

 in contact with the skin and under the clothing is warm 

 and nearly saturated. Someone has said that "with the 

 exception of head and hands we live in a tropical climate.'* 



Fever. The body temperature will rise above the 



