240 ADVANCED PHYSIOLOGY 



body can evidently be modified either (1) by changing the 

 amount of heat produced, through an increase or decrease in 

 the amount of food oxidized; or (2) by varying the amount oj 

 heat lost. Each of these methods is adopted in part; but under 

 ordinary conditions it is by controlling heat loss that this 

 regulation is chiefly effected. To appreciate this fact it 

 must be understood that the heat resulting from the ordinary 

 oxidation of food is more than enough to warm the body and 

 keep it at 98 F. To maintain the correct body temperature, 

 therefore, it is necessary that some heat be passed off. 



Loss of Heat through the Lungs. When the temperature 

 of the air is considerably lower than that of the body, as is 

 usually the case, one loses superfluous heat in breathing. 

 The inhaled air is cooler than the body, but when exhaled 

 its temperature has been raised. Of course, if the air has 

 thus been warmed the body has been correspondingly cooled. 

 The cooler the air breathed the more heat it will take from 

 the blood. On a cold day so much heat may be lost by this 

 means as to take away nearly all the surplus; but when the 

 air is warmer this loss is not sufficient for the purpose of keep- 

 ing the body temperature uniform. 



Loss of Heat from the Skin. The chief method of regulating 

 body heat is by the expansion and contraction of the blood 

 vessels in the skin. Since the air is almost always cooler 

 than the blood, blood will, of course, be cooled as it flows 

 through the skin; and the more rapidly the warm blood flows 

 through 'the skin, the more rapid will be the loss of heat. 

 But while this swift flow actually cools the body, it seems to 

 make it warmer. This is due to the fact that the skin is 

 very sensitive to temperature, and when an extra amount of 

 warm blood is flowing through it a feeling of extra warmth 

 will be experienced, though the body is actually cooling. 



One often feels this to be true when a sore finger is bandaged 

 and a string tightly tied about it; the end of the finger feels cold 

 because free movement of the blood has been prevented by the 



