136 Physiology. 



Heat and Exercise. When we exercise we produce more 

 heat ; we sweat more ; more heat is taken from the body 

 to evaporate this sweat. If we are not exercising and are 

 in cooler air, we sweat less, and less heat is given off. 

 When we exercise there is more blood in the skin, and 

 more heat is given off by radiation, convection, and con- 

 duction. When we exercise less, the skin, especially in 

 cool air, is paler, i.e. has less blood in it, and heat is econo- 

 mized. Thus the temperature of the body is kept uniform. 



Distribution of Heat in the Body. If more heat is pro- 

 duced in one part of the body than in others, the circula- 

 tion of the blood tends to equalize the temperatures of the 

 different parts. So, too, if one part is cooled, i.e. is losing 

 heat faster than others, the blood brings heat from other 

 organs to that part. If the hands and feet are exposed to 

 cold, it may do little good to have the rest of the body well 

 covered. A pair of wristers and a pair of leggings may 

 often add more to one's comfort than a heavy overcoat. 



Regulation of Temperature by Clothing. In cold weather 

 we put on more clothing and select non-conductors of 

 heat, as woolen, leather, and fur. Many authorities recom- 

 mend light woolen for summer wear, since with it we do 

 not cool off so rapidly. 



Regulation of Temperature by Food. In cold weather 

 we eat more. We also eat more fat and other heat- 

 producing foods. 



Effect of Wet Clothing. In getting the clothing wet the 

 cooling effect is not so much from the temperature of the 

 water as from the loss of heat in evaporating the water 

 from the clothing ; and this goes on for a long time. Of 

 course it is desirable to put on dry clothing as soon as 



