96 APPLIED PHYSIOLOGY 



temperature of 98.5 degrees F. A room at this warmth 

 would seem hot to us. Even 80 degrees F. is too warm. 

 70 degrees F. seems about right. This is only a little more 

 than half way between freezing and the warmth of our 

 body. So heat is always passing off from the skin and 

 warming the air. We get rid of a great deal of heat in 

 this way. 



On a cold day the heat goes off faster than on a warm 

 day. Then we should expect our bodies to be colder. 

 But nature causes the blood tubes of the skin to become 

 smaller so as to keep some of the blood away from the 

 skin. Then no more than the right amount of heat will 

 pass off, and we shall still feel warm. 



On a warm day the heat will pass off from the skin 

 more slowly. Then the blood tubes in the skin become 

 larger, and bring more blood to the surface. Thus more 

 heat can pass off, and the body will be kept at the right 

 warmth. 



178. How the perspiration affects our warmth. A wet 

 skin always feels cold, even if the water is warm when it 

 is put on the skin. This is because the heat passes off in 

 the steam as the water dries. The skin is always moist 

 with sweat or perspiration. We cannot see it, for it passes 

 off as fast as it comes out. But as it dries, it takes away 

 a great deal of heat. 



On cold days only a little perspiration is poured out, for 

 enough heat will pass off without it. On warm days a 

 great deal will often be produced, so that it may not dry 

 so fast as it is formed. Then it collects in drops, and 

 even runs down the face. 



The perspiration enables us to endure great heat. Men 

 have staid in hot ovens for some time without injury, for 

 the perspiration carried the heat away from their bodies. 



