214 THE HEAT OF THE BODY 



ditions as these, therefore, the advocates of wool as the 

 most adequate protection against both heat and cold, are 

 fully justified. 



Leather and furs. The skins of animals, although 

 a most satisfactory protection against wind and cold, 

 lack the power of absorbing moisture and of permitting 

 its evaporation without chill. Instead, they tend to keep 

 the perspiration upon the surface of the body with the 

 result that the clothing worn beneath them becomes wet. 

 Much of this bad effect can be avoided, however, if they 

 are worn loosely enough to permit beneath them the 

 ventilation which will allow for the evaporation of the 

 moisture. 



Thin or thick clothing. The method of wearing 

 clothing is quite as important as the materials used. 

 Its object is to economize the body's heat and yet per- 

 mit the perspiration to evaporate freely. To accom- 

 plish this in the most wholesome way, several layers 

 of thinner clothing are preferable to an equal amount 

 in one thick layer. This is especially true if, as is 

 customary, the clothing is worn somewhat loose so that 

 a certain amount of air is enclosed between each layer. 

 The enclosed air warmed by the body not only permits 

 the evaporation of moisture from the body's surface, 

 but also serves in itself to retain the heat. For the 

 same reason, porous underclothing is far superior to 

 that which is tightly woven, since it allows a sufficient 

 change of the enclosed air to permit the evaporation of 

 moisture. 



Bed clothing. Clothing for sleep is in some measure 

 even more important than that for daytime use, since 

 it cannot be as readily adjusted to sudden changes of 

 temperature. The bed clothing for cold weather should 

 consist, in addition to sheets, of wool blankets of mod- 



