HOW IS THE HUMAN MACHINE PROTECTED? 365 



Study this diagram carefully. What 



important story does it tell about the 



loss of heat from your body ? 



warmth is removed rapidly from one part of the body. 

 Curiously enough, although we feel warm when we per- 

 spire, much of the heat of 

 the body is taken away by 

 evaporation of the water 

 from the body surface. On 

 a hot muggy day, when the 

 atmosphere is moist, little 

 heat is lost by evaporation 

 and we feel much hotter 

 than on an equally hot, dry 

 day when we perspire freely. 

 On a humid day a blanket 

 of stagnant heated air forms 

 about the body, which 

 makes one feel very uncom- 

 fortable. For this reason electric fans have saved people 

 from much discomfort by keeping the air in motion, thus 

 evaporating the moisture and removing heat from the 

 body. 



Underclothes and Their Uses. In winter we need under- 

 clothes which are nonconductors of heat, and retain the 

 warmth of the body. In summer we need underclothes 

 that do not hold moisture, for wet, clammy underclothes 

 cool us by conduction if it is cold, or if it is warm, make 

 us uncomfortably hot by preventing evaporation, and 



sometimes even cause a 

 cold to develop. It does 

 not seem to make very 

 much difference what 

 kind of materials are 

 used, whether woolen, 

 cotton, linen, or silk 



Which weave of underclothes will be better fibeF ' SO lon g RS the Un ' 



for summer? why? derclothes are porous. 



^ teb isi 



wi|M s 



