524 APPLIED BIOLOGY 



Certainly at such times the warmer skin must radiate more 

 heat to the air, just as a hot-water pipe does when the tem- 

 perature of the circulating water increases. 



The importance of the evaporation of sweat as a method 

 of cooling depends upon the temperature and humidity of the 

 air, which determine the amount of water the air can absorb. 

 Dry cold air can take up little watery vapor, while dry warm 

 air may contain much more water than the cold air. Hence 

 in hot weather loss of heat by the evaporation of sweat be- 

 comes more important. Obviously, hot dry winds would favor 

 evaporation; while hot moisture-laden air prevents rapid 

 heat loss both by radiation and by evaporation. This is the 

 usual condition on oppressively hot days when heat pros- 

 trations and sunstrokes are common. The moist hot air 

 prevents proper loss of heat from the skin, and the internal 

 temperature rises too far above 99 F., which is best for 

 human protoplasm. Obviously, reduced heat production 

 will help avoid excessive internal heat ; and this means keep- 

 ing as quiet as possible and eating sparingly, thus reducing 

 the activity of muscles and the digestive organs. (Why do 

 people in tropical climates with hot sun and moisture-laden 

 winds suffer from the heat more than do the inhabitants of 

 equally hot but dry regions ?) 



Fever is due to increased production of heat (caused by 

 toxins of disease), and is usually accompanied with dry skin 

 and inactive sweat-glands; but occasionally even great 

 perspiration does not discharge the heat fast enough. The 

 so-called " wasting " indicated by loss of weight during pro- 

 longed fever is due to the rapid oxidation of tissues when 

 little or no food is available. Drugs act upon fevers by re- 

 ducing oxidation in tissues or by promoting perspiration and 

 consequent heat loss from the skin. 



The effect of cold baths upon heat regulation by the skin 

 is discussed in 458. 



