124 ELEMENTS OF GENERAL SCIENCE 



or the cooling effect of the evaporation. When the weather is 

 unusually warm or when we are making great exertion the 

 perspiration increases so that the body becomes moist and 

 the cooling effect is very evident. If the perspiration were to 

 stop suddenly, we should quickly feel a rise in the temperature 

 of the body. Indeed, that is what happens in a fever. 



The temperature of the body ordinarily varies but slightly 

 from normal, which is usually 98.6 F. When we. feel hot we 



FIG. 63. Rate of evaporation in the United States 



The map shows the estimated rate of evaporation in inches per annum. Note the 

 great differences between different parts of the country 



are really not much warmer than at other times, as would be 

 proved by a clinical thermometer. The temperature remains 

 constant because the amount of water thrown out for evapora- 

 tion is regulated by the perspiratory glands. But in case of 

 fever the perspiratory glands cease to work, the skin becomes 

 dry and hot, and the temperature of the whole body rises. 

 If the temperature becomes very high (say 4 or 5 F. above 

 normal), it indicates a serious condition, and death may result. 



