242 ADVANCED PHYSIOLOGY 



nerves in such a way that the brain can increase or decrease 

 the amount of their secretion. When the air becomes so warm 

 that it is difficult for the skin to lose by simple radiation an 

 amount of heat sufficient to keep the body temperature at 

 its proper point, the sweat glands increase their action. In 

 the evaporation of the extra moisture thus poured out on the 

 body surface so much heat is lost that the body temperature 

 is reduced to its proper level. 



After a bath, even though the water used be warm, and the 

 room at more than usual temperature, this same sense of cool- 

 ness is felt. People often say while swimming in a river or the 

 ocean, "The water is warm enough but the air is chilly." 



The extent to which body heat may be reduced through 

 sweat evaporation is really very great. One experimenter 

 found that he could remain for some time in a room in which 

 the air was warmer than 260 F. and in which the direct 

 effect of the air would be, of course, to warm the blood rather 

 than cool it. But evaporation of the profuse perspiration 

 resulting took so much heat from his body that he found it 

 perfectly possible to retain his normal temperature. Stokers 

 on ocean steamers, living and working as they do in a tem- 

 perature of over 130 F., are evidence that this principle 

 admits of constant and daily application. The fact that a 

 fever is accompanied by the lack of perspiration, partially 

 explains the rise in the temperature of the body at such 

 times. 



SUMMARY OF METHODS OF HEAT REGULATION 



As an illustration of heat regulation in the body, imagine 

 a hot summer day with the temperature of the air over 100 F. 

 The air is actually warmer than the body; the sweat glands 

 pour out an abundant secretion which rapidly evaporates. 

 This evaporation cools the skin and reduces the temperature of 

 Ghe body to the desired point. 



