164 PRINCIPLES OF PHYSIOLOGY 



body and added it to that produced in the 

 body itself, say in twenty-four hours, it would 

 normally be about equal to that given off by 

 the body in the same time. The income and 

 the expenditure would be about equal, and 

 the mean bodily temperature would be fairly 

 constant. If more heat were produced than 

 could be* got rid of, as in fever, the mean 

 temperature would rise, whereas if less heat 

 was produced than was given off the mean 

 temperature would fall. It would appear that 

 vital activities can be carried on efficiently 

 only within a narrow range of temperature. 

 Hence the danger to life, in many diseases, if 

 the temperature rises above 104 or 105. A fall 

 of temperature ten or twelve degrees below 

 normal temperature is not so dangerous. The 

 activity of the skin in producing sweat, and 

 the evaporation of the sweat, is the great 

 regulator. Hence there is danger to life in 

 certain parts of the tropics where there may be 

 an air temperature above 98 F., and where the 

 air, at that temperature, may be saturated 

 with aqueous vapour. Here evaporation from 

 the skin is impossible, heat penetrates from 



