THE MAINTENANCE OF THE BODY TEMPERATURE 199 



very likely had a metabolism of 100 Calories, and he has in 

 the same time discharged by radiation, conduction, and 

 evaporation a similar amount of heat. His blood is some 

 30 degrees warmer than the air around him. Let him now 

 take his place in a room where the thermometer stands at 

 84 F. Suppose him to remain for an hour in this disagree- 

 ably warm apartment. His temperature will be found to 

 rise but little, perhaps not at all. Yet the change has re- 

 duced the difference between his own temperature and that 

 of his surroundings from about 30 degrees to about 15. 

 The tendency of his environment to withdraw heat from 

 his body must have been halved. What, then, has 

 happened? Has his metabolism fallen to 50 Calories or has 

 there been a readjustment to facilitate the removal of the 

 full 100 Calories? The latter is found to be the case. 



The withdrawal of heat from the body is favored by two 

 reflex changes. One of these consists in an increase in the 

 amount of blood flowing through the skin and thus exposed 

 to the cooling influence of the outside air. The other is 

 seen in the breaking out of perspiration. The evaporation 

 of the water thus brought to the surface cools the skin and 

 the blood beneath it. The blood then mingles with that 

 which has been passing through the deeper tissues and the 

 rising temperature is checked. It is well to insist just here 

 that the appearance of the skin gives little indication of the 

 rate at which the sweat is being secreted. So long as evap- 

 oration keeps up with the arrival of the water at the pores 

 there will be no visible moisture. We notice the perspira- 

 tion most when it is failing to accomplish its object, that is, 

 when it accumulates instead of being vaporized. The 

 evaporation of water from the respiratory passages is, of 

 course, one means of removing heat, but with human 

 beings this is not a quantity which increases with external 

 warming. It does enter into the adaptive reaction in the 

 case of animals which pant. 



Let us now transfer our subject to the unusual tempera- 

 ture of 105 F. The radiation and conduction effects will 

 now be reversed; the blood will tend to be warmed rather 



