78 REGULATION OF BODILY TEMPERATURE. 



Partly, for example, by the air we breathe oat, which is 

 nearly always hotter than the air we breathe in: and so 

 carries heat away from the body. But the skin does 

 more than any other organ in regulating the bodily 

 temperature. 



The skin gets rid of the heat in two ways. In the first 

 place, its glands produce perspiration, and the evapora- 

 tion of this perspiration, as we have already learned, 

 carries off heat (p. 67). We thus see why it is useful that 

 we perspire more freely on a hot day, or when we are ex- 

 ercising and our muscles producing a great deal of heat. 



In the second place, except on the very hottest sum- 

 mer days, the air around us is cooler than the inside of 

 our bodies. Blood which has been made hot as it 

 flowed through the internal organs, is sent to the skin 

 and there, giving heat to the air, is cooled. It is then 

 carried back from the skin to the inside, picks up more 

 heat, flows again to the surface and gets rid of it; and 

 so on, all the time. 



14. How the Body is kept from getting too Cold. The 

 fat which lies beneath the skin may be compared to the 

 packing in the sides of a refrigerator. It checks the pas- 

 sage of external heat or cold to the inside. Accordingly, 

 thin persons cannot bear exposure to cold as well as 

 those who are fat. Too great loss of heat is also pre- 

 vented by the diminished activity of the sweat-glands in 

 cold weather, and by the fact that most of the blood is 

 then kept away from the skin, which accordingly becomes 

 pale. An exception to this is found when there has been 



14. How does fat aid in keeping us from too great cooling ? How 

 do the sweat-glands behave in cold weather? Why does the skin 

 usually become pale in a cold room ? When may the skin be red 

 and perspiring even in cold weather ? 



