158 REGULATION OF BODILY HEAT. 



In considering the regulation of the body's temperature, 

 we must bear in mind that the body is surrounded by air 

 almost always considerably cooler than itself. The body is, 

 therefore, almost always giving off heat. Our clothes do not 

 warm us: we warm them, and they keep us from warming 

 the air too fast ; i.e., keep us from losing too much heat. In- 

 door air in winter in the cooler parts of the United States is 

 kept at about 70 F. by artificial heat. This air does not 

 warm us. We being about 30 F. warmer, are warming it. 



The skin gives off heat by : 



1. Radiation : heat is given off in every direction. 



2. Conduction : whatever we touch that is cooler than our 

 bodies is warmed. We warm chairs, beds, clothing, etc. 



3. The air in contact with the skin is warmed and rises. 

 Our body's heat is thus carried off by Convection. 



4. The sweat leaving the body is warm ; i.e., it takes away 

 heat with it. 



5. But the Evaporation of the sweat is a much more im- 

 portant factor in heat-regulation. Any liquid, in evaporating? 

 absorbs heat. The cooling effect of alcohol or ether on the 

 skin is due to the fact that heat is taken from the body in 

 converting the liquid into a gas. 



Let the teacher, with a medicine-dropper, place a drop of 

 ether or cologne on the back of the hand of each pupil. 



When we put cologne (or alcohol or ether) on the hand or 

 face, we notice two facts : (1) It produces a cooling effect. 

 (2) The liquid soon disappears. To prove that it is not 

 merely that the liquid is cool, try the following : Tie a piece 

 of cheesecloth around the bulb of a thermometer; dip the 

 bulb into a dish of alcohol or ether, and note its temperatiire 

 (if these are not at hand, gasoline serves very well, or even 

 water, though the evaporation is slower) ; then lift the bulb 

 out of the liquid, and note any change in temperature. The 



