THE HEAT OF THE BODY 117 



elephant and rise to the top of the big tent with no apparent support 

 in a process called conduction. He also can walk a tight wire. 

 You recall how when you hold one end of a metal in the flame, heat 

 comes over and tells you to let go. This method of travel is called 

 radiation. Heat is an austere master; when he gets inside a vessel 

 of water and cracks his whip the molecules of water cower and 

 crowd together making the volume smaller. Heat is a fickle 

 fellow and changes partners often. Believe it or not, he likes ice 

 cream. I was called away from dinner last night when half 

 through my ice cream dessert and when I came back just a pasty 

 liquid was left. Why? Because heat had left the air and gone 

 into the ice cream. They call this a change of state but I call it 

 meddling. There is an instrument called the barometer which is 

 used to tell how hot or cold a body is. I had one under my tongue 

 once. Heat went into it from me and made me feel a lot cooler. 



PROBLEM III. HOW DOES CLOTHING AFFECT 

 THE HEAT OF THE BODY? 



What Keeps the Body Warm? We have already 

 learned that the heat of the body is caused by the oxida- 

 tion of food which we eat. The circulation of the blood 

 assists in keeping all parts of the body at about the same 

 temperature. But we know that on a cold day the out- 

 side of the body gets cold. We use clothes, bedclothes, 

 hot-water bottles, or electric pads to keep warm. Evi- 

 dently clothes should be worn not only for their good 

 looks but for their practical value. In hot climates 

 little clothing is needed, while in very cold parts of the 

 world furs and skins act as insulating materials against 

 the cold. In a temperate climate where changes are 

 frequent clothing ought to be adjusted to fit the tem- 

 perature. 



What Materials Are Used in Clothing? We know that 

 most of our clothing comes from five sources. Outside 

 of leather and rubber, our clothing is made from fibers of 

 wool, cotton, flax, silk, and rayon. Wool and silk are 

 of animal origin ; cotton and linen (from flax) are of 



