162 THE HUMAN BODY. 



98 J F. If it rises higher, he is sick, and has a fever. 

 Nor will it fall more than a degree or two below 98J F. 

 In the stomach and in the blood, the thermometer would 

 mark about 100 F., never rising much above, or falling 

 much below. 100 F. is, then, the natural temperature 

 of the inside of man's body. If he live under the tropi- 

 cal sun, it will not rise more than a degree or two above 

 this if he is well; and, if he live in Greenland, it will 

 not fall more than a degree or two below. 



13, If we undertake to keep a room at a fixed tempera- 

 ture, we must have a fire to warm it ; and we must have 

 means of cooling it if it is too warm. The human body 

 has its fire, and it has its cooling-apparatus; and this 

 heating and cooling apparatus is self -regulating, and 

 works so perfectly, that, throughout a long life, in heat 

 and in cold, the inward temperature never varies more 

 than two or three degrees in health. 



HOW THE HEAT IS MADE EQUAL, IN ALL, PARTS. 



14, The fire is not in any one part, but in all parts. In 

 every particle, the changes which take place, as the parti- 

 cle takes up oxygen from the blood, and gives out car- 

 bonic acid, make heat, as the changes which take place in 

 the coal or wood in the stove make heat. This heat is 

 given to the blood. It is warmer when it comes from 

 the capillaries, where it has been in close contact with the 

 particles ; and the blood, now divided in a thousand little 

 streams, and again united in one stream, at the heart, 

 diffuses the heat through the body. 



15, Suppose the feet, for example, to be more exposed 

 to cold than other parts. The blood in the feet might be, 

 for a very short time, colder than the rest of the body ; 



