154 CHEMISTRY. 



upon it here. Occasionally the fat which is deposited in 

 various parts of the body is used as fuel, the oxygen in the 

 blood seeking it out, and uniting with its constituents, car- 

 bon and hydrogen. This is done in sickness, when the ac- 

 cumulated fat disappears, and also in the hibernation of 

 many animals, as will be noticed farther on. 



201. Amount of Fuel Consumed. Some calculations have 

 been made in regard to the amount of fuel consumed in 

 keeping up animal heat. This is more easily done in regard 

 to carbon than hydrogen. A full-grown man requires 

 about 100 kilogrammes of charcoal to keep him warm 

 through the year. A horse needs about five times as 

 much 500 kilogrammes. 



202. The Windpipe the Smoke-pipe of the Body. We have 

 told you that in the combustion that is every where going 

 on in the body carbonic anhydride and water are formed, 

 and pass into the blood in the veins. Observe how they 

 are disposed of. They are for the most part carried in the 

 blood to the lungs,* where they are discharged through the 

 windpipe into the air. The water comes out in the form of 

 vapor mingled with the carbonic anhydride, just as the two 

 rise together from the flame of a candle. As these products 

 of combustion are discharged from the body by the wind- 

 pipe, this may be termed the body's smoke-pipe. It acts 

 thus as we breathe out, but when we breathe in it serves to 

 introduce to all the little heat-laboratories of the body oxy- 

 gen, the supporter of their combustion. 



203. Influence of Exercise on Animal Heat. When the 

 body is in a state of activity the heat is increased, or, in 

 other words, the fires within us burn more briskly. This is 



* For a particular description of the manner in which this is done we 

 refer to either Hooker's "Human Physiology" or his "First Book in 

 Physiology. " 



