FOODS AND THEIR PHYSIOLOGIC AI, VALUE. 311 



capable of replacing these nine pounds of loss. The sub- 

 stances lost from the body are, in the lungs, carbon dioxide 

 and watery vapors; in the kidneys, water and a number of 

 nitrogenous substances and salts; and from the skin, water 

 and salts mainly. The losses of the body in excretions poured 

 into the intestinal canal are certain ingredients of the bile, 

 to be discussed later. Possiby one ought to add in this con- 

 nection occasional losses of the cuticle of the skin or epi- 

 thelium cells from the mouth, which, however, do not 

 figure in a material sense in this calculation. 



2. In Energy. In energy the losses of the body are 

 mainly of two kinds. By far the greater part of the energy 

 is expended in the form of heat. A relatively small pro- 

 portion of it gives rise to muscular motion. It is a matter 

 of interest that in our bodies about one-fifth only of all the 

 energy is utilized in muscular activity ; but four-fifths in the 

 maintenance of the bodily temperature. While this seems 

 but a small per cent., it is much greater than in even the 

 best of engines, the amount of energy in these to be util- 

 ized in actual motion being from one-eighth to one-tenth, 

 while in the ordinary engines possibly not more than one- 

 fifteenth or one-twentieth is utilized. When one remembers 

 that in a locomotive only one bushel of coal out of ten is 

 really expended in pulling the train, and the other nine lost 

 in heating the engine and in friction, one is tempted to 

 believe that the most helpful discoveries of the future may 

 be in enabling us to realize a greater per cent, of the energy 

 in active work. 



The amount of heat lost by an average person in one 

 day is tolerably difficult to determine. Experiments have, 

 however, been made, the result of which show that if all the 

 heat radiated from a working body in one day were collected 

 it would be sufficient to raise the temperature of about 100 

 pounds of water from zero to the boiling point. This, too, 

 seems at first too much when we remember that the tem- 

 perature of the body remains fairly constant, rarely exceed- 

 ing that of 98 degrees Fahrenheit. It must, however, be borne 



