DAILY LOSS OF CARBON AND NITROGEN. 205 



It has just been remarked that man can live upon animal 

 matters alone, or upon vegetables. The structure of his teeth, 

 however, as well as experience, seems to declare that he is best 

 fitted for a mixed diet ; and the same inference may be readily 

 gathered from other facts and considerations. Thus, the food 

 a man takes into his body daily, represents or ought to repre- 

 sent the quantity and kind of matter necessary for replacing 

 that which is dally cast out by the way of lungs, skin, kidneys, 

 and other organs. To find out, therefore, the quantity and 

 kind of food necessary for a healthy man, it will, evidently, 

 be the best plan to consider in the first place what he loses by 

 excretion. 



For the sake of example, we may now take only two ele- 

 ments, carbon and nitrogen, and if we discover what amount 

 of these is respectively discharged in a given time from the 

 body, we shall be in a position to judge what kind of food 

 will most readily and economically replace their loss. 



The quantity of carbon daily lost from the body amounts 

 to about 4500 grains, and of nitrogen 300 grains ; and if a 

 man could be fed by these elements, as such, the problem 

 would be a very simple one ; a corresponding weight of char- 

 coal, and, allowing for the oxygen in it, of atmospheric air, 

 would be all that is necessary. But, as before remarked, an 

 animal can live only upon these elements when they are ar- 

 ranged in a particular manner with others, in the form of an 

 organic compound, as albumen, starch, and the like ; and the 

 relative proportion of carbon to nitrogen in either of these 

 compounds alone, is by no means the proportion required in 

 the diet of man. The amount, 4500 grains of carbon, repre- 

 sents about fifteen times the quantity of nitrogen required in 

 the same period ; and in albumen, the proportion of carbon to 

 nitrogen is only as 3.5 to 1. If therefore, a man took into 

 his body, as food, sufficient albumen to supply him with the 

 needful amount of carbon, he would receive more than four 

 times as much nitrogen as he wanted ; and if he took only 

 sufficient to supply him with nitrogen, he would be starved for 

 want of carbon. It is plain, therefore, that he should take 

 with the albuminous part of his food, which contains so large 

 a relative amount of nitrogen in proportion to the carbon he 

 needs, substances in which the nitrogen exists in much smaller 

 quantities. 



Food of this kind is provided in such compounds as starch 

 and fat. The latter indeed as it exists for the most part in 

 considerable amount mingled with the flesh of animals, re- 

 moves to a great extent, in a diet of animal food, the difficulty 

 which would otherwise arise from a deficiency of carbon fat 



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