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HANDBOOK OF PHYSIOLOGY. 



Of the excreta the carbon dioxide and ammonia, which are made up 

 of the elements carbon, oxygen, nitrogen, hydrogen, are given off 

 from the lungs. By the urine many elements are eliminated from the 

 blood, especially nitrogen, hydrogen, and oxygen. In the sweat, the 

 elements chiefly represented are carbon, hydrogen, and oxygen, and 

 these are also those of which the faeces are made. By all the excretions 

 large quantities of water are got rid of daily, but chiefly by the urine. 



The relations between the amounts of the chief elements contained 

 in these various excreta in twenty-four hours maybe thus summarized: 



From this should be subtracted the 29 G grms. water, which are pro- 

 duced by the union of hydrogen and oxygen in the body during the 

 process of oxidation (i. e. , 33 hydrogen and 262 oxygen). There are 20 

 grms. of salts got rid of by the urine, and G by the fasces; total, 

 32 grms. 



The quantity of carbon daily lost from the body amounts to about 

 281.2 grms. (nearly 4,500 grains), and of nitrogen 18.8 grms. (nearly 

 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 an animal can live only upon these elements 

 when they are arranged in a particular manner with others, in the form 

 of such food-stuffs as we have already enumerated, p. 326 et seq, ; more- 

 over, 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. Thus, in proteid, the proportion of carbon to nitrogen 

 is only as 3.5 to 1. If, therefore, a man took into his body, as food, 

 sufficient proteid 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 relatively to the 

 carbon. 



