456 



METABOLISM, NUTRITION, AND DIET 



absorbed substances from the food, together with products secreted into the 

 canal by the liver, pancreas, and mucous membrane. The secretion lost 

 daily by the kidney, aside from a large quantity of water, consists of nitrog- 

 enous waste products, chiefly urea, and inorganic solids, as were mentioned 

 in the chapter on Excretion. 



The relations between the amounts of the chief elements contained in these 

 various excreta in twenty-four hours may be thus summarized: 



From the water in this table should be subtracted the 296 grams of water 

 which are produced by the union of hydrogen and oxygen in the body during 

 the process of oxidation, and there should be added to the respective columns 

 the corresponding amounts of the constituent elements, i.e., 33 grams of 

 hydrogen and 262 grams of oxygen. There are 26 grams of salts eliminated 

 through the urine, and 6 by the feces; a total of 32 grams. 



The quantity of carbon daily lost from the body amounts to about 281 . 2 

 grams and of nitrogen 18.8 grams, and if a man could be fed by these ele- 

 ments, as such, the problem would be a very simple one; a corresponding 

 weight of charcoal and, allowing for the oxygen in it, of atmospheric air 

 would be all that is necessary. But an animal can live upon these elements 

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

 of such food stuffs as we have already enumerated, page 322 et seq.; more- 

 over, the relative proportion of carbon to nitrogen in either of these com- 

 pounds alone is by no means the proportion required in the diet of man. 

 Thus, in protein, the proportion of carbon to nitrogen is only as 3.5 to i. 

 If, therefore, a man took into his body, as food, sufficient protein to supply 

 him with the needed amount of carbon, he would receive more than four times 

 as much nitrogen as is needed; 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 an amount of nitrogen in proportion to the carbon he needs, substances 

 in which the nitrogen exists in relatively much smaller quantities than the 

 carbon. 



