METABOLISM, NUTRITION, AND DIET 



407 



The secretion lost daily by the kidney, aside from a large quantity of water, 

 consists of nitrogenous 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 hydro- 

 gen 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 elements, 

 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 297 el seq.; moreover, 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 i. If , therefore, a man 

 took into his body, as food, sufficient proteid 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. 



It is, therefore, evident that the diet must consist of several compounds, 

 not of one alone. 



Many valuable observations have been made with a view of ascertaining 

 the effect upon the metabolism of a variation in the amount and nature of 

 food. These are of great assistance in the consideration of dietetics. 



