262 DIGESTION. 



of his food, which contains so large a relative amount 

 of nitrogen in proportion to the carbon he needs, sub- 

 stances in which the nitrogen exists in much smaller 

 quantities. 



Eood 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, removes to a great extent, in a diet of animal 

 food, the difficulty which would otherwise arise from a 

 deficiency of carbon fat containing a large relative pro- 

 portion of this element, and no nitrogen. 



To take another example ; the proportion of carbon to 

 nitrogen in bread is about 30 to i. If a man's diet were 

 confined to bread, he would eat, therefore, in order to 

 obtain the requisite quantity of nitrogen, twice as much 

 carbon as is necessary ; and it is evident that, in this 

 instance, a certain quantity of a substance with a large 

 relative amount of nitrogen is the kind of food necessary 

 for redressing the balance. 



To place the preceding facts in a tabular form, and 

 taking meat as an example instead of pure albumen : . 

 meat contains about 10 per cent, of carbon, and rather 

 more than 3 per cent, of nitrogen. Supposing a man 

 to take meat for the supply of the needful carbon, he 

 would require 45,000 grains, or nearly 6\ Ibs, containing: 



Carbon . . " .-.''/ '-.''. . 4,500 grains 



Nitrogen . 1,350 



Excess of Nitrogen above the amount required . 1,050 



Bread contains about 30 per cent, of carbon and i per 

 cent, of nitrogen. 



If bread alone, therefore, were taken as food, a man 

 would require in order to obtain the requisite nitrogen, 

 30,000 grains, containing 



Carbon . . . . . . . 9,000 grains 



Nitrogen 300 



Excess of Carbon above the amount required . 4,500 



