206 DIGESTION. 



containing a large relative proportion of this element, and no 

 nitrogen. 



To take another example ; the proportion of carbon to ni- 

 trogen in bread about 30 to 1. If a man's diet were confined 

 to bread, he would eat, therefore, in order to obtain the requi- 

 site quantity of nitrogen, twice as much carbon as is neces- 

 sary ; and it is evident, that, in this instance, a certain quan- 

 tity 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, ........ 4500 grains. 



Nitrogen 1350 



Excess of Nitrogen above the amount required, 1500 " 



Bread contains about 30 per cent, of carbon and 1 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, 9000 grains. 



Nitrogen, 300 " 



Excess of Carbon above the amount required, 4500 a 



But a combination of bread and meat would supply much 

 more economically what was necessary. Thus : 



Carbon. Nitrogen. 

 15,000 grains of bread (or rather more than 



2 Ib). contain ...... 4500 grs. 150 grs. 



5,000 grains of meat (or about fib.) contain . 500 " 150 " 



5000 " 300 



So that f Ib. of meat, and less than 2 Ibs. of bread would 

 supply all the needful carbon and nitrogen with but little 

 waste. 



From these facts it will be plain that a mixed diet is the 

 best and most economical food for man ; and the result of ex- 

 perience entirely coincides with what might have been antici- 

 pated on theoretical grounds only. 



It must not be forgotten, however, that the value of certain 

 foods may depend quite as much on their digestibility, as on 



