128 FOOD. 



DAILY CONSUMPTION IN THE FOOD. 



O H O N S 



Albuminous matter, 130 grammes, containing 70 10 29 20 1 

 Starch . . 300 " 134 18 144 



Fat . . . 100 " " 76 12 12 



280 40 185 



Of these elementary bodies, carbon and nitrogen are considered 

 especially important as constituents of the food, carbon as forming 

 the most abundant and characteristic ingredient of all organic combi- 

 nations, and nitrogen, as the distinguishing element of albuminous 

 substances. Of these two, accordingly, the system requires daily, to 

 be supported in an active condition, about 20 grammes of nitrogen and 

 about 280 grammes of carbon. This fact alone makes it evident that a 

 mixed diet of animal and vegetable food is the most available for man. 

 Meat contains, according to the analyses of Pay en, 3 per cent, of nitrogen 

 and 11 per cent, of carbon. Consequently, if the diet were composed 

 exclusively of this food, the necessary quantity of nitrogen would be 

 supplied by 666 grammes of meat ; but in order to obtain the required 

 carbon, 2545 grammes would need to be consumed, thus involving a 

 great waste of its nitrogenous matter. On the other hand, bread, the 

 most nutritious of all vegetable substances, contains only 1 per cent, of 

 nitrogen and 30 per cent, of carbon. Therefore, if this were the only 

 food used, 933 grammes would be sufficient to supply all the carbon ; 

 but, in order to obtain the due amount of nitrogen, it would be neces- 

 sary to consume 2000 grammes. A mixture, accordingly, of the two 

 kinds of food, in which nitrogenous and hydrocarbonaceous matters 

 respectively preponderate, is best adapted to supply the wants of the 

 system without unnecessary expenditure of material. 



The changes undergone in the body, and the final destination of the 

 ingredients of the food, vary for different kinds. The carbohydrates no 

 doubt, after serving the purposes for which they are intended in the 

 animal economy, are finally expelled under the form of carbonic acid 

 and water. The action of the oxygen, introduced with the inspired air, 

 produces this result by uniting with the carbon of the organic body, 

 while its own hydrogen and oxygen, already present in the relative 

 quantities to produce water, are liberated under that form. This result 

 is expressed by the following formula : 



Starch. Carbonic acid. Water. 



C 6 H 10 5 + 12 = C 6 12 + H 10 5 . 



Thus the change undergone by starch and allied substances in the 

 animal body, where they are consumed, is precisely the reverse of that 

 taking place in plants during the act of vegetation, by which they are 

 produced. 



For the fats the change is a similar one, their only final products, so 

 far as we know, being carbonic acid and water. In this process, how- 

 ever, the fats require, as already mentioned, a greater supply of extra- 



