FOOD. 135 



substance separated by decomposition from the albuminous ingredients 

 of the system ; while carbonic acid represents its remaining carbona- 

 ceous elements in union with oxygen introduced by the breath. 



The quantities of the various substances taken with the food and 

 discharged with the excretions are liable to many variations from the 

 changing condition of the individual. If the body be increasing in 

 weight, the substances introduced will be more than those discharged ; 

 if it be diminishing, the material discharged will be more than that 

 introduced. Even in the healthy adult, where the body does not 

 sensibly gain or lose for long intervals, observation has shown that 

 there are frequent fluctuations of small extent, and that the income for 

 any single day rarely counterbalances exactly the outgo for the same 

 period. Consequently the preceding tables cannot be taken as furnish- 

 ing, in any case, a uniform and invariable standard, but only as showing 

 what, on the whole, are the relative quantities of the ingredients of 

 the food and the bodily frame. Although we are not yet able to 

 determine all the changes which they undergo in the system, there is 

 no doubt of the main result produced by their transformation. On the 

 one hand, we have certain nutritious substances introduced, and, on the 

 other, certain excrementitious products discharged, forming a double 

 series, which may be expressed as follows : 



INTRODUCED WITH THE FOOD. DISCHARGED WITH THE EXCRETIONS. 

 Albuminous matter. Urea. 



Fat. Carbonic acid. 



Carbohydrates. Water. 



This represents the decomposition and metamorphosis of the organic 

 substances proper ; while the mineral ingredients of the food, as a rule, 

 pass through the system unchanged. 



