EXCREMENTS. 297 



787. The vegetable substances which constitute 

 the food of animals contain more earthy and saline 

 matters than animals require, and they are ac- 

 cordingly passed from the body as excrementitious. 

 The food of animals in great part goes to supply the 

 waste occasioned by respiration. In this process, 

 carbonic acid is formed by the oxidation of carbon 

 in the body, by the oxygen of the air; hence, in 

 the air expired from the lungs, it is found that 

 the oxygen is more or less combined with carbon, 

 and converted into carbonic acid (107, 606). The 

 heat evolved by the combination of this carbon with 

 oxygen keeps up the warmth of the body. The 

 waste of organic matter in the body thus occasioned, 

 is supplied by food, the organic part of which sup- 

 plies that consumed by respiration; but as the great- 

 er part of the inorganic substances contained in food 

 are not required for this purpose, the excess is void- 

 ed in the solid and fluid excrements. 



788. There are few things of greater value as 

 manures than these offensive and apparently useless 

 substances, which consist of a mixture of organic 

 and inorganic matters ; the former, in consequence 

 of the nitrogen they always contain, ready to de- 

 compose, and furnish carbonic acid and ammonia ; 

 the latter, those very substances which we require to 

 add to the soil, being the very substances which are 

 removed with crops. In consequence of the volatile 

 nature of the products of their decomposition, every 

 means must be employed to prevent their loss. 



