EXCREMENTS.

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406. The knowledge of this fact necessarily leads tothe conclusion that all animal matter must be valuableas manure. The flesh and softer parts of animals, aswell as the bones and other solids of the body, are com-posed of the same substances, both inorganic and organic,as plants ; and during their decay yield them up againin a fit state to be absorbed by plants.

407. The vegetable substances which constitute thefood of animals contain more earthy and saline mattersthan animals require, and they are accordingly passedfrom the body as excrementitious. The food of animalsin great part goes to supply the waste, occasioned byrespiration. In this process carbonic acid is formed bythe oxidation of carbon in the body by the oxygen ofthe air ; hence in the air expired from the lungs it isfound that the oxygen is more or less combined withcarbon, and converted into carbonic acid (28,65). Theheat evolved by the combination of this carbon withoxygen keeps up the warmth of the body. The wasteof organic matter in the body thus occasioned, is suppliedby food, the organic part of which supplies that con-sumed by respiration ; but as the inorganic substancescontained in food are not required for this purpose, theexcess is voided in the solid and fluid excrements.

408. There are few things of greater value as manures,than these offensive and apparently useless substances,which consist of a mixture of organic and inorganicmatters; the former, in consequence of the nitrogen theyalways contain, ready to decompose and furnish carbonic