28 The Feeding of Animals 



tically the same divisions of plant or animal substance; 

 viz., organic and inorganic. In chemical literature, 

 the portion of a plant or animal which suffers combus- 

 tion is called the organic, and the ash is known as the 

 inorganic part. These terms are evidently based upon 

 the erroneous assumption that the compounds which 

 burn and break up into simpler ones are peculiarly 

 those which sustain necessary and vital relations to life, 

 and are formed through the functions of living organ- 

 isms. To be sure, the dry substance of the plant is 

 organized chiefly by building up compounds of carbon, 

 oxygen, hydrogen and nitrogen, which suffer combus- 

 tion; but compounds of sulfur, phosphorus, chlorine, 

 potassium, sodium and calcium are also constant and 

 essential constituents of the juices and tissues of the 

 plant and animal; and, although the latter elements 

 maj^ finally wholly appear in the incombustible part 

 or ash, they have, nevertheless, sustained in other com- 

 binations important relations to nutrition and growth. 

 It is true, however, that the portion of a food material 

 which is commonly spoken of as organic embraces those 

 compounds that furnish practically all the energy which 

 is utilized by animal life and much the larger part of 

 the building material. 



THE CLASSES OF COMPOUNDS 



The known compounds that belong to life in all its 

 forms ai-e almost innumerable, and doubtless many are 

 yet to be discovered. These sustain a variety of re- 

 lations to human needs, some serving as food, some 



