26 The Feeding of Animals 



CLASSES OF MATTER 



Before passing to a consideration in detail of the 

 proximate constituents of plants and animals, it is de- 

 sirable to reach a clear understanding of certain broad 

 divisions into which we classify all matter, either living 

 or dead, which has been organized by the vital forces 

 of the various forms of life. 



One of the most common and familiar phenomena 

 of the physical world is the destruction of vegetable or 

 animal matter by combustion, with the result that only 

 a small portion of the original material is left behind 

 in visible and solid forms. Fuel, such as wood or coal, 

 is largely consumed when ignited, and we have as a 

 residue the ashes. If we incinerate hay, corn or wheat 

 we get the same result. The gradual decomposition of 

 exposed dead vegetable matter that occurs in warm 

 weather is a process essentially similar to the com- 

 bustion of fuel, only more prolonged. In view of 

 these facts, it is customary to classify all the tissues of 

 plants and animals into the combustible and incombus- 

 tible portions, the former being that part of the ignited 

 or decayed substance which disappears in the air as 

 gases, and the latter the residue or ash. It should be 

 well understood that combustion does not involve a loss 

 of matter; only a change into other forms. If we were 

 to collect the gases which pass off from a stick of wood 

 that is burned, consisting mostly of carbon dioxid, 

 vapor of water, ammonia and, perhaps, certain other 

 compounds of nitrogen, we would find that their total 

 weight, plus that of the ash residue, is even greater 



