Classes of Matter 27 



than that of the dry wood, because the carbon and the 

 hydrogen of the wood have taken to themselves from 

 the air, during the combustion, an increased amount 

 of oxygen. The carbon, oxygen, hydrogen and nitrogen 

 of the plant or animal tissue belong to the combusti- 

 ble portion, although small amounts of two of these 

 elements are found in the ash, as it is usually esti- 

 mated. The remainder of the fifteen elements previ- 

 ously named are supposed to appear wholly in the ash. 

 The relation in quantity of the combustible and in- 

 combustible parts of vegetable and animal dry matter 

 is illustrated below: 



Combustible Incombustible 



(Ash) 

 Per cent Per cent 



Clover hay 92.8 7.2 . 



Potato tubers 95.5 4.5 



Maize kernel 98.3 1.7 



Wheat kernel 98. 2. 



Body of fat ox 91.2 8.8 



The significance of these facts in their relation to 

 cattle feeding is, that the chemical change which we 

 call combustion is one of the phenomena of animal nu- 

 trition. Substances which may suffer either slow or 

 rapid oxidation outside the animal may undergo com- 

 plete or partial combustion in the animal; or, stated in 

 another way, the part of the plant which "burns up" 

 in the fireplace or crucible is the part which in general 

 undergoes the same change within the animal organism 

 in so far as the food is digested. 



The terms combustible and incombustible are less 

 used, perhaps, than two others, which represent prac- 



