138 FIRST PRINCIPLES OF AGRICULTURE. 



Water. This is an important constituent. It is 

 essential to the proper distribution of the nourishing fluids 

 throughout the system, and usually constitutes more than 

 one-half of the total weight of the live animal. As is 

 the case with plants, it is contained in the greatest 

 amounts in the young or immature, and decreases as 

 growth proceeds, and maturity is reached. It is possi- 

 ble to remove it from animal substances without entirely 

 destroying their form, thus differing from the constitu- 

 ents that constitute the dry matter; these cannot be 

 removed without destroying the character of the sub- 

 stances themselves. Here, too, is a striking analogy 

 between plant and animal. 



Dry Matter. This may also be divided into two 

 general classes, first, that which is organic or volatile, 

 or that portion capable of being destroyed, or converted 

 into gaseous substances, by means of heat; and second, 

 ash or inorganic, mineral, or non-volatile, or that por- 

 tion which cannot be destroyed or dispelled by means 

 of heat. 



Organic Substances. These are usually divided 

 into two general classes, first, non-nitrogenous, or those 

 free from nitrogen, consisting of carbon, hydrogen, and 

 oxygen only ; and second, nitrogenous, those containing 

 nitrogen in addition to the carbon, hydrogen, and oxygen. 



Non-Nitrogenous Substances. The chief of these is 

 fat, a substance extremely rich in the element carbon, 

 and a very important constituent of food. It is found 

 distributed throughout the various organs of the animal 

 body, though mainly enclosed in cells on the kidneys 

 and between the muscular fibres. The fat contained in 



