4 FIRST PRINCIPLES. 



entire weight of the body ; the percentage being affected by 

 various conditions, of which age is as a rule the principal. 

 The proportion of water is highest at birth, and lowest in 

 old age. 



Nitrogenous matter is that in which nitrogen is found. It 

 is divided into several classes, the discussion of which comes 

 more within the province of physiology than within that of 

 stable management. One or more of these forms of nitro- 

 genous matter enter into the composition of every tissue 

 (muscles, nerves, and glands for instance) and fluid (blood, 

 saliva, and gastric juice for example) which are actively 

 engaged in vital work, and into that of bones, cartilage, 

 tendons, ligaments, skin, hair, hoofs, etc. The nitrogenous 

 matter of muscle has, according to Hoppe-Seyler, the follow- 

 ing composition : 



Fat, the amount of which varies greatly in different animals, 

 has the following average composition : 



Carbon . . . . 76.5 per cent. 

 Hydrogen .... 12.0 ,, 

 Oxygen . . . . 11.5 



IOO.O 



Mineral matters form about one-twentieth of the entire 

 weight of the body, and are chiefly found in the bones, seven- 

 eighths of the mineral matter of which consists of phosphate 

 of lime, the remainder being carbonate of lime, with traces of 

 magnesia, fluoride of lime, and common salt (sodium chloride). 

 Small quantities of lime exist in the muscles and other soft 

 tissues and in the fluids of the body. The percentage of lime 

 in the body varies directly as the age of the animal. In fact, 



