26 DIGESTION AND FOOD. 



certain essential elements, such as those constituting the 

 animal fabric. In studying the chemistry of animals, or their 

 food, we may adopt a complex qualitative or quantitative 

 analysis, and discover the ultimate elements composing them; 

 or we may, by a natural process of separation, obtain certain 

 compound substances, found in combination in any plant or 

 animal, and recognised as proximate principles. Thus, milk 

 may by analysis be found to contain hydrogen, nitrogen, 

 oxygen, carbon, sulphur, and other ultimate elements ; but, if 

 we simply allow milk to get sour, we shall prove it contains 

 a principle capable of curdling, called casein, in addition to 

 water, fat, and salts. Thus, blood is readily found by 

 spontaneous coagulation, or the application of heat, to contain 

 fibrin and albumen, which are both proximate principles. 

 The nature of these proximate principles must be investigated, 

 in order to study digestion, and in order to deduce the 

 general principles involved in the art of feeding our domestic 

 animals. 



In referring to the Chemistry of Food we must consider 

 the chemical composition of animals, and I gladly seize this 

 opportunity of entering somewhat fully into this important 

 subject. The proximate principles above referred to have 

 been classified under three heads : 

 I. Inorganic Constituents. 

 II. Hydro-carbonaceous, or Non-Nitrogenous. 

 III. Nitrogenous principles. 



I. The first inorganic constituent meriting special notice 

 is WATER. This universally diffused compound enters largely 

 into the composition of an animal or plant, and is there 

 destined not only to preserve a physical condition essential to 

 the preservation and manifestation of the phenomena of life, 

 but is chemically important. It is true that it holds in simple 

 solution many of the salts essential to the system, and when 



