144 FIRST PRINCIPLES OF AGRICULTURE. 



arated; and when this is done the result is stated as 

 "pure fat." 



Crude Fibre or Cellulose. — Crude fibre or cellulose 

 is determined by boiling the substance with weak acids 

 and alkalies, which dissolve the other constituents con- 

 tained in it. The residue is called " crude fibre/' rather 

 than "cellulose," since it contains all the woody sub- 

 stance of the plant, including "lignin." 



Ash or Mineral Matter. — The ash or mineral mat- 

 ter is determined by carefully burning the substance, by 

 which means the organic vegetable matter is completely 

 removed. 



Nitrogen-free Extract. — The nitrogen-free extract, 

 which includes starch, sugar, and gums, is usually deter- 

 mined by difference; that is, by subtracting the sum of 

 the water, crude protein, crude fat, crude fibre, and crude 

 ash from one hundred. This group, together with the 

 crude fibre, makes the total carbohydrates. 



Statement of Analysis. — An example of the usual 

 method of reporting an analysis of a food is here 

 given : — 



"Water 16.3 per cent. 



Crude Fat (extractive matter) 3.3 



Crude Protein (nitrogenous substances) .... 12.3 



Crude Ash (mineral matter) 6.2 



Crude Fibre (cellulose and lignin) 24.8 



Nitrogen-free Extract (starch, sugars, gums, etc.) 38.1 



Functions of the Animal Body. — The object of 

 feeding is to furnish material for maintaining life, and 

 for building up the animal body; and each of the com- 

 pounds of the food exerts a specific function in the pro- 

 cess, though alone they are incapable of completely 



