CHEMICAL ANALYSES. 65 



pancreas ; wheat-starch requires a much longer time, and 

 potato-starch is still more obstinate " (Church}. 



Crude fat is the term applied to all fatty, waxy and resinous 

 substances which exist in plants, and which can be dissolved 

 by ether. Although the fatty and oily compounds in the food 

 are readily absorbed, the waxy and resinous matters appear to 

 be indigestible. As the respective proportions of these con- 

 stituents vary considerably in different kinds of plants, the 

 feeding value of crude fat is no more fixed than is that of 

 nitrogenous matter or of carbo-hydrates. 



The name "fibre " is given to the fibrous and woody 

 material which is contained in plants, and which consists of 

 varying proportions of cellulose (C 6 H, O 5 ) and lignin 

 C 18 H 20 O 8 ). Cellulose forms the cell walls and first skeleton 

 of a plant. Lignin, which is also known as vasculose, " is the 

 chief constituent of the vessels which bind the wood-cells and 

 fibres together " (Bloxam}. Lignin is harder, denser and more 

 indigestible than cellulose. The fibre of hay and of the straw 

 of cereals (oats, wheat and barley for instance) has a smaller 

 percentage of lignin than that of the straw (stalks) of clover, 

 peas and vetches, and is consequently of higher feeding value. 

 Pure, or nearly pure, cellulose, as we find it in the membrane 

 which forms the walls of the cells of grain, is soft and tender. 



The most important mineral matters in plants, from a 

 feeding point of view, are common salt, the phosphates of 

 lime and magnesia, potassium chloride, and salts of iron. The 

 mineral matter of animals is much richer in salts of soda 

 (chiefly as common salt) than is that of vegetables. The 

 vegetable acids in forage consist chiefly of tartaric acid and 

 citric acid, which, with potash and soda, form soluble car- 

 bonates, and thus serve to keep the blood, tissues and certain 

 secretions alkaline. The following tables give the respective 

 percentages of the constituents of the mineral matter (ash) of 

 various foods. 



