218 Agricultural Chemistry. 



uents of the food supply the demands for heat and work and 

 the protein can be devoted to the rebuilding or increase of tissue. 



If an adult animal receives the small amount of protein and 

 salts necessary to repair the daily waste of tissue, it would be 

 expected that the whole of the remaining wants might be met by 

 supplying carbohydrates or fats. This is to some extent true; 

 but a ration very poor in protein is not found to be consistent 

 with real bodily vigor. There is some specific action of proteins 

 not as yet understood. They appear to stimulate cell activity, 

 a property not possessed by fats and carbohydrates. 



The ash constituents present in food are the same as those 

 found in the animal body. The animal simply selects from the 

 digested ash constituents those of which it is in need. The tissue, 

 the blood, digestive fluids, and the bony framework contain a 

 variety of these bodies, which are as essential as any of the other 

 substances considered for the building and maintenance of the 

 animal body. Without lime and phosphoric acid there can be 

 no bone formation, and the digestive juices would cease to be 

 active if deprived of chlorine. A cow from which common salt 

 is withheld will, in time, die. Not only must the growing calf 

 have ash material for constructive purposes, but the mature ox 

 must be supplied with them in order to sustain the nutritive 

 processes. The milch cow, which stores combinations of lime, 

 phosphoric acid, potash and other salts in the milk, must have 

 an adequate supply of these materials. Nothing else can take 

 their place. Lime and phosphoric acid, stored in abundance in 

 the framework of the animal, may at times of deficient supply 

 in the food, act as internal sources; but ultimately all ash ele- 

 ments must have been contained in the food. 



Digestion. "We have accepted so far without discussion the 

 self-evident fact that the food is the immediate source of the 

 energy and substance of the animal body. It is now necessary to 

 consider the way in which the nutrition of the animal is accom- 

 plished. Digestion is the important process by which the food 

 of an animal is rendered capable of being absorbed into the sys- 



