CARBOHYDRATES 19 



The greater part of the waste from the broken-down 

 protein material is passed off through the kidneys in the 

 urine. Small amounts are breathed out through the lungs 

 and some passes off through the skin. 



From the above it is evident that the animal uses pro^ 

 tein for repairing waste and building up new material, 

 and, when the protein is furnished in sufficient amount, to 

 supply heat and energy. The importance of protein in the 

 ration is obvious. No tissue building and consequently 

 no growth can take place unless protein food is furnished in 

 sufficient quantity. 



Carbohydrates. — The carbohydrates make up the 

 greatest bulk of the feeding stuffs. The digestive tracts of 

 farm animals are arranged to accommodate large amounts 

 of these substances. 



The changes in these food materials begin in the mouth. 

 While the food is being chewed, it is mixed with a liquid 

 known as saliva, secreted by glands in the mouth. The 

 function of the saliva is to moisten and soften the food so 

 that it may be easily swallowed; and to change the in- 

 soluble starch into a soluble sugar called maltose. The 

 action of the saliva continues on down the gullet and into 

 the stomach. The maltose is not yet in condition to be 

 absorbed by the system, but must be changed into a simpler 

 carbohydrate form known as glucose. 



The carbohydrate materials pass into the small intestine 

 where they are broken down into simpler forms which may 

 be absorbed from the digestive tract and assimilated by the 

 animal body. 



In the case of animals that live upon foods containing 

 large amounts of crude fiber, or cellulose, special digestive 

 structures are found. As has already been noted, the ox 



