THE PROCESS OF DIGESTION 77 



long, compared with 77 feet in the hog. The facts brought 

 out in these figures show that the horse and hog, with their 

 simple stomachs, and smaller relative capacity, should be 

 fed more concentrated, or more easily digested, food than 

 the ox or the sheep. 



The food in the body is used to maintain or support life, 

 to produce growth or energy or to promote certain other 

 features, as milk, fat, or wool. On this account persons who 

 feed live stock should regulate the kind and amount of food, 

 if they desire to secure the most satisfactory results. 



The protein in the food during digestion is acted on by 

 what are called digestive ferments. One of these, pepsin, 

 assisted by a very small amount of hydrochloric acid attacks 

 the protein in the stomach. The action of acid and pepsin 

 changes the protein into two more soluble forms known as 

 proteases and peptones. These with any of the unchanged 

 protein pass into the small intestine, where, by the aid of 

 two other ferments, trypsln and erepsin, all is converted into 

 a still more soluble form called amino acid. This latter 

 passes through the walls of the intestines and into the blood, 

 and thence throughout the body tissues. The animal can 

 not take the protein in the plant and use it at once as body 

 protein, but it must go through these changes in the digestive 

 organs before it can be used. The protein in the food is 

 changed to body protein, of which lean meat is the best 

 example. To some extent it may also be changed into fat. 

 Animals that depend entirely upon flesh for food can live 

 on protein alone, if necessary. During starvation, the body 

 loses a small but rather constant amount of protein. So we 

 regard this substance especially valuable for building up 

 the muscles, the hair, wool, internal organs, blood, and similar 

 tissues that are closely related to the vital processes. 



The carbohydrates in the food are largely changed into 

 sugar during digestion. Thus they are more easily absorbed 

 into the body. There are different kinds of sugars, but that 



