30 



FEEDS AND FEEDING, ABRIDGED 



stomach in small amounts, but nearly all the carbohydrates are carried 

 on into the small intestine. Here the starch which escaped being acted 

 upon in the mouth or stomach is changed into malt sugar by amylase, 

 an enzyme in the pancreatic juice. The compound cane, malt, and 

 milk sugars are then split into simple glucose- 

 like sugars by the action of the invertases, en- 

 zymes in the intestinal juice. These simple, 

 glucose-like sugars, which are the only carbo- 

 hydrates that can be used in the body, are ab- 

 sorbed thru the walls of the small intestine, and, 

 entering the capillaries, pass into the veins and 

 thence to the liver. Here they are for the most 

 part withdrawn from the blood and temporarily 

 stored in this organ as glycogen, a carbohydrate 

 which is closely related to starch and, having 

 the same percentage composition, is sometimes 

 called animal starch. Normally from 1.5 to 4.0 

 per ct. of the weight of the liver consists of 

 glycogen. The glycogen stored in the liver is 

 gradually changed back into glucose, and then 

 given out to the system as required, the amount 

 of glucose in the blood being kept at about 1 part 

 in 1,000. In addition to the liver, all the tissues 

 of the body, especially the muscles, have some 

 power to change glucose into glycogen. 



The cellulose and pentosans in the feed are 

 attacked by bacteria in the first three stomachs 

 of ruminants, in the caecum of horses, and to 

 some extent in the large intestine of other animals. These bacteria 

 break down the cellulose and pentosans into organic acids and also 

 gases (marsh gas, carbon dioxid, and hydrogen), heat being produced 

 in the process. The gases are of no value but the organic acids serve as 

 food the same as sugars. 



Digestion and absorption of protein. — The proteins of the food 

 are first attacked in the stomach by pepsin, which splits them into 

 proteoses and peptones. These are soluble and are simpler in com- 

 position than the proteins, but are still very complex in structure. 

 The proteoses and peptones, together with protein which escapes action 

 by pepsin, pass into the small intestine. There trypsin, an enzyme in 

 the pancreatic juice, not only splits the undigested protein into pro- 

 teoses and peptones, but also digests them further, splitting them into 

 amino acids, which are much simpler than the proteoses and peptones. 

 Erepsin, an enzyme in the intestinal juice, also acts on the proteoses 



Fig. 11. — Villi of 

 the Small In- 

 testine 



A, Lining cells of 

 intestine; b, net work 

 of capillaries; c, lac- 

 teals. For the sake 

 of simplicity the mus- 

 cle fibers in the villi 

 are not shown in this 

 diagram. (After 



Cadi at.) 



