THE ANIMAL BODY DIGESTION METABOLISM 29 



acid stomach or the alkaline small intestine. They do act, however, on the 

 cellulose and the pentosans, and in some cases on soluble carbohydrates, 

 in the first three stomachs of ruminants and in the caecum of the horse. 

 In the large intestine there develops a profuse bacterial growth of various 

 forms which thrive in the absence of air. The presence of more or 

 less undigested food, together with moisture, warmth, and the faint 

 alkaline reaction furnish ideal conditions for bacterial growth. Some 

 cellulose is decomposed by the bacteria, with the liberation of carbon 

 dioxid, marsh gas, and hydrogen. Sulfureted hydrogen is also produced 

 thru putrefaction of protein substances. Some nitrogen is found, but 

 this has its source in the air taken in with the food. Much of the gas 

 is doubtless absorbed into the circulation and eliminated from the lungs. 

 Products other than gas, which are mostly toxic or poisonous to the 

 animal, result in small quantity from bacterial growth in the large intes- 

 tine. To these substances the odor of the feces is largely due. If the 

 bowels do not function properly, the contents may remain for an undue 

 length of time, in which case excessive putrefaction may cause the animal 

 to suffer from poisoning, due to the absorption of the poisonous sub- 

 stances. 



52. Feces. As the intestinal contents pass thru the latter part of the 

 large intestine, some of the water is absorbed and a more or less solid 

 residue accumulates in the rectum. This is voided as the feces. With 

 farm animals these are chiefly undigested food that has never really 

 been within the body proper. This undigested food is mostly cellulose, 

 or crude fiber, which has escaped bacterial action. Also a portion of 

 the other nutrients usually escapes digestion. This may be due to in- 

 sufficient chewing of such food as seeds, or because some nutrients are 

 protected from the digestive juices thru being enclosed in resistant cell 

 walls of cellulose. In addition to undigested food the feces also contain 

 residues from the bile and other digestive fluids, waste mineral matter, 

 worn-out cells from the intestinal lining, mucus, and bacteria. They may 

 also contain such foreign matter as dirt consumed along with the food. 



53. Amid digestion. Those nitrogenous compounds of plants which 

 are classified as "amids" are, as before stated, simpler nitroge- 

 nous compounds than the proteins. They are either on their way to be 

 built into proteins, or result from a partial breaking down or cleav- 

 age of proteins, such as occurs in the plant for the purposes of trans- 

 portation. 



In many instances the amids are similar in character to some of the 

 intermediate products of digestion in the animal body. Their digestion 

 is therefore doubtless similar to that of the proteins. 



54. Mineral matter. Tho the digestion of the mineral matter of foods 

 has not been extensively investigated, it is known that the mineral mat- 

 ter is dissolved to a greater or less extent by the hydrochloric acid of 

 the gastric juice, and is absorbed principally from the small intestine. 

 Sulfur and phosphorus, which occur in feeds largely as a part of pro- 



