THE DIGESTIVE APPARATUS AND NUTRITION 235 



secreted in a day to kill three men ; but it is neutralized 

 in the intestines, in the liver, in the tissues, and in the 

 blood. Upon the food with which it mixes in the small 

 intestine bile seems to have little effect, and its function 

 there is supposed to be mainly to assist the pancreatic 

 juice in neutralizing the acid in the chyme, and in its 

 further action. Secretion of the bile goes on continu- 

 ally, but it passes into the intestine only when digestion 

 is proceeding. At other times it is carried by a side 

 branch of the bile duct to the gall bladder and there 

 stored. About two pints of bile is secreted daily. 



337. The Intestinal Juice is a secretion of the mucous 

 membrane of the small intestine itself, and contains a 

 ferment which changes cane and malt sugars into glucose, 

 besides having possibly further action upon the food. 



338. Bacterial Action. There have been found to exist 

 in the alimentary canal certain microorganisms which 

 modify the digestive processes. Bacteria are especially 

 numerous in the intestines. The antiseptic gastric juice 

 destroys bacteria, or neutralizes their action in the stomach; 

 but some escape into the intestines, where they multiply. 

 Their presence is shown to be, under normal conditions, 

 beneficial, though certain forms of bacteria produce disease. 



339. The Peristaltic Movements of the Intestines. By suc- 

 cessive contractions and relaxations of the muscular fibers 

 in the two muscular layers of the intestinal wall, a wave- 

 like motion passes along the whole length of the organ and 

 forces the contents, from the constricted to the relaxed 

 portion, slowly on into the large intestine, bringing the 

 different substances in contact with the absorbing cells in 

 the mucous membrane. 



340. Function of the Large Intestine. Most of the food 

 which can be used in the body is absorbed in the stomach 



