194 TEXT-BOOK OF PHYSIOLOGY 



hydrochloric acid, carbonic acid was given off, showing the presence of 

 carbonates. It contained proteins and mucins. 



Physiologic Action of the Intestinal Juice. The part played 

 by the intestinal juice in the digestive process is yet a subject of discussion, 

 as the results obtained by different observers are in some respects con- 

 tradictory, due to the fact that different animals, as well as human beings, 

 have been the subjects of experimentation. By reason of its contained 

 enzymes the intestinal juice acts : 



1. On Proteases and Peptones. Even though the proteins have been reduced 



by the action of the gastric and pancreatic juices to the stage of proteoses 

 and peptones they are not yet in a condition to be absorbed. The 

 further stage in their digestion appears to be their reduction, as stated 

 in a foregoing paragraph, to amino-acids or their immediate anteced- 

 ents. This change has been attributed to the action of the intestinal 

 juice or a contained enzyme to which the name erepsin was given by its 

 discoverer Cohnheim. 



2. On Compound Sugars. Saccharose, maltose and lactose, the three 



compound sugars, are believed by most observers to be not only non- 

 absorbable, but also non-assimilable and therefore are required to 

 undergo some digestive change before they can be absorbed and assimi- 

 lated. An extract of the intestinal mucous membrane or the intestinal 

 juice of the dog added to a solution of saccharose will cause it to com- 

 bine chemically with water after which a cleavage into dextrose and 

 levulose will take place, which together constitute invert sugar. The 

 enzyme to which this action is attributed has been termed invertase or 

 saccharase. Maltose undergoes a similar change. After its combina- 

 tion with water it undergoes a cleavage into two molecules of dextrose. 

 Lactose appears to be unaffected by the pure juice. As it is non-assimi- 

 lable it has been supposed to undergo conversion into dextrose and 

 galactose while passing through the epithelial cells of the intestinal mu- 

 cosa. In either case the transformation is brought about by two fer- 

 ments known respectively as maltase and lactase. 



3. On Trypsinogen. This zymogen when first discharged from the pan- 



creatic duct is inactive and incapable of effecting the necessary digestive 

 changes in the proteins. Shortly after its entrance into the intestine, it 

 becomes quite active and efficient, a change attributed to an agent 

 entero-kinase secreted by the mucosa in the upper part of the intestine. 



THE BILE 



The Bile. The bile is a product of the secretor activity of the liver 

 cells. As it is poured into the intestine in man and most mammals at a 

 point corresponding to the orifice of the pancreatic duct, and most abund- 

 antly at the time the food is passing through the duodenum, it is usually 

 regarded as a digestive fluid possessing an influence favorable if not nec- 

 essary to the completion of the general digestive process. It has not been 

 demonstrated, however, that it has any specific action on any of the 

 different food materials. 



Anatomic Relations of the Biliary Passages. After its forma- 

 tion by the liver cells the bile is conveyed from the liver by the bile capillaries, 

 which unite finally to form the main hepatic duct. This duct emerges 



