112 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



active, however, during intestinal digestion than at other times. 

 This appears to be reflex, but may be simply a result of the in- 

 creased amount of blood passing through the portal vein to the 

 liver during that period, for the whole alimentary canal is con- 

 gested while digestive activity is in progress. Again, it is known 

 that the best cholagogue is bile itself, and some of the bile is 

 absorbed in its passage down the intestine. Its presence in the 

 blood may account for the accelerated flow. 



Method of Secretion and Discharge. The bile is a product 

 of the liver cells. How they receive their normal stimulus is 

 obscure. But it is reasonable to suppose that a larger supply of 

 blood means a more abundant secretion. Such an increase of 

 blood supply occurs during digestion. 



The cells discharge the bile into the bile capillaries, which 

 pass it onward either to the intestine directly, or, during the 

 intervals of digestion, to the gall bladder. When food enters 

 the duodenum, a reflex influence causes the wall of the gall 

 bladder to contract and compress its contents. The only out- 

 let is through the cystic duct into the common duct, and thence 

 into the duodenum. This reflex does not take place until 

 food has entered the duodenum, and of different foods it is 

 found that proteids (peptones) and fats are the most efficient 

 stimuli. 



The secretion of bile is not stopped by ligation of either the 

 portal vein or the hepatic artery, showing that both of these 

 vessels contain bile materials. But it would be unreasonable to 

 suppose that the blood of the portal vein does not furnish the 

 bulk of secreting material. 



Glycogenic Function. The formation of glycogen is con- 

 nected with nutrition, but will receive some notice here. This 

 is an internal secretion. It is produced by the liver cells, and 

 can be demonstrated in their substance by the microscope and 

 by chemical reagents. It can also be shown to increase markedly 



