388 FOOD AND DIGESTION 



Bile is also an excretive fluid carrying waste products thrown off by the 

 liver. The liver during fetal life is proportionately larger than it is after 

 birth, and the secretion of bile is active, although there is no food in the in- 

 testinal canal upon which it can exercise any digestive property. At birth, 

 the intestinal canal contains concentrated bile, mixed with intestinal secretion 

 and this constitutes the mecanium, or feces of the fetus. In the fetus, there- 

 fore, the main purpose of the secretion of bile must be directly excretive. 

 Probably all the residue of the bile secreted in fetal life is incorporated in 

 the meconium, and with it discharged. 



Mode of Secretion and Discharge of Bile. In considering the flow 

 of bile into the intestine, two factors are involved. These are the emptying 

 of the gall-bladder and an increased secretion by the hepatic cells. 



The secretion oj bile can be studied by tying the common bile-duct of 

 a dog and then making a fistulous opening between the skin and the gall- 

 bladder; all the bile secreted is then discharged at the surface. In such 

 animals it has been found that the secretion of bile is continuous. With 



FIG. 274. Transverse Section through Four Crypts of Lieberkiihn, from the Large 

 Intestine of the Pig. They are lined by columnar epithelial cells, the nuclei being placed 

 in the outer part of the cells. The divisions between the cells are seen as lines radiating 

 from L, the lumen of the crypt; G, epithelial cells, which have become transformed into 

 goblet cells. X 350. (Klein and Noble Smith.) 



the great discharge of bile into the intestine that occurs during the third 

 hour after a meal, there is an increased secretion of this fluid. This in- 

 creased secretion of bile can also be evoked by the introduction of o . 4 per 

 cent, hydrochloric acid into the duodenum, and occurs even after the di- 

 vision of all connections between the liver and the central nervous system. 

 There is evidence that the increased secretion of bile is brought about 

 through a mechanism identical with that for the secretion of pancreatic 

 juice, and that in each case one and the same substance secretin is formed 

 by the action of the cells of the mucous membrane and absorbed into the 

 blood stream and excites both the liver and pancreas to increased activity. 

 The emptying of the gall-bladder has been investigated on dogs with a 

 Pavlov fistula. In this operation, the orifice of the duct, with the mucous 

 membrane around it, is cut out of the wall of the intestine and the latter 



