MODE OF SECRETION AND DISCHARGE OF BILE 343 



the intestinal canal is full of concentrated bile, mixed with intestinal secretion, 

 and this constitutes the meconium, or feces of the fetus. In the fetus, therefore, 

 the main purpose of the secretion of bile must be directly excretive. Probably 

 all the bile secreted in fetal life is incorporated in the meconium, and with it 

 discharged. 



Mode of Secretion and Discharge of Bile. The secretion of bile 

 is continually going on, but is retarded during fasting, and accelerated on 

 taking food. This is shown by tying the common bile-duct of a dog, and estab- 

 lishing a fistulous opening between the skin and gall-bladder, whereby all the 

 bile secreted is discharged at the surface. When the animal is fasting, some- 

 times not a drop of bile is discharged for several hours. In about ten minutes 

 after the introduction of food into the stomach, the bile begins to flow abun- 

 dantly, and continues to do so during the period of digestion. 



The bile is constantly being formed in the hepatic cells; thence, being dis- 

 charged into the minute hepatic ducts, it passes into the larger trunks, and 

 from the main hepatic duct may be carried at once into the duodenum. This 

 probably happens only while digestion is going on, i.e., for five to seven hours 

 after the introduction of food into the stomach. During fasting, it flows from 

 the common bile-duct through the cystic duct into the gall-bladder, where it 

 accumulates till, in the next period of digestion, it is discharged into the intes- 

 tine. The gall-bladder thus acts as a reservoir for the bile during the intervals 

 when digestion is not in progress. 



The mechanism by which the bile passes into the gall-bladder is simple. 

 The orifice through which the common bile-duct communicates with the 

 duodenum is narrower than the duct, and appears to be closed, except when 



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.) 



there is sufficient pressure behind to force the bile through it. The pressure 

 exercised upon the bile secreted during the intervals between periods of diges- 

 tion appears insufficient to overcome the force of the sphincter by which the 

 orifice of the duct is closed; and the bile in the common duct traverses the 



