326 DIGESTION. 



having tied the common bile-duct of a dog, and established 

 a fistulous opening between the skin and gall-bladder, 

 whereby all the bile secreted was discharged at the surface, 

 noticed that when the animal was fasting, sometimes not 

 a drop of bile was discharged for several hours ; but 

 that, in about ten minutes after the introduction of food 

 into the stomach, the bile began to flow abundantly, and 

 continued to do so during the whole period of digestion. 

 Bidder and Schmidt's observations are quite in accordance 

 with this. 



The bile is probably formed first in the hepatic cells ; 

 then, being discharged 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. But, 

 probably, this happens only while digestion is going on ; 

 during fasting it flows from the common bile-duct into 

 the cystic duct, and thence into the gall-bladder, where it 

 accumulates till, in the next period of digestion, it is dis- 

 charged into the intestine. The gall-bladder thus fulfils 

 what appears to be its chief or only office, that of a reser- 

 voir ; for its presence enables bile to be constantly secreted 

 for the purification of the blood, yet insures that it shall all 

 be employed in the service of digestion, although digestion 

 is periodic, and the secretion of bile constant. 



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 there- 

 is sufficient pressure behind to force the bile through it. 

 The pressure exercised upon the bile secreted during the 

 intervals of digestion appears insufficient to overcome the 

 force with which the orifice of the duct is closed ; and the 

 bile in the common duct, finding no exit in the intestine, 

 traverses the cystic duct, and so passes into the gall-bladder, 

 being probably aided in this retrograde course by the peri- 

 staltic action of the ducts. The bile is discharged from the 



