262 DIGESTION. 



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 hap- 

 pens 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 discharged into the intestine. The 

 gall-bladder thus fulfils what appears to be its chief or only 

 office, that of a reservoir ; 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 pres- 

 sure behind to force the bile through it. The pressure exer- 

 cised 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 peristaltic action of the ducts. The bile is dis- 

 charged from the gall-bladder, and enters the duodenum on 

 the introduction of food into the small intestine : being pressed 

 on by the contraction of the coats of the gall-bladder, and 

 probably of the common bile-duct also ; for both these organs 

 contain organic muscular fibre-cells. Their contraction is ex- 

 cited by the stimulus of the food in the duodenum acting so as 

 to produce a reflex movement, the force of which is sufficient 

 to open the orifice of the common bile-duct. 



Various estimates have been made of the quantity of bile dis- 

 charged in the intestines in twenty-four hours : the quantity 

 doubtless varying, like that of the gastric fluid, in proportion 

 to the amount of food taken. A fair average of several com- 

 putations would give thirty to forty ounces as the quantity 

 daily secreted by man. 



The purposes served by the secretion of bile may be considered 

 to be of two principal kinds, viz., excrementitious and digestive. 



As an excrementitious substance, the bile serves especially 

 as a medium for the separation of excess of carbon and hydro- 



