276 HAND-BOOK OF PHYSIOLOGY. 



found in most other secreted fluids. It is possible that the carbonate and 

 neutral phosphate of sodium and potassium, found in the ashes of bile, 

 are formed in the incineration, and do not exist as such in the fluid. 

 Oxide of iron is said to be a common constituent of the ashes of bile, and 

 copper is generally found in healthy bile, and constantly in biliary calculi. 



Gas A certain .small amount of carbonic acid, oxygen, and nitrogen, 

 may be extracted from bile. 



Mode of Secretion and Discharge. The process of secreting bile 

 is continually going on, but appears to be retarded during fasting, and 

 accelerated on taking food. This has been shown by tying the common 

 bile-duct of a dog, and establishing a fistulous opening between the skin 

 and gall-bladder, whereby all the bile secreted was discharged at the sur- 

 face. It was noticed that when the animal was fasting, sometimes not a 

 drop of bile was discharged for several hours; but that, in about ten min- 

 utes after the introduction of food into the stomach, the bile began to 

 flow abundantly, and continued to do so during the whole period of diges- 

 tion. (Blondlot, Bidder and Schmidt.) 



The bile is formed in the hepatic cells; then, being discharged into 

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

 main hepatic duct maybe carried at once into the duodenum. But, prob- 

 ably, this happens only while digestion is going on; during fasting, it 

 regurgitates 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 intestine. The gall-bladder thus fulfils what ap- 

 pears to be its chief or only office, that of a reservoir; for its presence 

 enables bile to be constantly secreted, yet insures its employment 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 sim- 

 ple. 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 ori- 

 fice 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 discharged 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 

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

 muscular fibre-cells. Their contraction is excited 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. 



