282 HANDBOOK OF PHYSIOLOGY. 



cylindrical cells, either scattered or still held together in layers. To the 

 presence of the mucus is probably to be ascribed the rapid decomposition 

 of the bile; for, according to Berzelius, if the mucus be separated, it 

 will remain unchanged for many days. 



(e) The /Saline or inorganic constituents of the bile are similar to 

 those found in most other secreted fluids. It is possible that the carbo- 

 nate 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. Small amounts of carbonic acid, oxygen, and nitrogen 

 gases may be extracted from bile. 



Mode of Secretion and Discharge. The secretion of bile is continu- 

 ally going on, but it appears to be retarded during fasting, and accele- 

 rated 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 surface. 

 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 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. 



The bile is formed in the hepatic cells; thence, 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 regurgitates from the common bile-duct through the cystic duct, into 

 the gall-bladder, where it accumulates till, in the next period of diges- 

 tion, 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, yet insures its employ- 

 ment 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 gall-bladder 

 and enters the duodenum on the introduction of food into the small in- 



