FOOT) ANT) DIGESTION". 303 



atoms of the glycerine are replaced by radicals of the fatty acids, usually 

 oleic and palmitic acids. 



(d) The Mucus in bile is derived from the mucous membrane and 

 glands of the gall-bladder, and of the hepatic ducts. It constitutes the 

 residue after bile is treated with alcohol. The epithelium with which it 

 is mixed may be detected in the bile with the microscope in the form of 

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

 the presence of the mucus is probably to be ascribed the rapid decom- 

 position of the bile; for, according to Berzelius, if the mucus be sepa- 

 rated, 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 car- 

 bonate 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. 



Functions of the Bile. Though it is not a true digestive fluid, in 

 that it has no ferment and digests nothing itself, yet it must be regarded 

 as an important aid to digestion for the following reasons: There is little 

 doubt that it (a) assists in emulsifying the fats of the food, and thus 

 rendering them capable of passing into the lacteals by absorption. For 

 it has appeared in some experiments in which the common bile-duct 

 was tied, that, although the process of digestion in the stomach was un- 

 affected, chyle was no longer well formed; the contents of the lacteals 

 consisting of clear, colorless fluid, instead of being opaque and white, as 

 they ordinarily are, after feeding. It is, however, the combined action 

 of the bile with the pancreatic juice to which the emulsification is due 

 rather than to that of the bile alone. The bile itself has a very feeble 

 emulsifying power. If the theory be accepted that fats are absorbed as 

 fatty acids and soaps, in solution, the action of the bile becomes very 

 important because solutions of bile salts have the power of dissolving 

 the fatty acids. 



(b) It is probable, also, that the moistening of the mucous membrane 

 of the intestines by bile facilitates absorption of fatty matters through it. 



(c) The bile, like the gastric fluid, has a certain but not very con- 

 siderable antiseptic power, and may serve to prevent the decomposition 

 of food during the time of its sojourn in the intestines. Experiments 

 show that the contents of the intestines are much more foetid after the 

 common bile-duct has been tied than at other times: moreover, it is 

 found that the mixture of bile with a fermenting fluid stops or spoils 

 the process of fermentation. This function may, very probably, be ex- 



