When the acid contents of the stomach are poured into the duodenum and meet with a gush of alkaline bile, a copious cheesy precipitate is formed which clings to the wall of the intestine. This precipitate consists partly of acid albumin (parapeptone) and peptones thrown down by the strong solution of bile salts, and partly of bile acids, the salts of wrhich have been decomposed by the hydrochloric acid of the gastric juice. With the bile acids the pepsin is mechanically carried down. Thus, immediately on their entrance into the duodenum the peptic digestion of the gastric contents is suddenly stopped not only by the precipitation of the soluble peptones and the shrinking of the swollen parapeptone, but also by the removal of the pepsin itself from the fluid, and the neutralization of the gastric fluid by the alkaline bile.
By thus checking the action of the gastric ferment the bile prepares the chyme for the action of the pancreatic juice.
As A Stimulant, the bile is of considerable use, for it excites the muscles of the intestine to increased action, and thereby aids in absorption and promotes the forward movement of food, and more particularly of those insoluble materials which have to be evacuated per anum. This stimulation may amount to mild purging.
The bile adds to the i ngesta an abundant supply of fluid and mucus, much of which passes along the intestine to moisten and lubricate the faeces and facilitate their evacuation. In cases of jaundice, or when the bile is removed by a fistula, the faeces are hard and friable, and with difficulty expelled, owing to the deficient fluid and mucus, as well as to the weaker peristaltic movements.
The bile having some soap in solution has a close relationship to both watery and oily fluids, and possibly on this account, as well as owing to a peculiar power possessed by the bile salts, a membrane saturated with bile allows an emulsion of fat to pass through it niuch more readily than if the same membrane were kept moistened with water. This can be seen experimentally with filter paper.
Although much of the bile is reabsorbed from the intestinal tract into the blood, and again used in the economy, some of its constituents pass off with the faeces, and are no doubt simply excrementitious matters that must be got rid of. Thus all the cholesterin, mucus, and coloring matter are normally eliminated, and a considerable quantity of the bile acids are split up, the cholic acid being found in the faeces.
The bile has some share in forming an emulsion, but far less than the secretion of the pancreas; however, the mixed secretions are probably more efficacious than either separately, from the presence of the free fatty acids, which form soaps and aid in forming the emulsion.
As An Antiseptic, bile has been said to have some function to perform. Possibly it restricts the formation of certain of the bye products, such as the indol resulting from pancreatic digestion; but it is certainly not antiseptic, since bacteria abound and thrive in it and in the duodenum.