iv DIGESTION IN THE INTESTINE 217 



of Oddi's sphincter and outflow of bile. This is effected by fats, 

 proteins, and also by the extractives of meat. Carbohydrates seem 

 to have no definite action on biliary excretion, (d) The course of 

 biliary . excretion is more or less typical for the different classes of 

 food-stuffs. Generally speaking, it may be said that excretion is 

 due to the exciting action, not of the food-stuffs, but of their 

 digestive products. In fact, raw egg-white, which passes undigested 

 from the stomach to the intestine, is unable to produce excretion 

 of bile, even if it be introduced into the stomach in large amounts. 

 Boiled egg-white, on the other hand, which remains in the stomach 

 and is digested there, regularly excites a flow of bile, (e) Psychical 

 influences seern to produce no effect on the flow of bile. No bile 

 flows when the animal. is brought into the presence of foods, or 

 given milk while the cannula in the gastric fistula is kept open, 

 so that the food runs out of the stomach as fast as it flows in 

 (sham feeding). When, on the contrary, the gastric fistula is 

 closed, ingestion of milk is regularly followed by a flow of bile 

 after 12-17 minutes. 



III. Various methods have been employed for studying natural 

 digestion in the intestine. The animal can be killed at different 

 periods of digestion to examine the contents of the several parts of 

 the intestine. Intestinal fistulae can be established in animals, 

 or pathological cases of intestinal fistula (anus preternaturalis) can 

 be utilised in man, both at the extreme end of the small intestine 

 and nearer the duodenum. 



The fact that bile is inert when set to digest with proteins 

 gives no idea of its action on the same substances when they are 

 already acidified and partly digested by the gastric juice, nor of 

 the inhibitory or coadjuvant influence which it may exert on the 

 digestive power of the gastric juice, the pancreatic juice, or the 

 succus entericus, with which it necessarily mixes in the duodenum. 

 If bile be added to the chyme collected from the stomach of an 

 animal killed in full digestive activity, a precipitate is immediately 

 formed, even when the added bile is not sufficient to neutralise 

 the acidity of the mixture. Bernard was the first to draw the 

 attention of physiologists to the thick layer of caseous substance, 

 which adheres tenaciously to the villi of the duodenum of dogs 

 killed in full digestion. This layer results from the precipitation 

 of syntonin (metaprotein) and of the proteoses or propeptone, 

 by the alkali of the bile, the bile salts decomposing under the 

 action of the gastric juice. It is generally held that the gastric 

 acid combines with all the bases of the bile salts, throwing out 

 the syntonin, whilst the liberated bile acids combine with the 

 proteoses or propeptone, and precipitate them, the pepsin also 

 coming down mechanically (Briicke, Burkart, Moleschott, Almquist, 

 Hammarsten). 



This process would result in the immediate suspension of 



