CHANGES OF FOOD IN THE INTESTINES. 561 



being first tied, in order to prevent the saliva, gastric juice, bile, and 

 pancreatic juice, from passing down. Other experiments have been 

 made, by isolating portions of the small intestine and its contents, by 

 including them between two ligatures. Various kinds of food have 

 also been subjected to artificial digestion, outside the body, at a proper 

 temperature, in the juices of the small or large intestine, or with por- 

 tions of the mucous membrane macerated in water. From such experi- 

 ments, several conclusions are obvious. The strongly alkaline intes- 

 tinal juice certainly converts starch into sugar, many believing that 

 this change is chiefly accomplished in the small intestine ; sugar itself 

 here also passes into lactic and butyric acids ; it acts still more power- 

 fully in the solution of albuminoid substances. Lastly, it is also more 

 or less capable of forming an emulsion with fat, and so of aiding the 

 pancreatic juice, or even of supplying its place. It would seem, there- 

 fore, that the intestinal juice operates as an auxiliary digestive agent 

 upon the three principal constituents of our food. Its effects do not 

 appear to be interfered with by those of the other digestive fluids. 

 The action of the secretion of Brunner's glands, and that of the inte-s- 

 tinal juice, separately, are quite unknown. 



Changes of the Food in the Small and Large Intestine. 

 Contents of those Intestines. 



In considering the changes in the food, which occur in any given 

 part of the intestine, it must be remembered, that the fluids poured 

 into the alimentary canal higher up, are still present, in greater or 

 less quantity, in the intestinal contents lower down, and doubtless ex- 

 ercise some digestive influence. Thus, gastric juice, and even saliva, 

 must be present in the upper part of the duodenum, and more or less 

 pancreatic juice and bile in the lower part of the small intestine. 

 The venous pulpy chyme, poured from the stomach into the small in- 

 testine, is acid, and brownish or variously colored ; but on its admix- 

 ture with the bile and pancreatic juice, it assumes a bright and yellow- 

 ish color, and becomes much more opaque, owing to the addition of 

 the biliary coloring substances, the decomposition of the acids by the 

 bile, and the gradual emulsification of the fatty substances by the 

 pancreatic juice. The contents of the upper part of the small intes- 

 tine are still acid, partly from the acid of the gastric juice and partly 

 from the acids of the bile, which are set free by the former ; but their 

 acidity is gradually diminished, not only by the alkaline pancreatic 

 juice, but also, and chiefly, by the even more powerfully alkaline in- 

 testinal juice. The hydrochloric acid of the gastric juice is probably 

 soon neutralized, and is then absorbed into the blood as chloride of so- 

 dium or common salt. At the lower end of the ileum, the reaction of 

 the residual intestinal contents is generally stated to be alkaline; but 

 near that point, in a case of accidental fistula in the human subject, 

 it has been found acid, notwithstanding the alkaline condition of 

 the mucous membrane. The contents of the caecum are said to be 

 acid ; but those of the large intestine generally, to be alkaline. Much, 

 however, depends on the nature of the food ; for, from the formation 



