ulcers. There are also the glands of Lieberkühn which secrete the succus entericus.
The arteries of the small intestine, which include the superior mesenteric, are from the celiac axis and the nerves are from the superior mesenteric plexus of the sympathetic. The veins empty chiefly into the portal system.
The movements of the intestine, like those of the esophagus, are peristaltic, but the action is complicated by the fact that the tube is not straight but in coils.
Intestinal Digestion.—The food, which enters the duodenum as chyme, there comes in contact with the bile and the pancreatic juice, which together but unmixed enter the duodenum from their respective ducts by a common orifice. As in the stomach, the digestive juices are called forth by the presence of food. The bile is secreted in the liver, from which it flows away through the hepatic duct, which joins the cystic duct from the gall-bladder to form the common bile duct. Through this it flows into the intestine during digestion, but between whiles it passes up into the gall-bladder, where it is stored for future use and whence it is expelled when needed. When pure it is a thick, viscid liquid, varying from a bright red to a greenish-yellow in color according to the pigments present, and of an alkaline reaction. It consists chiefly of the bile pigments, biliverdin, which gives the green color, and bilirubin, which gives the red color, and of bile salts in solution. cholesterin, which probably forms the basis of many gall stones, is also present. Bile is a disinfectant to the bowel and a lubricant for the feces. How much digestive action it has is a question, but it affords the necessary alkaline medium for the pancreatic juice to act in.
The pancreatic juice is secreted by the pancreas, from which it enters the intestine through the pancreatic duct, and is probably the most important fluid in the digestive process. It is clear, practically colorless, slightly viscid or gelatinous, and quite strongly alkaline in reaction, owing to the presence of sodium carbonate. It contains
