Ulcer and cancer of the stomach are both rather common. In the former there is apt to be hyper-acidity and in the latter hypo-acidity, but the rule does not always hold. In cases of ulcer there may be hemorrhage and even perforation. Such hemorrhage can be distinguished from hemorrhage from the lungs by its slightly acid odor and by the frothy character of hemorrhage from the lungs. There is much irritation at the pylorus and where there is irritation there is liable to be cancer.

Gastric Digestion.—In the stomach the food is churned and thoroughly mixed with the gastric juices, and it is also subjected to a propulsive movement that drives it on to the intestine. When it comes to the stomach it is semi-solid and when it has become fluid or semi-fluid, in which state it is known as chyme, it is ready to pass on. Before it can do so, however, it must overcome the strong pyloric sphincter, and this it does by the muscles about the sphincter pushing it constantly on until the sphincter gives way. Probably most of the propulsive movements take place within a few inches of the pylorus.

The gastric juice is secreted by glands in the wall of the stomach and poured out through little tubules which project from the surface. It is a thin, almost colorless fluid with a sour taste and odor due to the presence of free hydrochloric acid, an important element in digestion. Probably when the stomach is empty and for some twenty minutes after the appearance of food there is no hydrochloric acid present and, the food being alkaline, salivary digestion continues. Then, called forth by the presence of the food, the hydrochloric acid appears and salivary digestion ceases in the acid medium. Little digestion of starches or fats takes place, the chief action being on proteins, which are converted into soluble peptones. For besides hydrochloric acid the gastric juice contains two ferments: 1. pepsin, which is particularly active in aiding the digestion of proteins, and 2. rennin, which especially affects milk. Neither hydrochloric acid nor pepsin seems capable of digesting food alone, but each is essential to the other. They are secreted by different types of cells, secretion depending upon the nerve supply and upon the presence of food. Gastric digestion is favored by minute subdivision of the food and by the right proportion of hydrochloric acid, which should be 0.2 per cent. Body temperature is also advantageous. Except that proteins are put in solution and partly digested, little digestion goes on in the stomach, and though the rugæ afford a large absorbing surface, little absorption takes place, although more takes place than in the mouth and in time most foods, except fats, can be absorbed. The time of digestion varies with different foods and in different people, but probably three to five hours are necessary. The food leaves the stomach as chyme, a fluid of about the consistency of pea soup.

Vomiting is more or less the reverse of swallowing and is generally preceded by a feeling of nausea, which starts up retching, a more or less involuntary effort of the stomach to throw off its contents. To relieve the retching a long breath is taken, followed by a deep expiration that opens the cardiac end of the stomach and allows the abdominal muscles to force the food out. After much vomiting and prolonged retching the pyloric end of the stomach may be affected and bile will then appear in the vomitus. Artificial vomiting may be produced by irritation of the gastric nerve center in the brain or by irritation of the stomach itself.

Fig. 54.—The intestinal canal: 1, Stomach; 2, duodenum; 3, jejunum; 4, ileum; 5, cecum; 6, vermiform appendix; 7, ascending colon; 8, transverse colon; 9, descending colon; 10, sigmoid flexure; 11, rectum. (Leidy.)

Intestinal Canal.—From the stomach the food passes into the [intestinal canal], a convoluted tube which extends from the stomach to the anus and in which, more particularly in the upper portion, the greater part of the digestion and absorption of food takes place. This tube, which is about six times the height of its possessor, consists of two parts, the small and the large intestines, the first four-fifths, or about 25 feet, being small intestine. It occupies the central and lower parts of the abdominal cavity and a small portion of the pelvic cavity, and is attached to the spine by the mesentery, which, however, allows great freedom of motion, so that there is little fixation to the loops of the small intestines.

The Small Intestine.—The small intestine opens out of the stomach and has three divisions: 1. the [duodenum], which is only about ten to twelve inches long; 2. the [jejunum], so called because it is generally empty after death, which is about two-fifths of the remainder and lies chiefly in the umbilical region and the left iliac fossa, and 3. the [ileum] or curved intestine, the remaining three-fifths, which gets its name from its numerous coils and which lies in the middle and the right side of the abdomen. There is no direct division between the jejunum and the ileum, but the first part of the former and the last part of the latter are quite different in character. At its entrance into the large intestine the ileum is guarded by the ileo-cecal valve.

Fig. 55.—
1, Central lacteal;
2, capillary network;
3, columnar cells.