_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.