_The Mechanics of Digestion in the Stomach._—Recent investigations, especially those of Cannon, have thrown much light on this subject. The food introduced into the stomach from the esophagus is lodged first in the fundus or cardiac end of the stomach; from here it is moved by slow degrees toward the pylorus, from which it enters the small intestine. Formerly it was taught that this movement was brought about by a churning motion of the stomach throughout its entire length. Cannon has shown the error of this conclusion. From his observations it appears that the stomach is quiet at first. The waves of peristaltic constriction begin at the duodenal and middle portions and move the food toward the pylorus. In this way the constrictions that begin near the pyloric end gradually extend to the cardiac end. The latter part of the stomach is distended after a full meal, but gradually diminishes in size during digestion. Moreover, there is a difference in the character of the gastric juice coming from the different areas of the stomach; that from the middle portion being acid, and that from the cardiac and pyloric being neutral or nearly so. These facts show that the food remains for some time in the fundus and meets there a neutral liquid; consequently, the alkalinity of the mass is retained for a time, and the saliva acts upon the starch for a much longer period than has been supposed. It is believed that the length of time which food remains in the stomach varies with its kind. The digesting mass is not forced into the intestine until it becomes well saturated with the free acid of the stomach, a result that will be reached later with a meat than with a vegetable diet; for it is plain that much more acid will be required to combine with the proteins of meat than with the smaller amounts in the carbohydrate foods, and so free acid is longer in accumulating. Digestion is aided by the movements of the food mass through the contractions of the walls of the stomach, so that anything which lowers the tone of the stomach or impairs the integrity of its lining membrane seriously interferes with the digestive processes. The nature of the food influences the rate of its passage through the pylorus. It has been shown by means of the _x_-rays that when the meal consisted of lean meat, suet, and rice, properly cooked and prepared in such a manner that the constituents were properly mixed together, the carbohydrates (rice) began to leave the stomach in fifteen minutes, but the protein (lean meat) and fat did not begin to leave it under one-half hour, and were much longer in passing through.