According to the observations of Cannon, the contractile movements of the stomach commence shortly after the entrance of food, the contractions starting from about the middle of the stomach and passing on toward the pylorus. These waves of contraction follow each other very closely, certainly not more than one or two minutes apart, and perhaps less, while the resulting movements bring about an intimate commingling of food and gastric juice in the pyloric portion of the stomach; followed by a gradual diffusion of the semi-fluid mixture into the fundus accompanied by a gradual displacement of the more solid food in the latter region. These movements of the stomach are more or less automatic, arising from stimuli--the acid secreted--originating in the stomach itself, although it is considered that the movements are subject to some regulation from extrinsic nerve fibres, such as the vagi and the splanchnics. As digestion proceeds and the mass in the stomach becomes more fluid, the pyloric sphincter relaxes and a certain amount of the fluid material is forced into the intestine by the pressure of the contraction wave. This is repeated at varying intervals, depending presumably in some measure upon the consistency of the mass in the stomach, until after some hours of digestion the stomach is completely emptied. Especially interesting and suggestive are the experiments made by Cannon[9] on the length of time the different types of foodstuffs remain in the stomach. Using cats as subjects, he found that fats remain for a long period in the stomach; they leave that organ slowly, the discharge into the intestine being at about the same rate as the absorption of fat from the small intestine or its passage into the large intestine. Carbohydrate foods, on the other hand, begin to leave the stomach soon after their ingestion. They pass out rapidly, and at the end of two hours reach a maximum amount in the small intestine almost twice the maximum for proteids, and two and a half times the maximum for fats, both of which maxima are reached only at the end of four hours. Carbohydrates remain in the stomach about half as long as proteids. Proteids, Cannon finds, frequently do not leave the stomach at all during the first half-hour after they are eaten. After two hours, they accumulate in the small intestine to a degree only slightly greater than that reached by carbohydrates an hour and a half earlier. The departure of proteids from the stomach is therefore slower at first than that of either fats or carbohydrates. When a mixture of equal parts of carbohydrates and proteids is fed, the discharge from the stomach is intermediate in rapidity. When fat is added to either carbohydrates or proteids it retards the passage of both foodstuffs through the pylorus. [9] W. B. Cannon: The Passage of different Food-stuffs from the Stomach and through the Small Intestine. American Journal of Physiology, vol. 12, p. 387.