not pure substances, but mixtures, that the gastric juice has to deal with. And here a most important factor comes into play, to which further reference will be made later on. The amount and quality of the secretion of the gastric glands depends upon the nature of the food. Hence a food, or a combination of foods, which digest readily in the laboratory may take a long time to disappear from the stomach, and _vice versâ_. Digestibility depends upon the nature of the food. It depends also upon its physical state. To take simple illustrations: Cheese contains coagulated casein, one of the most easily digestible of proteins, but the casein is intimately mixed with fat, upon which gastric juice can make no impression. Even when finely divided, the particles of casein are protected from the action of the juice by fat. In the same way the meat of pork is as digestible as mutton, but the fat of pork is quickly melted and very liquid. In the process of cooking the muscle-fibres become saturated with fat. It is not the function of the stomach to complete digestion. Its business is to initiate it. Food which reaches the stomach in fragments is reduced to a condition in which its digestion will be readily completed by pancreatic juice. Gastric digestion produces a much larger proportion of intermediate products, proteoses or propeptones, than does digestion in the duodenum. Such intermediate products are quickly dealt with by pancreatic juice. Artificial tests of relative digestibility do not, as a rule, take the amount of propeptones formed in a given time into account. When considering the digestion of a typical meal, we must bear in mind that it is not the duty of the stomach to pass as much sugar, peptone, and fat as possible into the blood. In fact, very few of the products of digestion are absorbed by the bloodvessels of the stomach. The impermeability of its mucous membrane is shown by the fact that hardly any of the water swallowed passes through the stomach-wall. Practically all the water ingested leaves the stomach through the pyloric valve. Various salts, some sugar, and peptones are taken up by the vessels of the stomach; but the bulk of all the different kinds of food passes into the duodenum in a semi-digested state. The function of the stomach is to carry digestion through a preliminary stage. The process will be completed in the small intestine. It is to be noted that, although water is not absorbed by the stomach-wall, alcohol passes through it with great rapidity. The same is true of the various crystalline nitrogenous bodies found in meat-extracts, and also of the essential principles of tea and coffee, which chemically belong to the same class. All these substances are degradation products of proteins produced by oxidation, far advanced along the road to urea. In this selective absorption we see proof of the activity of the cells of the mucous membrane. They take up the substances which it is desirable to remove from the contents of the