The quantity of the gastric juice secreted in 24 hours was determined by Bidder and Schmidt (DieVerdauungs-safte, etc.) in the sheep to be VI, and in the of the weight of the body. If the latter ratio were true for men, a man of ten stone weight would secrete about 14 lbs. of this fluid daily. In the case of Catharine Nutt, the mean daily quantity amounted to no less than 81 lbs., or to more than a fourth part of the weight of her body. On this calculation, a man of ten stone would daily secrete 37 lbs. of gastric juice.
The uses of this fluid in reference to digestion are clear. It serves not only to dis solve, but also to modify the nitrogenous elements of the food (such as albumen, fibrin, casein, and, in short, all animal food except fat, and the blood•forming portion of vege table food), converting them into new substances, termed peptones, which, although they coincide in their chemical composition, and in many of their physical properties, with the substances from which they are derived, differ essentially from them iu their more ready solubility in water, and in various chemical relations. Thus, albumen is converted by the gastric juice into albumen-peptone, fibrin into fibrin peptone, etc. According to the investigations of 3feissner, the albuminates are simultaneously decomposed or broken up into peptones and substances which he terms parapeptones, which latter are not further changed by the action of the gastric juice, but are converted into peptones by the action of the pancreatic juice, with which they come in contact in the duodenum.
All the best observers agree that the gastric juice exerts no apparent action on the non-nitrogenous articles the fats and the carbohydrates (sugar, starch, etc.); as, however, the fats exert a favorable influence on the digestion of nitrogenous matters, it is probable that they undergo some slight, although not appreciable, modifi cation. Gelatine and the gelatinous tissues are, as far as is known, the only nitroge nous articles of food which arc not converted into peptones and parapeptones by the action of the gastric juice.
Although the main object of the gastric juice is to dissolve the albuminates, etc. (e.g., the contents of the egg, flesh, cheese, etc.), it appears from the experiments of Lehmann, Schmidt, and others, that it cannot dissolve the quantity necessary for the due nutrition of the organism. According to Lehmann, gastric juice can only dissolve of its weight of coagulated albumen, while Schmidt makes the quantity as low as t 11 . Now, since a dog secretes about of its weight of gastric juice daily, it would only be able—even taking Lehmann's estimate, which is more than twice as high as Schmidt's—to digest 5 parts of dry or coagulated albumen for every 1000 parts of its weight; but a dog, in order to keep in condition on an exclusive flesh diet—and this is its natural food—should take 50 parts of flesh, containing 10 parts of dry albuminates, for every 1000 pacts of its weight. Hence its
gastric juice only suffices for the digestion of half the albuminates necessary for nutrition—.a result which is in accordance with the ob served fact, that a considerable portion of the albuminates enters the duodenum in an solved state, and which will be explained when we consider the part which the intesti nal juice—the fluid secreted by the various glands lying in the mucous membrane of the small intestine—takes in the digestive process. On comparing the experiments made on dogs with those made on Catharine KiAt, it appears that in the human subject the gastric digestion of the albnminates is much more imperfect than even in the dog.
The process of gastric digestion is slow. According to Beaumont's researches on Alexis St. Martin, the mean time required for the digestion of ordinary animal food, such as butcher's meat, fowl, and game, was from two hours and three quarters to four hours.
The next point to be considered is: What becomes of the matters that are thoroughly dissolved in the stomach? Are they absorbed, without passing frirther down the canal? or do they pass through the pyloric valve into the duodenum, and are they finally taken up by the lacteals? Two of our highest authorities in physiological chemistry, Frerichs and Donders, maintain that the absorption of the peptones commences in the stomach; but the view generally adopted is, that the albuminates, etc., which are converted into peptones, are for the most part taken up by the lacteals. The rapidity with which aqueous solutions of iodide of potassium, the alkaline carbonates, lactates, citrates, etc., pass into the blood, and thence into the urine, saliva, etc., shows that the absorp tion of fluids must take place very shortly after they are swallowed, and there is little doubt that the blood-vessels (capillaries) of the stomach constitute the principal channel through which they pass out of the intestinal tract into the blood. As the veins of the stomach, which are formed by the union of these capillaries, contribute to form the portal vein (see CIRCULATION, ORGANS OF), the absorbed matters pass directly to the liver, and probably stimulate it to increased secretion (fig. 4).