STOMACH. The ancients conceived di gestion (q.v.) as a process of cooking, executed by the animal heat of the body. Not until the 17th century was the idea advanced that digestion in the stomach was 4 chemical process largely due to ferments. In 1752 Reaumur, and in 1783 Spallanzani, established that the main factor in digestion was a secre tion of the stomach, the gastric juice, which dissolved and transformed the ingested food stuffs chemically. Previous to that in the 17th century digestion was thought to be due to a mechanical trituration of the food, Reaumur knew that the secretion of the stomach was acid, but it was not until 1834 that Prout discovered that the acidity was due to hydrochloric acid (HCI). In 1836 Schwann recognized the active ferment of the gastric juice, the pepsin.
A research work of the most far-reaching importance concerning the nature of stomach digestion was executed by the American mili tary surgeon, William Beaumont, on the stomach of the Canadian hunter, Alexis St. Martin. After a gunshort wound had opened the organ, it healed not perfectly but, leaving a fistula permitting introspection and direct, ob jective study of digestion. The investigations of Beaumont constitute what may justly be designated as the most epoch-making research on the physiology of the human stomach. ((Experiments and Observations on the Gas tric Juice and the Physiology of Digestion,> Plattsburg, N. Y., 1833).
The digestive processes in the intestines were first systematically studied by Claud Bernard, who discovered in 1848 that the pancreatic juice digested fats. Corvoisart in 1857 discovered the albumen-digesting power of the pancreatic juice. In 1865 the secretion of the intestinal glands was gained in a pure state by Thiry.
Valuable contributions to the physiology of di gestion in the stomach and intestines have been made by J. P. Pawlow, of the Institute for Ex perimental Medicine, Saint Petersburg. These scholarly researches belong to the most recent acquisitions of our knowledge of the digestive tract. Still much remains to be worked out. Even at the present time the function of the bile is not completely understood, nor are the functions of the liver and pancreas satisfactor ily investigated. In a brief and practical ac count like this, the reader seeks only well ascertained facts and not hypotheses. What he wants to know is (1) how the stomach works under healthy conditions, what are its normal performances, and (2) how its abnormal con ditions are brought about, how its diseases are manifested, and what are the best means of avoiding or curing them.
Normal Gastric Digestion.— For an under standing of the normal functions of the stom ach, a brief reference to recent discoveries is indispensable. The stomach is not the main digestive organ, only one-seventh of the entire digestive process occurs in it. The remaining six-sevenths of digestion are carried on in the intestines. But it would be a grave error to assume for this reason that the stomach is not necessary, for the digestive process. For so de
pendent is intestinal digestion upon gastric di gestion that it is impossible to have a normal digestion in the intestines without a previous digestion in the stomach. It is also a mistake to assume that the intestinal digestion is normal in individuals who for surgical reasons have had to undergo the operation of the removal of the stomach as a whole or in part. None of such operated cases where the entire stomach was removed have lived over a year or six months, although they were kept under con stant supervision and the most careful dietetic control.
The chemical changes which the various food-articles undergo in the stomach are of far reaching importance ,for the changes which are to occur in these foods after they reach the intestines. Many of the old authors, beginning with the American physiologist, Beaumont, be lieve that the mechanical irritation of the foods causes the gastric secretion, but the expert-. meats in Pawlow's laboratory haveproved the fallacy of this view. In the first place, if the secretions were due to simple mechanical irrita tion, there is no reason why irritation with the point of a glass rod, with a feather, or with sand placed in the stomach, should not also cause the secretion. A secretion may be caused by me chanic irritation, but it is composed mainly of a liquid resembling plasma, containing mucus, and having no digestive power. The mistake of the older experimenters, according to Pawlow, grew out of the fact that they ignored the so-called psychic secretion, a secretion which can be set up by the mere smell or sight of food, or even by a very intense feeling of hunger. If the oesophagus of a dog be cut in the neck and its end sewed to the edges of the wound, and at the same time a gastric fistula be established, pieces of meat which are fed to the dog after healing of these fistulae will not reach the stom ach, but will fall out of the upper end of the fistula leading into the tesophagus. Neverthe less in five to six minutes after the swallowing of the food gastric juice begins to be secreted, running from the gastric canula first in drops and afterward in a continuous stream. If the dog be offered meat without receiving it, the gastric secretion will also appear, though not so plentifully as when the dog was actually allowed to chew the meat. A further interesting fact observed in 'dogs so experimented on was that no secretion followed the swallowing of indigestible substances like small stones. These experiments furthermore suggested that for every kind of food a definite gastric secre tion is formed of specific composition. There fore it has been said that the stomach provides a special gastric juice to meet each dietetic requirement. It must therefore be further studied whether the mucous membrane of the stomach is capable of distinguishing between the varieties and classes of foods that come in contact with it, much as the skin recognizes mechanical, chemical, thermic and electrical stimulation.