The changes in the mucous membrane are mainly the following: The inner surface of the healthy fast ing stomach is of a paler pink tint than after the introduction of food, and while in the latter case the reaction of the moisture on the surface is very acid, in the former it is neutral, or even alkaline. Dr.
Beaumont found (in the case of Alexis St. Martin) that, on the introduction of food into the stomach, the vessels of the mucous membrane became more injected, and that its color became changed from a pale pink to a deep red. A pure colorless and slightly viscid fluid, with a well-marked acid reaction, was then observed to distill from the surface of the membrane, and to collect in drops, which trickled down the walls, and mixed with the food.
That the gastric juice,which is the term applied to the acid fluid which Dr. Beaumont saw exuding from the mucous membrane, and which is secreted or formed in the gas tric tubes which we have already described, is capable of exerting a solvent action on food, is proved by numerous experiments. It was first ascertained by Reatimur (1752), who obtained some of this fluid by making animals swallow sponges with a string attached, by which lie could withdraw them. He thus showed that alimentary sub stances out of the body were altered by this fluid in the same manner as they are changed in the stomach, and disproved the favorite theory of that period, which ascribed all the changes which the food underwent in the stomach to a species of trit uration. The subject of artificial digestion, or digestion out of the body, has, since that period, been carefully investigated by many observers, and there is now no doubt that the changes which the food undergoes in the stomach are essentially chemical, and not mechanical.
Two years before Beaumont's experiments, Dr. Prout had ascertained not only that an acid fluid is secreted by the gastric mucous membrane of rabbits, hares, horses, dogs, etc., during digestion, but that the acid is the muriatic or hydrochloric acid, and it was supposed that the solvent action of the gastric juice was due to this source. But experi meats showed that the solvent action is not due simply to the acid of the gastric juice, and that the latter must contain some other ingredient which, either alone or iu bination with the acid, can exercise this power. It was then discovered that the addi
tion of a portion of the gastric mucous membrane to water acidified with hydrochloric acid produced a perfect digestive fluid, due attention being paid to the temperature, which should be kept at about 100°, or about the normal temperature of the interior of the animal body. Later observations showed that we can obtain from the gastric mucous membrane the special organic matter on which its digestive power depends, and to this substance the name of has been given. The two essential elements of the gas tric juice are then: 1. A free acid, which in some cases seems to be hydrochloric alone, and in others a mixture of hydrochloric and lactic acids; and 2. An organic matter, -which is found on analysis to be highly nitrogenous, and to lie allied to the albuminates, and which we term pepsine. The best analysis of human gastric juice is that made by Schmidt of Dorpat, who, in 1853, had an excellent and rare opportunity of examining it in the case of an Esthonian peasant, Catharine Kitt, aged .35 years, and weighing about 118 lbs., in whom there had existed for three years a gastric fistula or opening, three or four lines in diameter, under the left breast, between the cartilages of the ninth and tenth ribs. The introduction of dry pease and a little water into the stomach. through the opening, occasioned (even in the morning, on an empty stomach) the secre tion of from 5 to 7 ozs. of a clear limpid fluid with an acid reaction, which, however, was much less strong than Schmidt had observed in previous experiments on the gas tric juice of dogs and sheep, in which he had artificially established similar fistulous openings. The following table gives the mean of two analyses of the gastric juice of Catharine Kt'at, with corresponding mean results of the same fluid in the sheep, a purely herbivorous animal, and in the dog, a purely carnivorous The only impurity that could affect these analyses, is the saliva that possibly might have been swallowed.