physiologists believe that while they collectively secrete the gastric juice, one set may secrete the acid fluid and the organic matter termed pepsin, and the other mucus; the free acid and the pep sin are, as we shall shortly see, the two essential constituents of the gastric juice.
When food is introduced into the stomach, three special phenomena are induced in that vixen:: I 1) Certain movements dependent on the muscu lar coat; (2) the mucous membrane is altered in appearance: and (3) gastric juice is secreted. Each of these phenomena requires a brief notice.
On killing an animal while the act of digestion is going on, and at once laying open its abdomen, we find that the stomach is in a contracted state, firmly embracing its contents, and with both its orifices so closed as to prevent the escape of the food, this contraction being due to the stimula tion of the muscular coat by the food. if we examine the movements of the stomach during digestion, which we can do either by exposing the stomach of a living animal, or by sending a magneto-electric current through this organ in an animal just killed, we perceive that. in the cardiac half or two-thirds, the movements are extremely slow, the muscular coat apparently contracting on the food, and progressively send ing it toward the pylorus: while in the pyloric end of the stomach the movements are more energetic and rapid. resembling the peristaltic or vermicular movement, which we shall presently describe as occurring in the intestinal canal. When the transverse constriction has reached the firmly shut pylorus, a relaxation lasting about a minute ensues, followed by a repetition of the circular contractions. The movements which these contractions impress upon the food have been described in the following terms: "The food entering the cardiac end of the stomach, r, turns to the left, descends into the splenic extremity The changes in the mucous membrane are mainly the following: The inner surface of the healthy fasting 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 Saint Martin) that, on the introduction of food into the stomach, the ves sels of the mucous membrane became more in jected, and that its color 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 ap plied to time acid fluid which Dr. Beaumont saw exuding from the 11111COUA membrane, and which is secreted or formed in the gastric 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 mur (1752), who obtained some of this fluid by making animals swallow sponges with a string attached, by which he could withdraw. them. Ile thus showed that alimentary substances 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.
%stitch ascribed all the changes %%hid' the unihrsst lit in the stomach to :t species of tritura tion. The subject of digestion, or (li p -ti..11 out of the body, has. since that period.
it tareitill• investigated by ninny observers, al tl tin re is now no doubt that the changes which the food undergoes in the stomach are tssi i•tially chemical, and not mechanical.
Iwo year, before I:calumnies experiments, Dr. Trout had ascertained not only that an acid fluid is secreted by the gastric nmcous membrane of rabbits. hares, horses. dogs. etc., during diges tion, but that the acid is the muriatie or hydro ( Illorie acid, and it was supposed that the sob sent action of the gastric joke was clue to this source. ltut experiment, showed that the solvent action is not due simply to the acid of the gastric juice. and that time latter must contain sonic other ingredients which, either alone or in combinatilm with the acid, can exercise this power. It was then discovered that the addition of a portion of the gastric mucous membrane to water acidified with hydroehlorie acid produced a perfect digestive fluid, due attention being paid to the temperature, which should be kept at about 100° F.. or about the normal temperature of the interior of the animal body. later obs•rva tions showed that we can obtain from the gastric runcons membrane the special organic matter on which its digestive power depends, and to this substance the name of p‘psin has been given. WO essential element s of the gastric juice are, then: 11) it free acid, which in some seems to he hydrochloric alone. and in others a mixture of hydroehlo•ie and lactic acids: and (21 an organic matter, which is found on analysis to be highly nitrogenous. and to lie allied to the albuminat es, and which we term pepsin. The best analysis of human gastric juice is that made by Schmidt of Dorpat. who. in 1S53, had an excel lent and rare opportunity of examining it in the case of an Esthonian peasant. Catharine aged thirty-tive years. and weighing about his pounds. in whom there had existed for three a gast•ie fistula or opening, three or fatr lines in diameter. sunder the left breast, between the cartilages of the ninth and tenth ribs. The in troduction of dry peas and a little water into the salon:tell through the opening (even in the morning. on an empty stoma-R1 occasioned the secretion of from five to seven ounces 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 whirl.' lie had established similar fistulons openings. Che following table gives the mean of two anal yse- t f the gastric juice of Catharine 1:iitt, with corresponding nleall results .4 the 1111111 in the she. p, :t purely herbivorous animal. and in the a purely carnivorous animal: The only impurity that could affect these anal yses is the saliva that pos,ibly might have been swallossed.