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capillary blood vessels. The free surface of the gastric mucous membrane is not smooth, but is raised in minute ridges and projecting eminences. In the cardiac portion (Fig. 25), these ridges are reticulated with each other, so as to include between them

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Fig. 25. Free surface of GASTRIC MUCOUS MEMBRANE, viewed from above; from Pig's Stomach, Cardiac portion. Magnified 70 diameters.

Fig. 26.

Free surface of GASTRIC MUCOUS MEMBRANE, viewed in vertical section; from Pig's Stomach, Pyloric portion. Magnified 420 diameters.

Fig. 27.

polygonal interspaces, each of which is encircled by a capillary network. In the pyloric portion (Fig. 26), these eminences are more or less pointed and conical in form, and generally flattened from side to side. They contain each a capillary blood vessel, which returns upon itself in a loop at the extremity of the projection, and communicates freely with adjacent vessels. The gastric follicles are very different in different parts of the stomach. In the pyloric portion (Fig. 27), they are nearly straight, simple tubules, to of an inch in diameter, easily separated

MUCOUS MEMBRANE OF PIG'S STOMACH, from Pyloric

from each other, lined with portion; vertical section; showing gastric tubules, glandular epithelium, and ter

and, at a, a closed follicle. Magnified 70 diameters.

[graphic]

minating in cul-de-sacs at the under surface of the mucous mem

brane. They are sometimes slightly branched, or provided with one or two rounded diverticula, a short distance above their ter

Fig. 28.

GASTRIC TUBULES FROM PIG'S STOMACH, Pyloric portion, showing their Cæcal Extremities. At a, a cylindrical cast of epithelium, pressed out from a tubule, showing the size of its cavity.

mination. They open on the free surface of the mucous membrane, in the interspaces between the projecting folds or villi. Among these tubular glandules there is also found, in the gastric mucous membrane, another kind of glandular organ, consisting of closed follicles, similar to the solitary glands of the small intestine. These follicles, which are not very numerous, are seated in the lower part of the mucous membrane, and enveloped by the cæcal extremities of the tubules. (Fig. 27, a.)

In the cardiac portion of

[graphic]

the stomach, the tubules are very wide in the superficial part of the mucous membrane, and lined

Fig. 29. b

GASTRIC TUBULES FROM PIG'S STOMACH; Cardiac portion. At a, a large tubule dividing into two small ones. b. Portion of a tubule, seen endwise. c. Its central cavity.

with large, distinctly marked cylinder epithelium cells. (Fig. 29.) In the deeper parts of the membrane they become branched and considerably reduced in size. From the point where the branching takes place to where they terminate below in cul-de sacs, they are lined with small glandular epithelium cells, and closely bound together by intervening areolar tissue, so as to present somewhat the appearance of compound glandules.

The blood vessels which come up from the submucous layer of areolar tissue form a

close plexus around all these glandules, and provide the mucous

membrane with an abundant supply of blood, both for the purposes of secretion and absorption.

That part of digestion which takes place in the stomach has always been regarded as nearly, if not quite, the most important part of the whole process. The first observers who made any approximation to a correct idea of gastric digestion were Reaumur and Spallanzani, who showed by various methods that the reduction and liquefaction of the food in the stomach could not be owing to a mere contact with the gastric mucous membrane, or to compression by the muscular walls of the organ; but that it must be attributed to a digestive fluid secreted by the mucous membrane, which penetrates the food and reduces it to a fluid form. They regarded this process as a simple chemical solution, and considered the gastric juice as a universal solvent for all alimentary substances. They succeeded even in obtaining some of this gastric juice, mingled probably with many impurities, by causing the animals upon which they experimented to swallow sponges attached to the ends of cords, by which they were afterwards withdrawn, and the fluids, which they had absorbed, expressed and examined.

The first decisive experiments on this point, however, were those performed by Dr. Beaumont, of the U. S. Army, on the person of Alexis St. Martin, a Canadian boatman, who had a permanent gastric fistula, accidentally produced by a gunshot wound. The musket, which was loaded with buckshot at the time of the accident, was discharged at the distance of a few feet from St. Martin's body, in such a manner as to tear away the integument at the lower part of the left chest, open the pleural cavity, and penetrate, through the lateral portion of the diaphragm, into the great pouch of the stomach. After the integument and the pleural and peritoneal surfaces had united and cicatrized, there remained a permanent opening, of about four-fifths of an inch in diameter, leading into the left extremity of the stomach, which was usually closed by a circular valve of protruding mucous membrane. This valve could be readily depressed at any time, so as to open the fistula and allow the contents of the stomach to be extracted for examination.

Dr. Beaumont experimented upon this person at various intervals from the year 1825 to 1832. He established during the course of his examinations the following important facts: First, that the ac. tive agent in digestion is an acid fluid, secreted by the walls of the

Experiments and Observations on the Gastric Juice. Boston, 1834.

stomach; secondly, that this fluid is poured out by the glandular walls of the organ only during digestion, and under the stimulus of the food; and finally, that it will exert its solvent action upon the food outside the body as well as in the stomach, if kept in glass phials upon a sand bath, at the temperature of 100° F. He made also a variety of other interesting investigations as to the effect of various kinds of stimulus on the secretion of the stomach, the rapidity with which the process of digestion takes place, the comparative digestibility of various kinds of food, &c. &c.

Since Dr. Beaumont's time it has been ascertained that similar gastric fistula may be produced at will on some of the lower animals by a simple operation; and the gastric juice has in this way been obtained, usually from the dog, by Blondlot, Schwann, Bernard, Lehmann and others. The simplest and most expeditious mode of doing the operation is the best. An incision should be made through the abdominal parietes in the median line, over the great curvature of the stomach. The anterior wall of the organ is then to be seized with a pair of hooked forceps, drawn out at the external wound, and opened with the point of a bistoury. A short silver canula one-half to three-quarters of an inch in diameter, armed at each extremity with a narrow projecting rim or flange, is then inserted into the wound in the stomach, the edges of which are fastened round the tube with a ligature in order to prevent the escape of the gastric fluids into the peritoneal cavity. The stomach is then returned to its place in the abdomen, and the canula allowed to remain with its external flange resting upon the edges of the wound in the abdominal integuments, which are to be drawn together by sutures. The animal may be kept perfectly quiet, during the operation, by the administration of ether or chloroform. In a few days the ligatures come away, the wounded peritoneal surfaces are united with each other, and the canula is retained in a permanent gastric fistula; being prevented by its flaring extremities both from falling out of the abdomen and from being accidentally pushed into the stomach. It is closed externally by a cork, which may be with drawn at pleasure, and the contents of the stomach withdrawn for examination.

Experiments conducted in this manner confirm, in the main, the results obtained by Dr. Beaumont. Observations of this kind are in some respects, indeed, more satisfactory when made upon the lower animals, than upon the human subject; since animals are entirely under the control of the experimenter, and all sources of

deception or mistake are avoided, while the investigation is, at the same time, greatly facilitated by the simple character of their food.

The gastric juice, like the saliva, is secreted in considerable quantity only under the stimulus of recently ingested food. Dr. Beaumont states that it is entirely absent during the intervals of digestion; and that the stomach at that time contains no acid fluid, but only a little neutral or alkaline mucus. He was able to obtain a sufficient quantity of gastric juice for examination, by gently irritating the mucous membrane with a gum-elastic catheter, or the end of a glass rod, and by collecting the secretion as it ran in drops from the fistula. On the introduction of food, he found that the mucous membrane became turgid and reddened, a clear acid fluid collected everywhere in drops underneath the layer of mucus lining the walls of the stomach, and was soon poured out abundantly into its cavity. We have found, however, that the rule laid down by Dr. Beaumont in this respect, though correct in the main, is not invariable. The truth is, the irritability of the gastric mucous membrane, and the readiness with which the flow of gastric juice may be excited, varies considerably in different animals; even in those belonging to the same species. In experimenting with gastric fistula on different dogs, for example, we have found in one instance, like Dr. Beaumont, that the gastric juice was always entirely absent in the intervals of digestion; the mucous membrane then presenting invariably either a neutral or slightly alkaline reaction. In this animal, which was a perfectly healthy one, the secretion could not be excited by any artificial means, such as glass rods, metallic catheters, and the like; but only by the natural stimulus of ingested food. We have even seen tough and indigestible pieces of tendon, introduced through the fistula, expelled again in a few minutes, one after the other, without exciting the flow of a single drop of acid fluid; while pieces of fresh meat, introduced in the same way, produced at once an abundant supply. In other instances, on the contrary, the introduction of metallic catheters, &c., into the empty stomach has produced a scanty flow of gastric juice; and in experimenting upon dogs that have been kept without food during various periods of time and then killed by section of the medulla oblongata, we have usually, though not always, found the gastric mucous membrane to present a distinctly acid reaction, even after an abstinence of six, seven, and eight days. There is at no time, however, under these circumstances, any considerable amount of fluid present in

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