convoluted and more deeply situated. They are directly continuous with Brunner's glands in the duodenum. (Watney.)

Changes in the gland cells during secretion.-The chief or cubical cells of the peptic glands, and the corresponding cells of the pyloric glands during the early stage of digestion, if hardened in alcohol, appear swollen and granular, and stain readily. At a later stage the cells become smaller, but more granular and stain even more readily. The parietal

cells swell up, but are otherwise not altered during digestion. The granules, however, in the alcoholhardened specimen, are believed not to exist in the living cells, but to have been precipitated by the hardening re-agent; for if examined during life they appear to be confined to the inner zone of the cells, and the outer zone is free from granules, whereas during rest the cell is granular throughout. These granules are thought to be pepsin, or the substance from which pepsin is formed, pepsinogen, which is during rest stored chiefly in the inner zone of the cells and discharged into the lumen of the tube during secretion. (Langley.)

m m

Fig. 187.-Section showing the pyloric glands. s, free surface; d, ducts of pyloric glands; n, neck of same; m, the gland alveoli; mm, muscularis mucosa. (Klein and Noble Smith.)

Lymphatics.-Lymphatic vessels surround the gland tubes to a greater or less extent. Towards the fundus of the peptic glands are found masses of lymphoid tissue, which may appear as distinct follicles, somewhat like the solitary glands of the small intestine.

Blood-vessels.-The blood-vessels of the stomach, which first break up in the sub-mucous tissue, send branches upward between the closely packed glandular tubes, anastomosing around them by means of a fine capillary network, with oblong meshes. tinuous with this deeper plexus, or prolonged upwards from it, so to speak, is a more superficial network of larger capillaries, which branch densely around the orifices of the tubes, and form the

framework on which are moulded the small elevated ridges of mucous membrane bounding the minute, polygonal pits before referred to. From this superficial network the veins chiefly take their origin. Thence passing down between the tubes, with no

very free connection with the deeper inter-tubular capillary plexus, they open finally into the venous network in the submucous tissue.

Fig. 188.-Plan of the blood-vessels of the stomach, as they would be seen in a vertical section. a, arteries, passing up from the vessels of submucous coat; b, capillaries branching between and around the tubes; c, superficial plexus of capillaries occupying the ridges of the mucous membrane; d, vein formed by the union of veins which, having collected the blood of the superficial capillary plexus, are seen passing down between the tubes. (Brinton.)

Gastric Juice.

Gastric Juice. The functions of the stomach are to secrete a digestive fluid (gastric juice), to the action of which the food is subjected after it has entered the cavity of the stomach from the œsophagus; to thoroughly incorporate the fluid with the food by means of its muscular movements; and to absorb such substances as are ready for absorption. While the stomach contains no food, and is inactive, no gastric fluid is secreted; and mucus, which is either neutral or slightly alkaline, covers its surface. But immediately on the introduction of food or other substance the mucous membrane, previously quite pale, becomes slightly turgid and reddened with the influx of a larger quantity of blood; the gastric glands commence secreting actively, and an acid fluid. is poured out in minute drops, which gradually run together and flow down the walls of the stomach, or soak into the substances within it.

Chemical Composition.-The first accurate analysis of gastric juice was made by Prout: but it does not appear to have been collected in any large quantity, or pure and separate from food,

until the time when Beaumont was enabled, by a fortunate circumstance, to obtain it from the stomach of a man named St. Martin, in whom there existed, as the result of a gunshot wound, an opening leading directly into the stomach, near the upper extremity of the great curvature, and three inches from the cardiac orifice. The introduction of any mechanical irritant, such as the bulb of a thermometer, into the stomach, through this artificial opening, excited at once the secretion of gastric fluid. This was drawn off, and was often obtained to the extent of nearly an ounce. The introduction of alimentary substances caused a much more rapid and abundant secretion than did other mechanical irritants. No increase of temperature could be detected during the most active secretion; the thermometer introduced into the stomach always stood at 100° F. (37.8° C.) except during muscular exertion, when the temperature of the stomach, like that of other parts of the body, rose one or two degrees higher.

The chemical composition of human gastric juice has been also investigated by Schmidt. The fluid in this case was obtained by means of an accidental gastric fistula, which existed for several years below the left mammary region of a patient between the cartilages of the ninth and tenth ribs. The mucous membrane was excited to action by the introduction of some hard matter, such as dry peas, and the secretion was removed by means of an elastic tube. The fluid thus obtained was found to be acid, limpid, odourless, with a mawkish taste-with a specific gravity of 1002, or a little more. It contained a few cells, seen with the microscope, and some fine granular matter. The analysis of the fluid obtained in this way is given below. The gastric juice of dogs and other animals obtained by the introduction into the stomach of a clean sponge through an artificially made gastric fistula, shows a decided difference in composition, but possibly this is due, at least in part, to admixture with food.

The quantity of gastric juice secreted daily has been variously estimated; but the average for a healthy adult may be assumed to range from ten to twenty pints in the twenty-four hours. The acidity of the fluid is due to free hydrochloric acid, although other acids, e.g., lactic, acetic, butyric, are not unfrequently to be found therein as products of gastric digestion or abnormal fermentation. The amount of hydrochloric acid varies from 2 to 2 per 1000 parts. In healthy gastric juice the amount of free acid may be as much as 2 per cent.

As regards the formation of pepsin and acid, the former is produced by the central or chief cells of the peptic glands, and also most likely by the similar cells in the pyloric glands; the acid is chiefly found at the surface of the mucous membrane, but is in all probability formed by the secreting action of the parietal cells of the peptic glands, as no acid is formed by the pyloric glands in which this variety of cell is absent.

The ferment Pepsin can be procured by digesting portions of the mucous membrane of the stomach in cold water, after they have been macerated for some time in water at a temperature 80°-100° F. (27°°—37·8° C.) The warm water dissolves various substances as well as some of the pepsin, but the cold water takes up little else than pepsin, which is contained in a greyish-brown viscid fluid, on evaporating the cold solution. The addition of alcohol throws down the pepsin in greyish-white flocculi. Glycerine also has the property of dissolving out the ferment; and if the mucous membrane be finely minced, and the moisture removed by absolute alcohol, a powerful extract may be obtained by throwing into glycerine.

Functions.-The digestive power of the gastric juice depends on the pepsin and acid contained in it, both of which are, under ordinary circumstances, necessary for the process.

The general effect of digestion in the stomach is the conversion of the food into chyme, a substance of various composition according to the nature of the food, yet always presenting a characteristic thick, pultaceous, grumous consistence, with the undigested portions of the food mixed in a more fluid substance, and a strong, disagreeable acid odour and taste.

The chief function of the gastric juice is to convert proteids into peptones. This action may be shown by adding a little gastric juice (natural or artificial) to some diluted egg-albumin, and keeping the mixture at a temperature of about 100° F. (37·8° C.); it is soon found that the albumin cannot be precipitated on boiling, but that if the solution be neutralised with an alkali, a preci

pitate of acid-albumin is thrown down. After a while the propor tion of acid-albumin gradually diminishes, so that at last scarcely any precipitate results on neutralization, and finally it is found that all the albumin has been changed into another proteid substance which is not precipitated on boiling or on neutralization. This is called peptone.

Characteristics of Peptones.- Peptones have certain characteristics which distinguish them from other proteids. 1. They are diffusible, i.e., they possess the property of passing through animal membranes. 2. They cannot be precipitated by heat, by nitric, or acetic acid, or by potassium ferrocyanide and acetic acid. They are, however, thrown down by tannic acid, by mercuric chloride and by picric acid. 3. They are very soluble in water and in neutral saline solutions.

In their diffusibility peptones differ remarkably from eggalbumin, and on this diffusibility depends one of their chief uses. Egg-albumin as such, even in a state of solution, would be of little service as food, inasmuch as its indiffusibility would effectually prevent its passing by absorption into the blood-vessels of the stomach and intestinal canal. Changed, however, by the action of the gastric juice into peptones, albuminous matters diffuse readily, and are thus quickly absorbed.

After entering the blood the peptones are very soon again modified, so as to re-assume the chemical characters of albumin, a change as necessary for preventing their diffusing out of the blood-vessels, as the previous change was for enabling them to pass in. This is effected, probably, in great part by the agency of the liver.

Products of Gastric Digestion.-The chief product of gastric digestion is undoubtedly peptone. We have seen, however, in the above experiment that there is a by-product, and this is almost identical with syntonin or acid albumin. This body is probably not exactly identical, however, with syntonin, and its old name of parapeptone had better be retained. The conversion of native albumin into acid-albumin may be effected by the hydrochloric acid alone, but the further action is undoubtedly due to the ferment and the acid together, as although under high pressure any acid solution may, it is said, if strong enough, produce the entire conversion into peptone, under the condition of digestion in the stomach this would be quite impossible; and, on the other hand, pepsin will not act without the presence of acid. The pro

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