the stomach; but only just sufficient to moisten the gastric mucous membrane, and give it an acid reaction.

The gastric juice, which is obtained by irritating the stomach with a metallic catheter, is clear, perfectly colorless, and acid in reaction. A sufficient quantity of it cannot be obtained by this method for any extended experiments; and for that purpose, the animal should be fed, after a fast of twenty-four hours, with fresh lean meat, a little hardened by short boiling, in order to coagulate the fluids of the muscular tissue, and prevent their mixing with the gastric secretion. No effect is usually apparent within the first five minutes after the introduction of the food. At the end of that time the gastric juice begins to flow; at first slowly, and in drops. It is then perfectly colorless, but very soon acquires a slight amber tinge. It then begins to flow more freely, usually in drops, but often running for a few seconds in a continuous stream. In this way from ij to 3iiss may be collected in the course of fifteen minutes. After this it becomes somewhat turbid with the debris. of the food, which has begun to be disintegrated; but from this it may be readily separated by filtration. After three hours, it continues to run freely, but has become very much thickened, and even grumous in consistency, from the abundant admixture of alimentary debris. In six hours after the commencement of digestion it runs less freely, and in eight hours has become very scanty, though it continues to preserve the same physical appearances as before. It ceases to flow altogether in from nine to twelve hours, according to the quantity of food taken.

For purposes of examination, the fluid drawn during the first fifteen minutes after feeding should be collected, and separated by filtration from accidental impurities. Obtained in this way, the gastric juice is a clear, watery fluid, without any appreciable viscidity, very distinctly acid to test paper, of a faint amber color, and with a specific gravity of 1010. It becomes opalescent on boiling, owing to the coagulation of its organic ingredients. The following is the composition of the gastric juice of the dog, based on a comparison of various analyses by Lehmann, and Bidder and Schmidt:

In place of lactic acid, Bidder and Schmidt found, in most of their analyses, hydrochloric acid. Lehmann admits that a small quantity of hydrochloric acid is sometimes present, but regards lactic acid as much the most abundant and important of the two. Robin and Verdeil also regard the acid reaction of the gastric juice as due to lactic acid; and, finally, Bernard has shown,' by a series of well contrived experiments, that the free acid of the dog's gastric juice is undoubtedly the lactic; and that the hydrochloric acid obtained by distillation, is really produced by a decomposition of the chlorides, which enter into the composition of the fresh juice.

The free acid is an extremely important ingredient of the gastric secretion, and is, in fact, essential to its physiological properties; for the gastric juice will not exert its solvent action upon the food, after it has been neutralized by the addition of an alkali or an alkaline carbonate.

The most important ingredient of the gastric juice, beside the free acid, is its organic matter or "ferment," which is sometimes known under the name of pepsine. This name, "pepsine," was originally given by Schwann to a substance which he obtained from the mucous membrane of the pig's stomach, by macerating it in distilled water until a putrid odor began to be developed. The substance in question was precipitated from the watery infusion by the addition of alcohol, and dried; and if dissolved afterward in acidulated water, it was found to exert a solvent action on boiled white of egg. This substance, however, did not represent precisely the natural ingredient of the gastric secretion, and was probably a mixture of various matters, some of them the products of commencing decomposition of the mucous membrane itself. The name pepsine, if it be used at all, should be applied to the organic matter

Leçons de Physiologie Expérimentale, Paris, 1856, p. 396.

which naturally occurs in solution in the gastric juice. It is altogether unessential, in this respect, from what source it may be originally derived. It has been regarded by Bernard and others, on somewhat insufficient grounds, as a product of the alteration of the mucus of the stomach. But whatever be its source, since it is always present in the secretion of the stomach, and takes an active part in the performance of its function, it can be regarded in no other light than as a real anatomical ingredient of the gastric juice, and as essential to its constitution.

Pepsine is precipitated from its solution in the gastric juice by absolute alcohol, and by various metallic salts, but is not affected by ferrocyanide of potassium. It is precipitated also, and coagulated by a boiling temperature; and the gastric juice, accordingly, after being boiled, becomes turbid, and loses altogether its power of dissolving alimentary substances. Gastric juice is also affected in a remarkable manner by being mingled with bile. We have found that four to six drops of dog's bile precipitate completely with 3j of gastric juice from the same animal; so that the whole of the biliary coloring matter is thrown down as a deposit, and the filtered fluid is found to have lost entirely its digestive power, though it retains an acid reaction.

A very singular property of the gastric juice is its inaptitude for putrefaction. It may be kept for an indefinite length of time in a common glass-stoppered bottle without developing any putrescent odor. A light deposit generally collects at the bottom, and a confervoid vegetable growth or "mould" often shows itself in the fluid

Fig. 30.

after it has been kept for one or two weeks. This growth has the form of white, globular masses, each of which is composed of delicate radiating branched filaments (Fig. 30); each filament consisting of a row of elongated cells, like other vegetable growths of a similar nature. These growths, however, are not accompanied by any putrefactive changes, and the gastric juice retains its acid reaction and

CONFERVOID VEGETABLE, growing in the Gastric Juice its digestive properties for

of the Dog. The fibres have an average diameter of

1-7000th of an inch,

many months.

By experimenting artificially with gastric juice on various alimentary substances, such as meat, boiled white of egg, &c., it is found, as Dr. Beaumont formerly observed, to exert a solvent action on these substances outside the body, as well as in the cavity of the stomach. This action is most energetic at the temperature of 100° F. It gradually diminishes in intensity below that point, and ceases altogether near 32°. If the temperature be elevated above 100° the action also becomes enfeebled, and is entirely suspended about 160°, or the temperature of coagulating albumen. Contrary to what was supposed, however, by Dr. Beaumont and his predecessors, the gastric juice is not a universal solvent for all alimentary substances, but on the contrary, affects only a single class of the proximate principles, viz., the albuminoid or organic substances. Neither starch nor oil, when digested in it at the temperature of the body, suffers the slightest chemical alteration. Fatty matters are simply melted by the heat, and starchy substances are only hydrated and gelatinized to a certain extent by the combined influence of the warmth and moisture. Solid and semi-solid albuminoid matters, however, are at once attacked and liquefied by the digestive fluid. Pieces of coagulated white of egg suspended in it, in a test-tube, become gradually softened on their exterior, and their edges become pale and rounded. They grow thin and transparent; and their substance finally melts away, leaving a light, scanty deposit, which collects at the bottom of the test-tube.. While the disintegrating process is going on, it may be almost always noticed that minute, opaque spots show themselves in the substance of the liquefying albumen, indicating that certain parts of it are less easily attacked than the rest; and the deposit which remains at the bottom is probably also composed of some ingredient, not soluble in the gastric juice. If pieces of fresh meat be treated in the same manner, the areolar tissue entering into its composition is first dissolved, so that the muscular bundles become more distinct, and separate from each other. They gradually fall apart, and a little brownish deposit is at last all that remains at the bottom of the tube. If the hard, adipose tissue of beef or mutton be subjected to the same process, the walls of the fat vesicles and the intervening areolar tissue, together with the capillary blood vessels, &c., are dissolved; while the oily matters are set free from their envelops, and collect in a white, opaque layer on the surface. In cheese, the casein is dissolved, and the oil set free, as above. In bread, the gluten is digested, and the starch left unchanged. In

milk, the casein is first coagulated by contact with the acid gastric fluids, and afterward slowly liquefied, like other albuminoid sub

stances.

The time required for the complete liquefaction of these substances varies with the quantity of matter present, and with its state of cohesion. The process is hastened by occasionally shaking up the mixture, so as to separate the parts already disintegrated, and bring the gastric fluid into contact with fresh portions of the digestible substance.

The liquefying process which the food undergoes in the gastric juice is not a simple solution. It is a catalytic transformation, produced in the albuminoid substances by contact with the organic matter of the digestive fluid. This organic matter acts in a similar manner to that of the catalytic bodies, or "ferments," generally. Its peculiarity is that, for its active operation, it requires to be dissolved in an acidulated fluid. In common with other ferments, it requires also a moderate degree of warmth; its action being checked, both by a very low, and a very high temperature. By its operation the albuminoid matters of the food, whatever may have been their original character, are all, without distinction, converted into a new substance, viz., albuminose. This substance has the general characters belonging to the class of organic matters. It is uncrystallizable, and contains nitrogen as an ultimate element. It is precipitated, like albumen, by an excess of alcohol, and by the metallic salts; but unlike albumen, is not affected by nitric acid or a boiling temperature. It is freely soluble in water, and after it is once produced by the digestive process, remains in a fluid condition, and is ready to be absorbed by the vessels. In this way, casein, fibrin, musculine, gluten, &c., are all reduced to the condition of albuminose. By experimenting as above, with a mixture of food and gastric juice in test tubes, we have found that the casein of cheese is entirely converted into albuminose, and dissolved under that form. A very considerable portion of raw white of egg, however, dissolves in the gastric juice directly as albumen, and retains its property of coagulating by heat. Soft-boiled white of egg and raw meat are principally converted into albuminose; but at the same time, a small portion of albumen is also taken up unchanged.

The above process is a true liquefaction of the albuminoid substances, and not a simple disintegration. If fresh meat be cut into small pieces, and artificially digested in gastric juice in test tubes,