Great difference of opinion has existed with regard to the qualities and composition of this fluid; it would, however, appear that other secretions of a mucous nature take place in the stomach, with which it may be mixed: this circumstance, together with the difficulty of obtaining it in an isolated form, are sufficient to explain the contradictory results which different chemists have obtained. It is, moreover, by no means improbable that this liquor may vary in different stomachs, or even in the same stomach under different circumstances. M. Majendie observes, that the contact of different sorts of food upon the mucous membrane may possibly influence its composition: it is, at least, certain that the gastric juice varies in different animals; for example, that of man is incapable of acting upon bones, while that of the dog digests these substances perfectly; and according to the experiments of Tiedemann and Gmelin, its acidity is considerably increased by the presence of vegetables, or substances of difficult digestion. From high authorities upon this subject, the true gastric juice is stated to be a glairy fluid, not very diffusible in water, and possessing the power of coagulating certain fluids in a very eminent degree.

Dr. Fordyce states, that six or seven grains of the inner coat of the stomach, infused in water, gave a liquor which coagulated more than a hundred ounces of milk. Some authors have regarded it as colourless, and without taste or smell, while others have described it as being acidulous1. Dr. Young, of Edinburgh, is stated to have found that an infusion of the inner coat of the stomach, which had been previously washed with water, and afterwards with a dilute solution of subcarbonate of potass, still retained the power of coagulating milk very readily. We see, therefore, how unfounded that opinion is which attributes to the potation of water the mischief of diluting the gastric fluid, and thus of weakening the digestive process. The coagulating and efficient principle, whatever it may be, is evidently not diffusible in that liquid. After one fit of vomiting, should another take place after a short interval, the matter brought up will be little more than water, with a slight saline impregnation, and some mucus: it will not bo found to possess any power of coagulation; which.

Dr. Fordyce observes, evidently shows, that even water flowing from the exhalants, and which we should therefore expect would throw off the whole of any substance from the surface of the stomach, is incapable of detaching the gastric juice.

1 Dr. Prout has read a paper before the Royal Society, in order to prove that the stomach always contains muriatic acid. And it is now generally admitted that the gastric juice, in its healthy state, is more or less sour.

31. Since the foregoing paragraph was written, Dr. Combe, in a work entitled "On Digestion and Dietetics" has published from the work of Dr. Beaumont, of the American army, an account of the case of Alexis St. Martin, a young Canadian of eighteen years of age, good constitution, and robust health, who was accidentally wounded by a musket-ball; the ultimate result was a fistulous opening into the stomach, but with the perfect restoration of the digestive process, and all the other functions of the body. This enabled Dr. Beaumont to undertake a series of observations and experiments, which Dr. Combe has very ably introduced into the body of his work. For obvious reasons, such an investigation must be, more or less, obnoxious to the suspicion of fallacy, unless its results be supported by collateral testimony. In the case of Alexis St. Martin, however, this is remarkably striking, and we receive from Dr. Beaumout's history a confirmation of what we already regarded as facts, rather than any important addition to our previously acquired knowledge.

The following appear to me to be the most interesting of the facts that were thus ascertained. 1, That, the gastric juice is perceptibly acid, and possesses the property of coagulating albumen; that it is never found free in the stomach, but is always excited to discharge itself by the introduction of food or some other irritant. 2. That on the entrance of food into the stomach, the peristaltic motion becomes greater, arid its blood vessels so distended as to change the colour of the mucous membrane from a pale pink to a red: from the villi are then seen to arise innumerable minute lucid points, from which distils a colourless, and slightly viscid fluid which collects in drops, and trickles down the stomach till it is mingled with the food. This is the true gastric juice. 3. The contact not only of food, but of any mechanical irritant, such as the bulb of a thermometer, or other indigestible body, invariably gave rise to the exudation of the gastric fluid; but that in the latter cases, the secretion always ceased in a short time, as soon, apparently, as the organ could ascertain that the foreign body was one over which the gastric juice had no power. 4. That the motions of the stomach produce a constant churning of its contents, and admixture of food and gastric juice. 5. That chyme is homogeneous but variable in its colour and consistence. 6. That water, and most oilier fluids, are not affected by the gastric juice, but pass from the stomach soon after they have been received. 7. That the temperature of the stomach is about 100° of Fahr., but is not elevated by the injection of food.

Such are the only facts which I feel it necessary to enumerate in this place, I shall, hereafter, have occasion to advert to the observations, of Dr. Beaumont.

32. The mucous membrane of the small intestines secretes also a peculiar liquid, to which Haller gave the name of intestinal juice: the quantity that is formed in twenty-four hours, he estimated at eight pounds: and M. Majendie states, that if this mucous membrane be laid bare in a dog, and the layer of mucus absorbed by a sponge, it is renewed in a minute; and he says, that this observation may be repeated as often as we please, until the intestine becomes inflamed by the contact of the air and foreign bodies. It has never been submitted to an accurate analysis; it appears, however, to be viscous, thready, of a salt taste, and capable of reddening paper tinged with turnsol.