It has already been remarked, that, on pushing back the valve which filled up the opening into the stomach, the cavity within became visible to a considerable extent; and that when St Martin lay over for a time on the left side, a portion of the villous coat, large enough to exhibit several inches of its surface, generally protruded. Owing to these circumstances, Dr Beaumont could easily observe what changes occurred, both when food was swallowed in the usual way, and when it was introduced at the opening left by the wound. Accordingly, on examining the surface of the villous coat with a magnifying glass, he perceived an immediate change of appearance ensue whenever any aliment was brought into contact with it. The action of the neighbouring bloodvessels was instantly increased, and their branches dilated so as to admit the red blood much more freely than before. The colour of the membrane consequently changed from a pale pink to a deeper red, the vermicular or _worm-like_ motions of the stomach became excited, and innumerable minute lucid points and very fine nervous and vascular papillæ could be seen arising from the villous coat, from which distilled a pure, colourless, and slightly viscid fluid, which collected in drops on the very point of the papillæ and trickled down the sides of the stomach till it mingled with the food. This afterwards proved to be the secretion peculiar to that organ, or, in other words, the true _gastric juice_; the mucous fluid secreted by the follicles, which some have mistaken for it, is not only more viscid, but wants altogether the acid character by which it is generally distinguished. Pursuing his experiments, Dr Beaumont then found that 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 from these vascular papillæ; 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. But the small quantity obtainable in this way is perhaps more pure and free from admixture, and therefore better adapted for examination, than any which can be procured under any other circumstances.