Various methods have been employed for procuring the gastric fluid in a state of purity. Pieces of dry sponge, inclosed in a small hollow perforated ball with a string attached to it, have been swallowed both by man and by inferior animals, and afterwards withdrawn to have the juice expressed from them. In some instances the stomachs of criminals and animals killed after fasting have been opened, and the secretion collected. At other times the juice has been procured by voluntary or artificial vomiting. None of these methods is equal to that employed by Dr Beaumont; but of the three the first is unquestionably the best, because, although no gastric juice previously exists, the very contact of the ball excites the secretion of a quantity sufficient to moisten the sponge. In the second mode of proceeding, any portion of juice secreted in consequence of a stimulus applied _after_ the stomach is opened, must necessarily be very small and rendered impure by the large admixture of mucus which it will contain; while, by the third method, as the gastric juice does not exist ready made in the stomach, either none but merely mucus will be procured, or it will be expelled mixed with the food or substance which had previously elicited its secretion. Gastric juice, in its purest form, and unmixed with any thing except the small portion of mucus from which it can never be obtained entirely free, is described by Dr Beaumont to be a clear transparent fluid, without smell, slightly saltish (probably from the admixture of mucus), and very perceptibly acid. Its taste, he says, resembles that of thin mucilaginous water, slightly acidulated with muriatic acid. It is readily diffusible in water, wine, or spirits, and effervesces slightly with alkalis--a direct proof of its acid nature. It coagulates albumen, and is powerfully antiseptic, checking the progress of putrefaction in meat. When pure it will keep for many months, but when diluted with saliva it becomes fetid in a few days. According to Professor Dunglison, to whom some was submitted by Dr Beaumont for analysis, it contains free _muriatic_ and _acetic_ acids,--_phosphates_ and _muriates_ with bases of _potassa_, _soda_, _magnesia_, and _lime_,--together with an animal matter soluble in cold but insoluble in hot water. Tiedemann and Gmelin, again, describe it as composed principally of _muriatic_ and _acetic_ acids, mucus, saliva, _osmazome_, _muriate_, and _sulphate of soda_, with little or no albumen; and, according to the same physiologists, the proportion of acid is always greatest when vegetables or other substances of difficult digestion constitute the chief part of the diet. Other chemists give an analysis somewhat different from either of these; a circumstance which was, indeed, to be expected, considering not only the differences caused by variations of diet and of health, but also the necessarily different degrees of purity of the fluid submitted to examination.