The gastric juice is also powerfully _antiseptic_; that is to say, it prevents animal substances from becoming putrid, and even renders sweet such as have advanced a considerable way towards putrefaction. Dr Beaumont mentions that the pure juice will keep unchanged for almost any length of time, and according to Spallanzani meat may be preserved in it without taint for five or six weeks, or even longer. This antiseptic tendency of the gastric fluid, accounts for the circumstance that little or no mischief results from the common practice among epicures, of not making use of game till the putrefactive process is advanced farther than is agreeable to the palates of the uninitiated. The qualities of the gastric juice are so directly adapted to the natural food of the animal, that flesh introduced into the stomach of an ox or a sheep, for example, undergoes scarcely any change; while vegetable food, on the other hand, remains equally undigested in that of a beast of prey. Thus, “when a hawk or an owl has swallowed a small bird, in the stomach of which have been seeds, these bodies are not dissolved by the gastric fluid,”[28] but pass through the intestines unaltered. Man, the dog, and some other creatures, possess the power of digesting all sorts of aliment, whether vegetable or animal, and are hence called omnivorous or all-eating; but even in them, the relation which the properties of the gastric juice bear to the qualities of the food chiefly or exclusively used is so close, that, when a widely different kind is suddenly resorted to, indigestion is the almost inevitable consequence,--because then the gastric juice has not had time to acquire its requisite adaptation to the new materials on which it has to act. Hence also the danger arising from suddenly eating a full meal after having been long famished. The stomach accustomed for a time to the smallest quantity, is no longer able to provide gastric juice sufficient for the purposes of digestion; and being irritated by continued craving, its secretions are vitiated and its sensibility exalted to such a degree as to require the wisest management to enable it to regain its healthy tone. The gastric juice of carnivorous animals differs even in its chemical constitution from that of the herbivorous; a circumstance which accounts for the difference observed in their action. In the former, such as that of birds of prey, serpents, and fishes, no free or uncombined acid can be detected, although it is invariably found in the gastric fluid of vegetable-eaters. In crows and dogs, on the other hand, and such animals as can live on either kind of aliment, it is never acid except when they have been fed _chiefly_ on grain or plants. In man, the same relation has, by numerous experiments, been ascertained to exist.