The mucous coat appears on examination to be so entirely continuous with the skin, that no line of demarcation can be detected between them either at the mouth or at the anus. In structure they greatly resemble each other, and the sympathy between them is well known to be very rapid and intimate. Eruptions on the skin, for example, are almost always owing to disorder of the digestive organs; and bowel-complaint, on the other hand, is often produced by a sudden chill on the surface. In like manner, in enormous eaters like those formerly mentioned, an immense exhalation takes place from both the skin and the bowels, and in many instances the one supplies the place of the other in a considerable degree. We have seen, moreover, that in the lowest tribes of animals, the digesting surfaces and skin are not only undistinguishable, but actually convertible into each other by the simple process of turning the animal inside out, when each will perform the function of the other as well as if it had never done any thing else. In common with the skin, too, the mucous coat is charged with the double function of _excretion_ and _absorption_. For the former, it is eminently fitted by its plentiful supply of blood, and by the great number of minute vessels ramified on its surface, from the extremities of which the excretion takes place. It is by this channel that much of the waste matter requiring to be removed from the body is thrown out. Being poured into the cavity of the intestine from the small arterial branches, it mixes there with the indigestible residuum of the food and bile, and, united with them, forms the common fæces or excrement. When the blood is suddenly repelled from the surface by a chill, and thrown in upon these vessels in large quantity, the natural excretion is sometimes increased to such an extent as to constitute bowel-complaint; while at other times, that peculiar form of action is induced which constitutes inflammation. The local stimulus of some kinds of food, and of many medical substances, also excites the secretion to unusual activity. Salts, for instance, have this effect, and thus often _produce_ numerous fluid evacuations, the substance or materials of which did not before exist in the bowels; and hence the mistake into which many fall, of taking more medicine on the ground of this effect proving that much stuff was lodged in the bowels--when, in fact, it was not only removed but _created_ by the physic. It is from exciting a fluid discharge of this description, that saline purgatives are so useful for lowering the tone of the system when that is required; but, for the same reason, they are most improper where relaxation and debility already exist. In Asiatic cholera, almost the whole fluids of the body are carried off by this channel, leaving the blood too thick in consistence to circulate longer through the smaller vessels.