perhaps less and less, perpetually, in going from the stomach to the rectum. The sensibility of the alimentary duct is probably of the same kind with, and not much greater in degree than, that of the internal surfaces of the gall-bladder, urinary bladder, pelvis, ureters, and, in general, of the secretory and excretory vessels, and of the receptacles belonging to the glands. But I refer the sensations of this duct to the taste, on account of their connexion with those of the tongue, in respect of their causes, uses, and effects.
As to the particular and superior powers of the tongue, they may, in part, be deduced from the number and largeness of its papillæ, and from their rising above the surface in living persons more remarkably than any other sentient papillæ in the whole body, so as to be extreme parts in an eminent degree. To which we ought perhaps to add, that the tip and sides, in which the taste is most exquisite, are also extreme parts. But there may be likewise a different peculiar distribution, and other causes of an exquisite sensibility, in the nerves of the tongue.
It deserves notice here, that the friction of the tongue against the palate is necessary, in order to excite the tastes of the aliments, which we masticate, in perfection. This practice is analogous to that of rubbing the ends of the fingers upon such bodies as we examine accurately by feeling; and both appear suitable to the notion of vibrations; also to that of the distention and erection of the sentient papillæ: which may even be seen in the papillæ of the tongue.
It has been observed, that bitters and acids applied to funguses of the brain, and even to issues upon the vertex, have sometimes occasioned the sensations of the tastes respectively arising from the same bitters and acids, when applied to the tongue. This may perhaps be solved by supposing, that the bitters and acids, when applied to the nerves of the fifth pair, in the funguses of the brain, and to those of the seventh, or perhaps of the fifth also, in the issues (for the fifth pair may transmit some branches to the external integuments from the dura mater, at the vertex), send up their own specific vibrations into those regions of the brain, which are the peculiar residence of tastes, i.e. to the regions which correspond to the fifth pair, according to some anatomists. And these sensations may even afford some evidence, that the fifth pair, not the ninth, supplies the tongue with sensory nerves.
Here I observe, first, that heating any sapid liquid increases its taste, especially if it be of the bitter, spirituous, or acrid kind; and, conversely, that the impression of such tastes generates a
