As the pleasures of taste are in general greater than those of feeling, and the pains in general less, it follows that the ideas which are affixed to the several words expressing the several pleasant and unpleasant tastes, will be of a middle nature in respect of the ideas generated by tangible impressions; and lie between the ideas of the pains of feeling, and those of its pleasures.
Agreeably to this, it seems very difficult, or even impossible, to excite a genuine vivid miniature of an acid, sweet, salt, or bitter taste, by the mere force of imagination. However, the vibrations peculiar to each of these leave such vestiges of themselves, such an effect in the tongue, and corresponding parts of the brain, as, upon tasting the qualities themselves, at once to bring up the names whereby they are expressed, with many other associated circumstances, particularly the visible appearances of the bodies endued with these qualities. And these vestiges may be called ideas. Analogy leads us also to conclude, as before observed under feeling, that some faint vestiges or ideas must be raised in the parts of the brain corresponding to the tongue, upon the mere passage of each word, that expresses a remarkable taste, over the ear. And, when the imagination is assisted by the actual sight or smell of a highly grateful food, we seem able to raise an idea of a perceptible magnitude. This is confirmed by the manifest effect exerted upon the mouth, and its glands, in such cases.
The sight of what we eat or drink seems also, in several instances, to enable us to judge more accurately of the taste and flavour; which ought to be effected, according to this theory, by raising small ideas of the taste and flavour, and magnifying the real impression in consequence thereof. For an actual impression must excite vibrations considerably different, according to the difference in the previous ones; and where the previous ones are of the same kind with those impressed, the last must be magnified.
The motions dependent on the sensations of the tongue, and alimentary duct, may be thus enumerated: suction, mastication, deglutition, the distortion of the mouth and face in consequence of nauseous tastes, the peristaltic motion of the stomach and bowels, vomiting, ructus, hiccough, spasms, and violent motions in the bowels, the motions which empty the neighbouring glands, and the expulsion of the fæces.
First, then, Suction in new-born children appears to depend
