The sapid object is a kind of tangible object, and this is the reason why it does not require, in order to be perceived, any other medium than the body, for the Touch requires no other. The body in which is savour, is the gustable body, and the matter of savour is in fluid, and fluid is something tangible. Thus, were we in the water, and were any thing sweet cast into the water, we should be sensible of the sweetness, not through the water as a medium but, from its having been mixed with the water as with a potable fluid. Colour, however, is not thus made visible from having been mixed with anything, nor is it made visible by emanations; and as the medium, in the case of colours, plays no part and colour is the visible, so is savour the gustable. No object, however, without humidity can impart the sense of savour; and, therefore, every sapid object contains humidity, in an active or a potential state, as does salt; for salt is readily moistened and liquefied by contact with the tongue.
Now, vision is perceptive of the visible and the invisible (for darkness, although invisible, is still judged of by vision), and a very bright light (which is also invisible, although in a manner different from darkness), and so hearing is equally perceptive of sound and silence, of which that is audible and this inaudible, as well as a very loud sound, just as vision is of a very bright light; for as a very low sound is, in a certain sense, inaudible, so is a very loud and crashing sound. On the other hand, the term invisible, used absolutely, is analogous to the term impossible upon other subjects, and which may be significant of something generated without parts or with parts ill formed for their office, as an animal without feet, or a fruit without a kernel. So, too, the taste in its turn is perceptive both of what is sapid and insapid; and the insapid implies whatever has a faint or nauseous savour, or a savour altogether perversive of taste. The potable and the impotable seem alike to be the origin of taste, for they both are sapid; but then the first has a nauseous savour, and is perversive of taste, while the last is genial to the sense; the potable is common, besides, to the touch and taste. Since whatever is sapid is humid, it follows that the organ of taste may neither be humid really, nor yet be incapable of becoming humid; for the taste suffers impression by the sapid body, in so far as it is sapid. It is, therefore, necessary that the sentient organ, if not moist, should, for its function, be capable of becoming so: and, as proof of this, the tongue, when very dry or very moist, is not sensible of sapid impressions—as in the former instance, it is a tangible rather than a sapid impression which is made by a fluid when first tasted; and when very moist, it is sensible only of the fluid already present, just as it happens when, after tasting something pungent, we proceed to taste a different fluid. It is thus that all savours appear to the sick to be bitter, because the tongue, with which they taste, is charged with a moisture having that savour.
Kinds of savour are, like shades of colour, simple when in broad contrast—as the sweet and bitter with their sequences, of the former the oily and of the latter the brackish; and intermediate to these are the pungent, rough, astringent, and sour, which seem to include almost all the varieties of savour.
In fine, the sapid sense, when in potentiality, is such as is the sapid object; and the sapid object, when in reality, is productive, in the sense, of its own savour.