Nor is it only in the touch that smooth bodies cause positive pleasure by relaxation. In the smell and taste, we find all things agreeable to them, and which are commonly called sweet, to be of a smooth nature, and that they all evidently tend to relax their respective sensories. Let us first consider the taste. Since it is most easy to inquire into the property of liquids, and since all things seem to want a fluid vehicle to make them tasted at all, I intend rather to consider the liquid than the solid parts of our food. The vehicles of all tastes are water and oil. And what determines the taste is some salt, which affects variously according to its nature, or its manner of being combined with other things. Water and oil, simply considered, are capable of giving some pleasure to the taste. Water, when simple, is insipid, inodorous, colorless, and smooth; it is found, when not cold, to be a great resolver of spasms, and lubricator of the fibres; this power it probably owes to its smoothness. For as fluidity depends, according to the most general opinion, on the roundness, smoothness, and weak cohesion of the component parts of any body, and as water acts merely as a simple fluid, it follows that the cause of its fluidity is likewise the cause of its relaxing quality, namely, the smoothness and slippery texture of its parts. The other fluid vehicle of tastes is oil. This too, when simple, is insipid, inodorous, colorless, and smooth to the touch and taste. It is smoother than water, and in many cases yet more relaxing. Oil is in some degree pleasant to the eye, the touch, and the taste, insipid as it is. Water is not so grateful; which I do not know on what principle to account for, other than that water is not so soft and smooth. Suppose that to this oil or water were added a certain quantity of a specific salt, which had a power of putting the nervous papill? of the tongue into a gentle vibratory motion; as suppose sugar dissolved in it. The smoothness of the oil and the vibratory power of the salt cause the sense we call sweetness. In all sweet bodies, sugar, or a substance very little different from sugar, is constantly f............