farther suppose, in both cases, that where the vibrations approach so near in frequency as to overrule each other, and produce one species only, there results a taste, or a colour, that resembles a primary one; whereas, if the vibrations differ so much in frequency, as that two or more principal species keep their own frequency, the taste, or colour generated from them, cannot be likened to any primary one.
Seventhly, That there are different species of vibrations, which yet all constitute sweet or bitter, I conjecture not only from the foregoing general reasoning, but also because there are both sweets and bitters in all the three kingdoms, animal, vegetable, and mineral. Thus milk, sugar, and saccharum Saturni, all yield a sweet taste; gall, aloes, and crystals of silver, all a bitter one.
Eighthly, Some differences of taste may arise from the different time required for the solution, and consequent activity, of the sapid particles, also from the different local effect which they may have upon the papillæ, when absorbed by their venous vessels, &c.
Ninthly, Very nauseous and stupefacient tastes may perhaps arise from violent and irregular vibrations, and bear some analogy to the sensation, or want of it, impressed by the stroke of the torpedo.
Tenthly, It seems to deserve particular consideration here, that milk, and the flesh of certain domestic animals, yield tastes, which are naturally and originally pleasant, to a considerable degree, and yet not in excess, as sugar, and other very sweet bodies, are. For it is reasonable to conclude, that the particles of milk, and common flesh-meats, must agree very much in the strength and frequency of vibrations with the particles of our own solids and fluids. They may therefore just moderately increase the natural vibrations of the organ, when applied thereto, and enforced by suction, mastication, and friction of the tongue against the palate. For the same reasons we may guess, that the common diet of animals does not undergo very great changes, in respect of the vibratory motions of its particles, from its circulation, and consequent assimilation. However, there are some eminent instances to the contrary, especially in poisons. These last observations may be extended to vegetables, salutary and poisonous, respectively.
Eleventhly, Some acrid tastes, that of mustard for instance, affect the tip of the uvula, and the edge of the soft palate, in a particular manner. Now this may a little confirm the conjectures above made concerning the sensibility and irritability of extreme parts.
Twelfthly, It is easy to conceive, upon the principles of these papers, how sweets and bitters of an inferior degree should render those of a superior one less affecting, respectively, as they are found to do.
