The pleasures of the taste, considered as extending itself from the mouth through the whole alimentary duct, are very considerable, and frequently repeated; they must therefore be one chief means, by which pleasurable states are introduced into the brain, and nervous system. These pleasurable states must, after some time, leave miniatures of themselves, sufficiently strong to be called up upon slight occasions, viz. from a variety of associations with the common visible and audible objects, and to illuminate these, and their ideas. When groups of these miniatures have been long and closely connected with particular objects, they coalesce into one complex idea, appearing, however, to be a simple one; and so begin to be transferred upon other objects, and even upon tastes back again, and so on without limits. And from this way of reasoning it may now appear, that a great part of our intellectual pleasures are ultimately deducible from those of taste; and that one principal final cause of the greatness and constant recurrency of these pleasures, from our first infancy to the extremity of old age, is to introduce and keep up pleasurable states in the brain, and to connect them with foreign objects.
The social pleasures seem, in a particular manner, to be derived from this source; since it has been customary in all ages and nations, and is, in a manner, necessary, that we should enjoy the pleasures of taste in conjunction with our relatives, friends, and neighbours.
In like manner nauseous tastes, and painful impressions upon the alimentary duct, give rise and strength to mental pains. The most common of these painful impressions is that from excess, and the consequent indigestion. This excites and supports those uneasy states, which attend upon melancholy, fear, and sorrow.
It appears also to me, that these states are introduced, in a great degree, during sleep, during the frightful dreams, agitations, and oppressions, that excess in diet occasions in the night. These dreams and disorders are often forgotten; but the uneasy states of body, which then happen, leave vestiges of themselves, which increase in number and strength every day from the continuance of the cause, till at last they are ready to be called up in crowds upon slight occasions, and the unhappy person is unexpectedly, and at once, as it were, seized with a great degree of the hypochondriac distemper, the obvious cause appearing no ways proportionable to the effect. And thus it may appear, that there ought to be a great reciprocal influence between the mind and alimentary duct, agreeably to common observation; which is farther confirmed by the very large number of nerves distributed there.
