first lie within the limits of pleasure, and afterwards pass into the limits of pain. And when the sight of food, or any other associated circumstance, increases the sense of hunger instantaneously, it may be conjectured to do so, in great measure, by increasing the contractions of the muscular coat of the stomach.
But the sensibility and irritability of the nerves of the tongue are also increased by hunger; for common aliments yield a very different taste, according as the person is satiated or hungry. And it is probable farther, that the nerves of the upper part of the bowels sympathize with those of the stomach in hunger; and increase the uneasy sensation, in violent degrees of it.
Let us now consider in what way food may be supposed to lessen this sensibility and irritability of the nerves of the tongue, stomach, and bowels; and how abstinence, bitters, wines, &c. may increase them, upon the principles of these papers.
First then, As the small absorbing vessels in the mouth, stomach, and bowels, must, after eating for some time, be saturated with alimentary particles, those that are now applied will scarce make any impression for want of a sufficient attraction.
Secondly, Such as are attracted cannot make any considerable difference of vibrations, because the vibrations which they are qualified to excite, do already take place. And these two remarks, put together, shew, that a person may relish a second kind of food after being satiated with a first.
Thirdly, The actions of mastication, deglutition, and digestion, exhaust the neighbouring glands and glandular receptacles of their liquids, and the neighbouring muscular fibres of their ready power of contracting: these parts are therefore no longer susceptible of a pleasurable state, or only in a low degree.
Fourthly, Abstinence reverses all these steps; in which, however, the perpetual affusion, dilution, and ablution of the saliva has a considerable share. And thus after a proper interval the organs return to a state of great sensibility and irritability.
Fifthly, Bitters and acids exhibited in a moderate degree seem gently to increase the vibratory motions, and raise them before the due time to the degree that corresponds to hunger. A small quantity of food has the same effect, also agreeable motions of mind, fresh air, exercise, and many other things. But if the bitters, acids, &c. be carried beyond a certain degree, they occasion pain or sickness, which is very agreeable to the doctrine of vibrations, as laid down in these papers.
Sixthly, In fevers, the mouth, fauces, œsophagus, and stomach, are hot, dry, inflamed, and incrusted. They are therefore preoccupied by vibrations of a kind quite different from those which attend hunger, and therefore exclude this state.
It may not be amiss to observe here, that the sensation of hunger is a guide and guard to the organs of digestion in a still more eminent degree, than the tastes of the several aliments.
