Plutarch Quaestiones Convivales 6.2.1

[1] AFTER these things were spoke, Philo the physician started the first question, asserting that thirst did not arise from the want of nourishment, but from the different transfiguration of certain passages. For, says he, this may be made evident, partly from what we see happens to those that thirst in the night, who, if sleep chance to steal upon them, though they did not drink before, are yet rid of their thirst; partly from persons in a fever, who, as soon as the disease abates or is removed, thirst no more. Nay, a great many men, after they have bathed or vomited, perceive presently that their thirst is gone; yet none of these add any thing to their former moisture, but only the transfiguration of the pores causeth a new order and disposition. And this is more evident in hunger; for many sick persons, at the same time when they have the greatest need of meat, have no stomach. Others, after they have filled their bellies, have the same stomachs, and their appetites are rather increased than abated. There are a great many besides who loathe all sorts of diet, yet by taking of a pickled olive or caper recover and confirm their lost appetites. This doth clearly evince, that hunger proceeds from some change in the pores, and not from any want of sustenance, forasmuch as such kind of food lessens the defect by adding food, but increases the hunger; and the pleasing relish and poignancy of such pickles, by binding and straitening the mouth of the ventricle, and again by opening and loosening of it, beget in it a convenient disposition to receive meat, which we call by the name of appetite.