Plutarch Quaestiones Convivales 6.2.2

[2] I must confess this discourse seemed to carry in it some shadow of reason and probability; but in the main it is directly repugnant to the chief end of nature, to which appetite directs every animal. For that makes it desire a supply of what they stand in need of, and avoid a defect of their proper food. Now to deny that this very thing, which principally distinguishes an animate creature from an inanimate, conduces to the preservation and duration of such a creature, being that which craves and receives those things which the body needs to supply its wants, and, on the contrary, to suppose that such an appetite arises from the transfiguration or the greater or lesser size of the pores, is an absurdity worthy only of such as have no regard at all for Nature. Besides, it is absurd to think that a body through the want of natural heat should be chilled, and should not in like manner hunger and thirst through the want of natural moisture and nourishment. And yet this is more absurd, that Nature when overcharged should desire to disburden herself, and yet should not require to be filled on account of emptiness, but on account of some affection or other, I know not what. Moreover, these needs and supplies in relation to animals have some resemblance to those we see in husbandry. There are a great many like qualities and like provisions on both sides. For in a drought we water our grounds, and in case of excessive heat, we frequently make use of moderate coolers; and when our fruits are too cold, we endeavor to preserve and cherish them, by covering and making fences about them. And for such things as are out of the reach of human power, we implore the assistance of the Gods, that is, to send us softening dews, sunshines qualified with moderate winds; that so Nature, being always desirous of a due mixture, may have her wants supplied. And for this reason I presume it was that nourishment is called τροφή (from τηροῦν), because it watches and preserves Nature. Now Nature is preserved in plants, which are destitute of sense, by the favorable influence of the circumambient air (as Empedocles says), moistening them in such a measure as is most agreeable to their nature. But as for us men, our appetites prompt us on to the chase and pursuance of whatsoever is wanting to our natural temperament.

Now let us pass to the examination of the truth of the arguments that seem to favor the contrary opinion. And for the first, I suppose that those meats that are palatable and of a quick and sharp taste do not beget in us an appetite, but rather bite and fret those parts that receive the nourishment, as we find that scratching the skin causes itching. And supposing we should grant that this affection or disposition is the very thing which we call the appetite, it is probable that, by the operation of such kind of food as this, the nourishment may be made small, and so much of it as is convenient for Nature severed from the rest, so that the indigency proceeds not from the transmutation, but front the evacuation and purgation of the passages. For sharp, tart, and salt things grate the inward matter, and by dispersing of it cause digestion, so that by the concoctions of the old there may arise an appetite for new. Nor does the cessation of thirst after a bath spring from the different position of the passages, but from a new supply of moisture received into the flesh, and conveyed from thence to them also. And vomiting, by throwing off whatever is disagreeable to Nature, puts her in a capacity of enjoying what is most suitable for her. For thirst does not call for a superfluity of moisture, but only for so much as sufficeth Nature; and therefore, though a man had plenty of disagreeable and unnatural moisture, yet he wants still, for that stops the course of the natural, which Nature is desirous of, and hinders a due mixture and temperament, till it be cast out and the passages receive what is most proper and convenient for them. Moreover, a fever forces all the moisture downward; and the middle parts being in a flame, it all retires thither, and there is shut up and forcibly detained. And therefore it is usual with a great many to vomit, by reason of the density of the inward parts squeezing out the moisture, and likewise to thirst, by reason of the poor and dry state the rest of the body is in. But after the violence of the distemper is once abated, and the raging heat hath left the middle parts, the moisture begins to disperse itself again; and according to its natural motion, by a speedy conveyance into all the parts, it refreshes the entrails, softens and makes tender the dry and parched flesh. Very often also it causes sweat, and then the defect which occasioned thirst ceases; for the moisture leaving that part of the body wherein it was forcibly detained, and out of which it hardly made an escape, retires to the place where it is wanted. For as it fares with a garden wherein there is a large well,—if nobody draw thereof and water it, the herbs must needs wither and die,—so it fares with a body; if all the moisture be contracted into one part, it is no wonder if the rest be in want and dry, till it is diffused again over the other limbs. Just so it happens to persons in a fever, after the heat of the disease is over, and likewise to those who go to sleep thirsty. For in these, sleep draws the moisture out of the middle parts, and equally distributes it amongst the rest, satisfying them all. But, I pray, what kind of transfiguration of the passages is this which causes hunger and thirst? For my part, I know no other distinction of the passages but in respect of their number, or that some of them are shut, others open. As for those that are shut, they can neither receive meat nor drink; and as for those that are open, they make an empty space, which is nothing but a want of that which Nature requires. Thus, sir, when men dye cloth, the liquor in which they dip it hath very sharp and abstersive particles; which, consuming and scouring off all the matter that filled the pores, make the cloth more apt to receive the dye, because its pores are empty and want something to fill them up.