Plutarch's Rules for the Preservation of Health (14-15)

ZEUXIPPUS. It is absurd, as Democritus says, by the croaking of ravens, the crowing of a cock, or the wallowing of a sow in the mire, carefully to observe the signs of windy or rainy weather, and not to prevent and guard ourselves against the motions and fluctuations of our bodies or the indication of a distemper, nor to understand the signs of a storm which is just ready to break forth within ourselves. So that we are not only to observe our bodies as to meat and exercise, whether they use them more sluggishly or unwillingly than they were wont; or whether we be more thirsty and hungry than we use to be; but we are also to take care as to our sleep, whether it be continued and easy, or whether it be irregular and convulsive. For absurd dreams and irregular and unusual fantasies show either abundance or thickness of humors, or else a disturbance of the spirits within. For the motions of the soul show that the body is nigh a distemper. For there are despondencies of mind and fears that are without reason or any apparent cause, which extinguish our hopes on a sudden. Some there are that are sharp and prone to anger, whom a little thing makes sad; and these cry and are in great trouble when ill vapors and fumes meet together and (as Plato says) are intermingled in the ways and passages of the soul. Wherefore those to whom such things happen must consider and remember, that even if there be nothing spiritual, there is some bodily cause which needs to be brought away and purged.

ZEUXIPPUS. Besides, it is profitable for him who visits his friends in their sickness to enquire after the causes of it. Let us not sophistically or impertinently discourse about lodgements, irruptions of blood, and commonplaces, merely to show our skill in the terms of art which are used in medicine. But when we have with diligence heard such trivial and common things discoursed of as fulness or emptiness, weariness, lack of sleep, and (above all) the diet which the patient kept before he fell sick, then, — as Plato used to ask himself, after the miscarriage of other men he had been with, Am not I also such a one? — so ought we to take care by our neighbor’s misfortunes, and diligently to beware that we do not fall into them, and afterwards cry out upon our sick-bed, How precious above all other things is health! When another is in sickness, let it teach us how valuable a treasure health is, which we ought to keep and preserve with all possible care. Neither will it be amiss for every man to look into his own diet. If therefore we have been eating, drinking, laboring, or doing any thing to excess, and our bodies give us no suspicion or hint of a distemper, yet ought we nevertheless to stand upon our guard and take care of ourselves, — if it be after venery and labor, by giving of ourselves rest and quiet; if after drinking of wine and feasting, by drinking of water; but especially, after we have fed on flesh or solid meats or eaten divers things, by abstinence, that we may leave no superfluity in our bodies; for these very things, as they are the cause of many diseases, likewise administer matter and force to other causes. Wherefore it was very well said, that to eat — but not to satiety, to labor — but not to weariness, and to keep in nature, are of all things the most healthful. For intemperance in venery takes away that by which vigor our nourishment is elaborated, and causes more superfluity and redundance.