Plutarch Quaestiones Convivales 8.9.2

[2] And Diogenianus added, that even the passions and diseases of the mind go on in the same old road that formerly they did; and yet the viciousness of our inclination is exceedingly prone to variety, and our mind is mistress of itself, and can, if it please, easily change and alter. Yet all her inordinate motions have some sort of order, and the soul hath bounds to her passions, as the sea to her overflowing. And there is no sort of vice now among us which was not practised by the ancients. There are a thousand differences of appetites and various motions of fear; the schemes of grief and pleasure are innumerable: How then should the body be subject to new diseases, since it hath not, like the soul, the principle of its own alteration in itself, but by common causes is joined to Nature, and receives a temperature whose infinite variety of alterations is confined to certain bounds, like a ship rolling and tossing in a circle about its anchor. Now there can be no disease without some cause, it being against the laws of Nature that any thing should be without a cause. Now it will be very hard to find a new cause, unless we fancy some strange air, water, or food never tasted by the ancients, should descend to us out of other worlds or intermundane spaces. For we contract diseases from those very things which preserve our life; since there are no peculiar seeds of diseases, but the disagreement of their juices to our bodies, or our excess in using them, disturbs nature. These disturbances have still the very same differences, though now and then called by new names. For names depend on custom, but the passions on Nature; and these being constant and those variable, this mistake has arisen. As, in the parts of a speech and the syntax of the words, it is possible for some new sort of barbarism or solecism suddenly to arise; so the temperature of the body hath certain deviations and corruptions into which it may fall, those things which are against and hurtful to Nature being in some sort contained in Nature herself. The mythographers are in this particular very ingenious, for they say that monstrous uncouth animals were produced in the time of the Giants’ war, the moon being out of its course, and not rising where it used to do. And those who think Nature produces new diseases like monsters, and yet give neither likely nor unlikely reasons of the change, err, as I imagine, my dear Philo, in taking a less or a greater degree of the same disease to be a different disease. The intension or increase of a thing makes it more or greater, but does not make the subject of another kind. Thus the elephantiasis, being an intense scabbiness, is not a new kind; nor is the water-dread distinguished from other melancholic and stomachical affections but by the degree. And I wonder we did not observe that Homer was acquainted with this disease, for it is evident that he calls a dog rabid from the very same rage with which when men are possessed they are said to be mad.