Galen's Commentaries on the Aphorisms of Hippocrates

and is explicable to his followers. For nothing else formed the animal from its beginning, just as it did not increase it again, nor nourished it until death, except that innate heat of which we now speak. For this is the cause of all natural works. Because, indeed, it is most abundant in winter time, it therefore intensifies the appetite for food, increases concoctions, accumulates more blood, makes the body thicker, and provides that superfluities are excreted. But the surrounding heat [of summer] evacuates not only superfluities but all things equally, dissolving together both useless matter and those things which are contained in the body according to nature, through that which is called hidden evaporation by physicians, by which the innate heat operates. For the nature of animals is nothing else but this heat, according to the opinion of Hippocrates. Moreover, it has been shown by us in our commentaries on the natural powers that it not only desires, produces, and joins to individual parts their own natural nourishment, but also dissolves its superfluities; and the stronger the innate heat exists, the more the evaporation escapes the senses. And for this reason Diocles says that sweats are contrary to nature, since, if all things pertaining to the body were rightly administered and the nourishment subdued by nature, a sensible humor would never be excreted through the skin. For whatever men sweat out in baths, or through vehement exercises, or because of the summer heat, has its origin from violent causes. Therefore, all things are well administered in the body of an animal in winter time, provided the winter maintains a moderate state. For Hippocrates himself condemns immoderate intemperateness in what follows. Moreover, that all things are well administered in the body of an animal in winter time is evidenced by the stronger works of nature; for foods are concocted in the stomach because the innate heat is most abundant, and in longer sleeps superfluities are purged. Some are thoroughly refined through the skin; those indeed which are converted into vapors, through expiration; and those which have sufficient thickness, through the urine. For in these there is more sediment than in summer, besides the fact that the entire quantity of urine is sufficiently increased in winter; and indeed, bodies are more nourished and increase in flesh in winter, and they accumulate more of the best blood, unless they employ an altogether poor diet. For if you consider that winter, taking up our bodies when they have little blood in autumn and are thinned out, fills them with good humors and makes them thicker, from this (as I think) you will perceive the strength of the governing faculty, which is the innate heat. But unless this heat has abundant nourishment to enjoy, it will first be overcome by the surrounding cold, both by that which assails from without and by that which is drawn in through inspiration. Along with it, indeed, the concoction of foods will be weakened, as will the generation of the best blood, the nourishment of the animal's parts, and the expulsion of superfluities. But if it has as much nourishment as it can master, it will enjoy this copiously, and it will be increased more, and it will perfect all those things which we said before concerning the body of the animal. Indeed, that from the great amount of food offered, it is not only well processed in the stomach but also in the veins and the entire body of the animal, so that each animal is rendered more fleshy and abounds more in blood, men have discovered sufficiently by experience itself, not only in themselves but also in draft animals. For before the beginning of summer, around the last part of spring, they draw blood both from themselves and from those animals, because they recall to memory by what diseases they are seized when the summer heat suddenly comes upon them; for this heat further expands and diffuses the blood, and in a way causes it to boil over, so much so that what had hitherto been moderate can no longer be contained in the veins, but either bursts them or breaks out.