Galen's Commentaries on the Aphorisms of Hippocrates

Aristotle said that it [the innate heat] flees because of the coldness surrounding it from without, just as again in summer it extends itself toward what is akin to it; and thus it happens that its substance is indeed dissolved and dissipated in the summer time, but in the winter it is contained and restrained, and withdraws into the depth. For this reason, therefore, concoctions, sanguifications, and nutritions are better at these times. He added also another thing happening to them: namely, that sleeps become very long, on account of the length of the nights, which itself contributes not a little to the works of nature. As for what is added at the end, "The ages and athletes are proof," it is put forward as an argument that the most nourishment is necessary where heat superabounds. For children, because they have the most heat, for that reason both need more things and concoct more things. Athletes, however, because they increase their native heat through exercises, can for that reason enjoy much nourishment. We have therefore sufficiently explained what is said in the aphorism.

But if someone should examine the truth about these things more diligently, let him not extend the discourse to all animals, but let him except those that live in dens. For these, when they hide themselves away, do not need very much nourishment, since they can even endure without food. And if we were to suppose that they used as much food as they did before they were hidden, they would concoct it poorly. For what happens to humans washed with cold water, that also happens to animals in winter. It happens to humans who are bathed with cold water that, if they have a weak body, they are chilled and harmed. But if it be robust, first indeed the innate heat flees to the interior and collects itself, but afterwards, returning to the exterior, it becomes much stronger than it was before. Thus also for those animals which are then naturally colder, their innate heat is overcome by the winter cold, to such an extent that it is almost extinguished; wherefore many of them appear like the dead when they lie in their dens without sense or motion, and some indeed die entirely in this very state.

But those which abound in very much blood and heat suffer such a thing in winter as happens to strong bodies washed with cold water; for their heat collects itself to the interior (not, by Jove, because the flesh flees to these parts, having abandoned its primary seat), but the spirit along with the blood. Now there were three bodies which filled out the substance of our primary nature: spirit, blood, and airy moisture, from which in the first origin (as we said in the books On Semen) the more solid parts of the animal are made, but soon growth and nutrition are added to these. Therefore, that we concoct food better in winter, with the blood and spirit receding to the depth of the body, is manifest to everyone. Hippocrates, therefore, says not only this itself, but that it is beneficial to take more food. For at these times, he says—that is, in winter and in spring—more foods are to be given. But yet, if little flows out and is breathed out to the exterior in winter time, very much nourishment is not necessary for bodies, since nutrition is the replenishment of that which is evacuated. It is necessary, therefore, that the quantity of nourishment be proportional to the quantity of that which is breathed out. That it is true, therefore, that some in winter not only concoct food better, but also that those taking little are chilled and thus harmed, whereas if they take more, they fall into no plethoric diseases, the event itself shows manifestly.

But let the inquiry into the cause be proposed for everyone in common, for such an inquiry does not fatigue Hippocrates as much as it does all others. And so there is no one who does not agree that the bodies of animals are breathed out by that breathing-out which occurs through the pores hidden from the senses. For they come to this for the reason that they need nourishment, because they are evacuated. For if nothing flowed out from our bodies, but an equal mass of substance were always preserved, there would be no necessity for nourishment. But you, observe whether in this part the reasoning is indeed inexplicable to all others, but to Hippocrates alone, and—