Is it because the winter finds the body in a very moist state, and also the change from great heat is violent and not gradual, because the autumn as well as the summer has been hot, and so acute diseases are caused in some persons, if they have no rarity in their bodies (for in such persons the moist excretions tend to collect in the upper part of the body, because these parts provide room for them, whereas the lower parts differ in this respect)?