Michael Maier cites Ficino in his discussion of the philosopher's stone

Marsilio Ficino, in his book of preserving the health of students, recommends sucking the milk of a beautiful young woman, others recommend the eating of Vipers' flesh, but these remedies are more troublesome than Old Age itself, & could not be obtained by one in a thousand, although their effect should be certain. Paracelsus, in his book of Long life, says a sick man may attract to himself the Health of another by imagination only, & so an Old Man may gather Youth. But in this he seems rather to be guided by his fancy than experience. It is certain that the people called Psyllis, with their double pupils, & witches by their very aspect bewitch Cattle & Children, according to Virgil: "Nescio quis teneros oculus mihi fascinet agnos." These things are done without contact. But as for the Tree which is to restore the Old Man, the fruit of it is sweet, red & full ripe, turning into the best blood, as being easy of digestion, & affording the best Nutriment, leaving nothing in the body that is faecal or superfluous. But the Old Man abound with white Phlegm, has white Hair & Complection, which Humours, Color, & Hair are changed into that Red which appears in Youth & Vigor.Therefore the Philosophers say their Stone is first an Old Man that is white, & then a Young man, which is Red. And they say further that the Old Man must be placed together with the Tree, not in the open air, but in a House, & that not dry, but moist, with Dew. It may seem strange that Trees should spring & grow in a close place, but if it be moist, there is no doubt of their continuance. For the Nutriment of a Tree is moisture & Airy Earth that is fat, which can ascend into the body & Bough, & these produce leaves, blossoms & fruit. In which Natural work then is the concurrence of all the Elements.