The Art of Medicine

F Again, other parts of this kind are uniform, simple, and of the same genus, reason, and nature. Because they are divided everywhere into similar parts, they are called homoiomeres similar-parted by the Greeks; such are nerves, flesh, and bones. For every part of a nerve has the nature of a nerve and retains its nomenclature; the same is the reasoning for all other simple parts. But other parts arise from simple ones, and are of different reasoning and nature among themselves; therefore, the Greeks call them heterogeneis dissimilar-parted, and we call them multiform and parts of a different genus, such as foot, hand, eye, which (as I was just saying) can be absent. There are some among our own who call the former "dissimilar" and the latter "similar." Furthermore, G among simple parts, some act primarily, such as the humor crystalloides crystalline humor in the eye; some serve those that act primarily, such as other humors of the eye and the tunics. Differences are taken from the action, affection, and duty of all these. Therefore, it must be considered, not only in the genus of substance but in the genera of all other things, what each thing is born to do and what to suffer, as Galen teaches in the book on the method of healing. For substantial differences are taken from these as well: as the task of heat is to gather similar things and sequester dissimilar ones; of blackness, to contract the vision; of whiteness, to dissipate it. Therefore, the differences that are derived from these are substantial. H