Theory of Signatures
Paracelsus, alchemist, defined the concept of the active principle (the component of a drug that has a therapeutic effect). He then developed the theory of signatures: the shape and colour of plants, animals, hands, etc., indicate their affinities and correspondence with other things, such as the organs. For example, "the root of Satyrion is formed like the genital organs of man" (Greek: Orchis = testis). "Accordingly it promises to restore a man's potency and sexual desire as if by magic."