In Herbalism
The doctrine of signatures is a philosophy shared by herbalists from the time of Dioscurides and Galen. This doctrine states that herbs that resemble various parts of the body can be used to treat ailments of that part of the body. Although the doctrine of signatures was formalized in early modern times, the theme of natural objects' shapes having significance is a very old one and is not confined to Western thought. Examples include the plants liverwort; snakeroot, an antidote for snake venom; lungwort; bloodroot; toothwort; and wormwood, to expel intestinal parasites. The occasional resemblance of mandrake root to a human body has led to its being ascribed great significance (and supernatural powers) since ancient times and in many places. The 17th-century botanist and herbalist William Coles (1626–1662), author of The Art of Simpling and Adam in Eden, stated that walnuts were good for curing head ailments because in his opinion, "they Have the perfect Signatures of the Head". Regarding Hypericum, he wrote, "The little holes whereof the leaves of Saint Johns wort are full, doe resemble all the pores of the skin and therefore it is profitable for all hurts and wounds that can happen thereunto." Nicholas Culpeper's often-reprinted Complete Herbal takes the doctrine of signatures as common knowledge, and its influence can still be detected in modern herbal lore.
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