Word of the Day:

: a theory in old natural philosophy: the outward appearance of a body signals its special properties (as of magic or healing virtue) and there is a relationship between the outward qualities of a medicinal object and the diseases against which it is effective

Among the documents are the notes of a 17th-century physician, who discusses his use of the doctrine of signatures to determine which medicinal plants to use for which ailments.

"Lungwort (Pulmonaria) is legacy from the ancient doctrine of signatures, which included a belief that a plant resembling a part of the anatomy had medicinal properties for that part. The broad, elongated white-spotted leaves of this plant were thought to resemble the lung and used to treat pulmonary ailments." - From an article by Julie Finucane in The Argus-Press (Owosso, Michigan), November 12, 2012

The idea that a plant's appearance might give clues to its healing capacities is an old one (it was advocated by the Roman scholar Pliny the Elder). The word "signature" (from Latin "signare," meaning "to sign or mark") has been used to refer to a plant feature that suggests its potential medicinal value since the 1600s. For instance, bloodroot, with its red sap, was considered effective against blood disorders, and liverwort, which has a three-lobed leaf that resembles the liver, was used to treat-you guessed it-liver diseases. Many examples of the variety of herbal medicine espoused by the doctrine of signatures can be found in Nicholas Culpeper's pseudo-scientific A Physicall Directory, published in 1649.