Definition of DOS

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. Examples include the plants liverwort; snakeroot, an antidote for snake venom; lungwort; bloodroot; toothwort; and wormwood, to expel intestinal parasites. A theological justification was made for this philosopy: "It was reasoned that the Almighty must have set his sign upon the various means of curing disease which he provided."^[1] The concept is still reflected in the common names of some plants whose shapes and colors reminded herbalists of the parts of the body where they were thought to do good. Scientists see the doctrine of signatures as superstition. There is no scientific evidence that plant shapes and colors help in the discovery of medical uses of plants.
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Doctrine of Signatures the concept that the key to humanity's use of various plants was indicated by the form of the plant. The red sap of the bloodroot ( Sanguinaria canadensis ), for instance, was believed to cure diseases of the blood, while the fused leaves of boneset ( Eupatorium perfoliatum ) were used to heal broken bones. The concept was employed by the herbalists of the Renaissance, and was accepted until the latter part of the 19th cent. 
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A principle that assigns healing properties to plants on the basis of the association between their physical characteristics and those of the disease or the affected part of the body.
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A theory in old natural philosophy: the outward appearance of a body signalizes 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.
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