A species of willow native to Europe and western and central Asia. The name derives from the white tone to the undersides of the leaves. Hippocrates wrote in the 5th century BC about a bitter powder extracted from willow bark that could ease aches and pains and reduce fevers. This remedy is also mentioned in texts from ancient Egypt, Sumer, and Assyria. The Reverend Edmund Stone, a vicar from Chipping Norton in Oxfordshire England, noted in 1763 that willow bark was effective in reducing a fever. The bark is often macerated in ethanol to produce a tincture. The active extract of the bark, called salicin, after the Latin name Salix, was isolated to its crystalline form in 1828 by Henri Leroux, a French pharmacist, and Raffaele Piria, an Italian chemist, who then succeeded in separating out the acid in its pure state. Salicin, like aspirin, is a chemical derivative of salicylic acid.