 The major turning point for salicylate medicines came in 1763, when a letter from English chaplain Edward Stone was read at a meeting of the Royal Society, describing the dramatic power of willow bark extract to cure ague — an ill-defined constellation of symptoms, including intermittent fever, pain, and fatigue, that primarily referred to malaria. Inspired by the doctrine of signatures to search for a treatment for agues near the brackish waters that were known to cause it, Stone had tasted the bark of a willow tree in 1758 and noticed an astringency reminiscent of the standard — and expensive — ague cure of Peruvian bark. He collected, dried, and powdered a substantial amount of willow bark, and over the next five years tested it on a number of people sick with fever and agues. In his letter, Stone reported consistent success, describing willow extract's effects as identical to Peruvian bark, though a little less potent. (In fact, the active ingredient of Peruvian bark was quinine, which attacked the infectious cause of malaria, while the active ingredient of willow extract, salicin, relieved the symptoms of malaria but could not cure it.) Stone's letter (mistakenly attributed to Edmund rather than Edward Stone) was printed in Philosophical Transactions, and by the end of the 18th century willow was gaining popularity as an inexpensive substitute for Peruvian bark.
