Quinine is an alkaloid found in the bark of the cinchona tree. Used to treat malaria since the early 1600s, it was the best chemotherapeutic agent available to combat the disease until the 1920s. Malaria treatment by quinine marked the first successful use of a chemical compound against an infectious disease.

Variously called Jesuits' bark, cardinal's bark and sacred bark, the compound was first definitively used in 1630 by Jesuit missionaries in the Andes. However, a legend suggests an earlier use by the native population: an Indian with a high fever, lost in an Andean jungle, spotted a pool of stagnant water. When the water tasted bitter, he realized it had been contaminated by the surrounding quina-quina trees, and he thought he was poisoned. But his fever abated, and thereafter his village used extracts made from quina-quina bark to treat fevers. He had been suffering from malaria, and the...