2009 Spring, Anthony Dias Blue, “Mixology: Gin & Tonic”, inDrinks, the Magazine of Fine Wine, Spirits, and Living, page 8:
Tonic water's active ingredient is quinine, a chemical compound derived from the bark of the cinchona tree, native to South America. This alkaloid has long been known to relieve the pain and fever of malaria and other tropical diseases, making it a staple "tonic" in warm-weather countries.
