WHAT IS QUININE AND WHY IS IT IN TONIC WATER?
Quinine is a drug that comes from the bark of the cinchona tree, which grows in the rain forest. It was first brought to the attention of Europeans when the Spanish heard about the medicinal properties of the "fever tree" from the natives of South America. The drug is used to cure malaria and was so successful that a boatload was shipped back to Europe in 1640 and the Jesuits began using it in their missionary work. Before synthetics came along to offer a substitute, Quinine was the only effective treatment for malaria for 300 years.
Tonic water is a byproduct of the British colonization. They used Quinine to help combat fever, but in order to make it palatable, they mixed it with gin and lemon or lime. Over time, they developed a taste for the mixture (much like our GIs did for instant coffee).
By the way, the amount of quinine in tonic water (about 20 milligrams) is nowhere near the amount necessary to treat malaria (at least 1800 milligrams a day).