In 1700s a Scottish doctor, discovered that quinine could be used to prevent and treat malaria. In the early 19th century British Soldiers stationed in India, mixed the quinine, which was derived from the Cinchona bark, with a mixture of water, sugar and lime juice. They took to adding gin to this mixture to mask the powerful flavour of the quinine. Today's tonic water, contains a lot less quinine and therefore is much less bitter.