Tonic water glows blue under a black light because of quinine, a molecule this episode follows from the Andes to the bar cart. The Quechua people of Peru, Bolivia and Ecuador ground cinchona bark into sweetened water to stop shivering from cold. In the 1630s, Jesuit apothecary Agostino Salumbrino in Lima sent the bark to Rome, where malaria from the surrounding marshes was killing popes and cardinals, and it cured the disease. The episode calls this the first known use of a chemical compound to treat an infectious disease, and shows how quinine let European armies push into Africa and Asia.

Andean nations banned seed exports, but in 1865 Manuel Incra Mamani smuggled high yield seeds to Charles Ledger, who sold them to the Dutch, and Mamani later died after a beating. Dutch plantations on Java, controlled from 1913 by the Kina Bureau cartel, supplied 97 percent of the world’s quinine by the 1930s, until Japan seized Indonesia in World War II. Today it survives in tonic water at 83 parts per million, while the World Health Organization prefers artemisinins.

• The US Cinchona Missions and why trees taking 10 to 12 years to mature came too late
• Japanese troops dying of malaria despite controlling the supply
• William Henry Perkin’s failed 1856 synthesis that produced mauveine dye
• Woodward and Doering’s 1944 synthesis and why bark is still cheaper
• How quinine blocks the parasite’s heme crystallization, and the dangers of cinchonism