Quinine: The Jesuits discovered it. The Protestants feared it. The British vied with the Dutch for it, and the Nazis seized it. Because of quinine, medicine, warfare, and exploration were changed forever.

For more than one thousand years, there was no cure for malaria. In 1623, after ten cardinals and hundreds of their attendants died in Rome while electing Urban VII the new pope, he announced that a cure must be found. He encouraged Jesuit priests establishing new missions in Asia and in South America to learn everything they could about how the local people treated the disease, and in...