One such was “the milk sick.” People who drank milk in America sometimes grew delirious and swiftly died—Abraham Lincoln’s mother was one such victim—but infected milk tasted and smelled no different from ordinary milk, and no one knew what the infectious agent was. Not until well into the nineteenth century did anyone finally deduce that it came from cows grazing on a plant called white snakeroot, which was harmless to the cows but made their milk toxic to drink.
