The winged staff wrapped by two snakes on ambulances, uniforms, and drug ads is the caduceus, and this episode explains why it historically has nothing to do with medicine. Its roots go back to Mesopotamia between 4000 and 3000 BC, where the underworld god Ningishzida bore a staff with two intertwined snakes, carved on the libation vase of the Sumerian ruler Gudea around 2100 BC. The symbol also appears in temples of India’s Western Ghats and on punch marked coins linked to the Maurya Empire and King Ashoka. In Greek myth Hermes received the golden wand from Apollo in exchange for the lyre he had made from a tortoise shell.

Hermes was the god of messengers, boundaries, merchants, and thieves, and a guide of souls to the underworld, so his staff came to mark Roman diplomats, Renaissance printers such as Johann Froben, the planet and element mercury, and customs agencies today. The symbol of healing is the rod of Asclepius: one snake, a rough branch, no wings. The publisher John Churchill’s mark on 19th century medical books blurred the two, and in 1902 the U.S. Army Medical Corps adopted the caduceus.

• The myth of Tiresias, turned into a woman and back again after striking mating snakes with his staff
• Hermes separating two fighting serpents, and Roman envoys called caduceatores
• The caduceus on customs seals in China, Belarus, Bulgaria, and Russia and on Slovakia’s Financial Administration emblem
• A survey finding 62 percent of professional health associations use the rod of Asclepius while 76 percent of commercial health organizations use the caduceus
• Stuart L. Tyson’s 1932 critique in the Scientific Monthly of a trickster god’s emblem on doctors