A peeve of mine, which I record for posterity:

The proper symbol of medicine is called a Rod of Asclepius, and consists of a single snake wrapped around a central pole. It is not to be confused with the Caduceus, which consists of two snakes wrapped around a winged pole, and is associated with the god Hermes.

Rod of Asclepius and Caduceus. Pinterest.

The hero Askepios was the son of the god Apollo and either Coronis or Arsinoe, both mortals. Asklepios’s attributes are a snake and a staff, combined into a single symbol. The staff seems to have been simply the sign of an itinerant physician, while the snake can be seen in many ways:

sometimes the shedding of skin and renewal is emphasized as symbolizing rejuvenation, while other assessments center on the serpent as a symbol that unites and expresses the dual nature of the work of the physician, who deals with life and death, sickness and health. The ambiguity of the serpent as a symbol, and the contradictions it is thought to represent, reflect the ambiguity of the use of drugs, which can help or harm, as reflected in the meaning of the term pharmakon, which meant “drug”, “medicine”, and “poison” in ancient Greek. Products deriving from the bodies of snakes were known to have medicinal properties in ancient times, and in ancient Greece, at least some were aware that snake venom that might be fatal if it entered the bloodstream could often be imbibed. Snake venom appears to have been ‘prescribed’ in some cases as a form of therapy.

By an interesting coincidence a healing snake-and-pole device also appears in Numbers 21:

[The Israelites] traveled from Mount Hor along the route to the Red Sea, to go around Edom. But the people grew impatient on the way; they spoke against God and against Moses, and said, “Why have you brought us up out of Egypt to die in the wilderness? There is no bread! There is no water! And we detest this miserable food!”

Then the Lord sent venomous snakes among them; they bit the people and many Israelites died. The people came to Moses and said, “We sinned when we spoke against the Lord and against you. Pray that the Lord will take the snakes away from us.” So Moses prayed for the people.

The Lord said to Moses, “Make a snake and put it up on a pole; anyone who is bitten can look at it and live.” So Moses made a bronze snake and put it up on a pole. Then when anyone was bitten by a snake and looked at the bronze snake, they lived.

It’s interesting how snakes are generally symbols of evil in the Christian tradition, but ambiguous in Greek paganism. Here, however, is a Biblical example of a snake that does some good. (And I believe this passage has been used by Christians to justify their use of apotropaic images, in apparent violation of the second commandment.)

Medical bodies that are on the ball will identify themselves with a Rod of Asclepius. Left to right: the Emergency Services’ Star of Life, the coat of arms of Geisel School of Medicine at Dartmouth College, and the logo of the American Medical Association, all from Wikipedia.

The Caduceus, by contrast, comes from the Greek kērukeion, and simply means herald’s staff. Since Hermes was the herald of the gods, he is often depicted with a staff of some sort, usually with something wound around it; this has been formalized as two snakes, and the wings match the wings on Hermes’s helmet and shoes. The Caduceus, therefore, represents items in Hermes’s wheelhouse, chiefly commerce.

Coat of arms of Jyväskylä, Finland and of Metropolitan Toronto (1954-98) featuring Caduceuses. From Wikipedia and the Online Register of Arms, Flags, and Badges of Canada.

Or rather, the Caduceus ought to represent commerce. By the same process that saw methodology replace method, or discipline replace field, a device with two snakes (and two wings!) was seen as somehow grander than a device with one. See the Wikipedia entry on the Caduceus as a symbol of medicine.

Wikipedia.

Apparently the US Army was the chief culprit here. Daniel P. Sulmasy said that “It is hard to trust a profession that cannot even get its symbols straight,” but others have noted the ironic appropriateness of the American medical profession representing itself with a symbol of commerce.