The single serpent entwined around a staff is called the rod of Aesculapius, the son of the Greek god Apollo and Princess Coronis. While pregnant with Aesculapius, Coronis began having an affair with another mortal. This displeased Apollo immensely and he had his sister Artemis assassinate her. When they placed the princess’s body upon the pyre Apollo took pity on the unborn child and saved him from the flames. Having no where else to take the boy he sent the child, Aesculapius, to live with the Centaur Chiron, who taught him of the healing arts.
Eventually Aesculapius became so adept he was said to cure any disease and even bring the dead back to life. An action the gods feared greatly and punished him by striking him down. But his soul was just and honorable and the gods could not help but pay tribute by immortalizing him in the sky as the constellation called Ophiuchus, the serpent bearer.
There are a few theories surrounding this symbol, usually believed to predate the Greek legend. One is that the serpent represented rejuvenation because it could shed its skin and be born anew, lacking many of the injuries of its prior shell. This association of snakes with healing is almost universal, occurring time and time again from the early Mesopotamian god of medicine Ningishzida, who is often pictured as two serpents copulating around a staff, much like the Caduceus. To the Nehustan, a staff that according to Hebrew folklore Moses used to cure the Jewish people of snakebite after their god got a little streamed and sent fire snakes to plague them. The serpents close relation to medicine and healing can even be found in several indigenous cultures of North American such as the Deni and Cherokee.
Another theory is that the “serpent” is actually a parasitic worm. One of the services barbers and early doctors performed, besides bleeding, was parasite removal. This could be accomplished by slowing wrapping the worm around a stick to remove it from the flesh of the patient. Since few could read at the time tradesmen and businesses advertised their goods and services with pictures. Eventually the worm on a stick became a snake.
Whatever its origins the Rod of Aesculapius is now an internationally recognized symbol of medicine.