The Greek god Hermes, who served as herald and messenger to the other gods, carried a winged staff entwined with two snakes. The staff of Aesculapius, the god of healing, had one snake and no wings. The word ''caduceus," from Latin, is a modification of Greek karykeion, from karyx, meaning "herald." Strictly speaking, "caduceus" should refer only to the staff of the herald-god Hermes (Mercury to the Romans), but in practice the word is often applied to the one-snake staff as well. You might logically expect the staff of Aesculapius to be the symbol of the medical profession-and indeed, that is the symbol used by the American Medical Association. But you will also quite frequently see the true caduceus used as a medical symbol.