A caduceus is a (sometimes) winged staff with two snakes wrapped around it. It is sometimes mistakenly used as a symbol for medicine, by those confusing it with the rod of Asclepius, which features only a single snake and no wings.
A 1992 survey of American health organisations found that 62% of professional associations used the staff of Asclepius, whereas in commercial organisations, 76% used the caduceus.
Staff of Asclepius
Early confusion between the symbols almost certainly arose due to the links between alchemy and Hermes, whose symbol is the caduceus. The alchemists adopted the caduceus because Hermes, the God of Messengers, was also the patron lord of gamblers, thieves, tricksters and alchemists. By the end of the 16th century, alchemy became widely associated with medicine in some areas, leading to some use of the caduceus as a medical symbol.
The main reason for the modern confusion over the symbols occured when the caduceus was adopted by the Medical Department of the United States Army in 1902. This was brought about by one Captain Reynolds, who after having the idea rejected several times by the Surgeon General, persuaded the new incumbent (WH Forwood) to adopt it. The mistake was noticed several years later by the librarian to the surgeon general, but was not changed.
There was further confusion caused by the use of the caduceus as a printer's mark (as Hermes was the god of eloquence and messengers), which appeared in many medical textbooks as a printing mark, although subsequently mistaken for a medical symbol.
The International Council of Nurses (ICN) uses a version of the lamp as its own symbol, but in 1999 adopted a white heart as the international symbol for nursing. The ICN explains, "White was selected because it brings together all colours, demonstrating nursing's acceptance of all people. White also has a world-wide association with nursing, caring, hygiene and comfort. The heart shape communicates humanity and the central place that nursing has in quality health care."
ICN White Heart Symbol