The caduceus (κηρύκειον in Greek) or wand of Hermes is typically depicted as a short herald's staff entwined by two serpents in the form of a double helix, and sometimes surmounted by wings. In later Antiquity the caduceus may have provided the basis for the astrological symbol representing the planet Mercury and in Roman iconography was often depicted being carried in the left hand of the Greek god Hermes, the messenger of the gods, guide of the dead and protector of merchants, gamblers, liars and thieves.
The caduceus is sometimes used as a symbol for medicine, especially in North America, through confusion with the traditional medical symbol, the rod of Asclepius, which has only a single snake and no wings. Given the historically attested use of this emblem, its adoption as a symbol of medicine is a great irony.
Among the Greeks the caduceus is thought to have originally been a herald's staff. The Latin word caduceus (possibly caduceum) is an adaptation of the Greek kerukeion, meaning "herald's wand (or staff)", deriving from kerux, meaning "herald" or "public messenger", which in turn is related to kerusso, meaning "to announce" (often in the capacity of herald). The staff of the herald is thought to have developed from a shepherd's crook, in the form of a forked olive branch adorned with first two fillets of wool, then with white ribbons and finally with two snakes intertwined. However no explanation as to how such an object would be practically used as a functional crook by shepherds is offered.
One Greek myth of origin of the caduceus is part of the story of Tiresias, who found two snakes copulating and killed the female with his staff. Tiresias was immediately turned into a woman, and so remained until he was able to repeat the act with the male snake seven years later. This staff later came in to the possession of the god Hermes, along with its transformative powers. Another myth relates how Hermes played a lyre fashioned from a tortoise shell for Apollo, and in return was appointed ambassador of the gods with the caduceus as a symbol of his office. Another tale suggests that Hermes (or more properly the Roman Mercury) saw two serpents entwined in mortal combat. Separating them with his wand he brought about peace between them, and as a result the wand with two serpents came to be seen as a sign of peace.
In Rome, Livy refers to the caduceator who negotiated peace arrangements under the diplomatic protection of the caduceus he carried.
In some vase paintings ancient depictions of the Greek kerukeion are somewhat different from the commonly seen modern representation. These representations feature the two snakes atop the staff (or rod), crossed to create a circle with the heads of the snakes resembling horns. This old graphic form, with an additional crossbar to the staff, seems to have provided the basis for the graphical sign of Mercury widely used in works on astronomy, astrology and alchemy. Another simplified variant of the caduceus is to be found in dictionaries, indicating a “commercial term” entirely in keeping with the association of Hermes with commerce. In this form the staff is often depicted with two winglets attached and the snakes are omitted (or reduced to a small ring in the middle).
As god of the high-road and the market-place Hermes was perhaps above all else the patron of commerce and the fat purse: as a corollary, he was the special protector of the traveling salesman. As spokesman for the gods, he not only brought peace on earth (occasionally even the peace of death), but his silver-tongued eloquence could always make the worse appear the better cause. From this latter point of view, would not his symbol be suitable for certain Congressmen, all medical quacks, book agents and purveyors of vacuum cleaners, rather than for the straight-thinking, straight-speaking therapist? As conductor of the dead to their subterranean abode, his emblem would seem more appropriate on a hearse than on a physician's car.
However, attempts have been made to argue that the caduceus is appropriate as a symbol of medicine or of medical practitioners. Apologists have suggested that the sign is appropriate for military medical personnel because of the connotations of neutrality. Some have pointed to the putative origins of the caduceus in Babylonian mythology (as described above), particularly the suggested association with Ishtar as "an awakener of life and vegetation in the spring" as justification for its association with healing, medicine, fertility and potency.
A 1992 survey of American health organisations found that 62% of professional associations used the rod of Asclepius, whereas in commercial organisations, 76% used the caduceus.
The first known use of the caduceus in a medical context was in the printer's vignette used by the Swiss medical printer Johann Frobenius (1460-1527), who used the staff entwined with serpents, not winged but surmounted by a dove, with the biblical epigraph "Be ye therefore wise as serpents and harmless as doves The caduceus was also apparently used as a symbol by Sir William Butts, physician to Henry VIII. A silver caduceus presented to Caius College, Cambridge by John Caius and carried before him on the cushion he supplied in official visits to the college remains in the College's possession.
But widespread confusion regarding the supposed medical significance of the caduceus appears to have arisen as a result of events in the United States in the 19th century. It had appeared on the chevrons of Army hospital stewards as early as 1856. In 1902 it was added to the uniforms of Army medical officers. This was brought about by one Captain Reynolds, who after having the idea rejected several times by the Surgeon General, persuaded the new incumbent —Brig. Gen. William H. Forwood — to adopt it. The inconsistency was noticed several years later by the librarian to the Surgeon General, but the symbol was not changed. In 1901 the French periodical of military medicine was named La Caducée. The caduceus was formally adopted by the Medical Department of the United States Army in 1902. After World War I the caduceus was employed as an emblem by both the Army Medical Department and the Navy Hospital Corps. Even the American Medical Association used the symbol for a time, but in 1912, after considerable discussion, the caduceus was abandoned and the rod of Asclepius was prudently adopted instead.
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.