We are delighted that our article generated so much interest, and we are happy to address questions raised in correspondence. In-depth coverage will appear in our forthcoming book. Given the necessary brevity of our article, we were unable to include every theory behind the serpent and staff motif.

Regarding the guinea worm theory proposed by Müller (1), this attractive piece of post hoc speculation has developed substantial popular appeal within the medical community but has no standing in the light of extensive historical and archaeological evidence. The Asklepian has its origins in the strong association between serpent worship and healing cults throughout the pre-Hellenic Mediterranean, North African, and Eastern cultures (2-4). In artistic portrayals from the Egyptian old kingdom (2800 to 2250 BC), the goddesses Nekhebet and Sati are commonly depicted presenting Horus with the gifts of life and sovereignty, symbolized by a staff encircled by a single serpent (2). The serpent motif has long been associated with the gift of life and renewal in many cultures, but only in the cult of Asklepios was this association so purely medical (2-4).

Several correspondents noted the resemblance of the Asklepian to the biblical "serpent of brass," which Moses used to miraculously cure snake bites (5). Indeed, plague medals that depicted Moses holding the brass serpent became popular religious icons during the 14th century. They were worn in the hope of evoking the protection of Jesus and God against the bubonic plague, just as the Greeks and Romans of antiquity had used charms to evoke the protection of Asklepios (6). The brass serpent of Moses was a very popular Renaissance motif and was prominently depicted by Michelangelo in the Sistine Chapel. Schouten wrote, "In my opinion, this emblem, the brass serpent, greatly influenced the 16th century renaissance of the classical Aesculapius and his attribute, the rod and serpent, when Humanism infused new life into a number of antique motifs" (6). This symbol is known as the Tau cross and is featured on the coat of arms of the Royal Society of Medicine of the United Kingdom, where it is often mistaken for an Asklepian.

A caduceus symbol was actually first used by the U.S. Army between 1851 and 1887 to indicate the noncombatant status of hospital stewards; it was later replaced by the Red Cross (4). The U.S. Marine Hospital Service (the forerunner of the U.S. Public Health Service) then adopted a seal consisting of a caduceus and fouled anchor (4, 7, 8). However, the official history of the Public Health Service states that "the caduceus of mercury appears in the corps device because of its relationship with merchant seamen and the maritime industry" (7). Thus, the adoption of the caduceus symbol by the Public Health Service had no direct medical connotation but was used to symbolize seamen and the maritime trade, as was popular throughout the 18th and 19th centuries (3). Of interest, just like the U.S. Army Medical Corps, the Public Health Service seal inappropriately displays a modern caduceus (resembling that of the publisher Churchill) and not the ancient caduceus of Hermes–Mercury.

We liked Dr. Paparounas's suggestion but would prefer the combined term Asklepian iatrosema. However, we believe that Dr. Newman's suggested introduction of a third serpentine symbol consisting 2 snakes in a right-handed helix mimicking DNA would be entirely counterproductive. After all, the DNA of mice, rats, and monkeys is in essence very similar to that of humans, and we therefore champion the Asklepian symbol because it reminds us of the essentially humanistic nature of medical practice. An inscription found at the Asklepieion of Athens specifies the Asklepian commitment: "These are the duties of a physician ... he would be like the God, savior equally of slaves, of paupers, of rich men, of princes and to all a brother such help he would give" (9). The Asklepian tradition emphasizes integrity, sacrifice, compassion, and universal access to health care. People are most equal in their capacity for illness and suffering. Thus, physicians must seek to practice their craft without primary regard for the social status of their patients, personal advancement, or financial rewards. As Sir William Osler wrote, "The practice of medicine is an art, not a trade; a calling, not a business; a calling in which your heart will be exercised equally with your head" (10).