The caduceus is the symbol of medicine. This is a serpent wrap around a pole.
[2] The Staff of Asclepius (Æsclepius, Asklepios)
[Personification of Medical or healing Art and its ideals] 
Professional and patient centred organisations 
(such as the NZMA, in fact most medical Associations around the world including the World Health Organization) use the "correct" and traditional symbol of medicine, the staff of Asclepius with a single serpent encircling a staff, classically a rough-hewn knotty tree limb. Asclepius (an ancient greek physician deified as the god of medicine) is traditionally depicted as a bearded man wearing a robe that leaves his chest uncovered and holding a staff with his sacred single serpent coiled around it, (example right) symbolizing renewal of youth as the serpent casts off its skin. The single serpent staff also appears on a Sumerian vase of c. 2000 B.C. representing the healing god Ningishita, the prototype of the Greek Asklepios. However, there is a more practical origin postulated which makes sense [See Dracunculus medinensis].
And to add some biblical confusion, we have:
And the Lord said unto him [Moses], What is that in thine hand? And he said, A rod. And he said, Cast it on the ground. And he cast it on the ground, and it became a serpent; and Moses fled from before it. And the Lord said unto Moses, Put forth thine hand, and take it by the tail. And he put forth his hand and caught it and it became a rod in his hand. Exodus 4:2-4
 The Brazen Serpent [Julius Schnorr von Carolsfeld 1851-60)] |
And the Lord said unto Moses, Make thee a fiery serpent, and set it upon a pole: and it shall come to pass, that every one that is bitten [by a sepent], when he looketh upon it, shall live. Numbers 21:8. The etching "The Brazen Serpent" (to the right) by Schnorr von Carolsfeld shows this as only one snake, suggesting he interpreted this as a medical rather than mystical or magical symbol.
Apparently an Israelite cult subsequently formed worshipping Nehush'tan, the serpent Moses made (apparently twin snake images were inscibed on standards of the time) but the cult was eventually suppressed (over 600 years later) by King Hezekiah - "He removed the high places, and brake the images, and cut down the groves, and brake in pieces the brasen serpent that Moses had made: for unto those days the children of Israel did burn incense to it: and he called it Nehushtan (2 Kings 18:4).
And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up.
John 3:14-15
Now just in case you thought you had it all sorted out about which was the "good" symbol.... nothing is that simple, take a look at this interesting painting of Adam & Eve.......
