Can someone tell me the origin of Ring Around the Rosie?

It's a refernce to the plague:But like all folklore, the different versions do not always jibe with each other. The basic interpretation is that the first line refers to the rosie-red, round rashes which are supposed to be the first sign of plague. The second line refers to an alleged, superstitious method of warding off the disease by carrying or stuffing your pockets full of posies. The third line is difficult to interpret in my version ("Ashes, ashes"), but in many others it is clearly the sound of sneezing ("At-soo, at-soo" or even "A tissue! A tissue!"). The interpretive skills of the folk etymologizers aren't put to hard work to come up with the statement that, like the rosey rings, sneezing is a sign of plague. The last line is the clincher, for what else can we do once we've got the plague, but "All fall down," dead? Sometimes the plague referred to is the great London plague of 1665. More often the plague of 1347-50 is referred to; it is the one known as the Black Death. A few days ago I bought a book called Myth Information which purports to tell the truth about 590 pieces of common misinformation. The author claims that this rhyme is indeed a memory of that fourteenth century plague