The barber pole: “the red stripes signif[ied] blood, blue stripes … veins, and white stripes represented the gauze bandages [barber-surgeons] used to stem the bleeding. The pole itself was a symbol of the stick that patients would grip tightly as they were being bled and the ball atop the pole signified the blood collection basin (and the container they used to hold the leeches).”
During George Washington’s final illess he was bled – as a curiative by his doctors (& this method was standard practice at the time) – of “approximately 40 percent of [his] blood volume within a thirteen-hour period … For comparative purposes, the American Red Cross generally requires an eight-week period between blood donations of one-tenth the volume drained from the former president on what was to be his last day alive.”
So what was with all the bleeding? Illness, the prevailing orthodoxy had it, was caused (or, at least, worsened) by an excess of blood, blood being one of the humors that had to be kept in balance to maintain health. Illness was a result of an imbalance between the humors. For some reason blood was a prime suspect in imbalances – maybe because there was just so much of it and because its release can be so dramatic. Plus, you can get a little high from a bleeding, a temporary feeling of well-being.
source: Dark Banquet: blood and the curious lives of blood-feeding creatures by Bill Schutt