"Leech" is derived from an old English word meaning "physician," and in the practice of Dr. Gregory Hartig, based in Madison, Wisconsin, that makes sense. After performing a reconstructive surgery, Hartig still sometimes prescribes leeches. From prehistory to the present, the bloodsucking worms have been applied to treat everything from cancer to broken bones. Modern research has shown that leeches help blood circulate and prevent clots. The problem, according to Hartig, is that many patients don't like the idea of carnivorous parasites biting into their flesh and slurping down their blood. Moreover, leeches must be replaced every hour or so, after they've drunk their fill. And unless they are closely monitored, they can wander around and attack healthy tissue. On occasion, they've also been known to transmit bacterial infections.