Few images conjure up the horrors of primitive medical practice more powerfully than that of the leech. This parasitic worm was used to suck blood from the veins of sick people in the belief that it could draw out the “evil vapors” responsible for their disease.
Large numbers of leeches were employed. In 1837 alone, 96,000 leeches were applied to 50,557 patients at St. Bartholomew’s Hospital in London. Their use was so common in England that British-bred leeches became scarce, and foreign leeches had to be imported from India and Mexico.
In the 19th century more than 50 leeches were sometimes applied simultaneously to a patient. In modern-day plastic surgery usually only one or two leeches are used at one time. But if the arteries to the grafted area take a long time to develop, leeches may be applied at six-hour intervals over a week-some 28 leeches in all.
Read more: http://scienceray.com/biology/human-biology/return-of-the-leech/#ixzz0vIl5kMwj