Bloodletting
Bloodletting is the deliberate withdrawal of blood from a patient to prevent or cure illness and disease. Bloodletting, whether by a physician or by leeches, was based on an ancient system of medicine in which blood and other bodily fluids were regarded as "humors" that had to remain in proper balance to maintain health. It was the most common medical practice performed by surgeons from antiquity until the late 19th century, a span of over 2,000 years. In Europe, the practice continued to be relatively common until the end of the 19th century. The practice has been abandoned by modern-style medicine for all except a few very specific medical conditions. In the beginning of the 19th century, studies had begun to show the harmful effects of bloodletting.
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