Once upon a time you would visit your barber for a shave and a haircut -- and you might also have him extract a rotting tooth or even set a broken arm. Barbers, known then as barber-surgeons, were also bloodletters. (If you ever wondered why a barber pole is red and white, it's from this history of bloodletting).
Bloodletting was once practiced as a way to release evil spirits from the body, and it was also considered a treatment for a variety of conditions, from nosebleeds to pneumonia. It was also key therapy in what's known as humoral medicine, which is medicine based on the four humors in the body: phlegm, yellow bile, black bile and blood. Drawing blood was thought to help keep those humors balanced. While bloodletting can be traced back at least 3,000 years, most of us probably think of its practice in Victorian England in the late 18th and early 19th centuries, when millions of leeches were put into service instead of lancets (or, in ancient times, a thorn or sharp stick to cut open a vein).
Today, bloodletting still exists, although it's now known as phlebotomy therapy; it's used in limited instances such as to treat hemochromatosis (a condition where too much iron builds up in your body). Leeches, commonly used in bloodletting practices ever since the ancient Egyptians did employed them, also continue to have a place, albeit also limited, in modern medicine; the FDA approves of the use of the medicinal leech, Hirudo medicinalis, as a medical device in reattachment surgery as well as in skin grafting procedures because of its anticoagulant properties.