Bloodletting

Bloodletting (or blood-letting, in modern medicine referred to as phlebotomy) was a popular medical practice from antiquity up to the late 19th century, involving the withdrawal of often considerable quantities of blood from a patient in the hopeful belief that this would cure or prevent a great many illnesses and diseases. The practice, of unproven efficacy, has been abandoned for all except a few specific conditions as modern treatments proved or believed to be effective have been introduced. It is conceivable that historically, in the absence of other treatments for hypertension, bloodletting could sometimes have had a beneficial effect in temporarily reducing blood pressure by a reduction in blood volume.
Today the term "phlebotomy" refers to the drawing of blood for laboratory analysis or blood transfusion (see Phlebotomy (modern)). Therapeutic phlebotomy refers to the drawing of a unit of blood in specific cases like hemochromatosis, polycythemia vera, porphyria cutanea tarda etc., to reduce the amount of red blood cells