Bloodletting is one of the oldest medical techniques, practiced from antiquity through the 18th century. It involves the withdrawal of considerable quantities of blood from a patient, and practitioners believe it can cure or prevent a number of illnesses and diseases. Numerous bloodletting methods have been employed over the centuries, including drawing blood directly from large veins, puncturing arteries, and even using leeches. A form of bloodletting is still used today to treat what diseases? Discuss