Throughout history, humans have used “therapeutic” bloodletting (phlebotomy) for religious ceremonies. Many religions had as their base "blood sacrifices," either animal or human. Diseases were thought to be caused by evil spirits and demons, and the physician-priest (known by many different titles, for example, witch doctor) was called upon to drive out these supernatural causes. Bloodletting was one of the methods used to cleanse a sick person’s body of these nebulous impurities. It wasn’t until the advances in science around the 20th century that bloodletting was expanded to include the taking of blood for diagnostic purposes.
