Bloodletting is one of the most well-known medieval medical methods. It came from the Greek idea of humors and that there were four humors, blood, phlegm, black bile, and yellow bile. The idea was that many illnesses were caused by an imbalance of the humors, namely an excess of blood. So then came the idea of bloodletting to remove the excess blood and re-balance the humors. It was believed that women did this on their own at times through menstruation.
As the process progressed through the Middle Ages, a system was developed. It was believed that bloodletting near the affected area was the best way to a cure. It was also written that certain veins and locations would affect different organs or illnesses. Books and instructions were released for physicians to follow so that they could have the best results for their patients.
It was bloodletting that led to the distinction between a doctor and a surgeon. A physician in the Middle Ages was likely to recommend bloodletting but not likely to perform it, that was left to the barbers. The barber would be the one to cut the vein and drain the blood, sometimes not even under the supervision of the physician, so it was up to the barber to know the specific medical trends at the time.
Bloodletting was not a safe or reliable process. It was believed that enough blood had to be taken that the patient swooned or fainted. This created a delicate line between the right amount of blood and too much. It was not uncommon for a patient to be drained of too much blood and die or to have their wound get infected. It wasn’t until the 19th century that bloodletting really started to fall out of favor and was condemned as a dangerous and ineffective practice by physicians.