1804 bloodletting etching by James Gillray. A man sitting on a stool is being bled by another man standing next to him and holding his arm in one hand and, in the other, a bowl into which the blood spurts.Bloodletting (or blood-letting) is the withdrawal of often little quantities of blood from a patient to cure or prevent illness and disease. Bloodletting was based on an ancient system of medicine in which blood and other bodily fluid were considered to be "humors" the proper balance of which maintained health, but it often weakened sick patients. It was the most common medical practice performed by doctors from antiquity up to the late 19th century, a time span of almost 2,000 years.