Doctor bleeding a patient. 18th century print of a doctor bleeding a patient. An incision has been made in the patient's arm and the blood is being collected in a bowl. The incision was usually made, under the supervision of a physician, by a barber-surgeon. The red-and-white sign (signifying blood and a blade) associated with barbers stems from this traditional role. Despite the medical advances of the Renaissance, many physicians perpetuated medieval beliefs and practices. Illness was thought by them to be the result of an imbalance in bodily fluids which could be rectified by draining blood. This was done either by an incision or by attaching leeches.