This medieval text by Constantine the African discusses the three main branches of medical treatment: diet, pharmacy, and surgery, emphasizing the importance of mastering surgical techniques through observation and practice. It categorizes surgery into operations on veins, flesh, and bones, with detailed focus on phlebotomy-the practice of bloodletting from veins. The text provides guidelines on when and how to perform phlebotomy safely, stressing the importance of patient consent, proper tools, vein identification, and careful technique to avoid nerve damage and other complications. It also highlights specific considerations for phlebotomy on different body parts to prevent adverse effects such as spasms, headaches, or vision problems.