The treatment of injury and disease by physically cutting into, removing from, or repairing the living body — a deliberate, controlled wounding meant to heal. Surgery is ancient, found from prehistoric skull-drilling to the detailed operative texts of ancient India, yet for almost all of that history it was capped by three barriers: pain, bleeding, and infection. The conquest of pain by anesthesia in the 1840s, and of infection by antiseptic, germ-based method around 1867, remade it into the central, planned tool of modern medicine, able to open the abdomen, chest, and skull.
For most of human history, the surgeon's greatest skill was speed. A patient was awake, held down by strong assistants, and the fastest cutters could take off a leg in under a minute, because every extra second was extra agony. Surgery was a controlled wound: deliberate injury meant to heal, taken only when death was the alternative. Three walls capped it — pain that could not be stopped, bleeding that could not be controlled, and infection that killed days after a clean cut. In the nineteenth century two of those walls fell, and surgery became the most dramatic power medicine holds.