Surgery is a profession defined by its authority to cure by means of bodily invasion. The brutality and risks of opening a living person’s body have long been apparent, the benefits only slowly and haltingly worked out. Nonetheless, over the past two centuries, surgery has become radically more effective, and its violence substantially reduced — changes that have proved central to the development of mankind’s abilities to heal the sick.

Consider, for instance, amputation of the leg.

The procedure had long been recognized as lifesaving, in particular for compound fractures and other wounds prone to sepsis, and at the same time horrific. Before the discovery of anesthesia, orderlies pinned the patient down while an assistant exerted pressure on the femoral artery or applied a tourniquet on the upper thigh.

Surgeons using the circular method proceeded through the limb in layers, taking a long curved knife in a circle through the skin first, then, a few inches higher up, through the muscle, and finally, with the assistant retracting the muscle to expose the bone a few inches higher still, taking an amputation saw smoothly through the bone so as not to leave splintered protrusions. Surgeons using the flap method, popularized by the British surgeon Robert Liston, stabbed through the skin and muscle close to the bone and cut swiftly through at an oblique angle on one side so as to leave a flap covering the stump.

The limits of patients’ tolerance for pain forced surgeons to choose slashing speed over precision. With either the flap method or the circular method, amputation could be accomplished in less than a minute, though the subsequent ligation of the severed blood vessels and suturing of the muscle and skin over the stump sometimes required 20 or 30 minutes when performed by less experienced surgeons.

No matter how swiftly the amputation was performed, however, the suffering that patients experienced was terrible. Few were able to put it into words. Among those who did was Professor George Wilson. In 1843, he underwent a Syme amputation — ankle disarticulation — performed by the great surgeon James Syme himself. Four years later, when opponents of anesthetic agents attempted to dismiss them as “needless luxuries,” Wilson felt obliged to pen a description of his experience:

“The horror of great darkness, and the sense of desertion by God and man, bordering close on despair, which swept through my mind and overwhelmed my heart, I can never forget, however gladly I would do so. During the operation, in spite of the pain it occasioned, my senses were preternaturally acute, as I have been told they generally are in patients in such circumstances. I still recall with unwelcome vividness the spreading out of the instruments: the twisting of the tourniquet: the first incision: the fingering of the sawed bone: the sponge pressed on the flap: the tying of the blood-vessels: the stitching of the skin: the bloody dismembered limb lying on the floor.”

It would take a little while for surgeons to discover that the use of anesthesia allowed them time to be meticulous. Despite the advantages of anesthesia, Liston, like many other surgeons, proceeded in his usual lightning-quick and bloody way. Spectators in the operating-theater gallery would still get out their pocket watches to time him. The butler’s operation, for instance, took an astonishing 25 seconds from incision to wound closure. (Liston operated so fast that he once accidentally amputated an assistant’s fingers along with a patient’s leg, according to Hollingham. The patient and the assistant both died of sepsis, and a spectator reportedly died of shock, resulting in the only known procedure with a 300% mortality.)