The date of the first operation under anesthetic, Oct. 16, 1846, ranks among the most iconic in the history of medicine. ...
But what precisely was invented that day? Not a chemical - the mysterious substance used by William Morton, the local dentist who performed the procedure, turned out to be simply ether, a volatile solvent that had been in common use for decades. And not the idea of anesthesia - ether, and the anesthetic gas nitrous oxide, had both been thoroughly inhaled and explored. As far back as 1525, the Renaissance physician Paracelsus had recorded that it made chickens "fall asleep, but wake up again after some time without any bad effect," and that it "extinguishes pain" for the duration.
What the great moment in the Ether Dome really marked was something less tangible but far more significant: a huge cultural shift in the idea of pain. ... What needed to change first wasn't the technology - that was long since established - but medicine's readiness to use it.
Before 1846, the vast majority of religious and medical opinion held that pain was inseparable from sensation in general, and thus from life itself. ... Since time immemorial, pain had been seen in religious terms as a concomitant of original sin and, as such, an irreducible part of the human condition. Indeed, it was often explained as part of God's mercy, "the voice of nature" that kept us from harm by alerting us to physical dangers.
This view was echoed by the medical opinion of the day. Most doctors still believed it was only pain that kept patients alive through the trauma of operations. ...
Technical advances had led to more sophisticated and extended operations, and the patient's ability to endure them had become the limiting factor in their progress. It was the evolving requirements of surgeons, as much as the feelings of their patients, that eventually tipped the balance.
--Mike Jay, Boston Globe, on surgeons getting what they want (HT: Freakonomics).