Something I've never understood is why anesthesia was ever something that needed to be invented or discovered in the first place. Haven't people been aware of opium for hundreds, maybe thousands of years? Seems like every surgeon in town would have had his own garden for raising opium poppies.

I'm sure there are other plants with soporific or dissociative effects that would make surgery less painful. (Coca leaves, maybe?) But Papaver somniferum is the one that mostly comes to mind.