The day a carnival trick in Hartford, Connecticut revolutionized medicine forever began in December 1844, when a dentist named Horace Wells sat in the audience of a laughing gas show.
He watched as the showman, Gardner Colton, gave volunteers whiffs of nitrous oxide, much to the amusement of the crowd.
Then something incredible happened. One of the participants, Samuel Cooley, stumbled and gashed his leg open. He was bleeding, but he felt no pain at all. He just kept laughing.
While others saw a spectacle, Wells saw a solution to the terrifying pain of surgery. A thought took root in his mind that would change the world.
The very next day, Wells convinced the showman to bring a bag of the gas to his dental office. He sat in his own chair, inhaled the nitrous oxide, and had a fellow dentist pull one of his wisdom teeth. He felt nothing. 
He went on to perform about a dozen painless tooth extractions on his patients. But his career took a turn during a public demonstration at Massachusetts General Hospital in 1845. The patient groaned during the procedure, and Wells was booed offstage as a failure and a fraud.
Tragically, Wells’ life spiraled downward. He became addicted to chloroform and, in 1848, took his own life in a New York jail cell, disgraced and unknown.
But the truth of his discovery could not be buried. Years after his death, both the American Dental Association in 1864 and the American Medical Association in 1870 officially recognized Horace Wells as the true discoverer of anesthesia, a gift that has relieved the suffering of countless millions. 
Sources: Connecticut Historical Society, American Medical Association Records