"They put him under laughing-gas one year, poor lad, and drew all his teeth"
Horace Wells plaque
Public DomainHorace Wells plaque - Credit: Daderot, Wikipedia Commons
 Laughing gas, or nitrous oxide (N2O), was discovered in 1793 by Joseph Priestley. Humphry Davy experimented with it and found that people became hysterical with laughter. For the next few decades, it was used for amusement at parties, but in Hartford, Connecticut, in 1844, a local dentist, Dr Horace Wells, realised that it could be used to dull pain in tooth extraction. Unfortunately, he was booed off the stage at a demonstration the following year at the Harvard Medical School, and he committed suicide in 1848. However, laughing gas gradually began to be used as an anaesthetic, and it is still widely used in dental practices today.