James Young Simpson's Discovery of Anaesthetic Uses of Chloroform, 1847
Simpson, together with his assistants Matthew Duncan and George Keith, was in the habit of experimenting with chemicals in his dining room to see whether they had any anaesthetic effect. On the evening of 4 November 1847, they tried chloroform, a substance they had previously ignored as unpromising. The immediately effect was elation followed by a sudden loss of consciousness. On coming round the following morning, Simpson knew that he had found a substance that he could use as a general anaesthetic. He repeated the experiment on his niece with the same effect. He began to employ chloroform in childbirth on 8 November 1847 and described its uses in a pamphlet Account of a New Anaesthetic Agent. Within weeks of its appearance, chloroform had almost completely replaced ether as the standard anaesthetic.
It was quite by chance that Simpson happened upon the anaesthetic potential of chloroform. If he and his assistants had taken a higher dose they would most likely have died. If they had taken a lower dose, they would not have lost consciousness.