I read a book called The Ghost Map, which is about the discovery of the source of the cholera outbreak in London in 1854. It talks about the unique set of circumstances that gave John Snow a point a view that led him to the Broad street pump as the source of the outbreak. One thing that helped him was his experience with chloroform and ether, which had recently come into use in medicine. From experimentation on himself as well as his collection of lab animals, he was able to create a standard by which the gases were used. He was so renowned for his work in anesthetic gases, he was asked to administer chloroform to Queen Victoria during childbirth.