John Snow (15 March 1813 – 16 June 1858) was an English physician. He used anaesthesia and medical hygiene. He is a founder of modern epidemiology because he traced the source of a cholera outbreak in Soho, London, in 1854. His findings caused changes in the water and sewage systems of London. This led to similar changes in other cities, and a great improvement in general public health around the world.