<prompt> Which events occured before 1900 AD?Establishment of seat of social medicine at OxfordEpidemiological work on cholera by John SnowWork on scurvy by James LindUse of BCG vaccine  <response>: An english epidemiologist John Snow studied the epidemiology of cholera in London from 1848-1854 and established the role of polluted drinking water in spread of cholera. Ref : Park;s textbook of preventive and social medicine; 23rd edition 