John Snow

 John Snow (1813-1858) was an English physician and epidemiologist who identified the source of what caused the cholera outbreak in Soho, London in 1854. His work was significant in that it improved general public health across the world, since his discovery that the cholera disease was caused by consuming food or drinking water that was contaminated with the bacterium Vibrio Cholerae led to people being more hygenic. Cholera is infectious and results in severe watery diarrhoea, leading to dehydration and potentially death if left untreated. Diarrhoea is caused by the bacterium releasing a toxin in the intestines.