Cholera is an exotic disease outside its home and starting place in India, it has repeatedly invaded Western countries with devastating results. People know that both Plague and Cholera can be completely controlled, and pandemicity as well as endemicity of these diseases may be made to disappear from the face of the earth by measures well within people powers. John Snow practised medicine in London, his chief work for many years being that of an anaesthetist. This chapter also indicates the place of Max von Pettenkofer in the development of preventive medicine, especially as bearing on the spread of cholera and enteric fever. He investigated problems of ventilation of dwelling-houses, of clothing, and of the soil, and may be rightly described as the founder of experimental hygiene. The chapter discusses the important official reports of John Simon. Simon contrasted smallpox in which direct infection occurs, and cholera in which "if truly the disease be contagious, foulness of medium seems indispensable".