John.Snow has been a well-known doctor in London,London,when cholera broke out again,he started preparing for his investigation.He marked on a map through all the deceased,a resident of the exact place.He found that the outbreak of cholera bacteria rather than by air mass spread.Water is calling from the river,while the water was dirty water was discharged in London.To prevent this situation from happening again,John.Snow recommended so water must be tested.Water Corporation received instructions not let people touch contaminated water.Finally,the "King Cholera" has finally been defeated.