Pettenkofer's views on the relation of ground-water to disease had great weight in biassing the views of sanitarians on the relation of contaminated water supplies to cholera and typhoid fever, and they determined the trend of several years' work which I devoted to investigation of the causation of rheumatic fever and diphtheria. It is therefore desirable in these recollections to explain Pettenkofer's position in the history of Epidemiology and Public Health.