If persons who are engaged in the promotion of preventive medicine ever waver in their faith that progress will attend the effort, their courage and persistence should be further sustained by the recent records of the continued campaigns against yellow fever. The success of Gorgas in eradicating this disease by mosquito control in Havana, in Cuba and in the Panama Canal Zone, has been widely proclaimed as an outstanding, monumental achievement of modern hygiene and sanitation. Less known, though similarly gratifying, are the experiences of the late Oswaldo Cruz, the resourceful Brazilian who applied the methods of attack on the Stegomyia mosquito, so that Rio de Janeiro has long since been made “as safe as it is beautiful.” In a recent tribute to him, President Vincent of the Rockefeller Foundation has described how the undaunted leader, whose untimely death occurred in 1917, was appointed director of public health and loyally supported by President Alves, and gradually overcame traditional prejudices, professional opposition, the persistence of antiquated methods and apprehensive interests of many kinds, until the annual deaths from yellow fever had fallen from 984 in 1902 to 0 in 1909. The campaign has continued elsewhere and included the clearing up of Guayaquil in Ecuador, the chief endemic center of yellow fever on this continent in 1918-1919, the elimination of fever from Peru before the end of 1921, and the quick control of incipient epidemics in Central America. The Mexican government has participated actively in the movement, so that the authorities of the International Health Board have been able to give this summary of the situation in 1923: No cases reported from Mexico, Central America, Ecuador or Peru; outbreak in Colombia promptly put under observation; well organized control measures under way in northern Brazil, and workers in training to resume study and observation along the coasts of western Africa, from which cases of yellow fever have been reported.