In 1923, Buck1 isolated a virulent culture of Brucella abortus from the milk of a cow. This culture, after standing at room temperature for a year, remained smooth, and although its virulence was considerably reduced, its antigenic properties were retained. After hundreds of subcultures and passages through animals, the original virulence of this strain has not been regained. Because of these stable characteristics, the Bureau of Animal Industry of the United States Department of Agriculture has successfully encouraged the use of strain 19 for immunization of cattle against brucellosis. Persistent infections in animals have not been established in this manner.2 The question has often arisen as to whether humans are ever infected by strain 19. No evidence has ever been presented to show that persons have contracted brucellosis from cattle as a result of vaccination with this strain. Gilman,3 however, has put forth a cautionary note for