By the 1890's, some of the excitement had gone out of classic bacteriology. The germ theory of disease was widely accepted and the causative agents identified for many bacterial diseases. The nature of immunity preoccupied many scientists, but attention also shifted to the class of diseases which Patrick Manson called "tropical". 1898 has claim to be the year in which tropical medicine came of age. It saw the work of Ross and Grassi on mosquito transmission of malaria, the research on the sexual nature of Plasmodium reproduction by Simond and MacCallum, the planning of the schools of tropical medicine in London and Liverpool, the opening of the Laboratory in Senegal, the first issue of the Journal of Tropical Medicine and the publication of Manson's classic textbook, Tropical Diseases. My talk will examine the state of biomedical knowledge a century ago, in a time of confident imperialism.