This report of 272 pages and three plates concerns a review of the causal relationship of B. influenzae with the recent and the 1889-1892 pandemics of influenza. To this are added cultural and morphologic studies of B. influenzae by the author, as well as summaries of these features by others. It is reasonable to conclude, writes the author, that B. influenzae is not the primary influenza microbe. The morphologic and cultural characteristics of B. influenzae are given in detail. A comparison of B. influenzae with other hæmoglobinophilic bacteria is given. The text, therefore, appeals particularly to those interested in bacteriology.