The reported failure to produce influenza in man by direct inoculation with freshly isolated cultures of B. influenzæ in experiments conducted on volunteers by the United States Public Health Service[27] at Gallops Island, Boston, is interesting, but would seem to lack definite significance since attempts to transmit the disease from man to man by direct contact also failed. Since all the subjects of these experiments had been previously exposed to influenza during the epidemic, 30 per cent actually having contracted the disease, it would seem probable that the remaining 70 per cent were only very slightly if at all susceptible. It is noteworthy that the attack rate of influenza in most army groups was approximately 20 to 30 per cent during the epidemic, the remaining 70 to 80 per cent failing to contract the disease though equally exposed. No other explanation presents itself except that influenza is no longer transmissible when clinical symptoms have appeared. Conclusions 1. Consideration of all the evidence available makes it seem highly probable that B. influenzæ is the specific etiologic agent of epidemic influenza, because (_a_) it is always present in early uncomplicated cases of influenza; (_b_) it is predominantly so during the acute stage of the disease in cases going on to rapid recovery without development of complications; (_c_) its presence in varying numbers in normal individuals and in other diseases of the respiratory tract is not valid evidence against its etiologic relationship to influenza, but on the contrary is quite in harmony with what should be expected from our knowledge of other bacteria known to be the etiologic agents of various respiratory diseases; (_d_) its rapidly increasing prevalence in normal individuals simultaneously with the progress of the epidemic indicates that actual dissemination of B. influenzæ readily occurs and is very widespread during pandemic times; (_e_) cultures of B. influenzæ freshly isolated from early acute cases of influenza are pathogenic for animals, and may produce in monkeys a disease closely resembling influenza. 2. Final proof of the exact relationship of B. influenzæ to influenza must depend upon (_a_) more definite knowledge of the immunology both of the organism and of the disease, and (_b_) knowledge of the pathologic lesions of influenza and the production of these lesions in animals by inoculation with B. influenzæ. CHAPTER II CLINICAL FEATURES AND BACTERIOLOGY OF INFLUENZA AND ITS ASSOCIATED PURULENT BRONCHITIS AND PNEUMONIA FRANCIS G. BLAKE, M.D., AND THOMAS M. RIVERS, M.D.