Probably the greatest confusion in attempts to get a clear picture of this protean disease has been and is a non-recognition of influenza as a frequent complication of other diseases, such as measles (Jochmann, Susswein, Tedesko and very many others). The second cause for this confusion has been the misinterpretation of the facts demonstrating the rather frequent occurrence of carriers. During an epidemic the vast majority of patients show the disease as an upper respiratory infection of varying degrees of intensity, but which usually subsides after periods of from three to five days of fever. Along with this we have other graded manifestations of further involvement of the tract with laryngitis, bronchitis, bronchiolitis and all degrees of broncho-pneumonia. To prevent the severe lung involvement prompt treatment must be carried out, under which rest in bed is by long odds the most important. This will be discussed in another paper of this series, and was particularly well demonstrated in the results at the Naval Hospital as verbally reported to me by D. G. Richey. The interesting point is that the infection can be controlled, but this does not indicate the etiological factor as different from that acting in the more severe cases. The epidemiological evidence would seem to show very clearly that the incubation period is approximately two days, and that a period of six weeks is the usual limit for the severe wave of the epidemic in different localities. In my opinion, during this period every exposed individual in a community has received the influenza bacillus in the respiratory tract, and that all the susceptible individuals are attacked and show more or less evidence of the infection. As a consequence of this general distribution we have great numbers of individuals carrying the organism, and the aftermath is to be noted in other and later manifestations of the same infection.