The hypothesis of a filtrable virus as the primary etiologic agent in epidemic influenza has been advanced by Nicolle and LeBailly,1 von Angerer,2 Bradford, Bashford and Wilson,3 and by Gibson, Bowman and Connor.4 The great diversity of bacteriologic findings in the disease would seem to render such a conception very attractive. It would appear very difficult to explain the epidemiologic characters of the disease on the assumption that it is primarily caused by any of the well known bacteria which have from time to time been associated with it, but which are also known to be present and active in the inter-epidemic periods. The clinical conception of influenza as a comparatively mild disease, characterized by a well marked toxemia and giving evidence of special predilection for the respiratory tract, and only dangerous, as a rule, when complicated by the so-called "secondary" pneumonia, from which a great variety of bacteria have