Preparations of influenza-infected chick chorio-allantoic membrane made by two types of tissue culture and by sectioning, have been studied in the electron microscope. Comparisons have been made of influenza A' (FM1), influenza A (PR8), and swine influenza (V15), three strains which produce different relative numbers of filaments.
Normal surface projections which may be confused with influenza filaments are described. Extruded products of degenerating cells, usually bleb-shaped, may also be found both in uninfected allantoic fluid and tissue cultures.
It appears that the filaments and spheres of influenza virus, concurrently projecting from the free cell surface, represent the only visible change in the cells until late in the infection,—how late the present work does not tell. No definite evidence of a generalized infection throughout the cytoplasm or of inclusions was found. Additional evidence is presented for the assumption that the filaments have a significant role in the final development of the free virus.