STRUCTURE AND DEVELOPMENT OF VIRUSES AS OBSERVED IN THE ELECTRON MICROSCOPE : VII. INCOMPLETE INFLUENZA VIRUS.

Chicken embryos were infected by the chorioallantoic route with influenza virus, PR8 strain, in the form of undiluted chorioallantoic fluid. Electron microscopic examination 24 hours after infection revealed that membrane-bound fragments of cytoplasm appeared to be in process of release from entodermal cells of the chorioallantois. The number of such fragments was greatly increased in proportion to the number of typical viral particles after the third serial passage, which was accompanied by a reduction of the infectivity-hemagglutinin ratio (von Magnus effect). The lack of recognizable internal components, together with the presence of surface structure which closely resembled that of the virus and frequently contained viral antigen, suggested that many of these fragments were incomplete viral particles. It is proposed that concentrated inocula damage the cells and interfere with differentiation of the virus, but do not inhibit formation and detachment of cytoplasmic processes. Under these circumstances the accumulation of viral antigen at the surface of the cell will result in the predominant formation of incomplete virus.