Growth of Newcastle Disease Virus in the Embryonated Egg

1. Data are presented to support the contention that the growth of Newcastle disease virus in the developing chick embryo occurs in cycles of 4 hr. The apparent 4-hr latent period in the production of virus following the inoculation of an infective dose does not correspond to the lag phase in the multiplication of bacterial cells, but rather indicates an intercellular development of virus particles that cannot be determined by any of the present technics for measuring viral activity. The maximum adsorption of virus onto susceptible cells occurs within 10 minutes after its introduction into the embryonated egg. 2. The existence of an unequal development of infective and hemagglutinating titers during the growth of Newcastle disease virus is described and an attempted explanation for this discrepancy is made on the hypothesis that the hemagglutination unit results from a maturation of the infectious particles and cannot therefore be detected early in its growth.