The period and rate of liberation of influenza virus from entodermal cells of the allantois have been studied by deembryonating eggs within a few minutes after infection, exchanging the medium thereafter at hourly intervals and assaying the virus concentration in the harvests thus obtained (differential growth curves). If the inoculum was sufficiently large, presumably all available cells immediately became infected and only 1 infectious cycle was expected to occur. If the inoculum was small, so that only a fraction of the cells adsorbed virus, the infectious process was held to 1 cycle by continuous exposure of the remaining susceptible cells to RDE. In either case, the results obtained indicate that once cells have been infected they produce and liberate virus at nearly constant rates for periods of 30 hours or longer before the yields decrease rapidly. Evidence has been presented which strongly suggests that such prolonged periods of liberation are observed not only in deembryonated eggs but also in the intact chick embryo.

Attempts have been made in the discussion to reconcile these findings with previous estimates of the liberation period and to integrate them with histologic observations and electron micrographs of thin sections of infected allantoic membranes having a bearing on the mode of liberation.

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