SUMMARY

Two components, interferon and residual particles of input virus, con-tributed to the interfering activity recoverable from mouse embryo cultures treated with molluscum contagiosum virus. Physical and biological tech-niques were used to distinguish and allow the independent biological assay of each of these components. Cultural conditions greatly affected the induc-tion of interference by molluscum virus. Under optimal conditions, interferon was first detected in treated cultures 6 hr after virus adsorption, reached a maximal value at about i8 hr and then declined rapidly. Virus itself, dis-tinguished from interferon by its acid lability, sedimentability and failure to induce interference in L cells, declined rapidly in activity, during the early hours after adsorption to mouse embryo cells, to about 25 % of that calcula-ted to have been adsorbed. Although a direct correlation was not established between the amount of interferon produced and the decline in recoverable virus, a substantial part of this decline was interpreted as a significant biologi-cal event akin to 'eclipse ' of infective virus in a permissive host