Further Studies on Serial Passage of a Mixture of Influenza Viruses in Embryonated Eggs.

Undiluted allantoic fluids were used as inocula for serial passage of a mixture of the PR8 and Lee strains of influenza virus in embryonated eggs. Although wide differences were found in the relative concentrations of the two viruses in the various fluids, the mixture was successfully carried through 52 consecutive passages, and each agent was recovered in an apparently pure culture at the end of the experimental period. Since the two viruses have different growth rates and are capable of interfering with the multiplication of each other, the persistence of both agents during serial passage of the mixture suggests that multiplication of the PR8 and of the Lee viruses may not require the same host factors.