A Genetic Approach to Variation in Influenza Viruses: 3. Recombination of Characters in Influenza Virus Strains Used in Mixed Infections

When the non-encephalitogenic strain of influenza virus A, WSM, was mixed with the influenza strain NWS in suitable proportion no encephalitis followed intracerebral injection of the mixture in mice. When the amount of WSM relative to NWS was decreased partial interference resulted and from four mice so inoculated, virus strains referred to as WS-NM were isolated, which appear to be recombinants. The NM strains were encephalitogenic for mice, though in varying degree, their haemagglutinin was almost as resistant to heat inactivation as that of WSM and they had at least one character (position in the receptor gradient) in which they differed from both the original strains.