A genetic approach to variation in influenza viruses. 1. The characters of three substrains of influenza virus A

SUMMARY: When the strain NWS of influenza virus, which is adapted to multi-plication in mouse brain, is submitted to allantoic passage in the chick embryo, it maintains its original character if passed at limiting infective dilutions. When passage is made with a low dilution of the same virus preparation the strain changes toward a more ‘normal ’ character. These phenomena are regarded as providing formal proof that the changes are mutational in origin. In the course of work on the 0-D transformation of influenza virus A (Burne