THE EXPERIMENTAL PRODUCTION OF COMBINATION FORMS OF VIRUS

Abstract

Double infection of the allantoic sac with Melbourne and WSN viruses induced the formation of a combination virus, which had some of the antigenic properties of both parents and which maintained itself through serial passage in the chorioallantoic sac. In the course of prolonged passage in the egg, three varieties of combination virus were found. The first (X₁) occurred in ten passages and was characterized as follows: X₁ was produced in and could be successfully passed from those chick embryos that had received very large inocula of virus. The X₁ hemagglutinin was efficiently inhibited by both M and W antisera. Each passage fluid, containing X₁ as the predominant strain, also contained large amounts of the parent forms M and W. It is very likely that X₁ reverted to parent types of virus at a high rate.