The inhibition of multiplication of one poliomyelitis virus by a poliomyelitis virus of another immunologic type has been established by using tissue cultures of monkey testes. The degree of interference varied from none, to partial, to complete, depending upon the time between inoculation of the interfering and the challenge viruses, and the amount of each virus inoculated. Reciprocal interference was demonstrated between Types 1, 2, and 3 poliomyelitis viruses.
Under conditions which resulted in complete suppression of the growth of one poliomyelitis virus by another, interference by poliomyelitis virus with the multiplication of four antigenically distinct "orphan" viruses and of three antigenically related strains of Coxsackie virus could not be demonstrated.
Poliomyelitis virus rendered non-infective by formalin or by irradiation with high energy electrons or with ultraviolet light, or treated so that only traces of residual active virus remained, failed to interfere with the propagation of active homologous virus.