STUDIES ON T H E PROPAGATION IN VITRO OF POLIOMYELITIS VIRUSES II. A DESCRIFrlON 01~ TEE GROWTH ClmvE AND ITS RELATION TO THE CYTOPATHOGENICITY OF POLIOMYELITIS VIRUS* BY WILLIAM F. SCHERER, M.D., ArrD

The rate of change of a microbial population is commonly depicted by a growth curve. This reflection of the dynamic aspects of reproduction under relatively fixed conditions is established readily for most microbial agents by interval enumeration either of the viable forms, or of the viable and nonviable forms. Contrariwise, for viruses, an accurate temporal enumeration of the intracellular and extracellular population is made difficult by the obligatory intracellular parasitism that characterizes this group of noxious agents. This obstacle was successfully overcome for several viruses. For example, growth curves were determined for the T series of coliphage (1-3), the viruses of influenza (4, 5) and mumps (6) in embryonated eggs, and for mumps virus in tissue culture (7). However, the dependence of a virus in tissue culture upon the viability of the host cell has made poliomyelitis virus and other viruses with long incubation period less amenable to study, since it is essential for the maintenance of cellular metabolism to renew or to supplement the liquid medium. Nevertheless, it was possible in the present studies by taking cognizance of these factors to determine the pattern of growth for poliomyelitis virus, Yale-SK strain, in cultures of monkey testicular tissue and to relate the occurrence of cellular damage to the growth curve. I t is the purpose of this paper to report the findings which demonstrated that the growth in vitro of poliomyelitis virus in cultures of monkey testicular tissue occurred in discrete cycles and that viral multiplication was accompanied by cellular destruction.