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Bodian and C u m b e r l a n d h a v e described the growth curve of the Lansing strain of poliomyelitis virus in the rhesus m o n k e y (1). A l t h o u g h the mouse is used in m o s t laboratories for the s t u d y of poliomyelitis virus infection, the p a t t e r n of multiplication of virus has n o t been studied in this species. T h e present report deals with a description of this aspect of the pathogenesis of ex2o~rimental poliomyelitis in mice. Materials and MethodsVirus.--A pool of the 85th mouse passage, Lansing strain (2) of poliomyelitis virus which has been maintained in this laboratory 1 was used for all but the first experiments in which the 80th and 82nd mouse passages were used. The pools consisted of the entire central nervous system (CNS) of mice paralyzed within 5 days of intracerebral inoculation with virus, and of spinal cords and medullae (to be referred to subsequently as cords) of mice paralyzed thereafter. The infectivity titers of the pools measured by repeated intracerebral tests were between 10-4.0 and 10-4-~ LDs0 (50 per cent lethal dose). No significant differences were noted between titrations performed with 20 and ycith 8 mice per dilution.Suspensions containing virus were prepared in all instances by grinding the tissues with a small amount of alundum in a mortar with a pestle, with the addition of sterile saline (0.15 M NaCl). They were centrifuged at 2000 R.P.M. for 30 minutes, and the sediments discarded. The supernatant fluids, which thus constitute the preparations of virus, were usually tested for bacterial sterility before use. In some tests it was desired to inoculate mice without delay, so crystalline potassium penicillin G (final concentration 50 u/ml.) and streptomycin sulfate (final concentration 0.1 mg./ml.) were added to the suspensions in saline. No disturbing bacterial growth resulted in mice receiving the materials and the antibiotics had no effect on the resulting titer of virus.Growth Curves.--White Swiss mice, 3 to 5 weeks of age, were inoculated intracerebrally with 0.03 ml. of either a 10 per cent or 1 per cent suspension of virus. They were then closely observed for signs of infection. Groups of 5 to 10 unparalyzed or paralyzed mice were sacririced

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Subclinical infection with poliomyelitis virus among familial associates of cases has been adequately demonstrated (1-15). Although there is serological evidence of the development of antibodies in the patient, there is little information with regard to the antibody status of his familial associates. Early neutralization tests with the sera of cases (16--21) and of contacts (22, 23) utilized stock passage strains of virus which were not the specific strains responsible for the disease of the patients although Brodie et al. (24) also used a

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