Table 1. Bioassay of medium conditioned by infected Rov cultures.

Material	Incubation period,* days	No. affected/no. inoculated
Control (sample diluent)	>200	0/5
100,000 × g	76.8 ± 2.6	5/5
100,000 × g pellet floated on 2.3 M sucrose	78 ± 1.2	5/5

^*Mean ± SEM after intracerebral injection of tg338 mice (15)