Incubation periods of mice after challenge with scrapie. Mice were inoculated with extracts of soil incubated with a pool of classical scrapie isolates or with a dilution series of the same scrapie pool without soil incubation g/mL of brain inoculum are shown). Open circles: the PrPSc distribution phenotype G338; open triangles: Apl338ii; square: Cag338; solid triangles: G338/Apl338ii mix; diamond: P338/Apl338ii mix. Each vertical line indicates the mean incubation period of a group of mice irrespective of their PrPSc distribution phenotype. 1D and 13 M are the prion eluted from soil after a 1 day or 13 month incubation respectively.