PrPsc polymer growth scenarios for the case s* < s1. The parameters are n = 6, a = 0.05, b = 9 × 10−4, and β = 0.015, which corresponds to s* = 66.44 and s1 = 96.78. (Top) s(0) < s* (y10(0) = 5 × 105); (middle) s(0) > s* (y25(0) = 8 × 103); and (bottom) s(0) > s1 (y200(0) = 25,000). In all cases the initial inoculation is z(0) = 5 × 106.