Western blot analysis of inocula homogenates that were used to challenge the mice. Western blots were performed as described in Materials and methods using antibodies Sha31 (a and b) and 12B2 (c and d). Images a and c compare the western blot profiles obtained for the two different methods used to extract samples; solid tissues (T) and inocula (I). Images b and d show western blot profiles observed for the different prepared inolcula: 100% BSE (B), 50% BSE (50), 10% BSE (10), 2% BSE (2), 1% BSE (1) and 100% scrapie (S). For BSE/scrapie mixtures only the percentage BSE is indicated; the remainder indicates the percentage of scrapie. All inocula represent 10% (w/v) brain tissue in normal saline. An inoculum prepared from a TSE negative sheep was also analysed by Western blot (N). Molecular mass markers (M) are indicated in kDa. For (a) and (c) each sample was diluted to achieve optimum representation of banding profile; dilution of each source between (a) and (c) was kept constant. For (b) and (d) each lane was loaded with 15 μl of neat extracted sample, equivalent to 30 mg of brain tissue.