The products required from the tissues are extracted in the laboratories of the pharmaceutical companies using purification techniques involving many steps. Initially these steps are crude but increase in specificity as more extraneous materials are removed. These later, more specific purification steps involve stages which are appropriate for only the product of interest, and as such utilise particular physical or biochemical properties that would be shared with few other compounds. In this way it is possible to obtain an homogeneous product free from contaminating molecules. It might be expected, therefore, that any BSE present in a tissue would be reduced during purification steps.
Filtration is also effective, as the agent absorbs to the filters themselves.
S535 Purves para. Any part of this report may be reproduced subject to acknowledgement.