osidase substrate 3.3.-diaminobauidine tetrahydrochloride as described in reference IS. FISV-l-infected areas are identified by dark staining. (A to CI Tissue from a BAUM mouse 6 days after oral inoculation with I ISV-1 strain 17 4. (A) Dorsal sieve of the stomach, with the attached esophagus and duodenum,