Virus replication in mice. For the measurement of virus replication in the
brain and liver, at 5 days postinfection, mice were sacrificed and perfused with 10
ml of PBS, and brains and livers were removed. The left half of the brain and the
liver were placed directly into 2 ml of isotonic saline with 0.167% gelatin (gel
saline). The right half of the brain was used for histology and viral antigen
staining as described below. All organs were weighed and stored frozen at 80°C
until determination of virus titers. Organs were homogenized, and virus titers
were determined by plaque assay on L2 cell monolayers