Rickettsiae of epidemic typhus fever and Rocky Mountain spotted fever have been microscopically localized and identified in smears of exudates and tissue sections from infected cotton rats by means of homologous antibody labelled with fluorescein. Epidemic typhus has also been identified in smears from single infected human body lice.
Mumps virus antigen has been microscopically localized in the parotid of the experimentally infected monkey by the same method. The antigenic material, probably active virus, was found in the cytoplasm of the acinar cells. Such infected acini were scattered irregularly throughout the gland. Some antigen could be seen in the lumens of the parotid ducts and small amounts were present in the cytoplasm of the epithelial cells lining the ducts.