Electron microscopy of salivary gland viruses

A human and a mouse strain of the salivary gland virus have been examined by electron microscopy. The human strain was transmitted, prior to examination, to tissue cultures derived from human myometrial cells, while the mouse strain was examined in mice inoculated intraperitoneally. The nuclear forms associated with both strains of virus were morphologically similar. Nuclear inclusions, composed of particles interspersed with dense clumped chromatin, were a striking feature of infected cells. The cytoplasmic forms were of 2 types—one a 300 to 500 mµ homogeneous dense spherical form, and the other a target-like form composed of a central dense dot in a pale zone surrounded by a dense shell—the entire configuration measuring 100 to 180 mµ. The target-like particle appeared to be identical in both strains. The spherical cytoplasmic forms in cells infected with the human strain appeared to be solid, while in cells infected with the mouse strain there was evidence of formation of target-like forms within the spheres. Possible mechanisms by which infection of the cell may occur, as well as possible mechanisms and sites of multiplication of virus, are discussed.