Mumps virus in a carrier culture of human conJunctiva cells (C-M cultures) persisted through 5½ months of cultivation in a medium containing sufficient specific antiserum to keep the fluid free of infectious virus. Cells from the C-M cultures were cloned under antiserum with an efficiency equal to control, uninfected cultures (40 to 100 per cent). Of 269 C-M cell clones examined, the cells of 262 contained antigen. Eight infected clones were grown into cultures sufficiently large to demonstrate that they released infectious virus and adsorbed erythrocytes in a manner similar to the original C-M cultures. Two uninfected clones were as susceptible to the effects of a cytopathogenic line of mumps virus as were uninfected control cells.
In healthy, growing cultures of C-M cells 0.1 to 1.0 per cent of cells adsorbed erythrocytes to their surfaces, suggesting that these cells were releasing virus. Reduction of serum content of the medium to less than 3 per cent, depletion of the medium, or crowding of cultures resulted in hemadsorption by 50 to 90 per cent of cells and an increase of virus in the medium. In growing cultures hemadsorbing cells did not appear damaged. It was observed that cells could simultaneously exhibit hemadsorption and mitosis.