Transforming R cells into S cells
The presence of heat-killed S cells transforms live R cells into live S cells. (a) Mouse dies after injection with the virulent S strain. (b) Mouse survives after injection with the R strain. (c) Mouse survives after injection with heat-killed S strain. (d) Mouse dies after injection with a mixture of heat-killed S strain and live R strain. Live S cells were isolated from the dead mouse, indicating that the heat-killed S strain somehow transforms the R strain into the virulent S strain.