Process of giant cell formation estimated by colony formation. The morphology of colonies of HmLu cells infected with strain 007Lm at the 8th passage. Colonies of normal cell shape (A). Hybrid colonies of normal and giant cells (B, B'). A colony composed of giant cells (C). A multinucleated giant cell had several individual nuclei, as indicated by arrow (D) magnified from D in (B'). Giant cells of big nuclei with several condensed materials as indicated by arrows (E). Magnification: 40× (A-C), and 200× (D and E).