Morphology and cell growth kinetics for DF-1 and primary CEF (passage 4) cells. Cell images for DF-1 (P285) (A) and primary CEF (P4) (B) cells were obtained by inverted microscopy at 100× magnification. (C) Growth kinetics. Immortal DF-1 and primary CEF cells were seeded at 1 × 105 cells per 10-cm dish and the accumulated cell numbers were counted at each day for 7 days. Experiments were repeated three times.