Fig. 3.

Plot of proliferation index (BrdU⁺ cells/total cells in a 100 × 100 μm region) as a function of local cell density. Cultures were maintained in medium 199 and 10% FBS for 3 d, followed by medium 199 and N2 for 5 d, and received BrdU for the final 4 hr in vitro. Although all cells in the sampled regions were maintained in the same environment and were completely contacted by adjoining cells, the relative numbers of proliferating cells decreased with increased cell density.