Key points are not available for this paper at this time.
Evidence is presented to show the presence in normal rat serum of four different serum factors essential for growth of 3T3 or SV40-transformed 3T3 mouse fibroblasts: a factor that specifically promotes growth of normal 3T3 cells; two factors that specifically promote growth of transformed 3T3 cells; and a factor that sustains viability of both normal and transformed 3T3 cells in serum-free medium, probably without inducing growth of the cells. These factors are separated and partially purified.
Paul et al. (1971) studied this question.