Investigations of the induction period of an in vitro hemolysin response to sheep erythrocyte antigen revealed the following:
1. After antigen stimulation precursors of plaque-forming cells rapidly maturate to the point of hemolysin production.
2. Initial maturation probably occurs in the absence of cell division.
3. After initial maturation, a latent period of about 12 hr occurs before the first doubling of PFC.
4. At least the first three cell doublings are synchronous, with a generation time of 7–8 hr.
5. Synchronous cell division implies that all precursor cells are at the same point in the cell cyde when they are initially stimulated.