Growth-controlling factors produced during the logarithmic and stationary phases of Tetrahymena pyriformis.

Tetrahymena pyriformis grown to logarithmic phase and then inoculated into either fresh or conditioned medium exhibited a shorter lag phase than ciliates taken from stationary cultures. The growth inhibiting substance(s), which is probably produced by the growing ciliates, is thermostable and can be adsorbed to activated charcoal.