1. Cultures of Diplococcus pneumoniæ, Bacillus coli, Bacillus fluorescens liquefaciens and Bacillus prodigiosus, when grown in meat infusion broth exhibit an initial latent period when the culture used for inoculation is no longer growing at its maximum rate; if, however, the culture is growing at its most rapid rate the bacteria, upon subculture, show no latent period but continue to multiply at the same rate as that of the parent culture.
2. If broth cultures of pneumococcus are centrifuged at the beginning of the period of maximum rate of growth, the bacteria remaining in the supernatant fluid continue to grow at a rapid rate upon further incubation; if, however, the culture is centrifuged at the end of the period of maximum rate of growth, those bacteria which remain in the supernatant fluid show a prolonged latent period, during which many of the organisms die. While the death of these bacteria is taking place the process follows closely the law of unimolecular reactions.
3. Actively growing pneumococci inoculated into the supernatant fluid from a 4 day culture of the same strain continue to grow rapidly for an appreciable time after inoculation.
4. Filtrates from 24 hour cultures of pneumococcus inhibit the further growth of actively growing pneumococci when the latter are inoculated into such filtrates. This inhibitory action of the filtrates is lost in part as the culture from which the filtrate is obtained is allowed to incubate longer.
5. Actively growing pneumococci, after exposure at low temperatures to the action of the filtrate of a 24 hour broth culture of the same strain, show a greater lag than the controls.
6. The foregoing facts offer strong support for the view that lag is an expression of injury which the bacterial cell has sustained from its previous environment.