Abstract
The addition of active or irradiated T2 bacteriophage and T4 bacteriophage to E. coli B stops bacterial multiplication. The respiratory rate and respiratory quotient of the inhibited bacteria remained at the values observed just before infection. A respiratory rate decrease which occasionally appears can be roughly correlated with change of turbidity of the suspension. An intracellular inhibitor of multiplication appears to be liberated into lysates. A similar substance has been separated from normal E. coli B after sonic disintegration. These bacteriostatic preparations contain cytoplasmic granules with lactic acid dehydrogenase activity. The relationship of these phenomena to the interference effect in this system and others has been considered.