A Method for Measuring Mutagenic Action

SUMMARY: A procedure has been evolved which permits an evaluation of muta-genic activity. It appears to be relatively free of experimental bias and analyses the effect of the mutagenic agent more or less independently of selection in the growth medium. It separates the period of phenotypic expression into a distinct unit so that it may be studied separately. Its sensitivity depends on the ability to differentiate cultures containing mutants and its precision depends on the number of flasks employed for subcultures. In a previous paper Jordan, Mefferd & Wyss (1951) reported that broth cultures, inoculated from suspensions of Bacillus anthracis spores irradiated with ultraviolet light, contained mutants in excess of the spontaneous level, providing large enough inocula were used; suitably small inocula of irradiated organisms gave rise to cultures which were normal with respect to their con-centration of mutant cells. A given irradiated suspension would produce mutant-enriched subcultures only when the inoculum of the survivors used was large enough to include a t least one induced mutant. It seemed likely tha