The behavior of bacteria subjected to the influence of mutating agents has been studied in considerable detail, but the interpretation of the results is still largely dependent on analogy to those obtained with higher forms. The lack of clear-cut cytological evidence of a nuclear cycle has been a handicap to the bacteriologist. Studies with Tradescantia microspores by Sax (1940) showed considerable variation in the ease with which chromosomal aberrations could be induced during the various

more »

... s of the nuclear cycle. Aging of Dro8ophila sperm and of seed (cf. Sax) increased the yield of mutations induced by radiations. Clark et al. Haas et al. (1948) have studied the effect of mutating agents on Escherichia coli strains preceding sexual recombination, but the analysis was limited to the few pertinent biochemical deficiencies; no analysis was made of the effect of mutagens, applied during the course of association of the recombining strains, on other genetically controlled traits. Since it is possible that only a small fraction of the organisms in such mixtures of two recombining strains is actually involved in the transfer of genetic material, a change in mutability during the process might be difficult to evaluate. A definite change in the disposition of nuclear material has been reported in the transition of bacterial vegetative cells to spores (Kleineberger-Nobel, 1947; Delaporte, 1950) . A process akin to reduction division appears to occur, although the actual observation of chromosome numbers cannot be made. During spore germination the nuclear material returns to the state encountered in the vegetative cell. The effect of mutagenic agents on bacteria during such transition stages has not been reported previously and should yield additional information on the mechanism controlling heredity in these microorganisms. Although we have studied the quantitative aspects of ultraviolet-induced mutations through the entire spore to spore cycle of Bacillus anthraci8, this report emphasizes the results during the germination process. Spore formation with this organism in nutrient broth extends over a considerable period of time, and therefore a quantitative estimation of the effects of mutagenic action on the developing spore is difficult to obtain; spore germination, however, can be controlled more readily. As a measure of mutability we employed the convenient and widely used mutation to streptomycin resistance. Few reports on the induction of mutations in bacterial spores have come to 1