Genetic Aspects of Transformations of Pneumococci

Two discoveries were reported in 1927 and 1928 which indicated that the hereditary elements of living organisms were more open to modification by experimental intervention than had previously been supposed by geneticists. On the one hand, Muller, working with animal material, and Stadler, working with plants, demonstrated conclusively that X-rays could induce genes to mutate. On the other hand, Griffith (1928) showed that un encapsulated pneumo cocci could be made to synthesize a capsule of a given type, under the action of some material present in encapsulated pneumo cocci. The induced change was permanent and inherited by the descendants of the transformed bacteria. While the experiments with X-rays oriented genetical research for the succeeding decade, Griffith's discovery exerted virtually no influence on biological thought until nearly twenty years later, for the absence of sexual reproduction in bacteria was sufficient to discourage any geneticist from studying these induced transformations. Fortunately, Griffith's...