32 Perspectives in Microbiology 



vestigated in several places. Genetic exploration of vari- 

 ous morphological representations of bacterial sex is 

 overdue. 



Genetic Transduction 



We now depart from mechanisms that should be familiar 

 to every student of general biology, and must deal with a 

 unit not previously recognized in genetics: the hereditary 

 fragment that defines genetic transduction. In 1928, Grif- 

 fith transformed the capsular specificity of rough pneu- 

 mococci by heat-killed vaccines of smooth types (16). One 

 is again forced to acknowledge the fortuitous success en- 

 joyed by some irrationally designed but well-executed 

 experiments. Although not cited by Griffith, the literature 

 of the preceding decade (26) carried many accounts of 

 paragglutination, whereby a superficial attachment of 

 heterologous antigens to bacterial cells was misconstrued 

 as hereditary alteration. Griffith, however, soon realized 

 (as some of his successors have not) that the transformation 

 could not concern merely the capsular polysaccharide, but 

 must involve the machinery for its formation, as we would 

 now say, a "genetic" or metapoietic factor. Griffith also 

 conceded the theoretical qualification that his vaccines con- 

 tained residual bacteria not revealed by conventional 

 sterility controls, but resuscitated in the experimental mix- 

 tures. This caution has often been overlooked and can be 

 disposed of only with the help of strains differentiated by 

 several markers (23, 24), as was eventually done with the 

 pneumococcus also (4, 20). 



Unfortunately, the occasional notice taken of Griffith's 

 work by genetically minded workers was often confused 

 by the prescription of "directed mutation" and perhaps 

 by the indiscriminate use of "transformation" for any 

 species of change; it was not for another twenty years that 

 this transformation was again generally accepted (36) as 



