Genetics and Microbiology 35 



fiftyfold from one factor to another. Another phage-medi- 

 ated transduction has been found in E. coli, but this is 

 rigidly limited to a cluster of factors (for galactose fermenta- 

 tion) closely linked to the prophage site (25, 35), and a 

 special relationship of the transduced fragment to the de- 

 veloping phage is therefore certain. 



The distinctive features of phage-mediated transduction 

 in this context are: (a) the transductive competence of 

 any crop of phage is determined entirely by the genotype 

 of the host cells from which the crop is obtained, and 

 (b) lysogeny is separable from the transformation, that is, 

 transduction may be consummated without the necessary 

 establishment and maintenance of the lysogenic state, and 

 recipient bacteria may be lysogenized without usually 

 manifesting other genetic changes. In the lysogenic con- 

 versions, the competence of the phage is essentially inde- 

 pendent of the host, and lysogeny is both necessary and 

 sufficient for the concomitant changes. It is conceivable 

 that these conversions are a relic of "bacterial" genes not 

 yet redifferentiated in the phylogeny of the phage, but the 

 chief virtue of such ethereal speculations is to emphasize 

 the ambiguity of our concepts of organismic individuality 

 (8). 



Pofenfialifies of Recombination Methods 



Why emphasize the prospects of recombination over 

 other means of genetic analysis? First of all, it should lead 

 to the substantiation of life cycles (compare alteration of 

 generations in plants and animals), but we must confess 

 that the L-forms have eluded genetic analysis. Then, re- 

 combination is indispensable for understanding other 

 modes of genetic variation. For example, it furnishes proof 

 that the effects of acriflavine in yeast, already noted, are 

 cytoplasmic depletions rather than directed gene muta- 

 tions, while in lysogenic E. coli it has fixed the genie locali- 



