FATE OF INFECTING PHAGE PARTICLES 223 



/. Material transfer between unrelated phage strains. The first ex- 

 periment of this type was performed by Kozloff (1952b). Host 

 bacteria were infected with unlabeled T7 at a multiplicity of 6 

 and after incubation for 3 minutes were infected with P^Mabeled 

 T6 at a multiplicity of 1.5. The infected bacteria were centri- 

 fuged to remove unadsorbed phage and then permitted to lyse. 

 The final yields of the phages were 4.4 X 10^ T7 and 3.3 X 10^ 

 T6 per ml. The T6 and T7 phages were liberated from dif- 

 ferent bacteria because plating on mixed indicators gave no 

 clear plaques, confirming the occurrence of mutual exclusion be- 

 tween this pair of phages. The phage yield was purified in the 

 usual way by differential centrifugation and the T6 progeny 

 were then removed by repeated absorption of the phage mixture 

 with B/3,4,7. Of the original P^- present in the parent T6 

 phage, 37 per cent was found in the T6 progeny and 4.6 per cent 

 in the T7 phage. This experiment suggests the transfer of P^^ 

 from T6 to T7 in mixedly infected cells, although the amount 

 transferred is far less than in the homologous system. Unfor- 

 tunately the incorporation of the P'^^ \^^q ^j^^ 'py phage was not 

 further checked by determining the distribution of the isotope 

 after adsorption of the T7 phage to B/6, for instance, or after 

 precipitation with anti-T7 serum, so that the transfer cannot be 

 accepted as proved by these experiments. 



In experiments by French, Graham, Lesley, and van Rooyen 

 (1952) the transfer of V^"- from T2 to T7 and to Tl was tested. 

 The experimental conditions were such that T2 was almost com- 

 pletely excluded, the T2 yield being at the most 10 per cent of the 

 total phage. The amount of P^- which was found in the isolated 

 phage progeny varied from 3 to 6 per cent. However this repre- 

 sents maximum possible transfer values to heterologous phage 

 rather than actual transfer values, because in these experiments 

 neither parental labeled T2 phage which failed to absorb, nor 

 progeny T2 phage which should be relatively rich in P^^ label, 

 were removed from the phage yield. Therefore these experi- 

 ments do not demonstrate actual heterologous transfer of phage 

 materials, as was realized by the authors who concluded "that 



