S. S. COHEN 



299 



chamber was filled by perfusion and held identical aliquots of slightly more 

 than 3 cc. The background was determined between samples and yielded 

 8 to 11 counts per minute. This was subtracted from the count on the 

 sample. Samples and the time of counting were adjusted to yield 100 to 

 1000 counts. Comparisons of samples were made at similar total counts. 

 In Table II are presented data on four experiments of this type, in which 

 the increments in DNA in the infected bacteria and the yields of isolated 

 virus were comparable to the data presented previously. The radioactivity 

 of the virus isolated after synthesis under these conditions was far lower 

 than the radioactivity of the host P. It has therefore been concluded that 

 most of the P organized into virus is derived from the medium after in- 

 fection. 



Table III 

 Radioactivity of Virus Synthesized in Unlabeled Cells in Media Containing P^^ 



*Virus to cell ratio 5.0. 

 fVirus to cell ratio 3.0. 



Synthesis of Virus in Unlabeled Host Cells in Media Containing Radio- 

 active Phosphate — Bacteria were grown in the absence of radioactive P. 

 Virus was added immediately after the addition of 0.02 to 0.05 millicurie of 

 inorganic phosphate and tryptophan for the adsorption of T4. The cul- 

 tures were incubated, and the DNA increments, rates of virus liberation, 

 and isolated virus were studied as described previously. 



In Table III are presented some data on experiments of this type. The 

 radioactivity of the virus isolated after synthesis under these conditions was 

 70 to 75 per cent of that of the inorganic phosphate of the medium. These 

 data confirm the previous conclusion that most of the P organized into 

 virus is derived from the medium after infection. 



Nucleic Acid Turnover after Infection — Since the P^^ added to the F me- 

 dium was assimilated in DNA after infection, the distribution of the radio- 

 activity in the infected cell was studied. In a typical experiment bacteria 

 were grown to 2 X 10^ per cc. in 1 liter of F medium. The cells were centri- 

 fuged and resuspended in 100 cc. of F medium. To the culture were added 



120 



