124 BENZERETAL. 



i) Phage multiplication depends upon the presence of oxidizable 

 compounds in the suspending medium of infected cells. Phage 

 multiplication does not occur in buffer solutions and does not occur 

 if the respiration of the infected cells is blocked in one way or 

 another. 



2) Material from the medium is used not only for supply of 

 energy but finds its way into the newly produced phage particles 

 as well. This was shown by using the tracer technique with iso- 

 topic P, N, and C (Cohen, 1948; Putnam and Kozloff, 1950; Her- 

 shey, unpublished). 



Detailed data are available now for radioactive phosphorous. It 

 was found that 70 to 80% of the phosphorous content of T6 stems from 

 the inorganic phosphate of the medium. Only the remaining 20 to 

 30% are derived from host material present at the time of infection. 

 It should be mentioned here that apparently little of the phosphorus of 

 the infecting phage particle or particles, which start the multiplication 

 process, appears in their progeny. Most of it is found in the medium 

 after lysis in low molecular form or in the bacterial debris (up to 78% ) . 

 This observation supports once more the assumption that the infecting 

 phage particles disintegrate and are not recovered as such. 



Studies of the metabolic procedures involved in phage reproduction, 

 their mutual interaction and timing, have been done without too much 

 clarification. Various substances are capable of stopping multiplication 

 reversibly (proflavin, 5-methyl-tryptophan) or irreversibly (depending 

 strongly on time of removal of poison); other substances were found 

 to be indispensable for virus growth (Cohen, 1949). It is not yet clear 

 on which level such interactions occur. At least two alternatives are 

 always possible: either some sub-unit of the virus itself is affected 

 directly or the growth supporting metabolic machinery of the bacterium 

 is altered, consequently affecting virus multiplication, but in a more 

 indirect manner. 



Cohen studied gross chemical changes occurring in T2 -infected 

 bacteria during the latent period. He found that protein synthesis con- 

 tinues immediately after infection, DNA-synthesis is delayed by seven 

 to ten minutes but then goes on at a constant rate, RNA-synthesis is 

 stopped. In uninfected cells RNA-synthesis exceeds that of DNA-syn- 

 thesis about three times. Most of the material synthesized by infected 

 cells appears to be phage material. 



27. Premature lysis. — MultipUcation of phage particles proceeds 

 behind the cloak of the cell wall, and the result is not revealed until the 



