BIOCHEMICAL STUDIES 



119 



nucleic acid. But this would hardly be justified, since the infect- 

 ing phage particles may carry sufficient phage nucleic acid into 

 the bacteria to promote synthesis of a considerable amount of 

 phage protein. Furthermore, there is as yet no evidence that 

 bacterial nucleic acid present before infection does not partici- 

 pate in phage-protein synthesis. 



10 15 



Min. after infection 



20 



25 



Fig. 6. Synthesis of deoxy nucleic acid and of protein in E. coli after 



infection by phage. 



Further valuable information about the course of phage forma- 

 tion in bacteria has been obtained by the use of radiations. 

 Latarget (1948) studied the effect of X- irradiation of infected 

 cells. For up to 7 minutes after infection the results were char- 

 acteristic of a system in which it is necessary to secure only one 

 hit per original phage particle to prevent reproduction of that 

 particle. In the period from 9 to 13 minutes after infection it is 

 necessary to record more than one hit per infecting particle to de- 

 stroy the phage. From 13 minutes after infection until the 

 bursting of the bacteria the actual number of phage particles 

 present does not appear to increase, but the resistance of the 

 particles to irradiation does increase markedly. The rise in re- 

 sistance may be due to an increase in size of the new virus par- 

 ticles. 



