APPENDIX 483 



10^ to 10^/ml. A nephelometer described by Underwood and 

 Doermann (1947) has been used by Doermann (1948a) to 

 follow the course of lysis of bacteria infected with phages. The 

 instrument can be placed in an incubator and a bacterial 

 culture can be grown with aeration in the nephelometer tube 

 so that the culture is under continuous observation. The light 

 scattering of such a culture increases exponentially at the same 

 rate as the bacterial population as determined by plate counts. 

 When such a culture is infected with a sufficient multiplicity of 

 phage that all bacteria are infected within 1-2 min., the tur- 

 bidity remains essentially constant from the moment of infec- 

 tion to the end of the latent period, indicating that bacterial 

 growth ceases immediately on infection. At the end of the 

 latent period, turbidity rapidly decreases, and simultaneously 

 there is rapid increase in phage titer. These experiments 

 demonstrate that the initiation of lysis as observed by nephe- 

 lometric measurements in concentrated bacterial cultures occurs 

 after the same latent period as the liberation of virus in F.G.T. 

 and S.G.T. of the one-step growth curve. The evidence in- 

 dicates that bacterial lysis is coincident with phage liberation. 

 This is also indicated by electron microscope photographs of 

 bursting bacteria caught in the act of spilling out phage par- 

 ticles through a gap in the bacterial membrane (Luria, Del- 

 briick, and Anderson, 1943). 



[Adsorption of Phage Without Phage Development 



In many types of experiments it is essential that phage growth 

 start almost simultaneously in all of the infected bacteria. This 

 can be accomplished because phage will adsorb to bacteria in 

 media in which phage growth is not possible. Two such 

 methods are given below. (1) Broth-grown bacteria are washed 

 by centrifugation and resuspended in buffered -saline (0.067 M 

 phosphate pH 7.0, 0.1 M NaCl, 0.001 M MgS04, and gelatin 

 at 20 /xg./ml.). Adsorption is allowed to proceed in this 

 environment. The infected bacteria are then centrifuged and 

 resuspended in prewarmed broth. Phage development will 



