474 BACTERIOPHAGES 



infected with 2 different kinds of virus (Delbruck and Luria, 

 1942). 



Procedure. Details of a typical one-step growth experiment 

 will be given, followed by a discussion of the results. The 

 virus used will be coliphage T2 and the host cell, strain B of 

 E. coli grown in broth. The medium used throughout will be 

 broth. The number of infected bacteria will be determined by 

 neutralization of unadsorbed phage with anti-T2 serum, fol- 

 lowed by plating of a suitable dilution for plaque count. The 

 infection will be single, i.e., multiplicity about 0.1. All platings 

 for phage assay will be by the agar layer technique. It is 

 already known from other experiments that with strain B of 

 E. coli grown in broth at 37 °C., about 80 per cent of a given 

 sample of phage T2 will be adsorbed in 5 min.; also that with 

 the sample of anti-T2 serum available a dilution of 1 :50 will 

 neutralize about 95 per cent of a sam^ple of free phage in 5 n:iin. 

 It has been found from a preliminary trial experiment that the 

 latent period for T2 with B grown in broth at 37 °C. is between 

 20 and 25 min. and that burst size is about 100. This experi- 

 ment is designed to determine these characteristics more pre- 

 cisely. 



a. Reagents. 1. Culture of strain B grown in broth with 

 active aeration to a concentration of 5 X 10" cells ^ml. 



2. Stock of T2 phage diluted in broth to a concentration of 

 5X10' particles/ml. 



3. Anti-T2 serum diluted 1 :50 in broth. 



4. Nutrient broth for dilution of the infected culture. These 

 reagents are accurately dispensed in test tubes according to the 

 protocol and brought to 37 °C. before the start of the experiment 

 so that there will be no effect of temperature \ariations on 

 bacterial metabolism. 



/;. Other materials. Tubes containing 2.5 ml. each of U.7 per 

 cent melted agar inoculated with strain B for the agar layer 

 technique; agar plates, and 0.1 ml. pipets. 



