50 BACTERIOPHAGES 



with the effects of radiations, which will be considered separately 

 in Chapter VI. This chapter describes the effects of other 

 physical and chemical agents on phage particles. Some of the 

 agents that have been studied tend to be phage-specific in their 

 action, and can be used as aids to the classification of phage 

 types (Burnet, 1 933e) . This application is discussed in Chapter 

 XXII. 



1. Effect of pH 



Bacteriophages are usually stable over the pH range of 5 to 8. 

 At low temperatures the range can often be extended to pH 4 

 and pH 9 or 10. T2 can be precipitated at pH 4 without loss 

 of infectivity (Herriott and Barlow, 1952). Curves showing 

 stability as a function of pH are given for purified preparations 

 of coliphage T2 by Sharp, Hook, Taylor, Beard, and Beard 

 (1946), of coliphage T6 by Putnam, Kozloff, and Neil (1949), 

 and of coliphage T7 by Kerby, Gowdy, Dillon, Dillon, Csaky, 

 Sharp, and Beard (1 949) . Some kinetic data on phages CI 6 and 

 SI 3 are given by Wahl and Blum-Emerique (1947) over the 

 pH range between 3 and 8. 



2. Urea and Urethane 



Both urea and urethane denature proteins and inactivate 

 enzymes. They also inactivate viruses. Burnet (1933e) in his 

 studies on the classification of the dysentery-coli phages used 

 susceptibility to inactivation by concentrated solutions of urea 

 as a differential characteristic. He found large differences in 

 rate of inactivation from one strain to another. Sato (1956) 

 studied the action of urea on phage T4 and observed minimal in- 

 activating effects at temperatures near 15°. Urea has been 

 used also to extract nucleic acid from phage T2 (Cohen, 1947a). 

 The effect of urethane on the thermal inactivation of coliphage 

 T5 was investigated by Foster, Johnson, and Miller (1949). 

 The thermal inactivation rate was increased by urethane at all 

 concentrations above 0.05 M, the first-order velocity constant 

 increasing as the 2.3 power of the urethane concentration. The 



