CHEMICAL COMPOSITION 85 



of phage concentrates with alcohol in the cold and by acid pre- 

 cipitation at pH 4.2. These methods were also applied to the 

 purification of phage T7 by Putnam, Miller, Palm, and Evans 

 (1952). 



Herriott and Barlow (1952) reported yields of 2 to 5 X lO'^ 

 per ml. of phage T2 in a chemically defined medium. Ap- 

 parently, adequate aeration brought about by vigorous shaking 

 is the explanation of the high yields, as in the case of the results 

 with phage T3 of Fraser (1951a) noted above. The phage 

 stocks were filtered through a calcined diatomaceous earth 

 (Celite) to remove bacterial debris, and the phage was pre- 

 cipitated in the cold by acid at pH 4.0. The precipitated 

 phage was resuspended at pH 6.5 and treated with deoxyribo- 

 nuclease, after which it was purified by differential centrifuga- 

 tion. 



A fairly simple method of preparing T2 phage lysates in 10 

 liter quantities was described by Siegel and Singer (1953). A 

 defined medium was aerated by forcing air through a sintered 

 glass tube and lysates which titered 2 to 5 X 10^^ per ml. were 

 produced. Wyatt and Cohen (1953) obtained lysates titer- 

 ing up to 1 X 10^2 per ml. through the use of a thin film of en- 

 riched medium in which cells at 3 X 10^ per ml. were multi- 

 infected. 



Wahl and Blum-Emerique (1949a) used alcohol precipitation 

 for concentration of phage CI 6 with good recovery of activity. 

 Wahl, Terrade, and Monceaux (1950) used successive adsorp- 

 tion and elutions from calcium phosphate for concentration and 

 purification of a salmonella phage. Northrop (1955b) again 

 applied salting out and enzymatic treatment to purify a mega- 

 terium phage, which is inactivated by repeated centrifugation. 



2. Criteria of Purity 



Certain criteria of purity have been discussed from another 

 viewpoint in Chapter IV. From its dry weight and density one 

 can calculate the diameter of the infective particle. If the size 

 calculated in this way is larger than the true size but the effi- 



