84 BACTERIOPHAGES 



indicates that his phage preparations were probably as pure as 

 any up to date. 



Northrop (1938) concentrated and purified a staphylococcus 

 phage by applying the techniques so successfully used for enzyme 

 purification. The host bacteria were grown in a yeast extract 

 medium, and after phage lysis was complete much nonphage 

 material was removed by precipitation with lead acetate. The 

 supernatant fluid was concentrated in vacuo to 1 /20 of its volume 

 and digested with trypsin, which does not harm the phage. 

 The phage was then precipitated with ammonium sulfate and 

 further purified by ammonium sulfate fractionation. 



Kalmanson and Bronfenbrenner (1939) concentrated and 

 purified a strain of coliphage T2, using collodion membranes. 

 Hershey, Kalmanson, and Bronfenbrenner (1943a) prepared 

 highly concentrated phage suspensions by simply washing the 

 phage from the surface of agar plates on which large populations 

 of bacteria had been lysed. From 10^^ to 10^^ phage particles 

 per ml. were obtained in this way. This method was further 

 developed and applied to the seven coliphages of the T series 

 by Swanstrom and Adams (1951), with resultant phage concen- 

 trations about ten-fold greater than those obtained with broth 

 lysates. This method was applied by Cohen and Arbogast 

 (1950a) and Marshak (1951) and is useful in laboratories with 

 limited centrifuge facilities. Fraser (1951a) developed an ap- 

 paratus for growing bacteria in batches up to 6 liters under 

 conditions of vigorous aeration. He obtained yields of phage 

 T3 of better than 10^^ per ml. in large scale lots. 



Coliphage T2 had been concentrated on a large scale from 

 fluid lysates by means of the Sharpies continuous flow centrifuge 

 (Hook, Beard, Taylor, Sharp, and Beard, 1946). The concen- 

 trated phage suspensions were then further purified by sedi- 

 mentation in a high speed vacuum centrifuge. Similar methods 

 were used by Kerby, Gowdy, Dillon, Dillon, Csaky, Sharp, and 

 Beard (1949) for the purification of coliphage T7 and by Putnam, 

 Kozloff, and Neil (1949) for the purification of coliphage T6. 

 In the latter paper are preliminary reports of the fractionation 



