92 BACTERIOPHAGES 



by work from several laboratories. The presence of a hexose in 

 the material released from T4 by a specific lipocarbohydrate was 

 first mentioned by Jesaitis and Goebel (1953). Sinsheimer 

 (1954) independently found glucose attached to some but not 

 all of the HMC released from T2 phage DNA by the combined 

 action of pancreatic deoxyribonuclease and purified venom phos- 

 phodiesterase. Volkin (1954b) reported similar results for T2, 

 T4, and T6 phages, except that in T4 he found one mole of glu- 

 cose for each mole of HMC. In addition, he found no glucose in 

 Tl phage. Sinsheimer (1956) confirmed the difl?"erence between 

 T2 and T4, and found that glucose content is one of several 

 characters showing unusual inheritance in crosses between T2 

 and T4 (Streisinger and Weigle, 1956). 



Cohen (1956) reported that the r mutants of T2, T4, and T6 

 contain higher glucose/deoxyribose ratios than do the wild type 

 phages. Sinsheimer's (1956) analytical results do not support 

 this finding so that clarification must await further studies. 



6. Extinction Coefficients of Phage Preparations 



An analytical quantity of some interest to phage workers is the 

 light absorption at 2,600 A since this is a measure of the nucleic 

 acid content of the virus particle. However, there has been no 

 uniformity in the presentation of data. The absorbancy has been 

 expressed as extinction coefficient per infective phage particle, 

 per morphologically typical phage particle, or per mg. of phage 

 phosphorus per ml. In some cases the extinction coefficient has 

 been corrected for light scattering, in some cases not. This lack 

 of uniformity makes comparison of data difficult. The expres- 

 sion of analytical results in terms of the infective particle is very 

 convenient for the analyst but is only of comparative value be- 

 cause of unknown contamination of phage preparations with 

 inactive phage particles and uncertainties in the efficiency of 

 plating. Luria, Williams, and Backus (1951) avoided these 

 difficulties by giving the absorbancy per morphologically typical 

 phage particle counted in the electron microscope. Examples of 

 the available data are given in Table XI. They express optical 



