CHEMICAL COMPOSITION 87 



sorbancy (extinction at 2,600 A) was used as a criterion of homo- 

 geneity of purified T2 phage by Herriott and Barlow (1952). 

 The phage was assayed for these properties before and after 

 fractionation by alcohol precipitation, adsorption with alumina 

 or copper hydroxide, centrifugation, acid precipitation, adsorp- 

 tion to host cells, and treatment with antibacterial sera. 



The criteria of purity offered by an investigator for his ana- 

 lyzed preparations are an essential part of his evidence for any 

 unusual analytical results claimed. This point is too often dis- 

 regarded. 



TABLE VII 



Elementary Composition of Purified Bacteriophages 

 (per cent of dry weight) 



3. Elementary Composition 



Elementary analyses are available for only three serologically 

 distinct groups of phages, the staphylococcus phage of Northrop, 

 coliphage T7, and the group of phages closely related to T2. 

 Although these analyses (Table VII) are in good agreement 

 among themselves it is probably unwise to make generalizations 

 about phage composition from such a restricted sample. The 

 only seriously discrepant result is the low phosphorus content 

 reported by Kalmanson and Bronfenbrenner, which can prob- 

 ably be discarded as an error. It is specially noteworthy that 

 the assays on coliphage WLL by Schlesinger in 1934 are in such 

 excellent agreement with later results on T2 and T6. 



