94 BACTERIOPHAGES 



measure of contamination by impurities that contain nucleic 

 acid, on the one hand, or of the efficiency of the plaque count on 

 the other. 



7. Phosphorus and Nitrogen Contents per Infective Particle 



The content in phosphorus and nitrogen per plaque-forming 

 particle has been frequently measured, and a few data are given 

 in Table XII. The phosphorus content of some additional 

 phages is cited by Lwoff (1953) and Stent (1958). The results 

 are only moderately consistent among themselves and with the 

 expectations based on size measurements, composition, and 

 absolute infectivity. The results for T5 given by Smith and 

 Wyatt (1951) illustrate the uncertainties that are inseparable 



TABLE XII 



Phosphorus and Nitrogen per Plaque-Forming Particle 

 (yUg./lO" particles) 



