A. D. HERSHEY AND MARTHA CHASE 



51 



teria adsorbing lysing phage but not phage progeny. The latter test shows that 

 the S^^ is not contained in the phage progeny, and explains the fact that the 

 S^^ in early lysates not containing progeny behaves in the same way. 



The speciticity of the adsorption of S^^-labeled material contaminating the 

 phage progeny is evidently due to the lysing phage, which is also adsorbed 

 much more strongly to strain H than to B/2, as shown both by the visible re- 

 duction in Tyndall scattering (due to the lysing phage) in the supernatants 

 of the test mixtures, and by independent measurements. This conclusion is 

 further confirmed by the following facts. 



TABLE VII 



Adsorption Tests with Uniformly S^^-Labeled Phage and with Products of Their Growth in 



N on-Radioactive Medium 



The uniformly labeled phage and the products of their growth are respectively the seed 

 phage and the high speed sediment fractions from the experiment shown in Table VI. 



The uniformly labeled phage is tested at a low ratio of phage to bacteria: -{-\]V-h means 

 with added UV-killed h mutant in equal concentration to that present in the other test 

 materials. 



The adsorption of phage is measured by plaque counts of supernatants, and also sedi- 

 ments in the case of the resistant bacteria, in the usual way. 



1. If bacteria are infected with S" phage, and then lysed near the midpoint 

 of the latent period with cyanide alone (in salt-poor broth, to prevent read- 

 sorption of S^^ to bacterial debris), the high speed sediment fraction contains 

 S^^ that is adsorbed weakly and non-specifically to bacteria. 



2. If the lysing phage and the S^^-labeled infecting phage are the same 

 (T2), or if the culture in salt-poor broth is allowed to lyse spontaneously (so 

 that the yield of progeny is large), the S^^ in the high speed sediment fraction 

 is adsorbed with the specificity of the phage progeny (except for a weak non- 

 specific adsorption). This is illustrated in Table VII by the adsorption to H 

 and B/2/?. 



It should be noted that a phage progeny grown from S^Mabeled phage and 

 containing a larger or smaller amount of contaminating radioactivity could 

 not be distinguished by any known method from authentic S^^-labeled phage, 



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