178 THE PHYSICS OF VIRUSES 



fective. llio adsorjjtioii process includes l)()lli steps in attach- 

 ment, the electrostatic and enzymatic, for the ghosts can cause 

 bacterial cell lysis from without. 



Further study of this effect was made by Herriott (1951) who 

 showed that osmotic shock released the desoxyribose nucleic 

 acid (DNA) from the virus and left behind ghosts which were 

 free of nucleic acid. These ghosts still performed the attachment 

 and lytic functions. He made clear that this affords a j^owerful 

 method of separating the infective and surface functions of a 

 virus. 



This suggestion has been followed up with most interesting 

 results by Hershey and Chase (1952). The basic technique in 

 this important series of experiments is the use of P^^ and S^^ to 

 trace separately the nucleic acid and protein of the virus. The 

 phosphorus content of T-^ phage is 96% in nucleic acid (Her- 

 riott and Barlow, 1952). There is no sulfur at all in nucleic acid, 

 but some in protein, although, actually, proteins containing 

 sulfur are not typical. Thus the fate of P^^ tells the fate of 

 nucleic acid in any ])roccss, and S^'' reveals the course of protein. 



In some preliminary experiments, Hershey and Chase show 

 that the findings of Anderson and Herriott are confirmed and 

 that, in addition, the osmotically released ghosts contain all the 

 serological affinity of the phage, and that they are adsorbed to 

 susceptible bacteria and not to any bacteria. They then followed 

 up a discovery to Graham (see Hershey and Chase, 1952, p. 43) 

 that the adsorption of T-2 to heat-killed bacteria permitted en- 

 zymatic breaking up of the DNA by a si)ecific enzyme (DNA- 

 ase) which was powerless in the unadsorbed phage. Using radio- 

 actively labeled |)hage ])articles they showed that after i)hage was 

 adsorbed to heat-killed bacteria, the action of DNAase released 

 76% P'^- into solution, compared to 13% released in the absence 

 of enzyme. Adsorption to live bacteria does not free the DNA to 

 enzymatic attack, for only 8% P^- was rendered soluble after 

 phage adsorption to live bacteria and treatment with enzyme. 

 On the other hand, heating bacteria after infection produced a 

 release of P^^ nearly equal to that from heat-killed bacteria. 



