210 BACTERIOPHAGES 



were reached in the case of T5-infectecl bacteria by Y. T. Lanni 

 (1954) who found that the complement-fixing antigens of the in- 

 fecting phage could be removed from the bacterial surface by- 

 treatment in the Blendor. 



Conversely 65 to 80 per cent of phage P^^ [^ j^ot removable by 

 treatment in the Blendor, presumably because the phage DNA 

 has penetrated into the interior of the bacterial cell where it is in- 

 volved in intracellular phage multiplication. The general con- 

 clusion from these experiments is that following adsorption the 

 protein membrane of the phage serves as a syringe to "inject" 

 the phage DNA into the host bacterium. 



It may be assumed, but it has not yet been proved conclusively, 

 that nucleic acid is the sole agent of genetic continuity during 

 multiplication of the phage (Hershey, 1956a) and that the phage 

 protein, after injection of the DNA has been completed, plays no 

 further role in phage replication. If these assumptions are cor- 

 rect it greatly simplifies the problem of the fate of the infecting 

 phage particle. The phage protein after infection is discarded, 

 and so the fate of the phage DNA is all that remains to be con- 

 sidered. Remembering that these are tentative assumptions 

 rather than proved conclusions we can see what other evidence 

 can be brought to bear on this problem. 



2. The Breakdown of the Infecting Virus Particle 



We have seen that the infection of the host cell results in a 

 physiological fractionation of the phage particle into an external 

 protein portion and an internal nucleic acid portion. We may 

 now consider whether these two major segments remain intact 

 during infection, or whether there is a chemical degradation of 

 either portion into smaller fragments. The evidence in the case 

 of the phage protein seems to be more clear cut and will be 

 presented first. 



a. Absence of Breakdown of Phage Proteins 



In the experiments of Hershey and Chase (1952) with S^'^- 

 labeled phage T2, about 80 per cent of the phage methionine 



