236 BACTERIOPHAGES 



dull reading. Much of it consists of some such statement as 

 "inhibited by 0.01 M citrate" with no attempt to study the 

 mechanism by which citrate inhibits phage reproduction. 

 Therefore much of this literature is summarized in Table XV. 

 There are undoubtedly many additional references which have 

 been overlooked, but the table does suggest how broad is the 

 range of phage types that require calcium. For a discussion of 

 the more fundamental papers dealing with mechanisms see 

 Chapters X and XI. 



2. Metabolic Requirements for Phage Multiplication 



Phage multiplication involves the synthesis of about 100 copies 

 of the infecting phage particle in a period of time commensurate 

 with the generation time of the host cell. The total amount 

 of new phage protoplasm synthesized in a single host cell, per- 

 haps 10~^^ gram, is considerably less than the weight of the host 

 cell which is of the order of 10"^^ gram, so the effort involved in 

 producing the usual yield of phage is certainly no greater than 

 that required for duplicating the host cell. The raw materials, 

 the energy supply, and the anabolic enzymes required for phage 

 synthesis should be well within the capabilities of the host cell 

 insofar as phage protoplasm contains the same ingredients as the 

 host cell. The only building block so far found in phages but 

 not in the host cell is the hydroxymethylcytosine of the DNA of 

 phages related to T2 (Wyatt and Cohen, 1953). With this single 

 known exception, one might anticipate that the host cell would 

 be able to furnish everything needed for phage multiplication ex- 

 cept the unique patterns such as those which control the antigenic 

 specificity of the phage proteins. These patterns are presumably 

 furnished by the DNA of the invading phage particle. Despite 

 this apparent simplicity of the problem of phage nutrition, a 

 considerable amount of effort and ingenuity has been devoted 

 to work which is directly or indirectly related to the requirements 

 for phage multiplication. A question which has often been 

 asked is, does the phage particle contain any enzymes, or is it 

 entirely dependent on the metabolic activity of the host cell? 



