Introduction xi 



finally showed, in his second paper of this collection, that these arguments 

 were bedevilled by the circumstance that there exist not one but two com- 

 pletely different processes by which bacteriophages can lyse susceptible bac- 

 terial cells. One of these, lysis-from-without, represents an immediate dissolu- 

 tion of bacteria, often encountered when the multiplicity of infection is much 

 greater than one phage per bacterium (9, 123, 92, 124). Loss of the input 

 phages, rather than their multiplication, ensues from this form of lysis. Only 

 the second of the lytic processes, lysis-frorn-within, is really the form of lysis 

 properly connected with intracellular phage multiplication, and its onset 

 signals the end of the latent period. 



The one-step growth experiment demonstrated clearly the nature and 

 kinetics of the process by which bacterial viruses multiply within cultures of 

 susceptible bacteria. It thus brought into focus the question of fundamental 

 biologic interest: what is taking place inside the infected cell during the latent 

 period while the parental phage particle replicates itself several hundredfold? 

 In order to study the kinetics of intracelltdar phage multiplication, Doermann 

 (47) broke open phage-infected bacteria at various times during the latent 

 period and assayed the infectivity of the material released by premature lysis. 

 The result of this experiment, published in the paper included in this collec- 

 tion, was that the infectivity associated with the original parental virus is lost 

 at the outset of the reproductive process, since no infective particles whatso- 

 ever can be found in any of the bacteria lysed within ten minutes after theix 

 infection. After more than ten minutes have elapsed, however, ever-increasing 

 numbers of infective progeny viruses make their intracellular appearance, 

 until the final crop of progeny has been attained which would have been 

 released by spontaneous lysis-from-within at the end of the normal latent 

 period. The stage of intracellular bacterial virus growth during which the in- 

 fected host cell contains no material capable of infecting another bacterium is 

 the eclipse (107). Subsequent studies showed that the actual multiplication of 

 the infecting virus takes place during the eclipse, i.e. that the phage multiplies 

 in a non-infectious form, the vegetative phage (48). 



Schlesinger was also the first to purify a bacterial virus, a feat which he 

 accomplished by high-speed centrifugation of phage lysates ( 131 ) . Chemical 

 analysis of the purified virus revealed that it consists of approximately equal 

 proportions of protein and deoxyribonucleic acid (DNA) (132). Later studies 

 by Anderson (3, 4) and by Herriott (66) showed that the viral DNA resides 

 within a proteinaceous head membrane, from which it can be released by 

 osmotic shock. Hershey and Chase (75) then demonstrated that the two 

 viral moieties, protein and DNA, have independent functions in the infection 

 process. For, as can be seen in their first paper included in this collection, 

 Hershey and Chase found that practically all of the viral protein remains at 

 the surface of the infected cell, and that it is mainly the viral DNA which 

 enters the bacterium at the outset of intracellular phage growth. The bulk of 

 the phage protein appears to be relieved of any further function in the intra- 



