248 G. S. STENT 



whicli individual bacteria contain their first infective progeny is distributed 

 over many minutes and that after the termination of the echpse, the 

 infected bacteria pass through phases in which they first contain few 

 and then many progeny phages, the rate of increase of such phages in 

 individual cells indeed being constant (Bentzon et al., 1951; Doermann, 

 1951). 



The discovery of the eclipse period temporarily complicated the conclusions 

 which one might have hoped to draw from Doermann's intracellular growth 

 curve, for the question now posed itself as to just when it is during the latent 

 period that the actual multiplication of the infecting phage particle takes 

 place. It was possible that the eclipse period represents only a waiting stage 

 for the infecting phage particle, during which it is "masked" while the host 

 cell undergoes some necessary renovations preliminary to the onset of phage 

 multiplication. In this case, the first infective phage particle present within 

 the infected cell at the termination of the eclipse would be the original, once 

 more "unmasked" parental phage, which then proceeds to grow and divide 

 as does any other microbe (Fulton, 1953). The daughter viruses of the first 

 division would Hkewise divide mitil the final crop of several hundred progeny 

 viruses had been attained by the end of the latent period. One might expect 

 that such geometric mode of increase of intracellular infective progeny 

 should follow exponential rather than, as actually found, linear kinetics, 

 unless limiting conditions imposed by the fact that the bacterial ceU is a 

 bounded system have already been attained by the end of the eclipse 

 period. 



An alternative explanation of the significance of the echpse period was 

 that, far from being a stage of waiting, the eclipse is that part of the latent 

 period durmg which there occurs synthesis of the substance of the bacterio- 

 phage progeny. The increase in intracellular mfective progeny in that case 

 does not really represent the multiplication of the parental virus at aU but 

 constitutes, rather, a terminal process of maturation of previously synthesized 

 progeny structures into intact virus particles. Genetic studies described in 

 Chapter 5, as well as the experiments to be recounted now, have estabhshed 

 that it is this latter point of view which is correct, i.e., that the parental 

 bacteriophage particle not only metamorphoses into a noninfective form at 

 the outset of its infection of the host cell, but that it also multiplies in this 

 form to yield noninfective progeny structures whose maturation into 

 infective viruses signals the end of the eclipse. This noninfective form is 

 called the vegetative phage, in contradistinction to the resting phage represented 

 by the mature infective virus particle (Hershey, 1952; Doermann, 1953). The 

 vegetative phage is thus the connecting link between parental and progeny 

 viruses, and the elucidation of its structure and function the central problem 

 of phage growth. 



