X Introduction 



growth, i.e. the fixation, or adsorption, of the bacteriophage to its bacterial 

 host cell, were Krueger (91) and Schlesinger (129, 130). In his paper (130), 

 the second of this collection, Schlesinger demonstrates that phage adsorption 

 usually is an irreversible process which follows the kinetics expected from a 

 two-body collision model involving freely diffusing virus particles and bacterial 

 cells. Schlesinger 's work, which probably represents the first rigorous applica- 

 tion of physicochemical principles to the study of bacterial viruses, was 

 extended by Delbriick (39), who showed that the physiological state of the 

 bacteria affects the rate of adsorption, and by Garen and Puck (59), who 

 demonstrated clearly that, under certain conditions, a reversible union between 

 phage and bacterium can take place. Contrary to the predictions of the simple 

 two-body collision model of Schlesinger, however, it turned out that the rate 

 of phage adsorption reaches a maximum at high bacterial concentrations and is 

 strongly temperature-dependent. Hence, it appears that the irreversible fixa- 

 tion of the bacteriophage is a two-step process, involving at least one further, 

 temperature-sensitive, step in addition to the collision of virus and host cell 

 (146). Subsequent electron-optical observations by T. F. Anderson revealed 

 that the organ of adsorption is the phage tail (5), in particular, that it is the 

 thin tail fibers (155) which are the structures undergoing the stereospecific 

 fixation reaction with the phage receptors on the bacterial surface. (Reviews: 

 58, 148, 73, 125, 154. ) 



Convincing support for d'Herelle's conception that the infecting phage 

 particle multiplies within the bacterium and that i*^s progeny are liberated 

 upon lysis of the host cell was adduced in 1929 by Burnet (31), who showed 

 that 20 to 100 viruses suddenly appear some 20 minutes after a bacterial 

 suspension is infected with a single phage particle. The final demonstration, 

 however, that a burst of progeny of the parent virus is liberated by each 

 infected bacterial cell after a latent period was only provided in 1939 in the 

 one step growth experiment of Ellis and Delbriick (52), whose paper is 

 presented in this collection. In their publication, Ellis and Delbriick also 

 describe for the first time the single burst experiment, which made possible 

 the study of phage growth in individual infected bacteria, rather than in mass 

 culture. The appearance of this paper marks the beginning of modern phage 

 research. 



The interpretation of the phage-induced lysis of infected bacterial cultures 

 was one of the violent controversies during the first 20 years of phage research. 

 While d'Herelle (65) correctly thought that intracellular phage growth leads 

 to lysis of the host cell and liberation of the virus progeny, Bordet and Ciuca 

 (20, 22) maintained that the phage-induced dissolution of bacterial cultures 

 is merely the consequence of a stimulation of lytic enzymes endogenous to the 

 bacteria. Other workers, such as Bronfenbrenner (30), or Krueger and Nor- 

 throp (92), thought that lysis of the bacteria is only a secondary phenomenon, 

 which may or may not follow the growth of phage, and imagined that the 

 bacteriophage can pass freely in and out of bacterial cells. Delbriick (40) 



