CHAPTER II 



THE INFECTIVE PROCESS 



As d'Herelle found, the inoculation of a growing culture of 

 susceptible bacteria with an appropriate bacteriophage results 

 in a few hours in lysis of the bacterial cells and an increase in the 

 amount of bacteriophage far above that added. D'Herelle 

 conceived of this phenomenon as an infection of the bacterial 

 host cell by a virulent virus particle which as a result of its 

 multiplication brought about death and dissolution of the host 

 cell. He noted that in order for lysis to occur the host cells 

 must be growing in an appropriate physical and chemical en- 

 vironment. It is not difficult to find environmental conditions 

 of temperature, pH, salt concentration, or chemical composition 

 in which the host cells will multiply but lysis will not occur. 



For convenience in discussion d'Herelle divided the infective 

 process into arbitrary stages: (7) adsorption of the phage par- 

 ticle to the host cell, (2) penetration of the phage particle into 

 the bacterium, (3) the intracellular multiplication of the virus, 

 and (4) the lysis of the host cell and release of phage progeny. 

 This division is peculiarly appropriate from the experimental 

 viewpoint and leads to the following interpretation of the lytic 

 process. 



If to an actively growing fluid culture of susceptible bacteria 

 one adds a single phage particle, it will adsorb to a bacterial cell, 

 multiply therein, and eventually cause the cell to lyse. On lysis 

 about 100 phage particles will be liberated thus completing one 

 growth cycle. The 100 phage progeny from the first cycle will 

 then infect 100 bacteria to initiate the second growth cycle. The 

 progeny of the second cycle will initiate a third cycle and so the 

 process will continue at an exponential rate until all susceptible 

 bacteria are lysed. 



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