466 BACTERIOPHAGES 



exchanges of genetic material (see "Mutations of Bacterio- 

 phages," pp. 501-8). 



Other uses of antiphage sera are described in the section on 

 the single-step growth curve (pp. 473-85). 



Rate of Adsorption of Virus to Bacterium 



The first step in the growth cycle of a virus is adsorption of 

 virus to host cell. Since this step is most accessible to observa- 

 tion it has been more thoroughly studied than the subsequent 

 steps. Knowledge of the adsorption rate is necessary for the 

 design and interpretation of certain kinds of experiments to be 

 described later. Study of the effect of environmental factors 

 and of the physiologic state of the host cell on the rate of the 

 virus adsorption has contributed greatly to understanding of 

 the virus-host cell relationship. 



The adsorption of virus to bacteria occurs at a rate that is 

 proportional to the concentrations of virus and of bacteria. 

 It is also a function of temperature, of the viscosity of the medium 

 and of the past history of the bacteria. Under constant environ- 

 mental conditions and uniform cultural conditions of the 

 host cell, the rate of adsorption follows the equation : 



-dp/dt = K{B)p 



K= 2.2>/{B)t X\ogpo/p 



in which pQ = phage assay at zero time, p = phage not ad- 

 sorbed at time t min., (B) = concentration of bacteria as num- 

 ber of cells/ml., K = velocity constant with dimensions ml. /min. 



Example: Coliphage T2 is adsorbed on a broth-grown culture of E. coli of 

 a concentration of 5 X lO'^/ml. at a rate of 80 per cent in 5 min. at 37° C. 

 Substituting in the equation 



2.3 X log 100/20 



A' = -~ — - 6.4 X 10-»m . 'mm. 



5 X lOVml. X 5 min. 



