APPENDIX 473 



plated with a susceptible host. However, Luria and Delbriick 

 (1942) found that T2 killed in this manner retains its ability 

 to become adsorbed to the host cell and that this adsorption 

 results in death of the host cell. It is possible then to determine 

 the rate of adsorption of such ultraviolet-inactivated phages by 

 this technique when it could not be determined otherwise. 

 The method has been extensively used by Luria (1947) in 

 investigating the conditions necessary for "reactivation" of 

 ultraviolet-inactivated phage (see p. 514). 



The Single-Step Growth Curve 



One of the most important contributions to phage research 

 in recent years was the development of the one-step growth 

 experiment by Ellis and Delbriick (1939). This technique 

 was designed to determine quantitatively 2 important char- 

 acteristics of the virus — the latent period of intracellular virus 

 growth and the burst size. The latent period is the minimum 

 length of time from adsorption of virus to host cell to lysis of 

 the host cell and release of the progeny of the infecting virus 

 particle. Burst size is the average yield of virus particles per 

 infected host cell. Each of these characteristics of the virus 

 can be determined independently by other methods to be de- 

 scribed later, but the single-step growth method enables one to 

 determine both in 1 experiment with a minimum of effort. 

 The technique is extremely adaptable, permitting the experi- 

 menter to alter the physical and biochemical environment of the 

 host cell at will to see what effect these changes will have on the 

 course of the infection. In particular, the method should prove 

 useful in studying the mode of action of chemotherapeutic agents 

 against virus infections. 



The method has been used to compare the effects of single 

 infection with 1 virus particle per host cell with those of multiple 

 infection with 2 or more virus particles per cell (Delbriick and 

 Luria, 1942). It has also been used in determining the result 

 of mixed infection in which bacterial cells are simultaneously 



