APPENDIX 515 



tures were incubated for 10 min. at 37° C, then appropriately diluted and as- 

 sayed for infective centers by the agar layer method. Appropriate dilutions 

 of the adsorption mixture with the highest input ratio of phage to bacteria 

 were plated to determine the number of surviving bacteria from which the 

 multiplicity of infection, n, for that particular adsorption tube could be cal- 

 culated. Once n is known for 1 adsorption mixture it can be calculated for all 

 the other mixtures made with the same bacterial suspension and phage stock, 

 assuming only that the percentage adsorption in 10 min, is the same in all adsorp- 

 tion tubes. The data are shown in Table XXVI. 



TABLE XXVI" 



"From Luria (1947). 



As may be seen from Table XXVI about half the bacteria which 

 adsorbed 2 or more inactivated phage particles actually produced 

 plaques. The proportion of multiply infected bacteria which 

 produce plaques depends on the dose of irradiation to which the 

 phage particles have been subjected. For the phages T2, T4, 

 and T6, if the physiologic dosage of ultraviolet light is 3 r or less, 

 i.e., an average of 3 or less lethal hits/phage particle, all the mul- 

 tiply infected bacteria produce plaques. As the dose of irradia- 

 tion is increased, the probability of the bacteria which have ad- 

 sorbed 2 phage particles forming a plaque is decreased. How- 

 ever, an increase in average multiplicity of infection can over- 

 come this decrease in probability that multiply infected bacteria 

 will produce plaques. That is, as the number of lethal hits/ 

 phage particle is increased, the number of inactive phage parti- 



