122 S. E. LURIA AND R. DULBECCO 



DuLBECCO, R., 1949a The number of particles of bacteriophage T2 that can participate in intra- 

 cellular growth. Genetics 34: (in press). 



1949b Reactivation of ultraviolet inactivated bacteriophage by visible light. Nature (in 



press). 



Foster, R. A. C, 1948 An analysis of the action of proflavine on bacteriophage growth. J. Bact. 

 56: 795-809. 



Hershey, a. D., and R. Rotman, 1948 Linkage among genes controlling inhibition of lysis in 

 a bacterial virus. Proc. nat. Acad. Sci. 34: 89-96. 



1949 Genetic recombination between host-range and plaque-type mutants of bacteriophage 

 in single bacterial cells. Genetics 34: 44-71. 



Latarjet, R., and R. Wahl, 1945 Precisions sur I'inactivation des bacteriophages par les rayons 

 ultraviolets. Ann. Inst. Pasteur 71 : 336-339. 



Lea, D. E., 1947 Actions of radiations on Hving cells. xii-|-402 pp. Cambridge: University Press. 



Lea, D. E., and M. H. Salaman, 1946 Experiments on the inactivation of bacteriophage by 

 radiations, and their bearing on the nature of bacteriophage. Proc. roy. Soc, B, 133: 434-444. 



LuRiA, S. E., 1947 Reactivation of irradiated bacteriophage by transfer of self-reproducing units. 

 Proc. nat. Acad. Sci. 33: 253-264. 



1948 Bacteriophage mutations and genetic interactions among bacteriophage particles in- 

 side the host cell. A.A.A.S. Symposium on Genetics of Microorganisms (in press). 



Luria, S. E., and M. Delbruck, 1942 Interference between bacterial viruses. II. Interference 

 between inactivated bacterial virus and active virus of the same strain and of a different 

 strain. Arch. Biochem. 1 : 207-218. 



Luria, S. E., and R. Latarjet, 1947 Ultraviolet irradiation of bacteriophage during intracel- 

 lular growth. J. Bact. 53: 149-163. 



Rahn, 0., 1929 The size of bacteria as the cause of the logarithmic order of death. J. gen. 

 Physiol. 13: 179-205. 



APPENDIX 



ON THE RELIABILITY OF THE POISSON DISTRIBUTION AS A DISTRIBUTION OF THE 



NUMBER OF PHAGE PARTICLES INFECTING INDIVIDUAL BACTERIA 



IN A POPULATION 



R. DuLBECCO 



In calculating the average number x of phage particles adsorbed per bacteri- 

 um (multiplicity of infection) from the number of uninfected bacteria, and, 

 from X, the proportion of bacteria w^ith any given number k of particles, the 

 assumption is made that the distribution of particles per bacterium is a 

 Poisson distribution. One limitation to this assumption may arise from differ- 

 ences in the surface area of individual bacteria. This limitation was analyzed 

 as follows. 



In a mixture of P particles and B bacteria, each phage particle has a prob- 

 ability p = c{l/B) to be adsorbed by a given bacterial cell. In actual cases 

 where P and B are large and c is between 0.4 and 0.9, we have : x = cP/B. 



If c is constant for all bacteria, the distribution of ^ is a Poisson distribution; 

 if not, the distribution of k will be different. We assume, in first approximation, 

 that the adsorption capacity of a bacterium is proportional to its surface, and 

 that the surface is proportional to the length — considering bacteria as cylinders 

 with uniform diameter and negligible end surfaces. 



The distribution of bacterial lengths was obtained experimentally on stand- 

 ard cultures of E. coli B containing 10^ cells per ml. Negative stains with 



276 



