ANTIGENIC PROPERTIES 115 



unneutralized phage in a given phage-antiserum mixture. 

 Kalmanson and Bronfenbrenner (1942) analyzed this host 

 effect with a strain of T2 that plated on certain strains of Shiga 

 and Flexner dysentery bacteria with very nearly the same effi- 

 ciency as on E. coli. The host-range properties and suscepti- 

 bility to neutralization by antiserum were independent of the 

 bacterial strain used as host for production of phage stocks. 

 When the kinetics of neutralization were studied by plating 

 replicate samples of serum-phage mixtures on each of the three 

 host strains, it was found that the rate of neutralization 

 was decidedly greater when measured with the Shiga and Flex- 

 ner hosts than when measured with E. coli (see also Friedman, 

 1954; Tanami and Miyajima, 1956). This was interpreted 

 to mean that a certain fraction of the initial phage population 

 lost its ability to produce plaques on the dysentery strains while 

 retaining its infectivity for E. coli. Subculture of these "mono- 

 valent" survivors on E. coli resulted in a "polyvalent" phage 

 stock with full infectivity for all three host species. Reaction 

 with antiserum had seemingly produced a phenotypic modifica- 

 tion of host range. Bronfenbrenner had previously been able 

 to produce the same kind of modification of host range in this 

 phage by mild heat treatment. 



The authors suggested (see also Tanami and Miyajima, 1956) 

 that their experiments provide evidence for a serological hetero- 

 geneity inherent in individual phage particles. In the present 

 conceptual framework, this heterogeneity would be a feature of 

 the phage tail. It is not necessary, however, to postulate het- 

 erogeneity, either of antibody-attachment or of host-attach- 

 ment sites, in order to explain the results. The differential host 

 effects could easily be due to minor differences in the phage 

 receptor sites on the several bacterial hosts, such that there 

 would be differences in bonding strength between phage and 

 the different hosts. In the random reaction of antibody mole- 

 cules with uniform antigen sites on the phage particles, the 

 virus surface could be so altered that certain of the particles 

 would adsorb abortively, or even be unable to adsorb, to the 



