476 D. W. BRUNER AND P. R. EDWARDS 



genetic relations of the various forms with reference to antigenic 

 composition and to propose a theory of Salmonella phylogeny. 

 White believed that the Salmonella species as we know them 

 today arose from a primitive diphasic ancestral stock by varia- 

 tion in O and H antigens. He regarded the monophasic state, 

 as seen in S. paratyphi A, S. dbortus-equi and E. typhosa, as an 

 acquired characteristic which developed through loss variation. 

 The demonstration by Edwards and Bruner that antigen a could 

 be isolated from S. abortus-equi revealed that the organism was 

 more closely related to diphasic forms having the antigens a-enx 

 than was previously realized. They suggested that in mono- 

 phasic types, the antigens present in the original diphasic state 

 were not lost but merely suppressed. The isolation of non-specific 

 components from S. paratyphi A confirms this view. Both ob- 

 servations strengthen the theory of White that monophasic 

 types have evolved from a diphasic ancestry. 



White emphasized the close relationship that existed between 

 S. paratyphi A and Sendai, the only two types then known which 

 possessed antigen a. He used these two types to illustrate the 

 identity of the H antigens of monophasic types and the specific 

 antigens of diphasic types. The isolation of non-specific phases 

 from S. paratyphi A which are all but identical with the non- 

 specific phase of Sendai reinforces the relationship between the 

 specific phases of the two types and demonstrates the keen ap- 

 preciation of White of the evolutionary tendencies in the genus. 



With the exception of the recovery of specific phases from 

 "totally and permanently" non-specific types, the isolation of 

 antigen a from S. abortus-equi and of non-specific components 

 from S. paratyphi A constitute the only instances in which anti- 

 gens resembling the naturally occurring phases have been induced 

 in monophasic cultures. The stability of these induced antigens 

 has been mentioned. It is in direct contrast to the instability of 

 the phases of the diphasic types. These results indicate that 

 once an organism has lost the power of phase variation, it cannot 

 resume this function, even when suppressed components become 

 dominant. Only under the influence of a stimulant, such as 

 specific immune serum, does phase variation occur. 



