NON-SPECIFIC COMPONENTS IN S. PARATYPHI A 



473 



types. The latter display phase variation under normal condi- 

 tions of culture. As shown in figure 1, it is possible to produce 

 changes in the induced phases of S. paratyphi A by cultivation in 

 appropriate immune serums. The reversibility of the phases is 

 illustrated in figure 2. Phases 1, 2 and 3 were completely inter- 

 changeable and reversible. The changes illustrated in these 

 phases were accomplished repeatedly with cultures isolated from 

 single colonies. Phase 4, on the contrary, was more stable. It 

 was readily converted to phase 2 but not to phase 1 or phase 3. 

 Efforts to convert phase 4 to phase 1 or phase 3 resulted in the 



Pbaae t 



Phase 3 



Fig. 2. Reversibility of Phases of S. paratyphi A 228 

 Arrows indicate direction in which variation occurred 



production of a series of ill-defined, serologically-related variants. 

 This observation confirms the work of Gnosspelius (1939), who 

 concluded that through proper manipulation it was possible to 

 isolate an endless number of antigenic components from 

 Salmonella strains. 



It is known that "artificial" phases that display little or no 

 relationships to the normal antigens of the genus can be isolated 

 from a number of Salmonella types by induced variation. The 

 isolation of components closely related to the naturally occurring 

 antigens is much more unusual. The isolation of non-specific 



