ANTIGENIC STRUCTURE 711 



the variations in the antigenic constitution of the two phases till a little later 

 in this chapter (p. 716). It is sufficient to remark here that in Phase 1 there are 

 one or more antigenic components, and in Phase 2 there are two or more. 



The somatic antigens are monophasic, though occasionally a given strain may- 

 differ from the type species in its lack of one of the two, three, or four antigenic 

 components which most members possess. 



The identification and labelling of the Salmonella antigens was initiated by 

 White (1926, 1929a, h), and continued and extended by Kauffmann (1929a, h, 

 19306, 1931, 1934a). In their earlier studies the two investigators used a different 

 system of labelling, so that descriptions given in the English and German papers 

 during the period can be correlated only by the aid of an appropriate key giving 

 the equivalent numbers and letters in the two systems (see Lovell 1932a). Recently, 

 however, the terminology introduced by Kauffmann has been adopted for general 

 use by a special sub-committee of the International Society for Microbiology 

 (Report 1934) ; and each member of the Salmonella group is now allotted an 

 antigenic formula based on this system of notation. 



The somatic (0) antigens are accorded Roman numerals. The flagellar antigens 

 of Phase 1 are accorded small letters ; these antigens have already illustrated the 

 limitations of an alphabetical notation by exceeding twenty-six in number. By 

 convention, those discovered later than the antigen that received the label y have 

 been accorded an additional distinguishing numeral, Zj, Zg, and so on. The flagellar 

 antigens of Phase 2 are labelled in two different ways. At first they were accorded 

 arable numerals, but later it was found that the second phase of certain species 

 uniformly contained the antigens e and n, often associated with x or with one 

 of the z series of antigens. It thus happens that Phase 2 may contain antigenic 

 components of the 1, 2, 3 . . . series, or of the e, n, . . . series. The position 

 is confusing, because both the e and some of the z antigenic components may be 

 found in the first phase. More recently, strains have been described in which 

 Phase 2 contains neither the 1, 2, 3 . , . nor the e, n . . . series, but instead 

 antigenic components that are characteristic of Phase 1. 



A few examples may be given to illustrate the use of this notation. The formula 

 for Salm. paratyphi A, which is a monophasic flagellated baciUus, existing only in Phase 1 

 is [I], II, XII . . .a — ■ . The. square brackets indicate that the I somatic antigen may 

 be missing. The three dots after XII mean that traces of other somatic antigens are 

 present, but are excluded from the antigenic formula for the sake of simphcity. The 

 a represents the flageUar antigen, and the dash following it shows that there is no second 

 phase. The formula for Sahn. jMmiyphi B is [I], IV, [V], XII . . . b <~^ 1,2... 

 The square brackets show that antigenic components I and V may be missing ; b is the 

 flageUar antigen of Phase 1, and 1, 2 . . . the flagellar antigens of Phase 2. Again, the 

 dots following XII and 2 indicate an abbreviation of the antigenic formula. The double - 

 tipped arrow shows that the two flageUar phases are reversible. The formula for Salm. 

 amersfoort is VIi . VIj . VII . . . d < — > e, n, x . . . It wiU be seen that there are two 

 components to the VI somatic antigen ; and that, as indicated by the presence of the 

 e, n antigens in Phase 2, the organism shows the cc-^ type of phase variation (see p. 716). 

 The formula for Salm. meleagridis is 111. X. XXVI. e, h -< — >- 1, w. Phase 2 contams 

 neither the 1 , 2, 3 . . . nor the e, n , . . series of antigens, but two antigenic components, 

 1 and w, that are normally found in Phase 1 of other organisms. Salm. gallhiarum, which 

 is non-motUe, has the simple formula [I], IX, XII . . . — . — , the two dashes showing 

 that there is neither a first nor a second flageUar phase. An organism, so far met with 

 only in Phase 2, is Salm. abortus-equi, which has the formula IV, XII ... — . e, n, x ; 

 the dash shows that Phase 1 is absent. 



