ANTIGENIC STRUCTURE 773 



kina (1930) have found that saline suspensions of Past, pseudotuberculosis reduce 

 Schardinger's reagent (formolized M.B. solution) much more rapidly than those of 

 Past, pestis. Past, aviseptica is stated to form phenol in peptone water (Bunzl- 

 Federn 1891). 



Antigenic Structure. — Antigenically all the members of the group are closely 

 related. An agglutinating serum prepared against any one of them is said to 

 act not only on its homologous strain but to a less extent on the heterologous 

 strains. It is stated that the relationship between Past, pestis and Past, pseudo- 

 tuberculosis is very close, and that it is often impossible to distinguish between 

 them by direct agglutination. Past, aviseptica is not so closely allied, but never- 

 theless it may give a definite group reaction with sera prepared against either of 

 the other members. This, however, has not been our experience ; using low titre 

 sera we have had no difficulty in distinguishing between the three species by 

 direct agglutination. 



According to Schiitze (1932a), there are only two antigens in the plague bacillus, 

 one corresponding to the envelope and the other to the somatic substance. The 

 envelope antigen is developed best in cultures grown at 37° C. and is heat-labile ; 

 the somatic antigen is formed as well at 20° C. as at 37° C. and is heat-stable. 

 Both antigens may be present in avirulent as well as in virulent forms, though 

 variants lacking the power to form the envelope substance have been described 

 (Schiitze 1939). Wats, Wagle, and Puduval (1939) find that organisms provided 

 with an envelope agglutinate more rapidly than those containing only the somatic 

 antigen ; they differ also from these in forming larger flakes of varying size, and 

 a voluminous deposit, which is easily homogenized by shaking. The antigenic 

 structure of the flagellated Past, pseudotuberculosis is more complex. Arkwright 

 (1927) has shown that agar cultures incubated for 24 hours at 18 to 22° C. contain 

 a heat-labile H, and a heat-stable antigen. The H antigen is apparently associ- 

 ated with the flagella, and is destroyed by boiling for half an hour, though not 

 by exposure to 56° C. for a similar length of time ; it agglutinates in the form 

 of loose flocculi ; the antigen is apparently associated with the bacterial bodies, 

 is not destroyed by boiling for 1 hour, and agglutinates in the form of granules. 

 Further work by Schiitze (1928, 19326), Zlatogoroff and Moghilewskaja (1928a), 

 Kauffmann (1932), and Bhatnagar (19406) seems to show that the flagellar antigen, 

 which is formed only in cultures grown at 26° C. or lower, is common to all strains 

 within the species, but that the somatic antigen is more complex. One somatic 

 antigen is shared with the plague bacillus ; another is closely related to the 

 antigen present in Sahn. paratyphi B and related organisms of the Salmonella 

 group. In addition, there appear to be one or more type-specific antigens that 

 characterize individual strains or groups of strains. According to Bhatnagar 

 (19406) a serum prepared against the plague bacillus will agglutinate Past, pseudo- 

 tuberculosis by virtue of the antibody to their common somatic antigen, but a 

 serum prepared against Past, pseudotuberculosis will not agglutinate plague bacilli 

 grown at 37° C. because the somatic antigen is protected by the envelope substance. 



The antigenic structure of the members of the Pasteurella septica group of 

 organisms is still very uncertain. With regard to Past, muri septica, we have 

 found two distinct types, distinguishable either by direct agglutination or by 

 absorption of agglutinins. The two types were further distinguished by the fact 

 that one type fermented maltose and the other did not. Using the complement- 

 fixation reaction, Lai (1927) found that there was a cross-reaction between different 



