ANTIGENIC STRUCTURE OF THE MENINGOCOCCUS 539 



undergo antigenic degradation, render classification by such means arbitrary and 

 unconvincing. A change in the strains used for the preparation of typing sera 

 can easily result in an apparent change in the type of organism under study. 



Further observations by Branham and Carlin (1937) and others have led to 

 the broad conclusion that two main groups can be distinguished by agglutination 

 — Group I, which is mainly responsible for epidemic cases and tends to be anti- 

 genically homogeneous, and Group II, which is mainly responsible for sporadic 

 cases and tends to be antigenically heterogeneous. This concept receives support 

 from other methods of study such as chemical fractionation, and precipitation 

 and capsular-swelling reactions. 



The complement-fixation reaction has been used for classifymg meningococci. Nicolle, 

 Debains and Jouan (1918) found this reaction less specific than that of agglutination, 

 whereas BeU (see Report 1920) and Butterfield and NeiU (1920) regarded it as more specific. 

 Evans (1920) studied the opsonin reactions of antimeningococcal serum. By this means 

 she found that 63 strains fell sharply into 4 groups ; there were 4 atypical strains. A fifth 

 group could also be demonstrated, which was closely related to the other four ; its members 

 were able to effect a partial absorption of the sera prepared against strains of the other 

 groups. 



By chemical fractionation Rake and Scherp (1933a, h) have separated three 

 fractions from meningococci. There is a carbohydrate or " C " substance, common 

 to all meningococci and to some other micro-organisms, which is probably the 

 same as that described by Zozaya (1931) and Zozaya and Wood (1932). There 

 is a protein or " P " substance, which is also found in gonococci and Type III 

 pneumococci. The third fraction is a sodium salt of a polysaccharide acid (Scherp 

 and Eake 1935) and is responsible for the specificity of Types I and III strains. 

 More recently Menzel and Rake (1942) have brought evidence to show that the 

 specificity of Type II strains is determined by a protein substance. There appears 

 to be no difference between the type-specific polysaccharide found in Types I 

 and III. 



The presence of the polysaccharide is generally demonstrated by the precipita- 

 tion reaction, using as antigen a specially prepared extract of the organisms. 

 Petrie (1932), however, has described a simple alternative method. It consists 

 in growing the organisms on agar plates containing the homologous immune serum. 

 Characteristic haloes develop around the colonies. These consist of a precipitate 

 formed by the interaction of the specific polysaccharide, which has diffused out 

 into the medium, with the homologous antibody. 



It seems probable that the specific polysaccharide is also responsible for the 

 capsular-swelling (Quellung) reaction demonstrated by Clapp, Phillips and Stahl 

 (1935) in smooth Group I strains. A similar reaction with Group II strains was 

 at first thought not to occur, but further observations by Cohen (1940) have shown 

 that certain strains may exhibit capsular swelling and give a typical halo reaction 

 in the presence of serum made with a capsulated Group II strain. Branham and 

 Carlin (1942) have likewise described a separate sub-group of Group II strains, 

 referred to as Group II alpha, which are capsulated, give a Quelling reaction, 

 and are strongly antigenic, stinmlating the production of antibodies with a specific 

 protective action on mice. 



Pathogenicity. — -Mice. — In his original communication Weichselbaum (1887) observes 

 that subcutaneous injection into mice is without effect. Injected intrapleurally with 0-5 ml. 

 of a thick suspension from a 24 -hours' agar culture, the mouse becomes ill, develops paralysis 



