BACTERIAL ANTIGENS AND SPECIFICITY 359 



Landsteinei' (1936, p. 119) suggests that tlie iiiliibition phe- 

 nomenon may be due to an excess of antigen resulting in the forma- 

 tion of soluble compounds containing a larger proportion of 

 antigen, in comparison to antibody, than there is in precipitates. 



The "C" Species-specific But Not Type-specific Substance 

 OF TiLLETT AND Fkancis (1930). — This substant'c has been studied 

 by Tillett, Gocbel and Avery (1930). They find that it is a non- 

 protein fraction distinct from the type-specific polysaccharide. 

 The evidence seems to indicate that it is a ''nitrogenous i>oly- 

 saccharide analogous in chemical behavior ])ut not in sei'ological 

 reactivity to the Ty])e I soluble-specific substance." Since it 

 passes through collodion membranes with ease and quite read- 

 ily through parchment membranes, Tillett, Giroebel and Avery con- 

 clude that the molecule is smaller than that of the SSS previously 

 described. The "C" fraction is apparently common to all pneu- 

 mococci. It is evidently not related to virulence since it is present 

 in the avirulent "R" forms as well as the virulent "S" forms. 

 Heidelberger and Kendall have found the "C" substance in Type 

 IV pneumococci and have studied its chemical properties. Its 

 rotation is given as +40° and its nitrogen content as 6.1 per cent. 

 They also found approximately 0.9 per cent of amino nitrogen. 

 It differs from the pneumococcus type-specific substance in con- 

 taining phosphorus (4.0 per cent) (Heidelberger, 1932). The 

 somatic substance is said to include skin irritating nucleic acids 

 and nucleoproteins. 



Carbohydrate Fractions Adsorbed on Carbon Particles. — 

 While all previous work has shown that the soluble-specific sub- 

 stances (SSS) of Types II and III arc nonantigenic, yet Zozaya 

 and Clark have recently (1933) reported active immunization of 

 mice with the polysaccharides (SSS) of pneumococcus Types I, II, 

 and III. They used polysaccharides adsorbed on carbon particles 

 and also various dilutions of unadsorbed material. They claim that 

 the dilution factor is important. Their work needs further con- 

 firmation. It should also be noted that Wadsworth and Brown call 

 attention to tlie importance of dosage in the demonstration of the 

 antigenic nature of the carbohydrate fraction described by them. 



Synthetic Carbohydrate Haptens. — In Hie course of their in- 

 vestigations of the role polysaccharides ])lay in determining im- 

 munological specificity, Goebel and Avery (1929) synthesized two 



