352 BIOLOGY OF PNEUMOCOCCUS 



its. A definite minimum of the material was obviously necessary to 

 incite the formation of antibodies, but when the dose was in- 

 creased, a point was reached beyond which no immunity developed. 

 Saito and Ulrich (1928) 1214 also observed this zone of antigenic 

 effectiveness with a carbohydrate preparation in producing a state 

 of protection in animals. A similar observation on the cellular car- 

 bohydrate was reported by Wadsworth and Brown (1931). 1466 " 7 

 There can be no doubt that pneumococcal antigen, particularly 

 the capsular polysaccharide, in excess of a certain optimal amount 

 hinders its own immunizing action. 



Another manifestation of the antagonistic action of the soluble 

 specific substance is seen in the blocking of the reaction between 

 pneumococcal antigen and homologous antibody. Felton and 

 Bailey 419 drew attention to the inhibiting power of SSS frequently 

 noted in precipitin and protection tests when amounts of antigen 

 and serum greater than the optimum are used. The authors as- 

 cribed the antagonism to the presence of precipitable residues in 

 immune serum as well as to an excess of soluble specific substance 

 in the antigen. The work of Felton and Bailey and that of Sickles 

 (1927) 1277 point to at least one factor responsible for the inhibit- 

 ing power of the soluble carbohydrate. Through its precipitating 

 action, the polysaccharide removes some of the protective antibody 

 from immune serum and at the same time (Sickles) interferes with 

 phagocytosis, consequently robbing the serum of protective prop- 

 erties. The observation recalls that of Sia (1927), 1268 who found 

 that Pneumococcus could adsorb normal opsonin from the serum 

 of animals naturally resistant to pneumococcal infection — an ob- 

 servation later confirmed by Ward (1930) 1480 _1 for normal human 

 whole blood, and who also, like Sia, noted that the action was type- 

 specific. Ward suggested that the zone of inhibition was caused by 

 the specific precipitate formed by the antiserum and homologous 

 capsular polysaccharide, which interfered, perhaps mechanically, 

 with the ingestion of the pneumococci by leucocytes. 



Enders and Wu (1934) 362 reported that the A carbohydrate 



