HOST RESPONSE TO ANTIGENIC ACTION 431 



which were responsible for the pneumococcidal action of serum- 

 leucocyte mixtures received confirmation in a separate study by 

 Sia (1927), 1268 in which it appeared that the active principle op- 

 erative in the destruction of pneumococci in appropriate serum- 

 leucocyte mixtures could be specifically absorbed from the serum, 

 and that the native principle — the opsonin — was type-specific in 

 its selective action. 



It was found by Kelley (1932), 701 as Robertson and Sia had 

 previously discovered, that normal swine serum possessed the 

 property of protecting mice against infection with virulent pneu- 

 mococci and of agglutinating both virulent smooth and avirulent 

 rough strains of the organism. The protective action of swine 

 serum, although slight, was evidently specific for type, since the 

 protective antibody for one type of Pneumococcus could be ab- 

 sorbed by cultures of the homologous type without affecting the 

 content of antibody for other types. Unlike the protective sub- 

 stances in specific immune serum, those in normal pig serum were 

 thermolabile and disappeared after a few weeks' storage in the 

 cold and, moreover, they could be removed from the serum by ab- 

 sorption with avirulent rough pneumococci. Another difference be- 

 tween normal swine serum and specific immune serum lay in the 

 fact that although the former was type-specific in mouse-protec- 

 tive action, when mixed with soluble specific substance no precipi- 

 tation took place, nor was the protective action inhibited by the 

 carbohydrate. Kelley also confirmed Robertson and Sia's observa- 

 tion that swine serum shows type-specific agglutination for pneu- 

 mococci, and that agglutinins for one type may be specifically ab- 

 sorbed, leaving agglutinins for other types undisturbed. Inasmuch 

 as normal pig serum agglutinates avirulent, rough forms of pneu- 

 mococci and the agglutinative property is not destroyed by heat- 

 ing at 56°, Kelley assumed that this property probably depends 

 on factors other than those responsible for agglutination of 

 smooth forms of Pneumococcus and for protective action in mice. 



