ANTIBODIES TO PNEUMOCOCCUS 411 



the immunity so produced was probably cellular in nature. Ba- 

 rach, 74 employing mice and rabbits, was able by the injection of 

 heat-killed pneumococci of Types I and II, and of sterile culture 

 filtrates of the organisms, to demonstrate the presence of protec- 

 tive antibodies in the serum of the animals three days after injec- 

 tion. The degree of immunity produced was greater in the case of 

 Type I than of Type II vaccine, and Barach concluded that im- 

 munity was due to the elaboration of protective antibodies. Ba- 

 rach (1931) 76 obtained analogous results after injecting similar 

 vaccines prepared from heterologous strains of pneumococci into 

 patients suffering from lobar pneumonia. The average time of ap- 

 pearance of protective antibodies was between five and six days 

 after intravenous and intradermal administration of the killed 

 pneumococci. Similar effects followed the intradermal injection of 

 protein-free, type-specific polysaccharide from pneumococci of 

 Types I, II, and III into normal individuals, as reported by Fin- 

 land and Sutliff (1932). 448 



In the year previous, Avery and Goebel 45 had demonstrated that 

 the appearance of type-specific protective antibodies followed the 

 injection into rabbits of the capsular polysaccharide of Type III 

 Pneumococcus conjugated with horse-serum globulin, and that it 

 was the polysaccharide which determined the type-specificity of 

 the ensuing protective antibodies. Avery and Goebel 46 then (1933) 

 proved that the acetyl polysaccharide could induce the develop- 

 ment of the specific protective substance in animals. Confirmation 

 of the formation of type-specific protective antibodies after injec- 

 tion of the capsular polysaccharide was forthcoming from the 

 study of Francis (1934) 474 on the immunizing effect of the intra- 

 dermal injection of small amounts of pneumococcal carbohydrate 

 into man. 



CHEMICAL NATURE OF PROTECTIVE ANTIBODIES 



The work of Avery (1915) 32 yielded the first information con- 

 cerning the particular protein element in antipneumococcic serum 



