CHEMICAL CONSTITUENTS 283 



stance, according to the conditions of the test, in dilutions of 1 to 

 10 to 1 to 100 still protected mice against virulent pneumococcal 

 infection. On the contrary, the acetyl polysaccharide, under the 

 experimental conditions employed, exhausted the serum of protec- 

 tive antibodies. 



Further evidence of the specific antigenicity of the acetyl poly- 

 saccharide as compared to the incomplete antigenic action of its 

 deacetylated derivative was furnished by Avery and Goebel's ex- 

 periments on the immunizing action of the two carbohydrates on 

 mice. Three injections of 0.5 cubic centimeters each of a 1 to 

 2,000,000 solution of the acetyl polysaccharide protected all the 

 mice tested six days later against 10" 5 cubic centimeters of a cul- 

 ture of Type I Pneumococcus, of which 10" 8 cubic centimeters 

 killed the control mice. A similar series of injections of the same 

 amounts of the deacetylated polysaccharide, however, failed to af- 

 ford any protection to the mice tested. 



The outcome of the experiments just cited would explain the 

 previous consistent failure of Avery and his associates to induce 

 active immunity in mice and rabbits with their former prepara- 

 tions of the soluble specific substance, which were then used only 

 in the deacetylated form. "This difference in antigenic action, like 

 that already noted in the serological behavior of the two forms of 

 the polysaccharide, is referable to known differences in chemical 

 constitution."* 



A careful examination of the chemical and immunological data 

 presented in this communication would seem to justify Avery and 

 Goebel's conclusion: 



An analysis of the specific reactions of the acetyl polysaccharide dis- 

 closes a previously unsuspected similarity between this form of the spe- 

 cific carbohydrate and the antigenically active fractions described by 

 other investigators. From the chemical and immunological properties of 

 the acetyl polysaccharide it seems highly probable that this substance in 

 the purified state accounts for the antigenic action of the carbohydrate 



* Avery and Goebel. 



