CHEMICAL CONSTITUENTS 269 



type-specific antibody which was not neutralized by SSS and which 

 was apparently distinct from the anticarbohydrate precipitin. 

 Reasoning that this non-precipitable antibody could not have been 

 evolved in response to any antigenic stimulus from the soluble spe- 

 cific substance, Sabin sought an answer to the question, "Is there 

 another type-specific antigen in the Pneumococcus in addition to 

 the SSS?" After adding to Type I antipneumococcic serum the 

 required amount of SSS for complete precipitation, he centrifuged 

 the mixture after water-bath and ice-box incubation, and treated 

 portions of the supernatant liquid with a 50 and 100 per cent ex- 

 cess of SSS, with a saline suspension of heat-killed Type I pneu- 

 mococci, and with a similar suspension of heat-killed Type II 

 pneumococci. The experiment showed that the residual protective 

 antibody in the supernatant fluid was not neutralized by SSS or by 

 absorption with Type II pneumococci, but was definitely absorbed 

 with the homologous Type I pneumococci. Sabin assumed, there- 

 fore, that the neutralization was specific, and unless SSS in the 

 organism was capable of neutralizing the antibody which SSS in 

 solution could not, some other substance in Pneumococcus must be 

 the responsible agent. This proviso, however, is all important in 

 this connection. There is no proof that the SSS as prepared by 

 Sobotka for Sabin, even though by his tests it was practically 

 identical with the soluble specific substance of Heidelberger and 

 Avery, was identical with the specific polysaccharide as it exists 

 in the pneumococcal cell. 



In 1931, Wadsworth and Brown 1466 reported the isolation of a 

 carbohydrate which appeared to be analogous to the soluble spe- 

 cific substance and which yet more closely resembled the A sub- 

 stance of Enders. The original source material was a virulent 

 Type I strain, and the method consisted in removing the organ- 

 isms from fifteen-and-one-half hour broth cultures by means of the 



Danysz effect in the combination of toxin and antitoxin. More SSS was required 

 for complete precipitation when the total quantity was added at once, than 

 when it was added in fractions of the total on successive days. This effect had 

 also been observed by Heidelberger and Kendall in their studies on the precipi- 

 tin reaction. 



