POLYSACCHARIDES OF MICRO-ORGANISMS 355 



Although the Type I pneumococcus polysaccharide 

 contained nitrogen it gave no protein reaction and, as it 

 was first isolated^ was not antigenic. Since then, however, 

 by avoiding the use of alkpJi in its extraction, it has been 

 obtained in an acetylated form, containing one acetyl 

 group for each glucose unit ; the acetyl polysaccharide 

 is antigenic, and on removal of the acetyl group yields a 

 non-antigenic polysaccharide identical with that originally 

 isolated. Some doubt is cast on this finding by later 

 work by Felton who could find no correlation between 

 the acetyl content and antigenicity. Half the nitrogen of 

 the Type I polysaccharide is in the form of amino - 

 nitrogen since it is eliminated by treatment with nitrous 

 acid, with production of reducing sugar and loss of 

 serological activity. The polysaccharides of Types II 

 and III pneumococci are not affected b}^ treatment with 

 nitrous acid. Type I polysaccharide is amphoteric, 

 acting as a strong acid and a weak base ; it has an 

 iso -electric point at about pH 4. 



The Type II polysaccharide is a weak acid ; on acet}^- 

 ation it yields a serologically inactive product. Removal 

 of the acetyl groups restores the original activity of the 

 compound. The Type III polysaccharide is similar to 

 that of Type II, but is laevorotatory. On hydrolysis it 

 yields cellobiuronic acid, [a]D+10°, an aldobionic acid 

 having the structure 4-^-glucuronosidoglucose. In the 

 polysaccharide these units are linked through the 3- 

 carbon atom of the uronic acid to the reducing group of 

 the glucose in the next unit : — 



