CHEMICAL CONSTITUENTS 279 



more closely approximating that in which it probably exists as a 

 natural constituent of the cell capsule. They identified the type- 

 specific carbohydrate present in the intact bacterial cells and in 

 filtrates of autolyzed broth cultures as an acetyl polysaccharide. 

 According to Avery and Goebel this naturally occurring acetyl 

 polysaccharide differs chemically from the specific carbohydrate 

 as originally isolated principally in respect to the presence of ace- 

 tyl groups, which endow the native substance with additional spe- 

 cific properties not possessed by the polysaccharide after the re- 

 moval of these labile groups by alkaline hydrolysis. Avery and 

 Goebel claimed that, owing to the marked instability of the acetyl 

 groups and the ease with which they are removed by treatment 

 with alkali, the soluble specific substance as originally isolated, al- 

 though still retaining the dominant type-specificity of the native 

 substance, had, through the loss of its acetyl groups, suffered a 

 corresponding loss of certain specific properties possessed only by 

 the acetyl polysaccharide itself. Avery and Goebel further stated 

 that the specific differences between the properties of the cell frac- 

 tions studied by other investigators and those of the soluble spe- 

 cific substance as originally defined, appeared, as a result of their 

 experiments, to be due to the presence or absence of acetyl groups 

 in the polysaccharide molecule. They wrote : "Indeed, so distinctive 

 are the immunological reactions of the acetyl polysaccharide and 

 those of the deacetylated derivative, that it is now possible to 

 clarify many of the apparently conflicting views still current con- 

 cerning the nature and properties of the specific carbohydrate of 

 Pneumococcus Type I." 



By modified methods, in which treatment with alkali was pur- 

 posely avoided, the soluble specific substance of Pneumococcus 

 Type I was isolated by Avery and Goebel in the form of an ash- 

 free, acetyl polysaccharide possessing marked acidic properties. It 

 was readily soluble in water, and gave solutions of high viscosity 

 which showed a specific optical rotation of about +270°. The 

 naturally acetylated Type I polysaccharide was found to contain 



