CHEMICAL CONSTITUENTS 297 



and Type III Pneumococcus polysaccharide showed that the 

 viscosity effects decrease with the relative number of carboxyl 

 groups, or negative charges in the molecule. 



SUMMARY 



It should by no means be assumed that the last word has been 

 written about pneumococcal polysaccharides. Notwithstanding the 

 fact that the presence in any appreciable percentage of what is 

 considered the acetyl group may exert a marked influence on the 

 antigenic properties of these substances, we should not close our 

 minds to the many possibilities which the subject presents. We 

 cannot as yet be sure that any of the substances isolated from 

 Pneumococcus are truly representative of the actual components 

 of the living cell, even though the immunological action of the ace- 

 tyl polysaccharide most nearly approaches that of the unbroken 

 Pneumococcus. 



We can be sure that many of the methods employed up to the 

 present time have led to products far from pure by any standard 

 we set, and we can be equally certain that the majority of the pro- 

 cedures have caused more or less disturbance of the molecular ar- 

 rangement of the cells' constituents with a consequent loss of 

 chemical and immunological integrity. Many of the preparations 

 hitherto derived from Pneumococcus by natural means must be 

 looked upon as mixtures of carbohydrate, protein, and other cellu- 

 lar elements, and the majority of the preparations produced by 

 chemical methods cannot be accepted as anything but artifacts 

 containing, to be sure, a nucleus of intrinsic antigenic material 

 but, nevertheless, representing substances which eventually may be 

 discovered to be removed in varying degree from the native antigen. 



There are chemical groups other than the acetyl radical in pneu- 

 mococcal capsular polysaccharides, and until we have a more thor- 

 ough analysis and more exact identification of all these substances 

 supported by their respective immunological reactions, it would be 

 folly to take any dogmatic stand in this highly complex question. 



