CLASSIFICATION OF PNEUMOCOCCI 119 



within the species. Lately' it has been found that other and appar- 

 ently unrelated bacteria also elaborate complex carbohydrates, 

 and that these carbohydrates both as antigens and as haptens 

 exhibit immunological similarities to the polysaccharides of Pneu- 

 mococcus. Puzzling as these new developments are at present, they, 

 like the discovery of the transformative processes, will only lead to 

 the disclosure of new biological principles. 



There is no doubt that the members of other microbial species 

 and materials of vegetable origin contain polysaccharides which 

 may be found to possess chemical and immunological relations 

 analogous to the capsular carbohydrates of Pneumococcus but, as 

 Heidelberger and Avery concluded, this type of immunological cor- 

 respondence in no way invalidates the systematic classification of 

 bacteria based on the more usual and general methods of species 

 determination, and it is of greater immediate significance in con- 

 nection with the study of problems dealing with bacteria as disease- 

 producing agents than in the study of bacteria in their generic 

 relationships. 



Type Determination 



The immunity reactions which form the basis of serological 

 methods for the bacteriological differentiation of pneumococci are 

 of inestimable importance to students of Pneumococcus and to 

 clinicians. They aid in defining the relations and interrelations of 

 members of this bacterial species ; they afford clues in tracing the 

 spread of pneumococcal infection ; they reveal the influence of 

 chemical constitution in determining antigenic specificity and im- 

 mune response ; and have an eminently practical bearing on serum 

 treatment. 



Whatever benefit is to be derived from the use of antipneumococ- 

 cic serum depends on the rapid and accurate determination of the 

 type of Pneumococcus causing the infection. While the potency of 

 serum and the judgment directing its administration are of great 



