CHAPTER V 



PNEUMOCOCCAL DISSOCIATION AND 

 TRANSFORMATION 



Changes in the morphological, cultural, pathogenic, and immuno- 

 logical characters of pneumococci caused by various physical, 

 chemical, and serological conditions in their environment; the 

 transformation of the diplococci from one serological type to an- 

 other; and the relation of the species to streptococci. 



The constancy of the biological characters of Pneumococcus 

 depends on the conditions of its surroundings. When the con- 

 ditions are favorable, the morphological and serological integrity 

 of the cell remains stable. Subjected to unfavorable influences, 

 Pneumococcus exhibits great lability of form and function. The 

 form of the cell may pass through every stage from the typical en- 

 capsulated diplococcus to one completely denuded of capsule; 

 pathogenicity may be diminished from full virulence to entire ab- 

 sence of infectivity ; and antigenic and serological properties may 

 lose strict type-specificity and retain only the broader species- 

 specificity. With the restoration of favorable conditions, the deg- 

 radation process, if it has not proceeded too far, ceases and is re- 

 versed, the cell again assuming its typical characters. But, what is 

 still more remarkable, a degraded coccus originally derived from a 

 fixed type may, under appropriate stimulation, develop the vital 

 and immunological properties of a different specific type. Thus, in 

 addition to natural occurrence of variation or dissociation, the 

 actual transformation of pneumococcal types has been experi- 

 mentally induced and, possibly, species mutation has occurred. 

 Lack of knowledge of the existence of bacterial variants and of the 

 factors inducing dissociation has undoubtedly caused much confu- 

 sion in bacteriological diagnosis and in the interpretation of the 

 serum reactions of Pneumococcus. 



