24 BIOLOGY OF PNEUMOCOCCUS 



logical data, there is the account of a phenomenon, the meaning of 

 which the authors failed to realize, but which much later was to 

 assume wide biological significance. Studying forty-six strains of 

 diplococci of pneumonic origin under varying cultural conditions, 

 Kruse and Pansini noticed that the organisms when subjected to 

 unfavorable media, with succeeding generations began to differ 

 from the parent strain in morphology and colony formation. The 

 variations ran the gamut from typical Diplococcus lanceolatus to 

 Streptococcus pyogenes. Along with the changes in form there 

 took place loss of capsule and of virulence, although animal pas- 

 sage restored the original characters. Because of the loss of 

 capsule, diminution of virulence, and the appearance of chain 

 formation, Kruse and Pansini concluded that they had effected a 

 mutation of Pneumococcus into Streptococcus, and that both spe- 

 cies arose from a common saprophytic, streptococcal form. What- 

 ever may have been their conclusions, it seems certain that they 

 were observing the phenomenon of bacterial dissociation. 



A notation of Metchnikoff's 894 was undoubtedly the first record 

 of the agglutination of pneumococci by immune serum. He wrote 

 that the microbe of pneumonia formed very long plaquettes of 

 "streptococci" in the serum of vaccinated rabbits. 



Foa and Carbone (1891), 463 continuing their work with alcohol 

 and ammonium sulfate precipitates from culture filtrates, learnt 

 that the immunity induced by their preparations was less enduring 

 than that evoked by the untreated filtrates. Foa's later studies 

 (1893) 459 were, in a way, less productive, since, unknowingly, he 

 was apparently dealing with both pneumococci and meningococci. 

 He did show, however, that these two cocci differed from each other 

 in biological characters, and that the serum of animals immunized 

 against the one species was inactive against the other. 



Here, in the matter of time and because of its bearing on the dis- 

 cussion in some of the preceding pages, there may be interpolated 

 the final description which Sternberg (1892) 1321 gave to Pneumo- 

 coccus under the title, Micrococcus pneumoniae crouposae : 



