PNEUMOCOCCUS. 503 



.Rather scant growth occurs on the ordinary 

 culture media in the form of small colonies which 

 resemble those of the streptococcus, and unless spe- 

 cial media are used it usually can not be carried 

 through many generations. When grown in spu- 

 tum, or on a medium which contains ascitic fluid, 

 the blood or serum of man or some favorable ani- 

 mal, its virulence may be preserved for some time. 

 By growth at 39 C. virulence is lost rapidly. 

 Strains which are atypical in one of several ways 

 are encountered. They may show low virulence, 

 may grow well at ordinary temperatures (the typi- 

 cal organism not doing so), may produce long 

 chains in liquid media, or may grow without a 

 capsule. 



Recently the danger of confusing the pneumo- confusion 

 coccus with the streptococcus has received renewed strepto- 

 attention, and newer methods of differentiation c 

 render it extremely probable that such confusion 

 has occurred in the past. An important differen- 

 tial method is that of cultivation on agar plates 

 which contain blood (Schottmliller and Rosenow) ; 

 the streptococcus produces a clear zone of hemo- 

 lyzed corpuscles about its colonies, whereas the 

 colonies of the pneumococcus present a greenish 

 color and produce no hemolysis. In using this 

 test G. F. Ruediger found a surprising number of 

 pneumococci in normal throats, whereas previous 

 work had shown them to be less common than 

 streptococci. 



In spite of the poor viability of the organism on Resistance. 

 ordinary culture media, it is fairly resistant to 

 desiccation and sunlight, especially when embedded 

 in sputum. It is possible that the surrounding spu- 

 tum is protective and that the well-formed capsule 



