SUBFAMILIES AND GENERA OF COCCACE^E 91 



pneumococcus and the meningococcus, have made it 

 clear that they differ from the streptococci by their greater 

 power of decomposing carbohydrates, — inulin, in par- 

 ticular, offering a fairly constant differential test. Further- 

 more, it appears that the diplococci are closely related in 

 their response to immune sera, reacting to group aggluti- 

 nins which do not affect the streptococci. In all respects, 

 in habitat, in morphology, in growth on media, and in 

 power of attacking carbohydrates, these organisms form 

 the extreme end of the series of the Paracoccaceae. The 

 evidence on these points will be reviewed more fully in 

 Chapter V. 



It has seemed to us amply sufficient to warrant the recog- 

 nition of the genus Diplococcus of Weichselbaum, with 

 the following amplified definition: 



Genus I. Diplococcus (Weichselbaum) Winslow and 

 Rogers. Strict parasites, not growing, or growing very 

 poorly, on artificial media. Cells normally in pairs, sur- 

 rounded by a capsule. Fermentative powers high, most 

 strains forming acid in dextrose, lactose, saccharose, and 

 inulin. Hemolytic power generally lacking. Characteristic 

 group serum reactions. 



In one respect two species of diplococci depart from 

 the characters of the subfamily as a whole. Both 

 the gonococcus and the meningococcus decolorize by 

 Gram. Such conditions as this are common in systematic 

 biology, — some members of a group often differing 

 radically in a single property from the general character- 



