SUBFAMILIES AND GENERA OF COCCACE^ 89 



little doubt of the real importance of the subfamilies, 

 Paracoccaceae and Metacoccaceae. 



In our first paper, to" which reference has been made 

 in Chapter II, we included under the Paracoccaceae only 

 the genera Diplococcus and Streptococcus ; and charac- 

 terized the subfamily by parasitic habit, meager growth 

 on media, and grouping of cells in pairs or chains. It 

 is clear, in the light of the comparative study just 

 reviewed, that the group of the Paracoccaceae must 

 be broadened to include other characteristic parasitic 

 cocci which resemble the streptococci in important 

 biochemical characters. The new forms to be included 

 are the white and orange staphylococci. Both resemble 

 the streptococci in forming relatively small cell aggre- 

 gates and never producing packets; but they occur 

 in plates and groups rather than chains. On the 

 other hand, the new facts accumulated make it possible 

 to separate the subfamilies of the Coccaceae more sharply 

 than before in other ways. Streptococci, white staphylo- 

 cocci and orange staphylococci are alike differentiated 

 from the yellow and red saprophytes by their generally 

 positive Gram reaction, by their marked acid production, 

 and by their peculiar chromogenic power (growth white 

 or orange, not yellow or red). These three characters, 

 with the parasitic habitat, the meager or only moderately 

 vigorous surface growths, and the small cell aggregates, 

 clearly mark off a natural group; and the Metacoccaceae, 

 including the yellow and red color-types, differ from the 



