22 RELATIONSHIPS OF THE COCCACE^ 



and orange chromogens are the common cocci of the 

 skin. Both yellow and red types frequently show the 

 packet grouping; and in the yellow type we have con- 

 tinued the separation into two genera, Micrococcus and 

 Sarcina, which is now in almost universal use. In all 

 other respects the packet-forming and non-packet- 

 forming -yellow series are closely parallel. Both types 

 form a good growth on media, of a lemon yellow color, 

 and the distribution of these organisms on the color 

 chart, reproduced as the frontispiece of this volume, 

 shows that the type center of the yellow saprophytes is 

 separate and distinct from that of the orange para- 

 sitic forms. Both micrococci and sarcinae are generally 

 Gram negative. They form typically a slight acidity 

 in dextrose broth and none in lactose broth; and the 

 frequency curves for dextrose in Fig. II show a remark- 

 able parallelism between the two genera. Finally the 

 red chromogens, which we have grouped under the new 

 genus, Rhodococcus, form another distinct type by them- 

 selves. They resemble the yellow cocci in saprophytic 

 habit, negative Gram reaction, and low fermentative 



\ power. They differ from them in their peculiar pig- 



/ ment, in the absence of vigorous liquefying action, and 



in the fact that they reduce nitrates, if at all, to nitrites 



v. and not to ammonia. 



The result of our study was to convince us that these 

 six types represent true natural groups of the Coccacese, 

 liacTi marked by the occurrence of a peculiar complex 



