108 RELATIONSHIPS OF THE COCCACE^E 



power and in relation to gelatin and nitrates the red cocci 

 exhibit characters which are peculiar to themselves. 

 Reference to the comparative table on page 97 shows 

 that in the white, orange, and yellow groups between 60 

 and 70 per cent of the cultures studied liquefied gelatin; 

 and the average depth of liquefaction after 30 days was 

 from i to 2 centimeters. Among the red cocci, on the 

 other hand, only 2 out of 25 strains affected the gelatin 

 in this time and in each case to a depth of less than half 

 a centimeter. An examination of the published descrip- 

 tions of red cocci in the literature shows that these organ- 

 isms are in general characterized by extremely sluggish 

 and uncertain peptonizing power. Their action upon 

 nitrates is equally peculiar. From 10 to 30 per cent of 

 the organisms of other color-types attacked nitrates, and, 

 of the reducers, half formed ammonia and half nitrites. 

 Of the red cocci, on the other hand, 14 out of 25, or 56 per 

 cent, reduced nitrates; in every case nitrites were formed 

 but not ammonia. 



Evidently the red cocci constitute a natural group of 

 considerable definiteness ; and for this group we have 

 suggested the generic name Rhodococcus. Molisch 

 (1907) has since applied the same name to a genus of the 

 purple bacteria; but our use of the name has priority by 

 about a year. Both packet-forming and non-packet- 

 forming types are included in the genus; 10 of the former 

 and 15 of the latter occurred in our series. In no other 

 respect were the two types distinguished. Both showed 



