THE GENUS RHODOCOCCUS 243 



parative study, carried out by some method which will 

 measure this tendency with approximately quantitative 

 results, will form a sure basis for specific types. Such 

 data are at hand, altho on a small scale, in regard to 

 nitrate reduction and gelatin liquefaction, but not for 

 packet formation. It seems best, therefore, for the present 

 to include packet-forming red cocci with those in which 

 the property has not been observed. Packet-forming species 

 may be separated later, if it seems best to do so. 



The specific importance of gelatin liquefaction in this 

 group seems also open to serious doubt. Our own obser- 

 vations of the action of these forms on gelatin extended over 

 a period of thirty days. In that time twenty-two strains 

 failed to show any action, two liquefied to a depth of .4 centi- 

 meter and one to a depth of 1.2 centimeters. The last three 

 forms certainly do not furnish sufficient basis for a distinct 

 species. Red, liquefying cocci have been described by 

 many observers. In almost every case, however, it is 

 noted that the action upon gelatin is extremely slow. 

 Thus Migula (1900) says of M. roseus that liquefaction 

 occurs only after a long time and then to a very slight 

 extent; of M. rubens, that distinct liquefaction does not 

 occur even after several weeks; of M. persicus, that after 

 fourteen days the gelatin begins to soften ; of M. cumulatus, 

 that gelatin begins to liquefy after fourteen days, etc. Dyar 

 (1895) found that M. fragilis began to liquefy slowly after 

 six days, and Sarcina rosea often not for thirty or forty days. 

 It is clear that the rhodococci, when they liquefy at all, do 



