THE GENUS RHODOCOCCUS 247 



Minor differences in size and in colony morphology are of 

 course recorded for many of these forms. In several cases 

 a positive reaction to the Gram stain is noted {M. carneus, 

 M. cinnabarinus, and M. lactericeus) ; and M. lactericeus is 

 said to grow best at 37 degrees. None of these characters 

 seem to us from the descriptions to be of specific impor- 

 tance. Certain differences in the chemical nature of the 

 pigment produced are cited by Migula (1900). These 

 observations are suggestive, but require extension and 

 correlation before they can be interpreted from the sys- 

 tematic standpoint. 



Two other forms, sometimes included with the species 

 listed above, are the M. prodigiosus of Cohn and the 

 organism isolated by Babes from red sweat and named 

 M. hcematodes. The former is now known to be a short 

 bacillus, and the latter also, according to the original 

 description, appears to be a rod form. 



There remains to be considered one well-marked, but 

 exceptional, form among the red cocci, the form charac- 

 terized by the exhibition of motility. This was first 

 described by Ali-Cohen (1889) under the name Micro- 

 coccus agilis. It was a slow-growing coccus, isolated from 

 water, forming a pinkish growth mass and gradually 

 liquefying gelatin. There can be little doubt from Ali- 

 Cohen' s description that he was dealing with a truly 

 motile organism. A single flagellum could be demon- 

 strated by appropriate stains. Lehmann and Neumann 

 (1896) failed to find either flagella or motility in their 



