THE GENUS MICROCOCCUS 211 



B. Doubtfully chromogenic. Growth light yellow to 



yellowish white. 



1. Gelatin liquefied. 



2. Gelatin not liquefied. 



3. No growth on gelatin. 



C. Distinctly chromogenic. Form a pigment on gela- 



tin or agar. 



1. Pigment yellowish orange. 



a. Gelatin liquefied. 



b. Gelatin not liquefied. 



2. Pigment reddish, pinkish, flesh-colored. 



3. Pigment bluish black. 



From both these schemes, many of the forms which fail 

 to grow on gelatin may be eliminated, as too imperfectly 

 characterized to be classified at all. Chester's forms 

 which grow feebly on gelatin, or only at 37 degrees, are 

 for the most part parasitic diplococci. The blue and 

 violet forms are apparently short bacilli. No blue-pig- 

 ment-forming coccus has been recorded by any competent 

 observer in recent years. 



A consideration of biochemical characters from the bio- 

 metrical standpoint shows that this unwieldy genus (includ- 

 ing two hundred and twenty-eight species, according to 

 Migula) should be separated into several distinct types. 

 The orange chromogens and a majority of the white forms 

 are distinguished from the yellow and red chromogens 

 by parasitic habit, positive reaction to the Gram stain, and 

 acid production in dextrose and lactose, as well as by pig- 



