21 



here are either quoted or applied to the culture media in distinction 

 from the bacterial pigments. 



One difficulty, however, in determining bacterial pigment, is 

 the possible range of variation in any one organism under influence 

 of preliminary cultivation, reaction of media, and age of culture; 

 so that one color-determination may be insufficient for general 

 description. Neither can the mean of several determinations be 

 specified as the typical color of a given organism. But, allowing 

 for occasional degenerate or pigmentless cultures, if an organism 

 has been put through the regular course of rejuvenation and then 

 grown on slant agar of definite composition and reaction, the pig- 

 ment of young and of ten day old cultures can be fairly well charac- 

 terized. The appended tables will give an idea of the results of 

 this method; and the terms used in this paper to designate the 

 different reds will have definite meaning as follows : 



Bed Orange White Blue 



25 



22 3 



5 



(see Table I p. 22.) 



Of the cultures producing "insoluble" pigment on agar, which 

 are studied here, a division may be made into three groups, accord- 

 ing to color of pigment. 



I. The B. prodigiosus group, including 



B. prodigiosu s, 



B. ruber indicus, 



B. ruber plym outhensis, 



B. kiliensis (B. ruber balticus), 



B. miniaceus, 



B. rutilus (n. sp.), 



B. arayloruber (n. sp.), 



B. fuchsinus, 



B. ruber miquel. 



The members of this group develop on agar a pigment in 

 mass, which shows a large percentage of pure red, with varying 

 quantities of orange and sometimes a small amount of blue, which 

 gives a violet tinge, or of black. They are characterized by the 

 fact that the amount of orange diminishes as the cultures age; 

 at the same time there is an addition of black, i. e., the cultures 

 grow darker. This group includes the "carmine", "blood red", 

 and "violet red" cultures. 



II. The B. rubricus group, including 



B. rubricus, 



B. ruber zimmermann, 



B. ha vaniensis, 



