128 MICRO-ORGANISMS AND DISEASE [chap. 



True pigment bacteria form pigment on all media; this 

 pigment is either diffuse or is limited to the bacterial 

 bodies themselves; thus, bacillus fluorescens liquescens, 

 bacillus fluorescens putidus, bacillus pyocyaneus, form a 

 diffuse bluish-green pigment, while bacillus prodigiosus, 

 staphylococcus aurantiacus, spirillum rubrum, &c., &c., form 

 pigment limited to the bacterial bodies themselves. The 



Fig. 27. — Bacillus Phosphorescens, Film Specimen from a Culture on Gela- 

 tine Broth and Asparagine. 

 X 1000. 



meaning of the pigmentation is not understood, though a 

 large variety of pigmented species are known and com- 

 prise almost every tint : red, pink, orange, ochre, yellow, 

 lemon-yellow, green, greenish-blue, blue, violet, purple. 

 Some of them liquefy gelatine, e.g. bacillus prodigi- 

 osus, staphylococcus aureus, bacillus fluorescens liquescens 

 and pyocyaneus ; others are non-liquefying, as micrococcus 

 aurantiacus, spirillum rubrum, bacillus fluorescens putidus. 



