SUGAR IN THE NUTRIENT MEDIUM. 129 



bluish, with alkaline a green fluorescence. The 

 fluorescence of the cultures is at first blue, later 

 green, on account of the increase of the ammonia 

 formed by the bacteria. The pigment is not sensi- 

 tive to oxidizing substances. Colorless preliminary 

 stages have not been observed. Phosphoric acid and 

 magnesium are necessary to the development of bac- 

 terio-fluorescein. 



The variations in the chromogenic functions have 

 been the subject of numerous investigations. All 

 possible factors which have an unfavorable influence 

 on the growth of the bacteria also diminish the de-" 

 velopment of pigment. After continued culture upon 

 unsuitable nutrient media or at improper tempera- 

 tures, etc., the formation of pigment by later genera- 

 tions may remain permanently diminished. 



For example, there are races of bacterium syncy- 

 aneum which form no trace of coloring matter in agar 

 or milk, but on potato give a dark color even to the 

 parts around the culture. The development of pig- 

 ment appears to have been lost here simply on account 

 of the rare inoculation of the agar cultures. 



At 37 bacterium prodigiosum forms no pigment, 

 and if the cultures are kept up at this temperature for 

 a long time, the production of pigment will be lost 

 for many generations even under favorable conditions 

 (Schottelius). 



Yery interesting communications are scattered 

 throughout the literature on pigment-forming races 

 among otherwise colorless varieties. For example, 

 Fawitzky reports yellow to rusty red colonies of 

 streptococcus lanceolatus; Kruse and Pasquale ob- 

 served colored races of streptococcus pyogenes 

 9 



