VITAL PHENOMENA OF BACTERIA. 67 



common to both the animal and vegetable kingdoms 

 known as lipochromes, and to which belong the pig- 

 ments of fat, yolk of egg, the carotin of carrots, tur- 

 nips, etc. 



VIOLET PIGMENTS. Certain bacteria produce violet 

 pigments, also insoluble in water and soluble in alcohol, 

 but insoluble in ether, benzol, and chloroform. These 

 are colored yellow when treated in a dry state with sul- 

 phuric acid and ernerald-green with potash solution. 



BLUE PIGMENTS are also produced by the so-called 

 fluorescent bacteria, along with a pigment named bac- 

 terio-fluorescein. In cultures the fluorescence is at first 

 blue; later, as the cultures become alkaline, it is green. 



Numerous investigations have been made to deter- 

 mine the cause of the variation in the chrornogenic 

 function of bacteria. All conditions which are unfav- 

 orable to the growth of the bacteria decrease the pro- 

 duction of pigment, as cultivation in unsuitable media 

 or at too low or too high a temperature, etc. The B. 

 prodigiosus produce no pigment at 37 0., and when 

 transplanted at this temperature, even into favorable 

 media, the power of pigment production is gradually 

 lost. 



Otherwise colorless species of bacteria sometimes pro- 

 duce pigments. Thus yellow to red colonies of the 

 pneutnococcus have been observed, and colored varie- 

 ties of the streptococcus pyogenes. Occasionally colored 

 and uncolored colonies of the same species of bacteria 

 may be seen to occur side by side in one plate culture, 

 as, for example, the staphylococcus pyogenes. 



Alkaline Products and the Fermentation of Urea. Aero- 

 bic bacteria sometimes produce alkaline products from 

 albuminous substances in culture media free from sugar. 



