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, ete. 
VIOLET PigMENtTS. 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 emerald-green with potash solution. 
BiLveE PicMents 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 chromogenic 
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, ete. The B. 
prodigiosus produce no pigment at 87° C., and when 
transplanted at this teraperature, 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 
pneumococcus 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. Aéro- 
bic bacteria sometimes produce alkaline products from 
albuminous substances in culture media free from sugar. 
