£900 ] CHROMOGENIC BACTERIA 383 
from that produced by inorganic acids. Later experiments seem 
to indicate that this is more probably due to a difference of 
intensity of action. 
Ammonium hydroxid causes a change similar to that pro- 
duced by acids, but the red color in this case is of a different 
tint from that obtained with the latter. The addition of acids to 
the purple-red ammoniacal solution restores the blue color, but 
if the acids are added in great excess the red tint of acid solutions 
results. It is worthy of note that a decided excess is necessary. 
Fixed alkalies (potassium, sodium, barium hydroxids), in 
small amount, first produce a violet tint; if a little more of the 
teagent is added a pure blue results, but the color is somewhat 
paler than that of the original solution. When added in excess, 
the fixed alkalies give rise to a grass green solution. When the 
pigment has not been carefully purified, or when filtrates directly 
from a culture are employed, the change to green is much more 
tapid, and the amount of alkali required for its production is 
less. If the pigment is quite free from foreign bodies the green 
is rather persistent, but when impure rapidly fades away, leaving 
a yellowish liquid. The process of decolorization begins at the 
bottom and gradually extends upwards until the surface is 
teached; here, being in contact with the oxygen of the air, the 
color persists. If the yellowish alkaline liquid be shaken with 
air it immediately turns green, then blue; and if the agitation be 
continued there results a blue solution of almost the same inten- 
Sity as the original. Allowed to stand undisturbed a reverse 
change is observed, namely, rapid decolorization passing through 
a green. The blue can be restored even after several days 
by shaking with air, The addition of alcohol to the yellow- 
ish solution produces a dirty yellow precipitate which ae 
blue the instant it comes in contact with oxygen. This phe- 
Momenon explains why it is that porous potatoes pce mee 
Pigment, and why cutting the colored medium into thin 
and €xposing it to air before extracting, gives 4 larger quantity © 
the coloring matter; for it seems to be obvious that we have to 
do here with a case of oxidation. 
