PIGMENTS. 65 
(3) How are they acted on by acids, alkalies, and other reagents ? 
(4) Of what use are they to the organism? Are they oxidation-products ? 
_ Examine spectroscopically, if possible. 
On the addition of acids or alkalies, a bacterial pigment may remain unchanged, 
may be changed into some different color, may be destroyed, or may be converted 
into some colorless compound which will regain its original color on changing back 
the reaction. The yellow pigment of several species of Bacterium (Pseudomonas) 
remains unchanged in the presence of acids and alkalies. The blood-red color of 
Bacillus prodigiosus becomes carmine in the presence of certain acids and yellowish- 
brown in the presence of certain alkalies. The blue color of Bacterium syncyaneum 
is said to be produced only in acid milk. The beautiful green fluorescence of Bac- 
terium pericarditidis (Bacillus pyocyaneus pericarditidis), and probably of all this 
gtoup of bacteria, is produced only in alkaline media. According to Jordan two 
pigments are normally produced by many green-fluorescent organisms. The blue 
pigment pyocyanin is visible by gaslight and is soluble in chloroform. The green- 
fluorescent pigment is insoluble in chloroform and yellowish by gaslight. By 
this latter test the two can be distinguished when mixed. Soluble phosphates and 
sulphates are necessary for the production of green fluorescence. The ability to 
produce pyocyanin is easily lost. Its production in the culture-medium, unlike that 
of the fluorescine, is not dependent on the presence of phosphates or sulfates. 
Pyocyanin turns red with acids, fluorescine becomes colorless; both return to their 
original color on adding alkali sufficient to change the reaction. ‘ Asparagin, 
ammonium succinate, ammonium lactate, and ammonium citrate all proved suitable 
for the development of the fluorescent pigment.’? The yellow and black pigments 
are the result of oxidations. (See papers by Gessard, Thumm, and Jordan, Bibliog., 
XXIII). 
The pigments of bacteria range from one end of the spectrum to the other. 
Thus we have various shades of black, brown, violet, indigo, blue, green, yellow, 
orange, and red. Many bacteria produce no pigment, z. e., are white when seen in 
mass. Others produce several distinct pigments. Many of the plant parasites are 
yellow, ¢. g., Bacterium campestre, Bact. phaseoli, Bact. hyacintht, Bact. Stewarti, 
Bact. juglandis. Some of these yellow organisms stain the host-plant and certain 
nutrient substrata a deep brown. Other plant parasites are white but also stain the 
host and certain substrata brown, e.g, Bacterium solanacearum, Bacillus carotovorus, 
B. aroidee. Others are pure white and are apparently destitute of any pigment- 
producing powers, ¢.g., Bacillus amylovorus, B. tracheiphilus. Very many bacteria 
when grown on cooked potato produce a gray stain in this substratum, especially in 
that part freely exposed to the air, 2. ¢., out of the water. 
Some other color changes in the host should be mentioned. Various brown 
and red stains visible in certain plants when attacked by bacteria are not attributable 
directly to the presence of the microorganisms in the tissues. These are oxidation 
phenomena likely to occur when the plants are wounded or destroyed by any agent 
whatsoever. A few illustrations will make my meaning clear. When the limbs of 
pear trees are destroyed by blight the foliage becomes black, but this blackening 
