134 PRODUCTS OF VITAL ACTIVITY. 
rent culture medium, coloring especially the upper portion, in stab 
cultures in nutrient gelatin or agar. This is the case with Bacillus 
pyocyaneus, which produces a blue pigment which has been isolated 
and carefully studied by Gessard and others. The pigment, which 
is called pyocyanin, is soluble in chloroform and crystallizes from a 
pure solution in long blue needles. Acids change the blue color to 
red, reducing substances to yellow. It resembles the ptomaines in 
its chemical reactions, being precipitated by platinum chloride and 
phosphomolybdic acid. 
In some media the color produced by the Bacillus pyocyaneus 
(bacillus of green pus) is a fluorescent green. The recent studies of 
Gessard show that this isa different pigment. According to this 
author, cultures in a two-per-cent solution of peptone give a beautiful 
blue tint, the production of which is hastened by adding to the liquid 
five per cent of glycerin. In nutrient gelatin and agar cultures a 
fluorescent green color is developed, which, according to Gessard, 
is due to the presence of albumin. Peptone and gelatin are said to 
produce pyocyanin without the fluorescent-green pigment, and cul- 
tures in bouillon to give both this and pyocyanin. In milk the 
fluorescent-green color is first seen, but subsequently, when the ca- 
sein has been peptonized by a diastase produced in the culture, pyo- 
cyanin is also formed. Several other microédrganisms are known 
which produce a fluorescent-green color, due probably to the same 
pigment as is produced by the bacillus of green pus in albuminous 
media. 
Babes claims to have obtained two pigments from cultures of the 
Bacillus pyocyaneus in addition to pyocyanin: one, soluble in alcohol, 
has by transmitted light a chlorophyll-green color, by reflected light 
it is blue; the other, insoluble in alcohol and chloroform, by trans- 
mitted light is of a dark orange-red, by reflected light a greenish- 
blue. 
In Gessard’s latest publication (1891) he shows that the produc- 
tion of pyocyanin or of the fluorescent-green pigment does not de- 
pend alone upon the culture medium, but that there are different 
varieties of the Bacillus pyocyaneus. He has succeeded in producing 
four distinct varieties—one which produces both pyocyanin and 
fluorescence, one which produces pyocyanin alone, one which pro- 
duces the fluorescent-green pigment alone, and one which produces 
no pigment. The last-mentioned non-chromogenic variety was pro- 
duced by subjecting the second variety to the action of heat. A 
temperature of 57° maintained for five minutes destroyed the power 
to produce pigment without destroying the vitality of the bacillus, 
which was propagated through successive cultures without regainin g 
this power. 
