PRODUCTS OP VITAL ACTIVITY. 127 



rent culture medium, coloring especially the upper portion, in stick 

 cultures in nutrient gelatin or agar. This is the case with Bacillus 

 pyocyanus, 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 pyocyanus 

 (bacillus of green pus) is a fluorescent green. The recent studies of 

 Gessard show that this is a 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 cul- 

 tures 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 pig- 

 ment, and cultures in bouillon to give both this and pyocyanin. In 

 milk the fluorescent-green color is first seen, but subsequently, when 

 the casein has been peptom'zed by a diastase produced in the culture, 

 pyocyanin is also formed. Several other microorganisms 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 pyocyanus in addition to pyocyanin : one, soluble in alco- 

 hol, has by transmitted light a chlorophyll-green color, by reflected 

 light it is blue ; the other, insoluble in alcohol and chloroform, by 

 transmitted light is of a dark orange-red, by reflected light a green- 

 ish-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 pyocyanus. 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 regaining 

 this power. 



