PRODUCTS OF VITAL ACTIVITY. 131 



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

 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 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 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 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 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 regaining 

 this power. 



