804 PATHOGENIC MICROORGANISMS 



this pigment had no relation to the pathogenic properties of the 

 bacillus. It is found in cultures as a colorless leukobase which 

 assumes a green color on the addition of oxygen. Conversely, the 

 typical green "pyocyanin/' as the pigment is called, may be de- 

 colorized by reducing substances. This explains the fact that it is 

 not found in cultures sealed from the air. Pyocyanin may be 

 extracted from cultures with chloroform and crystallized out of 

 such solution in the form of blue stellate crystals. These, on chemical 

 analysis, have been found to belong to the group of aromatic com- 

 pounds, with a formula, according to Ledderhose, 25 of C 14 H 14 N 2 0. 



Besides pyocyanin, Bacillus pyocyaneus produces another pig- 

 ment which is fluorescent and insoluble in chloroform, but soluble 

 in water. 26 This pigment is common to other fluorescent bacteria, 

 and not peculiar to Bacillus pyocyaneus. The reddish-brown color 

 seen in old cultures 27 and supposed by some writers to be a third 

 pigment, is probably a derivative from pyocyanin by chemical 

 change. 



Chloroform extraction of pyocyanin from cultures may serve 

 occasionally to distinguish the pyocyaneus bacilli from other similar 

 fluorescent bacteria. Ernst has claimed that there are two types of 

 B. pyocyaneus, an a-type which produces only the fluorescent, water- 

 soluble pigment, and a /?-type which produces both this and pyo- 

 cyanin. 28 



Pathogenicity. Bacillus pyocyaneus is one of the less virulent 

 pathogenic bacteria. It is widely distributed in nature and may be 

 found frequently as a harmless parasite upon the skin or in the 

 upper respiratory tracts of animals and men. It has, however, occa- 

 sionally been found in connection with suppurative lesions of various 

 parts of the body, often as a mere secondary invader in the wake 

 of another incitant, or even as the primary cause of the inflam- 

 mation. In most cases where true pyocyaneus infection has taken 

 place, the subject is usually one whose general condition and resist- 

 ance are abnormally low. 29 Thus pyocyaneus may be the cause of 

 chronic otitis media in ill-nourished children. It has been cultivated 



25 Ledderhose, quoted from Boland, Cent. f. Bakt., xxv, 1889. 



26 Boland, loc. cit. 



27 Gessard, Ann. de 1'inst. Pasteur, 1890, 1891, and 1892. 



28 Ernst, Zeit. f. Hyg., ii, 1887. 

 "Rohner, Cent. f. Bakt., xi, 1892, 



