336 Jouryial of Agricultural Research voi. xvi. No. 12 



Gessard {21) made a comparative study of this organism and some other 

 fluorescent organisms. He concluded that it produces two pigments: a 

 yellow-green, water-soluble pigment, and a blue-green, chloroform-soluble 

 pigment, which he called "pyocyanin." He claims that it differs from 

 B. fluorescens liquefaciens and B. fluorescens putidus (the nonliquefying 

 type), as neither produces pyocyanin. Lehmann and Neumann (29, p. 

 272), however, claimed that the two organisms differ only in the intensity 

 of the pigment, and remark concerning B. pyocyanewn that according to 

 their conviction, this organism can not be sharply differentiated from 

 B. -jiiwrescens } The opposite conclusion was reached two years later 

 by Niederkom (40), who studied a series of fluorescent cultures from 

 various sources and decided that the fluorescens type and the pyocyaneus 

 type are distinct, although each has numerous subvarieties. He states 

 that the flagella of the pyocyaneus type are well defined,^ but those of 

 the fluorescens type are not ; that the former takes the Gram stain more 

 definitely than the latter; that the former grows best at 35° C, the 

 latter at room temperature. The contrary opinion is expressed by 

 RuziCka {42, 43), who mentions these and other differences (except in 

 regard to the Gram stain), but concludes that they are not constant 

 By cultivating the fluorescens type at 37° he obtains cultures of the 

 pyocyaneus type; by growing the blue-pus organism in water, aerated 

 with sterile air, he obtains cultures of the fluorescens type. Later 

 Lehmann and Neumann {30, p. 411-413) continue the discussion, referring 

 to the differences between the two types, laying considerable stress on 

 the denitrifying power of the blue-pus organism, but repeating their 

 earlier statement that one type grades imperceptably into the other. 

 They did not find either organism Gram-positive. Finally, Pribram and 

 Pulay {41) made a study of the fluorescent group by serological methods 

 and found it apparently to consist of several different species, B. 

 pyocyaneum appearing distinct from B. fluorescens, although closely 

 related to it. 



The ability of the pyocyaneus type to convert nitrate into free nitrogen 

 was apparently first mentioned by Lehmann and Neumann (29), who 

 do not, however, mention the source from which the culture they studied 

 was obtained. The following year, Weissenberg (57), apparently at 

 the suggestion of Lehmann or Neumann, made a further investigation 

 of pyocya'neus cultures from various sources, finding them all to be 

 denitrifiers, while observing this ability with no organism of the fluorescens 

 type. The same year Severin (45) wrote a paper on denitrifiers obtained 

 from manure, one of which is fluorescent. This fluorescent culture he 

 calls B. pyocyaneus, but does not show it to be the cause of blue pus. 



One striking fact in this connection is that no one seems to have found 

 a Gram-positive pyocyaneus culture which denitrifies or a Gram-negative 



' Den OrganisTnus scharf gegen B. fluorescens abzugrenzen, geht nach unserer Ueberzeugung nicht an. 

 " Wohl ausgepragte. 



