YAEIETIES OF BACILLUS PYOCYANEUS. 157 



capable of yielding, on the one hand, the maximum quantity of 

 indigo (in Lookeren's experiments 0.2 per cent, of the weight of 

 the plant), and on the other, producing at will any desired variety 

 of the pigment. A very promising tield of profitable enterprise 

 is thereby opened up to mycologists residing in the districts where 

 the indigo plant is cultivated. Moreover, it is incumbent on 

 fermentation physiologists in the centres of consumption to study 

 the fermentation of the indigo dyeing- baths the woad-vat, the 

 so-called potash bath, and, finally, the urine bath the preparation 

 and employment of which are carried on according to old-fashioned 

 rules and without any knowledge of the internal reactions occurring 

 therein. One thing is certain : these reductions are not purely 

 chemical operations, but are true fermentations, as already em- 

 phasised by A. FITZ (IY.) in 1878. Frequently they proceed in 

 an undesired direction ; two such maladies of the indigo bath 

 being : destruction of the colour, and blackening. However, as 

 regards these, mycological investigations are still lacking. 



97. Varieties of Bacillus Pyocyaneus. 



The number of bacterial species capable of producing blue 

 colouring matters is by no means exhausted by those mentioned 

 in the three preceding paragraphs. A fourth, which has been 

 repeatedly referred to in earlier chapters, is the Bacillus pyocyaneus, 

 described by C. GESSARD (II.). This organism, conveyed in atmos- 

 pheric dust, conies in contact with the pus exuded from wounds, 

 and developing therein, produces, as its name implies, a coloration 

 ranging from blue to verdigris green. This microbe, which really 

 belongs to pathological and not to technical mycology, is very 

 mutable, a property which must also be briefly dealt with here. 

 In addition to the blue pigment designated pyocyanine which 

 may be separated from the cultures by shaking them up with 

 chloroform, and which was first prepared in the pure crystalline 

 state by FORDOS (I.) the parasite in question, when cultivated in 

 bouillon, produces a green fluorescent colouring matter. By skil- 

 fully modifying the conditions of nutrition GESSARD (III. and IV.) 

 obtained three varieties, morphologically indistinguishable, one of 

 them producing only pyocyanine, the other only the fluorescent 

 pigment, and the third no colouring matter at all. Whilst these 

 three varieties can be re-transformed into the typical species, such 

 change cannot be effected with a fourth variety, cultivated by CHARRIN 

 and PHISALIX (I. ), which had permanently lost its chromogenic faculty. 

 Unaware of this variability, P. ERNST (III.) proposed to distinguish 

 between two species Bacillus pyocyaneus a and j3, a course which 

 Gessard considers incorrect. In contradiction to the results ob- 

 tained by the latter worker, and confirmed by HANS BUCHNER and 

 ROHRER (I.), K. THUMM (I.) asserted that B. pyocyaneus produces 

 only a single pigment, the blue. Undoubtedly this investigator, 



