120 CHROMOPAROUS BACTERIA 



fermentation have been recorded by ALVAREZ (I.). The fermentation may be 

 performed on a small scale bv comminuting fresh leaves of the indigo plant and 

 leaving them to stand in water, whereupon fermentation, attended with evolu- 

 tion of heat, will ensue in twelve to twenty-four hours, the surface of the liquid 

 becoming covered with a thin blue skin, which, when broken, subsides to the 

 bottom and is succeeded by a new one. Microscopical examination shows that 

 this skin consists of bacteria surrounded by fine blue acicular crystals. A 

 sterilised extract of the leaves, when inoculated with a little of this skin, 

 exhibits normal indigo fermentation, whereas without inoculation it remains 

 unaltered even when air is freely admitted. Indigo fermentation is therefore 

 due to the activity of a fission fungus, the Bacillus indigogeniis, which is asso- 

 ciated in the said skin with other species of bacteria that need not be taken into 

 account here. This bacillus is of variable dimensions, but generally 3 p long and 

 1.5 p. broad, and is always surrounded by a gelatinous envelope. Its microscopic 

 appearance is almost the same as that of Friedlander's pneumonia microbe (see 

 Fig. 7), and being motile, it is thereby able to collect at the surface of the liquid, 

 where the desired supply of oxygen is found. It also produces a disengagement 

 of gas, to which the formation of a froth or head on the liquid is attributable. 

 When introduced into the blood of the guir.ea-pig, Bacillus indigogenus proved 

 pathogenic, and therefore belongs to the group of organisms endowed with both 

 zymogenic and pathogenic properties. A second observation made by Alvarez 

 is also worthy of note, viz., that the microbe of pneumonia can set up indigo 

 fermentation, whereas on the other hand many other Dathogenic bacteria proved 

 incapable of so doing. 



Apparently unacquainted with these results obtained by Alvarez, C. J. VAN 

 LOOKEREN (I. and II.) expressed the opinion that the decomposition of indican 

 is not produced by micro-organisms, but by an enzyme present in the living 

 protoplasm of the leaf -cells. The reasons whereon this hypothesis is based do 

 not, however, carry conviction, since attempts made to isolate the alleged enzyme 

 proved unsuccessful. Apart from this, however, the treatise can be read not 

 without profit, and ife also affords several welcome supplementary additions to 

 the bibliographical references collected by G. v. GEORGIEWICZ (1.) in his mono- 

 graph on indigo. 



Alvarez's researches ought to be regarded as a thankworthy preliminary work 

 incentive to further study of the subject, but they do not afford a closer insight 

 into the progression of the fermentation process in question. It is in this case 

 not merely a matter of determining the nature of the ferment or ferments, but 

 rather of the solution of a whole group of problems of both scientific interest 

 and technical importance. Commercial indigo, as is well known, contains, in 

 addition to indigotin, a number of other organic constituents, such, for instance, 

 as the indigo red or indirubin, isomeric with the blue and soluble in alcohol ; 

 also indigo brown, obtained by treating the indigo with alkalies ; and finally, 

 indigo gluten, soluble in dilute acids. The proportion of these subsidiary 

 constituents influencing the shade of the colour is variable in different samples 

 of indigo. An investigation of the conditions affecting their production is a 

 necessary preliminary to the establishment of the most suitable method of 

 fermentation, 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 field 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 emplo}ment of which are 



