156 CHROMOPAROUS BACTERIA. 



Bcopical 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 indigogenus, which is associated 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 /x broad, and is always surrounded by a gelatinous envelope. 

 Its microscopic appearance is almost the same as that of Fried- 

 lander'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 disengage- 

 ment of gas, to which the formation of a froth or head on the 

 liquid is attributable. When introduced into the blood of the 

 guinea-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 pathogenic 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 it also affords several welcome 

 supplementary additions to the bibliographical references collected 

 by G. v. GEORGIEWICZ (I.) in his monograph 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, 



