( 504 ) 
I found that some species decompose indican with extraordinary 
facility. Especially the common ferment-bacteria of plant infusions, 
which of late I united in the genus Aérobacter'), decompose with so 
much intensity, that they may with some reason claim the name of 
„indigobacteria’’; they will later be discussed in particular. For the 
species which split with more difficulty this power depends on circum- 
stances not yet quite clear to me. It may occur that in pure 
cultures colonies of one and the same origin, and separated from the 
common stock by a few generations only, behave quite differently, so 
that species, which for a long time I considered as non-decomposing, 
later proved vigorous indigo-producers. This I observed for instance 
in the photogenic bacteria of the Northsea. I suppose this fact to 
be connected with the influence of the sugar freed at the splitting 
of the indican, as other experiences prove that this influence is not 
constantly the same for all individuals of a species. That especially 
glucose acts vigorously on the life of some bacteria, and, even in 
small quantities, e.g. 0.05 pCt. to 0.1 pCt. may be a violent poison 
for some photogenic bacteria, I proved before, and this is noteworthy 
as still smaller quantities are fayourable to the same species. 
That the different conditions of the bacteria may be of influence 
on their power for decomposition, follows for instance from the fact 
that Bacillus radicicola, from the tubercles of Pisum sativum and 
Trifolium, decomposes the indican, while this is not done by the 
bacteroids of the tubercles of these plants. Closely allied species may 
also behave differently; thus, Bacillus ornithopodis, from the root- 
tubercles of Ornithopus sativus, does not decompose at all and, among 
lactic-acid ferments, I observed vigorous decomposition by the rod- 
shaped ferments used in the yeast-industry (Lactobacter longus), and 
no decomposition by the diplococci and streptococci (L. lactis) of the 
dairy industry. The ease with which this reaction is effected and 
its clear result recommend it for further research. 
The splitting of the indican by microbes is operated in the same 
way as in indigo-plants, either by katabolism, i. e. by direct ferment- 
action of the living protoplasm on the indican, or by specific indigo- 
enzymes. Consequently the forms belonging to the former group 
decompose the indican in living condition only 2), those of the latter 
both living and dead. The experiment, demonstrating this, may be 
performed as follows. 
") Centralbl, f. Bacteriologie, 2e Abth. Bd. 6, N°. 7, pag. 193, 1900. 
2) The optimum temperature of the decompositon by katabolism agrees, for the 
examined species, with that of the growth. 
