344 



The indican, as a powtler, may bc added in a percentage of 0.5 to i pCt. to solid 

 or liquid nutrients, adapted for the examination of specific mikrobe groups. 



I found that some species decompose indican with extraordinary facility. Espe- 

 cially the common ferment-bacteria af plant infusions, which of late I united in the 

 genus Aërobacter^), 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 circumstances 

 not vet 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-decom- 

 posing, 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 o.i pCt. may be a violent poison for some photogenic bac- 

 teria, I proved before, and this is noteworthy as still smaller quantities are favour- 

 able to the same species. 



That the different conditions of the bacteria may be of influence on their power 

 for decompositioii, foUows for instance from the fact that Bacillus radicicola, from the 

 tubercles of Pisiiin sath'um and TrifoUum, 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 ornithof<odis, from the roottubercles of Ornithof'i'S 

 sativus, does not decompose at all and, among lactic-acid ferments, I observed vi- 

 gorous decomposition by the rodshaped ferments used in the yeast industry (Lacto- 

 bacter longlis), 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 fermentaction 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-), those of the latter 

 both living and dead. The experiment, demonstrating this, may be performed as 

 follows. 



Of a culture, grown on a solid iiulrit-iit substratuin with cupious access of air, 

 stme material is put on a glass-slide and killed in such a way that eventually present 

 enzyme remains unhurt. This may be done by immersing the material in strong al- 

 cohol, in which it should remain at least 24 hours to be quite sure that the microbes 

 are killed, or by exposition to ether-, alcohol- or chloroform-vapour'' I. In the latter 

 case the microbe-matcrial is placed in a glass-box bcside a vessel with chloroform, 



') Centralbl. f. Bacteriologie. 2c .\bth. Bd. 6. N». 7, pa>4. 193. igoo. 



■) The optimum tempcraturc of the decomposition by katabolism asrccs, for the 

 examined species, with that of the growth. 



') In alcohol vapour niany microbes die sooncr thaii in stroiiK .ilcohdl. this havinR 

 a water absorbing power and thus acting protcctinnly. 



