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strated as well by the vibrio- or spiril-form, as by the absence of 

 spores *). 



If sown in pepton gelatine, with Mohr's salt and an aerobic bac- 

 tery {B. tenno) for the absorption of oxygen, in deep experiment- 

 tubes, the microaërüphily becomes visible by a black „niveau" 

 of ferrosulfid, first formed at some distance beneath the surface 

 and thence, only slowly, growing towards the depth and upward. 

 When microscopically examined this niveau proves to be richest 

 in reducing spirilli, so that evidently not the function of the sul- 

 phate reduction as such, but the growth of the »S'pnv7//n;?, active in this 

 process, is furthered by a low oxygen tension. 



It is fit here to make a few remarks concerning the I'elation of 

 facultative anacrobics to free oxygen. By far the greater part of facul- 

 tatives is aërophilous. I mention for instance Miicor racemosus, all 

 alcohol yeasts. Bacterium coli commune^ B. ladis ncrogeneSj Granit- 

 lohader polymyxa, Bacillus tuberculosis, B. prodigiosus. If the pro- 

 duction of figures of respiration is possible, then the width of the 

 moving bacteria zone is very great, even in dense swarms, which 

 indicates a slow consumption of oxygen. This is especially the case 

 with the fermenting species, as coli and aërogenes, and sometimes, 

 too, with not fermenting species, such as Bacillus tuberculosis '^). 



Microaërophilous are among the facultatives, so far as I think I 

 can assert now, only the true lactic ferments, which may be brought 

 to two groups of which the most important representatives are: 

 Bacterium lactis (of buttermilk), and Bacillus lougus (of cheese and 

 of the yeast industry). 



As these forms have no motion and produce little living matter 

 in growing, the total quantity of absorbed oxygen is very small, 

 whence the experiments are difficult and subject to doubt. If 

 sown, however, in a proper solid culture mass, to which calcium 

 carbonate is added, in a deep experiment-tube, it may be observed 

 that, under favorable circumstances, at a certain depth below the 

 surface, the formation of acid is the most vigorous. This is caused 

 by the existence of a niveau, very rich in bacteria if compared with 

 deeper layers where less, as well as with those nearer to the 

 surface, where more oxygen is present. After some time, however, 

 so many colonies originate, as well at the surface as in the depth. 



') As I think the only well-described instance of a spore-free obligatous anaerobic . 



^) The mobility of Bacillus tuberculosis bas first been seen by Mr. Mac Gill.ivry. 

 The figures of respiration are troublesome to obtain and only with quite young cul- 

 tures, as for instance of flesh bouillon agar, not older than 24 hours. 



