1213 



feeble. Hence the experiment takes iiincli time, two or thiee weeks 

 or longer. 



To obtain pnre cnltnres on silica plates is niucli more troublesome 

 than on carefully extracted agar, although the nitratation takes place 

 very easily on that medium. 



Some other species of bacteria, eventually occurring in the crude 

 nitratations, may jiroduce colonies on the agar much resembling those 

 of the nitrate ferment. Those species which in the crude nitratations 

 do not multiply at all or only very little, are to be recognised on 

 the plates by their relative rarity. But there exists a species, the 

 denitrifying, spore-forming Bacillus nitnhvus ^), which can increase in 

 the nitratating fluid and on the plates with the same intensity as 

 the nitrate ferment itself and whose separation from the latter gives 

 rise to difïiculties. But here the formation of a new physiological 

 species comes to our assistance, in as much as the nitrate ferment, 

 on broth- or peptone agar, produces very characteristic although no 

 more niti'atating colonies. They are white-coloured, extensive and 

 thin ; at first dry and flat, they later become thicker, slimy and 

 moist, and are easily distinguished from the small, semi-spherical, 

 moist Nitroxus colonies. 



On the nitratating plates may further be found the colonies of 

 Bacillus oligocarbopldlus, which are directly recognised by their 

 white colour and paperlike appearance, and to which I shall return 

 later. Moreover a most characteristic species resembling Actinomyces, 

 but in fact nearly allied to B. oligocarhophilus . So, in all four species 

 which should be considered as characteristic for the crude nitrata- 

 tions, because, after repeated transplantations they ne\'er dissa[)pear, 

 whilst the numerous other species eventually obtained, are but 

 accidental inhabitants and at continued transferring to fresh media 

 maj be quite expelled. 



When the pure cultures of the nitrate ferment are kept in 

 continual contact with the above nitrite solutions, or on the nitrite 

 agar plates poor in soluble organic food, the faculty of oxidising 

 nitrites to nitrates remains unchanged, probably for an unlimited 

 length of time, that is, the ferment preserves its oligotrophic or 

 oligophagic- condition. Microscopically it makes the impression of a 

 small Micrococcus but in reality consists of very short rodiets of 

 0,2 X ö'l f*' which in nitratating condition alioays seem non-motile. 



If the ferment is now transferred to solid media or to culture 

 liquids richer in organic food, as for instance broth agar or agar 



1) To compare : Bildung uiul Verbrauch von Stickoxydul durch Bakterien. 

 Gentrabl. fur Bakteriologie ^ite Abt. Bd. 25, S. 30, 1910. 



