Vi] GENERAL CHARACTERS OF BACTERIA gi 



which can obtain this nitrogen from air and from nitrates, 

 — «.^. bacillus radicicola — a bacterium which forms part of the 

 substance of the nodules on the roots of leguminosae; other 

 bacteria can exist on organic nitrogen in low composition 

 — e.g. ammonium tartrate (in Pasteur's and Cohn's fluid); 

 or urea (micrococcus ureae and other bacteria that thrive 



Fig. 15.— Gelatine Plate-cultivation of Bacilll-s RadicicolAj 

 Colonies are liquefying. 

 Natural Size. 



in urine). Most bacteria thrive well in media like the usual 

 culture media containing albuminous substances. But also 

 in this latter case great differences exist ; while for instance, 

 the bacteria occurring in water (bacillus fluorescens liquescens, 

 bacillus sulcatus and others) can even when the water contains 

 only traces of albuminous matter, well thrive therein and under 



