KEY TO GENUS BACTERIUM. 195 



differentiations if we placed before him, as the first ques- 

 tion in the table of differentiation, the character and num- 

 ber of the flagella ; for if the staining of flagella is no 

 special art, yet it requires care and patience, and does not 

 yield regularly good results even to the expert. 



We have therefore been required to select the appear- 

 ance of the cultures in plates and the production of pig- 

 ment as the important points in the separation of the 

 bacteria, although we well know (and also always men- 

 tion it) how easily the production of pigment is lost in 

 some varieties. According to our conviction, however, at 

 present, the proper definition of a Bact. violaceum, syn- 

 cvaneum, etc., which has become colorless would consti- 

 tute an (almost) insurmountable difficulty, no matter 

 how one might construct the key for differentiation. 



Key to the Recognition of the Most Important Vari- 

 eties of the Genus Bacterium. 



I. Forming upon Nutrient Media, Roundish Colonies, with- 

 out OUTGEOWTHS OB LONGER RADIATING PROCESSES, NO 



Branches in Gelatin Stab. 



(A) No growth upon ordinary nutrient media ; on the contrary, 

 very delicate growth upon inorganic saline solutions. Forms 

 nitrate from nitrite, or nitrite from ammonia. 



Forming nitrite from ammonia, Bact. nitrosomonas (Win.), L. 

 and N., page 200. 



Forming nitrite from nitrate, Bact. nitrobacter (Win.), L. and N., 

 page 200. 



(B) Scarcely any growth on ordinary media, but grows well 

 upon pea-leaf decoction containing cane-sugar, gelatin, and 

 asparagin. Assimilates the nitrogen of the air. Grows in the 

 root-tubercles of leguminous plants. 



Bact. radicicola, Beijerinck, page 83. 



(C) Upon the ordinary nutrient media (including serum and 

 glycerin-agar) only a very scanty growth. Delicate, drop-like 

 colonies. Not stained by Gram's method. 



II. Small, thin, non-motile rods. 

 (a) For growth, the addition of a little blood is necessary. Bact. 

 influenzae (R. Pfeiffer), L. and N., page 202. 

 (6) Grow also without blood. Bact. aegyptiacum (Koch- Weeks), 

 L. and N., page 204. Bact. tussis convulsivae (Czapolew- 

 sky), L. and N., page 205. 

 2. Large rods arranged in pairs. Bact. duplex (Morax), L. and N., 

 ;e 206. 



