BACTERIUM NITROBACTER. 201 



as also those of Stutzer and Hartleb, regarding a polymorphous salt- 

 peter fungus are incorrect. Compare Frankel (C. B. L. IV, 8, 62) 

 and Gartner (C. B. L. iv, 1, 52, 109). 



Microscopic Appearance. — Short rods, 1 n long, 0.3- 

 0.4 /jl thick. Stain poorly. When stained with warm gen- 

 tian-violet solution and washed with a 10% solution of 

 chlorid of sodium, a stained capsule surrounds the bacilli, 

 which are unstained. With carbol-fuchsin the rods are 

 gradually stained, the pointed ends escaping. Alkaline 

 methylene-blue first stains the ends, then the central 

 portion. 



Motility is never observed. No growth occurs upon 

 the ordinary nutrient media, rich in organic substances 

 (bouillon, agar, gelatin), but it grows upon the following : 

 Nitrite-agar, which contains pure sodium nitrite 2 gm., 

 sodium bicarbonate 1 gm., potassium phosphate and agar 

 15 gm., water 1 liter ; or nitrite solution, which contains: 

 sodium nitrate 1.0, potassium phosphate 0.5, magnesium 

 .sulphate 0.3, sodium bicarbonate 0.5-1.0, sodium chlorid 

 0.5, a little iron sulphate, distilled water (distilled twice 

 over permanganate) 1000. If soda is used instead of 

 sodium bicarbonate, then also free C0 2 must be present. 

 The addition of more than 0.4% peptone, or of small 

 quantities of sugar, prevents the growth and the produc- 

 tion of nitrate. 



Nitrite-agar Colonies. — Deep: granular, dense, small, 

 sharply outlined, strongly refracting, appearing only after 

 weeks. On the surface delicate, cloud-like, homogeneous, 

 scarcely at all granular droplets develop equally slowly. 



Nitrite-agar Stab Culture. — Somewhat more luxuri- 

 ant, dirty white, greasy. 



Isolation from Soil. — Numerous plates are prepared 

 from nitrite-agar with larger and smaller quantities of soil 

 suspended in it. After standing for three or four weeks at 

 about 20°, test the plates to determine whether nitrate has 



I been formed. Inoculate from a number of the smallest 

 colonies into nitrite solution, and after about three weeks 

 prepare new plates of nitrite-agar from the tubes which 

 contain no nitrite, but nitrate. The pure culture should 

 behave as follows : (1) A scarcely perceptible precipitate 

 should appear, which rises as a column on shaking ; (2) 



