AUTOTROPHIC BACTERIA 73 



flagellum; the latter can be stained by the Loeffler method, by adding 

 10 to 15 drops of 1 per cent sodium carbonate solution to the ferro- 

 tannate, or by the method of Zettnow. 



In some cases the motile stage may be predominant over the zooglea 

 formation or vice versa. It is important to note that the predominance 

 of the particular stage is characteristic of the strain, so that one might 

 suspect that we are dealing here with two distinct races. The two 

 stages are also distinguished by their rapidity of oxidation of ammonia, 

 the motile stage being the stronger. Winogradsky suggested that the 

 cause for this lies in the fact that the active stage (monas) consumes 

 more energy and comes more readily in contact with the ammonia and 

 oxygen than the non-motile zooglea. The zooglea are probably resting 

 stages, being also more resistant to drying. Gibbs isolated the Nitro- 

 somonas from soils of North America and found it to be 1.2 to 1.5 by 

 0.9 to l.Ofj. in size, rounded or oval, which stained uniformly. The 

 organism was found chiefly in the free cell stage. Thermal death point 

 of the organism was between 53° and 55°C. (10 minutes). 



Other organisms also capable of oxidizing ammonia to nitrite, but 

 having different morphological characters, were isolated by Winogradsky 

 from soils in Europe. So, for example, the form isolated from soil of 

 St. Petersburg was a true coccus, about 1/jl in diameter, sometimes form- 

 ing zooglea and sometimes growing free, but never in the swarm stage. 

 A constant property of its morphology is a central nucleus-like body, 

 made visible by various stains, particularly by methylene blue. 



The Nitr. javanesis is a still smaller coccus (0.5 to 0.6/x) and has been 

 isolated by Winogradsky from the soil of Buitenzorg, Java. This form 

 grows both in the monas and zooglea stages, the first having very long 

 (up to 30m) flagella. Free cells are present only in the swarm stage, 

 mostly in pairs. Winogradsky also isolated from the soil of Quito, 

 South America, a non-motile coccus (Nitrosococcus) termed by Migula 

 Micr. nitrosus. This organism consists of large cocci 1.4 to 1.7/x in 

 diameter, always growing as free cells and never forming zooglea, 

 while the motile stage could never be demonstrated. It is obli- 

 gate aerobic, gram-positive. It forms rather large, opaque yellowish 

 colonies on the silica gel but the colonies are made up of free cells. 

 The cells appear larger in the living state than in the stained prepara- 

 tion, probably due to a thick gelatinous membrane which does not 

 stain or becomes invisible on desiccation. Bonazzi 31 isolated the 



"Bonazzi, 1919 (p. 71). 



