226 NITRIFICATION 



with a single short flagellum and in the early stages of the culture it 

 exhibits active powers of locomotion. It appears as short rods 

 SI. 2-1. 8 M long and 0.9-1.0 /* broad. The cells of Nitrosomonas 

 javanica obtained from the Botanical Garden at Buitenzorg, near 

 Batavia, are globular and only attain a diameter of 0.5-0.6 ju, but 

 they have a long flagellum, at times measuring as much as 30 //. 

 Those obtained from Tokio soil ( Nitrosomonas japonica) and from 

 Africa (Nitrosomonas africana), are very similar to the European 

 species, differing only in that they are somewhat smaller. 



Observations by Burri and Stutzer on impure cultures in mineral 

 media led them to believe that there was a difference in oxidizing 

 powers in organisms derived from different sources. By this means 

 they distinguished five classes from German and one from African 

 soil. 



Joshi has recently described a new species from the soils of 

 India which differ morphologically from others hitherto described. 



The different species show a variation in sensitiveness to heat. 

 Beddies found one species to live for one minute in steam at a 

 temperature of 100. The other two were more sensitive but 

 survived for several minutes in dry heat of 80 to 100 C. 



The genus, nitrococcus, found in the New World do not possess 

 cilia nor do they form zooglea. The one obtained from Quito 

 (Ecuador) is a coccus 1.5-1.7 ju in diameter. The species, Nitro- 

 sococcus braziliensis, obtained from Brazil soil is much larger, being 

 2 n in diameter. 



The nitromonas or nitrobacter differ from those already described 

 in physiological properties in that they oxidize nitrites into nitrates. 

 Morphologically, they differ in being smaller and more slender. 

 They are elongated, oval, mostly pear-shaped, 0.5 n in length and 

 0.15-0.25 ju in breadth. In liquid cultures they develop a thin 

 mucinous skin which adheres firmly to the walls of the vessel. 



From the variation in sensitiveness to heat, Beddies isolated 

 four forms of nitrobacter, one of which was capable of resisting 

 the action of steam at 100 C. for two minutes. But Burri and 

 Stutzer's comparative experiments with nitric organisms derived 

 from different localities showed no essential difference in physio- 

 logical action. 



Neither nitrosomonas nor nitromonas have been observed to 

 form spores, but their resistance to drying and to heat, as shown by 

 Beddies, makes it appear possible that some species may form spores. 



Influence of Moisture. Long before the process of nitrification 

 was known to be due to microorganisms, the underlying principles 

 governing the speed of the reaction had been investigated nation- 

 ally by France, Germany and Sweden. Among other things, they 

 had learned that there must be a certain proportion of water, and, 

 in order that the maximum vield of nitrates be obtained, that this 



