BACTERIA IN THE SOIL Itf 



Upon this medium it is possible to sub-culture a pure 

 growth from the film at the bottom of the flasks in which 

 the nitrous organism is first isolated. 



The Nitric Organism. It was soon learned that the 

 nitrous organism, even when obtainable in large quantities 

 and in pure culture, was not able entirely to complete the 

 nitrifying process. As early as 1881 Professor Warington 

 had observed that some of his cultures, though capable of 

 changing nitrites into nitrates, had no power of oxidising 

 ammonia. These he had obtained from advanced sub- 

 cultures of the nitrous organism, and somewhat later Wino- 

 gradsky isolated and described this companion of the nitrous 

 organism. It develops freely in solutions to which no 

 organic matter has been added ; indeed, much organic mat- 

 ter will prevent its growing. He isolated it from soils from 

 various parts of the world on the following media : 



Water 1000.0 



Potassium phosphate i.o 



Magnesium sulphate 0.5 



Calcium chloride A trace 



Sodium chloride 2.0 



About 20 cc. of this solution is placed in a flat-bottom 

 flask, and a little freshly washed magnesium carbonate is 

 added. The flask is closed with cotton wool, and the whole 

 is sterilised. To each flask 2 cc. of a 2 per cent, solution 

 of ammonium sulphate is subsequently added. The tem- 

 perature for incubation is 30 C. Winogradsky concluded 

 that the oxidation of nitrites to nitrates was brought about 

 by a specific organism independently of the nitrous organ- 

 ism. He successfully isolated it in silica jelly. He believes 

 the organism, like its companion, derives its nutriment 

 solely from inorganic matter, but this is not finally estab- 

 lished. 



The form of the nitric organism (or nitromonas, as it 



