234, SPECIAL BACTERIOLOGY 



NITRO-BACTERIA (WINOGRADSKY). 



This organism was isolated from Quito earth, and forms nitrates 

 out of nitrites. 



Microscopical Appearances. Very small rods, 0-2 to 0'25 by 0-5 /*. 

 Motility. Non-motile. 



Biological Characters. On Silicic Acid Plates they develop in 

 lenticular or club-shaped colonies. 



In Fluid Media it develops in the form of thin films, firmly adherent 

 to the walls and bottoms of the flasks there is no cloudiness. 

 Burri and Stutzer have with the assistance of silicic acid plates isolated 

 a nitrate builder in European earth, which is distinguished from the 

 above Winogradsky organism by being somewhat larger on solid media, 

 motile, and transferable to ordinary nutrient media (gelatine and 

 bouillon). When grown on the latter medium and again returned to a 

 nitrate solution, have mostly exhibited the remarkable faculty of pro- 

 ducing nitrification. 



Winogradsky ascertained by comparative investigations that the 

 nitroso-bacteria are the more active of the two. 



Both nitroso- and nitro-bacteria are always present in the soil, the 

 latter immediately oxidizing the nitrous acid generated (from the 

 ammonia salts) by the former. 



Whether nitrification commences in the dung-heap or in the field is 

 dependent on various circumstances. It takes place whenever a 

 sufficient amount of ammonia salts has been produced by the fermenta- 

 tion of urea, provided there is a free access of air. H. ImmendorfF 

 showed that in the outer layers of manure heaps (especially horse dung) 

 nitrous acid is produced briskly in a few days. On account of the 

 formation of easily lixiviable nitrates, which may moreover expose the 

 material to wasteful reduction processes, endeavours should be made 

 to minimise the aeration of the manure by battening the heaps well 

 down. 



It is well known that the soil has no power of fixing nitrates, as 

 according to P. Deherain and others a certain portion of the added 

 saltpetre invariably escapes in the drainage water, so that more has to 

 be added to the soil than is recovered in the crop. 



In manuring with salts of ammonia no such waste occurs, as they are 

 fixed by the soil and protected from wasteful lixiviation, the nitrifying 

 bacteria then oxidizing the ammonia and supplying the plant with 

 nitrites according to its requirements (Lafar's Tech. Mycology, 206, 

 208). 



