34 A MANUAL OF BACTERIOLOGY 



(1) free nitrogen ; (2) small quantities of nitrates in rain 

 water ; (3) ammonium salts, applied intentionally or 

 carried to the soil by rain or derived from the decay of 

 organic matter ; (4) various nitrogenous organic sub- 

 stances arising from the decay of animal and vegetable 

 matters. 



In 1877 Schloesing and Miintz showed that the pro-, 

 duction of nitrates in the soil is inhibited by antiseptics, 

 such as chloroform vapour, or by sterilising the soil by 

 heat. Such " inactive " soil may be rendered nitrifying 

 again by seeding with untreated soil. Both nitrates and 

 nitrites may be formed in nitrifying solutions, and in 

 1884 Warington concluded that the factor determining 

 the formation sometimes of nitric acid and sometimes 

 of nitrous acid was a difference in the character of the 

 organisms ; for it is possible to have two similar solu- 

 tions under identical conditions, and for nitrites to be 

 produced in- the one, and nitrates in the other. 



In 1886 Munro showed that the process of nitrification 

 could take place in solutions practically destitute of 

 organic matter. 



Nitrification in the soil takes place in three stages : 



I. Ammonisation. When complex organic compounds 

 such as albuminoids are applied to the land they are 

 broken up ; first they become liquefied, peptone-like 

 bodies being produced ; these are then further acted 

 upon and we get alkaloidal substances in small quantity, 

 indole, skatole, leucin, and tyrosin and amino-acids, 

 valerianic acid, volatile fatty acids, lactic acid, etc. 



These changes are brought about by numbers of 

 organisms, among which the varieties of Proteus (formerly 

 known as Bacterium termo), B. mesentericus, B. mycoides, 

 B. fluorescens liquefaciens, and B. putrificus are the more 

 important. 



The nitrogenous compounds are then further acted 



