AUTOTROPHIC BACTERIA 63 



organic compounds thoroughly mixed with the soil, (2) a thorough aera- 

 tion of all the layers of the heap, (3) a proper moisture content kept up 

 by moistening the heap at regular intervals, (4) the presence of bases, 

 like calcium carbonate (or soap water). The activities were found to be 

 noticeable at 5°C, became prominent at 12° and reached a maximum 

 at 37°. Higher temperatures (45°) exerted an injurious effect and at 

 55°C the process came to a standstill. 



Warington 6 confirmed the biological nature of nitrification not only 

 in soil, but also in ammoniacal solutions inoculated with soil. He 

 studied (1) the influence of organic substances upon nitrification, (2) 

 the abundant production of nitrites in the process of nitrification and (3) 

 the nitrification of organic nitrogen. Warington observed that in a 

 liquid medium containing ammonium chloride, chalk, and sodium- 

 potassium tartrate, the ammonia could be acted upon only to a very 

 limited extent; when sugar replaced the tartrate, there was a decided 

 injurious effect upon the process of nitrification, which could not be 

 explained, since the nature of the organism was unknown. The relative 

 amounts of nitrite and nitrate formed in the process of nitrification 

 presented another unexplainable difficulty. As to the nitrification of 

 organic nitrogenous substances (urine, milk, asparagine.) , Warington 

 demonstrated that this has to be preceded first by their transformation 

 into ammonia; in other words, only those substances can be nitrified 

 which can first be converted into ammonia. It was soon found that 

 nitrites arose from the oxidation of ammonia and not from the reduction 

 of nitrates; Munro 7 distinguished ammonia formation from ammonia 

 oxidation (nitrification) and, without suspecting the existence of the 

 different organisms, he had a rather clear idea of the two processes. 



All attempts to isolate the specific organisms concerned in the process 

 of nitrification failed, in spite of the fact that nitrification is an important 

 biological process not only in the soil but also in sewage purification. 

 This was chiefly due to the fact that the proper methods were lacking. 

 Although claims have been put forth by various investigators 8 that a 



6 Warington, R. On nitrification. Jour. Chem. Soc. (London), 33: 44-51. 

 1878;35:429-456. 1879;45:637-672. 1884; Chem. News. 61: 135. 1890; Trans. 

 Chem. Soc. London, 59: 484-529. 1891. 



7 Munro, J. H. M. The formation and destruction of nitrates and nitrites in 

 artificial solutions and in river and well water. Jour. Chem. Soc. 49: 632-681. 

 1886. 



8 Heraeus, W. Uber das Verhalten der Bakterien im Brunnenwasser, sowie 

 uber reducierende und oxydierende Eigenschaften der Bakterien. Ztschr. Hyg. 

 1: 193-235. 1886. 



