DFAlTIJIl'iCA'noN L'l!^ 



state the ()r<j;anisiiis res{)eetively eanvinu mi tliese rcNictioio. I.iii 

 liis experiments proved tliat tlie onlinarv procivss of nitrilK aiiMn 

 in soil etc., nnist l)e dne to two disiinci (.i'<:;iiiisnis, the iiiirmis 

 and nitric, eacli incapal)l(> of doinu the wm-k (.t llir (.tli.r. 

 Soon afterwards Warington's conclusions wciv coiiliniircl l.y 

 Winogradskv, who succeeded l)y a new nicthcMl in |uvparing 

 pure cuhures of the two organisms. 



The position in which Warington's investigation.^ K'fi the 

 question of nitrification has not been materially advanced since ; 

 the process is carried out by two distinct organisms present iit 

 enormous numbers in all cultivated soils, l)eingonly absent from 

 soils possessing an acid reaction like peat. The action of these 

 organisms is dependent on certain conditions of temperature 

 and aeration, on a supply of inorganic food like phosphates, 

 on the presence of a l)ase and on the absence of any excess of 

 soluble organic matter. 



II. — Dkmtiuficatklx. 



During the progress of the investigations on nitrification 

 Warington found that under certain conditions soils possessed 

 the power of destroying any nitrates which had been formed 

 previously. This had been observed before, and shown to be 

 due to the action of sundry living organisms which arc univer- 

 sally distributed in natm-al waters, sew^age, and soil. The main 

 conditions necessary for the development of this reducing action 

 are the ab.sence of oxygen and the presence of a suflicicncy of 

 readily oxidisable organic matter; it will then depend on the 

 conditions to which the soil is subjected whether the nitrate- 

 making or the nitrate-destroying organisms l)ecomc active. 

 AVarington, for example, showed that if an ordinary soil wci-c 

 deprived of air by keeping it in a waterdogged condiiii.n. 

 any nitrates added to it would be rapidly desti-oycd with the 

 evolution of nitrogen gas. 



The action of a number of organisms was sludir.l l.y intro- 

 ducing them into beef broth containing sonic nil rah- and 

 protected from the access of oxygen by a layer of pai-allin oil. 



