898 



(see Ann. de VInst. Pasteur, 4 (180«)), pp. 213, 257, 760; and 5 (1891), 

 J). 92; and also Exi)eriineut Station Record, vol. ii, p. 751). 



That Jill orj^aiii.sm unprovided vrith chloropliyll and ^^rowin-j in darkness shonld 

 he ahle to construct organic matter out of ammonium carbonate, is certainly a fact 

 of the highest interest. The prf>cess wouhl seem to us an impossil>le one but for the 

 energetic oxidation of ammonia, which lorms part of it; by this oxidation so much 

 energy is developed that the nutrition of the nitrifying organism by ammonium car- 

 bonate becomes part of a strongly exothermic reaction. » * * 



As soon as the fact had been established that nitrification was the work of aliving 

 organism it became important that this organism should be isolated and its proper- 

 ties studied. * ■ * The first successful attempt at isolation was made by Dr. P. 

 F. Frankland {Phil. Trans. Boy. Soc. 1890, B. 107). "* * * Two months afterwards 

 Winogradsky pulilished an account of his isolation of the same organism (Jiiii. 

 de V fnxlitiit I'asteur, 1H9(),21'S}. * * » Later in the same year I al.so succeeded in 

 obtaining a similar result ( Trang. Chrm. Sof.. 1891. .lO^). 



This oi'^^misni, which is described and illustrated, i»roved to !>«' a 

 purely nitrous ferment. 



Liciiire lY. — Xitrificatioii nnd dcnUritirat'utn (pj). <)()-76). — As early as 

 1881 the author was in possession of cultures wliich possessed the power 

 of converting nitrites into nitrates, but only until recently was he success- 

 ful in separating; the nitric orjranisui in the ]Mire state ( Trnnn. Clum. Soc, 

 1491, 484). Still nuire recently Winugradsky has announced the i.sohi- 

 tion of a nitric orjjanism by culture on jjelatinous silica [Conijft. mid., 

 113 (1891), and Experiment Station Eecord, vol. ii. p. 751). This organ- 

 ism is described and its properties discussed. Like the nitrous fer- 

 ment, it grows freely in inorganic nutrient solutions, but api)ears to be 

 without action on annnonia, while it readily c(»n\ erts nitrites to nitrates. 

 "The facts as at present ascertained lead us to believe that tlie 

 nitrification of annnonia in soil, and probably also the nitrificatiiui of 

 other nitrogenous matters, takes idace in two stages, each stage being 

 performed by a distinct organism. \\y one organism the ammonia is 

 converted into nitrite, by the other tlu* nitrite is converted int(t nitrate.'' 



In soil containing a sullicient amount of oxidi/ableorganii- matter and 

 an insufficient supply of oxygen (as in the case <»f water logged soils) jiroc- 

 esses of denitrification take place. The most comnuui form of action 

 is a reduction of nitrates to nitrites, but iji sonu^ cases tlie reduction is 

 carried further, resulting in the ])rodu(tio!i of nitric oxide, nitrous oxide, 

 and free nitrogen. 



Denitrification is not a process of general occurrence in arable soil. The investi- 

 gations which have been made show that the air in soil, even at considerable depths, 

 is not very deficient iu oxygen. Moreover the subsoils of our fields contain (save in 

 the case of ]>eaty and some alluvial soils) only a very small auKuint of organic mat- 

 ter, and the presence of this, we have seen, is indispensable for the reduction of 

 nitrates. The reduction of nitrates is to be feared only when the soil has been for 

 some time satnr.ited with water. 



K\i»eriui('n(s made at Kotlianistcd in iss.{. 1884, 18S.""), and 1886 

 (Trans. Chrm. Soc, 1884,645; I8S7. IIS) i»',spe<iing the depths to wliich 

 the nitrilying (»rganism can be found in tbf soil, sh«)wed "fhut the 

 uitrous organism was present in almost every tri;il down to 3 feet below 



