IOWA ACADEMY OF SCIENCES. 85 



chemists, Schloesinp: and Muentz"'*, who announced, in 1877, that they had estab- 

 lished, by a series of experiments, that nitrates in the soil were formed by a 

 micro-organism. They showed that 212 degrees Fahr. for one hour was sufficient 

 to destroy the agent that caused nitrification. Further experiments made by these 

 investigators show the importance of taking into consideration the temperature of 

 the soil. In summer the temperature is more favorable for nitrification. The 

 absence of strong light is a necessary condition for this same process. An alkaline 

 condition of the medium is essential, but the amount, as Warrington says, is 

 injurious if anything beyond a small proportion, and a large amount will prevent 

 the action altogether. 



The present theory of nitrification is that there are two stages, and each process 

 is brought about by a distinct organism. At least this is true in the nitrification 

 of ammonia, and the nitrification of nitrogenous matter falls under the same head. 

 Warrington, •'^° in an admirable paper, says: "By one organism the ammonia is 

 converted into nitrites; by the other the nitrite is converted into nitrate. The 

 existence of these two distinct agents, each of which has special conditions favora- 

 ble or unfavorable to its development, explains at once the particular formation of 

 nitrous or nitric acid, so frequently observed in laboratory experiments on nitrifi- 

 cation." In the soil these two different organisms are abundant; the conditions 

 for their growth being similar, they work together. The most interesting point in 

 connection with these organisms is their growth in nutrient media. Isolation has 

 been attended with much difficultv. The first attempt to grow them was made by 

 Schloesing and Muentz; although they may have had the nitrifying agent, they 

 worked with material that contained other germs. Koch's methods of growing 

 bacteria in solid media, like agar and gelatin, wholly failed to accomplish the 

 desired result. The first success in cultivating the nitrifying organism was made 

 by D. P. F.Frankland^"^ His cultures were started in an ammonical solution, and 

 by the dilution method he finally succeeded in obtaining a single species. 



Warrington'"' by the same method succeeded in isolating the organism in the 

 same way. Winogradsky'"- also succeeded in isolating and growing the germ. So 

 much for the isolation of the nitrous organism. The separation of the nitric 

 organism has been attended with equal difficulty, but Winogradsky'"' by an ingen- 

 ious method has succeeded in growing the nitric organism on gelatinous silica. A 

 most interesting feature of these organisms, the nitrous and nitric, is that they 

 grow in inorganic fluids. Warrington"'^ says: "That an organism unprovided 

 with chlorophyll and growing in darkness, should be able to construct organic 

 matter out of ammoniacal carbonate is certainly of the highest interest." Con- 

 nected with the subject of nitrification is that of denitrification. Numerous 

 investigators have called attention to the breaking up of nitrates in sewage. In 

 some cases as in Bacterium (hnitrijicnns^^^ the nitrate is changed into nitrogen gas. 

 But these nitrogen gas species are evidently not common. The species which 

 reduces the nitrates are numerous as shown by various recent investigations. 



iwCompt. Rend. Vol. LXXXIV, p. 301. 



105 1. c.p. 63. 



106 Phil. Trans. Roy. See, 1890. B.,p. 107. 

 lO'Transactlons Chem. See. 1891, p. 502. 

 lOSAnn. d 1" Instltut Pasteur, 1890, p. 213. 

 iwCompt. Rend., Vol. CXIII, 1891. p. 89. 



iioj. M. N. Munro, Trans. Chem. Soc, 1886, p. 651. 



Warrington 1. c. p. 49. 



Wlnogradsky, Ann. d 1' Instltut Pasteur, 1890, p. 268. 



iiiGayon and Dupetlt, Ann. de la Science Agronomlque I (1885), p. 226. 



