128 SEWAGE AND ITS PURIFICATION 



Another form of denitrification is the reduction of nitrate to 

 nitrite, MeuseP first showed in 1875 that well-water con- 

 taining nitrates on standing soon developed a reaction for 

 nitrites — a change that was prevented by sterilization or by 

 certain antiseptics — and Wagner of Darmstadt first elucidated 

 the importance of the reaction. According to Abelous a 

 soluble ferment exists in both animal and vegetable organisms 

 which is able to convert nitrates into nitrites.^ 



Percy Frankland^ gives the following list of thirty-two 

 species that he examined : 



1. Reducing Nitrate to Nitrite. — B. ramosus, violaceus, vermi- 

 cularis, liquidus^ ceveus, pestifer, plicatus, prodigiosus, chlorinus, 

 cj^ra^s* (strongly). B.nubilus, aurescens, fluorescens, aureus, pro- 

 fusus (slightly). Micrococcus carnicolor, rosaceus (very slight). 



2. Not Reducing Nitrate to Nitrite. — B. viscosus, arborescens, 

 aurantiaciis, suhtilis,^ aquatilis, Icevis, polymorphus ; Sarcina auran- 

 tiaca, lutea, liquefaciens ; Streptococcus liquefaciens ; Micrococcus 

 gigaSy albus, candicans, chryseus. 



He concluded that the chemical behaviour of these organisms 

 was the same, whether air was present or excluded, and that 

 none of them could either produce ammonia from nitrate or 

 oxidize ammonia to nitric acid. 



R. Warington"^ states that his results in cultivation did not 

 bear out the general opinion that wheat straw promoted 

 denitrification. Probably this is explained by the observation 

 of Matz and Wagner/ connected with what we have said 

 about humus, that as ** humification " proceeds the power of 

 destroying nitrates diminishes. W. Kruger and Schneidewind 

 attribute the action of straw to the pentosans present, while 

 sugars, glycerol, citrates, malates, etc., also promote the 

 activity of denitrifying organisms, as well as excess of moisture 



1 Berichte, viii., 1215. 



2 Comptes rendus Soc. Biol., 1903, Iv., 1080. 



2 Loc. cit., 372. See also on the same subject : Hatton, Chemical Society's 

 Transactions, 1881, 266 et seq. Gayon and Dupetit, Berichte, 1882, xv. , 2736 ; 1883, 

 xvi., 221 (anaerobic organisms.) Deherain and Maquenne, Berichte, 1882, xv., 

 3081 {B. butyricus). R. Warington, and Munro, Chemical Society's Transactions, 

 1886, 632 (organisms generally). Heraeus, Zeits. f. Hyg., 1886, 193 (pure 

 cultivations). Also Clark and Gage, Eug. News, N.Y., 1905, p. 27; Techn. 

 Quarterly, xviii., 1905, p. 5 ; /. Amer. Chem. Soc, xvii., 327, 1905. 



•* To these must be added Proteus mirahilis and vulgaris, B. mycoides, megaterium, 

 and acidi lactici, which powerfully reduce nitrates to nitrites, and sometimes even 

 to ammonia, and are frequent in sewage. 



^ Houston states that several varieties of B. suhtilis occur in sewage (Second 

 Report of the London County Council, 1899). 



^ Journal of the Royal Agricultural Society, 1897, III., viii,, 577. 



7 Landw. Versuchs Stat., 1897, xlviii., 247. 



