236 THE PHENOMENA OF PUTREFACTION 



Although these discoveries may justify the conclusion that no free nitrogen 

 is disengaged during the putrefaction of albuminoids, it must not, however, be 

 assumed that the same also applies to the decomposition of manures in general 

 under natural conditions ; since, under these circumstances, very considerable 

 quantities of this element can be liberated and become lost to the soil. This 

 result is, however, due to the reduction of nitric salts, and not to the putrefaction 

 of albuminoids. 



This de-nitrification in arable soil was first noticed by GOPPELSRODER (I.) in 

 1862, and was long regarded as a purely chemical process. The first reference 

 to the agency of bacteria in this decomposition was made by E. MEUSEL (I.) in 

 1875, and the earliest pure cultures of such organisms were obtained by 

 U. GAYON and G. DUPETIT (II.) in 1882. In succeeding years a large number 

 of species, all capable of reducing nitrates, was made known ; e.g. by W. 

 HERAEUS (I.) in 1886. Two years later P. FRANKLAND (II.) was able to 

 associate with the group in question 17 out of 32 species, and R. WAKINGTON (I.) 

 1 6 out of 25 species examined, among them being Bacillus ramosus, the so-called 

 " Wurzel-bacillus." All these reduce nitrates into nitrites, but these two 

 chemists do not say whether the latter substances in turn may be still further 

 reduced by the bacteria. For this reason we must revert to the labours of 

 GAYON and DUPETIT (III.), who made pure cultures of two bacterial species, 

 named Bacillus denitrificans a and /3, which exhibit a noteworthy difference in 

 their behaviour towards nitrates. Species a is the more energetic, decomposing 

 as much nitrate as is presented to its action, and reducing the same to nitric 

 oxide and free nitrogen. The /3 species, on the other hand, forms nitrites, and 

 ceases to act before the whole of the nitrate is destroyed, free nitrogen being the 

 only gaseous fermentation product. Quite distinct from these two species is the 

 Bacillus denitrificans, isolated from arable soil by E. GILTAY and J. H. ABERSON 

 (I.), which reduces the nitrates to free nitrogen in an almost quantitative degree. 

 When grown on nutrient gelatin the rods measure 0.5 p in breadth and 1.5-3 /* 

 in length, but in liquids they assume a somewhat more elongated form. Closely 

 allied to these three species is the Bacillus denitrificans II., discovered by R. 

 BURRI and A. STUTZER (II.) on old straw, but differing from them in that it 

 liberates as gas only some 80 per cent, of the nitrogen in the decomposed 

 nitrates, the remainder being elaborated into an organic compound (still 

 uninvestigated), which is precipitated in large flakes. The same observation 

 was made (though not with pure cultures) by E. BREAL (I.) in 1892. Like the 

 aforesaid three Schizomycetes, Bacillus denitrificans II. is anaerobic, and decom- 

 poses nitrates only when oxygen is excluded. Another (sporogenic) de-nitrifying 

 bacillus, isolated by J. SCHIROKIKH (I.) from horse-dung, may also be 

 mentioned. 



The facultatively anaerobic Bacterium coli commune exhibits a peculiarity 

 worthy of special consideration. When kept in a nutrient solution by itself and 

 with exclusion of air, it reduces nitrates to the condition of nitrites ; but the 

 decomposition proceeds in quite a different manner when the organism is grown 

 in symbiosis with a second species of bacterium, invariably found in horse-dung 

 by both the above-named workers, and named Bacillus denilrificans I. In such 

 case, even when air is admitted, the nitrogen of the nitrate is set at liberty, 

 though neither species is able to produce the same effect by itself. Bacterium 

 coli commune can, however, be replaced by Bacillus typhi abdominalis. The 

 potassium or sodium present in the nitrates or nitrites is converted into a 

 hydroxide, which accumulates in the medium, and eventually arrests the vital 

 activity of the bacteria in question. For this reason not more than 5 or 6 grams 

 of saltpetre (potassium nitrate) can be fermented per litre. The fact that Bac- 

 terium coli commune in the absence of air (e.g. in the intestines) converts nitrates 



