308 PHENOMENA OF PUTREFACTION. 



liquids they assume a somewhat more elongated form. Closely- 

 allied to these three species is the Bacillus denitrijicans II., dis- 

 covered by R. BURRI and A. STUTZER (IT.) 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 denitrijicans II. is 

 anaerobic, and decomposes nitrates only when oxygen is ex- 

 cluded. 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 pro- 

 ceeds 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 

 denitrificans 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 eventu- 

 ally 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 Bacterium coli com- 

 mune in the absence of air (e.g. in the intestines) converts nitrates 

 into the exceedingly poisonous nitrites is also of interest to Patho- 

 logical Mycology, but we cannot further discuss the matter here. 

 The important point, so far as we are now concerned, is, that the 

 disengagement of free nitrogen from nitric salts can go on even 

 in the presence of air. The de-nitrification occurring in stored 

 manure and in arable soil appears to be a twofold process : the 

 anaerobic nitrate destroyers acting in the lower strata away from 

 the air, whilst the symbiotic activity of the Bacterium coli com- 

 mune (so plentiful in animal excreta) and the Bacillus denitrijicans 

 I. comes into play at the surface. From this it is evident that 

 the theory which assumes the possibility of preventing the de- 

 struction of nitrates by thoroughly loosening, and consequently 

 aerating the soil, is of little value. The bacteria in question are 

 (for some unexplained reason) present in enormous numbers in the 

 excrement of various animals. First in this respect is horse-dung, 

 which has always been regarded by practical men as a hot manure, 

 a property which is explained by the foregoing observations. 

 Consequently such manure should not be applied, especially 

 when fresh, to soil that has recently received a dressing of nitrate 



