PRODUCTS OF VITAL ACTIVITY. 141 



among others, lay Bacillus butyricus. Certain aerobic bacteria also 

 accomplish the same result. Thus Herseus obtained two species 

 from water which reduced nitrates in a very decided manner. On 

 the other hand, a number of species are known to oxidize ammonia, 

 producing nitric acid. Schlosing and Miinz, as a result of numerous 

 experiments, arrived at the conclusion that in the soil nitrification is 

 effected by a single species. But it is doubtful whether they worked 

 with pure cultures, and more recent researches show that several, 

 and probably many, different bacteria possess this power. Accord- 

 ing to Heraaus, the following species, tested by him, oxidize am- 

 monia : Bacillus prodigiosus, the cheese spirillum of Deneke, the 

 Finkler-Prior spirillum, the typhoid bacillus, the anthrax bacillus, 

 the staphylococci of pus. The oxidation does not always go to the 

 point of forming nitrates, but nitrites may be formed in the soil 

 (Duclaux). Warrington states that certain bacteria which formed 

 nitrates in a suitable culture medium produced only nitrites when, 

 after an interval of four or five months, some of the culture was 

 transferred to a solution containing muriate of ammonia. The same 

 author states that the process of nitrification occurs only in the 

 dark. 



The researches of Winogradsky, of the Franklands, and of Jor- 

 dan show that the failure of earlier investigators to obtain the nitri- 

 fying bacteria from the soil in pure cultures was due to the fact that 

 these bacteria do not grow in the usual culture media. By the use 

 of certain saline solutions the authors named have succeeded in iso- 

 lating nitrifying bacteria in pure cultures, or nearly so. It is still 

 uncertain whether these investigators have obtained the same bac- 

 teria, but the microorganisms described by them, and obtained from 

 widely distant sources, are similar in their morphological and bio- 

 logical characters, and at least belong to the same group. In a com- 

 munication made in 1891 Winogradsky arrives at the conclusion 

 that the ferments which cause the oxidation of ammonia and pro- 

 duction of nitrites are not capable of producing nitrates, but that 

 other microorganisms are concerned in the oxidation of nitrites. 

 In sterilized soil to which a pure culture of his nitromonas was 

 added nitrites only were produced, and the presence of various 

 microorganisms common in the soil did not result in the forma- 

 tion of nitrates so long as the specific ferment was absent to which 

 this second oxidation is ascribed (nitrifying bacillus of Winograd- 

 sky). 



Phosphorescence. Several different bacteria have been studied 

 which, in pure cultures, give rise to phosphorescence in the medi- 

 um in which they are cultivated. In gelatin cultures the light 

 is sufficient in some instances to enable one to tell the time by a 



