144 PRODUCTS OF VITAL ACTIVITY. 



A peptonizing ferment for gelatin is produced by a considerable 

 number of bacteria, as stated under the heading " Liquefaction of 

 Gelatin." The jellified albumin in cultures in blood serum is also 

 liquefied by a peptonizing ferment produced by certain species of bac- 

 teria. 



Some authors also speak of a soluble ferment capable of inverting 

 cane sugar or milk sugar. According to Hueppe, such a ferment 

 is produced by the Bacillus acidi lactici. A soluble ferment for cel- 

 lulose is supposed by Fliigge to be produced by several species 

 among others by Bacillus butyricus and by Vibrio rugula. 



Several bacilli produce a soluble ferment capable of coagulating 

 the casein of milk. 



Reduction of Nitrates, and Nitrification. The researches of 

 Gayon, Dupettit, and others show that certain bacteria are able to 

 reduce nitrates with liberation of ammonia and free nitrogen. This 

 is effected in the absence of oxygen by anaerobic bacteria, and, 

 among others, by Bacillus butyricus. Certain aerobic bacteria also 

 accomplish the same result. Thus Heraaus 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 Herseus, 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 riot 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 



