VITAL PHENOMENA OF BACTERIA. 



Sulphuretted hydrogen may be formed: 



1. From albuminous substances. This power, ac- 

 cording to Petri and Maassen, of forming sulphuretted 

 hydrogen, particularly in liquid culture media contain- 

 ing much peptone (5 to 10 per cent.) and no sugar, is 

 possessed, though in different degree, by all bacteria 

 examined by them; only a few bacteria form H 2 S in 

 bouillon in the absence of peptone, while about 50 per 

 cent, in media containing 1 per cent, peptone. 



2. From powdered sulphur. All bacteria produce in 

 culture media to which pure powdered sulphur is added 

 considerably more H 2 S than without this addition. 

 Petri and Maassen suggest that this is due to the 

 nascent hydrogen produced by the bacteria. 



3. From thiosulphates and sulphites. Studied par- 

 ticularly in yeast, but demonstrated also by Petri and 

 Maassen in several bacteria. 



The presence of sugar in the culture does not affect 

 the production of H 2 S by bacteria, but saltpetre reduces 

 it, nitrites being formed. The absence of oxygen favors 

 the production of H 2 S. Light diminishes the develop- 

 ment of H 2 S by facultative anaerobes, sulphates being . 

 formed instead. 



Reduction Processes. All bacteria, as we have seen, 

 possess the property of converting sulphur into sul- 

 phuretted hydrogen, for which purpose is required the 

 presence of nascent hydrogen. The following pro- 

 cesses depend also in part upon the action of nascent 

 hydrogen : 



1. The reduction of blue litmus pigments, methylene- 

 blue, and indigo to colorless substances. The superficial 

 layer of cultures in contact with the air shows often no 

 reduction, only the deeper layers being affected. By 



