REDUCTION PROCESSES. 77 



dnoed by the bacteria; that is, they look upon this produotion of HjS 

 as a demonstration of the formation of nascent hydrogen. 



3. From hyposulphites and sulphites. Especially studied in 

 yeasts, but also demonstrated in some bacteria by Petri and Maassen. 



4. From sulphates. Beijerinck (C. B. L., Bd. i, 1) has proved 

 this practically important function for his motile obligate anaerobic 

 Spirillum desulfnricans, which has only slight morphologic character- 

 istics. With other bacteria it is rarely found developed. 



Eubner has pointed out that with the Bact. vulgare the liberated 

 organic sulphur always suffices for the formation of H^S. 



The presence of sugar in nutrient media only rarely diminishes or 

 prevents the formation of HjS, even if the bacteria are able to actively 

 ferment sugar. The breaking up of the carbohydrates does not pro- 

 tect the albuminous bodies from decomposition. The presence of salt- 

 peter operates injuriously ; under these circumstances only a little 

 HaS is formed, but abundant nitrite (Petri and Maassen). Exclu- 

 sion of oxygen favors the formation of HjS. With the passage of air 

 through cultures of facultative anaerobes which produce HjS, the 

 amount of HjS formed is markedly reduced, and, instead, sulphates are 

 produced. 



Some (probably many) bacteria which form HjS also 

 produce foul-smelling mercaptan, CHg — SH, which is 

 demonstrable by the green color that it imparts to the yel- 

 lowish-red isatin-sulphuric acid. One places upon the cul- 

 ture-glass a tube, open at both ends, filled with glass 

 pearls, which are moistened with a 1.6^ solution of isatin 

 in concentrated sulphuric acid. The presence of sugar in 

 the nutrient medium lessens or prevents the production of 

 mercaptan (Rubner, A. H. xix, 136). 



6. Reduction Processes. 



(Eeductiou of pigments, nitrates, etc.) 



We have seen that generally the aerobic bacteria are 

 able to change powdered sulphur into HjS, for which nas- 

 cent hydrogen is necessary. 



The following processes are, indeed, similar to, and in 

 part probably dependent upon, nascent hydrogen: 



1. Reduction of the complex blue litmus=pigment of 

 methylene-blue and indigo to colorless leuko-products. 

 The part near the surface in contact with the air often 

 shows no reduction, but only the deeper layer. By shak- 

 ing with air the color may return, but where there has 

 been simultaneous production of acid, the returning color 



