REDUCTION PROCESSES. 77 



duced by the bacteria; that is, they look upon this production of H 2 S 

 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 desulfuricans, which has only slight morphologic character- 

 istics. With other bacteria it is rarely found developed. 



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

 organic sulphur always suffices for the formation of H 2 S. 



The presence of sugar in nutrient media only rarely diminishes or 

 prevents the formation of H 2 S, 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 

 H 2 S is formed, but abundant nitrite (Petri and Maassen). Exclu- 

 sion of oxygen favors the formation of H 2 S. With the passage of air 

 through cultures of facultative anaerobes which produce H 2 S, the 

 amount of H 2 S formed is markedly reduced, and, instead, sulphates are 

 produced. 



Sonic (probably many) bacteria which form H 2 S also 

 produce foul- smell ing mercaptan, CH 3 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 1.5% 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. 



(Reduction of pigments, nitrates, etc.) 



We have seen that generally the aerobic bacteria are 

 able to change powdered sulphur into H 2 S, 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 litrnus=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 



