22 SULPHUR BACTERIA 



Selinsky and Brussilowsky succeeded in effecting the 

 decomposition of a substance in which the S was combined 

 with two carbon atoms, and such being the case, they con- 

 cluded that the formation of hydrogen sulphide could have 

 resulted only after an antecedent liberation of free sulphur ; 

 and that the hydrogen sulphide resulted from its subsequent 

 union with hydrogen. It must be noted that this implies the 

 union of hydrogen with sulphur at ordinary temperature. 

 As ferments, however, cause reactions within the living body 

 at ordinary temperatures, which, when carried out by acids, 

 demand heat, there should be no difficulty in accepting the 

 possibility of the union of hydrogen and sulphur at the ordinary 

 temperature when the reaction is controlled by vital forces. 



2. Reduction of Inorganic Compounds containing Sulphur. 



[a) Reduction of Sulphates. — Beijerinck (2) found that some 

 bacteria, cultivated under anaerobic conditions, effected the 

 reduction of sulphates to hydrogen sulphide. Again the pro- 

 duction of the sulphide is a common occurrence in muds 

 and other sediments in which the supply of oxygen is small 

 and the supply of organic matter large. One organism of 

 this kind which w^as isolated was named Bacterium hydro- 

 sulfureum. It is pointed out by Nadson that the ability to 

 reduce sulphate is characteristic of a large number of organisms, 

 given suitable conditions, and that many of such bacteria, 

 for example Proteus vulgaris and Bacillus vulgaris, are not 

 anaerobes, so that the reduction of sulphur may take place in 

 the presence of an abundant supply of oxygen. 



Beijerinck has studied the chemistry of this reduction and 

 states that in black mud the following changes take place: — 



(1) SO4-- > H,S. 



(2) H2S + Fe++ > FeS. 



(3) H2S + Fe+++ — > FeS + S. 



(4) FeS + H2CO3 — ^ FeCOg + H.S. 



(5) H^S — ^ S. 



(6) S > SO4- -. 



(7) S > Hp. 



(Quoted from Baas-Becking (i).) 



