THE PRODUCTION OF SULPHURETTED HYDROGEN 23 



Hence the sulphur atom in black mud runs the gamut of 

 changes from complete oxidation to the form of sulphate to 

 complete reduction to the form of the sulphide. His conclu- 

 sions are generally accepted although Baas-Becking points 

 out that in the case of one of the reactions, namely, No. (4), 

 the change is carried out in alkaline water with a considerable 

 buffer value, for the amount of COg must be considerable, which 

 first lowers the alkalinity and then effects the change indicated 

 in the reaction. He argues that to effect this reaction in the 

 mud the concentration of CO2 in the bottom of the sea over- 

 lying the black mud of the Black Sea must be at least sixty 

 times greater than the concentration known to exist at the 

 surface, and concludes that in such places this particular 

 change is not possible unless there is present another source 

 of acidity in addition to the carbon dioxide. It is highly 

 probable that the supply of carbon dioxide is supplemented 

 under these conditions, for such black sand contains not only 

 acid-producing organisms but also the organic material which 

 makes possible their multiplication. 



[h) Reduction of Thio sulphates. — Holschewnikoff found 

 that the two organisms Vibrio hydrosulfureiis and Bacterium 

 hydrosulfuricum ponticum, which he had isolated from mud 

 at Wiesbaden, effected the change of sodium thiosulphate 

 (NagSaOg) to hydrogen sulphide when cultivated in appropriate 

 media. 



(c) Reduction of Sulphites. — Beijerinck showed that the 

 yeast plant under appropriate conditions reduces oxy-sulphur 

 compounds to hydrogen sulphide. 



Hydrogen sulphide is thus a direct or an indirect deriva- 

 tive of the decomposition of organic matter under the agency 

 of various saprophytic microorganisms. Under aerobic con- 

 ditions it is broken off directly from a constituent of the protein 

 molecule. Under anaerobic or micro-aerobic conditions its 

 formation is more indirect and is bound up with a reduction 

 process. 



3. By Direct Union of Hydrogen and Sulphur. — The direct 

 union of hydrogen and sulphur may be effected by the vital 

 activity of microorganisms. Some writers have claimed that 



