24 SULPHUR BACTERIA 



a definite principle, a ferment, or something of a similar nature, 

 is secreted by certain microorganisms, and that this principle 

 effects the union of these elements. Miquel named it a 

 ferment sulf-hydrique. The use of the word ' ferment,' to denote 

 the agent of an endothermic reaction of this nature, is contrary 

 to the usually accepted meaning of that term. Duclaux 

 considered that hydrogen was liberated by the organism, and 

 that the union with sulphur took place outside the cells in 

 the surrounding medium, not inside them, as claimed by 

 Miquel. Beijerinck has confirmed this statement, and has 

 cited the following experiment in justification of his view. 

 Two flasks are filled, one with fresh water, ferrolactate, flowers 

 of sulphur, and ditch water, and the other with the first, second, 

 and fourth only, of these ingredients. Both are allowed to 

 decompose by the activity of the microorganisms contained 

 in the ditch water. It is found that ferrous sulphide is formed 

 in both flasks. As the sulphide is formed in the second flask 

 which contained no added sulphur, he concludes that in all 

 probability the sulphide in the first flask was also formed 

 independently of the sulphur added to it ; and hence that the 

 union of hydrogen and sulphur is in both cases a secondary 

 reaction which takes place outside the cell. 



It has been claimed by Rey-Pailhade that the synthesis 

 of hydrogen and sulphur is effected by certain yeasts, and 

 that a specific substance which he named Philothion is secreted 

 by the plant to effect the union. No experimental evidence 

 for the existence of this ferment has been supplied. 



The Production of Hydrogen Sulphide under Marine 



Conditions. 



The deeper layers of marine waters containing hydrogen 

 sulphide are completely devoid of the fauna and flora which 

 occupy the upper layers. The Black Sea, which was investi- 

 gated by the Russian Deep Sea Expedition of 1891, is a case 

 in point. The water was found to contain the sulphide at all 

 depths, and below 200 — 400 metres macroscopic organisms were 

 completely absent. The following table gives the amount of 

 hydrogen sulphide at the various depths : — 



