38 SULPHUR BACTERIA 



and for the execution of which sulphuretted hydrogen is neces- 

 sary. The sahent facts may now be considered. 



1. Sulphuretted Hydrogen. — The proof of the absorption 

 of this substance is well established. Provided that it is not 

 presented in too concentrated a form, large quantities are 

 absorbed, and the optimum estimated by Bavendamm for 

 Lamprocystis, namely, a 'concentration equal to 25 mm. 

 pressure of Hg is probably the optimum also for the majority 

 of the sulphur bacteria, if not for all of them. It is also 

 established that these organisms effect within their cells the 

 transformation of the sulphide into elementary sulphur, for 

 the latter is found in quantity inside the cells. The agency of 

 the bacteria in effecting the oxidation of the element to the 

 sulphate is more open to question. It is true that sulphate 

 accumulates in the neighbourhood of the cells, but more 

 definite proof is required of bacterial agency since the oxida- 

 tion of the sulphur to sulphate in an aqueous medium also 

 takes place in the complete absence of organisms. As the 

 sulphate in cultures of the sulphur bacteria is not found within 

 the cells, its formation may well be due to non-vital agencies. 



2. Organic Matter. — Winogradsky (i) and (2) came to the 

 conclusion that the sulphur bacteria do not assimilate organic 

 matter, and, further, that their development was hindered, 

 if not stopped, by the presence of organic matter in more 

 than the very smallest quantities. The second observation is 

 obviously incorrect, since under natural conditions these forms 

 flourish in waters which often contain very large quantities of 

 organic matter. It is a matter of common observation that 

 Beggiatoa alba, to take a prominent example, flourishes most 

 abundantly in water contaminated with sewage matter. 

 The present writer has found this organism in waters con- 

 taining sufficient organic matter for the support of hundreds 

 of thousands of bacteria per cubic centimetre. Again, Thio- 

 porphyra voliitans flourishes in pools that contain in many 

 cases saprophytic bacteria to the order of millions per cubic 

 centimentre. It is very seldom indeed that the sulphur 

 bacteria, under natural conditions, are found except in the 

 presence of organic matter in quantity. 



