48 SULPHUR BACTERIA 



sulphuretted hydrogen appear in certain cases to 

 be able to supply both food and energy. 



(3) Growth and multiplication may take place under the 



same conditions as the preceding, but without the 

 presence of sulphuretted hydrogen. 



(4) Under special cases both food and energy may be 



obtained without either organic matter or sulphur- 

 etted hydrogen. 



In all these modes, except the fourth, the presence of 

 organic remains is necessary, and they may be directly utilized, 

 or they may be used after the saprophytic bacteria have 

 effected the first stage in their decomposition, with the pro- 

 duction of peptones, ammonium compounds, etc. In the fourth 

 mode, the conditions are probably unnatural, and the organism 

 does not produce normal structures. In nature the sulphur 

 bacteria are always associated with organic matter, and whilst 

 normally the energy of the organism is never derived directly 

 from the organic remains before these have suffered decompo- 

 sition, they probably draw their nitrogen from the decomposing 

 remains at several stages in their decomposition of such 

 remains (peptones, ammonium compounds, nitrates, etc.). 

 It is also not improbable that in nature the assimilation of 

 several kinds of nitrogenous food takes place simultaneously. 

 There is no reason to suppose that the sulphur bacteria are 

 wanting in adaptability, and certainly the facts do not warrant 

 this supposition. In this respect the sulphur bacteria are 

 not different from the majority of other bacteria. Monocnergic 

 bacteria are probably not common, and the sulphur bacteria 

 behave as do the majority. 



The Denitrifying Sulphur Bacteria. — A study of the small 

 organism* isolated by Lieske is instructive because the sulphur 

 metabolism is combined with a process of denitrification. This 

 organism derives its carbon from CO2 in the form of either 

 carbonates or bicarbonates. According to Lieske it assimi- 



* This organism is not, strictly speaking, one of the sulphur bacteria 

 because it does not store sulphur in its cells, but the general course of the 

 metabolism is similar to that of these organisms and may appropriately 

 be considered in this work. 



