THE METABOLISM OF THE SULPHUR BACTERIA 47 



indicated by Baas-Becking. This view implies that the hydro- 

 gen sulphide is a part of the machinery that transfers energy 

 from what is presumably the less available to the more avail- 

 able condition. The decomposition of the hydrosulphide 

 is to be regarded as a respiratory process comparable in its 

 effect to the changes that follow the absorption of oxygen 

 in aerobic plants. It is also consistent with the fact that the 

 absorption of hydrogen sulphide is not absolutely necessary, 

 since this substance is not the source of either the food or the 

 energy of the sulphur bacteria. In spite of the statements of 

 Winogradsky, Skene and Bavendamm, that the addition of 

 sulphuretted hydrogen is indispensable to the growth of the 

 sulphur bacteria examined by them, there are facts to show 

 that growth may take place in the absence of this gas. Thus 

 Molisch (3) has found that Chromatiwn Okenii may develop 

 in a raw medium completely devoid of sulphuretted hydrogen, 

 and Ellis (11) has shown that Chromatiimi Linsbaiieri multi- 

 plies in a culture containing no trace of this substance. The 

 sulphur bacteria are therefore able to take advantage of more 

 than one mode of metabolism. Not only do they change 

 their form (pleomorphism), they also change their function. 

 The word pleoenergism may be coined to express this capacity 

 for adaptation to more than one mode of life. 



Pleoenergism of the Sulphur Bacteria. 



There are in this group at least four different modes of 

 obtaining food and energy. 



(i) The most important is that which may be regarded as 

 the' normal mode of existence. The interaction of 

 sulphuretted hydrogen with the products from the 

 first stages in the decomposition of organic remains 

 (sulphur amino-acids) supplies the energy, whilst 

 the nitrogen and carbon are obtained from non- 

 organic sources (ammonium compounds and carbon 

 dioxide, respectively). 



(2) Organic remains, or the products of their initial 

 decomposition (peptones, etc.) in association with 



