52 SULPHUR BACTERIA 



waters, the reader is referred to page 64, in which the numbers 

 found in waters containing growths of Thioporphyra vohitans 

 are given. Some sulphur waters contain saprophytic bacteria 

 to the order of milhons per cubic centimetre, whilst the majority 

 of such waters contain either tens or hundreds of tliousands 

 per cubic centimetre. It is exceptional to find that the num- 

 bers are only in the order of hundreds per cubic centimetre. 

 Even if it is held that the sulphur bacteria do not directly 

 assimilate organic matter, it is the case nevertheless, that 

 they must of necessity find nourishment in the products of 

 the decomposition of organic matter, and these will be found, 

 under natural conditions, only in waters containing organic 

 matter. It is also remarkable that in Baas-Becking's explana- 

 tion of the metabolism of the sulphur bacteria, an important 

 role is ascribed to the sulphur amino-acids, and yet it is claimed 

 that organic matter plays no part in the metabolism of the 

 sulphur bacteria. ' 



