126 SULPHUR BACTERIA 



Note oil Thiovuhmi.— -The discussion of this organism should 

 more appropriately appear in a work on the Flagellates, but 

 place is given to it in this work because the limits of the 

 group are defined by a physiological trait, namely the sulphur 

 metabolism. It is obvious, however, that the sulphur-organ- 

 isms are polyphyletic and that whilst the majority belong to 

 the Schizophytes, some, like Thiovulum, cannot be classed as 

 Bacteria. 



Family 3. — Thiospirilla cem. 



Free motile, colourless cells, containing sulphur. Division 

 by transverse fission. 



As the spiral sulphur bacteria differ from the Spirillacece 

 of the Eiibacteria only in the inclusion of sulphur granules, 

 the term Thiospirillum used by Omelianski is preferable to 

 the term Thiospira used by Wislouch. The former has also a 

 claim on the ground of priority. Following the nomenclature 

 adopted in this book the following generic terms may be 

 distinguished : — 



Spirillum. — Colourless spiral bacteria : sulphur absent. 



Thiospirillum. — Colourless spiral bacteria, containing 

 sulphur. 



Rhodothiospirillum. — Coloured spiral bacteria, containing 

 sulphur. 



Rhode spirillum. — Coloured spiral bacteria ; sulphur ab- 

 sent. 



The prefix " Rhodo " was first used by Molisch in his 

 Purpurbakterien to designate purple coloured bacteria, and 

 included the sulphur-containing and the sulphur-free forms. 



Genus i. — Thiospirillum (Omelianski). 



Literature. — Omelianski (2), 1905 ; Molisch (2), 1912 ; 

 Wislouch (2), 1914; Perliljeff, 1923; Bavendamm, 

 1924. 



Colourless, spirally wound, with polar cilia. Division by 

 transverse fission, as in all Spirilla. 



