THE LEUCO^THIOBACTERIA 117 



backward motion with an occasional rotation on its longi- 

 tudinal axis. No organs of movement have been found, 

 although Zacharias states that young individuals possess a 

 clearly visible cilium as long as the organism itself. This has 

 not been confirmed. 



Although probably first mentioned by Warming in 1875, 

 the fi.rst descriptive account of the organism was given by 

 Schewiakoff in 1893. He described and named Achromatiiim 

 oxaliferum, which is considered to be identical with the 

 organism subsequently described by Frenzel (1897) under the 

 name of Modderula Hartwigi, and by West and Griffiths (1909) 

 under the name of Hillhoiisia mirahilis. In the works of the 

 earlier writers (Schewiakoff, Frenzel, Lauterborn) an attempt 

 is made to distinguish between the peripheral layer (Rinden- 

 schicht) and the central body (Centralkorper), obviously under 

 the influence of Biitschli's now discredited view of the structure 

 of the bacterial cell, and so the plasma is described as being com- 

 posed of two layers, a central with larger, and a peripheral with 

 smaller, meshes. This marked distinction between the size of 

 the meshes has not been observed by later writers as Virieux, 

 and West and Griffiths, who have examined the structure of 

 the cells w4th greater accuracy. Dr. B. M. Griffiths regards 

 Hillhousia as specifically distinct from Schewiakoff's Achroma- 

 tiiim oxaliferum and Frenzel's Modderula Hartwigi, because in 

 it there is no distinction between a peripheral and a central 

 plasma. This distinction, however, does not occur in any mem- 

 ber of the sulphur bacteria nor in any one of their immediate 

 allies. The distinction apparently did not exist in the organism 

 examined by Schewiakoff and by Frenzel. It is noteworthy 

 that, although the organism named Modderula was stated 

 to be quite common, no organism of the bacterial group 

 containing a differentiated plasma has since been found. 

 If, therefore, we take the view that Modderula (including 

 Achromatium) does not possess a differentiated plasma, the 

 sole distinction between Hillhousia and this organism vanishes, 

 anrl on the groimd of priority the name Achromatium oxa- 

 liferum must be held to cover all three generic namics (see 

 Fig. 51 a and b, and pp. 182-4). 



