76 SULPHUR BACTERIA 



Another difficulty arose in the nomenclature of Thiothrix. 

 The author has found a coloured Thiothrix, which appears to 

 differ in no single particular from the normal uncoloured species, 

 except in colour. Its genetic connection with Thiothrix is so 

 patent that it must be retained in that genus in spite of its 

 possession of colour. 



(lO) Diversity of Habit. — Several attempts have been 

 made, notably by Bcijerinck and by Orla-Jensen, to frame 

 classifications based on differences in the mode of life of 

 different bacteria. Such attempts would have much to 

 recommend them, were it not that the majority of bacterial 

 organisms could be included not in one but in several 

 groups. It has already been pointed out that many para- 

 sites, like Bacillus cholercE for instance, lead a saprophytic life 

 when living cells are not available. Many other instances 

 may be cited in support, and it may be stated of bacteria in 

 general that the more that is known of their metabolism the 

 greater the conviction of the diversity of their habits. All 

 physiological systems fail to satisfy the first requisite of a 

 logical classification, namely, that it should not be possible 

 to place an organism in more than one group. 7he sulphur 

 bacteria are not cultivable on ordinary media, so it is not 

 possible to use such cultural characteristics as gelatine lique- 

 faction, or sugar reactions, for the diagnosis of species. The 

 reaction of the sulphur bacteria to the Gram stain has not 

 yet been investigated, so that its use is problematical. 



Summary. 



The foregoing remarks may now be summarized as follows : 

 (i) Spatial Division of the Cells. — Of limited application. 

 (2) Motility. — A positive result is valuable, but a negative 

 one is not. Absence of movement may be due to an abnormal 

 development of slime, with a consequent restriction of cilium 

 development. Caution must therefore be exercised. The 

 sulphur bacteria may be divided into three groups on the basis 

 of motility : (i) Motile with cilia ; (ii) Motile without cilia ; 

 (iii) Motility unknown. 



