282 THE SULPHUR BACTERIA 



of a single species of thread bacterium, viz., Beggiatoa roseo-persicina, which, 

 under certain circumstances, was said to appear as long threads (Leptothrix), 

 and under others as fractions of such threads, viz., as Monas, Spirillum, &c., 

 capable of developing once more into threads. 



The re-investigation of these discoveries (which were not made with pure 

 cultures) by Winogradsky led to the refutation of this assumed variability of 

 form, and also to the discovery that the above-named red sulphur bacteria are 

 not capable of progressive development, i.e. of growing into thread form. Some 

 little doubt still prevails as to the existence of retrogressive development, i.e. 

 the dismemberment of short cells from filamentous red Beggiatoa species. In 

 contradiction of Winogradsky's statement that the filamentous sulphur bacteria 

 (Beggiatoa and Thiothrix) are invariably colourless, and consequently cannot 

 throw off coloured cells, W. ZOPP (VIII.), in a subsequent communication 

 (1895), reported the existence of red Beggiatoa species which become dismembered 

 into short (sulphur-bearing) cells. The question must consequently be considered 

 as requiring further investigation. The results will, however, be chiefly of 

 botanico-morphological interest, and will not affect either the firmly established 

 theory of the pleomorphism of the Schizomycetes, or touch the physiology of the 

 sulphur bacteria, which latter is the sole property meriting consideration, so 

 far as we are concerned. So long, however, as Winogradsky's discoveries remain 

 uncontroverted by any thoroughly reliable investigations, his deductions must 

 be allowed to stand, viz., that the sulphur bacteria are not pleomorphic neither 

 the colourless, filamentous genera nor the non-filamentous red genera. The 

 Russian physiologist described a long series of species of the latter type, which, 

 as they are devoid of special physiological importance, we need not examine 

 more minutely. It will be sufficient to mention the chief forms. 



The aforesaid purple bacteria are only a single sub-gr-oup comprising all those 

 sulphur bacteria whose living cells are free and capable of locomotion. It is 

 divided into three genera, Chromatium, Rhabdochromatium, and Thiospirillum. 

 Of these terms the penultimate one is synonymous with Cohn's Rhabdomonas, 

 whilst the last one comprises all red sulphur-bearing spirilla, and consequently 

 includes Ehrenberg's Ophidomonas. A contrast to this sub-group of free cells 

 is afforded by the species of red sulphur bacteria which are genet-ally united as 

 colonies. In the genera Thiocystis and Thiocapsa this union is effected by a 

 mucioous sheath, which is absent in Thiosarcina. In all three cases reproduction 

 occurs by fission in three directions, and the same behaviour is exhibited by the 

 genus Lamproci/stis, which principally differs from the other three in the 

 structure of its bag-shaped zoogloea, which is hollow internally, and consists 

 solely of a lattice-like network. A good representation of this species was given 

 by COHN (II.) who described it, along with other organisms, as Clathrocystis 

 roseo-persicina. The genus Thiopedia is characterised by the division of the 

 cells in two directions of space, and by the consequent flat colonies. In the 

 remaining species cell fission occurs in one direction only. The Ama;bobac(er 

 species are distinguished by an amoeboid movement ; those of Thiodlctyon owe 

 their name to the reticular conjugation of their spindle-shaped cells ; whilst 

 Thiopolycoccus forms zoogloea of closely crowded cocci. The genus Thiothece is 

 distinguishable from all other sulphur bacteria by its particularly thick gelatinous 

 sheath. 



A few remarks with regard to the properties of bacterio-purpurin will be 

 opportune in this place. The difficulties in the way of preparing a quantity 

 sufficient for the performance of a chemical analysis have not even yet been 

 overcome ; consequently its chemical composition is still entirely undefined, and 

 we cannot yet say with certainty whether the colouring-matter is the same in 

 all red sulphur bacteria. This is, however, assumed to be the caee, on the 



