368 THE SULPHUR BACTERIA. 



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

 <fec., 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 invari- 

 ably colourless, and consequently cannot throw off coloured cells, 

 W. ZOPF (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-group com- 

 prising all those sulphur bacteria whose living cells are free and 

 capable of locomotion. It is divided into three genera, Chroma- 

 tium, Rhaldochromatium, 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 conse- 

 quently includes Ehrenberg's Opliidomonas. A contrast to this 

 sub-group of free cells is afforded by the species of red sulphur 

 bacteria which are generally united as colonies. In the genera 

 Thiocystis and Thiocapsa this union is effected by a mucinous 

 sheath, which is absent in Thiosarcina. In all three cases repro- 

 duction occurs by fission in three directions, and the same behaviour 

 is exhibited by the genus Larnprocystis, 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 character- 

 ised by the division of the cells in two directions of space, and by 

 the consequent flat colonies. In the remaining species cell fission 



