CHAPTER XXXV. 



THE SULPHUR BACTERIA. 



199. Morphology of the Genus Begfgiatoa. 



THE sulphur bacteria, so called on account of their peculiar properties, diller 

 both in structure and external appearance from the filamentous bacteria described 

 in the preceding chapter. They may be divided into two sub-groups, one of 

 which forms the species classified by Engelmann as purple bacteria, and already 

 noticed in chapter xiii. on account of their behaviour towards light. The other 

 sub-group of the sulphur bacteria, which assume the form of long threads, will 

 now be described. 



It will be useful to preface this description with a few hints concerning arti- 

 ficial cultivation and reproduction for the purposes of investigation. The sulphur 

 bacteria are seldom absent in marsh water, although their number is frequently 

 so small as to elude the inquiring eye of the microscopist. In order to cause 

 them to increase, the conditions of the environment must be rendered favourable, 

 and with this object the simple method proposed by their careful observer, S. 

 WINOGRADSKY (V.), is employed. A few cuttings of the fresh root-stock of the 

 flowering rush, Butomus umbellatus (found in every pond, and by no means rare 

 on river banks), are placed, along with the adherent mud, in a deep vessel con- 

 taining 3-5 litres (about a gallon) of water, a couple of grams of gypsum being 

 added, and the whole left to stand uncovered at room temperature. After five 

 to seven days the liberation of sulphuretted hydrogen will already be noticeable, 

 the gas being disengaged by various species of fission fungi present in the mud 

 and acting on the gypsum. In this manner the ground is prepared for the 

 sulphur bacteria also present, and the latter then develop rapidly. At the end 

 of three to six weeks their presence can be ascertained by the aid of the micro- 

 scope, and they gradually increase to such an extent as to be recognisable by the 

 unassisted eye. Generally, this diversified mixture of sulphur bacteria is not 

 deficient in the red species as well, but the colourless long thread forms are most 

 plentiful. 



Two genera were more closely investigated by Winogradsky. The one of 

 these bears the name of /tri/i/iatoa, given by TREVISAN (I.) in 1842 in honour of 

 the Italian physician K S. llc^iato of Vicenzn, who, in 1838, published a com- 

 munication on the flora of the sulphur springs of the Euganean Hills, near Padua. 

 The species of this genus occur as actively motile cylindrical filaments, which 

 may attain a length of i c.m. and more. The breadth is always constant in each 

 sej. Mi-ate species, and thus affords a means for differentiating between them. 

 Under favourable conditions of nutrition, and especially in presence of sul- 

 phuretted hydrogen, the interior of the individual threads (Fig. 70 a) is seen to 

 be well stocked with roundish, highly refractive granules, i.e. the sulphur 

 granules described later on. In this condition the transverse cell walls are 

 indiscernible or only detected with difficulty, as will be gathered from Fig. 70 r, 

 which shows the same thread after it has lost its enclosed sulphur granules by a 

 long sojourn in water devoid of su 1 pi m retted hydrogen. Moreover, the length 

 of the cells varies in the different species. If this organism be deprived of the 



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