CHAPTER XXXV. 



THE SULPHUR BACTERIA. 



199. Morphology of the Genus Beggiatoa. 



THE sulphur bacteria, so called on account of their peculiar pro- 

 perties, differ 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 artificial 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 

 containing 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 pre- 

 pared 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 microscope, 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 Beggiatoa, given by TREVISAN (I. ) 

 in 1842 in honour of the Italian physician F. S. Beggiato of Vicenza, 

 Avho, in 1838, published a communication on the flora of the sulphur 



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