280 



THE SULPHUR BACTERIA 



;. Tliiotrix nivi-a. 



200. The Species of the Genus Thiothrix, 



which has been newly established by Winogradsky, differ from Beggiatoa by the 

 absence of free motility, they being sessile, i.e. attaching themselves at one 

 extremity by means of a mucinous sucker to the walls of 

 the culture vessel, the cover-glass of the microscopical 

 preparation, to stones, remains of plants, and similar 

 quioccnt substrata in the situations where they occur 

 naturally; whilst the other end extends into and grows 

 in the liquid. Such a one is shown in Fig. 73. In this 

 genus, also, the articulation of the threads is ordinarily 

 concealed by the abundant content of sulphur, but if the 

 latter be washed out with absolute alcohol and the cells 

 stained, e.g. with fuchsine, the transverse walls are plainly 

 revealed. The length of the joints gradually increases 

 towards the free end, as will be seen from the subjoined 

 measurements given by Winogradsky : Length of joint 

 near the point of attachment, 4-8.5 p. ; at the apex, 

 8-15 p. However, there is no scarcity of considerably 



Group of young threads shorter C f lls - S fal> ^ & breadth f ^ G f hl \ ads J S 



with on.- Vnii lirmiy at- concerned the above conditions are reversed, the threads 

 to tin- Miiistrsitum tapering off towards the free end, where, for example, 

 their Diameter is only 1.5 p, compared with 2.0 p at the 



900. <.4fterniu>yratiitky.) base. Consequently the cells are more slender towards 

 the tip. 



A second characteristic point of difference from the genus previously described 

 is the appearance of a (merely slight) sheath, whereby the moribund members 

 are partly held together, whereas the Beggiatoa threads at this stage break into 

 short fragments and finally into separate cells. 



A third characteristic of the genus Thiothrix is the dislocation (termed 

 conidia-formation by Winogradsky) of the uppermost joint of the thread. The 

 rod-shaped cell, thus loosened from the chain, crawls a short distance along the 

 solid substratum, then develops a mucinous sucker and grows into a new thread, 

 from which in turn conidia subsequently wander and settle in the vicinity, the 

 result being the formation of the whitish, tufted, thread colonies characteristic 

 of Thiothrix. 



Here also the thickness of the threads constitutes a criterion for the clari- 

 fication of species. One of them, named by Winogradsky Thiothrix nivea, h:is a 

 diameter of 2-2.5 f- near the base, 1.7 p in the middle, and 1.4-1.5 p at the tip. 

 In a second species the diameter is almost uniformly i.o-i.i /* throughout the 

 whole extent of the thread. It is known as Thiothrix ttnuis, and is probaHy 

 identical with a fi-siOn fungus discovered by ENGLER (I.), in the so-called " dead 

 ground " of the Bay of Kiel, and which he held to be a Beggiatna and called by 

 the specific name B. albavar. universalis. The threads of a third species (Thio- 

 /////./ f''niiin>iitiiff), from a sulphur spring at Adelboden (Switzerland), measure 

 only 0.4-0.5 p. in breadth. W. XOPF (VII.) regarded the sessile sulphur bacteria 



: longing to the morphological cycle of the Het/i/ii/tod, and named them 

 "sessile He^iatoa," until NViiio.irradsky proved tiial two distinct genera are here 

 in question. 



As will be shown later on, the life of the sulphur bacteria is indiflBolubly 

 connected with the presence and availability of free oxygen. In the mode of 

 satisfying their needs in this respect the two genera differ. The B<'<j<jt<i'<>n, 

 being endowed with the power of locomotion, can more readily accomplish this 



