SPECIES OF THE GENUS THIOTHRIX. 



36S 



are 2.8-2.9 ^ * n thickness, whilst the length of the individual 

 members varies between 2.9 and 5.8 /",, the shortest of them being 

 thus symmetrical. A second species, with a diameter of 1.6-1.7 <"-, 

 the length of the separate cells being 4-8.5 /a, has been named 

 Beggiatoa media ; and a third kind, whose diameter is only 0.8 A&, 

 is called Beggiatoa minima. Both these species are shown in Fig. 

 72, magnified to the same extent as the first-named species. In 

 addition to these there is still a large number of species whose 

 threads vary in diameter between the above limits. Compared 

 with all these the Beggiatoa miralilis noted by COHN (XII.), 

 Warming, and Engler, but not yet more minutely examined, the 

 threads of which are said to attain a breadth of 30 AC-, is gigantic. 

 According to Winogradsky, the breadth of the cells of any given 

 species is to emphasise this point once more unalterable. 



The growth of these Schizomycetes is very slow, a thread re- 

 quiring at least twenty-four hours to double its length. They are 

 extremely susceptible, even merely the grip of the forceps being 

 fatal. For this reason they have to be sucked up by means of a small 

 tube, for purposes of examination, and protected from the pressure of 

 the cover-glass by introducing splinters of glass, &c., into the liquid. 



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 quiescent 

 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 trans- 

 Terse walls are plainly revealed. The 

 length of the joints gradually increases to- 

 wards 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 ^ ; at the apex, 

 8-15 At. However, there is no scarcity 

 of considerably shorter cells. So far as the breadth of the threads 

 is concerned the above conditions are reversed, the threads taper- 



FIG. 73. Thiotrix nivea. 



Group of young threads with 

 one end firmly attached 

 to the substratum by 

 means of the sucker (in- 

 dicated by dots). Magn. 

 900. (After Winogradsky.) 



