3 6 4 



THE SULPHUR BACTERIA. 



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 

 separate species, and thus affords a means for differentiating between 

 them. Under favourable conditions of nutrition, and especially in, 

 presence of sulphuretted 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- 



FIG. 71. Beggiatoa alba. 



Moribund through lack of H 2 S. Thread fall- 

 ing apart into its short members, which 

 thereupon assume a rounded form. Magn. 

 900. (After Winogradsky.) 



FIG. 70. Beggiotoa alba. 



The same portion of thread under dif- 

 ferent conditions of existence. 



a. in a medium rich in H 2 S ; the thread 

 is densely packed with sulphur 

 granules ; b. after twenty -four 

 hours' sojourn in a liquid devoid 

 of H,S ; only a few sulphur granules 

 remain ; c. at the end of a further 

 forty-eight hours ; sulphur totally 

 disappeared, transverse walls now 

 visible, contents of individual cells 

 granulated. Magn. 900. (After 

 Winogradsky.) 



FIG. 72. Terminal portion of threads of (x)i 



iatoa media and (y) B. minima. 

 Magn. 900. (After Winogradsky.) 



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

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

 granules by a long sojourn in water devoid of sulphuretted hydrogen. 

 Moreover, the length of the cells varies in the different species.. 

 If this organism be deprived of the said gas, which is indispens- 

 able to its continued existence, then the threads begin to break 

 up (Fig. 71^, the contents except a thin coating attached to the 

 walls vanish, and they finally perish. No success has attended 

 the search for spore formation in the Beggiatoa. The most abun- 

 dant species of this genus is Beggiatoa alba, the threads of which 



