SYSTEMATIC AND DESCRIPTIVE. 185 



The micro-organism appears in little whitish or 

 brownish tufts in wells and drain-pipes, and it not 

 only renders drinking-water foul, but may stop up 

 the narrower pipes. 



Genus II. Beggialoa. 



Beggiatoa alba, Vauch. Cocci, rods, spirals, 

 and threads. The threads are longer and thicker 

 than leptothrix, indistinctly articulated, actively 

 oscillating, and colourless ; their protoplasm con- 

 tains numerous, strongly refractive granules con- 

 sisting of sulphur. They occur as greyish- or 

 chalk-white gelatinous threads, 3 3*5 ^ thick, in 

 sulphur springs and marshes. 



Beggiatoa roseo-persicina (Cohnia roseopersi- 

 cina. Bacterium rubescens. Peach-coloured bacterium}. 

 Cocci, rods, spirals, and threads. The cocci, 

 globular or oval, reach 2*5 p in diam. They form 

 at first solid families, bound together by gelatinous 

 substance. Later they become larger, globular 

 or ovoid in shape, and hollow, containing watery 

 fluid in their interior. The families reach a 

 diameter of 660 JJL, in which the cocci form simply 

 a peripheral layer. The hollow families or vesicles 

 are often perforated, presenting a delicate reticu- 

 lated appearance, which finally may become broken 

 up into irregular structures. The red colouring 

 matter can be distinguished from other red pig- 

 ments, and is designated by the name bacterio- 

 purpurin. It is quite distinct from the pigment 



