BACTERIA OCCURRING IN SEWAGE 



79 



more common in continuous than in intermittent filtration. 

 Crenothrix only grows rapidly when the dissolved oxygen is 

 low and when certain metals are present, and is favoured by 

 the presence of much organic matter and of carbonic acid and 

 the absence of light. Jackson^ distinguishes three species: 

 (i) The common C. Kilhniana, red or reddish brown, pre- 

 cipitating ferric hydrate; (2) C. (formerly Leptothrix) ochracea, 

 white or yellowish, precipitating alumina ; and (3) C. manga- 

 nifera, dark brown or black, precipitating manganese. 



Fig. 13. — Beggiatoa alba. 

 Showing attached, free, curved, and 

 spiral forms, (a) Chain of spores ; 

 (b) free spores (motile) ; (c) portion 

 under a higher power, showing trans- 

 verse and longitudinal division; (d) 

 filaments breaking up (the small dark 

 circles are granules of sulphur highly 

 refracting) ; {e) free motile segment 

 with terminal flagella. 



Fig. 14.— Crenothrix Kuhniana. 

 ( X 600. ) 

 {a) Arthrospores ; (b) single seg- 

 ments ; (c) common sheath surround- 

 ing the separate spores. 



Among the species that have been identified as constituting 

 masses of " sewage fungus " are : Leptomitus lacteus (Sapro- 

 legnia^), soft, gelatinous, white, rusty, or black masses of long- 

 branching filaments, constricted at intervals, each segment 

 having a refractile nucleus. Sphcsrotilus natans, allied to the 

 leptothrix forms of bacteria, and possibly identical with 

 Beggiatoa. It is more gelatinous than Leptomitus; like it, 

 forms long wavy masses, usually whitish, but, according to 



^ Journal of the Society of Chemical Industry, 190-, P. 681. 



