IRON AND SULPHUR BACTERIA. 



163 



sheath. The great deposits of iron ochre found in nature 

 are probably <to be partly accounted for by the activity of such 

 bacteria. According to Molisch and others, they can also 

 digest considerable quantities of manganese. 



Fig. 31. Crenothrix Kiihniana (after Zopf)- a-e (600 : 1), Cocci in different stages of 

 division ;/(600 : 1), small, round cocci-zoogloea ; g (natural size), zooglcea; h (600 : 1), colony of 

 short filaments composed of rod-like cells, emanating from the germination of a small collection 

 of cocci ; i-r, filaments, partly straight, partly spirally curved (I, w), of very varying thickness, 

 with more or less pronounced contrast between the base and apex, and different stages of division 

 of their members and sheaths ; the sheathed filament r shows short rods at the base, which 

 higher up are divided into small cylindrical pieces ; at the apex the cocci are seen arising 

 from the longitudinal divisions of the cylindrical discs. 



