CHANGES BROUGHT ABOUT BY NON-PATHOGENIC ORGANISMS 67 



a city whose water supply contains a large percentage of sulphates 

 will develop hydrogen sulphid in considerable quantities if it is 

 put under anaerobic conditions. Other reductions of a similar 

 nature have been described for chlorates. 



Fig. 32. Denitrifying bacteria: A, .Boct'ZZus coli, which changes nitrates into 

 nitrites; B, Bacillus denitrificans, which produces free nitrogen from nitrates. 



Oxidation of Inorganic Compounds. Bacteria and other 

 microorganisms that live in the presence of oxygen are sometimes 

 active oxidizers of inorganic compounds, securing in this manner 

 the energy that is necessary for their various growth processes. 



Fig. 33. Sulphate reducing spirillum, Spirillum desulfuricans. 



Oxidation of Hydrogen Sulphid. Waters containing hydrogen 

 sulphid, as do many of the so-called mineral springs, usually 

 contain bacteria which gain their energy for food manufacture 



Fig. 34. Microorganisms that oxidize hydrogen sulphid: A, B, Beggiatoa 

 sp.; C, Thiophysa volutans (Hinze). 



and growth from the oxidation of this substance. The slimy 

 black and white deposit commonly found in such waters, when 

 examined microscopically, will be seen to be made up of masses of 



