Bacteria and Iron 



301 



the oxidation of sulfuretted hydrogen 

 by the sulfur bacteria. The sulfur is 

 not used by the latter as a food, but 

 only as a fuel a source of energy. Simi- 

 larly, in the case of the iron bacteria, 

 the iron which is made to take on 

 oxygen serves as a source of fuel. In 

 the one case, the final product is sul- 

 furic acid, which passes out of the bac- 

 terial cells. In the other, a soluble 

 compound, or compounds, of iron 

 passes into the outer sheath of the 

 microorganisms. 



The importance of iron bacteria. 

 The iron bacteria, represented chiefly 

 by Cladothrix dichotoma and Crenothrix 

 Kiihniana, have played in the past and 

 are playing in the present a role of 

 considerable significance in the accumu- 

 lation and migration of iron compounds 

 in certain localities. This applies par- 

 ticularly to swamps, meadows and 

 marshes 'n which deposits of bog iron 

 are, at t mes, formed. Soluble com- 

 pounds of iron of a lower state of oxida- 

 tion are carried to such places and are 

 there made to combine with more oxy- 

 gen, partly through the activities of 

 iron bacteria. One of these soluble 

 compounds of iron, Jmown as ferrous 

 sulfate, or copperas, is a substance quite 



Fig. 57. Iron bacteria. 

 1. Bog iron. 2. 

 Psichohormium an- 

 tliarium, showing 

 masses of iron sur- 

 rounding the cell- 

 walls. 3. The same, 

 after treatment 

 with dilute acid; 

 X 600. (Mo-lish.) 



