300 



Bacteria in Relation to Country Life 



the manner in which this potential energy is utilized by- 

 bacteria. The formation of nitrites and nitrates, the 

 production of carbon dioxid, of water, and the forma- 

 tion of sulfur, granules and their subsequent oxidation 

 to sulfate, are all instances of energy production by 

 various groups of bacteria under well-defined condi- 

 tions. Similarly, in the case of iron, a certain amount 

 of energy may be set free in the addition of oxygen to 

 this element. Iron rusts when exposed to the air, that 

 is, it combines with the oxygen of the atmosphere to 

 form an oxide of iron. Under ordinary conditions, 

 the rusting (oxidation) process is so slow as not to show 



any increase in 

 temperature. It 

 remains true, 

 none the less, 

 that heat is set 

 free in the rust- 

 ing of the iron. 



Iron rust and 

 bacteria. — Under 

 certain condi- 

 tions this rust- 

 ing is caused by 

 bacteria, and the 

 heat produced is 

 utilized by them 

 for their own 

 development. 

 We have an an- 

 alogy here to 



c? 

 o c 



\^31— 



6 



Fig. 56. Iron bacteria. — 1. LeptothrCx ochracea. 2. 

 Gallionella ferruginea, typical thread. 3. Spiro- 

 phyllum ferrugineum. 4. Gallionella ferruginea 

 cell division. 5. Spirophyllum ferrungineum, 

 twining individuals. 6. Gallionella ferruginea, 

 Qonidiafgrma'tiQn. (Aft^r Ellis.) 



