1 88 BIOLOGY OF SPECIALIZED GROUPS 



a double source of energy, that which is obtained by the use 

 of sulphuretted hydrogen, as in the group described above, 

 and also by means of the bacteriopurpurin which enables 

 them to synthesize organic matter with the energy obtained 

 from the sun's rays. 



Iron Bacteria. The iron bacteria are represented by the 

 organism Crenothrix polyspora, which was described by F. 

 Cohn in 1870. This bacterium consists of a filament of cells 

 attached to some object. The cells in this filament are smaller 

 at the base and increase in diameter higher up. The range in 

 size is from one and a half to five microns. These bacteria 

 occur in tufts and each filament is surrounded by a sheath. 

 The cells at the outer end of the filament break up into 

 gonidia. As ordinarily seen, these bacteria have their sheaths 

 permeated by reddish brown masses of ferric oxide. These 

 bacteria take ferric carbonate and oxidize it to ferric hydroxide, 

 as represented in the following formula : 



2 FeCO 3 + 3 H 2 O + O = Fe 2 (OH) 6 + 2 CO 2 . 

 As a result of this oxidation process, energy is obtained which 

 enables these bacteria to synthesize organic material. They 

 obtain their nitrogen from inorganic sources and are not de- 

 pendent upon organic matter for support. These bacteria 

 grow readily in waters free from organic matter providing the 

 iron salts are present. They are widely distributed in nature 

 and are found in swamps, meadows, and marshes, and are 

 especially likely to grow in deep well waters which are iron 

 bearing. Sometimes their growth is such as to render the 



