EVOLUTION OF BACTERIA 83 



nitrate formers, Nitrobactcr. These bacteria are not only in- 

 dependent of life compounds, but even small traces of organic 

 carbon and nitrogen compounds are injurious to them. Later 

 Nathanson (1902) and Beyjerinck (1904) showed that certain 

 sulphur bacteria possess similar powers of converting ferrous to 

 ferric oxide, and HoS to SOo. 



Such bacterial organisms may have flourished on the lifeless 

 earth and chemically prepared both the earth and the waters 

 for the lowly forms of plant life. The relation of the nitrifying 

 bacteria to the decomposition of rocks is well summarized by 

 Clarke in the following passage:^ "Even forms of life so low 

 as the bacteria seem to exert a definite influence in the decom- 

 position of rocks. A. Miintz has found the decayed rocks of 

 Alpine summits, where no other life exists, swarming with the 

 nitrifying ferment. The limestones and micaceous schists of 

 the Pic du Midi, in the Pyrenees, and the decayed calcareous 

 schists of the Faulhorn, in the Bernese Oberland, offer good 

 examples of this kind. The organisms draw their nourishment 

 from the nitrogen compounds brought down in snow and rain; 

 they convert the ammonia into nitric acid, and that in turn 

 corrodes the calcareous portions of the "rocks. A. Stutzer and 

 R. Hartleb have observed a similar decomposition of cement 

 by nitrifying bacteria. The effects thus produced at any one 

 point may be small, but in the aggregate they may become 

 appreciable. J. C. Branner, however, has cast doubts upon 

 the validity of Muntz's argument, and further investigation 

 of the subject seems to be necessary." 



It is noteworthy that it is the nitrogen derived from waters 

 and soils, rather than from the atmosphere, which plays the 

 chief part in the life of these organisms; in a sense they repre- 

 sent an early carbon stage of chemical evolution, since carbon 



1 Clarke, F. W., 1916, p. 485. 



