450 R. S. BREED, H. J. CONN AND J. C. BAKER 



the autotrophic bacteria, use inorganic food, but they obtain 

 their energy from sunhght instead of from chemical transforma- 

 tions. Jensen disregards this theory on the assumption that the 

 primordial earth was dark; but Chamberhn's theory of the earth's 

 origin has as much weight today as the nebular h5T)othesis, and 

 according to his theory sunlight may have reached the earth's 

 surface even in the earliest time.^ 



Another possibility not to be overlooked is that the earliest 

 bacteria had energy-bearing carbon compounds at their disposal. 

 These may have been formed by preceding life of still simpler 

 nature, which is either extinct today or has escaped detection; 

 or they may have been formed by inorganic agencies. Moore and 

 Webster (1913) have shown that organic matter (formaldehyde) 

 can be synthetized by the action of certain inorganic catalysts, 

 which utihze sunlight energy, and have pointed out the signif- 

 icance of this fact as a possible explanation of th"? source of 

 nutrition for the earliest life on the earth. If we assume that 

 organic matter was synthesized by inorganic agencies before the 

 existence of hfe, it is entirely unnecessary to look to phototrophic 

 or autotrophic organisms as the original ancestors. The first 

 organisms might have derived both food and energy from the 

 simple carbon compounds then in existence. 



The only justification for recognizing several genera of auto- 

 trophic bacteria is on the assumption that the few species we 

 know are the sole survivors of primitive genera. This assump- 

 tion, as just shown, is not the only reasonable hypothesis. A 

 more conservative course than to accept the entire list of genera 

 of Nitrobacteriaceae would be to recognize but one, or at the 

 most, two genera of prototrophic bacteria. If two genera are to 

 be recognized, one could include those forms capable of obtaining 

 both their carbon and nitrogen from inorganic sources, and the 

 other those requiring organic carbon but able to use elementary 

 nitrogen. For these two genera, the names Nitrosomonas Win- 

 ogradsky and Azotobacter Beijerinck would have to stand by 

 priority. 



* See Chamberlin (1916), p. 248. An earlier discussion of primordial con- 

 ditions by Chamberlin and Chamberlin (1908) shows that life may perhaps have 

 started under conditions not so very different from those of today. 



