IO2 AiilHCtJLTl/KAI. MACTKKIOUXJY. 



carbon from carbonate of ammonia, but others have shown 

 that they can obtain it directly from the CO 2 in the atmosphere. 

 It is still a little problematical where they obtain their energy, 

 but it is evidently from the oxidizing processes which they 

 bring about. Oxidizing processes, wherever they occur in 

 nature, furnish energy. These nitrobacteria, as we have seen, 

 induce the oxidation either of ammonia or of nitrites, and such 

 oxidation would yield some energy. Inasmuch as this appears 

 the only source of energy which we can detect in the growth 

 of these organisms, it has been believed that this oxidation 

 itself furnishes the nitrobacteria with the energy they need for 

 their carbon assimilation. Whatever be the exact source, it is 

 clear enough that these bacteria have a power of utilizing 

 some source of physical energy not possessed by any other 

 animal or plant so far as known to-day. Here, again, we see 

 them in the sharpest contrast to all other organisms. 



It is evident that with these nitrobacteria we are brought 

 very close to the mineral world and that such organisms may 

 be of considerable significance in explaining the beginning of 

 soil formation. It has long been suspected that bacteria do 

 actually play some part in the process of the disintegration of 

 rocks, although the suggestion has hardly been credited from 

 the fact that there seemed to be no source from which bacteria 

 could obtain their carbon and energy upon the surface of bare 

 rock. It was even suggested at one time that small traces of 

 alcohol in the air furnished the carbon and that, nourished by 

 such minute traces of alcohol, bacteria are engaged in produc- 

 ing the disintegration of rocks even on mountain peaks where 

 no vegetation is found. With our present understanding of 

 the nitrobacteria we can gain a further support for this gen- 

 eral agency of bacteria. If they can grow on the bare rocks, 

 using the minerals of the rocks and the carbon of the atmos- 

 pheric carbon dioxide, and obtain ammonia for oxidation from 

 the air, it would certainly seem that they might be the means of 



