THE MANURE HEAP AND SEWAGE. 



destruction of the compounds. This occurs in the soil, in the 

 manure heap, in the privy vault, in the sink drain or in sewage, 

 the phenomena being fundamentally the same in all cases, 

 although differing in details with differences in the kind of 

 compounds present, the amount of water, the temperature, the 

 access of oxygen, the species of bacteria present, and doubtless 

 other factors. It results in a purification of the soil or a puri- 

 fication of sewage from similar reasons. 



Such a disposal of sewage means, of course, a complete loss 

 of the nitrogenous material, for no method is adopted for utiliz- 

 ing the wasted nitrates. But this fact is no longer regarded so 

 seriously as it was a few years ago. Inasmuch as we have 

 learned that there are efficient forces in nature for bringing 

 back from the atmosphere the nitrogen dissipated from the 

 soil, it is a matter of less significance to throw away the sew- 

 age nitrogen than it appeared to be when the only known 

 source of nitrogen was supposed to be the fixed nitrogen of the 

 soil. Since the soil can readily replace its lost nitrogen through 

 the agency of certain species of bacteria (see Chapter VI.) it 

 is no serious matter if some of the nitrogen is thrown away. 



11 



