ORGANIC NITROGEN. ITS DECOMPOSITION. 55 



peptonizing bacteria, they are converted into peptone-like bodies 

 which are simpler than ordinary proteids. These are further 

 reduced into amido acids, and the latter finally converted into 

 ammonia, which is quite likely to unite at once with carbonic 

 dioxid, that is also being liberated, to form carbonate of ammonia 

 ((NH 4 ) 2 CO 3 ). The condition in which the nitrogen actually exists 

 in the humus has been a matter of considerable dispute. Some 

 have thought that it remains in the form of proteid in large part, 

 others have concluded that the humus nitrogen 

 is chiefly in the form of amido acids. But it 

 is evident that there is long series of stages 

 between the proteid and the final ammonia 

 compound, and that the nitrogen in any lot 

 of soil may be in any one of these stages. In 

 whatever form it exists in the humus, a certain _ 



FIG. 17. Bacteria pro- 

 portion of it IS being constantly reduced to the ducing ammoniacal fer- 



form of ammonia. This portion alone is lead- 



ing toward a condition where it can again be 



utilized by plants. The rest, whether in the form of proteid or 



otherwise, is, for the present, locked up out of the reach of plant 



life. The humus may thus contain a large amount of nitrogen and 



still have little of it available; i.e., within the reach of plants. 



Self-purification of the Soil. The universal occurrence of 

 such a decomposition of organic bodies is no new discovery. It 

 has long been known and its extreme significance is now recognized, 

 since it is the first step necessary to bring the nitrogen locked up 

 in the proteid back again within reach of plants. But its value 

 in producing what has been called the self-purification of the soil, 

 has been only recently appreciated. As we have seen, the final 

 end-products are largely gaseous (NH 3 ,CO 2 ,N, etc.), and these 

 will tend to pass off from the soil into the air. A little thought will 

 show us that without the existence of some such process the soil 

 would rapidly become unfit for the support of life simply by becom- 

 ing clogged up with the remains of past animals and plants. If 

 all the bodies of animals remained on the soil after death and if 

 the roots and stems of plants were not disposed of by some such 



