ORGANIC NITROGEN—ITS DECOMPOSITION. 6r 
((NH4)2COs). The condition in which the nitrogen actually exists 
in the humus has been a matter of considerable dispute. Quite 
a long list of complex chemical compounds have recently been 
isolated from it; but much of it still remains of unknown composi- 
tion. Itis evident that there is a 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 por- 
tion of it is being constantly reduced to the 
form of ammonia. This portion alone is id 
leading toward a condition where it can 4. L. 
again be readily utilized by plants. The ™ \ 
rest, whether in the form of proteid or other- at 4 ai. 
wise, is, for the present, largely, or possibly Sanam 1° 
wholly out of the reach of plant life. The Fic. 16.— Bacteria 
humus may thus contain a large amount Producing ammoniacel 
of nitrogen and still have little of itavailable; mycoides; B, B. stutzers. 
2.é., 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 1s now recog- 
nized, since it is the first step necessary to bring the nitrogen 
locked up in the proteid back again withinreach of plants. Butits 
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 (NH3, COs, 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 becoming 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 process, it is evident enough, from simple 
mechanical reasons, that vegetation would soon cease, since there 
