DECAY OF NITROGENOUS BODIES. 289 
From numerous other experiments, not published at 
this writing, Hellriegel believes himself justified in assum- 
ing that the highest yield thus observed, with 84 lbs. of 
nitrogen in 1,000,000 of soil, might have been got with 
70 lbs. of nitrogen in case of wheat, with 63 Ibs. in case 
of rye, and with 56 Ibs. in case of oats. On this assump- 
tion he has calewlated the yield of cach of these crops,| 
and the figures obtained (see Table) present on the whole 
a remarkable coincidence with those directly observed. 
§ 7. 
DECAY OF NITROGENOUS BODIES. 
We have incidentally noticed some of the products of 
the decay of nitrogenous bodies, viz., those which remain 
in the soil. We may now, with advantage, review the 
subject connectedly, and make our account of this process 
more complete. 
It will be needful in the first place to give some ex- 
planations concerning the nature of the familiar trans- 
formations to which animal and vegetable matters are 
subject. 
By the word decay, as popularly employed, is under- 
stood a series of chemical changes which are very differ- 
ent in their manifestations and results, according to the 
circumstances under which they take place or the kinds 
of matter they attack. Under one set of conditions we 
have slow decay, or, as Liebig has fitly designated it, 
eren ausis ;* under others fermentation; and under still 
others putrefaction. 
Eremecausis* is a slow oxidation, and requires the 
constant presence of an excess of free oxygen. It pro- 
ceeds upon vegetable matters which are comparatively 
©¥ rom the Greek, signifying slow combustion. 
13 
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