140 SOILS. 



manure), the great variability of the products from different 

 materials is very striking. When the nitrogen-content is de- 

 ducted the percentage composition of the products agrees 

 more nearly. Considering that the nitrogen is probably pres- 

 ent in the amid form, it is natural that hydrogen should in a 

 measure vary with it, as in the case of the clover, flour and 

 meat humus. Nitrogen being the most variable ingredient of 

 humus, it seems probable that the variation of the proportion 

 of the humus-amids present is the most potent factor in the 

 variability of the composition of natural soil-humus. 



Arranging these results in the order of their nitrogen-con- 

 tent as in the table below, we see that the latter approximately 

 corresponds to the original protein-content of the humified sub- 

 stances. 



Humus from meat scraps 10.96 % Nitrogen. 



" " green clover 8.24 



it (t cow manure 6.16 



" " wheat flour 5.05 



" " oat straw 2.50 



" " sawdust 32 



\Yhile the above data prove the correlation between the first 

 products of humification and the original substance, it must be 

 remembered that subsequently, under proper conditions, the 

 nitrogen-percentage in humus may. in the course of time, in- 

 crease very greatly, even to a proportion considerably above 

 that contained in flesh itself. \Yhen we consider that ordina- 

 rily, the latter, and the albuminoid substances generally, decom- 

 pose in contact with air with an abundant evolution of ammonia 

 compounds, sometimes leaving only a little fat (adipocere) 

 behind, it is surprising that the decomposition tcitliin the soil 

 should have exactly the opposite result, viz., an accumulation 

 of the nitrogen. The causes of this marked difference are not 

 yet well understood, but it is probably due to the differences 

 in the kinds of bacteria that are active in the two cases. 



Snyder has also shown that the richer the organic matter 

 humified is in nitrogen, the more energetically it acts in render- 

 ing available the mineral matters of the soil for plant nutrition. 



