MICHIGAN ACADEMY OF SCIENCE. 
43 
could not agree upon the composition of humic acid obtained from soil 
nor could the same composition be obtained for humic acid derived from 
different materials. Later a controversy arose over the question as to 
whether nitrogen was a constituent part of the humus or not. Some 
claimed that it was organically combined, while others claimed that the 
nitrogen was present as ammonium salts. 
Without going farther into a review of the literature on this point 
it will be seen that the one thing which characterized the work of the 
early investigators was the lack of anything like concordant results. In 
fact the same lack of definite results has characterized the work of all 
investigators down to the present time who have followed in the foot- 
steps of the early workers in their attempts to throw light upon this 
most interesting and difficult problem. Consequently there seems to be 
no valid reason why we should continue to use a method for determining 
humus, which, we must admit, removes not one compound but a mass of 
organic compounds about which we are only beginning to learn the least 
little bit. Aud furthermore it would seem to the writer that it would 
be a step in advance if we would discontinue the use of the term humus 
altogether and confine ourselves to the more comprehensive term — or- 
ganic matter. 
During the past few years much good work of a purely scientific char- 
acter has been done on the organic matter of soils. Shorey, now of the 
Bureau of Soils of the United States Department of Agriculture was the 
first to isolate a definite crystalline compound from soil. This he identi- 
fied as picoline carboxylic acid. Since then Schreiner and his associates 
have isolated several organic compounds, many of which have proved 
to be more or less toxic to wheat seedlings. Nearly all of the compounds 
isolated by these workers have been free from nitrogen. 
Nitrogen which is the most costly form of plant-food we have to con- 
sider, is present in the soil almost entirely in combination with organic 
matter and probably very largely in the form of protein compounds. 
If this is true, then the breaking down of the nitrogen compounds in the 
soil is largely one of proteolysis and one should expect to find many of 
the same compounds in the soil as results from the hydrolysis of protein 
compounds in the laboratory. 
Suzuki digested humus with hydrochloric acid and from the extract 
was able to isolate the following substances, long recognized to be de- 
composition products of protein : Alanin, Leucin, Aminovalerianic 
acid, Prolin, Aspartic acid together with traces of Glutamic acid, 
Tvrosin and Histidin. 
Three years ago Jodidi working in the chemical laboratory of the 
Michigan Experiment Station began a study of the organic nitrogen 
compounds in peat soils and from his work concluded that from two- 
thirds to three-fourths of the nitrogen extracted by boiling acids is in 
the form of monoamino compounds, about one-fourth in the form of 
amids and the rest is in the form of diamino compounds. 
Jodidi did not succeed in isolating any individual compounds although 
he was led to believe that tyrosine was present in traces. 
Mr. Robinson continuing the work of Jodidi has recently succeeded 
in isolating leucin and isoleucin from peat soils after boiling with acids. 
Also, by adapting to his conditions the method for amino nitrogen re- 
cently revived by Van Slyke, he has been able to determine with con- 
