THERE have been isolated in these laborator~ies from soil organic matter since this work was begun a large number of compounds which are so varied in their composition, properties, and origin, that they may be said to cover fairly well the principal classes of compounds encountered in other lines of biochemistry, and therefore the knowledge in regard to the chemical relationship, origin and processes of change accumulated in such other lines can be directly applied to the understanding of the biochemical changes in soils and the constitution of soil organic matter. Previous to these investigations the only organic soil compounds mentioned are the mythical humic acid, ulmic acid, geic acid, crenic acid, apocrenic acid, humin and ulmin, all of which are shown to be complex mixtures and therefore non-existent.
Of the compounds thus far isolated, some contain only carbon and hydrogen; some carbon, hydrogen and oxygen; some carbon, hydrogen, oxygen and nitrogen; and some carbon, hydrogen, oxygen, nitrogen and phosphorus. These compounds fall into the following classes: (I) Paraffin hydrocarbons, represented by hentriacontane; (2) hydroxy-fatty acids represented by ~-monohydroxystearic acid and dihydroxystearic acid; (3) organic acids of unknown constitution, represented by agroceric acid, parat~nic acid, l~qnoceric acid, and a number of resin acids; (4) esters and alcohols, represented by agrosterol,, phytosterol,