Humic substances are high-molecular substances in the humus soil, which have a non-uniform (amorphous) macromolecular structure. The dark colored substances represent the first sufficiently stable basic product, which is formed from the bodies of dead organisms (plants and animals). Although most of the chemical composition of macromolecules cannot be determined, their basic structure is recognizable: humic substances are composed of nuclei, bridges, and reactive side groups. The core often consists of benzene, indole, pyrrole, naphthalene, pyridine, quinoline or furan. Oxygen, nitrogen, carbon, simple hydrocarbons or secondary carboxylic acid amides primarily act as bridges. Carboxyl, carbonyl, methoxy, amino and hydroxyl groups are predominant in the side groups. Humic substances can only be described statistically in terms of their chemical structure, since the substance mixture varies according to location and season.