The biopsy slide stained with the HE method shows in the abscesses the presence of irregular formed blackish -blue clusters. These are typical grains of the bacteria Actinomyces israeli. The actinomycetes earlier were classified as fungi. Today they are reclassified and belong to the bacteria, but kept their fungal name. In German they were called "ray fungi" and the disease got a similar name. In animals the Actinomyces bovis is the species causing actinomycosis. In the industrial countries this infection nowadays is seldom, but it is seen still relatively frequent in the developing countries and in the tropics.