T HE causative organism of actinomycosis in man is Actinomyces bovis which is a fungus and one of the many microscopic members of the plant kingdom. It may be said in genera1 that the plant kingdom consists of four major groups: the thaIIi, the mosses, the ferns and the seed plants. The thalli may be further divided into algae and fungi depending upon the presence or absence of chIorophyI1. AIgae, because they contain chIorophyI1, may carry on a free and independent existence. Fungi, however, Iack this very important substance and, therefore, are either parasitic, Iiving on other organisms or saprophytic, Iiving on the dead remains of other organisms. Mycotic diseases of man may be superfIcia1 or deep seated. The superficia1 infections or dermatomycosis are due to the dermatophytes and may be classified as Microsporon, Epidermophyton, Trichophyton and Monilia. The deep seated infections are due to Actinomyces, Sporotrichum, RIastomyces, Coccidiodides and PhiaIophora and are characterized essentiaIIy by granuIomatous reactions. Any of these might cause primary fungus infections in those who tiI1 the soil or who contact pIants, hay, hay-straw, animals or their by-products, feathers, silk, wool and leather. SuperficiaI fungus infections are acquired by those who tend and care for pets, swimming ~001s and bath house attendants, dairymen and herders, bakers, preserve packers, fruit handIers and dishwaters. The deep seated infections are usuaIIy found in tiIIers of the soi1, cattlemen, florists, horticuIturists, wood-handIers and research workers. Actinomycosis in man was first reported by IsraeI in 1878 and since that time has been observed with increasing frequency. The occurrence of actinomycosis in the human, according to CuIIen and Gross, is seen most frequently in the region of the face, jaw or neck, comprising 6o per cent of instances. About 20 per cent of occurrences are found in the abdomina1 cavity particuIarIy in relation to the cecum or appendix or the adjacent abdomina1 waI1. In the next 13 per cent of instances the primary focus is in the bronchia tree, the puImonary tissue and the chest waI1. The remaining 3 per cent are confined to the skin or other viscera. In the generalized forms of actinomycosis the primary Iesion in the majority of instances is found in the Iung. The most noteworthy fact in regard to the primary lesion is that it may be so smaI1 as to be missed entireIy. It is frequentIy missed in the roentgenogram made of the chest. Likewise it is commonIy overIooked at autopsy even at the hands of the most skiIIed pathoIogist. Metastatic Iesions may be few or may invoIve many organs. The brain and the kidney head the Iist of most frequent sites of involvement. The cIinica1 course frequentIy presents a disease of marked chronicity in which the symptoms of maIaise, fatigue, low grade fever and weight Ioss may be so Iacking in importance as to disarm the clinician compIeteIy. It is onIy after the symptoms referabIe to the infected organs become sufflcientIy prominent and after the most exhausting diagnostic procedures are carried out that the true nature of the iIIness may be suspected onIy to be Iater con* From the Department of Urology, BeIoit Municipal Hospital, Beloit, Wisconsin.