F UNGUS infections have been shown in recent years to be common in both man and animals. Of these, actinomycosis occurs much more frequentIy than is generahy recognized. The offending organism, the actinomycete, is being exten.siveIy studied by various mycobacterioIogists who have demonstrated that there are a number of pathogenic, as we11 as saprophytic, species belonging to this group. The numerous cIassifications offered are unsatisfactory and do not incIude various synonyms, such as Discomyces bovis, Streptothrix foersteri, SphaevotiIus bovis, etc. For practica1 purposes the pathogenic forms may be divided according to the three weII-defined types of infection caused by them. The most common form, “Iumpy jaw,” is caused by Actinomyces bovis (Harz’). A second form, madura foot, is due to the Actinomyces madurae. The most interesting is that caused by the acid-fast organisms, the Actinomyces asteroides (Eppinge?), found most frequentIy in man, or the Actinomyces farcinica (Nocard3) that infects cattle. Magnusson4 on the basis of an investigation of actinomycosis in cattIe and swine, concluded that actinomycotic-Iike Iesions are frequently caused by bacteria of the type isoIated by Ligniers and Spitz,5 or staphyIococci of the type described by Magron.6 This probabIy expIains the faiIure of many investigators to cuItivate the actinomycete from certain chnical cases which are suspected of having actinomycosis. CoIebrook’ has found, in 80 per cent of human cases of actinomycosis, an associated cocco-bacihus, termed by KIinger8 B. actinomycetum comitans. That these organisms play an essentia1 part in the pathogenesis of the disease is doubted by Henrici,g who states that in the “metastatic lesions the ray fungi may be found without any associating bacteria which can be demonstrated either in smears or cuItures.” The origin and habitat of the actinomycetes, and the mechanism by which they gain entrance to the body are stiI1 in dispute. The organisms are widespread, occurring in dust, poIIen, or chaff from grain staIks. The saphrophytic members of the group, which at times acquire parasitic habits and become pathogenic, may also be found in soi and in the aIimentary tracts of IarvaI insects, as we11 as about the teeth, in the tonsiIIar crypts and in the gastrointestina1 tract in man. RegardIess of the reported modes of transmission of the Actinomyces, it wouId seem from the known data that the disease is not contagious and that the essential factors which cause the infection must be direct transmission into abraded skin or the presence of an aspirated or ingested virulent pathogenic organism in an area of decreased resistance. Actinomycosis occurs in a11 parts of the world in both sexes and at a11 ages. In the United States SanfordlO has shown that it is more prevaIent in the upper Mississippi VaIIey and the Northwestern states. Apparently exposure is important in its transmission; statistica data prove that 80 per cent of cases occur in the maIe and that it is more frequentIy observed in the third and fourth decades of life. No tissue or organ is immune to the ravages of actinomycosis, as was shown by Sanford and VoeIker” in their statistica