The principal cutaneous and mucous membrane lesions in which fusiform bacilli and spirochetes are found are well known. Their causative relationship, from a primary infective point of view, to such diseases as Vincent's angina, ulceromembranous stomatitis,1 erosive and gangrenous balanoposthitis, noma,2 putrid pneumonia and gangrene of the lung,3 would seem well established. However, it is still maintained by many that in most instances these organisms are but secondary invaders of tissue already injured or diseased. In fact, such conditions as ulcus tropicum, hospital gangrene, mercurial, bismuth and arsenical sore-mouth and certain putrid and gangrenous lesions are almost certainly the result of secondary invasion by these symbiotic "opportunists." In these conditions an orginal solution in continuity of the skin or preexisting disease has so often been determined before marked inflammatory symptoms have developed that there can be little doubt concerning their secondary character. On the other hand, whether