The association of these two organisms in the body has been noted by many observers in connection with both normal and diseased states. Many points, however, remain obscure, and the literature on the subject is scattered and more or less confusing. The relation of the bacillus to the spirochete is a subject about which differences of opinion exist. We will not discuss their identity or nonidentity here, assuming, however, their almost invariable association in certain localities and in certain processes. In this paper, we will attempt to furnish a background for a discussion of infections of a putrid and gangrenous character for which these organisms appear to be commonly responsible. In doing so, we shall first present data concerning their more common normal habitats about the body, a subject to which little attention has been given. Later, we shall discuss a number of disease processes with which they are intimately