“…Interactions between the members of a complex indigenous microbiota could be critical determinants of the delicate biochemical balance between the cohabiting microorganisms and the tissues of their host, the status of which determines the relative states of health and disease (Dubos, 1954). The existence of such complex, but little understood, interrelationships in the oral cavity is evident (Bibby et al, 1938;Van Kesteren et al, 1942;Bj6rnesjo, 1950;Thompson and Johnson, 1951). Although numerous antagonisms between members of the oral microbiota have been described, as manifested by inhibition of growth (reviewed by Rosebury et al, 1954), few instances have been reported of the inhibition of a specific biochemical activity of one microorganism by other microorganisms.…”