Individual constancy of numbers among the oral flora.

The inteinal environment of the human mouth is conditioned by a multitude of factors among which the interactions of bacterial species are particularly accessible to close scrutiny. In vitro models of mutual influences among microorganisms (Rosebury et al., 1954) furnish a means by which we can investigate some of the mechanisms which regulate the numbers of bacteria and the proportions among co-existing species. Appleton (1940) stated that "the qualitative and quantitative characteristics of a microbiota are in a state of dynamic equilibrium, determined by the kinds and relative numbers of the microorganisms already present and of those being introduced and of those being lost, and by the physical or nonorganic factors of the environment." Bibby (1939) observed in bacterial smears from the mouth that "given groups of organisms tended to maintain the same relative frequency of occurrence." Lammers (1953) speculated that "the impression of inertia conveyed by the constancy of the oral flora can result only from a balance of microbiologic forces." The quoted impressions may be sufficient justification for exploring the basic regulatory mechanisms. However, if "the quantitative interrelationships of the various microorganisms" are truly "characteristic for each person" (Williams et al., 1953), then this individual constancy should be amenable to more exact mathematical definition.