CONTROVERSY has surrounded the role of the normal microbial flora in health since the early days of microbiology. Pasteur, for one, hypothesized that the normal flora was essential to life.¹ Some years later, his hypothesis was tested and convincingly refuted by Reyniers and others at the Lobund Laboratory, University of Notre Dame, who demonstrated that the germ-free state could be maintained for successive generations in various laboratory animals.² Metchnikoff, in one of many differences with Pasteur, argued that indigenous microorganisms were antagonists that competed with the host for factors essential to life.³

Metchnikoff's proposal has not been so easily rejected. . . .