GERM THEORY--"A new look at the biological formulation of the germ theory seems warranted. We need to account for the peculiar fact that pathogenic agents sometimes can persist in the tissues without causing disease and at other times can cause disease even in the presence of specific antibodies. During the first phase of the germ theory the property of virulence was regarded as lying solely within the microbes themselves. Now virulence is coming to be thought of as ecological. Whether man lives in equilibrium with microbes or becomes their victim depends upon the circumstances under which he encounters them. This ecological concept is not merely an intellectual game; it is essential to a proper formulation of the problem of microbial diseases and even to their control. --Ren¿ J. Dubos"