The Concept of Stability and Some of Its Implications.

Following first recovery of a bacterium by cultural methods there is a period of laboratory manipulation designed to provide a finished product known as a "pure culture." This technical aspect of bacteriology has for its object the production of a bacterial growth, all organisms of which may be thought of as descended from a single parent cell. It is still the belief of many that such a pure culture, in fresh and vigorous growth, will on all occasions give identical reactions under like experimental conditions. Probably there are bacteriologists who look upon the process of obtaining a pure culture solely as the elimination of totally unrelated microbic species. Others, who more clearly comprehend the ecological and genetic considerations, realize that in addition to this factor there is a further point in the process of "domestication," namely the adaptation by the organism in question to life on culture mediums. It is quite conceivable that in this process the freshly isolated organism may present among its innumerable descendants some whose mode of reaction better adapts them for survival than others. Domestication is not complete until the culture is made up practically entirely of that type of cell best adapted for in vitro life. If the process stops short of this end subsequent propagation of the strain is likely to result in inconstant results. The total process of domestication to the point where subcultures of the organism under study will present constant and uniform reactions under optimum experimental conditions, Stuart, Griffin and Baker (1938) have called "stabilization." The capacity for prompt and complete stabilization of a bacterial culture is not a constant. Some isolations are much more readily stabilized than others. The degree, furthermore, to which