The Concept of Stability and Some of Its Implications

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Abstract
The authors discuss the "pure culture" concept and suggest that a factor of stabilization must also be considered. From work with coliform bacteria, particularly the "citrate mutant" and Bacterium colimutabile, and from observations made by Evans on the effects of a chemical stimulus on bacteria, the authors conclude that bacteria differ with respect to the ease with which they "domesticate" under laboratory handling to the point of stabilization and with respect to their retention of characteristics once recognized. Instability is apt to be more marked with respect to certain test substances than to others. The authors describe how one would proceed to obtain a large group of strains each distinct and yet all derived from a single parent cell; such complexity is fortunately not common. Workers are, however, urged to be on guard against unstable strains which confuse the laboratorian and complicate taxonomy. Such strains might be studied by the method of "multiple subculture." If a strain, concerning which there is doubt, is studied by the testing of each of 10 colonies chosen at random from each of 10 serial platings, done in not less than 10 weeks, and gives on each of the 100 tests so made the same reaction, the authors suggest that it be considered "stable.".

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