Abstract

ACTERIA are very promising as materials for studies of mutability, be-B cause of their great speed of reproduction and because of the opportunity they present for working with populations that comprise enormous numbers of individuals. Changes in bacterial cultures which make the bacteria resistant toward certain specific bacteriophage strains have been known for a long time and have been assumed by several workers to be due to mutations This assumption has recently been confirmed in an important study by The experimental method used by these investigators consists of determining how many resistant bacteria are present in small cultures of sensitive bacteria, especially when the size of cultures is kept so small that only a few resistants are found, on the average, in each culture. Under these conditions some cultures are still found to contain a comparatively large number of resistants. This indicates that such bacteria probably belong to a single clone stemming from an ancestor which mutated to bacteriophage resistance earlier in the growth of the culture.