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SUMMARY: During a stationary phase induced and maintained by the exhaustion of histidine, the total number of histidineless Escherichia coli (h−) remains constant as does the cytological appearance of the cells. If glucose is available to the starved bacteria they die at a rate of c. 10−2 per hr., while mutations to a histidine-independent (h +) condition occur at a rate of c. 10−9 per bacterium per hr. Bacteria adapted to use lactose behave essentially the same way when it, instead of glucose, is available during starvation; but if the starved cells are not fully adapted, death does not occur or is very slow (c. 10−3 per hr.) and the rate of mutation is c. 10−10. When no carbon source is available to the starved cells, mutations cannot be detected.
The following predictions served as tests of the hypothesis of cell-turnover, wherein some bacteria lyse only to be replaced at the same rate by the growth of others— the mutations are presumed to have occurred during this cryptic growth:
Reasons are given to suppose that the mutations result from errors in the replication of genetic material which is in the process of turnover within the non-dividing cells.