Abstract
One hundred and eighty-three strains of Escherichia coli were examined for lysogeny and colicinogeny: 40.4% were neither lysogenic nor colicinogenic; 31.1% were only colicinogenic; 13.1% were only lysogenic; 15.2% were lysogenic and colicinogenic. Though the detection of lysogeny could almost certainly be increased by using a greater number of sensitive indicator strains or by using more sensitive methods, the results of this study suggest: (a) that lysogeny in E. coli is more frequent than found in earlier studies (Fredericq, 1952); (b) that lysogeny and colicinogeny are not correlated but occur independently in E. coli strains.