PETER BENT BRIGHAM HOSPITAL NORBERT A, WILHELM, M. D. 721 HUNTINGTON AVENUE FRANCIS D. MOORE, M. D. DIRECTOR SURGEON-IN-CHIEF BOSTON 15, MASS. GEORGE W. THORN, M. O. MERRILL C. SOSMAN, M. D. GUSTAVE J. DAMMIN, M. D. PHYSICIAN-IN-CHIEF RADIOLOGIST PATHOLOGIST-IN-CHIEF October 24, 1956 Dr. Joshua Lederberg Department of Genetics University of Wisconsin Madison, Wisconsin Dear Dr. Lederberg: Thank you so much for sending us the four strains of Escherichia coli, requested in our letter of October 2, 1956, Since a reprint of your article entitled "Sex Compatibility in Escherichia coli" is not available, we would appreciate a recent reprint of any article dealing with F+ and F- characteristics in E. coli, Very sincerely, SE (Mrs.) Ruth Kundsin, Bacteriologist to Dr, Carl W. Walter \