March |, 1961

Dr. Walter Plaut
Department of Zoology
University of Wisconsin
Madison 6, Wisconsin

Dear Walter:

This Is Just a remark on your note In Nature for November 5 ( 1
hope, of course, that you will be sending me reprints).

Apart from the possible radioactive effect of tritium Introduced
with thymidine, | think you should also consider whether there Is not an
isotope effect. If so, there might still be some traces of It with deu-
terlated thymidine that you could pick up by its Influence on the Incor«
poration of Cy,cthymidine.

Best wishes,

Joshua Lederberg
Professor of Genetics