February 16, 1951.

Dr. R. 3. Benhes,
Department of Medicine,
University of Chicago,
Chicago 375 Diinois.

Dear Dr. Benham:

First I must express my appreciation for the friendliness and courtesy
which was shown me by your staff and yourself during ap visit earlier
thia week. I am writing now simply to recerd the favor which I asked of
you.

The cultures which we should be interested to test for genetic recon
binatéon againet E. coli K-12 ara:

a): all lactose-fermenters related to FE. coli, including typical
Eecherichia, Aerobacter, and Klebsiella, and intermediate
eitrate-utilisers, etc.

b): delayed, slow or non-fermentera which would be described os
Paracolobactrum owing to motility, aerogenicity or inability
to classify ae Salmonelia or Shigella. Please do not include
Proteus or other spreaders if possible.

Although any information would be welcomed, I do not wis§ to impose
upon your routine. May I suggest that only the identification nusber,
the souree (F, 0, or other), and any remarkable properties only of unusual
cultures, be mentioned. I hope to check back with you for further details,
if any, on any cultures of unusally interesting behavior.

I enclose some more address labels and postage; please let me know
On entlosed pesteards if these run short, or any other alnor communications.

We can, I think, handlegas many cuktures as you can throw at us, and
are looking forward to this opportdnity of extending the scope of our inves-
tigationa.
Youra sincerely,

Joshua Lederberg
Associate Professor of Genetics