UNIVERSITY OF ILLINOIS

DEPARTMENT OF BACTERIOLOGY

362 NOYES LABORATORY OF CHEMISTRY
URBANA

November 9, 1956

Dr, Joshua Lederberg
Department of Genetics
University of Wisconsin
Madison 6, Wisconsin

Dear Josh:

As I promised, I checked up on the nature of the
absolute negative in the Lac, cistron. It bears your number
W- 3133, equal to Lac,g,. All the other Iac,'s we have so far
tested are cryptics.

I wonder whether you would drop me the number of the
condenser you mentioned that could be used for both short and
long working distances, and which also permits dark field
illumination.

I want to take this opportunity to tell you that I
really had a wonderful few hours in your laboratory and I
have since enjoyed them in retrospect. I have repeated the
protoplast clonal growth with the coli. I intend to make a
serious attempt next week to get the megaterium to do the
same thing.

a

With kindest regards to Esther and yourself.
Sincerely yours,

Sek

S; Spiegelman
Professor of Bacteriology

SS: jb