February 20, 1951.
Dear Doctor Miller-
I certainly enjoyed my visit with Miss Bohnhoff, your colleagues, and yourself, and am sorry only that time was so short.
We are quite ready to begin plowing through some of the E. coli material from your mice that you referred to in our talk.  Aside from the routine isolations from feces, I wonder whether you have picked up any more or less virulent E. coli from the irradiated animals.
As I mentioned, N-12 seems to be remarkably toxic, and I have been losing a goodly number of my rabbits with IV doses of 10 9-10 10 cells.  I would like to follow this up somewhat, especially as some of the other strains to which K-12 can be crossed do not appear to be nearly so toxic.  Can you suggest a more convenient test system?
Our tests for crossability with K-12 are usually carried out in groups of 20 strains, so that this would be the most convenient unit, on our part at least.
Yours sincerely,
Joshua Lederberg,
Associate Professor of Genetics