July 27, 1951.

Mise Marjorie Bohnhoff,
Department of Medicine,
University of Chicago,
Chicago 37, Dlinois.

Dear Missa Bohnhoff:

Thank you for contiming, so diligently, to send the E. coli isolates
fram your mouse experiments. I am greatly indebted to Dr, Miller and your-
self for taking so much trouble for this purpose.

| Unfortunately, a very large proportion of the isolates from mise
receiving streptomycin in their drinking water are now turning out to be
highly S*. I suspect, but cannot be certain, that the situation has been
changing in the direction of the establishment of a relatively few types
of in the treated portion of your colony- that is, that they may appear
by infection rather than frequentbnew mitation. Nhat bearing this may have
on your own results, I cannot say, except that I should not be astounded
if atreptoayein therapy now proves to be somewhat less effective than it
may have been several somths agp. Of course, these observations are restric~
ted to EB. ooli, and may be irrelevant to the apre important organisms encountered
in your studies.

At any rate, these strains are no longer very useful in our own work,
and I see no reason why you should continue to go to the trouble of shipping
thea. However, the few strains from animals not receiving streptomycin thera~
py continue, in large part, to be useful, and if you hawe enough of theee,
i would appreciate ypur continuing to send theg.

The last issue of Science carries a note, submitted over aix months ago,
on our preliminary @indings. I regret that I had ho opportunity there to
acknowledge your cooperatian, which began subsequently. I will, of course,
reserve reprints of these and other relevant publications for you and Dr.
Miller. Meanwhile, I would appreciate reciprocity in respect to the publi-
cations of your own current studies, i.e., the papers in Sefence (and elsewhere?)
on Kepay effects.

With best regards,
Sincerely,

Joshua Lederberg.