February 23, 1951.

Dr. R. Se Benham,
Department of Medicine,
University of Chicago,
fhicago 37, Dlinois.

Dear Dr, Benham:

Thank you for your letter of the 20th, and for the 20 cultures
which arrived today. As it happens, 20 is the most convenient unit
for the number of cultures to be handled together, so I am glad to
note that the mailing cartons will accomodate this number. I will
return the empty tubes and carton in a few days.

After a little further thought, I see that there 1s no point in
restricting the specimens to one culture per individual. Therefore,
I will be pleased to have any number of clearly distingu&&haéble types
if, as your labels already suggest is idkely, it is apparent where
the different isolates originate.

I will, of course, be grateful for your courtesy in funnelling
Miss Turner's collections to se also.

I just recalled your remakk that streptomycin may have induced
fermentative changes in some of your enteric isolates. I cahnot re-
member whether this was an in vivo or an in vitro phencmenon. If it
was the latter, so that controlled experiments could be carried out
on pure cultures, I should be very much intereated to hear the details,
so that I might try to repeat the phenomenon. My own experience, with
a limited number of pure cultures, has not included such changes as
a concomitant of variation to streptomyoin-resistance.

If I repeat my appreciation for your assistance and trouble, you
will get tired of it, and think me insincere. I remain therefore,

Yours sincerely,

Joshua Lederberg