Qctober 2, 1954

Dr. Melvin Cohn

Dept. Microbiology

Washjngton University School of Medicine
St. louis, MO.

My dear Cohn;

I will aceept your note as greetings, and return them warmly, For its
formal purpose (repbinte) it was quite unnecessary, though I rather lazily
save reprint mailings for an annual chore, It might straighten out the records
if you could let me know which of the reprints you do already have, accerding
to the numcers on the attached lists and I will send on whatever is missing that
I can later,

Your new project sounds fascinating, and all success in it, For my own
information, has anyone succeeding in getting certain continuation of antibédy
syntheags in proliferating explants? The best I had known was still not very
dramatic, some older work (by Meede I tiak) on tubarculin sensitivity. or do
you know of any good evidence of the sensitisagion of once-established explants?
Again, what I've seen had left me wore confused than enlightened, But there's
the challenge, I suppose/

Unfortunately there are too many looses ands still be ve cleaned up in K. coli
genetios for me to be abie to look forward very soon to tie refreshment of a
change, Lately, I have been preoccupied with the microscopic characterization
ef conjugel pairs in K-12, which proves quite easy after tne first time, The
peire last about 1- 2 hours, then separate, Both exconjugants can then proliferate,
but recoubinants ars found only in the ciones from the « parent celi. So
fertilization is unilateral and, as nad been suspected without strong preof for
8 long tine, we can rather aloppily consider i~ as "feunle" anf 74 or Hir as
male" (or, more accurutely,as hermaphroditic). The older programs on Salmonella
and on E. coli transduction are also continuings Esther still ties these together
with lysoganicity, and then more recently we have some new atudies on actinonycetas
and yess’ (the latter being a new angle on cvtoplasamic transfer), [tm not doing
a thing now on lactase, but Jacques probably told vou 6f Roris Kotments interest
in factivation®,

Give our regards to Kornbergs if you find a chance to pay us a vieit,
do give ts the opportunity of adding at least two more to your many Friends
in Madison.

Yours sincerely

Joshua Lederberg