November 3, 1952

De. L. Dienes
isssachusetts General Hospital
Booton 14, Mass.

Deer Dr. Dienes:

As you may be already weil aware, I will have an opportunity shortly
to discuas with you some of the questions mentioned fn your letter of
Septemoer 12, Twili be speaking Friday, November 14 to the meeting of
tie Northeast Branch of the 3.A.8,, and hope very such tc sea you there,

Of course we were very mich influence: by your and Fliensberger's
work on L-forms, from several points of view. I am still not sure whether
thay may play some role in the "filtrability" of bacteria in phage-treated
cultures. Wa heave not ande a aystemtic study of this, and cannot assess
its significance, wut vur routine chservations certalaly have shown that

@ the frequencg of “come-backs" is auch higher in phage-treated filtrates,

(containing FA) than in filtrates from ordinary brotk. However, it seems
almost certein that FA itweif is phage, and not the more organized particles
of "I-forms". The genetic activity of FA would also be difficult to recon-
cile with the i-form hypothesis, as I was already uncomfortably aware
at the 1951 Cold Spring Harbor Conference (cf. p. 439, right column,4th par.).
Still. we have to contend with your irrefutable observations-~ concerning
which KLieneberger'y final retraction of her confliettig hypothesis mst
convines any skeptic. I agree that the small forms sust have some biological
importance, and hope we will have en opporténity to speculate together on
this,

I hava not lately paid auch attentiog to the L-form problem, having been
preoccupied with more specifically genetic questions in £, coli recombination
and Saimonella transduction. We never did succeed in growing out the L phase,
but must admit that we did not press the question. Would it be convenient
for you to have on hand about November 14 some active cultures of L-type
from Salmonella, or lacking that, from Proteus so that I could get a better
impression of what we mist look for? For recombinatiof experiments, the
existing serological differentials betweem, 9.g., S. typhimurium ahd S.
typhi should do very well, but it will be esseatial to rule out phage-
transduction, which can give similar results. Inwill be very happy to
discuss or cooperate with you in any way that I am able.

}e Yours sincerely,

Joshua Lederberg

ccc