dune 30, 1953

Dear Norton:

The cultures you requested abe being sent under separate cover. I
think you will have beéter success with the outrient broth + .6% agar
stabe.

ly notes are not haniy just now-— the tranaduction-protection expts,
were about as follows:

Infect SW#-950 with 22(LTa), mltiplieity about .15. Plate see- on
D(O) + meth, with and without 227(99950). Dilute out and plate on EMB Lac
with and without 227. ‘the ie done with untreated SW-950. The
results measure the protes against 22¥ resukting from infection with
22, and the recovery of (nearly) all the transductions in the 15% of
protected (1.0. 2infected, and subsequently lyso } S%950, It ds
essential to use suspensions nearly free of (rpugh) 22V-resiatant bacteria,
and to ensure that 227 le completely blocked by prior infection with 22.
Perhaps your 22 is sore virulent.

Owing to the low mitiplicities, the experiment is hardly feasible
except with this high rate of transduction in SH-950.

and some of the survivors still have)
or too uneven. It takes a long time for
to

catastrophe. Many of the tubes
was too
mo déffuse in ant accumilate. If we

Evelyn Witkin wrote recently for cultures for the E. coll crossing expts.
Do you think you cam ensure that they will be kept from year to year? The
1/2 mtrient agar stabs should do quite well for these too.

Sincerely. 3

Joshua Lederberg
P.S. Have you seen

Ineki's rat Acad.
Pea ee