July 15 1946.
Dear Dr, Luria-

Ee coli K-12 should te on its wey in a day or two; I've had to recover it
from our lyophilized stocks. While on the subject, can you tell me what is the
best way to put aside a phage suspension for preservation. We tried to lyophil
T-1 in milk without success. Can it be dried without inactivationy

I am preparing to isolate miltiple biochemical mutants in B/r per our
conversation last week. However, I must confess that I am a little confused
about the problem we discussed. As I see it, the inheritance of resistance
can be studied by using biochemical mutants only as the selective agent for
the occurrence of possible recombinations, The importance of establishing the
separability of the mutations in complex resistance (B/1,6 as compared with
B/1/6) is I think evident. It could be accomplished in two ways:

1, A~ X Bw/1,6 and isolate from the A+S+types A+B+/1 and A+B+/6

(susceptible )
2. A-/1 X B+/1,6 and fail to isolate A+B+, isolate A+B+/1, which would support
the allelis of the /l in the A~ anc the Be stocks here mentioned,

Conceiyably one could isolate using mitiple resistance as the selective
agent, but this is obviously confused by the occurrence of complex mutations
for phage resistanee. Recombination of nutritioml requirements should be demon-
strable using them alone as selectors, and only if attempts to obtain them
in this way fail would 1 suggest that it would be worthwhile to use the phage
‘selectors, I recall that you brought up another problem, but I would appreciate

it very mich if you could suimarize it for me.

Sincerely yours,

Joshua Lederberg