November 7, 1956

Dr. Al Hershey
Biol. Lab.
Cold Spring Harbor, L.I., N.Y.

Dear Al:

I am sorry to bother you with such a chore, but could you do me the
favor of sending us a series of "authentic" wild type T phages, Tl-?7
plus your favorite host/indicator strain? We have been somehhat careless
over the years about recording the history of our own stocks—~ when and
on what passaged, etc.—- and before we make some blunder, I would like
to start again with a standard point of reference; "ely whatever you have.

Our onn work has given us few occasions to use the 7 phages, except as
tests for bacterial resistance-markers; right now, some of them are giving
very encouraging results as the basis of selection of coli mitants with
defective wall synthesis, viz., "L-colony" mutants. The rationale of this
is the wall as receptor of phage adsorption, and 1s faintly hezy in prac-
tice so far. The main problem actually is growing these "wull-less" cultures,
which we are only beginning to understand. ‘For example, while 100 u penicillin
per mj. is adequate to prevent bucillary proliferagion, and to give quanti-
tative formation of protoplasts, these will not grow ag tecoldnies with
less then about 1000u and preferable 10,000! questions of concentration of
agar, cations, sucrose and other nutrients are e.ually fussy and irrational. |
Anyhow, now is none too soon to standardize our pli ge stocks.

Yours sincerely,

Joshua Lederberg