June 18, 1948.

Dear Bob,

I just want to remind pM to keep me informed héw that galactose~lactoseé
to galflac- works out. If that holds up, I wonder whether you could send
me a saaple. I'm interestad only in tying-it up with my las mtants 4n
KelZ, and pronise not to Decose inkerested in reciprocal mitations par s@.

A pro pos this igaue, have you considered using the mtetior to
streptonycin-resistance-requirement far such a system? Yany orcaniams
form a Glass of streptomycin resistant mtants whieh remire the drug
for growth (probably due to “overadantation"), Strentonyein sensitives
can be selected by plating on medium without strentomyein. Only 2 definite
fraetion of the streptomycin resistant mtants 2re, however, streptonycine .
dependent,

best regards fron ls, Lederberg,
" Sincerely,

f
2

Joshua “ederberz