June 29, 1951.

Dear Harry-

We returned from extended travels just a few days ago. The references
I promised to send you are:

Poltock, a.R., 1950 Penicillinase adaptation in B. cereus.... Br. J. Exp. Path.,
31:739-53 (Dec.) and, less important,

Strandskov,,F.B., 1947 J. Bact. 53:555-59 ( adaptation to Cl-pab). The latter
I am convineed is a case of selection of resistant mitants from microcolonies
on the plates containing the inhibitor.

Sincerely,

Josima Lederberg