August 5, 1948.
Dr. R. R. Roepke,
Stamford Research Labs.,
American Cyanamide Company,
Stuaford, Cont.
Dear Ray,

Thanks for arranging to send te that szapls of Phosphine Glv (IE assume
tact GAR und GR are syncnomous; one wes uged in the publication; the other
was on the bottle end in your letter). As far 2s we could tell, hal@ a dozen
transfers thoough barely bacterhestatic concentrations had no effect on the
lysogenichty of the Salmonelli. used. However, I huve hed tc interrupt this
work because, .uite sucdenly and unexpecte ly, 2 new lead cx.e up re the
bacterial aygute- quite pcessibly < mutation in cne of cur stocks which
modifies the life cycle sc that Lhe diplephase or heterozyrcte is somee
what stabilised, .s it is in yeust. Until I've learned how te renroduce the
phenomenon regularly, I don't dare let it go. But the dats se fur collected
should exclude, once and for all, the transforming substance sort of inter-
pretation for recombinatlon in K-12,

Incidentally, Z£ I haven't mentioned this before, the photonreflectometer
was completed according to the design you sent, and is working quite nicely.
However, I haven't had time to sit down and figure out how to calibrate it
fcr the appreciabha biank reading (light seatiered by water) I suppose, one
eun just subgract this.

Yours sincerely,

Joshua Lederberg.