Dear Dr. Lederberg--I haven't answered your letter before this, because I hoped I'd get around to testing that galact-lactose
bug and could give you a report. But I haven't yet, as I want to finish up incomplete lines of work first. I'll let
you know as soon as I know.
Yes, I have considered using drug-resistance and, in fact, fooled around with streptomycin resistance (by plating) for a couple
of weeks, early last spring but didn't get very encouraging results. I may get back to it sometime, if nothing better
works but for the forward-backward measurement problem.