vay 23, LOLE.
Dr. %. 1. Savage,
Reseurch Laboratories,
The Upjohn Cumpuny,
" Kalamazoo 99, «ich.
Dear Dr. Savage,

I shall be glad to give you any information that you would like. Your
letter, however, does not mike it clear what kinds of autants you are in-
terested in. A reprint is enclosed describing . technijyue for the recovery
of nutritionally exuctihg matants. Reverse atants, or mtants with a less
exicting nutrition are obtained by selecting for them in a synthetic nediun
ducking the grovth fectors concerned. Fersentative mtants (enzynatically |
deficient) are cbtuined by examination of colonies on Tosine ethylene Blue
agar containines the supaur in question. Yeverse mitants eeuin ure selected
for by incculating very heavily into synthetic mediun with the sugar in
question ae the sole carbon source in a concentrution of .05 -~.10 4%.

Virus resistant mutants are recovered us the survivors in s large pcpulation
of lysis by the phige, I aa now working on methods of detecting mutants
affecting enzynes which result in an over all chinge of rH rather than pH
{the lstter being tested for with the ™B mediug) but have had no pronounced
success,

Sincerely yours,

Joshua wederberg
Assistunt Professor of Genetics,