CARNEGIE INSTITUTION OF WASHINGTON

DEPARTMENT OF GENETICS

COLD SPRING HARBOR, LONG ISLAND, N. Y.

May 21, 1951

Professor Joshua Lederberg
Department of “enetics
University of Wisconsin
Madison, wisconsin

Dear Joshua,

Thanks for your MGB note. We do not expect a regular
issue until Fall, mainly because I am too busy now to
take the time to get one out.

I was most amused by your decal technique, mainly
beeause Niek Visconti, who is baek with us now, has been
working out the very same procedure. About 7 or 8 months
ago, he deopped an EMB plate butter side down, and was
very impressed by the neat imprint of colonies on the
floor. This started him off on the decal idea, end he
did some work with it in a easual way, but never got it
working quite perfectly, apparently because he was trving
filter paper instead of velvet. With paper, the whole
colony is occasionally pulled off the plate, and the
imprint is not always perfect. So you see, I wouldn't
think of knocking the idea -- we are very glad to hear
about velvet.

Have you thought of one use of this teehnique that
seems quite promising to us? That is to spot colonies
seectored for ch:racters that ure not visible, i.e., phage
sensitive and resistant. Plate irradiated gmimmzxx cells,
make imprints of the grown colonies, spray some with phage.
If a colony with a pissing sector turns up, find the
eorresponding colony on the original plate, and fish to
see if a sector of phuge-sensitve cells can be demonstrated.
The same principle could be used, as you can imagine, with
other types of mutational characters, and might be useful
in the study of phenotypic lag.

We are about to start a run on the local velvet supply.

Regards to all -- see you soon.

Sineerely yours,

Evelyn M. Witkin