June 22, 1952

Dr. Stuart Mudd

Department of Microblology
University of Pa. Medical School
Philadelphia 4, Pa.

Dear Dr, ,Mudd:

For some of the work I'm doing now, I should like to have two distinctive
vital stains that can be used to tag individual cells of F. coli. Triphenyl-
teérazolium works very well as such a stain, but unfortunately, the other
tetrazoles I've tried have a reddish tinge so that they cannot be readily
distinguished from it under the microscope. Can you suggest, from your own
experience, another tetrazolium derivative whose intracellular granules can
be microscopically distinguished from those of the triphenyl compound?

The application I have in mind is fairly obvious: to tag the cells of
each of two parent cultures so that I can identify mixed pairs, if they occur.
I have used only the single tetrazolium, but unfortunately, the granule does
not divide with the cell, so that after a period of growth one cannot be
sure of the parentage of an unstained cell.

Can you suggest any other vital stains that might be applicable?

Yours sincerely,

1. oe
‘Josma Lederberg ——