DEPARTMENT OF BACTERIOLOGY AND IMMUNOLOGY
HARVARD MEDICAL SCHOOL
25 SHATTUCK STREET

BOSTON 15, MASSACHUSETTS

January 22, 1958

Dr. Joshua Lederberg
Department of Genetics
University of Wisconsin
Madison 6, Wisconsin

Dear Doctor Lederberg:

I am sending you by airmail five ampoules of fluorescein
isocyanate in acetone which I promised you last month. Although
the material is moderately stable at room temperature I advise
you to keep it in the cold and in the dark. It can be used ac-
cording to the directions in the Journal of Experimental Medicine,
91, 1, (1950). After conjugation and dialysis to remove organic
solvents, the product can be put through a column of Dowex 2
chloride. We use 20 to 50 mesh | per cent cross-linked. This
removes the by-products of fluorescein which dialyze with diffi-
culty but which are not protein bound; this makes the problem of
non-specific staining considerably easier to solve. On tissue
sections we still unfortunately must use tissue powders as des-
cribed in the earlier papers but for bacterial cells this might
not be necessary. It is a matter for experiment.

Concerning the unpublished experiments which we talked
about, if you wish to cite them they should be ascribed to
Coons, A. H., and Tanaka, N. I intend to describe them briefly
in my Harvey Lecture next month which could perhaps be used as a
reference although it is not a very good one.

I greatly enjoyed talking with you and hope to see you
again soon. With best regards,

Sincerely yours,

t
Albert H. Coons

AH:VG

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