February 23, 1952

Dr. Felix L. Haas
Zoology Department
University of Texas
Austin 12, Texas
Dear Dr. Haas:

Thank you for your dotatled account of exveriments on auxotrochy and
phage resistance in E. coli 58-161. With respect to the spontaneous mtants,
there seems to be an irreducible discrepancy 1n our immediate experimental
findings, unless perhaps we are for some reason not recovering cr recog-
nizing the yeast—extract~requikAgg types. If you still have these, would
you be Kind enough to send a slant or two of a representative isolate so
that we can check it through on our complete and minimal media?

If this doesn't clear it up, we will try a few more runs, and let you
know if anything new happens. If you get back to the problem, I should be

interested to learn if the results are reproducible.

Yours sincerély

wd

Joshua Lederberg
Associate Professor of Oenetics