11th September, 1951.
Dear Spiegelman,
Thank you very much for your letter and reprints, and also for the manuscript of your recent paper which I have only just read, having been away on holiday.  I am very grateful to you for letting me see this manuscript which I found most interesting and stimulating.
There is just one question I would like to put to you; have you tested the effect of galactose concentration on the rate of reversion of cells subsequent to growth in the normal concentration of galactose?  If so, what effect did you find, i.e., did it effect the speed of reversion or the proportion of positive colonies appearing after the point when mass reversion occurred in galactose free medium?  And were there any critical conc-n above which no reversion occurred at all, or was the effect gradual?  It seems to me that this might have an important bearing on any possible interpretation of your phenomena; and, incidentally, are you satisfied that your galactose-free medium (containing both peptone and yeast extract) is really completely free from galactose?  It seems to me that this might conceivably have some bearing on the production of the small quantity of positive 'mutant' which you ascribe to genetic factors.
I wonder if you would mind my holding on to your manuscript for a week or two longer and whether you have any objection to my showing it to one or two colleagues who are also interested in the subject?  I suspect we may possibly see each other in Paris next year.
With best wishes,
Yours sincerely,
M. R. Pollock.
P.S. Please note my change of add on, too! MRP.