I am sending you a copy of our ms. on some of the serial transfer experiments I mentioned to you last spring. We now suspect
that periodic selection may be due to a series of types producing different colicines (of Fredericq), and are starting exps.
I have just seen the Novick and Szilard opus, but its too late to refer to it as the ms. was sent off several days ago (to
PNAS). Their finding of types more "fit" is obviously the same thing as we found.
Recent exps. with UV on heterokaryotic conidia show that they are not essentially different from your K12 case with respect
to production of isogenicity. While the numbers of survivors on minimal and supplemented media are almost the same (as I
reported last spring), the colonies on supplemented turn out to be mostly homokaryons, as in your case.
This means that an injured nucleus will
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nearly always recover in the presence of an uninjured nucleus, but where such recovery is unnecessary for growth (as on supplemented
medium) the uninjured nuclei have a head start and produce a lot of homokaryons. In your case the central spots of lact which
appear in many of the older colonies make sense according to the above hypothesis.
Do you think Novick and Szilard really mean to imply that their data on time proportionality of mutation is inconsistent with
the two hypotheses they mention, namely error in duplication and monomolecular reaction? If this is so I think their reasoning
is a little sloppy. The first idea remains perfectly tenable if we assume that some critical period during which errors can
be made is greatly prolonged in their experiments. Furthermore it would be consistent with the failure of mutants to accumulate
in stationary cultures, a [ . . . ] which they seem to have ignored. I don't see why they are worried about the value
of A for mutation being much lower
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than for "known monomolecular reactions in condensed systems". In fact, this strikes me as being a rather stupid
comparison. The range of A values for such reactions is simply a reflection of the fact that reactions slow enough for A
less than 105 sec. cannot ordinarily be detected (measured). Thus the value of A can by no means be considered a general
characteristic of such reactions. Radioactive decay (probably the only true monomolecular reaction) is easy to screen for,
like mutation, and consequently A much less than that for mutation is often found. Anyway, N. and S. are certainly not denying
that mutation is first order, and this is probably all that Delbruck and [ . . . ] meant.
If the above remarks seem overly snide, I will admit to being somewhat piqued at Szilard for not sending me his usual pre-publication
In regard to your question about Peg, I think she is clear-headed and industrious. She has applied for a fellowship to go
to Italy and work with Buzzati-Traverso, but
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this may be impossible by them. It would be worth while to ask Delbruck his opinion of Peg in a few months. The Columbus
performance was due to the problem she was working on.
Werner Maas reports that the selection of non-temperature-sensitive pantothemicless mutants in K12 consistently gives complete
loss of crossability.
Ryan writes that he has hot stuff on lac- mutagenesis with some lactose analogue, but gives no details.
The [ . . . ] were alive.
Best to you and Esther
P.S. The army is breathing down my neck (I'm IA), but Columbia may be able to keep me out temporarily. Would you please
return the ms. when you are finished with it?