YALE UNIVERSITY

OSBORN BOTANICAL LABORATORY
NEW HAVEN, CONNECTICUT

July 12, 1947.

Dear Evelyn:

Your more extensive paper, in Genetics, finally appeared, I
was glad to see.If you can spare it, I would appreciate a reprint.

There is only one point in your published work which I cm
bring myself to dispute about, and even this is more in the nature
of heckling than a serioud criticism. On pp. 233-234 you disouss
the question of the induction of the "/r" mutation by ultra-violet.
The application of a dose of 3800 ergs/mn was reported to increase
the frequency of "/r" from .001-.005 % to 3.3 - 4.9 %, measured in
the incubated population. In view of your very excellent selection
experiments, we may take it that differential multiplication plays
no large role. The major site of action of selection would be during
the radiation, by slective killing. In order to evaluate this factor
which as you say, certainly "exaggerates" the values, one looks for
a comparison of the survivals of B and B/r using this dose. Figure 1
however extends to doses of 1800 ergs/mm.< only. At this dosage, pS =
mxxx@5xforx ca. 5.5. From the induction experiment, pS (d=3800; coli B)
= -log 30/2x108 = 6.8. To account for an increase of a thousandfold,
pS (B/r) would have to be 6.8 - 3 = 3.8. Since pS (d= 1800) seems already
to be 3.5, such a contingency seems quite unlikely, but I would have liked
to see more specific data. To restate the argument, there were let us say
.005% x 2x10° mtanss or 104 in your original sample. After irradiation
there were 4.9% x 24 or about 1.2. For these mutants to have originated

as a sample of the original 104, the killing of B/r with this dose cannot

exceed kxxzmans |- .012%. At d= 1800 there is already ' 005%. Could there be

so sharp a break in the killing curve between 1800 and 3800 ergs/mm* ?
This question may arise in some other people's minds also.

To my mind, your "population" experiments were the best
part of the work. Have you tried at all to isolate inhibitory
materials from Mixed cultures held Rea for varying lengths of
time? After all, there are "natural" radiations, which should
have some slight selective action, accumulating over long periods.
The metabalic basis of the adverse selection which you observed
would be, I think, very important for the detailed interpreta-
tion of the mechanism of radiation resistance.

I am writing a review of bacterial genetics, partly for
my thests, and partly for publication. If you should happen to
have a carbon copy of your manuscript, or perhaps positive prints
of the lantern slides which you showed at the Symposium, I should
be most appreciative to recei@ve them on either loan or gift.
I am particularly ingterested in what you might have to say, either
for or off the record regarding the zero- and end-point manifestatzon
of your induced mtants. | -

Best regards,

Yours sincerely