20.10.52
Dear ‘pall, 7

Thank you very. much for your letter and manuscript, and
pardon me for. anawering 80. late. I have been busy on a variety of
duties,and was so pleased to’ be able to start experimental. ‘work again
that I forgot ahauk to write to you and everybody else, IT am enclosin,
--gome pictures taken at Pallanza,a few of which were sent to all ‘parti-
. cipants. Meanwhile 1 have had a letter from Joshua,who states 3s" T
was delayed a few days in studying the "final “version of tur JGM paper

I must admit that it does read better now even than the American |
version.In order to avoid confusion,I think that all corrections in
‘proof should ‘be cleared through you. If some changes are poasible,
I would like to discuss the following" ', Iam not giving’ details here
of the eorrections oshua, but am preparing a list of
. “them ange fe eome Aiea Rees Shes to my mind,so that & can send you
. & copy/ Or beitea with you and which might have to ‘be’ used, ‘in case T
~. @annot receive or send back "in time the copy of proofs which Tt hope
to receive from you. You do not need to send a cppy to Lederberg, —
as was earlier ‘planned, For some of the corrections I ‘shall ‘need’
_ your. help - I hope you have a copy of the manusottpt in my hands, s0
- that I can refer to it in. the liat ; the copy “an ‘Kederberg' 8 hands
has. an entirely. different “numbering: of pages and lines. |

Meanwhile I also had a letter fron. Watson . , suggesting a
hypothesis and inviting you und me to join in a note about it. Watson
's hypothesis is rather. nice,and you will undoubtedly have heard of
it.It fits most of Neweombe's data; as to mine, it fits only the othe
way round,i.e,assuming that the eliminated ‘chromosome. —0T,as I still
believe most likely - piece of chromosome, is the other one.This may
be a difference in the strains employed by Newcombe and mysetf and
am therefore trying to put to a test this hypothesis.

A rather interesting new strain has xturned up. It is an
F~ strain which I obtained three years ago,which crosses with F+ at
a rate about 20x smaller than any other F- strain. I have not succee-
ded in trying to infect it with F+. When crossing to Fe, half of the
prototrophs are F+,half Fe ,but I do not yet kmow,except for two of
then,if the F- prototrophs are uninfectable as the F- parent strain.
The funny thing is that this 1:1 segregation was found on crossing
to three indepenendt F+ auxotrobhs, and no linkage with any tested
marker was found,so that this watnfectable, or F~resistantzcondition,
seems to be due to a locus on a chpomosome inherited independently
from the other markers, This locus gor maintenance of F is not,of
course, unprecedented in microbial genetics; see for instance K,k and
kappa in Parameétum, or even lambda and the locus linked to Gal. in
K-12, However,at the present point there are other interpretati ns
possible, If this theory were true, I would feel very embarrassed of
_. having used the symbol F in the Jem paper; it would undoubtedly be
preferable to use the maxd symbol % and reserve P,f for the locus,
Would you see many objections to changing F into in proofs ? It
oaucurs an about twenty different occasions. I do not know which symbol
_ you have ysed in your paper.I must also hear Joshua's reactions to it.
~ I am sure ‘the printer would charge for the alteration but q do: not
"mind this point. too much.

Thank you for sending the ‘fly wheel toy motor, my children will
be ‘delighted about it, There is one further favour that I should like
to ask you. I remember that ‘in the earlier correspondence, you mentioned
(I think to Lederberg) that a man called Lightbown | had found a strepto-
mycinase. Ir should be- interested in it,not quite for research, but for
routine purposes (making a medium for blood cultures,and sputum). Could
you perhaps let. me have the information necessary to get hold of the
strain,and of the’ information necessary to produce the enzyme ?

. I have no. diéa whether it ‘will be possible to me to come to
England next year, However, ‘I trust I shall see you ,and I ‘hope ‘Nora,
again for the Genetics and Microbiology congresses, Dates Will be 24-
-31 August in Bellagio,and 6-12 Sept. Rome, respectively. Meanwhiia In
the interval ‘there will be the Biometric Conference,where I have again
some time to waste on organization, but you might like to spend - ‘the
_ interval sightseeing, There are lots of places worth visting between
_ Bellagio and Rome. Lederberg should come also. —

— With best greetings also from ‘Pupa for Nora and- you.Pupa_ ‘de
working hard at her examination in Physiology.
Yours ever. °