Central Enteric Reference Laboratory,
Central Public Health Laboratory,
Bolindale Avenue,

London N.W.9.

2oth September, 1955

Dear Josh,

I'm sorry that I apveared so obtuse in my reply to your last letier,
but the fact is that I hadnot connected my peculiar result in one of bhe
three way crosses with the F- tester stocks, Your impression is, in the

main, correct. The facts are as follows.

One of the last experiments I did was to do a triple cross between

W 1177 , W 2825 (= W 1875 cy, AHA W 2284, Certain anomolies were found
amongst the prototraphs which could be explained by reversion of W 2284
to F + , this was indicated by the heavy background growth present in
the control cross W 1177 x W 2284. On the other hand reversion at the
Ce locus in W 2825 would also explain the results and this too I think
had happened. W 1177 was perfectly alright in other control ctosses
and I did not regard W 2284 as a standard F = tester, hence my previous
reply. W 2284 was I think produced by passage through motility medium
by either Dave Skaar or Tom Nelson but I know no more about it. As I
left the lab a couple of days after reading the results I was unable to

check on the cause,

Helen is quite mystified by the absence of Weeds strains from
both stab and lyophil, as she is as certain as one can be at this
distance that they should be there. I can only suggest that somebody
has used them and misplaced them at some date after she had put them
away. Anyway she will send copies of the cultures when she is able to
get down to finding out if they are still viable ( I see no reason why
they should die). As I said in my last letter the only data she has,
other than her experimental results which will have had in reports, is
the fact that they are stated to be @oli B and that ane is Supposed to
be a copper 'mutant', She has no other information as to their history

or radiation resistance, etc.

I'm having medium trouble at present. EMS does not seem to be

working , i.e won't support recombinants, although the eosin is some of
the stock you gave to Clive. I'm now going to try DO instead, since I don't
really need the indicator fanction of EMS. Other than that just the usual
enteric routine, we are rather busy with para B outbreaks which mostly seem
to be due to Chinese frozen egg albumen - one outbreak over 400 - maybe its
a Red plot. ‘It certainly is giving the Ministry officials a headache.

Have just had a galaxy of Enterologists at the labs - Kaufiiman, Ewing ,
Hormaeche, and Lourie as part of a WHO commission on Shigella and coli =
lots of fatuous taxonomic arguments I gather,

Give our best wishes to Esther,

he,