The Wellcome Laboratories of Tropical Medicine,
183-193, Euston. Road,
London, N.W. 1.

17th Mey 1951.

Dear Dr. Lederberg,
Thank you for your letter of May 4th.

tI am sending under separate cover two reprints of the
paper as you request and also under separate cover sub-cultures
of the indicator strains 1404 and 1411. I must, however, tell
you that I have now succeeded in isolating a phage from the
former, using a third type of indicator strain. I have long
expected this to happen and I am now reasonably certain that in
time it will be possible to find phages in every strain of
Salmonella typhi-murium. It is all a question of discovering
the right indicator strain. As far as I can ascertain this
does not in any way invalidate the results which T have already
found, although the problems become more complicated.

I agree with you im thinkitg that it is unlikely that
cultures containing one phage type become superinfected with
another under natural conditions. It is not very easy to bring
“tWis= bout, even in artificial culture where the chances of such
‘dgubl¢@ infection taking place are of a high order. I have now
been able to carry out an investigation of a larger. series of
_ealtures from one area and the typéuel results agree practically

200K 9 With the epidemiological expectations:

 
 
 
  
  

* eo!

Yours sincerely, aE a ay