P.O. 326
Puerto Vallarta, Jal.
Mexico
I live in a very primitive way and I have no means to type a letter and less yet to have copies made.  So if you think the enclosed information might be useful to Dr. Morse please do send it to him in Denver.
Rene Cohen also has spent a year in Lwoff's lab in Paris and who now work with Delbruck on Phycomyees [?] has done a few experiments on lysogenization by [lambda] which might be useful in their results for us.  He measured lysogenic cells by Luria's "Lac technique" and I think that his measurements are correct.
He grew his bacteria (stain 112 of Wollan[?] [ . . . ]) to about 5 to 8 10 ^ 8 centrifuged and suspended then in buffer the phage were adsorbed for a short time, and
anti-lambda serum added to inactivate the non adsorbed phages and the instant[?] diluted in broth (tryptone) at 37 degrees.  Then at different times afterward 
he measured the number of lys-genic cells.  He obtained the following result [TABLE]  The multiplicity of infection was about 3 or 4 phages / bacterium ( as 
his absorption was not very good ~ 60 % he had used about twice as much as the adsorption mixture and he had [ . . . ] to use high titer anti lambda serum
to get rid of the unadsorbed phages.
The thought that his result could be due to the fact that before plating the bacteria they were introduced for a short time in melted top agar at 44 degrees Celsius thus giving them a temperature shock to shat they could be sensitive for about 20 to 30 minutes after infection.  He then proved the point by giving 3 to 4 minutes at 44 degrees Celsius  in broth then putting back the bacteria at 37 degrees and plating at different times as in the curve[?] above, since the curve obtained as exactly the above one (temperature shock at lower temperatures that 37 degrees C had no effect at all)
Cohen thinks also that the shock effect may be produced already in 30 " of 1 ' . Hence apparently to obtain results which are reproducible (with the plating techniques) one should leave the infected bacteria in broth at 37 degrees for 20 to 30 minutes.
Having thus controllable conditions Cohen studied the effect of multiplicity on the efficiency of lysogenization.  He does not find "refractory" bacteria as 
Peggy Lieb[?] and as I find them always and I don't know why.  His results are as follows (see verso)
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[BEGIN PAGE TWO]
[TABLE]
I think he calculates his percentage of lysogenes by dividing the number of lysogenic colonies by the total number of bacteria minus the number of non bacteria.
This sort of result can be explained but certainly do not prove the assumption, says Cohen if one assumes that a single phage fer[?] bacterium never lysogenizes, 2 ph/bact have a probability of lysogenization of 40%, 3 to 4 100 % , 5 30% etc.  The very low efficiency of lysogenization at small multiplicities could then be dueto the fact that at these multiplicities only a small proportion of the bacteria are infected with 2 or more phages.
I have sent these results to Arber in Geneva as he seems to find that the number of defection prophages introduced with the Gel [ . . . ] depend very much 
on the multiplicity of infection. . .
This is all for today. Maybe that this letter will reach you before the 1st of the new year.  So let me wish you that 1957 brings you a lot of success
Yours
J. Weigle