1-9-48
Dear Dr. Lederberg
Many thanks for your letter of August 24 and the culture of L-type [ . . . ] L-21.  When I have tested it, I will let you know my findings.
Under seperate corr I send the strain W 0459, 37-38 mutated[?] from blood, of L typhin[?] type 2 and for my experiments on the xylose-dulcitol relationship.  I do not think this phenomenon is due to a [ . . . ] shift mutation in which the capacity to ferment one sugar is accompanied by the loss on another, and vice versa.  The phase which does not ferment xylose grown on dulcitol medium as on the medium without dulcitol which the xylose-fermenting phase specifically
inhibited by dulcitol.  Perhaps this may be due to a fermentation of dulcitol without acid production by xylose of the original weakly fermenting form. I have
shown cases of simultaneously acquired fermentation of more than one sugar, but no cases of shift-mutation you ask about.
Yours sincerely
Martin Kirstensen