June 14, 1950

Dear Dr, Cavalli,

or. .ederberg has shown me your recent letter and thought
that 1 misne mention to you a similar experience with "pseudo-
prototrophs,

In a cross between two strains of 5. typhiemurium, both
with double nutritional deficiencies (histidine, threonine by
leusine, isoleucineevaline) there consistently arose numbers
of small colonies that did not have any nutritional require-
ments and yet did not atiain parental growth on a synthetic
medium, Jeveral fermentative markers were added to these stocks
and though both parental types were recovered, no recombinants
were found, ihe story was complicated as both parents were
lysoenic and mitually antagonistic with the resultant prototrophs
badly plaqued and often completely lost on transfer to a synthetic
medium, .he lysis would certainly afford opvortunity for
mutual feeding, but alone it can not explain the pseudctrophic
behavior of the offspring.

10 attempts were made at antigenic analysis although the
parents were of different phases, however in light of your

observation such might prove interesting.

Yours truly,

Yorton winder