dune 4, 1948.

Dr, Ye E. Luria, _*

Dept. Bacteriology, ,
Indians University,

Bloomington, Indiana,

ihorkoooienr
Dear luria,

dust a few remarks siamering from our conversation in Minneaphais,
I suppose that you are quite right that there are some obscurities in the
mechinisin of recombination in “#12 that have to be cleared up. In time, I
shall certainly be attending to it, but I still don't think thot so~ezlled
kinetic axperiments will contribute very mich. However, I have repeated
"timing" the occurrence of the recombinant prototrophs afainst wild type
Cells put on the suse nedlum at the same time, und find that my earlier
statement is quite incorrect. There is adifference amounting sometines te
Kmore than 24 hours between the growth of wild type and the dovelopment of
prototrophs. There fs also certainly a residual background growth of the
mutants {nooulsted, but ¢e. enough to allor the developnent ef double~
reverse-mtations. I hope 4 dorl't have to go into that ngadn. Your ealeulation
that inoculating, say,107 cells per ec. will result in « mean diatance between
"sells" (ise. the centere of micrpeolonies ) of 25 u or more is quite correct
( 100 ve or 46 uj. However, it met be obvious that if there is a random

tribution of distances, the proportion of cell pairs with ad distance

of less than x will be given by 1 - e “4, where a is «/46 to the third power,
For small values of a, this is mux merely a, and, for example, .1% of the
"calls? will be ppired at « distance of 4.6 u. Considering the formation of
miorocclonies, this leaves ample room for the ralativaly rare occurrence of
cell fusions, and I cun see no contradiction on these grounds. To go a ead
and prove that just this hanpens may be anather story. It is not so simple
a8 verying the concentrations of the " resetante!! » because a) the physiclogieal
snooul alent SeBSGH ASAE fMteS'ae, oF, the aletccolentge depends on the

But whet is strangest of all to my mind is the suggestion that has
been offered that transforming factors re « more likely interpretation. If
80, these substances wil) have to possess remarkable properties, even beyond
those of the pneunceoccus syaten; Put I imagine that the busis of this stg
gestion is the quirk that some bacteriologists beve for soley that bacteria
are a law unto thenssives and that what holds (4.0. séxuslity) for anything
else cannot be trus of « bacterium, red of course, they Ba right.