November 7, 1951

De. C. &. Clifton |
Departaent of BacterLology
Stanford University
California. —

Dear Dr. Clifton:

Thank you for sending the 20 additional ©. eold osultures in your
oKs series. They have just been subjected to preliminary tests for
crossabijity with K-12. Two of them, F-130 and K-201 appear to give
a ratner definite positive result; K-93. my also, but the initial test |
was ambiguous. If you ean give me any further information on the his- |
tory of these cultures, I would appreciate it.

In asking for additional cultures from you, I was aware of the posail—
bility that K-12 might turn up again. However, none of the cultures of
this set is likely to be especially close to K-12, for none of them
proved to be lysogenic on an indicator which reacts to K-12. If I am
wrong about this, I'd be glad to hear about it.

The proportdondit inter-fertility in this series is rather higher
than our general experience. However, most of the fergile strains have
come from human sources, either fecal or pathological, although they have
shown no other striking feature in common.

Yours sincerely,

Joshua Lederberg