DEPARTMENT OF GENETICS
FACULTY OF MEDICINE, OSAKA UNIVERSITY

Joancho-33, Kitaku, Osaka, Japan.

February |, 1957

Professor J. Lederberg

The University of Wisconsin,
College of Agriculture,
Agricultural Hall,

Madison 6, Wisconsin, U. S. A.

Dear Professor Lederberg: -

Thank you very mich for your kind letter of Jan. él,

1957. I talked the content to Mr. Hirota, and he desires to
go abroad and to work under your guidance. I can guarantees
his scientific ability, but as he is still not good at
English conversation, he worries about the possibility
whether he is able to pass the examination of the Fulbright
Commission, or not. However, even if he fails in it, he
wishes to go abroad as soon as possible by his own expense.
I shall be very glad if you would agree to accept Mr. Hirota's
application for a position under the condition. If so,
please send me or Mr. Hirota the formal permission of the
position, because it is necessary to present the permission

to the Fulbright Commission.

to hear
Both I and Mr. Hirota are very sorry,that you have

some difficulty in the attempt to reproduce the result on
the removal of F from E. coli by the treatment of cobalt.
Recently, however, Mr. Hirota has found that F= strains are

obtained more easily by the treatment of acriflavin than
cobalt. For example, if F+ cells are grown for 2), hrs in
the broth containing acriflavin (200 ug/ml) at 47°C, many
F- colonies will appear as shown below.

Strain used Y-lo F+ . F-colonites/total colonies
Control (Broth, no acriflavin) 0/10
Experiment (Broth tacriflavin,

100 ~g/ml ) 5/10
Experiment (Broth + acriflavin,
200 ~vig/ml ) 10/10

Therefore, he states that he will try to get the
F- strain from any F+ strain for you, if you wish to
obtain it. Please send your F+ strains to him, and let
him try various methods.

Yours sincerely,

H,. Kikkawa -——
Professor of Genetics.