Department of Stockholm, Sweden

Food Hygiene, February 2, 1950
The Veterinary

College,

Experimentalfaltet,

Stockholm

Professor Joshua Lederberg
Laboratory of Microbial Genetics
The University of Wisconsin
Madison 6, Wis,

Dear Professor Lederberg,

I have sent you to-day my 12 se-
lected typhi-murium phages and 41 cultures representing
22 of the established phage types of S. typhi murium. I
am not able to send any representative of type 17 because
the only strain I had at my disposal was lost. I have not
included strains of type 23 as I am no longer quite con-
vinced that this is an independent stable type.

I hope you will excuse my long
delay in sending the phages and cultures. The reason is
that I took over a new department last year and therefore
have not had time to control these phages until now, With
the exception of a couple of small unimportant deviations,
the typing results I now obtained completely corresponded
to the results I obtained in 1947 and 1948,

The ampullae of phages that I am
sending, I brought with me to London in 1948 when visiting
professor Felix. I don ‘t hardly believe that the trans-
portations caused any weakening of the lytic effect of the
phages. I wish to mention, however, that phage 2 and es-
pecially phage 28 B have showm a tendency to gradually
weaken even when stored in a cold-storage room.

Am enclosing a list of the phages
and their homplogous strains and also of the different
type representatives,

In order to obtain correct results,
it is necessary to follow the directions I have given in
my monograph. Especially important are the composition of
the agar substratum (agar concentration 1.4 %) the amount
of substratum in the Petri’s dishes and how long they are

dried, careful regard to critical test dilution, and length
of incubation time,