17/10 / (0d

Dear Dr. Hayes,

Thank you for your two letters,which reached me
with some delay, as I am at present in Italy, I am enclosing a
small sample of threoninex ,(dl~) about 1.2 gms, which T hope will
enable you to carry on with your researeh until you get your
supply. You don't need to bother about restitution, I am only sorry
I have a syall amount myself and cannot send you the 2 gms. As
concerns biotin, I have very limited quantities myself and only
in solution, which make it @ifficult to d@end a sample. Anyhow, you
wi-l find taoat BDH supplied regularly biotin vials cohtaining 0.1
microgram each, and ¥t Ashe Laboratories, 22 Vicboria St.,London,
supply biotin ig vials of 25 micrograms each. I have never invem
stigated tue biotin needs of 58-161, since I have found that my
culture either backgutated to biotin independence, or my glucose
contained biotin,since the strain could grow with methionine alone,
This is no embarrassment howverm,since ,at least for my purposes,
methionine alone was a sufficiently good marker ,better than any
~ have ever tested, In fact, it is extremely difficult to
get back mutation for methionine dependence. The ord r of nggnitude
of biotin requirements shouldm, anyhow, be kaw lower than 1078

other

I have dtarted to work with your Proteus cultures,
but I have found it difficult,so far, to obtain good markers. On
SMB with glucose, fructose, there is no apparent fermentation. Iiy
bacterlophuge cultures do not attack Proteusm,and so I am -ore or
less left with the biochemical deficiencies markers, which I am
trying to obtain at present. I shall let you know as soon ag I

am able to get souetiing done,
24 very glud to har tu:t you are taking an interest in
the problem of recombination, which I find very fascinating, bu'

very @ifficult indeed.

Yours sincerely