dune 17 » 1948.

Dear Francis,

I know you mist be very busy this time of‘ year, but I wonder whether
you could take time out to write a formal but informative letter of recom
mendation for “Ur, Zinder, I have to have such letters to support any recom
mendagions I make to the Graduate Office, which Had the final veto,

Have you tried that 1% yet? i've found it to be a very useful pH indicator,
to take the place of ZMH in looking for fermentative mtants, While the reaction
ie a reduction to an insoluble red pigment (which is by the way fat soluble acedg.
to Van Potter), it is pil sensitive and occurs only near neutrality. I'a writing a
note to suggest its application to the primary isolation of lactose—negative
entericcpathogens, Have you heard Guthrie's story yet?

Sincerely, & best regardap