dune 2, 1949.
Dear Max:

Your isolates of H168 were received in very good shape, and I had no trouble
relsalating the hoteronyggte. They all agree in being pure Iyl-, althohgh Lacy
and Mtly. The trouble 1 reported having with reisolating the heterozygotes from
the cultures you sent steas, I think, from my presumption that they were Xyly,
whieh they apparently heve not been since they reached you.

"@"~2l7 is being cheeked for its mtrition now; it is certainly a LacfMtl-
segregant. Are you surprised that it should have a lethal sib?, or just that
it was not predicted as such?

I really don't know what to make of the H-168 Xylose story. I have an old slant
ef it, which dces contain Xyl# cells, but I haven't been able to rehsolate any hetero~
sygotea from it, either on lactose or mannitol. This tube was a duplicate of the
one I sent you, and I am a little heistsant about. accepting the notion that this is
all a clerical error. I had just burnt my fingers then, you may remember, about
B-72: However, unless you happen to have earlier cultures from H-168, preferably
the one I sent you, to check up on the presence of Yyl# cells, I don't know how
it could be decided. Have you ever noted the presence of Xyl# cells in any deri~
vative of 1627?

Change of type could be a trivial coincidence. Segregation results in large nusbers
of cells with diverse requirements, and the technique used in reisolating y stocks
is identiesl with that used in the original isolation. Conseivably, the new H168
is the result of a new crossing. I am trying to reproduce the whcle phenomenon
with sone new isolates which are very similar to the original 168.

This week, I've finally 1aclated not one, but mo stocks which are heterozygous
for Mal, at the same time have repeated, affirmatively, reversion experiments
showing that this sane Mal, ds usually hemizygous. Althcugh Mal, vy, is very rare,
they do secur sometimes, and make the whole story that auch harder to interpret.
One of the Mal y came out of a cross (Lac) = x Lac,~) like that deapeibed in the
PHAS paper, not involving Het. Since this stock heterozygous for Lac, Mal, Xyl,
Mtl, and Gal, ani is a "spontaneous" heterosygote, it is certainly the culture of

choice fér the study of the latter. I'11 do some work on the segregation pattern
while youfire on you’ trips, and send He215 on to you later.

Don't distract yourself from your vacation, but if you can remenber anything else
about H-168, I'd appreciate hearing it.
Sincerely,

Joshua