Having watched the debate last evening I feel that a histotech should be
running
as a presidential candidate, certainly would instill a higher level of
intelligence and logic.

Re freezing
I have dipped my fingers in liquid nitrogen for second or so but no
longer.
Initially the heat of your skin forms a vapor barrier around your hand.
This
only lasts a very short time. There is an effect in that while skin
appears to
show no effects, even at the histochemical level, nails tend to become
more
brittle after even this very short exposure.
This vapor barrier is the rationale for using a heat conducting material
such as
isopentane or slam freezing  to dissipate the heat quickly, and in the
case of
isopentane so that a vapor barrier does not form around tissues and in
doing so
slow down the rate of cooling and allow ice crystal formation.
I have used the methods described previously and have found no
difference
between them except for convenience. However, I have only used
relatively thin
pieces of tissue and I think that therein lies the secret of success
when using
any of these techniques. It must also be mentioned that different
tissues may
freeze at different rates and that the use of cryoprotecive agents can
also
affect the rate of freezing.
Barry