X-Message-Number: 3587
From: Brian Wowk <>
Date: Wed, 4 Jan 95 01:25:07 CST
Subject: SCI.CRYONICS Flash Freezing

        Although I generally agree with Perry Metzger's responses to
Jan Coetzee, I must take issue with one minor but significant point.
There actually is a way to cool faster than Newton's law indicates
is possible with external cooling, and that is to cool internally.
In fact, we already do this during cryonics transports when
a heat exchanger in a heart-lung machine circulates cold blood 
through the patient to cool them rapidly prior to freezing.
 
        The internal cooling concept could even be extended below 
freezing by "perfusing" with cold gaseous helium as was suggested
by Darwin, Leaf (et al?) a few years ago.  Why is this not done? 
Cooling below freezing must be done *slowly* so that cells have
time to dehydrate and avoid freezing intracellularly (which is
extremely damaging).  There is therefore no motivation to freeze
much faster than we do today with external cooling.
 
       There is one exception to the last sentence, and that would
be if we could cool *much* faster, or flash freeze as Mr. Coetzee
suggests.  The size of ice crystals formed is inversely related
to the rate of freezing.  In the limit of flash freezing, ice
crystals are extremely small, and even intracellular freezing
is not that bad.  (For proof we need only consider that brain banks
for neurological research flash freeze brain *slices* and get
excellent histological and biochemical preservation.)
 
        How could we flash freeze an intact brain?  Mr. Coetzee's 
reference to the Peltier effect is ridiculous, as Perry Metzger has 
explained.  The only way I can think of (other than installing a 
nanotech Peltier cooler in every cell ;) ) is to perfuse the brain 
with a non-toxic mixture of some *enormously* endothermic (heat
absorbing) reactants.  The endothermic reaction must somehow be
suppressed until the brain is completely perfused, at which time 
the reaction is triggered (microwave pulse?) and the whole brain 
instantly freezes (cracking in half in the process?).
 
        I doubt that any simple, known endothermic reaction has
a delta H large enough to do this job.  In principle I believe
one could be designed, although it might take Drs. Merkle and
Drexler with a general molecular assembler to do it.  Flash
freezing of intact brains is clearly not practical today.  
        
        On a more serious note, though, does the excellent histology 
acheived by contemporary brain banks suggest that we too should 
section and flash freeze our brains in slices?  Only the future
knows for sure.
      
--- Brian Wowk

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