I did my "preaching" re: post-cryonics reassembly.
Then on Thu, 27 Apr 2000 hal@finney.org wrote:
> ... but I do want to point out that this model makes most sense if
> you think of the tissue as being frozen and then cracked apart.
Agreed.
> However in fact freezing is a dynamic, possibly chaotic process.
I don't think I would call it "chaotic". The question would be whether
there are specific molecules (perhaps those that are the most polar) that
serve as the nucleation sites for the ice crystals or whether the crystals
always start in a region of "pure" water. I would presume that crystals
will start inside and/or outside the cells and not near membrane surfaces.
> Ice crystals grow and spread through the tissues like spears, providing
> signifcant mechanical stresses to cells that are still in the unfrozen
> state.
Agreed, but they are either going to puncture the membranes leaving them
pretty much intact or else move the membranes as complete units. Your
comment does raise the interesting question of whether intracellular
or extracellular ice tends to form first. Intracellularly, cells are held
together by a fairly dense and strong cytoskeleton. They also have fairly
high concentrations of proteins and other molecules that are larger than
any ion channels. So, I suspect that intracellular crystals cannot grow
very much. That would leave extracellular crystals as the major source
of disruptions.
> The chemistry of the intercellular medium changes drastically, as
> water freezes and the concentration of larger molecules rises. The cells
> dehydrate as fluids flow through the channels or perhaps even through
> tears in the membrane, putting things into a highly unnatural state.
I generally agree with this, but the norms for cellular fluid content
and protein concentrations should be known, so "resetting" them should
not be particularly difficult. Harder will be the repair of membrane
tears, though if the scenario you describe is accurate, as the cells
dehydrate they should shrink until there is no remaining water and
you have a bag of condensed cytoskeleton, proteins, small molecules
and ice crystals.
We have to remember that in biology we freeze cells all the time.
In most cases this is highly reversible.
> This whole process occurs before the local tissue actually freezes.
> [ snip ] But even before things are frozen there will be damage.
> All of that occurs in the fluid state, and putting things back won't be
> as easy as assembling a jigsaw puzzle.
Agreed. But that is not the same as saying it will be "impossible".
You would have to have widespread dismantling of the fingerprints
of where the synapses were located and perhaps the loss of their
"qualities" to lose the information you need to recover the brain.
Robert
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