X-Message-Number: 4970
Date: Thu, 12 Oct 1995 08:04:57 -0700 (PDT)
From: Joseph Strout <>
Subject: straight freeze != homogenate

We are witnessing the gestation of a myth here on Cryonet, probably 
fathered by Mike Darwin but carried by most of the list, which I will 
attempt to abort before it gets too big.

Straight freeze, despite appearances, is NOT the same thing as a tissue 
homogenate.  A homogenate is made by placing tissue in a blender, which 
has two effects:

	1. parts are physically disconnected from their neighbors
	2. the relative location of each part is essentially randomized

(Note on #2: not really randomized, of course, but each part takes a 
chaotic path -- see physics of mixing.)  It is especially this second 
effect which makes reconstruction nearly impossible, even in principle.

A straight freeze, on the other hand, causes only effect #1, but not 
effect #2 since each "part" (disconnected bit of tissue) is locked firmly 
in place by the ice around it.  Position is preserved, and probably 
orientation as well.

A simple analogy should serve to illustrate the difference.  Imagine a
large, completed jigsaw puzzle.  For a homogenate, take the puzzle apart,
put the pieces back in the box, shake well, and then lay the pieces out
again (in random order) flat on the table.  For a straight freeze, take
the puzzle apart carefully, and put each piece back right where you found
it (spreading them out or overlapping a bit). 

If you stand back a bit and squint -- or turn the pieces over so you 
can't see the big picture -- then these two cases look very similar.  
This is, in fact, how it appears to the electron microscopist.  But when 
you actually sit down and start putting the puzzle back together, it is 
obvious that the first case is difficult, while the second is trivial.

Now.  I'm not actually suggesting that straight freeze be offered as 
anything but an emergency option -- a last-resort variation on what's 
already a last-resort procedure.  But it's not useless either, as the 
"hamburger" camp would have you believe.

,------------------------------------------------------------------.
|    Joseph J. Strout           Department of Neuroscience, UCSD   |
|               http://www-acs.ucsd.edu/~jstrout/  |
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