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/ | `------------------------------------------------------------------' Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=4970