X-Message-Number: 2188
Date: 30 Apr 93 21:12:56 EDT
From: Mike Darwin <>
Subject: Patient Racking

      I wish to echo Charles Platt's comments about Brian's cavalier
attitude about racking patients.  Patients are not big homogenous blocks
of ice that are interchangeable and may be cut from a frozen river with a
chain saw when more are needed.  Rather, they should be regarded as large
masses of poorly reinforced and incredibly fragile glass.  Furthermore,
shame on Brain for assuming that water-cryoprotectant mixtures will
behave like ice.  No way, Jose.  All that physics education...and it was
apparently just wasted!

	In vitreous blocks of solution and in frozen water-cryoprotectant
solutions just tapping on the container at -150*C can set off a wave of
fracturing.

      Finally, while not wishing to beat a dead horse, I would point out a
very simple experiment anyone with a soda bottle, a pencil, and a string
can do.  Attach the pencil to a length of string and try to lower the
pencil into the container without it touching the neck.  Now imagine that
the pencil is a 70 kg man on the end of a wire cable.  Unfortunately, I
don't have to imagine it.

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