2 thoughts:
One, you always drop the sample into the melted paraffin 
not-freshly-cut-end-first:

cut end > X====|
                     ^  < held toward freshly cut end

So, the " | " end drops in first, vertically. Fluid dynamics will 
quickly flip a long, thin sample like this, unless it goes in 
vertically, so the freshly cut end lands pointing down.
Easily tested: hold some specimens at one end and note if they land 
opposite-end down, then hold more specimens by the other end and 
repeat. Hold some sideways, and see how they land -- sideways, or one 
end perferentially.

If it's not that, I'd bet on a static charge. All of the materials 
involved (specimen, paraffin) are insulators, so when you cut the end 
of the sample, you could be generating a static charge. If the metal 
embedding mold is on something conductive, or charged (-), and the 
induced charge is (+), then this might be able to flip the specimen. 
Assuming a dry, staticy environment.
This could be tested with an anti-static gun, and zapping the 
specimen and mold.

So, how long before this shows up on a CAP inspection?

Phil

>I have noticed an odd phenomenon many times, so I assume others must have
>noticed it too?  I often have slender, cylindrical specimens like vessels or
>mouse spinal cord that have to be cut in cross section and therefore have to
>be embedded "on end". Sometimes a specimen is a little too long to mount on
>end without the cassette resting on top of the specimen.  In such cases I
>take a scalpel blade and trim a bit off the length, to make the specimen
>"shorter". When I take a specimen that has been trimmed in this way, and
>drop it back into the stainless steel embedding mold filled with paraffin,
>the specimen instantly flips around and attaches on end to the bottom of the
>mold, always by the freshly cut end, just as though it somehow became
>"magnetized" by my trimming it. Has anyone else observed this?  (Please say
>yes, I can't be the only one!)  If so, does anyone have any idea how/why
>this occurs?  Obviously it is not true magnetism operating here because (1)
>tissue does not become magnetized, and (2) stainless steel is not attracted
>to a magnet.
>
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-- 
Philip Oshel
Microscopy Facility Supervisor
Department of Biology
Central Michigan University
024C Brooks Hall
Mt. Pleasant, MI 48859
voice: (989) 774-3576
dept. fax: (989) 774-3462

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