big honkin' samples

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From:Beckers <> (by way of histonet)
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In reply to Jeff Crews:

In the past I had some experience with large mount prostate tissue
specimens.  Standard histo molds you can get in normal sizes also come in
extra large-probably 4" by 2" or there abouts.  Check with the major histo
suppliers.  They have them.  Embedding is crucial to large specimens
because repeat shaving and reembedded costs you precious tissue.  Do you
have a stamper made of wood or metal with a surface smaller than the
specimen.? If not,  get one.  Stampers are small instruments made of solid
metal or wood that you apply pressure to the top side of the tissue while
you are embedding it in wax. Also obtaine large embedding forceps.  The
molds may be too large but that's ok-you can customize the size to the
tissue by using pieces of cardboard or thick paper cut into rectangles.
When you embed the large tissue piece make sure you have as much of it as
flat as possible oriented the way you want.  Before you place any wax or
tissue in the large mold place the rectangular card where you need it to
decrease the size of the mold (if you need less than the large mold size.)
Then begin embedding.  Make sure you have enough wax in the block to keep
the tissue supported while shaving and cutting on the microtome.  If the
block is too small or thin it may crack or break up under pressure-too
thick and it may not fit between the knife blade and chuck holder.  You
will need a microtome which can handle large and wide blocks.  Oh most
important-there are cassettes you can mount-"super size"  I believe onto
the large specimen and block so you can attach them to a microtome -  this
is tricky when you are embedding after the tissue is flat and covered with
wax you place this super sized cassette on top in the middle of the large
mold and fill with wax.  Make sure the wax gets in through the holes of the
cassette and fill it almost up to the top.  You will have to shave excess
wax off later in order to fit this in the microtome holder.  I hope I
haven't confused you.  Basically you need large molds, a stamper, forceps,
super sixed plastic tissue cassette(they are the same dimensions as regular
cassettes except they are much deeper. Works wonderfully with large
blocks.) and lots of patience.  this technique takes practice.  The cutter
should be the embedder because it helps eliminate human bias/error.
Shaving can be a challenge-use your histo experience and common sense.
Also trim the block edges carefully.  And when cooling the molds let them
become solid cold.   We did alot of these where I use to work and we all
became proficient in our own ways.  I enjoyed the challenge alot. That's
why I answered your inquiry.  Good luck.  You would be amazed at how good
the thin sections look from a huge piece of tissue when they are embedded
correctly.  Good luck.

Sue Becker
Albany, NY

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