I am rather surprised to see the old toluene (or
carbon tet, or xylene--you name it, it's been done)
technique still being used.  And I used it for years
and years....what was I saying???  Oh yes.  Can't
remember what causes those memory lapses....

Anyway, seriously.  Several of the EM supply houses
sell a little "Heat Pen" unit that does a fantastic
job of flattening sections on the water in the knife
boat.  I switched to one of those over 15 years ago,
and at least exposure to solvent fumes at the
ultramicrotome no longer contribute to neuronal
necrosis!!!  I don't mean to slight anyone, (I'm at
home and don't have the catalogs at hand), but I do
know that Ted Pella carries the heat pen.  

As to knife angle, etc.  The usual 6 degrees should
work, and glass knives should last if treated kindly. 
However, if you can afford it, the "thick section"
diamond knife will speed things up a lot.  

Finally, heating the slide/water/section is critical,
but can be frustrating if you haven't done it before. 
I use a similar technique to those mentioned already,
but preheat the slide and drop of water briefly prior
to placing the section on the water surface.  You will
have to practice to figure out the best heating time,
temperature and drain/drying protocol for your tissue
and the size of the section.  I have done this for
block sizes that were nearly the whole embedding
capsule diameter (coronal sections of half a mouse
brain).  

Hope all of our responses will help.

Roger Moretz, Ph.D.
Dept. of Toxicology
Boehringer Ingelheim Pharmaceuticals

--- Elizaha@aol.com wrote:
> In addition to the heating all ready mentioned, you
> can also use an 
> applicator stick that the tip has been dipped/soaked
> in toluene and wave it 
> closely over/above the section ....either while its
> in your boat or still 
> floating on water on the hot plate...this spreads
> the section even more. 
> Don't touch the water or the section....
> 
> Elizabeth
> 
> 
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