Jerry Chi-Yuan Hu [mailto:ragnarok@ruf.rice.edu] wrote: "....I am looking
for an embedding medium that is not toxic and hardens to an appreciable
stiffness above 0oC..."

There is an albumin-gelatin method that uses glutaradehyde to set; it
produces a stiff rubbery gel that cuts pretty well frozen or with a
vibratome.  There is some toxicity from the glut but standard precautions
deal with it.  Reply if this might be of interest to you and I'll try to
find the details--we haven't used it in almost 20 years and I can't put my
hands on it right now.  Maybe another reader uses it?