The CO2 freezing microtome is very useful for studying peripheral nerves,
where one needs 40 micron or thicker sections to follow the nerve.  I have
found that 4 hr in 10% formalin is adequate fixation prior to looking for
cholinesterase in 40 micron sections.
   Alkaline phosphatase allows one to follow capillaries in 40-60 micron
sections from a CO2 freezing microtome.   I have found that 4 hr. fixation
is usually adequate.
   I have occasionally used a CO2 freezing microtome on unfixed skin with
good results in studying phosphorylase and glycogen synthase.  Unfixed
stomach, on the other hand, tends to fall apart.