Rena....

We use a derivation of a formol-mercuric chloride fixative for use with
marine molluscs and a variety of other invertebrates.  It is a distilled
water, zinc clhoride, potassium dichromate mix.  The formalin is added
just prior to use.  Fixation times must be monitored and tissues removed
as the fixative denatures over time and has oxidized within 24 hours.  As
a less hazardous chemical, we adapted the use of zinc chloride in the
place of the mercuric chloride in the following formulation and it works
beautifully!  This fixative is ideal for the preservation of the cytoplasmic
granuoles and as a mordant for trichromes if tissues were not fixed in
this or Bouin's fixative.

HELLY'S FIXATIVE
20,000 ml   deionized water
  1,000 gm  Zinc chloride
     500 gm  potassium dichromate

Add 1 ml 37% formaldehyde solution added to 20 ml Helly's solution at the
time of use.

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Dodi Borsay Horowitz, HT
U.S. Environmental Protection Agency
NHEERL-Atlantic Ecology Division
Narragansett, Rhode Island
borsay.dodi@epamail.epa.gov