Paul is absolutely correct and a great explanation of the way to define 
formalin pigment quickly.  It is always best to be sure they have fresh 
formalin in the morgue and if possible with tissues of interest to change 
the solution within a reasonable time frame of a minimum of once a 
month.  Brain tissue particularly will be fixed better and more completely 
if the formalin is changes several times in the first one to two weeks of 
fixation as the autolysis occurring naturally changes the pH.  This can 
cause the buffering salts to form a crust around the outer areas.  This 
will prevent penetration of the fixative and cause poorly fixed center of 
the brain.

I have also used the old standard of an iodine step followed by sodium 
thiosulfate solution at the end of my deparaffinization step with good 
rinsing prior to staining to remove pigment.

Best Regards,

Pamela A Marcum
Manager, Histology Special Procedures
University of Pennsylvania
School of Veterinary Medicine
R.S. Reynolds Jr.  CORL
New Bolton Center
382 West Street Road
Kennett Square, PA 19348

Phone - 610-925-6278
Fax     - 610-925-8120
E-mail - pmarcum@vet.upenn.edu


At 11:10 AM 1/9/2006, Paul Bradbury wrote:
>The situation you are decribing, with old solutions of formaldehyde, long 
>storage times ususally associated with morgue specimens, is a classical 
>formalin pigment-producing scenario.
>
>To confirm that the pigment is formalin pigment (correctly known as acid 
>formol hematin) just examine  a section containing the pigment using a 
>polarized light microscope. Formalin pigment is birefringent and will 
>appear bright on a dark background. No other common pigments are 
>birefringent. Also if it tends to be more concentrated in areas where 
>there are numerous red blood cells, in blood vessels, in spleen, etc., you 
>can be pretty sure you are dealing with formalin pigment.
>
>To get rid of the pigment from the sections, treat the de-waxed sections 
>with saturated alcoholic picric acid for about 30 minutes, then wash the 
>sections very well to remove the yellow staining, then stain as usual.
>
>Paul Bradbury
>Kamloops, BC, Canada
>
>
>MARY JOHNSON wrote:
>
>>hi histonette, I am having problems with formalin pigments, I am sure it 
>>is because of the out dated Formaldehyde that the moruge is using. Can 
>>any one help me prove this  what test can i use? Is the paper pH ok to 
>>prove this. I need help with this one
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