formalin pigment

[fôrmə-lĭn]
n.
  1. A pigment formed in blood-rich tissues that come in contact with aqueous solutions of formaldehyde that have acidic pH values.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.