Picric acid is a strong coagulant of nucleoprotein and leaves DNA soluble. It is particularly recommended for fixation of glycogen and for tissue that is receptive to which type of dyes?

• A. Acid dyes
• B. Basic dyes
• C. Lipid stains
• D. Silver stains

Answer: (A)

Picric acid acts as a strong protein coagulant while leaving nucleoproteins soluble, which reduces nuclear basophilia because DNA isn’t fixed as tightly. With nuclei less strongly stained by basic dyes, the tissue’s staining shifts toward components that bind acidic dyes. Acidic dyes like eosin readily color the cytoplasm and connective tissue proteins, so tissues fixed with picric acid are particularly receptive to acid dyes. The fixative’s ability to preserve glycogen also fits with its overall staining pattern, but the key idea is that DNA solubility and protein coagulation favor acid-dye uptake over basic-dye uptake.