pyronin

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of a group of xanthene dyes used as a biological stain, especially to detect or track the presence of RNA by staining it red.

from The Century Dictionary.

• noun A basic aniline dye, of a red color, used in histological technique. Chemically it is the chlorid of tetramethyl- or tetraethyl-diaminodiphenyl-carbidtrioxid.