Hematein and hematin can be formed by the action on formaldehyde.

• A. True
• B. False
• C. Not applicable
• D. Sometimes

Answer: (B)

The essential idea is that the staining power of hematoxylin comes from its oxidation to hematein, which then forms the active dye complex with a mordant to stain nuclei. This oxidation is achieved by oxidizing agents or by exposure to air—not by formaldehyde. In histology, formaldehyde acts as a fixative that cross-links proteins, and it does not convert hematoxylin into hematein. Hematin, meanwhile, is a different compound derived from heme and is not produced in the hematoxylin staining reaction. Because formaldehyde does not drive the formation of hematein (or hematin) in this context, the statement is not correct.