Feulgen stain is a staining technique discovered by Robert Feulgen and used in

histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vi ...

to identify chromosomal material or DNA in cell specimens. It is darkly stained. It depends on acid

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolys ...

of DNA, therefore fixating agents using

strong acid Acid strength is the tendency of an acid, symbolised by the chemical formula HA, to dissociate into a proton, H+, and an anion, A-. The dissociation of a strong acid in solution is effectively complete, except in its most concentrated solutions ...

s should be avoided. The specimen is subjected to warm (60 °C)

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...

, then to

Schiff reagent : The Schiff test is an early organic chemistry named reaction developed by Hugo Schiff, and is a relatively general chemical test for detection of many organic aldehydes that has also found use in the staining of biological tissues. The Schiff ...

. In the past, a sulfite rinse followed, but this is now considered unnecessary. Optionally, the sample can be

counterstain A counterstain is a stain with colour contrasting to the principal stain, making the stained structure easily visible using a microscope. Examples include the malachite green counterstain to the fuchsine stain in the Gimenez staining technique ...

ed with

Light Green SF yellowish Light green SF, also called C.I. 42095, light green SF yellowish, is a green triarylmethane dye. Uses Biomedical It is used in histology for staining collagen; for that purpose it is a standard dye in North America. In Masson's trichrome i ...

. Finally, it is dehydrated with

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

, cleared with

xylene In organic chemistry, xylene or xylol (; IUPAC name: dimethylbenzene) are any of three organic compounds with the formula . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are s ...

, and mounted in a

resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on n ...

ous medium. DNA should be stained red. The background, if counterstained, is green. The Feulgen reaction is a semi-quantitative technique. If the only aldehydes remaining in the cell are those produced from the

of DNA, then the technique is quantitative for DNA. It is possible to use an instrument known as a

microdensitometer A microdensitometer is an optical instrument used to measure optical densities in the microscopic domain. J. C. Dainty and R. Shaw, ''Image Science'' (Academic, New york, 1974).T. H. James, ''The Theory of the Photographic Process'' (Eastman Kodak ...

or microspectrophotometer to actually measure the intensity of the pink Feulgen reaction for a given organelle. Using this procedure, it was early determined that interphase cells were composed of two populations, those with diploid DNA and those with

tetraploid Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains ...

DNA (two complete genomes). The nuclei looked identical, but one contained twice as much DNA. This gave rise to the division of the interphase period of the

cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication) and some of its organelles, and sub ...

to G1, S, and G2 phases based on the synthesis of that extra DNA.

References

{{Reflist Biochemistry detection reactions Microscopy Microbiology techniques Laboratory techniques Staining Histotechnology Staining dyes