Feulgen stain

The specimen is subjected to warm (60 °C) hydrochloric acid, then to Schiff reagent.

Optionally, the sample can be counterstained with Light Green SF yellowish.

Finally, it is dehydrated with ethanol, cleared with xylene, and mounted in a resinous medium.

It is possible to use an instrument known as a microdensitometer or microspectrophotometer to actually measure the intensity of the pink Feulgen reaction for a given organelle.

This gave rise to the division of the interphase period of the cell cycle to G1, S, and G2 phases based on the synthesis of that extra DNA.

Black and white microphotograph of Feulgen stained , intact tick salivary glands infected by deer tick virus . Hypotrophied salivary acinus filled with amorphous masses of pinkstaining (=Feulgen positive) material (arrows). Scale bar = 10 μm.