Often tissue sections, squashes, or whole-tissue fragments tend to detach from the surface of the slide as it is moved from Coplin jar to Coplin jar of various reagents. This problem can often be solved by applying a thin film of Parlodion (also called celloidin) to coat the slide with a very thin plastic sac that holds the tissue against the slide surface. Such slides can then be carried along with other preparations during acid hydrolysis and through the rest of the steps of Feulgen reaction as detailed in Subheading 3.4. (see Note 8).
1. Put all slides to be coated into absolute ethanol for 2-3 min.
2. Transfer 40 mL of the stock 0.25% Parlodion solution into a 50-mL-capacity coplin jar or glass vial of a size to accommodate dipping of slides.
3. Transfer each slide from the absolute ethanol. Dip it into the coating solution and drain briefly on the edge of the jar.
4. Place each slide directly into 95% ethanol in a Coplin jar to harden the film.
5. Transfer sets of coated slides from 95% ethanol to 70%, 50%, and 20% ethanol solutions.
6. Rinse the slides in several changes of deionized water before proceeding with the acid hydrolysis step of the Feulgen reaction.
7. After coating as many slides as needed, decant the remaining Parlodion solution back into the stock solution bottle and keep stoppered in a safe place for later use.
8. Depending on the number of slides processed and the rate of evaporation of the solvent, the stock solution can be used for a year or more, but may require the addition of more of the 1 : 1 (v/v) ether/absolute ethanol solvent mixture to thin the solution. It should not be poured into a sink for disposal, but must be treated as a hazardous liquid waste.
9. Most of the Parlodion film on a coated slide can be removed after completing the Feulgen reaction to provide a minimal amount of background material when mounting cells in refractive index liquids for cytophotometry (see Note 9).
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