What is the first step in the hydration process?

The first step in the hydration process in histology is to wash in decreasing alcohol concentrations. This step is essential because prior to hydration, tissues are typically cleared of xylene, which is a solvent used in the processing of tissue samples. By washing in decreasing concentrations of alcohol, starting from 100% ethanol (the highest concentration) and moving towards a lower concentration, the residual xylene is effectively removed from the tissue. This gradual transition prepares the tissue for subsequent hydration with aqueous solutions.

As the percentage of ethanol decreases, the tissue becomes more compatible with water, facilitating the final step of rehydration which involves introducing a staining solution or further aqueous solutions necessary for the staining procedures. In this context, washing with decreasing alcohol concentrations directly addresses the need to transition from a lipid-soluble medium to an aqueous medium, ensuring that the tissue specimens are adequately prepared for the next steps in the staining process.