Which reagent is used as the fixative in Wright's stain?

Wright's stain is a widely used staining technique in hematology for the examination of blood smears and bone marrow. The reagent that serves as the fixative in this process is methanol. Methanol is effective because it preserves the cellular morphology and allows for the staining of cells without significantly altering their structure. Fixation with methanol prevents the degradation of cellular components and facilitates the adherence of the cells to the glass slide, which is critical for obtaining accurate staining and visualization under the microscope.

While ethanol, formalin, and acetic acid are also common fixatives in histology and cytology, they serve different purposes or have varying effects on cellular structures. Ethanol can cause dehydration and ultimately is not typically used for the fixation in Wright's stain. Formalin, while a very effective fixative for many tissues, introduces cross-linking that can obscure cellular details. Acetic acid tends to lyse red blood cells, which would not be desirable when preparing blood smears for examination. Therefore, methanol is specifically chosen for its suitability in preserving blood cell morphology while allowing for the optimal application of Wright's stain.