Phase-partition fixation and staining of Drosophila eggs

Aqueous solutions of alcohol-acetic acid-formalin or glutaraldehyde-acrolein were shaken with heptane and heptane phase used for fixation. Phase-partition fixation is akin to fixation with vapor. The organic solvent, immiscible with water, penetrates hydrophobic membranes and carries the fixative in contact with water phase of the tissue. Only the fixative enters the tissue, without changing the ionic and water-soluble substance concentrations in the tissue. The quality of this fixation for optical or electron microscopy was as good as that of any conventional fixation method. Staining with basic fuchsin after 2 N HCl hydrolysis gave brilliant staining of nuclei, more intense than that with Feulgen reagent, while cytoplasm remained nearly colorless. Fixing and staining procedures for Drosophila eggs are given.