Glutaraldehyde fixative tonicity for scanning electron microscopy of delicate chick embryos

Fresh pullet eggs (White Leghorn strain) were incubated from 19-2ldium-gold and observed in a Cambridge S4 scanning electron microscope. Shrunken cells with intracellular yolk granules embossed on the surface are produced by the strongly hypertonic Karnovsky's fixer (Final: 2010 mOsm). Embryos fixed with modified Karnovsky's fixer (Final: 373 mOsm) possess surfaces with irregular microappendages. Swollen cells with few microappendages are observed when embryos are fixed in a hypotonic environment (Final: 250 mOsm or less). Ideal fixatives preserve a relatively flat surface, with cells bordered by smoothsurface microappendages. For adequate SEM fixation, fixative vehicle should be approximately isotonic for tissue, with aldehyde (2% or less) added to vehicle.