Mixtures containing formaldehyde and glutaraldehyde.
The combination of formaldehyde with glutaraldehyde as a fixative for electron microscopy benefits from the rapid penetration of small HCHO molecules (paraformaldehyde), which initiate tissue structure stabilization. Rapid and complete cross-linking is induced by the slower-penetrating glutaraldehyde oligomers. This mixture is associated with the name of Morris J. Karnovsky from Boston. It is an example of a significant innovation that was only published in an abstract (Karnovsky, 1965). The original mixture contained 4% glutaraldehyde, which was a higher concentration than many people wanted to use (Hayat, 1981). Terms like “half-strength Karnovsky” became commonplace in the 1960s and 1970s. Fixatives of this kind allowed definitive descriptions of EM at the histological level, achieved within 5 or 6 years following the introduction of Karnovsky’s fixative, and they are still commonly used.