The original Karnovsky’s fixative, developed by Dr. M. Karnovsky, was extremely hypertonic with 5% Glutaraldehyde and 4% Paraformaldehyde in 0.1M Cacodylate buffer. This fixative has been modified to lower aldehyde concentrations and even the use of Phosphate buffer. In fact, the name “Karnovsky’s” is now a general term for any fixative which contains both Glutaraldehyde and Paraformaldehyde of various concentrations in a buffer of choice. The aldehydes in this fixative complement each other; paraformaldehyde is a small single carbon mono aldehyde which penetrates the tissue quickly and denatures proteins by reacting with the alpha amine group; glutaraldehyde is a larger 5 carbon dialdehyde which has a slower penetration rate, approximately 1 mm/hr, but crosslinks proteins with the two aldehyde groups

stabilizing the structure better, reducing possible extraction during the subsequent processing steps.

View the Kirsch Note here