[Use of potassium ferricyanide in histochemistry]

Karnovsky and Roots offer to use potassium ferricianide for coloured detecting the products of acetylcholine hydrolysis by cholinesterase. The method is based on the reduction of ferricianide to ferrocianide which forms with copper ions, present in the solution, unsoluble ferrocianide. Some properties of ferricianide ion, however, (stability, large size and great hydratation) make it difficult for the substance to penetrate the native cell membranes. The method by Karnovsky and Roots applied to laminated muscular tissue and to the rat nonfixed whole diaphragm, and to the sections from nonfixed tissue of the cat skeletal muscle verifies space isolation of ferricianide from the enzyme localized at the other side of cell membrane.