Abstract
A study has been made of factors influencing the effectiveness of the "direct-coloring" thiocholine technique in demonstrating intracellular cholinesterases in motor neurons. It has been found that certain procedures likely to produce disruption of the neuronal membrane are necessary for efficient penetration of the ferricyanide component of the staining medium. The procedures used were osmotic shock and brief freezing of the tissue. The results are discussed with regard to application of the direct-coloring technique to electron-microscopy.