A General-Purpose Method of Silver Staining

A method of silver staining for paraffin sections has been described. Sections should be fixed in either Nonidez fixative, 4 % formaldehyde, or 4 % formaldehyde saturated with mercuric chloride. The sections are impregnated for 16 hours in 1/20,000 silver nitrate at pH 8 or 9 and developed in a glycine physical developer after the reducible silver has been removed with a 2 % solution of sodium sulphite. The effect of pH on impregnation has been described. A spectrum of staining was obtained in which nerve fibres began to stain appreciably at pH 7, cell nuclei at pH 8, cell cytoplasm at pH 9, and connective tissue at higher pH values. Therefore, impreg-nation should be carried out at pH 8 to obtain a good staining of nerve fibres and at pH 9 if some staining of cell bodies is also required. IN recent years, a number of methods for the silver staining of paraffinsections of nervous tissue have been described. Probably the most impor-tant have been those of Holmes (1947), Romanes (1950), and Samuel (19536). Although these methods vary in detail, they have the common factor that impregnation is carried out at a controlled pH in a dilute solution of a silver salt. Holmes and Samuel used silver nitrate and Romanes used silver chloride