[Modified impregnation method for staining apical dendrite and spine (modified Golgi's method)]

A silver impregnation method for the demonstration of apical dendrites and spines in materials long preserved in folmalin is reported. This method is a modified version of Golgi's Silver method and consists of the following procedures: The formalin-fixed tissue blocks were incubated in a solution containing 3% potassium bichromate (150 ml), 96% ethyl alcohol (50 ml), and concentrated acetic acid (50 ml) for 24 hrs. at 37 degrees C, and 4 more days at room temperature after changing the solution twice. The tissue blocks were then kept for 5 days at room temperature in a 5% potassium bichromate solution. After making a thorough rinsing for one day in tap water and three washings in distilled water, the blocks were impregnated for 1/2 to 1 hr. in a 0.5% AgNO3 solution, for a further 4 days at room temperature in a 1% AgNO3 solution, washed three times briefly in distilled water and again impregnated for 4 to 5 days in a 2% AgNO3 solution. Following a thorough rinsing in distilled water the tissue blocks were embedded in paraffin and 50 to 100 micron sections were prepared.