The golgi stain is a histological method used to study tissues, particularly tissues of the nervous system. It was first used back in 1873 when Camillo Golgi first employed it in the study of the nervous system. The “black reaction” became known as the Golgi stain which was then used prolifically by Santiago Ramón y Cajal to extensively document the nervous system of a variety of organisms.
It is stunning that even though this technique is 142 years old, and is still used in the study of neuroanatomy, yet we don’t actually know how the stain works. Why does the silver stain selectively enter some neurons and not others? In the case of the above through focus animated gif from the photoreceptor layer through to the bipolar cell layer, the golgi stain has selectively entered two bipolar cells in this field and not any of the others surrounding it, save for some wider field processes from other neurons that have also been selectively stained.