Golgi's method is a nervous tissue staining technique discovered by Italian physician and scientist Camillo Golgi (1843-1926) in 1873. It was initially named the black reaction (la reazione nera) by Golgi, but it became better known as the Golgi stain or method later.
Golgi' staining was famously used by Spanish neuroanatomist Santiago Ramón y Cajal (1852-1934) to discover a number of novel facts about the organization of the nervous system, inspiring the birth of the neuron doctrine.
The cells in nervous tissue are densely packed and little information on their structures and interconnections can be obtained if all the cells are stained. Furthermore, its thin filamentary extensions—the axon and the dendrites—are too slender and transparent to be seen with normal staining techniques. Golgi's method stains a limited number of cells at random in their entirety. The mechanism by which this happens is still largely unknown. Dendrites, as well as the cell soma, are clearly stained in brown and black and can be followed in their entire length, which allowed neuroanatomists to track connections between neurons and to make visible the complex networking structure of many parts of the brain and spinal cord.
This technique has since been refined to substitute the silver precipitate with gold by immersing the sample in gold chloride then oxalic acid, followed by removal of the silver by sodium thiosulphate. This preserves a greater degree of fine structure with the ultrastructural details marked by small particles of gold.