The black reaction.

Camillo Golgi (1843-1926) invented the black reaction in 1873, when he was head physician at the hospice for old people in Abbiategrasso, near Milan. Unlike the procedures that were available before its invention, the black reaction was able to reveal neurons in their entirety, i.e., with all their processes. This weighty event at first passed unnoticed. The first stirring of interest in the black reaction outside Italy began in 1885. The reasons the Golgi technique took so long to receive wide international attention are here analyzed. After it became known, the black reaction was widely employed for almost 30 years, during which time it was responsible for bringing about major advances in our knowledge of the microscopic anatomy of the nervous system, as well as in other fields of study. A number of results obtained by other researchers with the black reaction were vitally important for establishing the neuron theory. In the period between the two World Wars, the Golgi technique was almost forgotten, but returned in vogue once more around the middle of the 20th century following the introduction of the electron microscope to neurocytological research. One-hundred and twenty years after its invention, the black reaction is still widely employed, not only in combination with electron microscopy, but also as an autonomous technique for light microscope studies on the organization of the nervous system in normal conditions and after experimental manipulations.