Camillo Golgi (Italian: [ka'millo 'goldZi]; 7 July 1843 - 21 January 1926) was an Italian physician and pathologist known for his works on the central nervous system. He studied medicine at the University of Pavia (where he later spent most of his professional career) between 1860 and 1868 under the tutelage of Cesare Lombroso. Inspired by pathologist Giulio Bizzozero, he pursued research in nervous system. His discovery of a staining technique called black reaction (sometimes called Golgi's method or Golgi's staining in his honour) in 1873 was a major breakthrough in neuroscience.
Black reaction or Golgi's staining
Central nervous system was difficult to study during Golgi's time because the cells were hard to identify. The available tissue staining techniques were useless for studying nervous tissue. While working as chief medical officer at the Hospital of the Chronically Ill, he experimented with metal impregnation of nervous tissue, using mainly silver (silver staining). In the early 1873, he discovered a method of staining nervous tissue that would stain a limited number of cells at random in their entirety. He first treated the tissue with potassium dichromate to harden it, and then with silver nitrate. Under microscope, the outline of the neuron became distinct from the surrounding tissue and cells. The silver chromate precipitate, as a reaction product, only selective stains some cellular components randomly, sparing other cell parts. The silver chromate particles create a stark black deposit on the soma (nerve cell body) as well as on the axon and all dendrites, providing an exceedingly clear and well-contrasted picture of neuron against a yellow background. This makes it easier to trace the structure of the nerve cells in the brain for the first time. Since cells are selective stained in black, he called the process la reazione nera ("the black reaction"), but today it is called Golgi's method or the Golgi stain. On 16 February 1873, he wrote to his friend Niccolo Manfredi:  I am delighted that I have found a new reaction to demonstrate, even to the blind, the structure of the interstitial stroma of the cerebral cortex.  His discovery was published in the Gazzeta Medica Italiani on 2 August 1873.

Q: what is golgi straining
A: a method of staining nervous tissue that would stain a limited number of cells at random in their entirety.
is black reaction a sickness?
he called the process la reazione nera ("the black reaction"),
he called the process la reazione nera ("the black reaction"),