Golgi black reaction and the history of the study of living axons

In 1873, the famous Italian morphologist C. Golgi invented a unique technique for coloring the nervous tissue with which he received magnificent preparations that opened the world a microscopic picture of the brain and the peripheral nervous system. The technique, called the black reaction, was characterized by a surprisingly contrasting identification of a structure that neurohistologists called an axon or axial cylinder. The name of this structure lasted almost a century and a half, but suddenly the intravital microscopy revealed that the argentophilic techniques, including the black reaction, reveal not the axon, but only the sharply compressed, thinned structure of the axoplasmic cytoskeleton, which we call the axial line. As a result, the Ranvier intercept cone becomes invisible. It turns out that in the course of the argentophilic treatment of myelinic nerve fibers, the filamentous-tubular protein polymers of the axoplasm is aggregated, which leads to a decrease in the degree of their dispersity and aggregation. As a result, a tight, thin, elastic cord is formed. Around him, between him and the myelin sheath, unremembered in neurohistology the Mautner space is formed. Intravital microscopy thus, transforming static morphology into kinetic studies, is able to clarify the knowledge of the structure of the nervous system.