The gemato-encephalic barrier and its importance for the penetration of various substances into the central nervous system

In 1921, Stern and Gauthier found that between the blood on one side and the cerebrospinal fluid and nerve elements of the brain and spinal cord on the other, there is a barrier, which they called the gemato-encephalic barrier. In what is its essence, what is the mechanism of its work and even where it is located, is not known exactly; but the fact of its existence is undoubted, as many substances circulating in the blood, even in significant quantities, never appear in the central nervous system and in the cerebrospinal fluid. Their action does not appear in the brain, not because they have no such action, but because there is a barrier to their penetration into the brain tissue, and under normal conditions they are retained at the border between the blood and the cerebral medium.