Illustration of early brain barrier experiments by Ehrlich and Goldmann. These early experiments elegantly demonstrated the compartmentalisation between the central nervous system (brain and spinal cord) and the peripheral organs. A. Trypan blue is delivered peripherally [86, 88]. The dye does not penetrate any organs of the central nervous system, which both researchers suggested was due to the central nervous system having a lower affinity than other tissues. B. Trypan blue is injected into the brain . The brain and spinal cord were stained, while the peripheral organs were not.