There were two scientists Paul Ehrlich and Edwin Goldman who experimented on animals by injecting blue dye into their blood stream, that was between 1880 and 1913.
All the tissues of the body, except the brain and the spinal cord turned blue. The scientist theorized that there was something isolating the brain from the elements that are exposed to the rest of the body. Another scientist, M. Lewandowsky then called this, “The blood Brain - barrier”
They determined that, neurotoxic agents only affected brain function when they are directly injected to the brain. The location of the brain barrier is the capillary endothelial cells within the brain. The endothelial cells of the brain are different from those of other organs because they are woven in a tight fashion that keeps paracellular molecular movement from occurring because the have no other connections called, “Transendothelial pathways or Intracellular vesicles”. In other …