The Blood Brain Barrier

TLDR: The concept of a barrier between blood and brain and the brain and spinal cord derives from the classical studies of Ehrlich and of Goldmann on vital staining but in the thirties and forties some doubt was cast on this concept.

Abstract: The concept of a barrier between blood, on the one hand, and the brain on the other derives from the classical studies of Ehrlich and of Goldmann on vital staining; it was noted that a large variety of acid dyes, of which trypan blue was one, would pass out of the blood into the tissues of the body making them voloured; the brain and spinal cord stood out in contrast to the rest of the tissues in that, with the exception of highly localized regions, such as the area postrema, they remained unstained. In the thirties and forties of this century some doubt was cast on this concept of a barrier between blood and brain; thus King in 1938 (1) argued that the essential phenomenon was one of failure to stain, and this could have been due to the absence of suitable connective tissue to take up the stain.