Intra-arterial basie dye studies of the blood-CSF and blood-brain barriers.

1. The permeability of the blood-CSF barrier was tested by injecting highly diffusible basic dyes into the common carotid artery and aspiration of the cisterna magna during or shortly after the injection. None of the dyes appeared in the CSF. 2. The appearance of similarly administered basic dyes were observed in the exposed cerebral cortex. Some of the basic dyes appeared in the cortex immediately after a few drops of dye were injected. This contradicts the assumption that staining of the brain by basic dyes is a post-vital process. 3. The difference between the permeability of the blood-CSF barrier and the blood-brain barrier proves the fundamentally different characters of the two barriers.