Sodium fluorescein is a dyestuff that has been used to determine the permeability of the meningeal barrier in health and in disease. The studies of Kafka,1 Schönfeld,2 Jervell3 and others have established the fact that sodium fluorescein given by mouth in doses of about 3 Gm. per patient, or 0.030 Gm. per kilogram, will not permeate the meninges of the normal adult in two and one-half hours. In patients with meningeal disease permeation occurs in this length of time, as evidenced by the presence of the dyestuff in the cerebrospinal fluid. Jervell3 employed this test in an investigation of the meningeal permeability of seventy-four patients, eighteen of whom were suffering from some form of meningitis, chiefly tuberculous meningitis. The dyestuff could be demonstrated in the cerebrospinal fluid of only those having meningitis. He concluded that the presence of sodium fluorescein in the spinal fluid within three