The determination of the existence or absence of a direct communication be-tween the spinal subarachnoid space and the perineurial spaces would contribute data regarding the circulation of the cerebrospinal fluid. Much has already been written in attempts to prove or deny this communication. Key and Retzius (9, 10) were among the first to conclude that pathways existed by which cerebrospinal fluid escaped from the subarachnoid space into the substance of the nerves as well as into the perineurial spaces. They injected gelatin solutions, colored with Berlin blue, into the spinal subarachnoid space of cadavers and found the blue color to extend outward along the spinal nerves for a considerable distance. However, the injections were made under increased pressure (up to 60 mm. Hg) and could certainly have forced the gelatin into the perineurial space by mechanically rupturing a barrier, thus entering potential tissue spaces rather than passively following previously existing anatomical chan-nels. The changes imparted by the high degree of pressure are evident in the sagittal section of the skull, which shows the cisterna magna to be distended with blue gelatin and the cerebellum compressed and pushed upward. Earlier, Quincke (11) had injected mercuric sulfide repeatedly into the subarachnoid space of living animals and post-mortem examination several days later showed the spinal nerves colored red. He thought this was the mode-of absorption of cerebrospinal fluid. However, histological studies revealed that an inflammatory reaction had been produced by the chemical agent with a result-ant, phagocytosis of particles of mercuric sulfide. The migration, therefore, of such granule-laden cells from the subarachnoid space can hardly be taken as evidence that any pathway for the escape of cerebrospinal fluid exists normally. Goldmann (6), in 1913, repeated these experiments using trypan blue and found the blue color in the spinal nerves at various distances from the spinal cord. As with the mercuric sulfide, trypan blue produced an immediate toxic reaction and later an inflammatory reaction of which the animals died. Others, who believed that such a communication exists, included Cathelin (2), who thought the peripheral nerves are bathed to their very termination by the same fluid as covers the central nervous system. More recently, Funaoka (5) was able to inject 25 cc of dekalin colored with ultramarine into the peroneal nerve of a rabbit and noted the blue dye in the subarachnoid and subdural spaces. In addition, he used a solution of amyl acetate, ether and olive oil colored with dye and observed the same distribution of color as with the dekalin. Unfortunately, there were no measurements of the pressures used for injection. Also, the use of