In the initial article of this series1 evidence was presented to show that in fresh human cadavers the normal ventriculosubarachnoid spaces of the brain remain in free communication with the subarachnoid spaces of the spinal cord during various experimental changes in the pressure of the subarachnoid fluid, and that such variations of pressure, however rapid, do not produce any apparent movement of the tentorium, cerebellum or medulla. In the succeeding paper2 experimental evidence was reported indicating that sudden release of high intracranial fluid tension in dogs causes cellular injury to the central nervous system accompanied by an increased fluid content of the nerve tissues. In the third article3 the literature in the field was reviewed and the possibility suggested that many of the untoward effects following the rapid drainage of cerebrospinal fluid could in the majority of cases be attributed to shock and edema of the central