Abstract
The presence of a watery fluid that could also be found in large amounts within the brain has been known for many centuries. The idea that this fluid circulated was inspired largely by investigations of the 19th century anatomists. According to Cushing (1) the modern era in research on cerebrospinal fluid (CSF) circulation began with Magendie who was probably the first to fully appreciate the physiological importance of the fluid. Magendie and Luschka described in the roof of the fourth ventricle of the brain, the foramina which bear their names and through which CSF can flow into the subarachnoid space. The existence of these openings may not be present in all animal species. In one investigation in the mid-19th century, they were not found in human pathological studies by Hilton (2); in this particular case, there was an abnormal accumulation of fluid in the interior of the brain.
The source of the CSF had been relegated to the choroid plexus, a view favored by Faivre and by Luschka but not by some who regarded the pia as the source. Though proof was lacking, less doubt remained after Cushing (1) observed the fluid exuding from the surface of the choroid plexus at the bottom of a porencephalic cavity. In the same decade, Weed (3) made extensive studies on the embryological development of the CSF spaces. He correlated the appearances of the villous tufts of the choroid plexus with the extraventricular spread of CSF, the separation of the meninges into its layers and the formation of the cisterns. Further evidence to show that CSF is formed by the choroid plexus was provided by Schaltenbrand and Putnam (4) who observed the formation of greenish fluid on the surface of the choroid plexus after an intravenous injection of fluorescein. More definitive proof of the secretory activity of the choroid plexus was provided in 1963 by Welch (5) who determined the CSF formation rate in rabbits from measurements of choroidal blood flow and of increases in the hematocrit of choroid plexus blood.
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