After more than a century of speculation, the ingenious experiments of Dandy,1 in 1919, demonstrated without question that the main source of the cerebrospinal fluid is the choroid plexus. He was able to occlude both foramens of Monro in a dog and to remove the choroid plexus from one lateral ventricle without disturbing the other. A few weeks later, the animal was killed and its brain examined. The ventricle with the intact choroid plexus was distended with fluid, while the other was collapsed and contained only a small amount of liquid similar in character to the blood plasma.
Cushing2 had previously observed the choroid plexus through a porencephalic communication with the lateral ventricle and had seen small drops of fluid appearing on its surface.
I have seen this "sweating of the choroid" in experimental animals by direct examination with a stereoscopic microscope. Undoubtedly, certain elements are added to
HOWE HS. PHYSIOLOGIC MECHANISM FOR THE MAINTENANCE OF INTRACRANIAL PRESSURE: SECRETION AND ABSORPTION OF THE CEREBROSPINAL FLUID: THE RELATION OF VARIATIONS IN THE CIRCULATION. Arch NeurPsych. 1928;20(5):1048–1064. doi:10.1001/archneurpsyc.1928.02210170155003
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