In the study of normal and abnormal physiology of the nervous system it would be of considerable assistance to the clinician to know the quantitative return of the cerebrospinal fluid into the blood stream per unit of time.
It has long been known that certain substances when injected subarachnoidally eventually appear in the urine. In their study of such agents, the quantitative output of which from the subarachnoid space could easily be determined in the urine, Dandy and Blackfan1 adopted neutral phenolsulfonphthalein for clinical use. After experimental trials it was concluded by these investigators that the quantitative results of the absorption of this dye from the human subarachnoid space are similar to those in animals; that is, for approximately three to four hours the absorption is fairly constant and then diminishes progressively as dilution with fresh fluid occurs. The dye appears in the urine in from six to eight
GARDNER WJ, NOSIK WA. QUANTITATIVE ABSORPTION OF PHENOLSULFONPHTHALEIN FROM SUBARACHNOID SPACE. Arch NeurPsych. 1939;41(3):484–488. doi:10.1001/archneurpsyc.1939.02270150058004
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