The quantitative method in use for eleven years at the Massachusetts General Hospital and for the past four years at the Boston City Hospital consists essentially in the measurement, by means of a suitable colorimeter, of the turbidity produced by adding a solution of sulphosalicylic acid to the cerebrospinal fluid. The method was described by Denis and Ayer.1 We have made two minor modifications in the original method: (1) in the preparation of a protein standard solution, and (2) in the dilution of spinal fluid used when the protein content is very low, thereby eliminating the need of a second protein standard. The original method required the use of a special colorimeter. This is no longer necessary. These modifications and the fact that the normal values given in the original paper (from 35 to 100 mg. per hundred cubic centimeters) are entirely too high are the reasons for publishing
AYER JB, DAILEY ME, FREMONT-SMITH F. DENIS-AYER METHOD FOR THE QUANTITATIVE ESTIMATION OF PROTEIN IN THE CEREBROSPINAL FLUID. Arch NeurPsych. 1931;26(5):1038–1042. doi:10.1001/archneurpsyc.1931.02230110136007
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