A COLORIMETRIC METHOD FOR THE DETERMINATION OF THE pH OF CEREBROSPINAL FLUID.*

Recently the pH of the blood has been exhaustively studied but that of the cerebrospinal fluid has received little attention. Because the composition of spinal fluid is less complex, the determination of pH and interpretation of the results should be simpler than for blood. Cerebrospinal fluid is not only free from hemoglobin but also contains so little protein as to be, for practical purposes, protein-free. Is spinal fluid a transudate or a secretion? Is its relation to the blood such that it fulfills the laws of the Donnan equilibrium? The simultaneous determination of the reaction of blood and of spinal fluid give data applicable to such questions. In the course of an investigation on the ionization of calcium it became evident that test-tube experiments, involving a simple water system, could not be applied directly to the body fluids in which the protein effect is at present not subject to quantitation. Therefore, an effort was made to apply such consideration to a body fluid free from protein, namely, cerebrospinal fluid. One of the necessary determinations is an accurate estimation of pH.