Figure 2. Comparison of human cerebrospinal fluid density measurements reported by Davis and King [4]and Levin et al., [5]and those measured in this study. Densities are presented as mean+/-three standard deviations (g/ml). Mean density minus three standard deviations has been defined as the upper limit of hypobaricity, [1,4]previously taken to be 0.99940 g/ml, [3,5]and determined by us to range from 1.00016 to 1.00037 g/ml.