W E HAVE RECENTLY COMPLETED a detailed study of human brain lipid composition changes with age. The unexpected nature of the changes and their obvious general importante prompted us to report at once findings derived from the data. In our study, lipid class composition, including most of the minor components, and the fatty acid composition of each lipid class were determined in 13 normal, male, human, whole brains (age range, 6 months fetus to 98 years). Accuracy and precision were insured by determination of lipid class composition of each sample by at least two different methods involving spectrophotometric assay following separation by twodimensional thin-layer chromatography alone or in combination with column chromatography (1-3) and by repeat analysis of each sample by each method. The data were then submitted to various forms of graphic analysis. Semilogarithmic plots of lipid values at different ages were found to give a series of straight lines, indicating periods following curvilinear regression of a very precise nature. A typical semilogarithmic plot is shown in Fig. 1 where the steady decline of total phospholipid as percentage of the total lipid (excluding gangliosides) is apparent, up to about 33 years of age. Similar results were obtained with the individual lipid classes when values were plotted as weight percentage of the total lipid, micromoles/100 mg of lipid, or millimoles/100 g fresh weight or dry weight. Use of the log scale for age is convenient because the scale is expanded at the early ages where changes are greatest. Plots of lipid data show that development and aging of brain are continuous processes without a fully stable intermediate period.

Once the straight line periods are recognized from plots on semilogarithmic paper, regression equations can be calculated for each period. The equations (Table 1) calculated for water content and total lipid as percentage of the fresh weight, and for lipid classes as millimoles/100 g fresh weight, were found to give values with a maximum deviation of-----2% of the measured values. Values as millimoles/100 g fresh weight calculated from the equations of Table I are convenient for general use, since from them values in terms of dry weight,