The effect of age on the metabolism of the lens can be studied by two diverse methods: Comparisons may be made of lenses representing different age periods of a species, or of successive zones of the adult lens. Thus data on the quantitative distribution of the lens proteins in whole bovine lenses from animals of different ages (fetuses, calves, steers, old cows)1 parallel those derived from analysis of the zones of the adult lens from without inward.2 Just as a contrast of the biochemical findings in the cortex and nucleus of the normal lens gives an insight into the aging process, so a further comparison of corresponding data on cataractous lenses may indicate to what extent age influences cataractous degeneration. Certain mineral changes are characteristic of cataract, namely, a loss of potassium and a gain in sodium and calcium. Since the osmotic pressure of a tissue is dominantly