SUMMARY

The persistent high calorie intake and rapid somatic growth in young rats, which was initiated by a super-abundant milk supply in the first weeks of life, was accompanied by an accelerated growth in the size and number of cells in the liver. The adult concentration of serum protein was also attained earlier. An increased food intake in the adult which was produced by hypothalamic lesions, did not significantly affect growth of the skeleton, but it had the same effect on the liver as very rapid somatic growth. The increase in weight of the liver could not be accounted for merely by increased consumption of protein. If part of the liver was removed from an adult rat, both the rate of regeneration and the ultimate size and composition of the remainder were also determined by the calorie intake. The increased size of the liver of hyperphagic rats was associated with a greater blood volume, and consequently an increase in total serum protein, although the concentration of serum protein remained normal. Although hyperphagia after hypothalamic lesions may continue for many weeks, with a progressive increase in obesity, the maximum weight of the liver was often achieved within 1 or 2 days. The chemical composition of the liver, however, changed progressively, and the effect