Dr. Reiner has studied some of the enzymatic changes involved in the process of aging in brain and liver tissue, using rats as experimental animals. These studies are concerned with the overall carbohydrate metabolism, investigated by means of reinforced homogenates. He finds that the oxidation of carbohydrate by brain is virtually constant through the second year of life, after which it declines sharply. Anaerobic utilization, on the other hand, has a pronounced maximum in animals from 2 to 4 months old, and then slowly and steadily decreases. This enyzme pathway therefore seems roughly to parallel the processes of maturation and senescence. The changes in the metabolism of liver tissue are pronounced in going from embryonic to post-natal life. Thereafter they are much smaller and of doubtful significance. As a consequence of the above findings, closer investigations of specific enzymes, especially those concerned with energy accumulation and transfer, are indicated. The need to study directly the mechanism of self-renewal of enzymes is discussed