“…Certainly it does not suggest that aging is a simple degenerative affair, but that even in a single bodily structure, changes occur which are characteristic for the area and organ involved (20, 21). Glycine‐2‐C 14 was injected intraperitoneally into female rats 5 weeks old and 2 years old respectively, and the rats were sacrificed 1, 3, 7, 11, 20 and 31 days later in order to determine the rapidity and amount of formation of new collagen and the rate of decay in the two groups (24). Data for the soluble and insoluble collagen fractions in the femur, rib, vertebra and skull, plotted on a semilogarithmic scale, are shown in Figure 11.…”