Autoradiography following labeling with H-3-thymidine was used to study the pattern of growth of injury-induced lentomas in Rana pipiens. This reaction to injury was compared with the more controlled reaction in the rabbit lens, which has been extensively studied by others.

These studies show that, unlike that of the rabbit, the entire lens epithelium of the frog reacts within a day to the injury stimulus by disarrangement of its normal architecture. H-3-thymidine is incorporated between 24 and 40 hours post-injury, followed subsequently by widespread mitotic activity. Peak thymidine incorporation occurs at three days and peak mitosis at five days post-injury. However, the stimulus to mitotic activity is propagated after the first week largely among the superficial cells of the enlarging lentoma and adjacent normal epithelium; DNA synthesis and mitosis in the deeper cells of the lentoma diminish at a week and cease by two weeks post-injury, and by three weeks in the superficial cells.

It is concluded that the frog lentoma is formed by accretion from the surface as a result of extensive multiplication of cells throughout the injured epithelium. The reaction of frog and rabbit lenses to injury differs both in the extensiveness of the initial reaction and the duration of the stimulus to proliferation.