Abstract
While the organs and tissues of the young rat are known to increase in size with age (Donaldson, 1924), little is known of the role played by the component cells in this increase. There is evidence that cells enlarge (Levi, 1906; Plenk, 1911) and new cells are added (Strasburger, 1893), but we do not know to what extent the enlargement and proliferation of the cells cause the growth of organs and tissues. The present work is an attempt to clarify this problem.