In the newborn rat, weighing about 6 gm. there were lesser cytoplasmic and greater nuclear volumes per unit volume of the hepatic cell than for these components of the hepatic cells of the adult rat weighing about 160 gm. No difference between the volume occupied by the hepatic sinusoid per unit volume of the hepatic acinus was found.

In the newborn rat the ratio of hits on cytoplasm of the hepatic cell to hits on nuclei of the hepatic cell throughout the zones of the hepatic acinus was fairly uniform. However, the hepatic sinusoid of Zone 3 or the pericentral area was wider than that of the other zones.

In the adult rat the ratio of hits on cytoplasm to hits on nuclei of the hepatic cell throughout the zones of the hepatic acinus was not significantly different. However, the hepatic sinusoid of Zone 3was wider than that of Zone 2 and the sinusoid of Zone 3 was not significantly different from that of Zone 1 in volume.

Consequently it was concluded that the quantitative morphological or histological features of hepatic tissue components conformed to the points of regions or zones of the hepatic acinus in different ages in the normal albino rat.