Transmission and scanning electron micrographs of baboon livers. In the young baboon (a & c) the endothelium (E) is thin & fenestrated and the space of Disse (D) is free of fibrosis. In the old baboon (b & d) the endothelium is thickened & defenestrated. H and L indicate the hepatocyte and sinusoidal lumen, respectively. Bar = 1 –m.