The hepatic structural and functional unit of the mouse was demonstrated by the relative enzymatic activity of succinic dehydrogenase in the hepatic parenchyma, empIoying the method for succinic dehydrogenase of Nachlas et al. (1957), using Nitro-BT to frozen sections of about 1O micra.
In the hepatic structure of the mouse, three different geometricaI areas were classified: the perivascular area of the portal stem, which continued into the preter- minal portal branch; the area of the preterminal portal vein, and the area of the terminal portal twig, this being considered to be the real functional unit, which extends into the neighbouring hepatic lobule according to the pattern of distribution or activity of succinic dehydrogenase.
The hepatic parenchyma, which showed strong succinic dehydrogenase activity, was considered to correspond with the heavily loaded parenchymal area with mitochondria, according to the previous observa-tions of hepatic mitochondria in the mouse, as presented by the author (1961).
The periphera1 areas or zones, including the pericentral area around a central vein, of the real functional hepatic unit, which was described by Rappaport et al. (1954) and others, showed less activity of succinic dehydrogenase, and the perivascular areas of branches of the hepatic vein reacted weakly.
Acknowledgments: This work was carried out With the help of grants from the Research Committee Of Yonsei University College of Medicine and With a supply of chemicals from the China Medical Board. I wish to thank Dr. K. D. Choi, Department of Anatomy for helpful encouragement.
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