Electron Microscopic Study on Differentiation of the Mast Cell of Mice Skins

Electron and light microscopic studies on the development of mast cells of the fetal, newborn and adult mouse skin were undertaken, with special reference to the mast granule formation. So far, the earliest mast cells in the mouse fetal skin were those which the author observed in the subepidermal mesenchyme of mice fetuses 15 days in utero. They were very small in number and contained a few mast granules in the cytoplasm. With the growth of fetus in utero, the number of mast cells in the skin as well as mast granules in their sytoplasm showed a tendency of gradual increase. In the adult skin, mast granules increased in number andfilled up the cytoplasm. The mast granules observed in the skin of mice were divided into following two types