Mast cells in the peripheral blood of doubly transgenic animals. Peripheral blood from affected animals was examined for the presence of mast cells (modified Wright-Giemsa stain). Granulocytes in varying stages of development are shown, including immature myeloid forms, each with a few metachromatic granules (top row), immature or atypical mast cells (middle row), and mature mast cells (bottom row). Original magnification, × 63 in all panels.