The main stages of the reproductive cycle in the control rats. Swab smears (unstained) shown with the original microscope magnification of 100×. A:Estrus stage: large cornified cells in clumps. B: Metestrus stage: large numbers of leucocytes with smaller numbers of non-nucleated epithelial cells (note characteristic clumping together of two cell types at the center-right). C: Diestrus stage: predominantly leucocytes with a small number of epithelial and cornified cells. D: Proestrus stage:epithelial cells are mostly rounded but some cells shows early stages of cornification of approaching estrus.