Notes:
Vaginal cell morphology changes in exposure to estrogen. In all animals except those that are menstrual, there is change in vaginal cell morpohology (cells flatten out and nucleus disappears). Two “chromic shifts” occur, evidenced by color change in differently-stained cells. Determines if pro estrus and estrus cycle. First chromic shift goes from blue cells to pink cells. It occurs 9 days before ovulation in Pandas and 18 days before breeding in Sun bears. With the second chromic shift, cells become kerotenized; they take up a yellow dye and the cell nucleus disappears completely.