68 



BIOLOGY OF THE LABORATORY MOUSE 



smearing with a spatula tends to disturb the regularity of the cycle (113, 

 133). The addition of a small amount of methylene blue to the water used 

 gives a very satisfactory stain. With this stain smears can be examined at 

 once without waiting for the water to dry. 



Three types of cells are found in vaginal smears, i. Leukocytes (Fig. 

 34A). In unstained preparations these appear at first as small, round, 

 highly refractive cells, but they swell rapidly in water with resulting rupture 

 of the cell wall. In preparations stained with methylene blue the poly- 

 morphic nucleus takes a strong stain. 2. Cornified cells {¥\g. 2,A^)- These 



IOO%i 



50% 



o%J 



I I I I 



DAYS 10 19 

 Fig. 35. — Graph showing the percentages of each of the three types of cells in the 

 vaginal smear of a mouse during the normal estrous cycle. Smears taken daily. 

 cornified cells, nucleated epithelial cells, leukocytes. {Voss 1930.) 



are the largest cells in the smear. They are flattened, angular in outline, 

 quite regular in size, and lack nuclei. 3. Nucleated epithelial cells (Fig. 34A). 

 The typical epithelial cell is round, oval or polygonal, with clear cytoplasm 

 and a centrally placed nucleus that takes a strong methylene blue stain. A 

 number of variations occur. As estrus approaches the smear may contain 

 epithelial cells with dark staining cytoplasm and karyolytic nuclei. The 

 cytoplasm may contain droplets (of mucus?). A highly modified mucus- 

 secreting type also occurs (no). This characteristically is goblet-shaped 

 with the nucleus at the apex. The presence of mucus can be proved by the 

 use of appropriate stains. Cells intermediate between cornified cells and 

 nucleated epithelial cells occasionally occur. 



More or less mucus may occur in the smear. Different accounts dift"er 

 greatly as to the amount normally present. It is possible that smearing 

 or other forms of irritation increase the amount. In adult ovariectomized 

 rats, mucification is produced by the combined administration of oestrone 

 and progesterone (115). During the latter two thirds of pregnancy in the 

 rat the vaginal mucosa actively secretes mucus (54, 75). 



