VAGINAL EPITHELIUM OF GUINEA-PIG 439 
Following this stage, Stockard and Papanicolaou described 
another, which they called the fourth, during which blood was 
found in vaginal samples. In these investigations only two cases 
were observed in which blood was found in the smears, and in 
both cases it occurred at the end of stage 4. Itis hardly probable 
that this is a common occurrence. Because of the thin epithelial 
covering over the submucosa at this stage, it seems highly prob- 
able that an instrument inserted into the vagina might injure 
some of the many blood vessels in the submucosa and thus 
permit blood to escape into the vagina. 
Because of the differences in the stages of the cycles of the 
guinea-pig as found by Stockard and Papanicolau and in these 
investigations, the following table (1) has been constructed in 
TABLE 1 
A comparison of the stages in the oestrous cycles in the guinea-pig and rat 
GUINEA-PIG 
(STOCKARD AND PAPANICOLAOU) 
GUINEA-PIG (NEW) 
stage 
Ae 
First period: 
Squamous epithelial cells 
Second period: 
Cornified cells 
2. 
Cheesy mass, epithelial 
cells 
3. 
Leucocytes and epithelial 
cells 
4. 
Appearance of blood in 
lumen 
5. 
Interval: 
Leucocytes and epithelial 
cells 
RAT (LONG AND EVANS) 
stage 
ils 
Large irregular epithelial 
cellsonly. (Superficial 
epithelial cells) 
2. 
Cornified cells only 
3. 
Cornified cells and small 
epithelial cells, or small 
epithelial cells only 
4, 
Leucocytes and epithe- 
lial cells 
5. 
Interval: 
Leucocytes (few epithe- 
lial cells) 
stage 
ibs 
Superficial epithelial 
cells only 
9 
a“ 
Cornified cells only 
3: 
Many cornified cells 
(cheesy) 
4, 
Leucocytes and cornified 
cells (sometimes epi- 
thelial cells) 
a: 
Interval: 
Leucocytes and epithe- 
lial cells 
