440 RAYMOND M. SELLE 
order to point out the similarities as well as the differences. It 
will be seen that these newly determined stages in the guinea-pig 
correspond more closely to stages in the rat as described by Long 
and Evans. © 
Interval 
At the end of stage 4 or at the beginning of the interval the 
vaginal closure membrane began to form as described by Stockard 
and Papanicolaou, growing very rapidly and, if not disturbed, 
closing the vagina in one to three days. This membrane remained 
intact until mechanically destroyed or until the next cycle, 
when it was normally broken during the cornified stage by the 
tension produced by the swollen vulva and accumulated fluid in 
the lumen. When samples were taken daily, the membrane was 
prevented from forming for an indefinite period. 
It will be recalled that toward the end of stage 4 and the be- 
ginning of the interval the rapid rate of desquamation of the 
epithelial cells gradually diminished, while the leucocytes in- 
creased until they were in the majority. The transitional period 
between stage 4 and the interval is indicated by the decreasing 
numbers of epithelial cells and increasing numbers of leucocytes 
in the smears. Samples taken up to the middle of the interval 
contained a few epithelial cells, but for the next week or more only 
leucocytes. From this time on until the beginning of stage 1 
vaginal smears were found to exhibit leucocytes and some atypical 
cells. ; 
A section through the vagina during the middle of the interval 
showed the epithelium to be only one or two cells high. This 
reduction in height was no doubt caused by the continued drop- 
ping off of the epithelial cells which were found in the vaginal 
fluid following stage 4. 
Toward the end of the interval and immediately before the 
beginning of stage 1 the epithelium was rebuilt to a height of ten 
to twelve cells (fig. 2). The uppermost of these cells became 
vacuolated as described under the interval at the beginning of the 
discussion on stages. 
It is interesting to note that, although there was the above 
rapid transformation in the epithelium, such a condition could 
lati gl pe ——— 
