246 CHARLES R. STOCKARD AND G. N. PAPANICOLAOU 



tion through the uterus at four and a half days after the last 

 oestrus. At this thne the epithelial cells present a normal and 

 vigorous aspect. No loss or breaking down is to be noticed. A 

 few leucocytes are occasionally seen among the cells of the 

 stroma, but never in large numbers. Mitoses are not frequent 

 at this time but they are to be seen now and then. 



When the heat period begins, the epithelium loses its normal 

 appearance (figs. 11, 12 and 13). The epithelial cells become 

 tall and columnar and are fiUed with mucus which they begin 

 to form in abundant quantity The nuclei of the columnar 

 cells appear closely pressed one against the other and are pressed 

 into different levels in the various cells so as to give an appear- 

 ance of several rows of nuclei. The epithelium thus takes on a 

 pseudo-stratified arrangement. At the same time, a large num- 

 ber of leucocytes begin to migrate from the capillaries through 

 the stroma and towards the epithelium. The stroma itself is 

 congested and possesses a more profuse circulation than usual. 



These appearances are to be seen in animals killed during the 

 first phase of their period, that is, when the vagina contains an 

 abundant mucous fluid filled with desquamated epithelial cells. 

 A smear of this fluid is illustraed in figure 1. 



As soon as the second phase of the vaginal fluid appears (figs. 

 2, 3 and 4), the uterus shows another aspect. The leucocytes are 

 accumulating in large numbers below the epithelium, forming in 

 some places a perfect wreath of leucocytes under the epithelium 

 or actually a separate layer of cells (fig. 14). The stroma shows 

 a more advanced degree of congestion. 



During the third stage, smears figiu'es 5 and 6, the leucocytes 

 penet;rate more and more into the epithelium some of them mak- 

 ing their way into the lumen of the uterus by passing between the 

 epithelial cells. Other leucocytes actually enter the epithelial 

 cells and penetrate into their interior (fig. 15). A stage more 

 advanced in appearance corresponding to a late third stage 

 though from the same animal as figure 15, is shown in figure 

 16, where the entire epithelium is almost completely disintegrated. 

 A great number of leucocytes has already penetrated the epithe- 

 lium the cell structure of which has become largely destroyed. 



