226 CHARLES R. STOCKARD AND GEORGE N. PAPANICOLAOU. 







In the present account we wish to describe the exact moment 

 at which copulation takes place during the sexual cycle and to 

 show definitely the conditions of the vagina and uterus at this 

 moment. From the condition of the vagina or uterus the ovarian 

 condition is readily estimated, as we have shown in the former 

 paper. After determining the exact cestrous condition of a 

 female at the moment she is ready for copulation we may then 

 recognize a corresponding moment in any female by an examina- 

 tion of the vagina without the necessity of introducing the male 

 or permitting copulation to occur. 



In order to designate the copulation time exactly, we must 

 review r briefly the characteristics of the four very clearly defined 

 stages of the oestrus or "heat period" proper. During stage 

 one the uterine epithelium swells, the cells becoming distended 

 with an abundant mucous secretion which very soon pours into 

 the lumen and reaches the vagina. At this time a desquamation 

 of the epithelial cells from the lower part of the vagina also begins. 

 The second stage shows a great accumulation of leucocytes 

 below the uterine and vaginal epithelium with a slowly progress- 

 ing desquamation of epithelial cells. The third is the stage of 

 exodus of the leucocytes, myriads of them coming through the 

 epithelial lining of the walls of the uterus and vagina, with an 

 accompanying extensive destruction of the epithelium. During 

 the fourth stage the broken down epithelium falls away in masses 

 and at the same time a regeneration of epithelium takes place 

 beginning from the mucosa of the uterine glands. 



The Graafian follicles of the ovary rupture and ovulation occurs 

 at the end of the second stage or the beginning of the third stage, 

 while during the fourth stage the recently ruptured Graafian 

 follicles are already well under way in their development into 

 new corpora lutea. 



A recent abstract by Long ('19) seems to indicate that four 

 similar stages may be recognized during the oestrus in the rat, 

 and that these stages agree almost exactly in significance "with 

 the comparable ones in the guinea-pig: Ovulation also occurring 

 in the rat at the end of the second or beginning of the third stage. 



During our initial investigation we made no attempt to locate 

 the exact moment of copulation and, of course, did not describe 



