THE VAGINAL CLOSURE MEMBRANE, COPULATION, 



AND THE VAGINAL PLUG IN THE GUINEA-PIG, 



WITH FURTHER CONSIDERATIONS OF THE 



(ESTROUS RHYTHM. 



CHARLES R. STOCKARD AND GEORGE N. PAPANICOLAOU, 

 CORNELL UNIVERSITY MEDICAL COLLEGE, NEW YORK CITY. 



Two years ago we recorded the results of a detailed study of the 

 oestrous cycle in the guinea-pig. A rather full description of the 

 histological and physiological changes which take place in the 

 ovary, uterus and vagina during the " heat period " was presented. 

 We emphasized particularly the importance of changes occurring 

 in the microscopic composition of the vaginal fluid as indicative 

 of the exact conditions in the uterine wall and ovarian follicles 

 at corresponding moments. 



Since that time we have somewhat extended the analysis of 

 these phenomena. It has been found that a membrane covering 

 the orifice of the vagina furnishes a most valuable and simple 

 means of diagnosing certain periods in the oestrous cycle. This 

 we have termed the "vaginal closure membrane." The exact 

 moment of copulation and the conditions in the walls of the 

 vagina and uterus at this time have been carefully followed, 

 along with a consideration of the formation and significance 

 of the vaginal plug. In the present paper a discussion of these 

 several topics will be undertaken. 



Certain points in the literature will also be discussed, a more 

 complete review having been given in the previous article. 



i. THE VAGINAL CLOSURE MEMBRANE. 



In the former communication attention was called to the fact 

 that "the external vaginal orifice, which during the period of 

 oestrous activity is more or less open, actually showing in many 

 cases a little fluid or some blood, closes and becomes less accessible 

 after the period." During ovulation the vagina is open, but the 

 fact of its being open is not unmistakable proof of the time of 



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