DIOESTROUS CYCLE IN THE GUINEA-PIG 261 



fluid, which is not sufficiently abundant to be readily detected 

 on the vulva but is easily observed by an examination of the 

 interior of the vagina. 



4. The composition of the vaginal fluid changes with the 

 several stages of change occurring in the uterus and vagina. 



a. To begin with, during what we term the first stage, the 

 fluid consists of an abundant mucous secretion containing great 

 numbers of desquamated vaginal epithelial cells. At this time 

 sections of the vagina show an active shedding or desquamation 

 of its epithelial lining cells. The cells of the uterine epithelium 

 are loaded with mucus, and an active migration of polynuclear 

 leucocytes is taking place from the vessels of the vagina and 

 uterus out into the stroma and towards the epithelial layer. 



b. During the second stage the contents of the vagina become 

 thick and cheese-like on account of the great accumulation of 

 desquamated epithelial cells. The walls of the uterus and 

 vagina become congested and the migration of leucocytes becomes 

 still more active. 



c. The leucocytes reach the epithelium and vigorously invade 

 its cells and intercellular spaces during the third stage. These 

 wandering cells become enclosed within and apparently dissolve 

 the breaking-down dead cells of the epithelium. The vaginal 

 fluid becomes thinner under the dissolving or digesting action 

 of the leucocytes. The congestion in the uterus and vagina 

 becomes still more pronounced giving rise to small blood masses 

 or haematomata beneath the epithelium. The epithelium of the 

 uterus is highly disorganized, vacuolized and richly invaded by 

 the leucocytes, so that portions of it tall away en masse actually 

 carrying with it in some cases cells of the stroma. 



d. The fourth stage is merely a continuation or result of the 

 acti\dties of the third. The falling away of the epithelial pieces 

 and stroma cells permits the escape of the small haematomata 

 or blood knots thus causing a slight bleeding into the lumen of 

 the uterus and vagina. These traces of blood often give a red- 

 ish aspect to the vaginal fluid. At this same stage a regenera- 

 tion process begins from the necks of the uterine glands and also 

 apparently from the epithelial infoldings in the vagina, so that 



