The Vagina

(a) Cornification of the vaginal epithelium. In 1917 Stockard & Papanicolaou found that a periodic cornification of the vagina occurred in certain animals and could be easily recognized by the microscopical examination of vaginal smears. A simple test was thus provided by which the sexual cycle could be followed easily and with precision. In 1923 Allen & Doisy obtained from the liquor folliculi of the sow's ovary a hormone which would induce cornification in the mouse's vagina. These two discoveries, followed as they were in 1929 by the preparation of oestrone in a pure crystalline form, have been the foundations of a great deal of subsequent research.

Oestrone given in an effective dose to a spayed mouse will produce a change in the vagina within 24 hours. An early result is a rapid multiplication of the epithelial cells, which not only increase numerically but undergo a metaplasia, so that the vagina instead of being lined by two thin layers of atrophic cells becomes lined by a squamous, keratinizing epithelium many cells in thickness. If no more oestrone be given a copious infiltration of the epithelium with leucocytes occurs, and the epithelium desquamates. On the other hand, if the dosage with oestrone is continued at sufficiently short intervals, leucocytic infiltration may be absent, so that the vagina becomes filled by a keratinous mass (Burrows & Kennaway, 1934). These vaginal changes are not equally pronounced in all animals. They are relatively inconspicuous in the rabbit, and in the mare it is said that vaginal cornification does not take place in spite of a plentiful production of oestrogen. Papanicolaou (1933) has shown that vaginal cornification occurs in women between the 8th and 12th day of the menstrual period. At this stage, he says, there is a complete or almost complete absence of leucocytes from the vaginal smears while the epithelial cells, though usually nucleated, are cornified. Mucus at this stage is abundant. He states that the commonest date for a typical oestral smear in women is the 11th day of the cycle.