Paper - The Sexual Cycle in the Human Female as revealed by Vaginal Smears
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Papanicolaou GN. The Sexual Cycle in the Human Female as revealed by Vaginal Smears. Am J Anat. 1933;52: 519–637.
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The original black and white photomicrographs were hand-coloured by the author to match his microscopic observations. |
The Sexual Cycle In The Human Female As Revealed By Vaginal Smears
George N. Papanicolaou
Department of Anatomy, Cornell University Medical College, and Woman’s Hospital, New York City
- This work has been aided by the Committee for Research on Sex Problems of the National Research Council, and by the National Committee on Maternal Health.
Three Figures and Ten Plates (Eighty-One Figures)
I. Introduction
The study of the female sexual functions in mammals has been greatly stimulated and advanced in recent years by the application of the vaginal smear method. This method, as originally applied to the guinea pig by Stockard and Papanicolaou in 1917, consists in the microscopic examination of smears prepared at frequent intervals from the fluid content of the vagina. The vaginal fluid usually has a mucous consistency and contains a variety of desquamated cells, as well as leucocytes, lymphocytes, often erythrocytes, and a large number of bacteria. As the relative number and the distribution of these elements change periodically, smears prepared from such fluid show modifications in their composition and structure. The successive alternation of periods of sexual activity and inactivity, which characterizes the mammals, imparts to the vaginal fluid a rhythmical sequence of typical cellular stages which can be easily recognized.
These cyclic changes affect the entire genital tract, and, consequently, every change in the vaginal fluid is strictly correlated With corresponding changes in the other organs of
the female genital system, particularly the uterus and the ovaries. The time of ovulation may be accurately detected by this method in living mammals, while, before its application, no such information could be obtained without an operation or the sacrifice of an animal.
In the guinea pig, which is polyoestrous, the sexual cycles
return periodically throughout the year every 15 to 16 days
(15.73 in average). The longest part of each sexual cycle,
i.e., about 12 days, is occupied by a period of relative inactivity or rest, which is called ‘clioestrus.’ During this time
the vaginal smear, as described by Stockard and Papanicolaou ( ’l7), consists chiefly of leucocytes and a varying num-
ber of atypical squamous cells. The period of increased
sexual activity lasts 3 to 4 days and is characterized by a
succession of stages, which have been designated as stages
I, II, III, IV. During stage I the leucocytes almost disappear
from the smear, the secretion of mucus becomes more abundant, and the cells which dominate the smear are of a squamous type with very small pyknotic nuclei which are at times
fragmented. At the end of stage I there is an intermediate
period, characterized by the prevalence of ‘elongate, cornified
cells Without nuclei.’ Stage II also shows a scarcity of leucocytes and a prevalence of cells which are derived from the
deeper layers of the vaginal epithelial wall, being thus less de-
generated and having a larger nucleus and a more compact
form. Stage III is characterized by the reappearance of
myriads of leucocytes and by cells mainly of the II and III
type. The III cells are as a rule modified type II cells, the
bodies of which had been penetrated by the invading leucocytes. Stage IV is practically the same as stage III, with the
difference that erythrocytes are also present in the smear as
the result of slight bleedings.
These four smear stages are of short duration, succeeding one another rapidly and are strictly coordinated with corresponding stages of the uterine and ovarian cycles. During
stage I the ovary contains large ripening follicles and regressing corpora lutea. The uterus is congested and hypertrophied and its epithelial lining consists of high cuboidal or columnar cells. During the intermediate or cornified stage the follicles as well as the uterus reach their highest development. The onset of the catabolic processes, i.e., the bursting
of the ripe follicles and the denudation of the uterine mucosa,
is associated with the appearance of vaginal stages II and III.
Ovulation in the guinea pig is thus characterized by definite
vaginal changes and occurs at about the time of the sloughing
off of the uterine mucosa. Comparable conditions have been
found to exist in other rodents, such as the rat and the mouse.
Long and Evans (’22), in their monograph on the oestrous
cycle in the rat, described definite relations between the vaginal cycle, as revealed by vaginal smears, and the uterine and
ovarian cycles. The rat has normally a very short sexual
periodicity of about 5 days’ duration. Long and Evans recognized five smear stages: Stage 1: Leucocytes disappear;
great numbers of small round nucleated epithelial cells of
strikingly uniform appearance and size; duration 12 hours.
Stage 2, or ‘cornified cell stage’: leucocytes still absent;
appearance of cornified cells. Stage 3, or ‘late cornified cell
stage’: leucocytes absent; rich in cornified cells, forming
large cheesy masses; duration of stages 2 and 3 about 30
hours. Stage 4, or ‘leucocytic—cornified cell stage’: reappearance of leucocytes; gradual disappearance of the cornified
cells and appearance of epithelial cells; duration 6 hours.
Stage 5 corresponds to the dioestrus, which is of an approximate duration of 3 days and is characterized by the presence
of leucocytes and atypical epithelial cells in the vaginal smear.
The cornification of the vagina is much more pronounced
in the rat than in the guinea pig and this accounts for some
of the smear differences between these two animals. In the
rat the cornification extends over two well-defined stages, the
second and third of Long and Evans, whereas in the guinea
pig it is usually overlapped by the I and II to the III stages;
on this account, it had been originally described by Stockard
and Papanicolaou as an intermediate period. In the rat the
uterine growth is completed during the first and second
stages. The catabolic processes in the uterus begin during
the cornified cell stages, and the ovulation occurs during the last hours of this same period. The uterine epithelium is
vacuolized and degenerated, but an actual denudation, as in
the guinea pig, does not occur. The various phases of the
sexual cycle in the rat proceed in rapid succession, but their
coordination is maintained.
The corresponding vaginal smear stages in the guinea pig and the rat could be illustrated as follows:
| Vaginal Smear Comparison Table | |
|---|---|
| Guinea pig | Rat (Long and Evans) |
| I. Superficial squamous cells with pyknotic nuclei; progressive leucopenia. | 1. Small round nucleated cells; disappearance of leucocytes. |
Intermediate (cornification) period
|
Cornification period
|
| II, III, IV. Appearance of deep layer cells; reappearance and great exodus of leucocytes; gradual disappearance of cornifiecl cells; sometimes erythrocytes present. | 4. Leucocytic-cornified cell stage; reappearance of leucocytes; gradual disappearance of the cornified cells. |
| V. Dioestrus: Leucocytes and atypical atypical vaginal cells. | 5. Dioestrus: Leucocytes and vaginal cclls. |
| |
This comparison indicates that the succession of stages is similar in both animals. Ovulation occurs at practically the same moment in relation to the above stages, i.e., at the end of the intermediate period in the guinea pig and during the last hours of the cornification period (second and third) in the rat.
In the mouse, Allen (’22) has also recognized five stages, the entire sexual cycle averaging about 4% days.
Selle (’22) has reclassified the vaginal smears of the guinea pig after a detailed study of the changes in the vaginal epithelium. He has recognized a separate ‘cornified cell stage’ similar to the same stage in the rat. Such a stage may be actually present in a large number ‘of cases, but, as a rule, it is indistinct and overlaps both the preceding and the following stages. This cornified cell stage of Selle corresponds to the ‘intermediate period’ of Stockard and Papanicolaou, and not to the stage 2 as given in Selle’s table. His stage 3 corresponds to the intermediate +II, whereas his stage 4 is equivalent to the stages III and IV of Stockard and Papanicolaou.
Murphey (’22) and Frei and Metzger (’26) have recognized four stages in the oestrous cycle in the cow with the vaginal smear method. Hartman (’23), in his study of the oestrous cycle in the opossum, also recognized four stages corresponding to the ones described in the rodents.
In 1924, McKenzie and Zupp, and in 1926, Wilson studied vaginal smears in swine. They found periodic variations in the cellular and leucocytic make-up of the smears, indicative of a cyclic rhythm.
A further step was made by Corner’s (’23) application of
this method to the Primates. His observations on Macacus
rhesus, though not entirely in line with the smear findings
in the rodents, yet revealed a rhythm in the vaginal reactions.
The average length of cycle in the Macacus, when the regular
cycles are considered, is about 27 days, which is almost the
same as in the human. During menstruation, which lasted
4 to 6 days, the vaginal smear contained erythrocytes, epithelial cells, and leucocytes. In the first half of the intermenstrual interval there were relatively few epithelial cells and
many leucocytes. About the middle of the interval a sharp
drop in leucocytes occurred or even total disappearance.
Leucocytes sometimes reappeared a few days later or were
absent until onset of next menstruation or a few days before.
During the second half of the intermenstrual interval there
was an increased desquamation of epithelial cells. The pre-menstrual smear seemed to be thick and caseous, whereas the
postmenstrual smear was rather thin and scanty.
These observations, though not establishing a definite succession of clear-cut stages, reveal the existence of a rhythm expressed mainly in the periodical increase and decrease in the number of the leucocytes and the epithelial cells. As Corner concludes:
- There is to some degree a cycle of the vaginal secretion in this species. There is hardly enough evidence to warrant a correlation with the much sharper cycle of the rodents; moreover there was seen in the monkeys no massive desquamation of completely cornified epithelial cells and no swarming of leucocytes into the epithelial debris. However, . . . . it seems very likely that the disappearance, or diminution in number of vaginal leucocytes, which usually happened about the tenth to the fifteenth day before the onset of menstruation (in regular cycles of 25 to 30 days) is to be compared with the disappearance of leucocytes from the vagina of rodents at oestrus or shortly before the moment of ovulation.
In a later paper, 1927, in which the presence of menstruation without ovulation in Macacus rhesus was reported, Corner stated that daily vaginal smears, taken from animals with ovulative and non-ovulative cycles, were practically alike. The presence or absence of ovulation could not be ascertained by the examination of vaginal smears.
Allen, in 1927, also studied vaginal smears of the monkey, Macacus rhesus, and found varying numbers of epithelial cells in different stages of cornification. Some of these cells were quite normal, others were flattened and their nuclei were pyknotic. The epithelial elements were present in greatest numbers during the latter half of the second and the whole third week of the cycle. Completely cornified, non-nucleated cells frequently also appeared at these times. Leucocytes were present in greatest numbers before, during, and after menstruation and in least numbers or absent between the tenth and the twentieth to twenty-fourth day of the shorter cycle. During menstruation varying numbers of erythrocytes were present.
Allen’s findings are more or less in line with Corner’s observations, especially in regard to leucocytes. Corner found many leucocytes during and after menstruation and Allen before, during, and after. At about the tenth day both noticed a progressive diminution in the number of the leucocytes. This diminution lasted for a few days or almost up to the onset of next menstruation. In regard to ovulation, they agree that, whenever present, it occurs in the mid-period, between the tenth and the fifteenth days.
The preparation of vaginal smears from the human has been in usein pathology for a long time for the study of various conditions, especially of bacterial infections. However, the application of smears to morphological and physiological studies has been extremely limited up to the last decade.
As early as 1847, Pouchet, in his book on “Ovulation and other related phenomena,” gave a description of human vaginal smears, which is chiefly interesting from a historic standpoint. Though unaided by modern technical methods, he
was able to recognize the existence of a rhythmical reaction
in the vaginal secretion. His work, however, was largely lost
sight of and in no way stimulated attention upon the value
of the vaginal content as an indicator in analyzing the phases
of the sexual cycle. The recent interest and activity in these studies can in no sense be connected with or attributed to this early pioneer effort by Pouchet.
He describes the vaginal mucus as becoming less dense
shortly before menstruation and as acquiring a peculiar odor
(une odeur ‘sui generis’), to which he attributed an exciting
effect upon sex desire. Microscopically, the vaginal fluid
showed fragments of epithelium and lacerated pieces, some
consisting only of the ‘tubercule central’ (he evidently meant
the ‘nucleus’), also large numbers of ‘globules muqueux’ (meaning probably the leucocytes) and some erythrocytes.
During the menstrual phase (‘période d’état’) he records the enormous quantity of erythrocytes, of mucous globules, and of small and transparent epithelial fragments. He believed that ovulation occurs toward the end of the menstrual phase, when the sex desire is most imperative. The menstrual phase is followed by a ‘period of desquamation,’ lasting approximately 10 days. This period is characterized by the detachment of a considerable quantity. of epithelial plates (‘Plaques d ’épithélium ’) .
During the sixth and seventh days after the end of menstruation (eleventh to twelfth day after onset) the vaginal mucus begins to lose its transparency and becomes heavier.
Plates
Plate 9
Drawings of various types of cells found in normal human vaginal smears.
- 36 to 60 Cells from human vaginal smears at different stages of the normal menstrual cycle.
Plate 10
Drawings of various types of cells found in normal human vaginal smears.
- 61 to 68 Cells from human vaginal smears at different stagesrof the normal menstrual cycle.
- 69 to 79 Characteristic types of cells found in human vaginal smears during pregnancy.
- 80 Normal mononuclears during menstruation.
- 81 Large mononuclears found in post—partum.
- 82 to 84 Cliaraeteristic types of cells found in postpartum.
Cite this page: Hill, M.A. (2024, May 5) Embryology Paper - The Sexual Cycle in the Human Female as revealed by Vaginal Smears. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_The_Sexual_Cycle_in_the_Human_Female_as_revealed_by_Vaginal_Smears
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
