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The very first sign of sexual arousal in men, of course, is erection of the penis - a marked increase in its size, and a rise in its angle of protrusion from the body. Erection may be triggered by stimulation of the penis itself or by a sexually stimulating sight or by an erotic train of thought. It occurs within a few seconds, regardless of the nature of the stimulation.
During erection a small penis may double or more than double in length. In a large penis, the lengthening is less marked. Thus there is less variation in length among erect than among flaccid penises.
Erection is due to the engorgement of the penis with blood; indeed, as we shall see, many of the most important sexual responses occurring in both men and women are the direct result of this kind of engorgement. More blood flows into an organ than flows out of it; the result is engorgement or vasocongestion. This change in blood supply, occurring not only in the penis but also in other male and female organs, is the primary reflex action to sexual stimuli. The secondary reaction is a contraction of various muscle fibres, muscles, and groups of muscles.
The first sign of sexual response in women may seem to be different from either engorgement or muscular contraction; it is the moistening of the vagina with a lubricating fluid. This lubrication occurs quite promptly - within ten to thirty seconds of the onset of sexual stimulation. The lubrication appears with equal promptness whether the stimulus is direct stimulation of a woman's genital region, or of her breasts, or is an erotic train of thought.
Identification of the vagina's lubricating mechanism was been one of the most interesting aspects of the first anatomic study of the human female's sexual response cycle. Some earlier investigators had believed that the fluid comes down into the vagina from the uterus, through the cervix. During many hundreds of observations inside the vagina, however, Masters and Johnson observed a little fluid trickling down through the cervix on only one occasion - and this occurred late in the response cycle, after the vagina was already fully lubricated from some other source. They also observed full vaginal lubrication among women who had had complete hysterectomies, and who therefore possessed neither a uterus nor a cervix. Thus the uterus could be ruled out as a source of vaginal lubrication.
Another theory held prior to the Masters-Johnson research attributed vaginal lubrication to a pair of glands, known as Bartholin's glands, at the entrance to the vagina. This theory proved to be not entirely mistaken. Bartholin's glands do sometimes contribute a few drops of a lubricating fluid to the vaginal entrance - but only late in the response cycle, following prolonged sexual activity and following copious lubrication of the vagina from some other source.
The true source of vaginal lubrication is a "sweating reaction" occurring on the walls of the vagina. Beads of moisture appear on these walls much as beads of sweat appear on the forehead - despite the fact that there are no sweat glands in the vagina. As sexual excitation continues, these drops coalesce to provide a lubricating film, readying the vagina for the entrance of the penis.
To lay readers, the increase in the size of the penis and the "sweating" of the vaginal walls may seem completely different responses; but they may have a common cause. More blood enters the tissues around the vagina than can leave, producing vasocongestion. Both the walls of the smaller blood vessels and the walls of the vagina are "semi-permeable membranes"; they hold fluids back under some conditions but let them seep through under others. The droplets of moisture that appear on the surface of the vagina during sexual excitation, it seems probable, have seeped out of the congested blood vessels. Thus engorgement with blood is the cause of both the male erection and vaginal lubrication.
The appearance of vaginal lubrication very early in the female response cycle is a point that deserves stress. Some sex manuals state, and some men no doubt believe, that the appearance of vaginal lubrication signals a woman's readiness to engage in sexual intercourse. This is true in a sense. The woman is beginning to respond, and lubrication does ready the vagina for the entrance of the penis. Entry prior to the appearance of adequate lubrication can be difficult and uncomfortable, or even painful. But, as we shall see, many more changes must follow before a woman is fully aroused erotically and ready for sexual penetration and orgasm. Important changes occur, for example, in the clitoris.
This organ is located just above the entrance to the vagina. Like the penis, it is a shaft with a bulb or "glans" at the tip. Both the shaft and the glans vary in size from woman to woman. The size and location of the clitoris bear no relation whatever to a woman's sexual responsiveness or her ability to achieve orgasm.
The glans of the clitoris is packed with sensitive nerve endings. The stimulation of the glans thus contributes greatly to heightening a woman's sexual response. Direct contact with the clitoris is not necessary in order to stimulate it. The glans is covered with a hood or prepuce; and this hood is attached to the inner lips (minor labia) of the vagina. Thus during ordinary sexual intercourse the rhythmic thrusting of the penis through the inner lips produces a rhythmic friction between the clitoral hood and the glans.
In addition, the clitoris is responsive to purely psychological stimuli, such as an erotic train of thought. In the laboratory, changes in the clitoris can be directly observed during purely psychological stimulation, even though the clitoris and other genital organs remain untouched. Changes in the clitoris can also be observed following stimulation of the breasts.
The first of these changes is the swelling of the clitoral glans. In some women on some occasions, the glans may actually double in size. In other women, the swelling may be so slight that it can only be observed with the help of a device which enlarges the object viewed by forty diameters or so. The amount of swelling, however like the size and location of the clitoris - is not related to either sexual responsiveness or to ability to achieve orgasm. The swelling of the glans of the clitoris, like the swelling of the glans of the penis, is no doubt the result of engorgement of the blood vessels inside it. Simultaneously with the swelling of the clitoral glans, the clitoral shaft also increases in diameter.
The time at which these changes occur depends upon the nature of the sexual stimulation to which the woman is responding. If her mons veneris - that is, the area surrounding her clitoris - is being stimulated directly, the engorgement of the clitoral glans and shaft may occur quite promptly after the appearance of vaginal lubrication. If the stimulus is breast manipulation or an erotic train of thought, the clitoral response generally takes somewhat longer.
A series of changes also occurs in the female breasts during this initial or "excitement phase" of erotic response. The first of these changes is an erection of the nipples. This erection is caused by contraction of muscle fibres. Often one nipple erects first and the other follows immediately, or after a considerable delay. In addition, the nipples increase both in length and in diameter as a result of blood-vessel engorgement similar to the engorgement of the penis and clitoris. The pattern of veins ordinarily visible on the surface of the breasts becomes more distinct, and veins previously invisible may make their appearance during this engorgement process.
The female breasts also increase in size late in the excitement phase; this is a sign of heightened sexual tension preliminary to the transition to the next phase of sexual response. The swelling of the breasts is more noticeable in women who have not breast-fed babies. Late in the excitement phase, too, the areolas - that is, the rings of darker skin surrounding the nipples - become engorged and swell.
Response of the male breast is less consistent. However, at least partial nipple erection was observed in three-fifths of the men participating in studies. It generally occurred late in the excitement phase.
The outer lips (major labia) at the entrance to the vagina respond in several ways during the excitement phase. In an unexcited state, they generally meet in the mid-line of the vagina, protecting the inner lips and the other structures within. During excitation they open a bit, and may be displaced a bit upward, toward the clitoris. These changes are likely to occur quite late in the excitement phase. In women who have not had a baby, the outer lips also thin out and flatten themselves against the surrounding tissues.
In women who have had several babies, and especially in those who have developed varicose veins in their outer lips, the outer lips become noticeably distended and engorged with blood instead of flattening. In extreme cases there may be a two-fold or even three-fold increase in size, so that the outer lips come to resemble a sort of curtain surrounding the vaginal opening. In these cases, too, the lips tend to open outward toward the sides as erotic tension increases, so that they do not interfere with the entry of the penis.
The inner lips (minor labia) also tend to swell during the excitement phase; indeed, it may be the swelling of the inner lips that produces the opening-out of the outer lips, an invitation for the entry of the penis.
The vagina, too, responds. It can be thought of as a cylinder or "barrel",
which remains in a collapsed state in the absence of erotic stimulation. Studies have established that the outer third of this barrel
reacts in one way and the inner two-thirds in a very different way during the
successive phases of sexual response. As sexual tension mounts during the
excitement phase, the inner two-thirds of the vaginal barrel begins to expand,
and then relaxes again. Slowly the demand to expand overcomes the tendency to
relax, and the clinically distended vaginal barrel of the sexually responding
woman is established.
The cervix and uterus are pulled up and back at about this time, producing a
"tenting" of the vaginal walls surrounding the cervix. The net result of these
and other changes is a dramatic "ballooning" of the inner two-thirds of the
vagina. The diameter at the widest point of the ballooning may be three times
the diameter of the erotically unstimulated vagina; and the total length of the
vaginal barrel may be increased as much as a full inch. (The swelling of the
inner lips of the vagina also contributes to this lengthening.) The ballooning
is accompanied by a change in the appearance of the vaginal walls; the wrinkles,
or "rugae", are smoothed out and the colour of the walls changes from a normal
purplish red to a darker purple, indicating engorgement of the surrounding blood
vessels.
In addition to these responses in the sex organs and breasts, there are many
indications that the entire body, in both women and men, is participating in
this gradual process of sexual arousal. In both women and men, the voluntary
muscles tend to tense up, and there may also be some contraction of groups of
involuntary muscles. The pulse rate speeds up, and the blood pressure rises.
Most remarkable of all, perhaps, a "sex flush" often appears upon the skin.
This sex flush appears first on the upper portion of the abdomen, then spreads
up over the breasts. It often takes the form of a measles-like rash. The time of
appearance is variable. In most men, and in some women, it does not appear until
later in the response cycle, and in some it does not appear at all. But about
three-quarters of the women, and one-quarter of the men, exhibit the sex flush
prior to orgasm on at least some occasions.
Changes are also noted in the male testes and scrotum during this first phase of sexual response. There is a tensing and thickening of the skin of the scrotum; and the whole scrotal sac is elevated and flattened toward the body. The spermatic cords, by which the testes are suspended, shorten, so that the testes are pulled farther up in the sac. Just as the nipple of one breast often becomes erected before the other, so one of the testes often rises before the other.
Human sexual response falls into four phases - excitement, plateau, orgasmic, and resolution - for reasons of convenience. There is no sharply defined moment in time when one phase ends and the next begins - and this is particularly true of the relatively vague boundary which separates the excitement from the plateau phase.
In the male full erection of the penis is ordinarily completed during the excitement phase. The only additional changes in the penis during the plateau phase are a slight increase in diameter of the "coronal ridge" at the base of the glans of the penis; and in some men on some occasions, a deepening of the reddish-purple colour of the glans.
The testes increase in diameter about 50 per cent over their unstimulated size; and they are pulled up even higher into the scrotum by a further shortening of the spermatic cord Indeed, the full elevation of the testes is a sign that a man has reached the "point of no return", and that his orgasm is imminent. If the man's nipples did not erect earlier, they may erect now.
In both men and women, the rate of breathing increases during the plateau phase, and there is a further increase in pulse rate and blood pressure. The sex flush may now appear, or may become more marked and widespread if it appeared earlier. The tension of both voluntary and involuntary muscles is heightened; and there may be almost spastic contractions of some sets of muscles in the face, ribs, and abdomen. The sphincter muscle, which holds the rectum closed, may tighten up; indeed, some men and women tighten up both this muscle and the muscles of the buttocks as a deliberate means of heightening tension.
In the female breasts, there is a further swelling of the areolas surrounding the nipples. This is often so marked as partially to mask the erection of the nipples; they may look shorter as a result. But in fact, there may be a further swelling of the nipples under the areolar mask.
If coitus is prolonged, a few drops of moisture may emerge from the Bartholin's glands imbedded in the woman's outer lips, as noted above. A few drops of moisture may also emerge from the male urethra. This fluid probably comes from Cowper's glands - the male equivalent of the female Bartholin's glands. The fluid is not semen; but it is important to know that large numbers of active sperm cells are sometimes found in it. Thus there is at least a possibility that a woman may become pregnant following the secretion of these preliminary droplets - even though the man withdraws his penis before semen is actively ejaculated. A man who does not ordinarily emit this preliminary fluid, moreover, may do so on some occasions.
The most dramatic change in women during the plateau phase is the appearance of the "the orgasmic platform." This is the engorgement and swelling of the tissues surrounding the outer third of the vagina. As a result of this swelling, the diameter of the outer third is reduced by as much as 50 per cent. It thus actually grips the penis, and the erotic stimulus experienced by the man is notably increased. The appearance of the orgasmic platform, however, does not necessarily mean that a woman is ready for orgasm.
Accompanying the appearance of the orgasmic platform is a further elevation of the uterus, and a further ballooning of the inner two-thirds of the vagina. The uterus also becomes enlarged during this phase; it may even double in size in women who have had babies. Among women who have not had babies, the size increase is less impressive, but it is noticeable in many cases.
Another dramatic change during the plateau phase is the elevation of the clitoris. In the process of elevation, the clitoris rises from its normal position overhanging the pubic bone, and seems to become retracted. It is drawn further away from the vaginal entrance. The clitoral shaft is shortened by as much as 50 per cent following elevation, and it may seem to be lost altogether, or harder to find. It continues to respond to stimulation, however, either directly applied to the mons veneris, or indirectly through the thrusting of the penis into the vagina.
The outer lips of the vagina of women who have had babies may become even more engorged during the plateau phase than during the excitement phase; and even in women who have never had a child there may be some swelling of the outer lips if erotic stimulation has been prolonged. The inner lips change colour late in the plateau phase, from bright red to a deep wine colour in women who have had children, and from pink to bright red in women who have not. This colour change is important, for it is a sure sign that orgasm will occur - usually within a minute or a minute and a half - if effective erotic stimulation is continued. On occasions when a woman fails to reach orgasm despite prolonged stimulation, she also fails to show this tell-tale colour change of the inner lips.
While these many changes, occurring in many parts of both male and female bodies, may seem complex and different from one another, all or almost all of them, as noted earlier, seem to fall into two main classes: the engorgement of blood vessels and other organs, and increases in muscle tension. Both the male and female achieve readiness for orgasm, it seems likely, when these two processes of increased engorgement with blood and increased muscular tension reach adequate peaks. The plateau phase is the period during which "the female gathers psychological and physiological strength from the stockpile of mounting sexual tension, until she can direct all her physical and mental forces toward a leap into the third, or orgasmic phase of sexual tension expression.
The major observable feature of the female orgasm is a series of rhythmic contractions of the orgasmic platform, that is, of the outer third of the vaginal barrel and the engorged tissues surrounding it. These rhythmic contractions are muscular contractions.
The first few contractions occur at intervals of four-fifths of a second. Thereafter the intervals tend to become longer, and the intensity of the contractions tends to taper off. A mild orgasm may be accompanied by only three to five contractions, an intense orgasm by eight to twelve. In an extreme case, actually recorded on an automatic recording drum in the laboratory, twenty-five rhythmically recurring contractions of the orgasmic platform followed one by another over a period of forty-three seconds.
The onset of orgasm as experienced subjectively occurs simultaneously with an initial spasm of the orgasmic platform preceding the rhythmic train of contractions by a few seconds. Along with this series of contractions of the orgasmic platform, the uterus also contracts rhythmically. Each contraction begins at the upper end of the uterus and moves like a wave through the raid-zone and down to the lower or cervical end. The more intense the orgasm, the more severe are these contractions of the uterus. Labour contractions prior to childbirth move similarly downward along the uterus in a wavelike progression, but are much stronger. Other muscles, such as the anal sphincter muscle, may also undergo rhythmic contractions.
The male orgasm is rather similar in several respects. The central occurrence is a series of rhythmic contractions timed, as in the female, at intervals of four-fifths of a second. Following the first few contractions, in the man as in the woman, the intervals between contractions tend to become longer and the intensity of the contractions tapers off. As in the case of women, men may subjectively identify the onset of orgasm a few seconds before the occurrence of the first observable contraction.
The ejaculation of semen, which occurs during the male orgasm, is a complex process. Prior to orgasm, fluid containing millions of sperm cells from the testes has collected in the sacs known as seminal vesicles and in a pair of flask-like containers known as ampullae. These organs contract rhythmically, expelling their contents into the urethra. At the same time the prostate gland contracts rhythmically and expels prostatic fluid into the urethra. A bulb in the urethra near the base of the penis doubles or triples in size to receive the fluids. These changes constitute the first stage of ejaculation. The subjective feeling of orgasm occurs during this first stage.
During the second stage, a series of rhythmic contractions of the urethral bulb and of the penis itself projects the semen outward under great pressure, so that if it is not contained, the semen may shoot as much as two feet beyond the tip of the penis. In older men, the contractions may be somewhat less vigorous, and the pressure of expulsion somewhat lessened. The urethra may undergo a series of minor contractions for several seconds after the contractions of the penis as a whole are no longer perceptible.
In both men and women, the events occurring in the genital organs during orgasm are accompanied by changes in the rest of the body. Pulse rate, blood pressure, and breathing rate reach a peak. The sex flush is most pronounced. And muscles throughout the body respond in various ways.
The face, for example, may be contorted into a grimace through the tightening of muscle groups. The muscles of the neck and long muscles of the arms and legs usually contract in a spasm. The muscles of the abdomen and buttocks are also often contracted. Of special interest are the reactions of the hands and feet. Often a man or woman grasps his partner firmly during orgasm; the hand muscles then clench vigorously. If the hands are not being used in grasping, a spastic contraction of both hands and feet known as "carpopedal spasm" can be observed. Men and women are usually quite unaware of these extreme muscular exertions during orgasm; but it is not unusual for them to experience muscle aches in the back, thighs, or elsewhere the next day as a result.
One major function of the orgasm becomes clearly visible in both men and women soon after it subsides. Orgasm initiates the release of muscular tensions throughout the body, and initiates the release of blood from the engorged blood vessels.
The first notable occurrence in women during the resolution phase that follows orgasm is the immediate return to normal of the areolas surrounding the nipples. Indeed, their rapid subsidence gives an observer the impression that the nipples are undergoing a further erection - though they are in fact only becoming more visible as the swelling around them subsides. The increased prominence of the nipples is a sign that the woman has in fact experienced orgasm. This sign appears so rapidly that it might almost be assigned to the end of the orgasmic phase rather than to the beginning of the resolution phase. Another sign of orgasm is the rapid disappearance of the sex flush in women who have had the flush during orgasm.
Accompanying the disappearance of the sex flush, a filmy sheen of perspiration appears on many women. In extreme cases it may cover a woman's entire body from shoulders to thighs. In other cases the perspiration may appear only on the soles of the feet and the palms of the hands, and there are other variations. About one-third of the women have this tendency to perspire following orgasm.
About one-third of the men also perspired at this time, but the reaction was more often limited to the soles and palms.
Neither this perspiration nor the sex flush is related to the degree of muscular effort prior to or during orgasm. Yet women often show a marked flush phenomenon over the entire body during plateau and orgasm, and during resolution may be completely covered by a filmy, fine perspiration. Within five or ten seconds after a woman's orgasm subsides, several other changes can be noted. The clitoris promptly returns to its unstimulated position, overhanging the pubic bone; however. five or ten minutes may elapse, or in extreme cases half an hour, before it shrinks to normal size. Soon after this the orgasmic platform relaxes so that the outer third of the vaginal barrel increases in diameter. The ballooning of the vagina begins to diminish, and the uterus begins to shrink. The cervix descends into its normal position, and the passageway through the cervix enlarges perhaps to make easier the ascent of the sperm cells into the uterus. These processes continue at various rates for various periods of time; as long as half an hour may elapse following orgasm before the entire female body is restored to its erotically unstimulated state.
If a woman who has reached the plateau phase does not experience orgasm, the resolution phase takes much longer - an hour or so in many cases. In men the most obvious sign of the resolution phase is the prompt loss of erection of the penis and its shrinkage back to its unstimulated size. This shrinkage occurs in two stages. The first is quite rapid, but leaves the penis still noticeably enlarged. The remainder of the shrinkage is often a much slower process.
The male sex flush, like the female, rapidly disappears. The return of the scrotum and testes to their unstimulated state may be either rapid or slow. If the male nipples have erected, many minutes may elapse before they return to normal.
In both men and women, the pulse rate, blood pressure, and breathing rate gradually return to normal.
A significant feature of the male resolution phase is the "refractory period" that accompanies it. During this period. a man cannot again become sexually aroused or have another erection. In some men this period may be quite brief; one young man under laboratory conditions was able to achieve three orgasms in ten minutes, for example. But in most men it lasts for many minutes at least; and it tends to increase in duration as a man grows older.
Women do not have a similar refractory period. Indeed, if effective sexual stimulation is renewed immediately following orgasm, many women can promptly reach a second orgasm. A series of half a dozen or even a dozen orgasms without intervening resolution phases is not unusual for some women; during such a series, some women do not fall below the plateau level of arousal. This "multi-orgasmic response" is described further below.
No single sexual experience, let us stress, proceeds in precisely the way described, just as no individual human being precisely matches the characteristics of the "usual", or "average", or "typical" human being. Thus the above description should not be considered a model or norm toward which men and women should strive. On the contrary, it is simply a description of what often or usually happens. The sexual responses of any individual man or woman will almost certainly fail to show some of the characteristics described above, and will show features omitted from the description. It is usual and normal to vary from the norm. Individual variations are often in fact improvements rather than defects.
Note that the description we have presented above makes almost no distinction among sexual responses to masturbation, to sexual intercourse, or to other forms of stimulation including breast manipulation and artificial coition. The reason is quite straightforward. The same responses occur, in very much the same order, regardless of the type of stimulation that evokes them.
Some responses, it is true, may tend to occur a little more promptly, or to be a bit more intense, when evoked in one way rather than another. Some individuals no doubt respond more readily to one kind of stimulation than to another. Psychologically, the experiences may feel altogether different. But the basic pattern of bodily responses remains the same.