In the case of women, it is my contention that when during intercourse the vagina is rubbed and the womb is disturbed, an irritation is set up in the womb which produces pleasure and heat in the rest of the body. A woman also releases something from her body, sometimes into the womb, which becomes moist, and sometimes externally as well, if the womb is open wider than normal. Once intercourse has begun, she experiences pleasure throughout the whole time, until the man ejaculates. If her desire for intercourse is excited, she emits before the man, and for the remainder of the time she does not feel pleasure to the same extent; but if she is not in a state of excitement, then her pleasure terminates along with that of the man. What happens is like this: if into boiling water you pour another quantity of water which is cold, the water stops boiling. In the same way, the man's sperm arriving in the womb extinguishes both the heat and the pleasure of the woman. Both the pleasure and the heat reach their peak simultaneously with the arrival of the sperm in the womb, and then they cease. If, for example, you pour wine on a flame, first of all the flame flares up and increases for a short period when you pour the wine on, then it dies away. In the same way the woman's heat flares up in response to the man's sperm, and then dies away. The pleasure experienced by the woman during intercourse is considerably less than the man's, although it lasts longer. The reason that the man feels more pleasure is that the secretion from the bodily fluid in his case occurs suddenly, as the result of a more violent disturbance than in the woman's case.
Another point about women: if they have intercourse with men their health is better than if they do not. For in the first place, the womb is moistened by intercourse, whereas when the womb is drier than it should be it becomes extremely contracted, and this extreme contraction causes pain to the body. In the second place, intercourse by heating the blood and rendering it more fluid gives an easier passage to the menses; whereas if the menses do not flow, women's bodies become prone to sickness.
When a woman has intercourse, if she is not going to conceive, then it is her practice to expel the sperm produced by both partners whenever she wishes to do so. If however she is going to conceive, the sperm is not expelled but remains in the womb. For when the womb has received the sperm it closes up and retains it, because the moisture causes the womb's orifice to contract. Then both what is provided by the man and what is provided by the woman is mixed together. If the woman is experienced in matters of childbirth, and takes note when the sperm is retained, she will know the precise day on which she has conceived.
Now here is a further point. What the woman emits is sometimes stronger, and sometimes weaker; and this applies also to what the man emits. In fact both partners alike contain male and female sperm (the male being stronger than the female must of course originate from a stronger sperm). Here is a further point: if (a) both partners produce a stronger sperm, then a male is the result, whereas if (b) they produce a weak form, then a female is the result. But if (c) one partner produces one kind of sperm, and the other another, then the resultant sex is determined by whatever sper prevails in quantity. For suppose that the weak sperm is much greater in quantity than the stronger sperm: then the stronger sperm is overwhelmed and, being mixed with the weak, results in a female. If on the contrary the strong sperm is greater in quantity than the weak, and the weak is overwhelmed, it results in a male. It is just as though one were to mix together beeswax with suet, using a larger quantity of suet than of beeswax, and melt them together over a fire. While the mixture is still fluid, the prevailing character of the mixture is not apparent: only after it solidifies can it be seen that the suet prevails quantitatively over the wax. And it is just the same with the male and female forms of sperm.