This section is from the book "Human Sexuality", by J. Richardson Parke. Also available from Amazon: Human Sexuality.
But the erection-center is not alone influenced by the venereal passion.1 The nervous excitement is distributed to all the motor nerves of the spinal axia and arteries, There are great swelling and redness (engorgement) of the penis, the clitoris, and the lips of the vulva; injection of the conjunctivae, starting of the eyes, dilatation of the pupils, quick palpitation of the heart, with shivering, nervous tremors, and short, gasping breath. In fact, both the muscular and nervous systems are highly affected; more highly in the male than the female, though the pleasurable feeling of the act, while slightly weaker, is continued longer in the latter than the former.
The climax of the pleasure resulting to the male from the ejaculatory act is synchronous with the passage of the semen through the ve#iculce seminalet into the urethra; that which precedes it being the pleasant tit-illation of the Bensory nerves which surround the head of the penis, which continues to grow in intensity with the progress of the intercourse, until it at last culminates in the supreme nervous Bhock—the discharge of the stored up nerve-energy of the whole period of tumescence—which accompanies the emission of the semen, and which then gradually subsides and disappears, poat-ejaculationem.
From the moment the penis enters the vagina, however, there is pleasure to the male; while, from a variety of causes—irritability, or disease, of the vaginal mucous membrane; shortness of the vaginal tract; abnormal length of the penis, forcibly driven against the mouth of the womb; in fact from any one of a dozen different causes—the same may not be true as regards the female.
 
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sexuality, reporduction, genitals, love, female, humans, passion