Five Quarts_ A Personal and Natural History of Blood - Bill Hayes [102]
Naturally, the impetus for arousal varies from person to person, but regardless of the accelerant—a look, a smell, a touch—the biology is consistent. As ardor takes hold and heartbeats quicken, the brain green-lights the circulatory system to rush blood to certain sexually pleasing places as well as others less obvious. Capillaries in your earlobes and those lining the interior of your nostrils, for instance, will fill with freshly oxygenated blood, causing the skin to plump and become extra sensitive. Likewise, the tiny vessels in the lips and tongue fatten and warm, literally raising the temperature of your kisses.
Though it sure may feel like it, blood doesn’t increase in volume during arousal but gets redirected. In women, blood turns the pelvic area into a tropical zone, the labia and clitoris swelling, sensitivity building. The breasts, too, become fuller, the nipples stiffening from the blood-soaked spongy tissue within. Male nipples perform similarly, though, being of smaller stature generally, at a more modest scale. Of course, a grander transformation occurs in the groin, where arteries dilate to allow increased blood flow to the penis. Here, forming the length of the shaft, are three clustered cylinders that dangle like a soggy noodle when the penis is flaccid. (The urethra runs through the bottommost of these.) As these spongy tubes soak up blood, however, the organ bulges in all dimensions—on average, about two extra inches in length, more than half an inch in girth—raising the pressure within until it stands erect.
That it is called an erection merits a wee digression: How very male and grandiose the word sounds to my ear, bringing to mind such awe-inspiring feats of engineering as hoisting an ancient obelisk or raising a modern skyscraper. In point of fact, achieving an erection requires less blood to the penis than one might imagine, though don’t tell this to your typical size-sensitive male. About two ounces—or, one-eightieth of a 150-pound man’s total blood volume—is all it takes to make him hard.
Leonardo da Vinci
From the classical age to the Renaissance, it was believed that an erection was due to a breath-like substance brewed in the liver, Natural Spirits, which inflated the penis as, to use a modern analogy, air does a tire. The brilliant Leonardo da Vinci, a visionary in conceiving of such marvels as flying machines and diving gear, was also prescient in identifying the inner workings of male genitalia. More than a hundred years before blood’s role in erection was first correctly described in Western medical literature, Leonardo accurately summed it up in one of his illustrated notebooks. In 1477 he’d attended the public hanging of a criminal in Florence and, like others in the crowd, couldn’t help noticing that an erection was a consequence of this form of execution. During the subsequent dissection of the man’s body, Leonardo saw that it was in fact blood that had filled the organ, a result of the violent, downward jolt. (Incidentally, the phrase well hung, slang for “having large genitals,” does not derive from such observations. Rather, it dates back to an early-seventeenth-century description of a man’s jumbo ears, of all things, a usage that soon broadened to encompass any oversized body part. In any event, grammatically speaking, a noose and a fall lead to being well hanged, not well hung.) Following the dissection, Leonardo wrote, “If an adversary says wind caused this enlargement and hardness, as in a ball with which one plays, I say such wind gives neither weight nor density. Besides,” he added, referring now to the head of the phallus, “one sees that an erect penis has a red glans, which is the sign of the inflow of blood; and when it is not erect, this glans has a whitish surface.”
In his work A Mind of Its Own (2001), a “cultural history of the penis,” David M. Friedman writes with an implied wink that Leonardo, whom modern scholars