Aristotle's Problems

...[hairs] are vigorous for performing their duties.
Why are the same [eunuchs] shrill-voiced? Because from an overabundance of moisture, the windpipe, becoming soft, is made narrower; and the spirit, passing through narrow places, renders the voice shrill. Whereas through more spacious places, it emits a great voice like that of men. Take for yourself an image from the sounds of flutes: when they are filled with very much moisture, they will be muffled. This is also manifest from the fact that they become obese and develop womanly breasts; their eyelids are also thick, their hair is long, and they turn white with much grayness.
Why do some eunuchs desire sexual union to some extent, and sometimes love passionately? Because in many, the testes were suppressed or damaged while they were reaching puberty, and they are, as it were, imperfect eunuchs. But those who are by nature of a warmer liver and have large genital vessels conceive the vision of the use, but do not perform what they have desired, because the private parts themselves grow flaccid. For the spirit, which had continuously swelled, deserts them; just as it was prepared from a woman, it was carried through the female pores from those parts which are around the hips, just as in boys the descending female pores are obstructed.
Why do we produce grayness in every hairy place, but not in the armpits? Because the place is warm. For it is filled with both arteries and veins; otherwise, since it also has open pores, it continuously carries off phlegmatic superfluities, which the perpetual sweat emanating from it indicates.
Why do some, overcome with shame or full of joy, emit sweat from the armpits? In whomever the pores are more open: for when nature is turned back by honor or a worthy reverence, it retreats moderately with the blood into the greatest veins and arteries, which, being filled, exude; but in those who are joyful, as the body relaxes and becomes rare, it happens that they do this more intensely in the armpits.
Why do those who fear grow pale? Because our nature and the force of the body dreads an unforeseen event, lest it suffer something from without; just as we also flee into a house, so it too flees strongly into the interior of the body for the sake of protecting itself. It draws back with itself the blood, which it uses as nourishment and a vehicle, as it is the only thing useful to it. And it was this which rendered the skin rosy and ruddy.
Why also do we tremble? Since nature is agitated toward itself in every animal, fleeing, it abandons the nerves it was guarding—parts which do not usually fall under trembling—but because of this they also defecate and urinate against their will. For the muscles closing the pores of the superfluities, being then powerless, relax the superfluities.
Why do those who rejoice redden? Because nature, devoted by its own character to pleasure, runs out toward whatever is present outside, just as we do toward a friend or our children; the blood follows this, which we know renders the skin ruddy by its color. But they grow pale from the contrary cause.
Why do those who are bashful also redden? Because nature, instructed by itself and conscious of something, fears lest it lose the dignity of honor; just as an honorable pupil is moderately withdrawn inward and receives the intestines into the heat of the body. Therefore, the blood being mixed and poured forth, the skin is stained with the color of the blood; there are those who say it is poured forth as a means of covering. For thus, at the dictate of nature, they also place the hand before the face.
Why do some collapse dead before dread? Because the natural force, retreating strongly inward with the blood, drowns the innate and vital heat produced by the heart when it is oppressed in a mass, and brings on a fatal corruption; by this reasoning, much oil poured all at once upon the flame of a lamp extinguishes it; surely the heat which is in the heart has a proportion with the flame of a lamp. Thus, those afflicted by immoderate grief have collapsed dead by the same reasoning: because the internal heat is abolished by external motion, just as a fire that is covered and cannot exhale is extinguished.

Why do some [redden] from shame?

What is the cause that redness is born in the body from the shame of the soul? And he said: Nature, when something worthy of honorable shame occurs to it, penetrates the blood by seeking the depths; by which being moved and diffused, the skin is stained, and from there redness is born. Physicians also say that nature, touched by shame, thus spreads the blood before it as a veil, as we see everyone who is blushing frequently place a hand before his face; nor can you doubt these things, since redness is nothing other than the color of the blood. Servius adds: And why do those who rejoice redden? And he said, quite differently: it happens externally that nature hastens with a spirited course toward this, which the blood, accompanying as if with the alacrity of its integrity, stains the skin, and from there a similar color is born. He relates the same regarding those who fear, by what reasoning they grow pale; nor is this, he says, hidden quite differently. For nature, when it fears something from external events, is entirely submerged into the depths; just as we also fear and seek hiding places and spots that conceal us. Therefore, failing entirely so that it may hide, it draws with it the blood, by which it is always carried as if by a chariot; when this is submerged, a thinner humor remains in the skin, and from there it grows pale. Therefore, those who fear also tremble, because the virtue of the soul, fleeing inward, leaves the nerves by which the strength of the limbs was held, and from there they are agitated by the leap of fear; hence also a relaxation of the belly accompanies fear, because the muscles by which the passages of the dregs were closed, deserted by the virtue of the soul fleeing inward, relax the bonds by which the dregs were contained until the opportunity for digestion.