John O. Hunwick, Eve Troutt Powell, The African diaspora in the Mediterranean lands of Islam

Making of a eunuch in the Ottoman Empire:

Details of the operation

The operator seizes the penis, the scrotal sacs and the testicles and ties them together tightly with a thin but tough cord. Then, with a single razor stroke, he cuts off everything below the ligature. The huge wound is then covered with ashes to stop the bleeding, then boiling oil is poured on and finally, if the first two methods have proved ineffective, it is cauterised with a red-hot iron. This having been done, a crude probe of metal, usually of lead, is inserted in the urethra right up to the bladder to facilitate the flow of urine. This probe is held in place by a harness of the most primitive type which remains in place until healing is complete. 

When all these measures have been taken, the patient is immersed to the waist in the muddy silt of the Nile and left there for five or six days to help the formation of scar tissue. The Nile—that supreme god—ought to heal all ills. These details are horrible, but true. Therefore, I have no fear of exposing them in all their hideousness and fearfulness.

The general appearance of eunuchs after the operation. 

This is the appearance most generally presented by the genitals, or rather their place, after the operation: a huge broad scar of very irregular shape, with raised edges, the scar tissue being of a lighter colour than the surrounding skin, full of folds and wrinkles. There is a purulent discharge, mixed for a long time—often several months—with a great deal of matter tinged with blood. There is almost continuous pain in the perineum, sharp and stabbing at first, later dull. Then come loss of appetite, nostalgia, strange dreams, terrible nightmares; the brain becomes empty, ideas flee, thought is wiped out. The eunuch turns into a brute. The man has disappeared. 

Incontinence, especially during the night during sleep, is almost always one of the inevitable results of castration. From the accursed day henceforth the wretched eunuch always has with him, at home or on his person, a probe which he uses to project his urine to a distance. Sixty percent die during the operation or as a result of it. Those who survive receive assiduous attention and usually attain to more or less complete healing towards the end of the third month after the operation. From then on they are merchandise having a value and are soon sent off to Cairo to become the property of beys and pashas, or towards Alexandria from where they are sent on to Syria and Turkey. A young eunuch is then sold for about 25 purses, the value of a purse being 80 francs.

Also: Jane Hathaway: Eunuchs in Islamic Civilization