From The Sultans, by Noel Barber (Simon & Schuster, 1973), pp. 69-70:
The servant problem was non-existent, for the Constantinople slave market was open daily, except on Fridays, from 8 a.m. to midday. Behind an enormous wooden gate a large colonnaded courtyard was surrounded by small chambers (and a coffee shop for would-be purchasers who liked to dawdle). This was the slave market for ‘domestic servants’, mostly negresses, whose teeth, muscles, legs were examined with the methodical attention of a horse-trader. It was, of course, quite another matter to purchase a beautiful Georgian or Circassian girl as a mistress, for the best were inevitably snapped up for the Sultan, and indeed there was such a shortage that the Circassians, so it is said, soon had to start their own slave farms where ‘they grew beautiful women as other countries might grown wheat or cattle — for sale’. At least the slave farms produced one benefit for posterity, for ‘the avid demand for them in Istanbul encouraged parents to preserve their girl children from the disfigurement of the widespread smallpox by innoculation’ [by variolation].
It was from Circassia that innoculation spread westwards to the many European doctors living in Constantinople. However skilful the medical men might have been, their chances of curing female patients was somewhat restricted because they were never allowed to see them. They did the best they could — and it usually consisted of delivering a few leeches to bleed a patient, for leeches could be applied by eunuchs or slaves in the harem. They were a government monopoly, and huge numbers were exported to Germany and Russia. The best ones came from Anatolia — ‘they are said to be more eager to perform their duty’ — and when the cure was ended the haemorrhage was arrested by the Turkish equivalent of a modern styptic, a coating of pounded coffee, which was not uncomfortable unless the patient had to remain in bed, for as the coffee dried and fell off the bed became covered with grit.