“Now, when suffering is always the first of the arguments marshalled against life, as its most questionable feature, it is salutary to remember the times when people made the opposite assessment, because they could not do without making people suffer and saw first-rate magic in it, a veritable seductive lure to life. Perhaps pain - I say this to comfort the squeamish - did not hurt as much then as it does now; at least, a doctor would be justified in assuming this, if he had treated a Negro (taken as a representative for primeval man) for serious internal inflammations which would drive the European with the stoutest constitution to distraction; - they do not do that to Negroes.”

The curve of human capacity for pain actually does seem to sink dramatically and almost precipitously beyond the first ten thousand or ten million of the cultural elite; and for myself, I do not doubt that in comparison with one night of pain endured by a single, hysterical blue stocking, the total suffering of all the animals who have been interrogated by the knife in scientific research is as nothing.
Essay 2, Section 7
On the Genealogy of Morality (1887)