But here's an interesting an interesting quote regarding blacks' supposed insensitivity to pain:
Negroes can also bear pain better than whites. "I have amputated the legs of many negroes," White quotes a surgeon as saying, "who have held the upper part of the limb themselves." The logical conclusion is, of course, not that such Negroes are brave but that they are insensitive to pain.
--Race: The History of an Idea in America, p. 49. Here Gossett was quoting Dr. Charles White's An Account of the Regular Gradation in Man
[Edit 3/10/2008] And here's another person apparently quoting the same surgeon, so you can get the surgeon's name, a longer quote, and evidence that more people were spreading this idea than just one.