In the instances noted by baffo, these were very likely case studies in projection; at least it is read as such by many of those who have studied medieval Christian forms of anti-semitism, including many 20th-century Christian writers, such as Paul Johnson. Historic instances of blood libel (sometimes also called blood accusation) have included:

  • Accusations by Antiochus IV, who was said to have found a non-Jew who claimed that Jews kidnapped him and held him for a year, fattening him up to be sacrificed.
  • Norwich, England (1144). Jews accused of kidnapping William, a local child and tormenting him exactly as they had Jesus. Rioting and massacres of Jews followed these accusations.
  • Until the 1600's, the primary Blood Accusation was that Jews needed Christian blood to reenact the crucifixion of Jesus.
  • It was also widely thought that Jews needed Christian blood to cure the side-effects of circumcision and (if my sources are correct) to prevent Jewish men from menstruating. (This is consistent with some widely held Christian beliefs of the time, which persist in some circles to this day, no doubt, regarding Jewish sexuality in general. But that's a topic for a whole other set of nodes.)
  • Although Pope Innocent IV wrote a strong official letter to discredit all of these beliefs, the rumors and related killing of Jews in "retaliation" persisted.
  • In the 17th century, the belief surfaced that Jews needed Christian blood to make Passover matzah. This became the classic Blood Libel accusation from that time onward. Rational proofs by Christian leaders and Jews alike that Jews were forbidden to consume any kind of blood, did little or nothing to stop these accusations or restrain mob actions. This aspect of blood libel is most curious, in light of Christian (or at least Catholic) beliefs regarding transubstantiation. See the note above, regarding projection. The historical timing of this particular element in the blood libel story also may suggest a connection between this myth and the rise of Protestant sects within Christianity? (see: subjects for further research.)
  • Blood accusations were used frequently in Czarist Russia to encourage anti-semitism among the peasantry, and probably relates closely to the high frequency of pogroms in the Pale of Settlement, the area that most Russian Jews were restricted to in Russia under the Czars.
  • David E. Lipman. Gates of Jewish Heritage (web essay)
  • Paul Johnson. A History of the Jews (book)