Contends that the confessions of the Jews accused of the ritual murder of Simon of Trent in 1475 allows the formulation of a hypothesis of magic and symbolic use of blood, dried and reduced to powder, among certain Jewish extremist circles, in the liturgy of Passover, especially as part of the rite of cursing the Christians. That custom may have given support to the accusation of ritual murder and a tendentious interpretation by the judges. Discusses, also, other cases of blood libels, such as Norwich in 1144, Regensburg in 1467, and Endingen in the 1470s. During the Middle Ages, several factors may have contributed to the formation of the stereotype of the Jew as a ritual murderer: the widespread use, among them, of blood in magic and medicine, passages in the Bible referring to sacrifices and blood, which were related again and again in the churches to an ignorant and superstitious audience, the Jewish practice of circumcision, the narratives about Jews who killed their own children during the Crusades to avoid conversion, and possibly, the violent response of Jewish extremists against Christian persecution as well as the possible existence of criminal murderers who just happened to be Jews. Concludes that there is no doubt about the fact that the practice of ritual murder, or infanticide, by the Jews belongs to the category of myth. Pp. 363-398 of the second edition present a defense of this research work against the criticism which arose in academic circles.