Host desecration is an anti-semitic myth similar to the blood
libel myth. It started in late 13th century England and France
(a century after the blood libel myth started), were it was
claimed that Jew would steal consecrated host
wafers and torture them. According to the theory of
transubstantiation, a consecrated host wafer became the flesh of
Christ, so it was believed that Jews would steal and torture
these wafers to reenact the crucifixion of Christ. This myth
portrayed Jews in an even worse light than before, since it
implied that they believed that Jesus was the Messiah and Son
of God, yet they still tortured him; if they didn't believe, then
why would they go to the trouble of stealing an ordinary cracker
and stabbing it with a knife?
In some variants of the myth, the stabbed wafer bled, causing the
Jew to freak out and convert. Later this variant changed to
the wafer bleeding, and the Jew, rather than converting in the
face of this miracle, buried the wafer in an attempt to hide it;
where the wafer was buried, a new spring burst forth from the
ground. Regardless of the variation, many Jews were killed
because of this myth until it started to wane with the advent of
Protestantism.
Sources:
Title: Antisemitism; The Longest Hatred
Author: Robert S. Wistrich
Publisher: Methuen London
ISBN: 0-413-65320-X
Title: Ideology of Death
Author: John Weiss
Publisher: Ivan R. Dee
ISBN: 1-56663-088-6