+214. Manias, delusions.+ The phenomena of manias, popular delusions, group hallucinations, self-immolation, etc., show the possibilities of mental contagion in a group. They are responses to hope or fear which affect large numbers at the same time. They are often produced by public calamities, or other ills of life. Those who suffer feel themselves selected as victims, and they ask, Who has done this to us, and why? Often people who are not victims interpret a natural incident by egoistic reference. This is done not on account of the destruction wrought by an earthquake or a tornado, but from pure terror at what is not understood, e.g. an eclipse.[440] Pilgrimages and crusades were cases of mania and delusion. The element of delusion was in the notion of high merit which could be won in pursuing the crusades. Very often manias and delusions are pure products of fashion, as in the case of the children's crusades, when the children caught the infection of the crusades, but did not know what they were doing, or why, and rushed on their own destruction. Often manias are logical deductions from notions (especially religious notions) which have been suggested, as in the case of the flagellants. It is the ills of life which drive people to such deductions, and they bear witness to excessive nervous excitement. The mediaeval dancing mania was more purely nervous. The demonism and demonology of the Middle Ages was a fertile source for such deductions, which went far to produce the witchcraft mania. The demonistic notions taught by the church furnished popular deductions, which the church took up and reduced to dogmatic form, and returned as such to the masses. Thus the notions of sorcery, heresy, and witchcraft were developed.