position in regard to this and allied superstitions, see Reginald Lane
Poole's Illustrations of the History of Medieval Thought, London, 1884.

The first great tributary poured into this stream, as we approach the
bloom of the Middle Ages, appears to have come from the brain of Michael
Psellus. Mingling scriptural texts, Platonic philosophy, and theological
statements by great doctors of the Church, with wild utterances obtained
from lunatics, he gave forth, about the beginning of the twelfth
century, a treatise on The Work of Demons. Sacred science was vastly
enriched thereby in various ways; but two of his conclusions, the
results of his most profound thought, enforced by theologians and
popularized by preachers, soon took special hold upon the thinking
portion of the people at large. The first of these, which he easily
based upon Scripture and St. Basil, was that, since all demons suffer by
material fire and brimstone, they must have material bodies; the second
was that, since all demons are by nature cold, they gladly seek a genial
warmth by entering the bodies of men and beasts.(348)

(348) See Baas and Werner, cited by Kirchhoff, as above; also Lecky,
Rationalism in Europe, vol. i, p. 68, and note, New York, 1884. As to
Basil's belief in the corporeality of devils, see his Commentary on
Isaiah, cap. i.

Fed by this stream of thought, and developed in the warm atmosphere of
medieval devotion, the idea of demoniacal possession as the main source
of lunacy grew and blossomed and bore fruit in noxious luxuriance.

There had, indeed, come into the Middle Ages an inheritance of
scientific thought. The ideas of Hippocrates, Celius Aurelianus,
Galen, and their followers, were from time to time revived; the Arabian
physicians, the School of Salerno, such writers as Salicetus and Guy de
Chauliac, and even some of the religious orders, did something to keep
scientific doctrines alive; but the tide of theological thought was
too strong; it became dangerous even to seem to name possible limits to
diabolical power. To deny Satan was atheism; and perhaps nothing did so
much to fasten the epithet "atheist" upon the medical profession as the
suspicion that it did not fully acknowledge diabolical interference
in mental disease. Following in the lines of the earlier fathers, St.
Anselm, Abelard, St. Thomas Aquinas, Vincent of Beauvais, all the great
doctors in the medieval Church, some of them in spite of occasional
mi