After stating what a dream is, the author discusses the origin and causes of dreams further. Some are from the devil or at least are influenced by demons, as when a monk was led to become a Jew by a dream in which he saw Moses with a chorus of angels in white, while Christ was surrounded by men in black. But when we see chimeras in dreams, this is generally due to impurity of the blood. The author also opines that, while the sage can judge from the nature of the dream whether there is fallacy and illusion of the demon in it, the origin of virtues and vices is mainly in ourselves. He who goes to sleep with an easy conscience is unlikely to be disturbed by nightmares and is more likely in quiet slumber to behold secrets and mysteries. The author next discusses the effect of the passions and exercise of the mental faculties upon the liver, heart, and brain. He adopts the common medieval view that the brain contains three ventricles devoted respectively to imagination, reason, and memory. He explains that the so-called _incubus_, popularly thought of as a dwarf or satyr who sits on the sleeper, is really a feeling of suffocation produced by blood-pressure near the heart. The interpretation of a dream must vary according to the social rank of the person concerned. As images in a mirror deceive the ordinary observer but are readily accounted for by the geometer, and as the philosopher notes the significations of other planets than the sun and moon, whose effects alone impress the vulgar herd, so there are dreams which only a skilled interpreter can explain. Dreams are affected by food and by the humors prevailing in the body, and also by the occult virtues of gems, of which a list is given from “Evax” or Marbod.[944] [Sidenote: Interpretation.] The second book takes up again the varying significations of dreams according to the person concerned, and also the significance of the time of the dream. The four seasons, the phases of the moon, nativity of the dreamer, and hour of the night are discussed. The remaining two-thirds of the treatise consists in stating the interpretation to be placed upon the varied persons and things seen in dreams, beginning with God and Jesus Christ, and continuing with crucifixes, idols, statues, bells, hell, the resurrection of the dead, and so on and so forth. Early mention of eunuchs and icons suggests a Byzantine source. More especially in the last third of the treatise, various marginal headings indicate that the interpretations are “according to the Indians” or “according to the Persians and Egyptians,” which suggests that use is being made of the work of Achmet or of Leo Tuscus’ translation thereof. [Sidenote: William of Aragon on prognostication from dreams.]