The causes of this malady are hereditary or accidental. Pale, delicate, thin, scrofulous, anæmic, very intelligent or irritable children are easily attacked; predisposed to it also are children of excitable parents, or of those troubled with nervous affections. Amongst occasional causes of the _pavor nocturnus_ may be specially mentioned strong emotions, fever, and diseases of the digestive organs. In general the children recover; the prognosis, as we say, is favourable. Some retain their excessive nervous excitability, are subject to palpitation of the heart, but only in very exceptional conditions have the attacks of _pavor nocturnus_ exercised a lastingly injurious influence. IV The dreams of children are more real, vivid, fearful than of adults, because their brain is excessively impressionable, as is shown by the fact that things seen in childhood are indelibly impressed on the memory, and because their life is made up of emotions, while their weakness renders them more timorous, exaggerates every danger, and makes every enemy appear disproportionately superior to them in strength. Emotions and fright may become so great in dreams that some children have had actual epileptic fits in consequence, as has recently been proved by Prof. Nothnagel. In adults dreams seem sometimes so vividly real, that they resemble delirious paroxysms. What terrible events have taken place, what catastrophes at which we shudder, recognising the fragility of the human mind and the awful power of dreams! I quote a single case which took place in Glasgow in 1878. A man, twenty-four years old, of the name of Fraser, rose suddenly during the night, took his child and hurled it against the wall, shattering its skull. The screams of his wife awakened him, when, to his horror, he found that he had killed his son whom he had thought to save from a wild animal which he had seen enter the room and spring on to the child’s bed to devour it. Fraser gave himself up to justice at once and was set at liberty, because it was evident that he had acted unconsciously.