In my work on sleep I was greatly impressed with the place fear holds in animal life existence. From the lowest representative, such as the insect to the highest, such as man, fear rules with an iron hand. Every animal is subject to cataplexy of fear and to the hypnoidal state itself, the consequence of fear-adaptations to the external conditions of a hostile environment. Cataplexy and the consequent hypnoidal state which paralyze the animal, depriving it of all defense, are grounded in the imperfections of living protoplasm. Man is subject to the hypnoidal periods of primitive life. It is during those periods that the shafts of suggestion are most apt to strike his subconsciousness, divorced as it is during those moments from the nodding self consciousness. During these nodding moments of his life he is exposed to harmful suggestions, since they are apt to arouse the fear instinct, the most sensitive of all human instincts. It seems as if the fear instinct is never fully asleep, and is the easiest to arouse. It seems to be watchful or semi-watchful during the most critical moments of man’s helplessness. Fear of darkness and fear of invisible foes are specially strong in man, because of the deeply rooted fear instinct, but also because of his memories of accidents and dangers that have befallen him, and which may befall him. Man’s fears hang round dark places, gloomy corners and nooks, caves and forests, and more especially during the darkness and shades of night, appearing as treacherous visions and specters of lurking dangers. And still from the very nature of his being man must rest and sleep, hence the association of terrors with night time. He can only overcome his night terrors by living and sleeping in more or less secure corners, in the neighborhood of his fellow-beings who by the mere fact of numbers multiply not only the means of defense, but actually increase susceptibility for the scent of danger and possible speedy defense. In the society of his fellows the sense organs of the individual are increased by the presence of others who are in various stages of vigilance, and hence there is greater protection against dangers and invisible foes that lurk in the darkness of night, foes of which primitive man is in terror of his life. The fear of the unknown, the mysterious, and the dark, peoples the mind of primitive man with all sorts of terrible spectres, ghosts, spirits, goblins, ghouls, shades, witches, and evil powers, all bent on mischief, destruction and death. _Primitive man suffers from chronic demonophobia._ Fear states are specially emphasized at night when the “demons” have the full power for evil, and man is helpless on account of darkness and sleep which paralyze him. Hence the terrors of the night, especially when man is alone, and defenseless.