The special significance of this form of fear, particularly in early childhood, has escaped the notice of the older school of child psychologists; it has lately been established by Groos and by us. “Fear of the unaccustomed seems to be more a part of primitive nature than fear of a known danger” (Groos, p. 284). If the child meets with anything that does not fit in with the familiar course of his perception, three things are possible. Either the impression is so alien that it is simply rejected as a foreign body, and consciousness takes no notice of it. Or the interruption of the usual course of perception is pronounced enough to attract attention but not so violent as to effect disturbance; it is rather surprise, desire for knowledge, the beginning of all thought, judgment, enquiry. Or, lastly, the new suddenly breaks in upon the old with violent intensity, throws familiar ideas into unexpected confusion without a possibility of an immediate practical adjustment; then follows a shock with a strong affective-tone of displeasure, the fear of the mysterious (uncanny). Groos now has pointed out with keen insight that this fear of the uncanny is also distinctly founded on instinctive fear; it corresponds to a biological necessity which works from one generation to the next. Stern gives many instances, among others fear of a suddenly opened umbrella and “the frequent fear of mechanical toys”. The former, by the way, is very strong in horses and cows: a large herd can be driven into headlong flight by it, as I have verified. My own boy’s terrors, under this head, were just such as Stern describes. The shadows that frightened him were vague quickly-moving shadows thrown into a room by unseen objects (such as omnibuses) passing in the street. I cured him by making shadows on the wall and the floor with my fingers, and getting him to imitate me; before long, he felt that he understood shadows and began to enjoy them. The same principle applied to mechanical toys: when he had seen the mechanism he was no longer frightened. But when the mechanism was invisible the process was slow. Some one gave him a cushion which emitted a long melancholy whine after being sat upon or pressed. This alarmed him for a long time. In no case did we entirely remove the terrifying object: we put it at a distance, where it was only slightly alarming; we produced gradual familiarity; and we persisted till the fear completely ceased. Generally the same mysterious quality which caused fear at first produced delight when the fear had been overcome. I think an irrational fear should never be simply let alone, but should be gradually overcome by familiarity with its fainter forms.