Let it be granted that a person has undergone a strongly emotional experience—for example, a sudden shock or fright. If the person is highly nervous, the shock may result in some degree of dissociation. This may take the form of a loss of memory for certain parts of the experience. Let it be so. The ultimate result may be an unreasonable fear of some entirely harmless object or situation. The person is afraid of a crowd, or afraid of a closed door, or has an intense fear of some animal or person. For this fear he can give no reason; he cannot tell when it began nor why it persists. He may more or less overcome it; but he may not. All through his future life he will go about with a helplessly unreasonable fear of a closed door (claustrophobia) or of a crowd (agoraphobia). Minor varieties of such an affection are to be found in every person’s experience. On investigation, however, the root of the fear can be discovered: it is the product of the original emotional shock. The intellectual details of the emotional experience have completely vanished from the memory, but the emotion remains, and it is attached to some accidental object or circumstance present in the original experience. Thousands of illustrations could be given. They are, unfortunately, only too numerous. In this essay on the Interpretation of Dreams the reader will find many simple cases. If, now, the person so affected is placed in a quiet room, if he is requested to concentrate his mind on the disturbing object or idea associated with his fear, if he is encouraged to observe passively the chance ideas which float up to him when he thus concentrates himself, if he utters, under the direction of his medical attendant, every such idea as it comes into his mind, there is a strange result. These ideas, coming apparently by chance from nowhere in particular, are, when carefully studied, found to be linked up with some past experience, dating, perhaps, from months or years away. If each idea as it emerges is followed up, if the other ideas dragged into consciousness by it are carefully recorded, it is found that sooner or later entirely forgotten experiences come into clear consciousness. There are many ways of helping this process. One of the ways is this: Let a series of words be arranged; let the doctor speak one of them to the patient; let the patient, in the shortest time possible to him, say right out whatever idea is suggested to him by the word; let the time taken to make the response be recorded in seconds and fractions of a second—a thing easy enough to do with a stop-watch. Then, when the responses to a long series of words are all recorded, and the time each response has taken, it is found that some responses have taken much longer than others. This prolongation of the response-time is always found whenever the test word has stirred up a memory associated with emotion. By following up further the ideas stirred by this word, more ideas of a related kind are