Psychoanalysis holds a key to the problem of sleep walking, which alone has been able to unlock the mysteries of its causes and its significance. This key is the principle of wish fulfilment, an interpretative principle which explains the mechanisms of the psyche and illuminates the mental content which underlies these. Sleep walking as a method of wish fulfilment evidently lies close to the dream life, which has become known through psychoanalysis. Most of us when we dream, according to the words of Protagoras, “lie still, and do not stir.” In some persons there is however a special tendency to motor activity, in itself a symptomatic manifestation, which necessitates the carrying out of the dream wish through walking in the sleep. The existence of this fact, together with the evidence of an influence of the shining of the moon upon this tendency to sleep walking, give rise to certain questions of importance to medical psychology. The author of this book has pursued these questions in relation to cases which have come to him for psychoanalysis, in the investigation of actual records of sleep walking given in literature and in the study of rare instances where it has been made the subject of a literary production or at least an episode in tale or drama. In each case the association with moonlight or some other light has been a distinct feature.

The author's application of psychoanalysis to these problems has the directness and explicitness which we are accustomed to find in Freud's own writings. This is as true in the literary portion of the work as in the medical but it never intrudes to mar the intrinsic beauty of certain of the selections nor the force of the intuitive revelations which the writers of the preceding science have made in regard to sleep walking and walking in the moonlight. Sadger has skilfully utilized these revelations to convince us of the truth of the psychoanalytic discoveries and has used the latter only to make still more explicitly and scientifically clear the testimony of the poetic writers and to point out the applicability of their material to medical problems. The choice of this little understood and little studied subject and its skilful presentation on the part of the author, as well as the introduction to the reader of the literary productions of which use has been made, give the book a peculiar interest and value. It is also of especial service in its brief but profoundly suggestive study of the psychic background of Shakespeare's creative work as illustrated in the sleep walking of Lady Macbeth. The endeavor in the translation has been to make accessible to our English readers the clear and direct psychoanalysis of the author and the peculiar psychologic and literary value of the book.