The most direct way into the complexities of the unconscious mental processes of a person is afforded by a study of his more “unusual” actions and thoughts. For few persons are so completely adapted to their environment or so perfectly balanced that moments never arise in which their mental behaviour is not surprising, either to themselves or to others. And even the Admirable Crichtons of our acquaintance are not entirely immune from errant moments—at least in their sleep. The dream, then, is the chief gate by which we can enter into the knowledge of the unconscious. For in sleep, the relatively considerable control which most of us in waking life possess over the coming and going of mental events is almost if not entirely abrogated. Thoughts and desires, which, if they attempted to dominate consciousness in waking life, would be promptly suppressed, arise, develop and expand to an astounding extent in the dream. This statement, of course, is entirely independent of the implications of any one “theory of dreams.” Its truth is evident to anyone who has honestly recorded or considered his own dreams for even a short period. Other unusual mental processes are manifested in such events as “slips of the tongue,” “slips of the pen,” the mislaying of important objects, the forgetting of significant facts, or conversely the inability to get an apparently unimportant memory out of one’s mind. All these phenomena, common enough in the normal individual, are usually more frequent in the abnormal mind. Besides the patient’s voluntary account of, and comments upon, these events,[42] other methods of obtaining data are possible to the physician. He will note the matters about which in conversation the patient is apt to become silent, embarrassed or inexplicably irritated, to hesitate, to say he has forgotten, or even to lie. All these sidelights upon the mental make-up are carefully noted by the physician and the deductions from them compared, not only with the patient’s accounts of himself on different days—narratives which when put together may show important discrepancies and thin places—but also with the information obtainable from his family. These devices serve to bring to light in an extraordinary manner a whole number of memories, many of them of immense significance for the comprehension of the patient’s present mental state, which it would be utterly impossible to discover in mere conversation or even by cross-questioning.