But the unconscious is not always, or even often, such a useless intruder upon our everyday life. It economises our energies, and often takes us by short cuts to ends which would otherwise need continued reasoning. 'Intuition' is the product of previous experience, and rises into the consciousness as a finished judgement without the owner of the gift being aware of the factors concerned in its formation. One kind of intuition is improperly called in my profession 'clinical instinct', but, unlike instinct, it is a result of training and experience, and is never seen without them. Here is an example which came under my notice: An ophthalmic house-surgeon, busy with new patients, sees a man aged about thirty-five, who complains of failing sight, and without further investigation he writes on the man's book, 'Tobacco amblyopia?' and sends him in to his chief. Later on his chief asks him, 'How did you spot this case?' and the house-surgeon answers, 'I don't know, but he looked like it'. The chief agrees that there is something which can be seen but not described in the looks of a sufferer from this complaint. Now this house-surgeon, though keen on his work, had seen only a few cases of that disease, and I do not now accept his explanation of how he 'spotted' it. A man of thirty-five may find his sight failing from various causes, but the common ones are not many. If the cause had been 'long-sight', he would have complained that he could not see to read; certain general diseases causing loss of sight at that age would perhaps have visible symptoms; the man was too young for cataract, and his eyes looked healthy. In short, tobacco amblyopia was a reasonable guess, and, when we remember that the disease is caused by smoking strong pipe tobacco, and that the man who smokes that tobacco generally smells of it, it is fair to suppose that it was not the evidence of his eyes alone that guided the house-surgeon in his guess, though he was not conscious of any train of reasoning nor was he aware of the smell of stale tobacco. This suggests that a stimulus may act upon our thoughts without our being conscious of the origin of the feeling produced, and this is what happens in connection with that well-known sensation, felt on visiting a new place, that one has been there before. If a close examination is made it will be found that there is really something--a picture, a scent, or even so slight a stimulus as a puff of warm air--which has stirred a memory in the unconscious; this memory fails to reach the consciousness in its entirety, or it would immediately be recognised as caused by the particular stimulus, but in its incomplete form it appears as a memory of nothing in particular. Such a memory being inconceivable it is at once joined on to the whole scene, and one feels 'I've surely been here before'. This feeling may be regarded as an intuition in its most useless and incomplete form, but its theoretical importance will be seen later.