These five subject-complexes do not form independent automatisms or isolated systems which may intrude themselves in any conscious field, but comprise large associations, memories of experiences in a special field of thought. Within that field the ideas of the system are no more strongly organized than are ideas in general; but it can be recognized that the system as a whole with its affective tones is fairly well delimited from the other complexes of other spheres of thought. It is difficult, for certain individuals at least, to introduce the associations of one subject-complex into the focus of attention so long as another is invested with personal interest and occupies the attention of consciousness. They find it difficult to switch[146] their minds from one subject to another and back again. On the other hand, it is said of Napoleon that he had all the subjects of his experiences arranged in drawers of his mind, and that he could open each drawer at will, take out any subject he wished, and shut it up again as he wished. Ability of this kind involves remarkable control over the mind and is not given to all. I have frequently made observations like the following on myself, showing the organization and differentiation of systems: I collect the various data belonging to one of the problems discussed in these lectures. I arrange all in an orderly fashion in my mind, work out the logical relations and the conclusions to which they lead, as well as their relations to other data and problems. The whole is then schematically arranged on paper to await proper elaboration the next morning, when it will be written out on waking, the preliminary mental arrangement having been done at night. A large complex has been created, the various details of which are luminously clear and the sequence of the ideas vividly conceived, the conclusions definite. There is, further, an affective tone of joy and exaltation which is apt to accompany the accomplishment of an intellectual problem and which produces a feeling of increased energy. The next morning, as I awake and gradually return to full consciousness, another and very different kind of complex almost exclusively fills my mind, owing probably to the fatigue following the previous night’s work. All sorts of gloomy thoughts, memories of experiences better forgotten, course through the mind; and entirely different emotions (instincts), and a strong feeling of depression dominate the mental panorama. The whole—ideas, emotions, and feelings—makes a complex which has been experienced over and over again, and is recognized as such. The same old ideas, emotions, thoughts, and memories, conserved as neurograms, repeat themselves almost in stereotyped fashion. The mental complex has completely changed and the exuberant energy of the night before has given place to listless inertia. All this is commonplace enough, merely morning depression you will say, due to fatigue; and so it is. But mark the sequel.