Level by level the mind builds itself up, in the race and in the individual; and level by level, under the influence of old age, disease or drugs, the planes of consciousness break down in the inverse order to that in which they developed, the more recently organised higher centres going first, and the automatic mind, the oldest and most stable, with æons of habit behind it, working on to the last, keeping the bodily mechanism running long after all that made the organism a man has withdrawn from its dishonoured vehicle. CHAPTER VI COMPLEXES Having studied the levels into which the mind is divided, we must next consider the nature of the material that is stored in them, and to do this we must study the workings of MEMORY. When an idea enters the mind it does not remain an independent unit for very long. It seems to be a fundamental characteristic of ideas that they form alliances among themselves, and these groups of ideas are technically known as COMPLEXES. A complex may be compared to the branching growth of a pond-weed; it has a central starting-point from which ramify threads that divide and subdivide, and branch in every direction, and connect it with other systems of ideas that have similar branching threads. Thus it is that if an idea on any subject enters our consciousness, we find that it is not an isolated unit, but one end of a chain which branches into all sorts of side issues; we have not touched a single line of thought, but a whole railway system. These systems of ideas spread and ramify through all the levels of the mind, but if we trace them far enough, we shall invariably find that they have their roots in one of the great primal instincts, deep down in the subconscious. It is from this that they derive the vitality that binds them together, for all complexes have a core of emotion, and it is from the instincts that the emotions spring. Let us take an example from actual life, and see how these principles work. A man may, for example, be a grocer; he will therefore have a Grocery Complex, that is to say, all his ideas connected with the buying and selling of household commodities will be linked together, so that if a train of thought be started in connection with any one aspect of his business, by an easy transition many other aspects may drift into his mind. Now, grocery is not in itself an absorbing subject, like literature or science, yet the man is interested in it; and why? because his grocery complex has its root in his self-preservation instinct, for it is the means by which he keeps himself alive. If his grocery business prospers, he feels pleasure, because it means a fuller and pleasanter life for him; if it diminishes, he feels pain and fear, because his means of keeping himself alive are threatened.