In the exhaustive study of consciousness which I gave in the tenth chapter of the _Riddle_ I sought to show that this enigmatic function--the central mystery of psychology--is not a transcendental problem, but a natural phenomenon, subject to the law of substance, as much as any other psychic power. The child's consciousness only develops long after its first year, and grows as gradually as any other psychic function; like these, it is bound up with the normal anatomic and chemical condition of its organs, the phroneta in the cortex. Consciousness develops originally out of unconscious functions (as an "inner view," or mirroring, of the action of the phronema); and at any time an unconscious process in the cortex may come within the sphere of consciousness by having the attention directed to it. On the other hand, conscious actions, which need a good deal of attention when they are first learned (such as playing the piano), may become unconscious through frequent repetition and practice. The fact that chemical energy is converted in the phronetal cells during any of these actions is proved by the fatigue and exhaustion which prolonged mental work causes in the brain, just as mechanical work does in the muscles. Fresh matter has to be supplied by the food before the mental work can be continued. Moreover, it is well known that various drinks have a considerable influence on consciousness (coffee and tea, beer and wine); and the temporary extinction of it under chloroform or ether is an analogous fact. Again, the familiar phenomena of the dream, the deviations from normal consciousness, hallucinations, delusions, etc., must convince every impartial thinker that these mental functions are not of a metaphysical character, but physical processes in the neuroplasm of the brain, and thoroughly dependent on the law of substance.