up the life of the lowest animals are doubtless quite unconscious, even when in their general character they simulate conscious actions, as they often do. In the case of such creatures, the famous hypothesis of Descartes, that animals are automata, is doubtless mainly correct. In the case of instincts also, where the instinctive actions are completely organized before birth, and are repeated without variation during the whole lifetime of the individual, there is probably little if any consciousness. It is an essential prerequisite of consciousness that there should be a period of delay or tension between the receipt of an impression and the determination of the consequent movement. Diminish this period of delay and you diminish the vividness of consciousness. A familiar example will make this clear. When you are learning to play a new piece of music on the piano, especially if you do not read music rapidly, you are intensely conscious of each group of notes on the page, and of each group of keys that you strike, and of the relations of the one to the other. But when you have learned the piece by heart, you think nothing of either notes or keys, but play automatically while your attention is concentrated upon the artistic character of the music. If somebody thoughtlessly interrupts you with a question about Egyptian politics, you go on playing while you answer him politely. That is, where you had at first to make a conscious act of volition for each movement, the whole group of movements has now become automatic, and volition is only concerned in setting the process going. As the delay involved in the perception and the movement disappears, so does the consciousness of the perception and the movement tend to disappear. Consciousness implies perpetual discrimination, or the recognition of likenesses and differences, and this is impossible unless impressions persist long enough to be compared with one another. The physical organs in connection with whose activity consciousness is manifested are the upper and outer parts of the brain,--the cerebrum and cerebellum. These organs never receive impressions directly from the outside world, but only from lower nerve-centres, such as the spinal cord, the medulla, the optic lobes, and other special centres of sensation. The impressions received by the cerebrum and cerebellum are waves of molecular disturbance sent up along centripetal nerves from the lower centres, and presently drafted off along centrifugal nerves back to the lower centres, thus causing the myriad movements which make up our active life. Now there is no consciousness except when molecular disturbance is generated in the cerebrum and cerebellum faster than it can be drafted off to the lower centres.[5] It is the surplus of molecular disturbance remaining in the cerebrum and cerebellum, and reflected back and forth among the cells and fibres of which these highest centres are composed,