Every bodily movement or function that you can start or stop at will, even to such seemingly unconscious acts as winking, walking, etc., is controlled through the cerebro-spinal system. All other functions of the body, including the great vital processes, such as heart pulsation and digestion, are performed unconsciously, are beyond the direct control of the will, and are governed through the sympathetic nerve system. [Sidenote: Organs of Consciousness and Subconsciousness] It is obvious that the cerebro-spinal nerve system is the organ of consciousness, the apparatus through which the mind exercises its conscious and voluntary control over certain functions of the body. It is equally obvious that the _sympathetic system is not under the immediate control of consciousness, is not subject to the will, but is dominated by mental influences that act without, or even contrary to, our conscious will and sometimes without our knowledge._ Yet you are not to understand that these two great nerve systems are entirely distinct in their operations. On the contrary, they are in many respects closely related. [Illustration: SEPARATE NERVE CENTERS, PLEXUSES AND GANGLIA, THE "LITTLE BRAINS" OF THE HUMAN BODY] Thus, the heart receives nerves from both centers of government, and besides all this is itself the center of groups of nerve cells. The power by which it beats arises from a ganglionic center within the heart itself, so that the heart will continue to beat apart from the body if it be supplied with fresh blood. But the rapidity of the heart's beating is regulated by the cerebro-spinal and sympathetic systems, of which the former tends to retard the beat and the latter tends to accelerate it. In the same way, your lungs are governed in part by both centers, for you can breathe slowly or rapidly as you will, but you cannot, by any power of your conscious will, stop breathing altogether. Your interest in the brain and nerve system is confined to such facts as may prove to be of use to you in your study of the mind. These anatomical divisions interest you only as they are identified with conscious mental action on the one hand and unconscious mental action on the other. It is, therefore, of no use to you to consider the various divisions of the sympathetic nerve system, since the sympathetic nerve system in its entirety belongs to the field of unconscious mental action. It operates without our knowledge and without our will. [Sidenote: Looking Inside the Skull]