When body is dead, mind, so far as its reactions to the world we know are concerned, ceases to act. But when the conscious mind is "dead" the body may yet live as a vegetable lives, with all its distinctively human functions lost. Motionless, save for the beating of the heart and the reaction of the lungs to air, the body may still be alive, though the mind long since has ceased all earthly activity. So we discover that an organ of mind is an essential, here, to life of mind, and that mind only can induce this organ to any action above the vegetative stage. But, on the other hand, we find that life can exist without conscious mind, even if untended by others, for a limited time. If the direct nerve connections between the brain and the hand, the brain and the foot, or the brain and the trunk are cut off, the mind henceforth realizes nothing of that part except as the sense of sight reports upon it; for the optic nerves relate the hand and mind, through this sense, as truly as the motor nerves which carry the mind's message for motion to the hand, and the sensory nerves which carry back to the mind the hand's pain. But let the optic nerve be inert, the sensory and motor connections broken between brain and hand, or foot and trunk, or brain and trunk, and the hand or foot may be amputated and the mind never sense the fact; the trunk may be severely injured and the mind be serenely unconscious. So the brain in man is "the one immediate bodily condition of the mental operations." Take away all the brain and man's body is a useless mass of protoplasm. The brain's varied and intricate nerve connections with all parts of the body, through nerves branching from the main trunks in the spinal cord, we shall not discuss, for you know them through your study of anatomy. For the purpose of our psychology we need consider only two of the main divisions of the brain--the _cerebrum_, which includes what we call the right and left hemispheres, and the _cerebellum_. THE CEREBRUM OR FOREBRAIN For convenience the various lobes of the cerebrum are known as frontal, temporal, parietal, and occipital, according to the parts of the brain referred to: as forehead, temples, crown, or occiput. The cerebellum, or hind brain, is also divided into two hemispheres, and is situated behind and below the hemispheres of the cerebrum. A system of localization has been roughly mapped out, the result of careful laboratory work on animals and of studying the loss of various functions in human beings as related to the location of brain injuries. From these experiments it seems proved that consciousness belongs only to the cortex or surface of the upper brain, and that the vast realm of the unconscious belongs to the lower brain centers. Hence the cortex is the organ of consciousness, and the lower centers are the repository of the unconscious until it again becomes conscious.