THE mechanism of mental states?the mental machinery by means of which we feel, think, and will?consists of the brain, nervous system, and the organs of sense. No matter what may be the real nature of mind,?no matter what may be the theory held regarding its activities,?it must be admitted that the mind is dependent upon this mechanism for the manifestation of what we know as mental states. Wonderful as is the mind, it is seen to be dependent upon this physical mechanism for the expression of its activities. And this dependence is not upon the brain alone, but also upon the entire nervous system. The best authorities agree that the higher and more complex mental states are but an evolution of simple sensation, and that they are dependent upon sensation for their raw material of feeling and thought.