Before inquiring into these facts it should be observed that there is no movement which the uninjured frog ever performs to restore his equilibrium that the brained frog does not also make with equal promptness. Lay it on its back, on its head, twist its legs into unnatural positions, fix it as you may, so soon as released this unconscious automaton restores itself to its sitting posture. This being the case, it is plain that all the machinery of equilibration must be present in the mutilated frog, and must therefore be situated in the lower brain and its dependencies; and, further, that when the uninjured frog consciously attempts to maintain the erect position or to alter the gait, it simply calls into action the machinery provided for it in the lower regions of the nervous system. What is true of the frog is also true of the man; and the question naturally arises, What is the character of this machinery which the conscious will employs? This apparatus consists of two parts: first, certain exterior parts which are affected by disturbances of the equilibrium, and which when thus excited send up impulses to the lower brain; beyond, certain nerve-centres which when aroused by impulses derived from the external parts send back in a reflex manner impulses to the various muscles, which by their contraction produce motion or rectify the mistakes of position. Touch has much to do with equilibration: sight also has much to do with it. There is a disease of the spinal cord known as locomotor ataxia which destroys the sense of touch in the legs. A person suffering from this disorder is said to be ataxic. When a completely ataxic man puts his feet upon the pavement he feels nothing. Under these circumstances the man is unable to walk with his eyes shut. Even if the ataxia be not complete and some sense of feeling remain, the gait becomes so uncertain that progression is impossible. The pavement feels nearer or farther off than it is, and the result reminds one of his experiences in going up stairs in the dark and stepping out at the top in the belief that another step exists. Long before sensation is completely paralyzed the power of walking in the dark is entirely lost by the ataxic; for, indeed, the man, who has still as much muscular power as ever in his legs, may be unable to walk under any circumstances or even to stand unaided by a cane. The movements are vigorous, but uncontrollable: the legs fly about in all directions, refusing to obey at all the most strenuous efforts of the will.