That the conscious processes in voluntary movements tend toward simplification has been mentioned in § 10. A whole series of movements, which was originally performed by each movement being consciously anticipated in order, is now performed without further consciousness as soon as the series has once begun. One fact, however, is highly interesting in this connection because it shows how the several movements of the series are actually caused. Although consciousness of all those anticipations of the movements is no longer required, the physiological sensory functions must run their course in the normal order or disturbances occur in the movement. This may be demonstrated in an animal by cutting all the sensory nerves of a limb, but carefully leaving all the motor nerves intact. The limb nevertheless appears paralyzed. A similar case in man has been described by Strümpell. A workman received a knife wound in the spinal cord. Complete recovery occurred, with the exception that the right hand and lower arm remained perfectly anesthetic: no kind of cutaneous or organic sensation was any longer perceived. The muscles of the hand and arm functioned almost normally. But movements, even very moderately complicated, could no longer be performed unless the man saw his hand and its movement. The illustration (figure 18) shows his behavior when requested to form a ring with his thumb and index finger. He could do this fairly well when permitted to look at his hand. Otherwise it was impossible, in spite of his will and the muscular capacity to perform this action. We see, then, that the peripheral impressions are necessary to bring about the several partial movements in this case of acquired serial activity, although these impressions have long ceased to become conscious whenever the act is done. [Illustration: FIG. 18.--VISUAL AND KINESTHETIC CONTROL OF VOLUNTARY ACTION: THE FORMER INTACT, THE LATTER LOST.]