No exhaustive demonstration is needed to prove that the same conditions prevail in experimentation with touch stimuli and the observation of motion, which is so often connected with it. “In the first year,” says Preyer, in speaking of the manifold and apparently aimless movements of the infant, “exercise of the muscles is the _raison d’être_ of all this activity which appears to be aimless. An adult lying on his back could not repeat the commonest movements of a seven to twelve months child without extreme fatigue.”[159] In arm movements the development of right-handedness is of especial interest. Formerly it was attributed to the mother’s or nurse’s method of carrying the child, to the greater weight of one side of the body, and similar pretexts; but Baldwin’s investigations show that such extraneous influences have little to do with it, for he found on excluding such agencies a marked preference for the right hand in the seventh and eighth months, displayed first in strenuous grasping movements.[160] An entirely satisfactory explanation has not yet been offered, though Sticker’s theory, is perhaps most probable—namely, that the left brain hemisphere has a better blood supply than the right.[161] When there is some difficulty to overcome, some opportunity to display dexterity, there are heightened stimulus and greater directness in the movements of arms and hands. Older children delight to set themselves such tasks as, for instance, clasping the hands behind the back, so that one arm crosses the shoulder, or placing the open hand on a table and raising the ring finger without any of the others, or laying the fingers over one another, etc. When such efforts are overlooked and directed by parents and teachers, we have the beginning of gymnastics, which remains a play so long as the subject enjoys it. Free-hand movements, exercises with dumb-bells and weights and the like, so far as the interest is not centred in the foreign body, all belong here. The intense desire for movement in many forms of mental disease should also be noted in this connection, since they have an indirect playful character, and by their very exaggeration are calculated to throw some light on the conduct of normal humanity. No psychic derangement shows this more clearly than does mania. The voice of such patients, says Kraepelin, “is usually high-pitched.... They are contented, feel inclined to all sorts of fun, and teasing, singing, and joking,” yet all this is invariably followed by a sudden plunge into the contrary mood. “That grave symptom of derangement, strong propensity to movement seems to stand in the closest connection with liveliness of spirits. The patient fairly revels in emotion; he is uneasy, can not long lie or sit still, stirs about, skips, runs, dances. He gesticulates wildly, claps his hands, makes faces, scribbles and rubs on the ground, walls, and windows, beats and drums on the floor, strips off his clothes, tears