The experiment consisted in testing the effect of educating one of the feet to tap as rapidly as possible on a telegraph key. The apparatus is shown in Fig. 1. The clocklike instrument is really a piece of clockwork actuated by a magnet, so that it counts up one point every time the electric circuit is closed. The electric circuit is comprised of a battery and two keys. Any form of battery will do; the one in the figure is a "lamp battery"--that is, an arrangement of lamps in series and in shunt, such that the ordinary high-voltage city current is conveniently transformed into a low-voltage current. The key to the left is the experimenter's key, and that to the right the subject's key. When the subject is set to tapping on the latter key the counter will register whenever the experimenter keeps his key closed. For the actual experiments by Professor Davis the subject's key was removed to a distant room. Here there were three keys of this kind, any one of which would register. One key each was arranged for tapping with the big toes; the third key could be tapped by either right or left index finger. On the first day all four digits--right and left index fingers and right and left large toes--were carefully tested in tapping as rapidly as possible. Thereafter the right large toe was practiced daily in tapping for several weeks, the other digits being left unpracticed. At the end all four digits were again tested. Four of the six persons experimented upon showed a gain for the right large toe--that is, for the digit practiced; the other two showed a slight loss, due unquestionably to "over-practice," or "over-training." All of those who gained for the right large toe gained for the other digits also. Their average gains were: Right foot, thirty-three per cent; left foot, thirty-one per cent; right hand, twenty-one per cent; left hand, thirty-one per cent. Even both of the "over-trained" men gained for the left foot and one of them gained for the left hand. Thus we have reached the third step--the effects of practice are extended to various parts of the body. Beyond the third step the experimental investigations have not yet advanced, but I believe that sooner or later we shall be able to establish the fact that development of those forms of the will involved in simple muscular activities does also develop the more complicated forms that express themselves in acts of a mental nature.