Page:American Journal of Psychology Volume 21.djvu/558

546 as in speech or in the visual centre as in hand movements, and therefore there may be controlled movements without kinæsthetic sensations from the limb to be moved.

Sherrington, however, writing after further experimentation bearing upon the relation of sensation to movement seems to modify somewhat his original rather rigid and sweeping position. He writes: "It is found that the destruction of sensitivity in particular regions brings about objectively observable disturbances of movement." . . . "the effects of apaesthesia upon the musculature of the part are three (i) paralysis, (2) ataxia, (3) atonia." (Proc. Roy. Soc., Vol. 60.)

Munk repeated the experiments of Mott and Sherrington and at first obtained the same results, but later found that monkeys recovered to a degree their ability to use the hands that had been rendered anaesthetic. These movements, however, were always inaccurate and exaggerated. Moreover only single voluntary movements could be made at all. Munk's animals at first dropped food placed in the anaesthetic hand but later learned to grasp it and carry it to the mouth. After getting it to the mouth the monkey at first removed the fingers from the food with his teeth but after some practice learned to let go "actively" when the hand reached the mouth. Then instead of placing the food in the monkey's hand, Munk simply presented it to him. With the sound hand tied behind him the monkey after experience learned to take the food from Munk's hand and carry it to his mouth with the anaesthetic hand.

What Munk specifically denies in Mott and Sherrington' s deductions from these facts is that the entire sensory mechanism is and must be operative in voluntary movements, that the entire sensory path from the periphery to the cortex is necessarily active in volitional control. Munk points out that the only movements that are entirely and permanently destroyed are the reactions that normally take place to an immediate stimulation of the member concerned. All other movements which the extremity normally makes are more or less defective because the "Einstellung der centralen Organe von welchen die Bewegungcn der Extremitat herbeigefuhrt worden, verandett ist. Die Stbrung ist immer desto grosser, je mehr Mu skein oder Gleider der Extremitat an der Bewegung beteiligt sind." The important differences between Mott and Sherrington and Munk appear to lie in the fact that the former seem to regard kinaesthetic elements as the essential sensory elements in the voluntary arc, while the latter holds that any sense elements, visual, auditory, etc., will serve the same purpose quite or nearly as well in the absence of kinaesthetic elements, especially after practice.