Page:Mind (New Series) Volume 12.djvu/71

ANTAGONISTIC REACTIONS. 57 movements. The forearm was bandaged firmly along its whole length to a bar of wood, and a string, arranged so as to loop over the button of the sphygmograph, was attached to the forefinger, or in later experiments to the end of the bar of wood. The position of the sphygmograph was changed in successive experiments in order to admit of testing move- ments of the arm up and down, to the right and left. The two individuals referred to above were again subjects : the right arm was employed as in all the other experiments. In every direction of movement, up or down, to the right or left, there were observed preliminary movements in the direction opposite to that intended by the reagent. The movements are not equally constant in both cases, but the curves of both persons show the phenomenon unmistakably. It may be concluded from these observations that the an- tagonistic movement is not limited to any special set of muscles and that it occurs whether the intended movement is performed by flexor or extensor muscles, the degree of distinctness and frequency depending on the special groups of muscles employed. In seeking for an explanation of these phenomena we may look at the problem first from the point of view of physiology. In any rapid movement there is an effort not merely to secure speed, but also to give the movement a certain degree of force or energy. Now it is a well-known fact in the physiology of muscle that preliminary tension of a muscle increases the out-put of energy : within certain limits the greater the load, the more work is done. We may assume then that wherever the tension of a group of muscles, e.g. the extensors, is mo- mentarily heightened by the contraction of the flexors, the subsequent contraction of the extensors will be more forcible and powerful. Applying these ideas to the phenomena of antagonistic reaction, we could easily understand that in this form of reaction the final movements would tend to be more forcible, while their appearance, as determined by the ordinary reaction method, would be delayed : the involuntary adjustment of innervation would be directed to the attain- ment of force rather than of speed. The fact may be here referred to that in some cases in attempting to perform a rapid and at the same time vigorous action, such as striking from the shoulder, even when the movement starts from a position of considerable flexion, there is a tendency involun- tarily to produce a momentary increase of flexion before the extension movement is carried out. It has been shown by Sherrington l that when one of a pair of antagonistic muscles 1 Proc. Royal Society, lii. et seq.