BILATERAL ASYMMETRY OF FUNCTION. 109 draw upon the power of the non-preferred hand than the latter had to weaken the former. If, instead of a symmetrical move- ment, the other hand made a maximal effort of tensing the exten- sor instead of the flexor muscles of the hand, or opening it as far and forcibly as possible, no constant effect on the simultaneous clenching power of the other hand was observed. III. A submaximal standard clenching effort was made with one hand, and, after the lapse of two seconds, an attempt was made to repeat this effort by making another of the same in- tensity. The most constant result here obtained was that, when it was attempted to repeat the standard movement with both hands simultaneously instead of with one, the effort was too great, indicating summation in repeated sub-maximal movements ; when the standard movement was repeated with but one hand it was generally underestimated. IV. The attention, so far as controlled by fixing the eye on one hand, has power to intensify the maximal energy of the clenching effort of the hand to which it at the instant is directed, and was so potent and disturbing a factor that it had to be controlled by being directed to some intermediate object. The attention seems to have more power over the right hand than over the left hand, but, if fixed on the left, very commonly causes its maximal power to develop slightly in excess of the right. Throughout the above observations we have been increasingly impressed with the very wide range of individual variation, and we have no data as yet for inferring a more general validity from what we have found to be the case with some or all of the four cases to which our observations have been more or less restricted. Ye need careful studies, both anatomical and functional, of a great number of cases ; farther and more detailed research in each of the above directions, A., B., C., Ac., and by other methods, before we can distinguish confidently between individual and general laws. We are, however, convinced (1) that every devia- tion from perfect bilateral symmetry of form or function is to be accounted for without recourse to occult causes of any sort ; (2), that the key to the entire bilateral problem which shall reveal a common principle for all the various paired organs is to be sought in the study of bilateral muscle-tension and contraction, the only act of will ; and (3), that the solution of this problem, when reached, now seems likely to shed light on the nature of con- sciousness.
