halves of the body. As she had not learned to speak or to utter articulate sounds with much distinctness, we may say also that right or left handedness may develop while the motor speech center is not yet functioning.
5. In most cases involving the marked use of one hand in preference to the other, the second or backward hand followed slowly upon the lead of the first, in a way clearly showing symmetrical innovation of accompanying movements by the second hand. This confirms the inference as to such movements drawn from the phenomena of mirror-writing, etc., by Fechner and E. H. Weber.
Some interesting points arise in connection with the interpretation of these facts. If it be true that the order of rise of mental and physiological functions is constant, then for this question the results obtained in the case of one child, if accurate, would hold for others apart from any absolute time determination. We would expect, therefore, that these results would be confirmed by experiments on other children, and this is the only way their correctness can be tested.
If, when tested, they should be found correct, they would be sufficient answer to several of the theories of right-handedness heretofore urged. The phenomenon can not be due to differences in balance of the two sides of the body, for it arises before the body begins to stand erect. It can not be due to experience in the use of either hand, since it arises when there is no such difference of experience, and since the hand preferred is used, as a matter of fact, for purposes for which in experience the other would be altogether more convenient. The rise of the phenomenon must be sought, therefore, in more deep-going facts of physiology than such theories supply.
If, on the other hand, heredity be brought to the aid of these "experience" theories, it is possible to claim that, as structure is due to function, experience of function must have been first; and only thus could the modification in structure which is now sufficient to produce right-handedness in individual cases have been brought about. On the other hand, if we go lower in the animal scale than man, analogies for the kinds of experience which are
- Vierordt says concerning such experiments: "Adequate observations are wanting on the grasping movements of the infant's left and right arm a a—kind of observations which would be of the first importance for this inquiry" (Physiologie des Kindesalters, p. 428); and Wilson: "Only a prolonged series of observations, such as those by Prof. Baldwin already noted, made at the first stage of life, and based on the voluntary and the unprompted actions of the child, can supply the needful data" (Left-handedness, p. 209).
- An additional point, which I think is true, is that a right-handed child learns to shake hands properly using—the more inconvenient hand across his body—more easily than the left-handed child.