Page:Popular Science Monthly Volume 44.djvu/623

Rh planned with very great care and with especial view to the testing of several hypotheses which, although superficial to those who have studied physiology, yet constantly recur in publications on this subject. Among these theories certain may be mentioned which my experimental arrangements were aimed to test. It has frequently been held that a child's right-handedness arises from the nurse's or mother's constant method of carrying it; the child's hand which is left free being more exercised, and so becoming stronger. This theory is ambiguous as regards both mother and child. The mother, if right-handed, would carry the child on the left arm, in order to work with the right arm. This I find an invariable tendency with myself and with nurses and mothers whom I have observed. But this would leave the child's left arm free, and a right-handed mother would be found with a left-handed child. Again, if the mother or nurse is left-handed, the child would tend to be right-handed. Or if, as is the case in civilized countries, nurses replace the mothers, it would be necessary that most of the nurses be left-handed in order to make most of the children right-handed. Neither of these positions is true. Further, the child, as a matter of fact, holds on with both hands, however it is itself held. Another theory maintains that the development of right-handedness is due to differences in weight of the two lateral halves of the body; this tends to bring more strain on one side than the other, and so to give more exercise to that side. This evidently assumes that children are not right or left handed before they learn to stand. This my results given below show to be false. Again, we are told that infants get right-handed by being placed on one side too much for sleep: this can be shown to have little force also, when the precaution is taken to place the child alternately on its right and left sides for its sleeping periods.

In the case of the child H certain precautions were carefully enforced. She was never carried about in arms at all—never walked with when crying or sleepless (a ruinous and needless habit to cultivate in an infant); she was frequently turned over in her sleep; she was not allowed to balance herself on her feet until a later period than that covered by the experiments. Thus the conditions of the rise of the new right-handed era were made as simple and uniform as possible.

The experiments included, besides reaching for colors, a great many of reaching for other objects, at longer and shorter distances, and in unsymmetrical directions. The following table (I)