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 with regard to which my experiments were conclusive. 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 so a right-handed mother would be found with
a left-handed child! Again, if the mother or nurse be left-handed, the
child would tend to be right-handed. Or if, as is the case in civilized
countries, nurses largely 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. Now, none of these deductions are 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 to
give more exercise, and so more development, 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; 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 right-handed era were made as simple and uniform as
possible.

The experiments included, besides reaching for colours, a great ma