LECTURE  IX

§    I.   MUSCLE-SENSATIONS :    THEIR     INFLUENCE    UPON      LOCALISATION.
§    II.   CONNECTION    OF    SENSATIONS    OF    MOVEMENT WITH   OTHER

Sensations. § III. Influence of Practice upon Reflex
Movements. § IV. Arrangement in Space a Process of
Association.

§  I

REFLEX movements become transformed from their
original purposelessness and irregularity, so that they
conform to definite ends and follow definite laws. And the
essential factor in this transformation can only be looked for in
the movements, themselves. So the question arises as to our
measurement of muscular movement.

When we move the legs in walking, we measure off the length
of each step, without having to follow the movement with the
eye. The practised pianist has acquired such skill in estimating
the distances of the various keys, that his fingers scarcely go
wrong by a hair's-breadth. And we possess an accurate judg¬
ment of the force of muscular movement. We discriminate the
magnitude of different weights by lifting them. (It has been
already shown that this discrimination is not made in terms of
the pressure of the weights upon the skin, but by reference to
the act of lifting. You will remember that if lifting is allowed,
a difference of -jY can be distinguished ; while in the case of
simple pressure upon the skin a difference of ^ is only just
noticeable. Cf, above, p. 27.) So that we possess a very
accurate measure of the force and extent of movement in the
movement itself. And such a measure can have been acquired
only by aid of the sensation which accompanies muscular move¬
ment. For sensations are, as we know, the only means by which
we receive intimation of changes, whether outside of us or within
our own body.