an
uncontrolled discharge of energy, we may see whence arise their special
characters--how it happens that certain classes of muscles are affected
first, and then certain other classes. For an overflow of nerve-force,
undirected by any motive, will manifestly take first the most habitual
routes; and if these do not suffice, will next overflow into the less
habitual ones. Well, it is through the organs of speech that feeling
passes into movement with the greatest frequency. The jaws, tongue, and
lips are used not only to express strong irritation or gratification;
but that very moderate flow of mental energy which accompanies ordinary
conversation, finds its chief vent through this channel. Hence it
happens that certain muscles round the mouth, small and easy to move,
are the first to contract under pleasurable emotion. The class of
muscles which, next after those of articulation, are most constantly set
in action (or extra action, we should say) by feelings of all kinds, are
those of respiration. Under pleasurable or painful sensations we breathe
more rapidly: possibly as a consequence of the increased demand for
oxygenated blood. The sensations that accompany exertion also bring on
hard-breathing; which here more evidently responds to the physiological
needs. And emotions, too, agreeable and disagreeable, both, at first,
excite respiration; though the last subsequently depress it. That is to
say, of the bodily muscles, the respiratory are more constantly
implicated than any others in those various acts which our feelings
impel us to; and, hence, when there occurs an undirected discharge of
nervous energy into the muscular system, it happens that, if the
quantity be considerable, it convulses not only certain of the
articulatory and vocal muscles, but also those which expel air from the
lungs.

Should the feeling to be expended be still greater in amount--too great
to find vent in these classes of muscles--another class comes into play.
The upper limbs are set in motion. Children frequently clap their hands
in glee; by some adults the hands are rubbed together; and others, under
still greater intensity of delight, slap their knees and sway their
bodies backwards and forwards. Last of all, when the other channels for
the escape of the surplus nerve-force have been filled to overflowing, a
yet further and less-used group of muscles is spasmodically affected:
the head is thrown back and the spine bent inwards--there is a s