nx, the limbs, etc.,
may be affected, and trembling be the result. On the other hand, the
laryngeal and other muscles may be toned up, and the voice rendered
better than usual, as a result of applause--_i.e._, by nervous
impulses through the ear--or, again, by the sight of a friend. Even a
very tight glove or a pinching shoe may suffice to hamper the action
of the muscles required for singing or speaking. All this is a result
of reflex action--_i.e._, outgoing messages set up by ingoing
ones--the "centre" being either the brain or the spinal cord. From all
this it is evident that the singer or speaker must guard against
everything unfavorable, to an extent that an ordinary person need not.
The stomach, as the diagram is also meant to show, may express itself
on the brain, and give rise, as in fact it often does, owing to
indiscretion in eating, to unpleasant outward effects on the muscles
required in singing or speaking. Of course, no attempt has been made
in the above figure to express anatomical forms and relations
exactly.]

When all the ingoing impulses from the lungs, etc., are cut off, if
respiration does not actually cease, it is carried out in a way so
ineffective that life cannot be long sustained. It follows that as the
muscular contractions necessary for the chest and other respiratory
movements are dependent on the impulses passing in from the lungs,
etc., breathing belongs to the class of movements known as
reflex--chiefly so, at all events. It will thus be seen that
respiration is a sort of self-regulative process, the movements being
in proportion to the needs of the body. The greater the need for
oxygen, the more are the nerve-terminals in the lungs and the centre
itself stimulated, with, as a result, corresponding outgoing impulses
to muscles.

As the respiratory centre is readily reached by impulses from every
part of the body, like one who keeps open house, there are many
different sorts of visitors, not all desirable. If, for example, a
drop of a fluid that produces no special effect when on the tongue
gets into the larynx, trachea, or lungs, the most violent coughing
follows. This is one illustration of the _protective_ character of
many reflexes. This violent action of the respiratory apparatus is
not in itself a desirable thing, because it disturbs if it does not
exhaust, but it is preferable to the inflammation that might result if
the fluid, a bread-crumb, etc., were to pass into the lungs.