on, but chronic roaring is caused by paralysis of the
muscles of the larynx; and almost invariably it is the muscles of the
left side of the larynx that are affected.

In chronic roaring the noise is made when the air is drawn into the
lungs; only when the disease is far advanced is a sound produced when
the air is expelled, and even then it is not nearly so loud as during
inspiration.

In a normal condition the muscles dilate the aperture of the larynx by
moving the cartilage and vocal cord outward, allowing a sufficient
volume of air to rush through. But when the muscles are paralyzed the
cartilage and vocal cord that are normally controlled by the affected
muscles lean into the tube of the larynx, so that when the air rushes in
it meets this obstruction and the noise is produced. When the air is
expelled from the lungs its very force pushes the cartilage and vocal
cords out, and consequently noise is not produced in the expiratory act.

The paralysis of the muscles is due to derangement of the nerve that
supplies them with energy. The muscles of both sides are not supplied by
the same nerve; there is a right and a left nerve, each supplying its
respective side. The reason why the muscles on the left side are the
ones usually paralyzed is owing to the difference in the anatomical
arrangement of the nerves. The left nerve is much longer and more
exposed to interference than the right nerve.

In chronic roaring there is no evidence of any disease of the larynx
other than the wasted condition of the muscles in question. The disease
of the nerve is generally far from the larynx. Disease of parts
contiguous to the nerve along any part of its course may interfere with
its proper function. Enlargement of lymphatic glands within the chest
through which the nerve passes on its way back to the larynx is the most
frequent interruption of nervous supply, and consequently roaring. When
roaring becomes confirmed, medical treatment is entirely useless, as it
is impossible to restore the wasted muscle and at the same time remove
the cause of the interruption of the nervous supply. Before roaring
becomes permanent the condition may be benefited by a course of iodid of
potassium, if caused by disease of the lymphatic glands. Electricity has
been used with indifferent success. Blistering or firing over the larynx
is, of course, not worthy of trial if the disease is due to interference
of the nerve supply. The administration of strych