nd bleared
aspect of the organ. Both are the result of chronic inflammation, which
crowds the blood into the vessels of the cornea, making them bloodshot and
visible. The nerves controlling the circulation of the eye are partially
paralyzed, and thus the relaxed vessels become distended.

But more serious results ensue. Long use of intoxicants produces diseases
of the retina, involving in many cases marked diminution of acuteness as
well as quickness of vision, and at times distorted images upon the
surface of the retina. In other instances, the congestion of the optic
nerve is so serious as to involve a progressive wasting of that organ,
producing at first a hazy dimness of vision which gradually becomes worse
and worse, till total blindness may ensue.

It is beyond question that a wide comparison of cases by careful
observers proves that a large fraction of those who indulge in strong
drink suffer from some form of disease of the eye.

341. Effect of Tobacco upon Vision. Tobacco, in its distribution of
evil effects, does not neglect the senses and especially the eye. A
variety of vicious results is produced. The pungent smoke inflames the
lids. The narcotic dilates the pupil, causing dimness and confusion of
vision. A diseased condition occurs with severe pain in the eye followed
by impaired vision.

Oculists speak impressively of the ill effects of tobacco, and especially
of cigarettes, upon the eyes of the young. They mention a well-known
disease, tobacco blindness, usually beginning with color-blindness, and
progressing occasionally with increasing dimness of vision to entire loss
of sight.[47]

342. The Sense of Hearing. The structure of the human ear is much
more complicated than is generally supposed. It is an apparatus
constructed to respond to the waves of sound. As a whole, it may be
considered a peculiar form of nerve-ending.

The external ear forms only a part of a most elaborate apparatus whereby
sound waves may be transmitted inwards to the real organ of hearing. The
really sensitive part of the ear, in which the auditory nerve ends, is
buried for protection deep out of sight in the bones of the head; so deep
that sounds cannot directly affect it. Some arrangement, therefore, is
required for conducting the sounds inwards to this true organ.

[Illustration: Fig. 138.--The Pinna, or Auricle.]

In studying the structure of the ear, and how it is fitted to respond to
sonorous vibrations, we may d