uces, as already stated (page 56), a dangerous nervous
derangement called "tobacco heart," and it causes a serious disorder
of the retina (retinitis) which leads in some instances to loss of
vision. Tobacco smoke also acts as an irritant to the delicate
lining of the eyes, especially when the tobacco is smoked indoors.

113 Of 4117 boys in the Illinois State Reformatory, 4000 used tobacco,
and over 3000 were cigarette smokers. Dr. Hutchison, of the Kansas
State Reformatory, says: "Using cigarettes is the cause of the
downfall of more of the inmates of this institution than all other
vicious habits combined."

114 The term "mind" is used in this and preceding chapters in its
popular, not technical, sense.

115 The problem of social adjustment is but a phase of the general
problem of establishing proper relations between the body and its
surroundings.

116 A vibrating body is one having a to-and-fro movement, like that of a
clock pendulum or the string of a violin on sounding. Bodies to give
out sound waves must vibrate rapidly, making not less than sixteen
vibrations per second. The upper limit of hearing being about 40,000
vibrations per second, certain bodies may even vibrate too rapidly
to be heard.

117 Somewhat as the waves on a body of water impart motion to the sticks
and weeds along the shore, sound waves are able to cause bodies that
are small or that are delicately poised to vibrate.

118 Some idea of how the movements of the cartilages change the tension
of the cords may be obtained by holding the fingers on the larynx,
between the thyroid and cricoid cartilages, and making tones first
of low and then of high pitch. For the high tones the cartilages are
pulled together in front, and for the low tones they separate. As
they pull together in front, they of course separate behind and
above, where the cords are attached.

119 It is only the central portion of the pinna that aids the entrance
of sound into the auditory canal. If by accident the outer portion
of the pinna is removed, there is no impairment of the hearing.

120 The middle ear is also called the _ear drum_, and, by the same
system of naming, the membrana tympani is referred to as the _drum
membrane_.

121 The inner projection of the temporal bone is known as t