tal.
Such a condition produces a serious defect of vision. It can be
corrected by means of cylindrical lenses of the proper strength so
placed before the eye as to correct the defect in curvature.

Still another defect of vision is known as presbyopia or farsightedness
due to old age. It has the following explanation: In early life, when we
look at near objects, the crystalline lens automatically becomes
thicker, more convex. This adjustment brings the rays to a focus on the
retina, which is required for good vision. As we get old, the
crystalline lens loses its power to change its adjustment for near
objects, although the eye may see at a distance as well as ever. The
old person, therefore, must wear convex glasses when looking at near
objects, as in reading and sewing.

Another visual defect of a different nature is known as partial color
blindness. The defects described above are due to misshapen eyes.
Partial color blindness is due to a defect of the retina which makes it
unable to be affected by light waves producing red and green. A person
with this defect confuses red and green. While only a small percentage
of the population has this defect, it is nevertheless very important
that those having it be detected. People having the defect should not be
allowed to enter occupations in which the seeing of red and green is
important. It was recently brought to the author's attention that a
partially color-blind man was selling stamps in a post office. Since two
denominations of stamps are distinguished by red and green colors, this
man made frequent mistakes. He was doing one of the things for which he
was specially unfitted. It is easy to detect color blindness by simple
tests.

So great is the importance of good vision in school work and the later
work of life, that every teacher should know how to make simple tests to
determine visual defects. Children showing any symptoms of eyestrain
should be required to have their visual defects corrected by a competent
oculist, and should be warned not to have the correction made by a
quack. There is great popular ignorance and even prejudice concerning
visual defects, and it is very important that teachers have a clear
understanding of the facts.

=Defects of Hearing.= Hearing defects are only about half as frequent as
those of sight. They are nearly all due to catarrhal infection of the
middle ear through the Eustachian tube. The careful and frequent
medical examination of