to be of the same color, whether of lighter or darker shades.  A color-blind person will select amongst others some of the confusion-colors, e.g., pink, yellow.  A colored plate showing these should be hung up in the room.  Any one who selects all the greens and no confusion-colors has normal color vision.  If, however, one or more confusion-colors be selected, proceed as follows:  select as a test color a skein of pale rose.  If the person be red-blind, he will choose blue and violet; if green-blind, gray and green.

Select a bright red skein.  The red-blind will select green and brown; the green-blind picks out reds or lighter brown.

339.  Practical Hints on the Care of the Eyes.  The eye is an exceedingly delicate and sensitive organ.  While it is long-suffering, its endurance has a limit.  Like all the other organs of the body, the eyes are better for moderate and rational use.  More than any other organ they require attention to the general health, as the condition of the skin, exercise in the open air, good food, and proper habits of daily living.

The tissues of the eyes are peculiarly sensitive to any general influence.  Certain constitutional diseases, like rheumatism, lead-poisoning, diphtheria, and measles often affect the eyes.  Special care should be taken with children’s eyes during and after an attack of measles and scarlet fever.  The eyes of young infants should not be exposed to glaring lights or to the direct rays of the sun, as when taken out in baby carriages.

[Illustration:  Fig. 136.—­Showing the Relative Position of the Lacrymal Apparatus, the Eyeball, and the Eyelids.

  A, lacrymal canals, with the minute orifices represented as two black
     dots (puncta lacrymalia) to the right;
  B, tendon of the orbicularis palpebrarum muscle; apparently under B is
     seen the lacrymal sac.  The minute openings of the Meibomian glands are
     seen on the free margins of the eyelids.

Below A is seen a small conical elevation, with black dots (the lacrymal papilla or caruncle).]

Glasses should be worn when they are needed.  A failure to do this ususally causes much unnecessary suffering.  It is far from wise to postpone as long as possible the first use of glasses.  The selection and proper fitting of glasses call for the combined skill of both the physician and the optician.  Obstinate headaches are often caused by defective vision, and may disappear after discontinuing improper glasses.

The habit of reading, in the cars or elsewhere, the daily paper and poorly printed books, with their blurred and indistinct type, is a severe strain on the accommodation apparatus of the eyes.  It is a dangerous practice to read in bed at night, or while lying down in a darkened or shaded room.  This is especially true during recovery from illness.  The muscles of the eyes undergo excessive strain in accommodating themselves to the unnatural position.  The battered type, wood-pulp paper, and poor presswork, now so commonly used in the cheap editions of books and periodicals, are often injurious to the eyesight.